全文获取类型
收费全文 | 8212篇 |
免费 | 674篇 |
国内免费 | 954篇 |
专业分类
化学 | 479篇 |
晶体学 | 8篇 |
力学 | 601篇 |
综合类 | 163篇 |
数学 | 7531篇 |
物理学 | 1058篇 |
出版年
2024年 | 10篇 |
2023年 | 101篇 |
2022年 | 86篇 |
2021年 | 132篇 |
2020年 | 169篇 |
2019年 | 185篇 |
2018年 | 206篇 |
2017年 | 213篇 |
2016年 | 214篇 |
2015年 | 184篇 |
2014年 | 326篇 |
2013年 | 579篇 |
2012年 | 307篇 |
2011年 | 439篇 |
2010年 | 387篇 |
2009年 | 534篇 |
2008年 | 577篇 |
2007年 | 517篇 |
2006年 | 536篇 |
2005年 | 461篇 |
2004年 | 391篇 |
2003年 | 464篇 |
2002年 | 400篇 |
2001年 | 352篇 |
2000年 | 328篇 |
1999年 | 294篇 |
1998年 | 274篇 |
1997年 | 255篇 |
1996年 | 166篇 |
1995年 | 110篇 |
1994年 | 96篇 |
1993年 | 75篇 |
1992年 | 51篇 |
1991年 | 47篇 |
1990年 | 33篇 |
1989年 | 22篇 |
1988年 | 32篇 |
1987年 | 23篇 |
1986年 | 21篇 |
1985年 | 38篇 |
1984年 | 39篇 |
1983年 | 22篇 |
1982年 | 32篇 |
1981年 | 24篇 |
1980年 | 28篇 |
1979年 | 15篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1974年 | 7篇 |
排序方式: 共有9840条查询结果,搜索用时 359 毫秒
41.
A method for computing low Mach number flows using high‐resolution interpolation and difference formulas, within the framework of the Marker and Cell (MAC) scheme, is presented. This increases the range of wavenumbers that are properly resolved on a given grid so that a sufficiently accurate solution can be obtained without extensive grid refinement. Results using this scheme are presented for three problems. The first is the two‐dimensional Taylor–Green flow which has a closed form solution. The second is the evolution of perturbations to constant‐density, plane channel flow for which linear stability solutions are known. The third is the oscillatory instability of a variable density plane jet. In this case, unless the sharp density gradients are resolved, the calculations would breakdown. Under‐resolved calculations gave solutions containing vortices which grew in place rather than being convected out. With the present scheme, regular oscillations of this instability were obtained and vortices were convected out regularly. Stable computations were possible over a wider range of sensitive parameters such as density ratio and co‐flow velocity ratio. Copyright © 2004 John Wiley Sons, Ltd. 相似文献
42.
Let f :X→X be a continuous map of a compact metric space to itself. We prove that f is topologically conjugate to an adding machine map if and only if X is an infinite minimal set for f and each point of X is regularly recurrent. Moreover, if X is an infinite minimal set for f and one point of X is regularly recurrent, then f is semiconjugate to an adding machine map. 相似文献
43.
基于粗糙集理论的知识约简及应用实例 总被引:5,自引:0,他引:5
在保持分类能力不变的前提下 ,通过利用粗糙集理论中的知识约简方法 ,在保护知识库分类不变的条件下 ,删除其中不相关或不重要的知识 ,从而导出问题的决策 .利用基于决策表的粗糙集模型算法 ,实例分析如何数字化表示决策表 ,并对其进行属性约简和属性值的约简 ,从而提取决策规则 . 相似文献
44.
Gerald Moore. 《Mathematics of Computation》2004,73(245):211-242
We present an algorithm, based on approximation by Laguerre polynomials, for computing a point on the stable manifold of a stationary solution of an autonomous system. A superconvergence phenomenon means that the accuracy of our results is much higher than the usual spectral accuracy. Both the theory and the implementation of the method are considered. Finally, as an application of the algorithm, we describe a fully spectral approximation of homo- and heteroclinic orbits.
45.
Typical behaviour of the solution of a linear system of equations obtained iteratively by Krylov methods can be characterized by three stages. Initially the residual diminishes steadily; this is followed by stagnation and finally rapid convergence near the algebraic grade. This study examines this behaviour in terms of the concepts of approximately invariant subspace and what we have called the analytic grade of a Krylov sequence. It is shown how the small Ritz values play a vital role in the convergence and how this knowledge helps in the construction of an effective preconditioner. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
46.
Mean value in invexity analysis 总被引:1,自引:0,他引:1
In this paper, a generalization of the mean value theorem is considered in the case of functions defined on an invex set with respect to η (which is not necessarily connected). 相似文献
47.
48.
Annegret K. Wagler 《4OR: A Quarterly Journal of Operations Research》2005,3(4):329-336
Shepherd95 proved that the stable set polytopes of near-bipartite graphs are given by constraints associated with the complete
join of antiwebs only. For antiwebs, the facet set reduces to rank constraints associated with single antiwebs by Wagler2004.
We extend this result to a larger graph class, the complements of fuzzy circular interval graphs, recently introduced in ChudnovskySeymour2004.
Received: November 2004 / Revised version: June 2005 相似文献
49.
Krzysztof Pawaowski 《K-Theory》1998,13(1):41-55
The paper presents a procedure for constructing smooth actions of finite perfect groups on spheres with fixed point sets having certain prescribed properties (Theorem A); in particular, having any prescribed configuration of Chern and Pontryagin numbers (Corollary C). The main ingredients used are equivariant thickening and equivariant surgery. 相似文献
50.
GLOBAL ATTRACTOR OF A SPATIALLY DISCRETIZED REACTION-DIFFUSION SYSTEM WITH HAMILTONIAN STRUCTURE 总被引:1,自引:0,他引:1
1HamiltonianStructureinReaction-DifusionsystemConsiderasystemofreaction-difusionequationsut=uxx+f(u,v)vt=vxx+g(u,v){(1.1)wher... 相似文献