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   49141篇
  免费   4027篇
  国内免费   4883篇
化学   10043篇
晶体学   109篇
力学   2282篇
综合类   339篇
数学   10792篇
物理学   11313篇
综合类   23173篇
  2024年   144篇
  2023年   423篇
  2022年   817篇
  2021年   953篇
  2020年   1108篇
  2019年   1011篇
  2018年   988篇
  2017年   1252篇
  2016年   1448篇
  2015年   1436篇
  2014年   2385篇
  2013年   2999篇
  2012年   2655篇
  2011年   3096篇
  2010年   2446篇
  2009年   2910篇
  2008年   3056篇
  2007年   3554篇
  2006年   3137篇
  2005年   2732篇
  2004年   2346篇
  2003年   2213篇
  2002年   2009篇
  2001年   1653篇
  2000年   1540篇
  1999年   1250篇
  1998年   1123篇
  1997年   938篇
  1996年   778篇
  1995年   674篇
  1994年   532篇
  1993年   551篇
  1992年   519篇
  1991年   418篇
  1990年   433篇
  1989年   408篇
  1988年   328篇
  1987年   278篇
  1986年   193篇
  1985年   184篇
  1984年   158篇
  1983年   91篇
  1982年   122篇
  1981年   114篇
  1980年   98篇
  1979年   103篇
  1978年   78篇
  1977年   76篇
  1976年   71篇
  1973年   62篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
This paper puts forward a new integrated design met ho d based on fuzzy matter-element optimization.On the based of analyzing the mod el of multi-objective fuzzy matter-element , the paper defines the m atter-element weightily and changes solving multi-objective fuzzy optimization into solving dependent function K(x) of the single-objective optimization according to the optimization criterion. The paper particularly describes the realization approach of GA process of multi -objective fuzzy matter-eleme...  相似文献   
132.
Calibration of a basket option model applied to company valuation   总被引:1,自引:0,他引:1  
Applying real options thinking to company valuation seems theoretically and intuitively appealing. However, the real option analogy of a single European option as well as the compound option proxy perform poorly when applied to company valuation. We therefore suggest to rework the building blocks of real option applications to corporate valuation.  We introduce a framework to delineate the distribution of the underlying asset in the risk neutral world, which is important in order to value any derivative. This is achieved by an algorithm to calibrate a basket option model using real world data of observed share prices. The fitting takes account of the class of stable distributions. The index of stability of asymmetric α stable distribution serves as an over-all parameter to characterise the specific distribution.  相似文献   
133.
This document presents theoretical considerations about the solution of dynamic optimization problems integrating the Benders Theory, the Dynamic Programming approach and the concepts of Control Theory. The so called Generalized Dual Dynamic Programming Theory (GDDP) can be considered as an extension of two previous approaches known as Dual Dynamic Programming (DDP): The first is the work developed by Pereira and Pinto [3–5], which was revised by Velásquez and others [8,9]. The second is the work developed by Read and others [2,6,7].  相似文献   
134.
In this paper we present two definitions of possibilistic weighted average of fuzzy numbers, and by them we introduce two different rankings on the set of real fuzzy numbers. The two methods are dependent on several parameters. In the first case, the parameter is constant and the results generalize what Carlsson and Fuller have obtained in (2001). In the second case, the parameter is a function, not fixed a priori by the decision maker, but it depends on the position of the interval on the real axe. In all the two cases we call the parameter degree of risk, which takes into account of a risk-tendency or aversion of the decision maker.  相似文献   
135.
金天允 《光学学报》1991,11(3):78-282
本文在相干理论的基础上,推导了光栅成像中的光强分布和物像位置关系,并给出一组具有不同参数的实验照片及一组借助计算机绘制的强度分布图。  相似文献   
136.
137.
A graph G is called rigid if the identical mapping V(G)→V(G) is the only homomorphism GG. In this note we give a simple construction of a rigid oriented graph on every set. © 2002 John Wiley & Sons, Inc. J Graph Theory 39: 108–110, 2002  相似文献   
138.
定义了一种新的函数──Z域正实函数(Z-PRF);导出了该函数的一些性质和定理.  相似文献   
139.
Optimization theory provides a framework for determining the best decisions or actions with respect to some mathematical model of a process. This paper focuses on learning to act in a near-optimal manner through reinforcement learning for problems that either have no model or the model is too complex. One approach to solving this class of problems is via approximate dynamic programming. The application of these methods are established primarily for the case of discrete state and action spaces. In this paper we develop efficient methods of learning which act in complex systems with continuous state and action spaces. Monte-Carlo approaches are employed to estimate function values in an iterative, incremental procedure. Derivative-free line search methods are used to obtain a near-optimal action in the continuous action space for a discrete subset of the state space. This near-optimal control policy is then extended to the entire continuous state space via a fuzzy additive model. To compensate for approximation errors, a modified procedure for perturbing the generated control policy is developed. Convergence results under moderate assumptions and stopping criteria are established.  相似文献   
140.
Let g be a Lie algebra all of whose regular subalgebras of rank 2 are type A1×A1, A2, or C2, and let B be a crystal graph corresponding to a representation of g. We explicitly describe the local structure of B, confirming a conjecture of Stembridge.  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