全文获取类型
收费全文 | 6371篇 |
免费 | 500篇 |
国内免费 | 644篇 |
专业分类
化学 | 806篇 |
晶体学 | 16篇 |
力学 | 795篇 |
综合类 | 99篇 |
数学 | 4486篇 |
物理学 | 1313篇 |
出版年
2024年 | 10篇 |
2023年 | 79篇 |
2022年 | 143篇 |
2021年 | 147篇 |
2020年 | 201篇 |
2019年 | 185篇 |
2018年 | 174篇 |
2017年 | 204篇 |
2016年 | 201篇 |
2015年 | 143篇 |
2014年 | 241篇 |
2013年 | 473篇 |
2012年 | 296篇 |
2011年 | 380篇 |
2010年 | 319篇 |
2009年 | 488篇 |
2008年 | 464篇 |
2007年 | 428篇 |
2006年 | 386篇 |
2005年 | 354篇 |
2004年 | 274篇 |
2003年 | 258篇 |
2002年 | 223篇 |
2001年 | 185篇 |
2000年 | 190篇 |
1999年 | 168篇 |
1998年 | 197篇 |
1997年 | 140篇 |
1996年 | 112篇 |
1995年 | 62篇 |
1994年 | 54篇 |
1993年 | 42篇 |
1992年 | 44篇 |
1991年 | 36篇 |
1990年 | 25篇 |
1989年 | 20篇 |
1988年 | 22篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 13篇 |
1984年 | 19篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有7515条查询结果,搜索用时 218 毫秒
61.
Youssef Saab 《Journal of Heuristics》1997,3(3):207-224
A heuristic optimization methodology, Dynamic Contraction (DC), is introduced as an approach for solving a wide variety of hard combinatorial problems. Contraction is an operation that maps an instance of a problem to a smaller instance of the same problem. DC is an iterative improvement strategy that relies on contraction as a mechanism for escaping local minima. As a byproduct of contraction, efficiency is improved due to a reduction of problem size. Effectiveness of DC is shown through simple applications to two classical combinatorial problems: The graph bisection problem and the traveling salesman problem. 相似文献
62.
Algorithms for systematical search of inverse in arithmetic operations with fuzzy numbers are discussed. The fuzzy number derived is considered either in a discrete representation of its support or described by the parameters of the corresponding membership function formula. Both algorithms are easy to be programmed for desk calculators. 相似文献
63.
Bai-suo JIN~ 《中国科学A辑(英文版)》2007,50(9):1303-1315
In the factor analysis model with large cross-section and time-series dimensions,we pro- pose a new method to estimate the number of factors.Specially if the idiosyncratic terms satisfy a linear time series model,the estimators of the parameters can be obtained in the time series model. The theoretical properties of the estimators are also explored.A simulation study and an empirical analysis are conducted. 相似文献
64.
65.
对于多属性群决策问题的处理,有时需要采用先决策、后综合的处理方法,而含有语言评价信息的多属性群决策问题,定性目标一般用语言评价信息描述,由决策人给出定性目标和权系数的语言变量评价,用梯形模糊数表示,对定量目标进行无量纲化处理;将决策人对于单一目标的评价指标聚合成多个目标的评价模糊数,采用Bass-Kw akernaak模糊数排序方法对方案进行排序;群体的评价通过Borda函数来集结方案集的群体排序. 相似文献
66.
For any given positive integer n≥1,the Euler functionφ(n) is defined to be the number of positive integers not exceeding n,which is relatively prime to n.ω(n) is defined to be the number of different prime divisors of n.In order to know the solvability of the function ofφ(φ(φ(n)))=2~(ω(n)),properties of the number theoretical functionφ(φ(n)) is studied in the paper. 相似文献
67.
68.
Two different problems are proposed as approximations of the usual system modelling natural convection under the Oberbeck-Boussinesq assumptions. The error is evaluated by means of the norm of its gradient in the Hilbert space. The average Nusselt number is also estimated. 相似文献
69.
Kang Hai TAN Xiao Ping YANG 《数学学报(英文版)》2006,22(3):701-710
In this paper we give a geometric interpretation of the notion of the horizontal mean curvature which is introduced by Danielli Garofalo-Nhieu and Pauls who recently introduced sub- Riemannian minimal surfaces in Carnot groups. This will be done by introducing a natural nonholonomic connection which is the restriction (projection) of the natural Riemannian connection on the horizontal bundle. For this nonholonomic connection and (intrinsic) regular hypersurfaces we introduce the notions of the horizontal second fundamental form and the horizontal shape operator. It turns out that the horizontal mean curvature is the trace of the horizontal shape operator. 相似文献
70.
I. P. Rochev 《Mathematical Notes》2007,81(1-2):247-259
We consider generalizations of Pólya’s theorem to the case of entire functions taking algebraic values at natural or integer points. 相似文献