全文获取类型
收费全文 | 36224篇 |
免费 | 915篇 |
国内免费 | 799篇 |
专业分类
化学 | 15664篇 |
晶体学 | 355篇 |
力学 | 1792篇 |
综合类 | 58篇 |
数学 | 9597篇 |
物理学 | 10472篇 |
出版年
2023年 | 124篇 |
2022年 | 232篇 |
2021年 | 317篇 |
2020年 | 291篇 |
2019年 | 279篇 |
2018年 | 1387篇 |
2017年 | 1651篇 |
2016年 | 1005篇 |
2015年 | 824篇 |
2014年 | 821篇 |
2013年 | 1177篇 |
2012年 | 3786篇 |
2011年 | 2957篇 |
2010年 | 2260篇 |
2009年 | 1945篇 |
2008年 | 1061篇 |
2007年 | 1028篇 |
2006年 | 1000篇 |
2005年 | 4772篇 |
2004年 | 4204篇 |
2003年 | 2534篇 |
2002年 | 724篇 |
2001年 | 444篇 |
2000年 | 211篇 |
1999年 | 288篇 |
1998年 | 210篇 |
1997年 | 149篇 |
1996年 | 126篇 |
1995年 | 113篇 |
1994年 | 89篇 |
1993年 | 74篇 |
1992年 | 218篇 |
1991年 | 205篇 |
1990年 | 161篇 |
1989年 | 130篇 |
1988年 | 121篇 |
1987年 | 76篇 |
1986年 | 56篇 |
1985年 | 52篇 |
1984年 | 41篇 |
1983年 | 36篇 |
1976年 | 80篇 |
1975年 | 39篇 |
1974年 | 41篇 |
1973年 | 52篇 |
1972年 | 41篇 |
1970年 | 40篇 |
1969年 | 37篇 |
1968年 | 35篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
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
43.
Covering numbers of precompact symmetric convex subsets of Hilbert spaces are investigated. Lower bounds are derived for sets containing orthogonal subsets with norms of their elements converging to zero sufficiently slowly. When these sets are convex hulls of sets with power-type covering numbers, the bounds are tight. The arguments exploit properties of generalized Hadamard matrices. The results are illustrated by examples from machine learning, neurocomputing, and nonlinear approximation. 相似文献
44.
The notion of balanced bipartitions of the vertices in a tree T was introduced and studied by Reid (Networks 34 (1999) 264). Reid proved that the set of balance vertices of a tree T consists of a single vertex or two adjacent vertices. In this note, we give a simple proof of that result. 相似文献
45.
We give counterexamples to the following conjecture of Auslander: given a finitely generated module M over an Artin algebra Λ, there exists a positive integer nM such that for all finitely generated Λ-modules N, if ExtΛi(M,N)=0 for all i?0, then ExtΛi(M,N)=0 for all i?nM. Some of our examples moreover yield homologically defined classes of commutative local rings strictly between the class of local complete intersections and the class of local Gorenstein rings. 相似文献
46.
It can be conjectured that the colored Jones function of a knot can be computed in terms of counting paths on the graph of
a planar projection of a knot. On the combinatorial level, the colored Jones function can be replaced by its weight system.
We give two curious formulas for the weight system of a colored Jones function: one in terms of the permanent of a matrix
associated to a chord diagram, and another in terms of counting paths of intersecting chords.
Electronic supplementary material to this article is available at and is accessible to authorized users.
* S. G. was partially supported by an NSF and by an Israel-US BSF grant.
† M. L. was partly supported by GAUK 158 grant and by the Project LN00A056 of the Czech Ministry of Education. 相似文献
47.
M.V. Nazarov J.H. Kang E.-J. Popovici B.S. Tsukerblat 《Solid State Communications》2005,133(3):183-186
Samples of yttrium oxide doped with trivalent europium have been prepared by ceramic techniques, under different synthesis conditions; barium chloride (BaCl2) and sodium tetraborate (Na2B4O7) were tested as flux. The improvement of luminescence properties in dependence on substitution of Eu3+ for Y3+ in the host lattice, under electron and UV excitations is demonstrated. The lattice parameter as a quantitative assessment of activator incorporation degree is proposed. The obtained results are discussed with respect to the employed processing method. 相似文献
48.
We study a class of shape optimization problems for semi-linear elliptic equations with Dirichlet boundary conditions in smooth
domains in ℝ2. A part of the boundary of the domain is variable as the graph of a smooth function. The problem is equivalently reformulated
on a fixed domain. Continuity of the solution to the state equation with respect to domain variations is shown. This is used
to obtain differentiability in the general case, and moreover a useful formula for the gradient of the cost functional in
the case where the principal part of the differential operator is the Laplacian.
Online publication 23 January 2004. 相似文献
49.
50.
Abnormalities in the cochlear function usually cause broadening of the auditory filters which reduces the speech intelligibility. An attempt to apply a spectral enhancement algorithm has been undertaken to improve the identification of Polish vowels by subjects with cochlear-based hearing-impairment. The identification scores of natural (unprocessed) vowels and spectrally enhanced (processed) vowels has been measured for hearing-impaired subjects. It has been found that spectral enhancement improves vowel scores by about 10% for those subjects, however, a wide variation in individual performance among subjects has been observed. The overall vowels identification scores obtained were 85% for natural vowels and 96% for spectrally enhanced vowels. 相似文献