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   2495篇
  免费   64篇
  国内免费   51篇
化学   508篇
晶体学   3篇
力学   202篇
综合类   10篇
数学   1285篇
物理学   602篇
  2023年   59篇
  2022年   52篇
  2021年   29篇
  2020年   41篇
  2019年   27篇
  2018年   29篇
  2017年   49篇
  2016年   64篇
  2015年   70篇
  2014年   93篇
  2013年   166篇
  2012年   216篇
  2011年   138篇
  2010年   92篇
  2009年   183篇
  2008年   140篇
  2007年   152篇
  2006年   117篇
  2005年   59篇
  2004年   71篇
  2003年   73篇
  2002年   46篇
  2001年   50篇
  2000年   43篇
  1999年   30篇
  1998年   45篇
  1997年   42篇
  1996年   48篇
  1995年   29篇
  1994年   27篇
  1993年   28篇
  1992年   17篇
  1991年   17篇
  1990年   17篇
  1989年   11篇
  1988年   13篇
  1987年   12篇
  1986年   18篇
  1985年   32篇
  1984年   24篇
  1983年   16篇
  1982年   25篇
  1981年   21篇
  1980年   15篇
  1979年   12篇
  1978年   28篇
  1977年   6篇
  1976年   6篇
  1975年   5篇
  1974年   2篇
排序方式: 共有2610条查询结果,搜索用时 0 毫秒
41.
电子电路的计算机辅助设计方法是促进电子技术发展的一种有效工具。本文介绍如何将行之有效的正交优化法与国际盛行的模拟电子电路的分析程序SPICE相结合,形成了ACOD软件,将CAA扩展为CAD。  相似文献   
42.
图的超常边连通度是图的边连通度概念的推广,对于n阶点可迁或正则边可迁的简单连通图来说,它的h阶超常边连通度λ_h一定存在(1≤h≤n/2)。本文证明了:当d_-正则的n_-阶点可迁简单连通图满足n≥6,d≥4且围长g≥5时,或d_-正则的n_-阶边可迁简单连通图满足n≥6,d≥4且围长g≥4时,对于任何的h:1≤h≤min{g-1,n/2},λ_h达到其最大可能值,即λ_h=hd-2(h-1)。  相似文献   
43.
44.
前苏联和俄罗斯模糊理论研究与应用情况概述   总被引:1,自引:0,他引:1  
对前苏联20世纪80年代及苏联解体后俄罗斯20世纪90年代的模糊理论研究与应用情况作了概述,列举了在人工智能认知的模糊原理、信息论的模糊性和模糊空间、随机模糊规划、工业用综合模糊控制系统等领域的研究成果,并列出90多篇(部)俄文文献资料。  相似文献   
45.
The problem of optimizing some contiuous function over the efficient set of a multiple objective programming problem can be formulated as a nonconvex global optimization problem with special structure. Based on the conical branch and bound algorithm in global optimization, we establish an algorithm for optimizing over efficient sets and discuss about the implementation of this algorithm for some interesting special cases including the case of biobjective programming problems.  相似文献   
46.
Let be a convex set for which there is an oracle with the following property. Given any pointz∈ℝ n the oracle returns a “Yes” ifzS; whereas ifzS then the oracle returns a “No” together with a hyperplane that separatesz fromS. The feasibility problem is the problem of finding a point inS; the convex optimization problem is the problem of minimizing a convex function overS. We present a new algorithm for the feasibility problem. The notion of a volumetric center of a polytope and a related ellipsoid of maximum volume inscribable in the polytope are central to the algorithm. Our algorithm has a significantly better global convergence rate and time complexity than the ellipsoid algorithm. The algorithm for the feasibility problem easily adapts to the convex optimization problem.  相似文献   
47.
D. Favaretto  B. Viscolani 《TOP》1996,4(2):301-318
Summary We consider the problem of maximizing the discounted net profit of a firm which purchases a quantity of some product at a given time and afterwards advertises and sells the product progressively. We distinguish among the three possibilities of assuming the final time to be either fixed, or bounded, or free. In all cases, after stating the problem in the optimal control theory framework, we prove the existence of an optimal solution and characterize it using the Maximum Principle necessary conditions. Furthermore, we prove that the convexity of the purchase cost function is a sufficient condition for the uniqueness of the optimal solution. Partially supported by MURST.  相似文献   
48.
改进的粒子群算法在虚拟企业合作伙伴选择中的应用   总被引:1,自引:0,他引:1  
根据虚拟企业合作伙伴选择的原则,给出了合作伙伴选择的多目标决策模型,用定量的方法对合作伙伴进行描述.同时,给出了改进的二进制粒子群优化算法,并对本文的多目标优化问题进行求解.通过仿真试验测试,证明该方法是可行性.  相似文献   
49.
Summary In controlling the mean of a multivariate normally distributed quality characteristic the main disadvantage of the globalT 2-control charts is that they don't indicate the component of the quality characteristic which gives rise to an alarm. To avoid this disadvantage the joint use of¯x-charts is proposed in this paper, where — for the sake of simplicity — the investigations are restricted to the case of independent components and to one-sided¯x-charts. On the basis of an economic objective function an approximation to the optimal design of the¯x-charts procedure is derived and discussed. It turns out that at least in the bivariate case the nearly optimal economic design is very close to the exact solution.Supported by the Deutsche Forschungsgemeinschaft (DFG).  相似文献   
50.
This paper focuses on the production control of a manufacturing system with time-delay, demand uncertainty and extra capacity. Time-delay is a typical feature of networked manufacturing systems (NMS), because an NMS is composed of many manufacturing systems with transportation channels among them and the transportation of materials needs time. Besides this, for a manufacturing system in an NMS, the uncertainty of the demand from its downstream manufacturing system is considered; and it is assumed that there exist two-levels of demand rates, i.e., the normal one and the higher one, and that the time between the switching of demand rates are exponentially distributed. To avoid the backlog of demands, it is also assumed that extra production capacity can be used when the work-in-process (WIP) cannot buffer the high-level demands rate. For such a manufacturing system with time-delay, demand uncertainty and extra capacity, the mathematical model for its production control problem is established, with the objective of minimizing the mean costs for WIP inventory and occupation of extra production capacity. To solve the problem, a two-level hedging point policy is proposed. By analyzing the probability distribution of system states, optimal values of the two hedging levels are obtained. Finally, numerical experiments are done to verify the effectiveness of the control policy and the optimality of the hedging levels.  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