全文获取类型
收费全文 | 9047篇 |
免费 | 408篇 |
国内免费 | 373篇 |
专业分类
化学 | 407篇 |
晶体学 | 4篇 |
力学 | 388篇 |
综合类 | 102篇 |
数学 | 8393篇 |
物理学 | 534篇 |
出版年
2023年 | 41篇 |
2022年 | 80篇 |
2021年 | 93篇 |
2020年 | 103篇 |
2019年 | 117篇 |
2018年 | 132篇 |
2017年 | 169篇 |
2016年 | 184篇 |
2015年 | 129篇 |
2014年 | 376篇 |
2013年 | 487篇 |
2012年 | 508篇 |
2011年 | 397篇 |
2010年 | 392篇 |
2009年 | 553篇 |
2008年 | 578篇 |
2007年 | 627篇 |
2006年 | 455篇 |
2005年 | 387篇 |
2004年 | 312篇 |
2003年 | 327篇 |
2002年 | 302篇 |
2001年 | 268篇 |
2000年 | 272篇 |
1999年 | 233篇 |
1998年 | 206篇 |
1997年 | 189篇 |
1996年 | 213篇 |
1995年 | 186篇 |
1994年 | 136篇 |
1993年 | 141篇 |
1992年 | 140篇 |
1991年 | 134篇 |
1990年 | 103篇 |
1989年 | 71篇 |
1988年 | 94篇 |
1987年 | 54篇 |
1986年 | 84篇 |
1985年 | 119篇 |
1984年 | 80篇 |
1983年 | 23篇 |
1982年 | 55篇 |
1981年 | 44篇 |
1980年 | 35篇 |
1979年 | 31篇 |
1978年 | 51篇 |
1977年 | 49篇 |
1976年 | 27篇 |
1975年 | 12篇 |
1974年 | 13篇 |
排序方式: 共有9828条查询结果,搜索用时 162 毫秒
161.
A hybrid technique using constraint programming and linear programming is applied to the problem of scheduling with earliness and tardiness costs. The linear model maintains a set of relaxed optimal start times which are used to guide the constraint programming search heuristic. In addition, the constraint programming problem model employs the strong constraint propagation techniques responsible for many of the advances in constraint programming for scheduling in the past few years. Empirical results validate our approach and show, in particular, that creating and solving a subproblem containing only the activities with direct impact on the cost function and then using this solution in the main search, significantly increases the number of problems that can be solved to optimality while significantly decreasing the search time. 相似文献
162.
以美国南弗洛里达州递避飓风袭击为例建立了紧急输送情况下的线性规划模型。其中具体建立了以SCEPD(美国南弗洛里达州紧急情况预防部门)提出的公路反向,地区分块撤离,使用小路等三个最受人们关注的策略的模型。模型的灵敏度分析能很好地解释建立更多的临时避难所、限制车辆等策略对撤离的影响。在相近的环境下,中模型解得的结果很接近官方预测的结果,并且本的模型能对更广泛的情况进行分析.可给SCEPD提供一定参考。 相似文献
163.
This paper defines a set of material compatibility constraints for use in order promising mixed integer programs. The constraints always represent a necessary condition for compatibility and, in certain cases, are both necessary and sufficient. The underlying analysis represents incompatibilities using bipartite graphs and applies results from the perfectly matchable subgraph polytope. 相似文献
164.
关于非线性多目标规划问题非劣解解法的探讨 总被引:3,自引:0,他引:3
非线性多目标规划是一类复杂的规划问题,由于其往往没有最优解,因此求其非劣解具有重要的意义。本首先探讨了无约束条件下非线性多目标规划的解法,然后提出了有约束条件下非线性多目标规划的一种解法。所述方法具有一定的普遍意义。 相似文献
165.
A linear inequality system with infinitely many constraints is polynomial (analytical) if its index set is a compact interval
of the real line and all its coefficients are polynomial (analytical, respectively) functions of the index on this interval.
This paper provides an example of analytical system whose solution set cannot be the solution set of any polynomial system.
Research supported by DGES of Spain and FEDER of UE, Grant BFM2002-04114-C02-01.
Research supported by CONACyT of Mexico, Grant 130036.
Research partially supported by CONACyT of Mexico, Grant 44003. 相似文献
166.
带有随机因素的逆DEA模型 总被引:3,自引:0,他引:3
韩松 《数学的实践与认识》2003,33(3):23-29
本文讨论含有随机因素的逆 DEA模型 .逆 DEA模型解决的问题是 :对于某个决策单元 (DMU ) ,若增加其输入 ,在保持相对效率水平不变的情况下 ,估计 (预测 )输出应增加多少 .因此逆 DEA模型可用于短期预测问题 .带有随机因素的逆 DEA模型 ,是将该问题转化成机会约束的多目标规划问题 ,在某些特殊情况下 ,成为机会约束的线性规划问题 . 相似文献
167.
168.
Nicholas I. M. Gould Dominique Orban Annick Sartenaer Phillipe L. Toint 《4OR: A Quarterly Journal of Operations Research》2005,3(3):227-241
In this paper, we examine the sensitivity of trust-region algorithms on the parameters related to the step acceptance and
update of the trust region. We show, in the context of unconstrained programming, that the numerical efficiency of these algorithms
can easily be improved by choosing appropriate parameters. Recommended ranges of values for these parameters are exhibited
on the basis of extensive numerical tests.
MSC classification:
65K05, 90C26, 90C30 相似文献
169.
Rüdiger Schultz Leen Stougie Maarten H. van der Vlerk 《Mathematical Programming》1998,83(1-3):229-252
In this paper we present a framework for solving stochastic programs with complete integer recourse and discretely distributed right-hand side vector, using Gröbner basis methods from computational algebra to solve the numerous second-stage integer programs. Using structural properties of the expected integer recourse function, we prove that under mild conditions an optimal solution is contained in a finite set. Furthermore, we present a basic scheme to enumerate this set and suggest improvements to reduce the number of function evaluations needed. 相似文献
170.
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