全文获取类型
收费全文 | 20799篇 |
免费 | 1019篇 |
国内免费 | 917篇 |
专业分类
化学 | 6845篇 |
晶体学 | 79篇 |
力学 | 903篇 |
综合类 | 225篇 |
数学 | 10155篇 |
物理学 | 4528篇 |
出版年
2023年 | 168篇 |
2022年 | 317篇 |
2021年 | 465篇 |
2020年 | 428篇 |
2019年 | 450篇 |
2018年 | 404篇 |
2017年 | 456篇 |
2016年 | 500篇 |
2015年 | 433篇 |
2014年 | 737篇 |
2013年 | 1195篇 |
2012年 | 878篇 |
2011年 | 796篇 |
2010年 | 743篇 |
2009年 | 1146篇 |
2008年 | 1240篇 |
2007年 | 1330篇 |
2006年 | 1036篇 |
2005年 | 820篇 |
2004年 | 701篇 |
2003年 | 693篇 |
2002年 | 736篇 |
2001年 | 632篇 |
2000年 | 604篇 |
1999年 | 522篇 |
1998年 | 471篇 |
1997年 | 350篇 |
1996年 | 329篇 |
1995年 | 320篇 |
1994年 | 257篇 |
1993年 | 283篇 |
1992年 | 363篇 |
1991年 | 238篇 |
1990年 | 191篇 |
1989年 | 143篇 |
1988年 | 172篇 |
1987年 | 144篇 |
1986年 | 174篇 |
1985年 | 179篇 |
1984年 | 149篇 |
1983年 | 65篇 |
1982年 | 136篇 |
1981年 | 205篇 |
1980年 | 213篇 |
1979年 | 205篇 |
1978年 | 210篇 |
1977年 | 146篇 |
1976年 | 133篇 |
1974年 | 42篇 |
1973年 | 76篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
61.
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
62.
Twenty-five years ago, we introduced the phenomenon of negative luminescence (NL) into semiconductor physics. This paper provides an overview of work conducted to develop this fundamental concept. Initially, we consider the first-principle approach to radiation interaction with basic matter and the major properties of NL. Then we describe the problems of NL direct measurements in homogeneous materials and structures. Finally, we emphasize the use of NL approach in applications involving devices for infrared (IR) wavelength (3–12 μm) high-temperature (300–400 K) optoelectronics. Our subjects will include NL IR emitting diodes, radiative coolers, IR dynamic scene simulators, light up-conversion devices, and the Stealth effect in IR. 相似文献
63.
64.
65.
G. Z. Ruan S. Y. Wang Y. Yamamoto S. S. Zhu 《Journal of Optimization Theory and Applications》2004,123(2):409-429
In this paper, a model of a linear multilevel programming problem with dominated objective functions (LMPPD(l)) is proposed, where multiple reactions of the lower levels do not lead to any uncertainty in the upper-level decision making. Under the assumption that the constrained set is nonempty and bounded, a necessary optimality condition is obtained. Two types of geometric properties of the solution sets are studied. It is demonstrated that the feasible set of LMPPD(l) is neither necessarily composed of faces of the constrained set nor necessarily connected. These properties are different from the existing theoretical results for linear multilevel programming problems. 相似文献
66.
Lahcne Mezrag 《Mathematische Nachrichten》2004,266(1):60-67
In [5], it is proved that a bounded linear operator u, from a Banach space Y into an Lp(S, ν) factors through Lp1 (S, ν) for some p1 > 1, if Y* is of finite cotype; (S, ν) is a probability space for p = 0, and any measure space for 0 < p < 1. In this paper, we generalize this result to uv, where u : Y → Lp(S, ν) and v : X → Y are linear operators such that v* is of finite Ka?in cotype. This result gives also a new proof of Grothendieck's theorem. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
67.
A carousel is a dynamical system that describes the movement of an equilateral linkage in which the midpoint of each rod travels parallel to it. They are closely related to the floating body problem. We prove, using the work of Auerbach, that any figure that floats in equilibrium in every position is drawn by a carousel. Of special interest are such figures with rational perimetral density of the floating chords, which are then drawn by carousels. In particular, we prove that for some perimetral densities the only such figure is the circle, as the problem suggests. 相似文献
68.
A server needs to compute a broadcast schedule for n pages whose request times are known in advance. Outputting a page satisfies all outstanding requests for the page. The goal is to minimize the average waiting time of a client. In this paper, we show the equivalence of two apparently different relaxations that have been considered for this problem. 相似文献
69.
Robust linear optimization under general norms 总被引:1,自引:0,他引:1
We explicitly characterize the robust counterpart of a linear programming problem with uncertainty set described by an arbitrary norm. Our approach encompasses several approaches from the literature and provides guarantees for constraint violation under probabilistic models that allow arbitrary dependencies in the distribution of the uncertain coefficients. 相似文献
70.
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