全文获取类型
收费全文 | 13644篇 |
免费 | 1496篇 |
国内免费 | 389篇 |
专业分类
化学 | 1321篇 |
晶体学 | 31篇 |
力学 | 1099篇 |
综合类 | 145篇 |
数学 | 6717篇 |
物理学 | 1521篇 |
无线电 | 4695篇 |
出版年
2024年 | 61篇 |
2023年 | 233篇 |
2022年 | 429篇 |
2021年 | 480篇 |
2020年 | 401篇 |
2019年 | 391篇 |
2018年 | 387篇 |
2017年 | 514篇 |
2016年 | 556篇 |
2015年 | 488篇 |
2014年 | 837篇 |
2013年 | 842篇 |
2012年 | 971篇 |
2011年 | 819篇 |
2010年 | 636篇 |
2009年 | 754篇 |
2008年 | 775篇 |
2007年 | 808篇 |
2006年 | 659篇 |
2005年 | 586篇 |
2004年 | 436篇 |
2003年 | 411篇 |
2002年 | 370篇 |
2001年 | 331篇 |
2000年 | 301篇 |
1999年 | 227篇 |
1998年 | 251篇 |
1997年 | 209篇 |
1996年 | 156篇 |
1995年 | 172篇 |
1994年 | 143篇 |
1993年 | 127篇 |
1992年 | 107篇 |
1991年 | 90篇 |
1990年 | 76篇 |
1989年 | 64篇 |
1988年 | 50篇 |
1987年 | 40篇 |
1986年 | 38篇 |
1985年 | 56篇 |
1984年 | 50篇 |
1983年 | 15篇 |
1982年 | 22篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 32篇 |
1978年 | 20篇 |
1977年 | 31篇 |
1976年 | 19篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
111.
吴慧卓 《纯粹数学与应用数学》2003,19(1):16-21
典型的进化策略受自然进化过程的启发而成为求解全局优化问题的重要方法。传统的ES变异算子作为一个主要的进化技术是建立在正态分布的随机变量基础上的,本文提出了基于指数分布的进化策略由于采用了新的变异算子有效地减少了产生探试解的成本,从而优于传统的进化策略。 相似文献
112.
In this paper we present a new method for the solution of optimization problems with PDE constraints. It is based on simultaneous pseudo-time stepping for evolution equations. The new method can be viewed as a continuous reduced SQP method in the sense that it uses a preconditioner derived from that method. The reduced Hessian in the preconditioner is approximated by a pseudo-differential operator, whose symbol can be investigated analytically. We apply our method to a boundary control model problem. The new optimization method needs 3.2-times the overall computational effort of the solution of simulation problem alone. 相似文献
113.
Researchers first examined the problem of separable concave programming more than thirty years ago, making it one of the earliest branches of nonlinear programming to be explored. This paper proposes a new algorithm that finds the exact global minimum of this problem in a finite number of iterations. In addition to proving that our algorithm terminates finitely, the paper extends a guarantee of finiteness to all branch-and-bound algorithms for concave programming that (1) partition exhaustively using rectangular subdivisions and (2) branch on the incumbent solution when possible. The algorithm uses domain reduction techniques to accelerate convergence; it solves problems with as many as 100 nonlinear variables, 400 linear variables and 50 constraints in about five minutes on an IBM RS/6000 Power PC. An industrial application with 152 nonlinear variables, 593 linear variables, and 417 constraints is also solved in about ten minutes. 相似文献
114.
A method of simulated annealing in optimization of a computer generated holo-gram(CGH)is presented.The characteristics of energy in annealing curve are analyzed.Thecooling schedule such as giving an initial temperature,the temperature function,the numberof interactions and stopping criterion are discussed.As an example,an optimization of phaserelief kinoform,a CGH with multiple phase levels,is implemented. 相似文献
115.
Andrew V. Goldberg Michael D. Grigoriadis Robert E. Tarjan 《Mathematical Programming》1991,50(1-3):277-290
Goldfarb and Hao (1990) have proposed a pivot rule for the primal network simplex algorithm that will solve a maximum flow problem on ann-vertex,m-arc network in at mostnm pivots and O(n
2
m) time. In this paper we describe how to extend the dynamic tree data structure of Sleator and Tarjan (1983, 1985) to reduce the running time of this algorithm to O(nm logn). This bound is less than a logarithmic factor larger than those of the fastest known algorithms for the problem. Our extension of dynamic trees is interesting in its own right and may well have additional applications.Research partially supported by a Presidential Young Investigator Award from the National Science Foundation, Grant No. CCR-8858097, an IBM Faculty Development Award, and AT&T Bell Laboratories.Research partially supported by the Office of Naval Research, Contract No. N00014-87-K-0467.Research partially supported by the National Science Foundation, Grant No. DCR-8605961, and the Office of Naval Research, Contract No. N00014-87-K-0467. 相似文献
116.
Preparation of Papers 总被引:8,自引:0,他引:8
We motivate the study of a vector variational inequality by a practical flow equilibrium problem on a network, namely a generalization of the well-known Wardrop equilibrium principle. Both weak and strong forms of the vector variational inequality are discussed and their relationships to a vector optimization problem are established under various convexity assumptions. 相似文献
117.
Fernández F. R. Monroy L. Puerto J. 《Journal of Optimization Theory and Applications》1998,99(2):403-421
In this paper, we deal with multicriteria matrix games. Different solution concepts have been proposed to cope with these games. Recently, the concept of Pareto-optimal security strategy which assures the property of security in the individual criteria against an opponent's deviation in strategy has been introduced. However, the idea of security behind this concept is based on expected values, so that this security might be violated by mixed strategies when replications are not allowed. To avoid this inconvenience, we propose in this paper a new concept of solution for these games: the G-goal security strategy, which includes as part of the solution the probability of obtaining prespecified values in the payoff functions. Thus, attitude toward risk together with payoff values are considered jointly in the solution analysis. 相似文献
118.
灰色模型的最优化及其参数的直接求法 总被引:2,自引:0,他引:2
基于灰色模型的内涵表达式和白化方程响应式均为等比级数的观点,提出了一种不用求ago值、均值,不涉及灰色微分方程,白化微分方程概念,直接求灰色模型参数a,c的方法,通过此方法建立的新模型不仅从理论上可保证是在满足给定评价标准为模拟绝对误差平方和最小(或模拟相对误差平方和最小)、给定精度条件下的最优化模型,从而结束了灰色模型只有更优,没有最优的历史.并从理论上证明了新模型具有白化指数律重合性、白化系数律重合性,伸缩变换一致性.最后通过实例编程验证该方法具有可操作性,且预测精度高,效果好. 相似文献
119.
CONE-DIRECTED CONTINGENT DERIVATIVES AND GENERALIZED PREINVEX SET-VALUED OPTIMIZATION 总被引:2,自引:0,他引:2
丘京辉 《数学物理学报(B辑英文版)》2007,27(1):211-218
By using cone-directed contingent derivatives, the unified necessary and suffi-cient optimality conditions are given for weakly and strongly minimal elements respectively in generalized preinvex set valued optimization. 相似文献
120.
We consider a class of non-linear mixed integer programs with n integer variables and k continuous variables. Solving instances from this class to optimality is an NP-hard problem. We show that for the cases with
k=1 and k=2, every optimal solution is integral. In contrast to this, for every k≥3 there exist instances where every optimal solution takes non-integral values.
Received: August 2001 / Accepted: January 2002?Published online March 27, 2002 相似文献