全文获取类型
收费全文 | 15552篇 |
免费 | 362篇 |
国内免费 | 156篇 |
专业分类
化学 | 888篇 |
晶体学 | 68篇 |
力学 | 220篇 |
综合类 | 23篇 |
数学 | 13665篇 |
物理学 | 1206篇 |
出版年
2023年 | 31篇 |
2022年 | 75篇 |
2021年 | 70篇 |
2020年 | 70篇 |
2019年 | 341篇 |
2018年 | 394篇 |
2017年 | 206篇 |
2016年 | 178篇 |
2015年 | 175篇 |
2014年 | 403篇 |
2013年 | 993篇 |
2012年 | 439篇 |
2011年 | 946篇 |
2010年 | 769篇 |
2009年 | 980篇 |
2008年 | 1146篇 |
2007年 | 1139篇 |
2006年 | 798篇 |
2005年 | 608篇 |
2004年 | 495篇 |
2003年 | 399篇 |
2002年 | 325篇 |
2001年 | 264篇 |
2000年 | 266篇 |
1999年 | 389篇 |
1998年 | 341篇 |
1997年 | 272篇 |
1996年 | 350篇 |
1995年 | 328篇 |
1994年 | 330篇 |
1993年 | 277篇 |
1992年 | 266篇 |
1991年 | 192篇 |
1990年 | 164篇 |
1989年 | 168篇 |
1988年 | 107篇 |
1987年 | 123篇 |
1986年 | 110篇 |
1985年 | 172篇 |
1984年 | 166篇 |
1983年 | 87篇 |
1982年 | 148篇 |
1981年 | 148篇 |
1980年 | 91篇 |
1979年 | 69篇 |
1978年 | 93篇 |
1977年 | 70篇 |
1976年 | 50篇 |
1975年 | 18篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Yanghyun Byun 《Topology》2007,46(5):507-525
We construct a sphere fibration over a finite aspherical Poincaré complex X, which we call the tangential end fibration, under the condition that the universal cover of X is forward tame and simply connected at infinity. We show that it is tangent to X if the formal dimension of X is even or, when the formal dimension is odd, if the diagonal X→X×X admits a Poincaré embedding structure. 相似文献
52.
P. Rowlinson 《Linear algebra and its applications》2007,421(1):157-162
Suppose that the positive integer μ is the eigenvalue of largest multiplicity in an extremal strongly regular graph G. By interlacing, the independence number of G is at most 4μ2 + 4μ − 2. Star complements are used to show that if this bound is attained then either (a) μ = 1 and G is the Schläfli graph or (b) μ = 2 and G is the McLaughlin graph. 相似文献
53.
Michèle Audin 《manuscripta mathematica》2007,124(4):533-550
In this paper, we investigate symplectic manifolds endowed with a Morse–Bott function with only two critical submanifolds,
one of which is Lagrangian while the other one is symplectic. 相似文献
54.
In this paper, we establish a theorem on the distribution of primes in quadratic progressions on average. 相似文献
55.
Various types of LU-factorizations for nonsingular matrices, where L is a lower triangular matrix and U is an upper triangular matrix, are defined and characterized. These types of LU-factorizations are extended to the general m × n case. The more general conditions are considered in the light of the structures of [C.R. Johnson, D.D. Olesky, P. Van den Driessche, Inherited matrix entries: LU factorizations, SIAM J. Matrix Anal. Appl. 10 (1989) 99-104]. Applications to graphs and adjacency matrices are investigated. Conditions for the product of a lower and an upper triangular matrix to be the zero matrix are also obtained. 相似文献
56.
In this paper we investigate the electrostatic problem of determining conductivity profiles from the knowledge of boundary
currents and voltages. We obtain an improved estimate for the voltage potential of a two-dimensional conductor having finitely
many circular inclusions and piecewise constant conductivity profile. We derive an asymptotic expansion for the voltage potential
in terms of the reference voltage potential and the location, size, and conductivity of the inhomogeneities. This representation
is used to formulate the nonlinear least squares problem for estimating the location and size of the inhomogeneities. Required
boundary data for the voltage potential are generated numerically by solving a system of integral equations. Computational
experiments are presented to demonstrate the effectiveness of our identification procedure. 相似文献
57.
C. Foias A. E. Frazho I. Gohberg M. A. Kaashoek 《Integral Equations and Operator Theory》1997,29(4):455-490
The family of all solutions of the three chains completion problem with a prescribed tolerance is described explicitly. It is shown that this family can be parameterized by a natural set of contractive upper triangular operators. As an application all solutions to a suboptimal nonstationary Nehari problem are described. 相似文献
58.
59.
By exploiting the construction of charged field algebras as canonical extensions of CCR current algebras in 1+1 dimensions and nonregular representations of extended algebras, we provide an algebraic construction of local Fermi fields as ultrastrong limits of bosonic variables in all representations which are locally Fock with respect to the ground-state representation of the massless scalar field. 相似文献
60.
R. M. Dudley 《Probability Theory and Related Fields》1994,100(2):175-189
Summary In a separable metric space, if two Borel probability measures (laws) are nearby in a suitable metric, then there exist random variables with those laws which are nearby in probability. Specifically, by a well-known theorem of Strassen, the Prohorov distance between two laws is the infimum of Ky Fan distances of random variables with those laws. The present paper considers possible extensions of Strassen's theorem to two random elements one of which may be (compact) set-valued and/or non-measurable. There are positive results in finite-dimensional spaces, but with factors depending on the dimension. Examples show that such factors cannot entirely be avoided, so that the extension of Strassen's theorem to the present situation fails in infinite dimensions.This research was partially supported by a Guggenheim Fellowship, by National Science Foundation grant DMS 8505550 at MSRI-Berkeley, and other NSF grants 相似文献