|
|
|
题名
|
作者
|
年代
|
出处
|
被引量
|
| 1 | Plant abiotic stress response and nutrient use efficiency显示文摘Abiotic stresses and soil nutrient limitations are major environmental conditions that reduce plant growth,productivity and quality.Plants have evolved mechanisms to perceive these environmental challenges,transmit the stress signals within cells as well as between cells and tissues,and make appropriate adjustments in their growth and development in order to survive and reproduce.In recent years,significant progress has been made on many fronts of the stress signaling research,particularly in understanding the downstream signaling events that culminate at the activation of stress-and nutrient limitation-responsive genes,cellular ion homeostasis,and growth adjustment.However,the revelation of the early events of stress signaling,particularly the identification of primary stress sensors,still lags behind.In this review,we summarize recent work on the genetic and molecular mechanisms of plant abiotic stress and nutrient limitation sensing and signaling and discuss new directions for future studies. | Zhizhong Gong Liming Xiong Huazhong Shi Shuhua Yang Luis R.Herrera-Estrella Guohua Xu Dai-Yin Chao Jingrui Li Peng-Yun Wang Feng Qin Jigang Li Yanglin Ding Yiting Shi Yu Wang Yongqing Yang Yan Guo Jian-Kang Zhu | 2020 | Science China(Life Sciences)2020，63，5： | 94 |
| 2 | Unraveling salt stress signaling in plants显示文摘Salt stress is a major environmental factor limiting plant growth and productivity. A better understanding of the mechanisms mediating salt resistance will help researchers design ways to improve crop performance under adverse environmental conditions. Salt stress can lead to ionic stress, osmotic stress and secondary stresses, particularly oxidative stress, in plants. Therefore,to adapt to salt stress, plants rely on signals and pathways that re-establish cellular ionic, osmotic, and reactive oxygen species(ROS) homeostasis. Over the past two decades, genetic and biochemical analyses have revealed several core stress signaling pathways that participate in salt resistance. The Salt Overly Sensitive signaling pathway plays a key role in maintaining ionic homeostasis,via extruding sodium ions into the apoplast. Mitogenactivated protein kinase cascades mediate ionic, osmotic,and ROS homeostasis. SnR K2(sucrose nonfermenting1-related protein kinase 2) proteins are involved in maintaining osmotic homeostasis. In this review, we discuss recent progress in identifying the components and pathways involved in the plant's response to salt stress and their regulatory mechanisms. We also review progress in identifying sensors involved in salt-induced stress signaling in plants. | Yongqing Yang Yan Guo | 2018 | Journal of Integrative Plant Biology2018，60，9： | 66 |
| 3 | U-Pb zircon age for the Daohugou Biota at Ningcheng of Inner Mongolia and comments on related issues显示文摘SHRIMP U-Pb zircon dating was carried out for the Daohugou Biota near Ningcheng of Inner Mongolia and for lavas overlying or underlying sala-mander-bearing strata at Reshuitang in Lingyuan of West Liaoning. The results suggest that the Dao- hugou Biota occurred at an interval from 168 Ma to 164―152 Ma. Both the Daohugou Biota and the salamander-bearing fossil assemblage are the same biota and thus developed from 168 to 152 Ma, i.e. from late Middle Jurassic to the early Late Jurassic. The Daohugou Biota-bearing rocks, resting on the Jiulongshan Formation in disconformity and being overlain in unconformity by Late Jurassic Tuchengzi Formation and Early Cretaceous rocks containing the Jehol Biota, are mainly composed of volcanic-sedi- mentary rocks in a normal sequence. It is recom- mended that the Daohugou Biota and the related stratigraphy should be correlated with the Tiaojishan Formation (Lanqi Formation in West Liaoning) or its synchronous rocks. It is suggested that the Dao- hugou Biota and the Jehol Biota would be neither taken into one biota nor considered as the earliest elements of the Jehol Biota. The Daohugou Biota and the related rocks and the Yixian Formation were respectively formed in different periods of volcanic-sedimentary tectonics. | LIU Yongqing LIU Yanxue JI Shu'an YANG Zhiqing | 2006 | Chinese Science Bulletin2006，51，21： | 23 |
| 4 | Protein kinases in plant responses to drought, salt,and cold stress显示文摘Protein kinases are major players in various signal transduction pathways. Understanding the molecular mechanisms behind plant responses to biotic and abiotic stresses has become critical for developing and breeding climate-resilient crops. In this review,we summarize recent progress on understanding plant drought, salt, and cold stress responses, with a focus on signal perception and transduction by different protein kinases, especially sucrose nonfermenting1(SNF1)-related protein kinases(Sn RKs),mitogen-activated protein kinase(MAPK) cascades,calcium-dependent protein kinases(CDPKs/CPKs),and receptor-like kinases(RLKs). We also discuss future challenges in these research fields. | Xuexue Chen Yanglin Ding Yongqing Yang Chunpeng Song Baoshan Wang Shuhua Yang Yan Guo Zhizhong Gong | 2021 | Journal of Integrative Plant Biology2021，63，1： | 13 |
| 5 | Generation of seed lipoxygenase-free soybean using CRISPR-Cas9显示文摘Beany flavor induced by three lipoxygenases(LOXs, including LOX1, LOX2, and LOX3)restricts human consumption of soybean. It is desirable to generate lipoxygenase-free new mutant lines to improve the eating quality of soybean oil and protein products. In this study, a pooled clustered regularly interspaced short palindromic repeats(CRISPR)-CRISPRassociated protein 9(Cas9) strategy targeting three GmLox genes(GmLox1, GmLox2, and GmLox3) was applied and 60 T_0 positive transgenic plants were generated, carrying combinations of sg RNAs and mutations. Among them, GmLox-28 and GmLox-60 were gmlox1 gmlox2 gmlox3 triple mutants and GmLox-40 was a gmlox1 gmlox2 double mutant.Sequencing of T_1 mutant plants derived from GmLox-28, GmLox-60, and GmLox-40 showed that mutation in the GmLox gene was inherited by the next generation. Colorimetric assay revealed that plants carrying different combinations of mutations lost the corresponding lipoxygenase activities. Transgene-free mutants were obtained by screening the T_2 generation of lipoxygenase-free mutant lines(GmLox-28 and GmLox-60). These transgeneand lipoxygenase-free mutants could be used for soybean beany flavor reduction without restriction by regulatory frameworks governing transgenic organisms. | Jie Wang Huaqin Kuang Zhihui Zhang Yongqing Yang Long Yan Mengchen Zhang Shikui Song Yuefeng Guan | 2020 | The Crop Journal2020，8，3： | 9 |
| 6 | Kindlin-2 expression in adult tissues correlates with their embryonic origins显示文摘Kindlin-2 functions in the maintenance of homeostasis and in human diseases.This study investigated the interrelationship between Kindlin-2 expression in tissues and the corresponding germ layers from which these tissues originated.Kindlin-2 expression was examined in normal adult human organs and human cancer tissues by immunohistochemical analyses.Analysis of Kindlin-2 mRNA levels in adult human organs in the Oncomine dataset revealed Kindlin-2 is highly expressed in mesoderm-derived organs.However,Kindlin-2 was negative or weakly expressed in endoderm/ectoderm-derived organs.Interestingly,the abnormal expression of Kindlin-2 was observed in a variety of human cancers.In agreement with its expression profile in humans,Kindlin-2 was also highly expressed in mesoderm-derived organs in mouse embryos with the exception of strong Kindlin-2 expression in ectoderm-derived spinal cord and ganglia,tissues that are highly mobile during embryonic development.Importantly,we demonstrated the expression level of Kindlin-2 in adult organs correlated with their embryonic dermal origins and deregulation of Kindlin-2 in tissues is associated with tumor progression.This finding will help us understand the dual role of Kindlin-2 in the regulation of tumor progression and embryonic development. | ZHAN Jun YANG Mei CHI XiaoChun ZHANG Jing PEI XueLian REN CaiXia GUO YongQing LIU Wei ZHANG HongQuan | 2014 | Science China(Life Sciences)2014，57，7： | 8 |
| 7 | Phase Transformation in a β-Ti Alloy with Good Balance Between High Strength and High Fracture Toughness显示文摘Ti-1300合金是一种亚稳β钛合金,为了从组织形貌方面解释其高强高韧的特性,对此钛合金的相变特征进行了研究。研究结果表明,由于α相的球化,此钛合金抗拉强度可达1400MPa以上,同时发现特定的板条状α相有利于保持此钛合金较高的断裂韧性(KQ≥81MPa·m1/2),与针状二次α相相比,板条状二次α相应力集中程度较轻,因此有利于获得较高的韧性。对时效过程中α相的形貌变化进行了研究,并从热力学和动力学上进行了描述,同时给出了一种比较合理的热处理制度。 | Li Yang Wei Qiang Ma Chaoli Zheng Lijing Li Huanxi Ge Peng Zhao Yongqing | 2009 | Chinese Journal of Aeronautics2009，22，5： | 7 |
| 8 | Could CMIP6 climate models reproduce the early-2000s global warming slowdown?显示文摘The unexpected global warming slowdown during 1998–2013 challenges the existing scientific understanding of global temperature change mechanisms,and thus the simulation and prediction ability of state-of-the-art climate models since most models participating in phase 5 of the Coupled Model Intercomparison Project(CMIP5)cannot simulate it.Here,we examine whether the new-generation climate models in CMIP6 can reproduce the recent global warming slowdown,and further evaluate their capacities for simulating key-scale natural variabilities which are the most likely causes of the slowdown.The results show that although the CMIP6 models present some encouraging improvements when compared with CMIP5,most of them still fail to reproduce the warming slowdown.They considerably overestimate the warming rate observed in 1998–2013,exhibiting an obvious warming acceleration rather than the observed deceleration.This is probably associated with their deficiencies in simulating the distinct temperature change signals from the human-induced long-term warming trend and/or the three crucial natural variabilities at interannual,interdecadal,and multidecadal scales.In contrast,the 4 models that can successfully reproduce the slowdown show relatively high skills in simulating the long-term warming trend and the three keyscale natural variabilities.Our work may provide important insight for the simulation and prediction of near-term climate changes. | Meng WEI Qi SHU Zhenya SONG Yajuan SONG Xiaodan YANG Yongqing GUO Xinfang LI Fangli QIAO | 2021 | Science China Earth Sciences2021，64，6： | 5 |
| 9 | Changes in feed intake, nutrient digestion, plasma metabolites, and oxidative stress parameters in dairy cows with subacute ruminal acidosis and its regulation with pelleted beet pulp显示文摘The objectives of this study were to 1) determine the variation of nutrient digestion, plasma metabolites and oxidative stress parameters triggered by induced subacute ruminal acidosis(SARA); and 2) evaluate the ability of pelleted beet pulp(BP) as a replacement for ground corn to alleviate SARA. Eight Holstein-Friesian cows were fed four diets during four successive17-day periods: 1) total mixed ration(TMR) containing 0% finely ground wheat(FGW)(W0); 2) TMR containing 10% FGW(W10); 3) TMR containing 20% FGW(W20); and 4) TMR containing 10% BP as a replacement for 10% ground corn(BP10). The SARA induction protocol reduced the mean ruminal pH from6.37 to 5.94, and the minimum ruminal pH decreased from 5.99 to 5.41 from baseline to challenge period. Mean ruminal pH increased from 5.94 to 6.05, and minimum daily ruminal pH increased from 5.41 to 5.63, when BP was substituted for corn. The apparent digestibility of nutrients was not affected by the dietary treatments, except that the digestibility of neutral detergent fibre(NDF) and acid detergent fibre(ADF) was reduced in cows fed the W20diet compared with cows fed the W0 and W10 diets, and cows fed the BP10 diet had higher NDF and ADF digestibility than the cows fed the W20 diet. Cows fed the W20 diet had a lower plasma concentration ofβ-hydroxybutyrate(BHBA), non-esterified fatty acids(NEFA), cholesterol, triglyceride, and total antioxidative capacity(TAC), and a higher plasma concentration of glucose, insulin, malonaldehyde(MDA), super oxygen dehydrogenises(SOD), and glutathione peroxidase(GSH-Px) than cows fed the W0 diet. Substitution of BP for corn increased concentrations of plasma BHBA and TAC, but decreased concentrations of plasma MDA. Our results indicate that reduction of fibre digestion; the concomitant increase of plasma glucose and insulin; the decrease of plasma BHBA, NEFA, cholesterol, and triglyceride; and changes of plasma oxidative stress parameters are highly related to SARA induced by W20 diets. These variables may be alternative candidates for SARA diagnosis. We also suggest that the substitution of BP for corn could reduce the risk of SARA, increase fibre digestion, and improve the antioxidant status in dairy cows. | Yongqing Guo Xiaofeng Xu Yang Zou Zhanshan Yang Shengli Li Zhijun Cao | 2014 | Journal of Animal Science and Biotechnology2014，5，1： | 5 |
| 10 | Functional assembly of root-associated microbial consortia improves nutrient efficiency and yield in soybean显示文摘Root-associated microbes are critical for plant growth and nutrient acquisition. However, scant information exists on optimizing communities of beneficial root-associated microbes or the mechanisms underlying their interactions with host plants. In this report, we demonstrate that rootassociated microbes are critical influencers of host plant growth and nutrient acquisition. Three synthetic communities(SynComs) were constructed based on functional screening of 1,893 microbial strains isolated from root-associated compartments of soybean plants. Functional assemblage of SynComs promoted significant plant growth and nutrient acquisition under both N/P nutrient deficiency and sufficiency conditions.Field trials further revealed that application of SynComs stably and significantly promoted plant growth, facilitated N and P acquisition, and subsequently increased soybean yield. Among the tested communities, SynCom1 exhibited the greatest promotion effect, with yield increases of up to 36.1% observed in two field sites. Further RNA-seq implied that SynCom application systemically regulates N and P signaling networks at the transcriptional level, which leads to increased representation of important growth pathways, especially those related to auxin responses. Overall,this study details a promising strategy for constructing SynComs based on functional screening,which are capable of enhancing nutrient acquisition and crop yield through the activities of beneficial root-associated microbes. | Cunhu Wang Yanjun Li Mingjia Li Kefei Zhang Wenjing Ma Lei Zheng Hanyu Xu Baofeng Cui Ran Liu Yongqing Yang Yongjia Zhong Hong Liao | 2021 | Journal of Integrative Plant Biology2021，63，6： | 5 |
| 11 | Preparation of copper nanoparticles modified with [BMIm]BF_4 ionic liquid显示文摘Copper nanoparticles was prepared by ascorbic acid reducing CuCl2 solution modified with [BMIm]BF4 ionic liquid. The size of copper nanoparticles was obviously affected by the concentration of Cu2+. The diameter of nanoparticles was smaller than 10 nm when the Cu2+ concentration was smaller than 2×10-2 mol/L. The pH and temperature of reductive reaction had no obvious effect on the size of copper nanoparticles. | Su Yongqing Li Cong Yang Mingdi Cai Ying Ren Nianjun | 2010 | Engineering Sciences2010，8，2： | 5 |
| 12 | Dynamic changes of phosphatidylinositol and phosphatidylinositol 4-phosphate levels modulate H^(+)-ATPase and Na^(+)/H^(+) antiporter activities to maintain ion homeostasis in Arabidopsis under salt stress显示文摘Plant metabolites are dynamically modified and distributed in response to environmental changes.How-ever,it is poorly understood how metabolic change functions in plant stress responses.Maintaining ion ho-meostasis under salt stress requires coordinated activation of two types of central regulators:plasma membrane(PM)H^(+)-ATPase and Na^(+)/H^(+) antiporter.In this study,we used a bioassay-guided isolation approach to identify endogenous small molecules that affect PM H^(+)-ATPase and Na^(+)/H^(+) antiporter activities and identified phosphatidylinositol(PI),which inhibits PM H^(+)-ATPase activity under non-stress conditions in Arabidopsis by directly binding to the C terminus of the PM H^(+)-ATPase AHA2.Under salt stress,the phosphatidylinositol 4-phosphate-to-phosphatidylinositol(PI4P-to-PI)ratio increased,and PI4P bound and activated the PM Na^(+)/H^(+) antiporter.PI prefers binding to the inactive form of PM H^(+)-ATPase,while PI4P tends to bind to the active form of the Na^(+)/H^(+) antiporter.Consistent with this,pis1 mutants,with reduced levels of PI,displayed increased PM H^(+)-ATPase activity and salt stress toler-ance,while the pi4kβ1 mutant,with reduced levels of PI4P,displayed reduced PM Na^(+)/H^(+) antiporter activity and salt stress tolerance.Collectively,our results reveal that the dynamic change between PI and PI4P in response to salt stress in Arabidopsis is crucial for maintaining ion homeostasis to protect plants from un-favorable environmental conditions. | Yongqing Yang Xiuli Han Liang Ma Yujiao Wu Xiao Liu Haiqi Fu Guoyong Liu Xiaoguang Lei Yan Guo | 2021 | Molecular Plant2021，14，12： | 4 |
| 13 | Bipartite Consensus of Linear Multi-Agent Systems by Distributed Event-Triggered Control显示文摘For multi-agent systems with competitive and collaborative relationships,signed graph can more intuitively express the characteristics of their interactive networks.In this paper,the bipartite consensus is investigated for multi-agent systems with structurally balanced signed graph.In order to reduce actuation burden in dynamical network environment,the event-triggering strategy is applied to bipartite consensus protocol for the multi-agent systems.The triggered condition for each agent is designed by using its own information and transmitted information of its neighbors at sampling instant and make the number of triggers of the whole systems be reduced.Based on the distributed eventtriggered control,some sufficient conditions are derived to guarantee the leaderless and leader-following bipartite consensus.Finally,some numerical examples are shown to demonstrate the effectiveness of the theoretical results. | YANG Ruitian PENG Li YANG Yongqing ZHU Fengzeng | 2021 | Journal of Systems Science & Complexity2021，34，3： | 3 |
| 14 | A new barycenter code discriminator for multi-access interference显示文摘The performance of code tracking loop in direct sequence spread spectrum system decreases because of multi-access interference.In order to solve this problem,this paper presents a new code discriminator based on barycenter algorithm.By calculating the barycenter of code phase by multiple PN code branches’correlation results,PN code phase error can be obtained.Theoretical analysis of new discriminator’s performance is given,and it is indicated that the code tracking loop using this algorithm can also solve the problems of low ranging precision and large mean deviation caused by multi-access interference.The efciency of the proposed algorithm is verified by simulation and measurements and the new discriminator is used in an aerospace engineering project successfully. | WANG YongQing LI Cong XU Duo YANG Na | 2014 | Science China(Information Sciences)2014，57，2： | 3 |
| 15 | Construction of the Chinese Veteran Clinical Research (CVCR) Platform for the assessment of non-communicable diseases显示文摘 | Tan Jiping Li Nan Gao Jing Guo Yuhe Hu Wei Yang Jinsheng Yu Baocheng Yu Jianmin Du Wei Zhang Wenjun Cui Lianqi Wang Qingsong Xia Xiangnan Li Jianjun Zhou Peiyi Zhang Baohe Liu Zhiying Zhang Shaogang Sun Lanying Liu Nan Deng Ruixiang Dai Wenguang Yi Fang Chen Wenjun Zhang Yongqing Xue Shenwu Cui Bo Zhao Yiming Wang Luning | 2014 | Chinese Medical Journal2014，，3： | 3 |
| 16 | Study on the Influence of Airgun Excitation Conditions on Airgun Signals and Travel Time Variation Measurements显示文摘Because of the different excitation conditions of the airgun source,there will be subtle differences in airgun signals.Travel time variation of airgun signals often mix into source information which can’t fully reflect the evolution of the medium.This article uses the airgun signals from the Binchuan Transmitting Seismic Station to analyze the airgun signal′s characteristics of phase and correlation.We conducted a comparative analysis of the effects of the pair difference method and the deconvolution method on eliminating the influence of the excitation conditions in travel time variation.The results show that:(1)The pressure pulse and its subsequent wave of airgun source wavelet are less affected by excitation conditions that we can use it to obtain high-precision excitation moments.(2)Deconvolution can improve the correlation of the airgun signal.(3)The pair difference method can’t eliminate the influence of excitation conditions in travel time variation.Deconvolution can reduce excitation condition interference and the influence of the excitation condition in the travel time variation after deconvolution of the vertical signal is significantly reduced. | XIANG Ya YANG Runhai WANG Bin ZHOU Yunyao LU Yongqing WU Huan QI Junwei PENG Jing | 2019 | Earthquake Research in China2019，33，2： | 3 |
| 17 | Soil restoration research advances of artificial sand-binding vegetation ecosystem in the Tengger Desert, Northern China显示文摘Soil plays an important role in desert ecosystem, and is vital in constructing a steady desert ecosystem. The management and restoration of desertified land have been the focus of much discussion. The soil in Shapotou desert region has developed remarkably since artificial sand-binding vegetation established in 1946. The longer the period of dune stabilization, the greater the thickness of microbiotic crusts and subsoil. Meanwhile, proportion of silt and clay increased significantly, and soil bulk density declinced. The content of soil organic matter, N, P, and K similarly increased. Therefore, soil has developed from aeolian sand soil to Calcic-Orthic aridisols. This paper discusses the effects brought about by dust, microbiotic soil crust and soil microbes on soil-forming process. Then, we analyzed the relation between soil formation and sand-binding vegetation evolution, in order to provide a baseline for both research on desert ecosystem recovery and ecological environment governance in arid and semi-arid areas. | LiWen Yang LiChao Liu DaYong Wang YongQing Zhang | 2010 | Research in Cold and Arid Regions2010，2，4： | 3 |
| 18 | Overview of the Mars climate station for Tianwen-1 mission显示文摘The background and scientific objectives of the Mars Climate Station(MCS)for Tianwen-1 are introduced,accompanied by a comparative review of the status of related meteorological observation missions and of advanced sensing technologies.As one of the China Tianwen-1 Mission’s principal scientific payloads,the MCS contains four measurement sensors and one electronic processing unit that are specially designed to measure local temperature,pressure,wind,and sound on the Martian surface.The MCS’s measurement principles,technical schemes,ground calibration techniques,and adaptability evaluation to the Mars surface environment of MCS are introduced in details.The conclusion presents measurement performance specifications of the MCS,based on ground test results,that will provide guidance to future research based on data from the Tianwen-1 and later Mars missions. | YongQing Peng LeiBo Zhang ZhiGuo Cai ZhaoGang Wang HaiLong Jiao DongLi Wang XianTao Yang LianGuo Wang Xu Tan Feng Wang Jing Fang ZhouLu Sun HongLiang Feng XiaoRui Huang Yan Zhu Ming Chen LiangHai Li YanHua Li | 2020 | Earth and Planetary Physics2020，4，4： | 2 |
| 19 | Projective Group Consensus of Multi-Agent Systems with Arbitrary Parameter显示文摘In this paper,the projective group consensus issue for second order multi-agent systems(MASs)in directed graphs with a dynamic leader is investigated.The proposed projective group consensus with arbitrary parameter includes traditional consensus,reverse group consensus and cluster consensus as its special cases.Novel distributed control protocols are designed to obtain projective group consensus without analyzing signed directed graph as in most current literatures on bipartite consensus problem.On the basis of Lyapunov stability property,algebraic graph and some necessary matrix theory,sufficient conditions for delay and delay-free cases are derived.Finally,simulations of nonlinear chaotic MASs are adopted to testify the theoretical results. | CHEN Liangkang GUO Liuxiao YANG Yongqing | 2021 | Journal of Systems Science & Complexity2021，34，2： | 2 |
| 20 | A facile ionic liquid approach to prepare cellulose fiber with good mechanical properties directly from corn stalks显示文摘It is very difficult to directly spin the lignocellulose without pretreatment.Ionic liquids(ILs)are promising solvent to dissolve lignocellulose to prepare cellulose fiber.However,the degree of cellulose polymerization(DP)is reduced when lignocellulose is dissolved in ILs,and the lignin removal rate is low.The elongation at break and tensile strength of the fibers obtained by spinning the lignocellulose dissolved in ILs are poor.In this paper,preparing cellulose fiber directly from lignocellulose based on dissolving corn stalk via[C4mim]Cl-L-arginine binary system is achieved.It shows that the removal rate of lignin can reach 92.35%and the purity of cellulose can reach 85.32%after corn stalk was dissolved at 150℃C for 11.5 h when the mass fraction of arginine is 2.5%.The elongation at break of fiber reached 10.12%and the tensile strength reached 420 MPa.It is mainly due to the fact that L-arginine not only inhibits the degradation of cellulose but also promotes the delignination.Without any pulping or pretreatment,preparing cellulose fibers via direct dissolution and extrusion may provide a simple and effective way to prepare many novel cellulose materials. | Jiming Yang Xingmei Lu Yanqiang Zhang Junli Xu Yongqing Yang Qing Zhou | 2020 | Green Energy & Environment2020，5，2： | 2 |
您所在的机构暂未开通此部分的功能，请联系管理员