全文获取类型
收费全文 | 9296篇 |
免费 | 565篇 |
国内免费 | 205篇 |
专业分类
化学 | 271篇 |
晶体学 | 4篇 |
力学 | 380篇 |
综合类 | 178篇 |
数学 | 8712篇 |
物理学 | 521篇 |
出版年
2023年 | 36篇 |
2022年 | 96篇 |
2021年 | 175篇 |
2020年 | 113篇 |
2019年 | 122篇 |
2018年 | 120篇 |
2017年 | 212篇 |
2016年 | 239篇 |
2015年 | 173篇 |
2014年 | 464篇 |
2013年 | 449篇 |
2012年 | 523篇 |
2011年 | 411篇 |
2010年 | 412篇 |
2009年 | 580篇 |
2008年 | 572篇 |
2007年 | 614篇 |
2006年 | 437篇 |
2005年 | 410篇 |
2004年 | 316篇 |
2003年 | 312篇 |
2002年 | 298篇 |
2001年 | 240篇 |
2000年 | 263篇 |
1999年 | 203篇 |
1998年 | 198篇 |
1997年 | 167篇 |
1996年 | 201篇 |
1995年 | 190篇 |
1994年 | 130篇 |
1993年 | 139篇 |
1992年 | 149篇 |
1991年 | 127篇 |
1990年 | 99篇 |
1989年 | 77篇 |
1988年 | 93篇 |
1987年 | 54篇 |
1986年 | 83篇 |
1985年 | 129篇 |
1984年 | 86篇 |
1983年 | 31篇 |
1982年 | 53篇 |
1981年 | 43篇 |
1980年 | 38篇 |
1979年 | 28篇 |
1978年 | 48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 0 毫秒
1.
Motor Imagery Electroencephalography (MI-EEG) has shown good prospects in neurorehabilitation, and the entropy-based nonlinear dynamic methods have been successfully applied to feature extraction of MI-EEG. Especially based on Multiscale Fuzzy Entropy (MFE), the fuzzy entropies of the τ coarse-grained sequences in τ scale are calculated and averaged to develop the Composite MFE (CMFE) with more feature information. However, the coarse-grained process fails to match the nonstationary characteristic of MI-EEG by a mean filtering algorithm. In this paper, CMFE is improved by assigning the different weight factors to the different sample points in the coarse-grained process, i.e., using the weighted mean filters instead of the original mean filters, which is conductive to signal filtering and feature extraction, and the resulting personalized Weighted CMFE (WCMFE) is more suitable to represent the nonstationary MI-EEG for different subjects. All the WCMFEs of multi-channel MI-EEG are fused in serial to construct the feature vector, which is evaluated by a back-propagation neural network. Based on a public dataset, extensive experiments are conducted, yielding a relatively higher classification accuracy by WCMFE, and the statistical significance is examined by two-sample t-test. The results suggest that WCMFE is superior to the other entropy-based and traditional feature extraction methods. 相似文献
2.
M. M. Kostreva 《Journal of Optimization Theory and Applications》1989,62(1):63-76
Murty's algorithm for the linear complementarity problem is generalized to solve the optimality conditions for linear and convex quadratic programming problems with both equality and inequality constraints. An implementation is suggested which provides both efficiency and tight error control. Numerical experiments as well as field tests in various applications show favorable results.The author thanks K. G. Murty for his encouragement and helpful comments. 相似文献
3.
Dean A. Carlson 《Journal of Mathematical Analysis and Applications》2002,276(2):561-588
The method of equivalent variational methods, originally due to Carathéodory for free problems in the calculus of variations is extended to investigate feedback Nash equilibria for a class of n-person differential games. Both the finite-horizon and infinite-horizon cases are considered. Examples are given to illustrate the presented results. 相似文献
4.
根据生产任务选择加工设备进行制造资源重组是实现可重构制造系统的关键问题之一,由于设备的选择涉及到多种因素,既有定量指标,又有定性指标,传统的依靠人工经验的方法显得力不从心。本文首先结合实际情况,提出了一套设备选择评价体系,通过对模糊判断矩阵采用最小对数二乘法确定各评价因素的权重系数,针对定性指标和定量指标采用不同的方法确定其性能指标值,通过模糊积分对评判指标进行综合评判,最后进行了实例研究。所提出的方法有效地简化了决策过程,为可重构制造系统设备选择提供了一套行之有效的方法。 相似文献
5.
Mikhail Andramonov 《Journal of Global Optimization》2002,24(2):115-132
We consider applications of disjunctive programming to global optimization and problems with equilibrium constraints. We propose a modification of the algorithm of F. Beaumont for disjunctive programming problems and show its numerical efficiency. 相似文献
6.
Boban Marinković 《Mathematical Methods of Operations Research》2006,63(3):513-524
We present local sensitivity analysis for discrete optimal control problems with varying endpoints in the case when the customary regularity of boundary conditions can be violated. We study the behavior of the optimal solutions subject to parametric perturbations of the problem. 相似文献
7.
We consider the problem of maximizing a linear fractional function on the Pareto efficient frontier of two other linear fractional functions. We present a finite pivoting-type algorithm that solves the maximization problem while computing simultaneously the efficient frontier. Application to multistage efficiency analysis is discussed. An example demonstrating the computational procedure is included. 相似文献
8.
Dual fractional cutting plane algorithms, in which cutting planes are used to iteratively tighten a linear relaxation of an integer program,
are well-known and form the basis of the highly successful branch-and-cut method. It is rather less well-known that various primal cutting plane algorithms were developed in the 1960s, for example by Young. In a primal algorithm, the main role of the cutting
planes is to enable a feasible solution to the original problem to be improved. Research on these algorithms has been almost
non-existent.
In this paper we argue for a re-examination of these primal methods. We describe a new primal algorithm for pure 0-1 problems based on strong valid inequalities and give some encouraging computational results. Possible extensions to the case of general
mixed-integer programs are also discussed. 相似文献
9.
Constraint Programming and Operations Research: Comments from an Operations Researcher 总被引:4,自引:0,他引:4
Michel Gendreau 《Journal of Heuristics》2002,8(1):19-24
This paper relates the author's personal experience with constraint programming and gives a personal assessment of the relationships between constraint programming and operations research. 相似文献
10.
最速下降规则不失为一可用规则 总被引:5,自引:4,他引:1
本从统计意义上平均迭代次数的观点出发,指出求解线性规划的最速下降规则是可取的,好用的。 相似文献