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   4005篇
  免费   287篇
  国内免费   368篇
化学   1574篇
晶体学   13篇
力学   294篇
综合类   73篇
数学   1944篇
物理学   762篇
  2024年   3篇
  2023年   23篇
  2022年   58篇
  2021年   88篇
  2020年   86篇
  2019年   87篇
  2018年   85篇
  2017年   102篇
  2016年   127篇
  2015年   62篇
  2014年   163篇
  2013年   253篇
  2012年   224篇
  2011年   206篇
  2010年   233篇
  2009年   235篇
  2008年   241篇
  2007年   287篇
  2006年   225篇
  2005年   235篇
  2004年   180篇
  2003年   192篇
  2002年   137篇
  2001年   132篇
  2000年   122篇
  1999年   96篇
  1998年   79篇
  1997年   72篇
  1996年   66篇
  1995年   49篇
  1994年   84篇
  1993年   53篇
  1992年   57篇
  1991年   36篇
  1990年   36篇
  1989年   30篇
  1988年   30篇
  1987年   28篇
  1986年   28篇
  1985年   30篇
  1984年   19篇
  1983年   8篇
  1982年   20篇
  1981年   8篇
  1980年   10篇
  1979年   5篇
  1978年   7篇
  1977年   5篇
  1976年   7篇
  1969年   3篇
排序方式: 共有4660条查询结果,搜索用时 15 毫秒
51.
meso-四(2-羟基-5-磺酸苯基)卟啉的合成及其酸碱平衡的研究   总被引:1,自引:0,他引:1  
本文对 meso-四(2-H-5-SP)P 的提纯方法进行了改进,同时以光度法研究了该试剂在水溶液中的酸碱平衡、测得其 pKa_1、pKa_2、pKa_3、pKa_4分别为2.99,4.21,8.68,10.28。  相似文献   
52.
In this paper, we study the existence, uniqueness, and the global exponential stability of the periodic solution and equilibrium of hybrid bidirectional associative memory neural networks with discrete delays. By ingeniously importing real parameters di > 0 (i = 1,2, …, n) which can be adjusted, making use of the Lyapunov functional method and some analysis techniques, some new sufficient conditions are established. Our results generalize and improve the related results in [9]. These conditions can be used both to design globally exponentially stable and periodical oscillatory hybrid bidirectional associative neural networks with discrete delays, and to enlarge the area of designing neural networks. Our work has important significance in related theory and its application.  相似文献   
53.
54.
Systems that involve more than one decision maker are often optimized using the theory of games. In the traditional game theory, it is assumed that each player has a well-defined quantitative utility function over a set of the player decision space. Each player attempts to maximize/minimize his/her own expected utility and each is assumed to know the extensive game in full. At present, it cannot be claimed that the first assumption has been shown to be true in a wide variety of situations involving complex problems in economics, engineering, social and political sciences due to the difficulty inherent in defining an adequate utility function for each player in these types of problems. On the other hand, in many of such complex problems, each player has a heuristic knowledge of the desires of the other players and a heuristic knowledge of the control choices that they will make in order to meet their ends.In this paper, we utilize fuzzy set theory in order to incorporate the players' heuristic knowledge of decision making into the framework of conventional game theory or ordinal game theory. We define a new approach to N-person static fuzzy noncooperative games and develop a solution concept such as Nash for these types of games. We show that this general formulation of fuzzy noncooperative games can be applied to solve multidecision-making problems where no objective function is specified. The computational procedure is illustrated via application to a multiagent optimization problem dealing with the design and operation of future military operations.  相似文献   
55.
Using the thermodynamical approach and the method of York, the back-reaction of anti-de Sitter Schwarzschild black hole in thermal equilibrium with conformal spin-2 field is studied. It is found that both approaches give identical results.  相似文献   
56.
We consider the problem of a self-consistent determination of an essentially inhomogeneous equilibrium state of classical plasma. The solutions of the stationary Vlasov–Poisson equations are constructed in the form of a localized transition layer that separates the domains of homogeneous plasmas with different equilibrium parameters. The layer can also transform into a local perturbation inside a homogeneous plasma. In both cases, the solution contains neither mass currents nor electric currents, and all electrodynamic and hydrodynamic quantities and their derivatives are continuous. The parameters of the adjacent domains uniquely determine the transition layer structure.  相似文献   
57.
引进集值映射的锥真拟凹概念,讨论一类具有集值映射的广义向量衡问题解的存在性与解集的凸性。  相似文献   
58.
有消费或投资的华氏宏观经济模型   总被引:1,自引:0,他引:1  
本文对华罗庚教授的宏观经济模型进行了推广 ,在原来模型的基础上 ,分别增加了消费、投资 ,得到两种不同的模型 ,并对模型具有经济意义的解进行了研究  相似文献   
59.
In Leitmann (Ref. 1), a coordinate transformation method was introduced to obtain global solutions for free problems in the calculus of variations. This direct method was extended and broadened in Carlson (Ref. 2) and later in Leitmann (Ref. 3). The applicability of the original work of Leitmann (Ref. 1) was further developed in Dockner and Leitmann (Ref. 4) to include the class of open-loop dynamic games. In the present work, we improve the results of Ref. 4 in two directions. First, we enlarge the class of open-loop dynamic games to permit coupling among the dynamic equations via the states of the players; second, we incorporate the modifications given in Refs. 2 and 3. Our results greatly increase the applicability of this method. An example arising from the harvesting of a renewable resource is presented to illustrate the utility of our results.  相似文献   
60.
A Tandem Queue with Coupled Processors: Computational Issues   总被引:2,自引:0,他引:2  
In Resing and Örmeci [16] it is shown that the two-stage tandem queue with coupled processors can be solved using the theory of boundary value problems. In this paper we consider the issues that arise when calculating performance measures like the mean queue length and the fraction of time a station is empty. It is assumed that jobs arrive at the first station according to a Poisson process and require service at both stations before leaving the system. The amount of work that a job requires at each of the stations is an independent, exponentially distributed random variable. When both stations are nonempty, the total service capacity is shared among the stations according to fixed proportions. When one of the stations becomes empty, the total service capacity is given to the nonempty station. We study the two-dimensional Markov process representing the numbers of jobs at the two stations. The problem of finding the generating function of the stationary distribution can be reduced to two different Riemann-Hilbert boundary value problems, where both problems yield a complete analytical solution. We discuss the similarities and differences between the two problems, and relate them to the computational aspects of obtaining performance measures.  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