全文获取类型
收费全文 | 24597篇 |
免费 | 2773篇 |
国内免费 | 3372篇 |
专业分类
化学 | 9779篇 |
晶体学 | 105篇 |
力学 | 2059篇 |
综合类 | 177篇 |
数学 | 7855篇 |
物理学 | 10767篇 |
出版年
2024年 | 82篇 |
2023年 | 264篇 |
2022年 | 565篇 |
2021年 | 614篇 |
2020年 | 776篇 |
2019年 | 724篇 |
2018年 | 719篇 |
2017年 | 800篇 |
2016年 | 948篇 |
2015年 | 851篇 |
2014年 | 1225篇 |
2013年 | 2069篇 |
2012年 | 1306篇 |
2011年 | 1567篇 |
2010年 | 1225篇 |
2009年 | 1590篇 |
2008年 | 1631篇 |
2007年 | 1683篇 |
2006年 | 1401篇 |
2005年 | 1199篇 |
2004年 | 972篇 |
2003年 | 988篇 |
2002年 | 917篇 |
2001年 | 727篇 |
2000年 | 744篇 |
1999年 | 624篇 |
1998年 | 570篇 |
1997年 | 431篇 |
1996年 | 295篇 |
1995年 | 285篇 |
1994年 | 240篇 |
1993年 | 237篇 |
1992年 | 223篇 |
1991年 | 182篇 |
1990年 | 200篇 |
1989年 | 189篇 |
1988年 | 166篇 |
1987年 | 166篇 |
1986年 | 138篇 |
1985年 | 140篇 |
1984年 | 139篇 |
1983年 | 80篇 |
1982年 | 112篇 |
1981年 | 106篇 |
1980年 | 94篇 |
1979年 | 98篇 |
1978年 | 77篇 |
1977年 | 76篇 |
1976年 | 70篇 |
1973年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Doug Bullock 《Topology and its Applications》1994,60(3):235-248
This paper addresses two problems in the skein theory of homotopy spheres first posed by P. Traczyk. Solutions to both problems are obtained for a large class of manifolds and, since one of the basic techniques used requires the first homology group of the ambient manifold to be torsion free, the extent to which this hypothesis is actually necessary is further explored. 相似文献
72.
73.
矩孔金属光栅矢量模式理论的数值计算 总被引:1,自引:0,他引:1
根据矩孔金属光栅的矢量模式理论,计算了不同入射方向,波长及偏振态情况下衍射场的分布,研究了不同光栅结构对衍射效率,偏振态变化的影响;同时,根据实际需要,加工制作了一批不同深度的矩孔光栅样品,进行了实验测量,并将计算值与实验值进行了比较,两者基本相符。 相似文献
74.
Let G=(V,E) be a (directed) graph with vertex set V and edge (arc) set E. Given a set P of source-sink pairs of vertices of G, an important problem that arises in the computation of network reliability is the enumeration of minimal subsets of edges (arcs) that connect/disconnect all/at least one of the given source-sink pairs of P. For undirected graphs, we show that the enumeration problems for conjunctions of paths and disjunctions of cuts can be solved in incremental polynomial time. Furthermore, under the assumption that P consists of all pairs within a given vertex set, we also give incremental polynomial time algorithm for enumerating all minimal path disjunctions and cut conjunctions. For directed graphs, the enumeration problem for cut disjunction is known to be NP-complete. We extend this result to path conjunctions and path disjunctions, leaving open the complexity of the enumeration of cut conjunctions. Finally, we give a polynomial delay algorithm for enumerating all minimal sets of arcs connecting two given nodes s1 and s2 to, respectively, a given vertex t1, and each vertex of a given subset of vertices T2. 相似文献
75.
This paper is concerned with the spectral analysis of a one-velocity transport operator with Maxwell boundary condition in
L
1-space. After a detailed spectral analysis it is shown that the associated Cauchy problem is governed by a C
0-semigroup. Next, we discuss the irreducibility of the transport semigroup. In particular, we show that the transport semigroup
is irreducible. Finally, a spectral decomposition of the solutions into an asymptotic term and a transient one which will
be estimated for smooth initial data is given. 相似文献
76.
77.
The projector formalism of Zwanzig-Mori type is extended to obtain generalized Fokker-Planck and generalized nonlinear Langevin equations for coarse-grained variables when the underlying microscopic dynamics is dissipative and noisy (stochastic). 相似文献
78.
79.
This paper presents a generalized Adadorov theory for anisotropic thin—walled beams. The theory takes account of the shear strain of the middle surface, which exerts a significant influence on the anisotropic thin-walled beams. A new approach is established to solve the governing equations, which have the same form for both open and closed section beams. The numerical examples show that the effects of the shear strain cannot be neglected for this class of beams.This work was part of research project supported by the National Natural Science Foundation of China 相似文献
80.
Wilfried B. Kr tzig Jian-Wu Zhang 《Journal of Computational and Applied Mathematics》1994,50(1-3):361-373
A simple and accurate four-node quadrilateral finite element based on the Mindlin plate theory and Kirchhoff constraints is presented for general thin plate bending applications. The derivation of the element stiffness properties is straightforward, starting with a specified eight-node interpolation; usual discrete Kirchhoff (DK) constraints are employed to constrain out the four midside nodes of the element. The present resulting DK element passes patch tests with elements of arbitrary and even highly distorted mesh types. Numerical studies of the element convergence behaviours are undertaken for various plate bending problems so far investigated. It is indicated from comparative examples that fairly good convergence characteristics have been achieved. 相似文献