全文获取类型
收费全文 | 21568篇 |
免费 | 670篇 |
国内免费 | 771篇 |
专业分类
化学 | 4296篇 |
晶体学 | 863篇 |
力学 | 458篇 |
综合类 | 75篇 |
数学 | 14375篇 |
物理学 | 2942篇 |
出版年
2023年 | 86篇 |
2022年 | 114篇 |
2021年 | 195篇 |
2020年 | 178篇 |
2019年 | 513篇 |
2018年 | 513篇 |
2017年 | 385篇 |
2016年 | 370篇 |
2015年 | 359篇 |
2014年 | 708篇 |
2013年 | 1131篇 |
2012年 | 679篇 |
2011年 | 1358篇 |
2010年 | 1398篇 |
2009年 | 1632篇 |
2008年 | 1678篇 |
2007年 | 1661篇 |
2006年 | 1331篇 |
2005年 | 1019篇 |
2004年 | 964篇 |
2003年 | 776篇 |
2002年 | 651篇 |
2001年 | 478篇 |
2000年 | 428篇 |
1999年 | 417篇 |
1998年 | 389篇 |
1997年 | 297篇 |
1996年 | 444篇 |
1995年 | 403篇 |
1994年 | 384篇 |
1993年 | 332篇 |
1992年 | 264篇 |
1991年 | 157篇 |
1990年 | 145篇 |
1989年 | 134篇 |
1988年 | 84篇 |
1987年 | 105篇 |
1986年 | 103篇 |
1985年 | 143篇 |
1984年 | 90篇 |
1983年 | 59篇 |
1982年 | 87篇 |
1981年 | 86篇 |
1980年 | 57篇 |
1979年 | 31篇 |
1978年 | 45篇 |
1977年 | 61篇 |
1976年 | 49篇 |
1975年 | 8篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Piotr Ko?cielniak 《Topology and its Applications》2007,154(9):1951-1955
Let M be a compact manifold with dimM?2. We prove that some iteration of the generic homeomorphism on M is semiconjugated to the shift map and has infinite topological entropy (Theorem 1.1). 相似文献
102.
Eliza P. de Jager 《Topology and its Applications》2007,154(10):2117-2126
We show that the infimum of any family of proximally symmetric quasi-uniformities is proximally symmetric, while the supremum of two proximally symmetric quasi-uniformities need not be proximally symmetric. On the other hand, the supremum of any family of transitive quasi-uniformities is transitive, while there are transitive quasi-uniformities whose infimum with their conjugate quasi-uniformity is not transitive. Moreover we present two examples that show that neither the supremum topology nor the infimum topology of two transitive topologies need be transitive. Finally, we prove that several operations one can perform on and between quasi-uniformities preserve the property of having a complement. 相似文献
103.
104.
Jan P. Boroński 《Topology and its Applications》2007,154(18):3156-3166
A set (or a collection of sets) contained in the Euclidean space Rm is symmetric if it is invariant under the antipodal map. Given a symmetric unicoherent polyhedron X (like an n-dimensional cube or a sphere) and an odd real function f defined on vertices of a certain symmetric triangulation of X, we algorithmically construct a connected symmetric separator of X by choosing a subcollection of the triangulation. Each element of the subcollection contains the vertices v and u such that f(v)f(u)?0. 相似文献
105.
Michael Holcomb 《Topology and its Applications》2007,154(1):124-143
One can form a polygonal linkage by identifying initial and terminal points of two free linkages. Likewise, one can form a multipolygonal linkage by identifying initial and terminal points of three free linkages. The geometric and topological properties of moduli spaces of multipolygonal linkages in the plane are studied. These spaces are compact algebraic varieties. Some conditions under which these spaces are smooth manifolds, cross products or disjoint unions of moduli spaces of polygonal linkages, or connected, are determined. Dimensions in smooth manifold cases and some Euler characteristics are computed. A classification of generic multiquadrilateral linkages is also made. 相似文献
106.
The q-Catalan numbers studied by Carlitz and Riordan are polynomials in q with nonnegative coefficients. They evaluate, at q = 1, to the Catalan numbers: 1, 1, 2, 5, 14,…, a log-convex sequence. We use a combinatorial interpretation of these polynomials
to prove a q-log-convexity result. The sequence of q-Catalan numbers is not q-log-convex in the narrow sense used by other authors, so our work suggests a more flexible definition of q-log convex be adopted.
Received January 2, 2007 相似文献
107.
Paul Fabel 《Topology and its Applications》2007,154(3):635-638
With a certain natural topology, the fundamental group of a locally path connected metric space X becomes discrete if and only if X is semilocally simply connected. We include some related material and offer a counterexample to a similar result. 相似文献
108.
In the present paper, a Lotka–Volterra type mutualism system with several delays is studied. Some new and interesting sufficient conditions are obtained for the global existence of positive periodic solutions of the mutualism system. Our method is based on Mawhin’s coincidence degree and novel estimation techniques for the a priori bounds of unknown solutions. Our results are different from the existing ones such as those in of Yang et al. [F. Yang, D. Jiang, A. Ying, Existence of positive solution of multidelays facultative mutualism system, J. Eng. Math. 3 (2002) 64–68] and Chen et al. [F. Chen, J. Shi, X. Chen, Periodicity in a Lotka–Volterra facultative mutualism system with several delays, J. Eng. Math. 21 (3) (2004) 403–409]. 相似文献
109.
We study the inverse scattering problem for the nonlinear Schrödinger equation and for the nonlinear Klein–Gordon equation with the generalized Hartree type nonlinearity. We reconstruct the nonlinearity from knowledge of the scattering operator, which improves the known results. 相似文献
110.
采用光学显微镜和扫描电子显微镜等手段,对某轻型汽车40Cr后桥半轴断裂件的组织及断口特征进行了分析结果表明:半轴在调质处理时的淬火温度不够高,使其表层和心部组织中存在较多的铁素体相,造成了工件最终的硬度和疲劳强度不足,导致半轴在使用中发生扭转疲劳断裂. 相似文献