全文获取类型
收费全文 | 6623篇 |
免费 | 318篇 |
国内免费 | 406篇 |
专业分类
化学 | 599篇 |
晶体学 | 5篇 |
力学 | 272篇 |
综合类 | 119篇 |
数学 | 5291篇 |
物理学 | 1061篇 |
出版年
2024年 | 7篇 |
2023年 | 38篇 |
2022年 | 88篇 |
2021年 | 107篇 |
2020年 | 185篇 |
2019年 | 183篇 |
2018年 | 165篇 |
2017年 | 141篇 |
2016年 | 137篇 |
2015年 | 144篇 |
2014年 | 332篇 |
2013年 | 835篇 |
2012年 | 311篇 |
2011年 | 431篇 |
2010年 | 376篇 |
2009年 | 465篇 |
2008年 | 474篇 |
2007年 | 463篇 |
2006年 | 335篇 |
2005年 | 221篇 |
2004年 | 239篇 |
2003年 | 218篇 |
2002年 | 205篇 |
2001年 | 150篇 |
2000年 | 124篇 |
1999年 | 134篇 |
1998年 | 128篇 |
1997年 | 110篇 |
1996年 | 85篇 |
1995年 | 71篇 |
1994年 | 67篇 |
1993年 | 49篇 |
1992年 | 33篇 |
1991年 | 30篇 |
1990年 | 44篇 |
1989年 | 24篇 |
1988年 | 24篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 13篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 13篇 |
1976年 | 8篇 |
1975年 | 4篇 |
排序方式: 共有7347条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Y. Wardi 《Journal of Optimization Theory and Applications》1989,61(3):473-485
A stochastic algorithm for finding stationary points of real-valued functions defined on a Euclidean space is analyzed. It is based on the Robbins-Monro stochastic approximation procedure. Gradient evaluations are done by means of Monte Carlo simulations. At each iteratex
i
, one sample point is drawn from an underlying probability space, based on which the gradient is approximated. The descent direction is against the approximation of the gradient, and the stepsize is 1/i. It is shown that, under broad conditions, w.p.1 if the sequence of iteratesx
1,x
2,...generated by the algorithm is bounded, then all of its accumulation points are stationary. 相似文献
5.
José E. Valdés 《Operations Research Letters》2006,34(1):49-52
Components C1 and C2 form a series system. Suppose we can allocate the spare R1 in parallel with C1 and the spare R2 in parallel with C2, or otherwise, allocate R1 with C2 and R2 with C1. In this paper, we compare these two options using hazard rate ordering. 相似文献
6.
7.
Fabio Schoen 《Journal of Global Optimization》1991,1(3):207-228
In this paper stochastic algorithms for global optimization are reviewed. After a brief introduction on random-search techniques, a more detailed analysis is carried out on the application of simulated annealing to continuous global optimization. The aim of such an analysis is mainly that of presenting recent papers on the subject, which have received only scarce attention in the most recent published surveys. Finally a very brief presentation of clustering techniques is given. 相似文献
8.
9.
Kasper K. Berthelsen Jesper Møller 《Bulletin of the Brazilian Mathematical Society》2002,33(3):351-367
This primer provides a self-contained exposition of the case where spatial birth-and-death processes are used for perfect
simulation of locally stable point processes. Particularly, a simple dominating coupling from the past (CFTP) algorithm and
the CFTP algorithms introduced in [13], [14], and [5] are studied. Some empirical results for the algorithms are discussed.
Received: 30 June 2002 相似文献
10.
Several a priori tests of a systematic stochastic mode reduction procedure recently devised by the authors [Proc. Natl. Acad. Sci. 96 (1999) 14687; Commun. Pure Appl. Math. 54 (2001) 891] are developed here. In this procedure, reduced stochastic equations for a smaller collections of resolved variables are derived systematically for complex nonlinear systems with many degrees of freedom and a large collection of unresolved variables. While the above approach is mathematically rigorous in the limit when the ratio of correlation times between the resolved and the unresolved variables is arbitrary small, it is shown here on a systematic hierarchy of models that this ratio can be surprisingly big. Typically, the systematic reduced stochastic modeling yields quantitatively realistic dynamics for ratios as large as 1/2. The examples studied here vary from instructive stochastic triad models to prototype complex systems with many degrees of freedom utilizing the truncated Burgers–Hopf equations as a nonlinear heat bath. Systematic quantitative tests for the stochastic modeling procedure are developed here which involve the stationary distribution and the two-time correlations for the second and fourth moments including the resolved variables and the energy in the resolved variables. In an important illustrative example presented here, the nonlinear original system involves 102 degrees of freedom and the reduced stochastic model predicted by the theory for two resolved variables involves both nonlinear interaction and multiplicative noises. Even for large value of the correlation time ratio of the order of 1/2, the reduced stochastic model with two degrees of freedom captures the essentially nonlinear and non-Gaussian statistics of the original nonlinear systems with 102 modes extremely well. Furthermore, it is shown here that the standard regression fitting of the second-order correlations alone fails to reproduce the nonlinear stochastic dynamics in this example. 相似文献