全文获取类型
收费全文 | 5300篇 |
免费 | 459篇 |
国内免费 | 324篇 |
专业分类
化学 | 209篇 |
晶体学 | 3篇 |
力学 | 877篇 |
综合类 | 64篇 |
数学 | 3951篇 |
物理学 | 979篇 |
出版年
2024年 | 9篇 |
2023年 | 82篇 |
2022年 | 76篇 |
2021年 | 100篇 |
2020年 | 133篇 |
2019年 | 120篇 |
2018年 | 148篇 |
2017年 | 166篇 |
2016年 | 178篇 |
2015年 | 128篇 |
2014年 | 251篇 |
2013年 | 505篇 |
2012年 | 228篇 |
2011年 | 296篇 |
2010年 | 295篇 |
2009年 | 367篇 |
2008年 | 337篇 |
2007年 | 358篇 |
2006年 | 273篇 |
2005年 | 215篇 |
2004年 | 230篇 |
2003年 | 184篇 |
2002年 | 179篇 |
2001年 | 139篇 |
2000年 | 146篇 |
1999年 | 143篇 |
1998年 | 111篇 |
1997年 | 109篇 |
1996年 | 71篇 |
1995年 | 73篇 |
1994年 | 48篇 |
1993年 | 63篇 |
1992年 | 57篇 |
1991年 | 44篇 |
1990年 | 29篇 |
1989年 | 20篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 15篇 |
1985年 | 25篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 23篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1957年 | 2篇 |
排序方式: 共有6083条查询结果,搜索用时 15 毫秒
41.
42.
Jim Foster 《Journal of Combinatorial Theory, Series A》2007,114(8):1515-1525
We show that for an n-gon with unit diameter to have maximum area, its diameter graph must contain a cycle, and we derive an isodiametric theorem for such n-gons in terms of the length of the cycle. We then apply this theorem to prove Graham's 1975 conjecture that the diameter graph of a maximal 2m-gon (m?3) must be a cycle of length 2m−1 with one additional edge attached to it. 相似文献
43.
Hans C. Fogedby 《Journal of statistical physics》1992,69(1-2):411-425
We elaborate in some detail on a new phase space approach to complexity, due to Y.-C. Zhang. We show in particular that the connection between maximal complexity and power law noise or correlations can be derived from a simple variational principle. For a 1D signal we find 1/f noise, in accordance with Zhang. 相似文献
44.
Duan-zhi ZHANG School of Mathematical Sciences Peking University Beijing China 《中国科学A辑(英文版)》2007,50(6):761-772
In this paper, we study the Maslov-type index theory for linear Hamiltonian systems with brake orbits boundary value conditions and its applications to the existence of multiple brake orbits of nonlinear Hamiltonian systems. 相似文献
45.
In a previous paper we gave a new formulation and derived the Euler equations and other necessary conditions to solve strong, pathwise, stochastic variational problems with trajectories driven by Brownian motion. Thus, unlike current methods which minimize the control over deterministic functionals (the expected value), we find the control which gives the critical point solution of random functionals of a Brownian path and then, if we choose, find the expected value.This increase in information is balanced by the fact that our methods are anticipative while current methods are not. However, our methods are more directly connected to the theory and meaningful examples of deterministic variational theory and provide better means of solution for free and constrained problems. In addition, examples indicate that there are methods to obtain nonanticipative solutions from our equations although the anticipative optimal cost function has smaller expected value.In this paper we give new, efficient numerical methods to find the solution of these problems in the quadratic case. Of interest is that our numerical solution has a maximal, a priori, pointwise error of O(h3/2) where h is the node size. We believe our results are unique for any theory of stochastic control and that our methods of proof involve new and sophisticated ideas for strong solutions which extend previous deterministic results by the first author where the error was O(h2).We note that, although our solutions are given in terms of stochastic differential equations, we are not using the now standard numerical methods for stochastic differential equations. Instead we find an approximation to the critical point solution of the variational problem using relations derived from setting to zero the directional derivative of the cost functional in the direction of simple test functions.Our results are even more significant than they first appear because we can reformulate stochastic control problems or constrained calculus of variations problems in the unconstrained, stochastic calculus of variations formulation of this paper. This will allow us to find efficient and accurate numerical solutions for general constrained, stochastic optimization problems. This is not yet being done, even in the deterministic case, except by the first author. 相似文献
46.
A systematic study of the upper semicontinuity and the lower semicontinuity of the solution map in parametric affine variational
inequalities is given in this paper. Several examples are constructed to analyze the results.
This work was supported by Korea Research Foundation Grant (KRF 2001-015-DP0049), the APEC Postdoctoral Fellowships Program,
and the KOSEF Brain Pool Program. 相似文献
47.
We propose general variational inclusion problems which are slightly different from corresponding problems considered in several recent papers in the literature and show that they are advantageous. Sufficient conditions for the solution existence are established. As applications we derive consequences for several special cases of variational inclusion problems, quasioptimization problems, equilibrium problems and implicit variational inequalities and show that they improve the results of some recent existing papers. 相似文献
48.
Numerical analysis for stochastic age-dependent population equations with Poisson jumps 总被引:1,自引:0,他引:1
In this paper, stochastic age-dependent population equations with Poisson jumps are considered. In general, most of stochastic age-dependent population equations with jumps do not have explicit solutions, thus numerical approximation schemes are invaluable tools for exploring their properties. The main purpose of this paper is to develop a numerical Euler scheme and show the convergence of the numerical approximation solution to the true solution. 相似文献
49.
A generalized inverse problem for the identification of the absorption coefficient for a hyperbolic system is considered. The well-posedness of the problem is examined. It is proved that the regular part of the solution is an L 2 function, which reduces the inverse problem to minimizing the error functional. The gradient of the functional is determined in explicit form from the adjoint problem, and approximate formulas for its calculation are derived. A regularization algorithm for the solution of the inverse problem is considered. Numerical results obtained for various excitation sources are displayed. 相似文献
50.
本篇文章首先定义了向量变分不等式的严格可行点概念,其次在假设了映射是强(D)-伪单调的情况下,证明了向量变分不等式解集非空有界与其严格可行点存在的等价性问题,推广了在数量变分不等式上得到的相应结果. 相似文献