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   10715篇
  免费   825篇
  国内免费   235篇
化学   593篇
晶体学   9篇
力学   398篇
综合类   180篇
数学   7442篇
物理学   542篇
无线电   2611篇
  2023年   53篇
  2022年   129篇
  2021年   154篇
  2020年   174篇
  2019年   161篇
  2018年   168篇
  2017年   225篇
  2016年   269篇
  2015年   261篇
  2014年   529篇
  2013年   535篇
  2012年   642篇
  2011年   560篇
  2010年   522篇
  2009年   636篇
  2008年   701篇
  2007年   778篇
  2006年   557篇
  2005年   500篇
  2004年   433篇
  2003年   378篇
  2002年   367篇
  2001年   312篇
  2000年   315篇
  1999年   240篇
  1998年   211篇
  1997年   169篇
  1996年   207篇
  1995年   189篇
  1994年   121篇
  1993年   131篇
  1992年   131篇
  1991年   120篇
  1990年   96篇
  1989年   64篇
  1988年   87篇
  1987年   53篇
  1986年   79篇
  1985年   112篇
  1984年   75篇
  1983年   23篇
  1982年   46篇
  1981年   37篇
  1980年   33篇
  1979年   26篇
  1978年   47篇
  1977年   46篇
  1976年   26篇
  1975年   12篇
  1974年   12篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
61.
为了解决蛋白质三维结构比对需要处理大量的旋转、平移变换,直接用动态规划将变得十分繁琐这一问题,在保留蛋白质空间结构属性特征的基础上,对蛋白质三维数据进行了预先的处理.通过计算蛋白质结构在旋转和平移下的几何不变量,将蛋白质的三维结构坐标变换为具有旋转、平移不变性的一维序列.进一步给出了“距离”以及“相似得分”的定义.在此基础上采用动态规划方法给出了新的蛋白质结构比对算法.对专家分类的蛋白质结构数据库进行测试,结果显示准确、快速.  相似文献   
62.
Two independent proofs of the polyhedrality of the split closure of mixed integer linear program have been previously presented. Unfortunately neither of these proofs is constructive. In this paper, we present a constructive version of this proof. We also show that split cuts dominate a family of inequalities introduced by Köppe and Weismantel.  相似文献   
63.
In this paper,the UV-theory and P-differential calculus are employed to study second-order ex-pansion of a class of D.C.functions and minimization problems.Under certain conditions,some properties ofthe U-Lagrangian,the second-order expansion of this class of functions along some trajectories are formulated.Some first and second order optimality conditions for the class of D.C.optimization problems are given.  相似文献   
64.
A new algorithm based on Genetic Programming (GP) for the problem of optimization of Multiple constant Multiplication (MCM) by Common Subexpression Elimination(CSE) is developed. This method is used for hardware optimization for DSP systems. A solution based on Genetic Programming is shown in this paper. The performance of the technique is demonstrated in one- and multi-dimensional digital filters with constant coefficients.  相似文献   
65.
基于SUN5500小型计算机并行开发环境,给出了消息传递模型和蕴式行模型的实现方法,通过实例分析了SUNMPI实际编程,并对选取不同模型有不同参数的运算时间进行了比较,结果表明,在SUN5500计算机上MPI模型和蕴式并行模型均能较大地提高运算速度,而且MPI在灵活性和并行程度方面更优。  相似文献   
66.
In the present paper we develop our approach for studying the stability of integer programming problems. We prove that the L-class enumeration method is stable on integer linear programming problems in the case of bounded relaxation sets [9]. The stability of some cutting plane algorithms is discussed.  相似文献   
67.
The Dantzig-Wolfe reformulation principle is presented based on the concept of generating sets. The use of generating sets allows for an easy extension to mixed integer programming. Moreover, it provides a unifying framework for viewing various column generation practices, such as relaxing or tightening the column generation subproblem and introducing stabilization techniques.  相似文献   
68.
In this paper we propose a general integration scheme for a Multi-Criteria Decision Making model of the Multi-Attribute Utility Theory in Constraint Programming. We introduce the Choquet integral as a general aggregation function for multi-criteria optimization problems and define the Choquet global constraint that propagates this function during the Branch-and-Bound search. Finally the benefits of the propagation of the Choquet constraint are evaluated on the examination timetabling problem.  相似文献   
69.
This paper introduces a novel approach for extracting the maximum number of non-overlapping test forms from a large collection of overlapping test sections assembled from a given item bank. The approach involves solving maximum set packing problems (MSPs). A branch-and-bound MSP algorithm is developed along with techniques adapted from constraint programming to estimate lower and upper bounds on the optimal MSP solution. The algorithm is general and can be applied in other applications including combinatorial auctions. The results of computer simulations and experiments with an operational item bank are presented. An erratum to this article is available at .  相似文献   
70.
We study convergence properties of a modified subgradient algorithm, applied to the dual problem defined by the sharp augmented Lagrangian. The primal problem we consider is nonconvex and nondifferentiable, with equality constraints. We obtain primal and dual convergence results, as well as a condition for existence of a dual solution. Using a practical selection of the step-size parameters, we demonstrate the algorithm and its advantages on test problems, including an integer programming and an optimal control problem. *Partially Supported by 2003 UniSA ITEE Small Research Grant Ero2. Supported by CAPES, Brazil, Grant No. 0664-02/2, during her visit to the School of Mathematics and Statistics, UniSA.  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