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   13730篇
  免费   1689篇
  国内免费   394篇
化学   1509篇
晶体学   30篇
力学   1646篇
综合类   191篇
数学   8973篇
物理学   3464篇
  2024年   20篇
  2023年   126篇
  2022年   391篇
  2021年   413篇
  2020年   264篇
  2019年   263篇
  2018年   284篇
  2017年   390篇
  2016年   396篇
  2015年   297篇
  2014年   602篇
  2013年   770篇
  2012年   817篇
  2011年   683篇
  2010年   685篇
  2009年   832篇
  2008年   892篇
  2007年   952篇
  2006年   804篇
  2005年   680篇
  2004年   512篇
  2003年   528篇
  2002年   479篇
  2001年   454篇
  2000年   403篇
  1999年   322篇
  1998年   345篇
  1997年   309篇
  1996年   221篇
  1995年   232篇
  1994年   196篇
  1993年   172篇
  1992年   156篇
  1991年   127篇
  1990年   106篇
  1989年   85篇
  1988年   74篇
  1987年   63篇
  1986年   62篇
  1985年   78篇
  1984年   64篇
  1983年   22篇
  1982年   36篇
  1981年   32篇
  1980年   26篇
  1979年   37篇
  1978年   28篇
  1977年   34篇
  1976年   22篇
  1957年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Pure adaptive search constructs a sequence of points uniformly distributed within a corresponding sequence of nested regions of the feasible space. At any stage, the next point in the sequence is chosen uniformly distributed over the region of feasible space containing all points that are equal or superior in value to the previous points in the sequence. We show that for convex programs the number of iterations required to achieve a given accuracy of solution increases at most linearly in the dimension of the problem. This compares to exponential growth in iterations required for pure random search.  相似文献   
172.
In this paper, we argue that vehicle routing solutions are often tactical decisions, that should not be changed too often or too much. For marketing or other reasons, vehicle routing solutions should be stable, i.e. a new solution (when e.g. new customers require service) should be as similar as possible to a solution already in use. Simultaneously however, this new solution should still have a good quality in the traditional sense (e.g. small total travel cost). In this paper, we develop a way to measure the difference between two vehicle routing solutions. We use this distance measure to create a metaheuristic approach that will find solutions that are “close” (in the solution space) to a given baseline solution and at the same time have a high quality in the sense that their total distance traveled is small. By using this approach, the dispatcher is offered a choice of Pareto-optimal solutions, allowing him to make a trade-off between changing his existing solution and allowing a longer travel distance. Some experiments are performed to show the effectiveness of the approach.  相似文献   
173.
Analysis of Static Simulated Annealing Algorithms   总被引:1,自引:0,他引:1  
Generalized hill climbing (GHC) algorithms provide a framework for modeling local search algorithms to address intractable discrete optimization problems. This paper introduces a measure for determining the expected number of iterations to visit a predetermined objective function level, given that an inferior objective function level has been reached in a finite number of iterations. A variation of simulated annealing (SA), termed static simulated annealing (S2A), is analyzed using this measure. S2A uses a fixed cooling schedule during the algorithm execution. Though S2A is probably nonconvergent, its finite-time performance can be assessed using the finite-time performance measure defined in this paper.  相似文献   
174.
陈同英 《运筹与管理》2002,11(1):118-122
本主要介绍原木经销商在周期内原木变价销售情况下的最佳期初贮存量的决策方法,在建立期望机会成本的数学模型基础上,探讨原木随机存贮策略的最优化问题。  相似文献   
175.
利用驻波实验研究混沌现象   总被引:4,自引:2,他引:2  
吴本科  肖苏  高峰 《物理实验》2006,26(1):7-10,13
利用驻波实验演示了混沌现象,并对其进行了理论分析和计算机仿真研究.仿真结果与实验结果都表明:当连接点接近驻波波节处时,振动系统处于混沌运动状态;而当连接点接近驻波波腹处时,系统处于稳定驻波运动状态.  相似文献   
176.
A domain partitioning algorithm for minimizing or maximizing a Lipschitz continuous function is enhanced to yield two new, more efficient algorithms. The use of interval arithmetic in the case of rational functions and the estimates of Lipschitz constants valid in subsets of the domain in the case of others and the addition of local optimization have resulted in an algorithm which, in tests on standard functions, performs well.  相似文献   
177.
The Cross-Entropy Method for Continuous Multi-Extremal Optimization   总被引:3,自引:0,他引:3  
In recent years, the cross-entropy method has been successfully applied to a wide range of discrete optimization tasks. In this paper we consider the cross-entropy method in the context of continuous optimization. We demonstrate the effectiveness of the cross-entropy method for solving difficult continuous multi-extremal optimization problems, including those with non-linear constraints.   相似文献   
178.
简并光学参量振荡器混沌反控制   总被引:5,自引:0,他引:5       下载免费PDF全文
冯秀琴  沈柯 《物理学报》2006,55(9):4455-4459
提出一种实现简并光学参量振荡器混沌反控制的方法,用正弦信号调制简并光学参量振荡器的基模衰减率,使简并光学参量振荡器从定态输出转化为混沌态.数值模拟结果表明,选择不同的调制幅度和调制角频率,只要满足系统的最大李雅谱诺夫指数大于零,即可实现不同的混沌轨道重构.通过比较最大李雅谱诺夫指数λmax随调制幅度和调制角频率变化曲线, 指出系统从周期态调制到混沌态比从无亚谐波输出的定态调制到混沌态更容易,有更宽的调制幅度和调制角频率选择范围. 关键词: 简并光学参量振荡器 混沌反控制 调制  相似文献   
179.
In this paper there is stated a result on sets in ordered linear spaces which can be used to show that some properties of the sets are inherited by their convex hulls under suitable conditions. As applications one gives a characterization of weakly efficient points and a duality result for nonconvex vector optimization problems.  相似文献   
180.
We give a concise review and extension of S-procedure that is an instrumental tool in control theory and robust optimization analysis. We also discuss the approximate S-Lemma as well as its applications in robust optimization.The many suggestions and detailed corrections of an anonymous referee are gratefully acknowledged.  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