首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   22903篇
  免费   643篇
  国内免费   39篇
系统科学   1167篇
丛书文集   263篇
教育与普及   30篇
理论与方法论   344篇
现状及发展   9241篇
研究方法   737篇
综合类   11590篇
自然研究   213篇
  2018年   765篇
  2017年   765篇
  2016年   492篇
  2012年   470篇
  2011年   1349篇
  2010年   900篇
  2009年   532篇
  2008年   744篇
  2007年   1027篇
  2006年   307篇
  2005年   334篇
  2004年   514篇
  2003年   429篇
  2002年   332篇
  2001年   486篇
  2000年   451篇
  1999年   333篇
  1992年   294篇
  1991年   225篇
  1990年   240篇
  1989年   238篇
  1988年   204篇
  1987年   242篇
  1986年   280篇
  1985年   337篇
  1984年   236篇
  1983年   229篇
  1982年   215篇
  1981年   223篇
  1980年   228篇
  1979年   582篇
  1978年   486篇
  1977年   451篇
  1976年   356篇
  1975年   413篇
  1974年   577篇
  1973年   471篇
  1972年   481篇
  1971年   562篇
  1970年   717篇
  1969年   553篇
  1968年   557篇
  1967年   552篇
  1966年   440篇
  1965年   377篇
  1959年   198篇
  1958年   334篇
  1957年   248篇
  1956年   191篇
  1955年   192篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Unesco     
Ohne Zusammenfassung  相似文献   
932.
WILKINSON G 《Nature》1947,160(4077):864
  相似文献   
933.
934.
The spectrum of a chromophore may change as a result of perturbations in its environment. The spectral changes resulting from the perturbation are often followed by measurements at just one or two wavelengths but it is usually no more difficult to collect entire spectra. The problem comes in analysing the data from such a series of spectra. In this paper we will suggest a simple procedure in which the spectrum observed under any particular set of conditions may be considered to consist of the sum of two distinct spectral forms. The method, which is free of any assumptions regarding the quantitative relationship between the perturbation and the extent of spectral change, defines any given spectrum in terms of an apparent molar fraction of the contributing spectral forms. The variation of this apparent molar fraction provides information from which a quantitative relationship can be developed to describe the dependence of the spectral change on the perturbant. The method is illustrated using the model system of phenol red protonation and is applied to the characterization of the binding of azide ions to cobalt-substituted carbonic anhydrase.  相似文献   
935.
In order to describe collaborative decision-making process, the command and control model is put forward based on complex information relation integrtion and OODA. The characteristics of individual decision-making are analyzed, the complex information relation is considered as the cause of OODA difficulty to describe collaborative decision-making exactly. From the perspective of armament system of systems combat, the information, data, intelligence and knowledge is defined based on knowledge management and Shannon's entropy theory. The basic element is confirmed and the information flow way is analyzed which in the physical, information, cognitive and social domains. From the perspective of information, the armament system of systems complex networks model framework is put forward based on the idea of using OODA to guide armament system of systems complex networks model design. The data, information, intelligence and knowledge flow is analyzed and the describing meta-model is put forward. Using the reticular structure of OODA to describe collaborative decision-making idea is proposed, the command and control model is put forward based on the idea, the simulating tool ExtendSim is used for simulation analysis and results show that our work offer a reference for innovate command and control thory. ©, 2015, The Journal Agency of Complex Systems and Complexity Science. All right reserved.  相似文献   
936.
This paper addresses a nonlinear feedback control problem for the chaotic arch microelectro- mechanical system with unknown parameters, immeasurable states and partial state-constraint subjected to the distributed electrostatic actuation. To reflect inherent properties and design controller, the phase diagrams, bifurcation diagram and Poincare section are presented to investigate the nonlinear dynamics. The authors employ a symmetric barrier Lyapunov function to prevent violation of constraint when the arch micro-electro-mechanical system faces some limits. An RBF neural network system integrating with an update law is adopted to estimate unknown function with arbitrarily small error. To eliminate chaotic oscillation, a neuro-adaptive backstepping control scheme fused with an extended state tracking differentiator and an observer is constructed to lower requirements on measured states and precise system model. Besides, introducing an extended state tracking differentiator avoids repeated derivative for the virtual control signal associated with conventional backstepping. Finally, simulation results are presented to illustrate feasibility of the proposed scheme.  相似文献   
937.
This paper is drawn from PhD research funded by the Saudi government on the policy and governance of Saudi schools (Algraini 2017. A critical systemic approach to human development in education: a case study of the Ministry of Education in Saudi Arabia). The aim of this article is to address human development challenges using the Critical Systems Heuristics approach. The results show that the central policy framework limits the opportunity for teachers and learners to contribute to shaping the curriculum and the process for human development. The Saudi Ministry of Education needs to: a) develop policy that takes into account the structure and the processes that shape education outcomes and b) to represent the voices of service users and service providers who have different and overlapping views.  相似文献   
938.
This paper is devoted to the investigation of stability for a class of coupled impulsive Markovian jump reaction-diffusion systems on networks (CIMJRDSNs). By using graph theory, a systematic method is provided to construct global Lyapunov functions for the CIMJRDSNs. Based on Lyapunov functions and stochastic analysis method, some novel stability principles associated with the topology property of the networks are established.  相似文献   
939.
This paper is devoted to a study of the null controllability problems for one-dimensional linear degenerate wave equations through a boundary controller. First, the well-posedness of linear degenerate wave equations is discussed. Then the null controllability of some degenerate wave equations is established, when a control acts on the non-degenerate boundary. Different from the known controllability results in the case that a control acts on the degenerate boundary, any initial value in state space is controllable in this case. Also, an explicit expression for the controllability time is given. Furthermore, a counterexample on the controllability is given for some other degenerate wave equations.  相似文献   
940.
This paper obtains some stability results for parametric generalized set-valued weak vector equilibrium problem. Under new assumptions, which do not contain any information about solution mappings, the authors establish the continuity of the solution mapping to a parametric generalized set-valued weak vector equilibrium problem without monotonicity. These results extend and improve some results in the literature. Some examples are given to illustrate the results.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号