全文获取类型
收费全文 | 8684篇 |
免费 | 799篇 |
国内免费 | 312篇 |
专业分类
化学 | 1021篇 |
晶体学 | 50篇 |
力学 | 616篇 |
综合类 | 67篇 |
数学 | 5486篇 |
物理学 | 2555篇 |
出版年
2023年 | 67篇 |
2022年 | 79篇 |
2021年 | 191篇 |
2020年 | 251篇 |
2019年 | 218篇 |
2018年 | 216篇 |
2017年 | 192篇 |
2016年 | 232篇 |
2015年 | 181篇 |
2014年 | 310篇 |
2013年 | 895篇 |
2012年 | 356篇 |
2011年 | 383篇 |
2010年 | 354篇 |
2009年 | 438篇 |
2008年 | 474篇 |
2007年 | 514篇 |
2006年 | 423篇 |
2005年 | 357篇 |
2004年 | 284篇 |
2003年 | 316篇 |
2002年 | 331篇 |
2001年 | 304篇 |
2000年 | 333篇 |
1999年 | 254篇 |
1998年 | 249篇 |
1997年 | 162篇 |
1996年 | 123篇 |
1995年 | 124篇 |
1994年 | 123篇 |
1993年 | 85篇 |
1992年 | 98篇 |
1991年 | 83篇 |
1990年 | 75篇 |
1989年 | 71篇 |
1988年 | 58篇 |
1987年 | 74篇 |
1986年 | 48篇 |
1985年 | 92篇 |
1984年 | 67篇 |
1983年 | 36篇 |
1982年 | 51篇 |
1981年 | 26篇 |
1980年 | 28篇 |
1979年 | 34篇 |
1978年 | 22篇 |
1977年 | 34篇 |
1976年 | 23篇 |
1974年 | 12篇 |
1973年 | 12篇 |
排序方式: 共有9795条查询结果,搜索用时 31 毫秒
31.
32.
The Sample Average Approximation Method Applied to Stochastic Routing Problems: A Computational Study 总被引:1,自引:0,他引:1
Bram Verweij Shabbir Ahmed Anton J. Kleywegt George Nemhauser Alexander Shapiro 《Computational Optimization and Applications》2003,24(2-3):289-333
The sample average approximation (SAA) method is an approach for solving stochastic optimization problems by using Monte Carlo simulation. In this technique the expected objective function of the stochastic problem is approximated by a sample average estimate derived from a random sample. The resulting sample average approximating problem is then solved by deterministic optimization techniques. The process is repeated with different samples to obtain candidate solutions along with statistical estimates of their optimality gaps.We present a detailed computational study of the application of the SAA method to solve three classes of stochastic routing problems. These stochastic problems involve an extremely large number of scenarios and first-stage integer variables. For each of the three problem classes, we use decomposition and branch-and-cut to solve the approximating problem within the SAA scheme. Our computational results indicate that the proposed method is successful in solving problems with up to 21694 scenarios to within an estimated 1.0% of optimality. Furthermore, a surprising observation is that the number of optimality cuts required to solve the approximating problem to optimality does not significantly increase with the size of the sample. Therefore, the observed computation times needed to find optimal solutions to the approximating problems grow only linearly with the sample size. As a result, we are able to find provably near-optimal solutions to these difficult stochastic programs using only a moderate amount of computation time. 相似文献
33.
The F- F+-photoconversion in oxygen-deficient corundum, induced by 210 nm irradiation at different temperatures, was analyzed. It was shown that the dosimetric trap and known deep trap contribute little to these transformations. The dose dependencies of detectors in initial and sensitized states were studied. The interactive processes between different traps in TLD-500 were examined directly. 相似文献
34.
The control of piecewise-deterministic processes is studied where only local boundedness of the data is assumed. Moreover the discount rate may be zero. The value function is shown to be solution to the Bellman equation in a weak sense; however the solution concept is strong enough to generate optimal policies. Continuity and compactness conditions are given for the existence of nonrelaxed optimal feedback controls. 相似文献
35.
K. Kubilius 《Acta Appl Math》2003,78(1-3):233-242
We consider the integral equation driven by a standard Brownian motion and by a fractional Brownian motion. Sufficient conditions under which the equation has a weak solution are obtained. 相似文献
36.
37.
38.
39.
A. Debussche 《Journal de Mathématiques Pures et Appliquées》1998,77(10):967-988
The notion of random attractor for a dissipative stochastic dynamical system has recently been introduced. It generalizes the concept of global attractor in the deterministic theory. It has been shown that many stochastic dynamical systems associated to a dissipative partial differential equation perturbed by noise do possess a random attractor. In this paper, we prove that, as in the case of the deterministic attractor, the Hausdorff dimension of the random attractor can be estimated by using global Lyapunov exponents. The result is obtained under very natural assumptions. As an application, we consider a stochastic reaction-diffusion equation and show that its random attractor has finite Hausdorff dimension. 相似文献
40.
集值Lebesgue—Stieltjes积分 总被引:8,自引:2,他引:6
本文首先刻划了B(R_ )上的集值测度,其次建立了(R_ B(R_ ))上的集值Lebesgue-Stieltjes积分.最后,进—步建立了集值随机Lebesgue-Stietjes积分的理论. 相似文献