全文获取类型
收费全文 | 8129篇 |
免费 | 729篇 |
国内免费 | 956篇 |
专业分类
化学 | 7440篇 |
晶体学 | 69篇 |
力学 | 381篇 |
综合类 | 99篇 |
数学 | 802篇 |
物理学 | 1023篇 |
出版年
2024年 | 20篇 |
2023年 | 100篇 |
2022年 | 294篇 |
2021年 | 234篇 |
2020年 | 324篇 |
2019年 | 311篇 |
2018年 | 305篇 |
2017年 | 473篇 |
2016年 | 511篇 |
2015年 | 435篇 |
2014年 | 466篇 |
2013年 | 532篇 |
2012年 | 586篇 |
2011年 | 542篇 |
2010年 | 484篇 |
2009年 | 469篇 |
2008年 | 392篇 |
2007年 | 477篇 |
2006年 | 405篇 |
2005年 | 330篇 |
2004年 | 284篇 |
2003年 | 235篇 |
2002年 | 231篇 |
2001年 | 171篇 |
2000年 | 184篇 |
1999年 | 155篇 |
1998年 | 135篇 |
1997年 | 139篇 |
1996年 | 136篇 |
1995年 | 101篇 |
1994年 | 89篇 |
1993年 | 28篇 |
1992年 | 21篇 |
1991年 | 22篇 |
1990年 | 32篇 |
1989年 | 17篇 |
1988年 | 17篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 24篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1959年 | 4篇 |
排序方式: 共有9814条查询结果,搜索用时 15 毫秒
21.
In this paper,the concept of the infinitesimal realization factor is extended to the parameter-dependent performance functions in closed queueing networks. Then the concepts of realization matrix (its elements are called realization factors) and performance potential are introduced,and the relations between infinitesimal realization factors and these two quantities are discussed. This provides a united framework for both IPA and non IPA approaches. Finally,another physical meaning of the service rate is given. 相似文献
22.
工件带到达时间的两阶段柔性流水作业的近似算法 总被引:1,自引:0,他引:1
研究了工件带到时间的两阶段柔性流水作业的排序问题,基于求解流水作业和平行机问题的算法思想,提出两个相应的近似算法H(R)和H(MR(?)),证明了这两个算法的最坏情况性能比分别为3-1/m和2/5-1/m,讨论了界的紧性,并利用数值模拟以分析算法与最优值的近似性能比. 相似文献
23.
Rafael Caballero Mercedes González Flor M Guerrero Julián Molina Concepción Paralera 《European Journal of Operational Research》2007
In this work we present a multiobjective location routing problem and solve it with a multiobjective metaheuristic procedure. In this type of problem, we have to locate some plants within a set of possible locations to meet the demands of a number of clients with multiple objectives. This type of model is used to solve a problem with real data in the region of Andalusia (Spain). Thus, we study the location of two incineration plants for the disposal of solid animal waste from some preestablished locations in Andalusia, and design the routes to serve the different slaughterhouses in this region. This must be done while taking into account certain economic objectives (start-up, maintenance, and transport costs) and social objectives (social rejection by towns on the truck routes, maximum risk as an equity criterion, and the negative implications for towns close to the plant). 相似文献
24.
25.
We study a leader follower game with two players: a terrorist and a state where the later one installs facilities that provide support in case of a terrorist attack. While the Terrorist attacks one of the metropolitan areas to maximize his utility, the State, which acts as a leader, installs the facilities such that the metropolitan area attacked is the one that minimizes her disutility (i.e., minimizes ‘loss’). We solve the problem efficiently for one facility and we formulate it as a mathematical programming problem for a general number of facilities. We demonstrate the problem via a case study of the 20 largest metropolitan areas in the United States. 相似文献
26.
Roberto D. Galvão Luis Gonzalo Acosta Espejo Brian Boffey 《Annals of Operations Research》2006,143(1):31-44
A study has been carried out aimed at reducing perinatal mortality in the municipality of Rio de Janeiro through a better
distribution of health care facilities. The algorithmic aspects are detailed elsewhere and here the emphasis is on practical
issues and difficulties encountered.
A 3-level hierarchical model was developed. Both uncapacitated and capacitated versions are briefly described together with
some results based on actual data. The project brought to light many contradictions between OR theory and practice in developing
countries and, unfortunately, the models developed were not implemented by the municipality health authorities. Possible reasons
for this outcome are analysed. 相似文献
27.
一种供应链中的知识管理绩效评价方法研究 总被引:7,自引:0,他引:7
作为知识管理的重要组成部分,知识管理绩效评价旨在帮助企业找出影响绩效提高的关键因素并及时采取有效措施,提高知识管理水平。本文从创造顾客价值、知识的获取能力、知识的共享与传播能力、知识的运用水平、知识的存量水平和知识管理平台等六个方面,分析了评价供应链的知识管理绩效应考虑的主要因素,建立了供应链的知识管理绩效评价指标体系,在此基础上,提出了运用D-S证据推理方法,对供应链知识管理绩效进行评价,并给出了证据推理的算法步骤,最后通过算例分析,说明该方法的有效性、实用性。 相似文献
28.
Nash Equilibria,Variational Inequalities,and Dynamical Systems 总被引:2,自引:0,他引:2
Cavazzuti E. Pappalardo M. Passacantando M. 《Journal of Optimization Theory and Applications》2002,114(3):491-506
In this paper, we introduce some relationships between Nash equilibria, variational equilibria, and dynamical equilibria for noncooperative games. 相似文献
29.
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
30.
给定一组工件的加工时间与工期,要求确定这些工件在一台机器上的加.工排列,使相应的总延误达到最小,这就是总延误问题.该问题在近年已被证明是NP困难的.由Wilkermn和Irwin(1971),林勋(1983)等所研究的顺时安排法能得到相邻交换意义下的局部解.在本文中,我们进一步证明该算法能得到前移邻域意义下的局部解,并确定了该算法的性能比. 相似文献