全文获取类型
收费全文 | 14442篇 |
免费 | 1097篇 |
国内免费 | 860篇 |
专业分类
化学 | 3367篇 |
晶体学 | 39篇 |
力学 | 835篇 |
综合类 | 181篇 |
数学 | 9439篇 |
物理学 | 2538篇 |
出版年
2024年 | 22篇 |
2023年 | 210篇 |
2022年 | 219篇 |
2021年 | 415篇 |
2020年 | 503篇 |
2019年 | 460篇 |
2018年 | 469篇 |
2017年 | 534篇 |
2016年 | 502篇 |
2015年 | 411篇 |
2014年 | 800篇 |
2013年 | 1578篇 |
2012年 | 803篇 |
2011年 | 869篇 |
2010年 | 708篇 |
2009年 | 1020篇 |
2008年 | 1057篇 |
2007年 | 838篇 |
2006年 | 709篇 |
2005年 | 660篇 |
2004年 | 497篇 |
2003年 | 385篇 |
2002年 | 376篇 |
2001年 | 248篇 |
2000年 | 285篇 |
1999年 | 284篇 |
1998年 | 238篇 |
1997年 | 212篇 |
1996年 | 184篇 |
1995年 | 124篇 |
1994年 | 100篇 |
1993年 | 87篇 |
1992年 | 71篇 |
1991年 | 47篇 |
1990年 | 36篇 |
1989年 | 30篇 |
1988年 | 26篇 |
1987年 | 27篇 |
1986年 | 29篇 |
1985年 | 56篇 |
1984年 | 61篇 |
1983年 | 25篇 |
1982年 | 34篇 |
1981年 | 34篇 |
1980年 | 27篇 |
1979年 | 20篇 |
1978年 | 19篇 |
1977年 | 11篇 |
1976年 | 14篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
131.
在s波超导体绝缘层dx2-y2波超导体结(sId)中,考虑到结界面粗糙散射,运用BogoliubovdeGennes(BdG)方程和FurusakiTsukada(FT)电流公式,计算超导结中的准粒子传输系数和直流Josephson电流.结果表明:sId超导结的直流Josephson电流随温度以及结两侧的相位差变化的关系曲线强烈地依赖于d波超导体的晶轴方位;结界面的粗糙散射对Josephson电流有抑制作用
关键词:
s/I/d超导结
dx2-y2波超导体
直流Josephson电流 相似文献
132.
Veronica Felli Susanna Terracini 《Calculus of Variations and Partial Differential Equations》2006,27(1):25-58
This paper deals with a class of nonlinear elliptic equations involving a critical power-nonlinearity as well as a potential featuring multiple inverse square singularities. When the poles form a symmetric structure, it is natural we wonder how the symmetry affects such mutual interaction. The present paper means to study this aspect from the point of view of the existence of solutions inheriting the same symmetry properties as the set of singularities.
Mathematics Subject Classification (2000) 35J60, 35J20, 35B33 相似文献
133.
Although quantum field theory allows the local energy density negative, it also places severe restrictions on the negative energy. One of the restrictions is the quantum energy inequality (QEI), in which the energy density is averaged over time, or space, or over space and time. By now temporal QEIs have been established for various quantum fields, but less work has been done for the spacetime quantum energy inequality. In this paper we deal with the free Rarita-Schwinger field and present a quantum inequality bound on the energy density averaged over space and time.Comparison with the QEI for the Rarita-Schwinger field shows that the lower bound is the same with the QEI. At the same time, we find the quantum inequality for the Rarita-Schwinger field is weaker than those for the scalar and Dirac fields. This fact gives further support to the conjecture that the more freedom the field has, the more easily the field displays negative energy density and the weaker the quantum inequality becomes. 相似文献
134.
Mark L. Lewis 《Algebras and Representation Theory》2002,5(3):277-304
Let G be a solvable group with five character degrees. Suppose that there is some prime p so that G/O
p
(G) is not Abelian. Also, assume that cd(G) contains a degree that is not divisible by p. Under these hypotheses, we show that the derived length of G is at most 4. 相似文献
135.
Two matrix approximation problems are considered: approximation of a rectangular complex matrix by subunitary matrices with
respect to unitarily invariant norms and a minimal rank approximation with respect to the spectral norm. A characterization
of a subunitary approximant of a square matrix with respect to the Schatten norms, given by Maher, is extended to the case
of rectangular matrices and arbitrary unitarily invariant norms. Iterative methods, based on the family of Gander methods
and on Higham’s scaled method for polar decomposition of a matrix, are proposed for computing subunitary and minimal rank
approximants. Properties of Gander methods are investigated in details.
AMS subject classification (2000) 65F30, 15A18 相似文献
136.
Thomas Andreae 《Journal of Graph Theory》2002,39(4):222-229
For a graph A and a positive integer n, let nA denote the union of n disjoint copies of A; similarly, the union of ?0 disjoint copies of A is referred to as ?0A. It is shown that there exist (connected) graphs A and G such that nA is a minor of G for all n??, but ?0A is not a minor of G. This supplements previous examples showing that analogous statements are true if, instead of minors, isomorphic embeddings or topological minors are considered. The construction of A and G is based on the fact that there exist (infinite) graphs G1, G2,… such that Gi is not a minor of Gj for all i ≠ j. In contrast to previous examples concerning isomorphic embeddings and topological minors, the graphs A and G presented here are not locally finite. The following conjecture is suggested: for each locally finite connected graph A and each graph G, if nA is a minor of G for all n ? ?, then ?0A is a minor of G, too. If true, this would be a far‐reaching generalization of a classical result of R. Halin on families of disjoint one‐way infinite paths in graphs. © 2002 Wiley Periodicals, Inc. J Graph Theory 39: 222–229, 2002; DOI 10.1002/jgt.10016 相似文献
137.
The elastic constants of dilute alloys based on bcc metals have been calculated using the Green’s function method obtaining
explicit expressions for change in elastic constants in terms oft-matrix. The crystal impurity problem is discussed within an impurity model containing central and non-central force constant
changes extended up to second neighbours of the impurity. The effect of volume change on elastic constants and a contribution
from electron pressure term are considered. Numerical results for changes in three elastic moduli have been presented for
a number of dilute alloys based on Mo, Nb, W, Ta and V. 相似文献
138.
The asymptotic null distribution of the likelihood ratio test for two cases of ordered hypotheses in a particular genetic model is considered. A simple iterative process is proposed in order to get the restricted estimates. It is shown that both tests have asymptotically a chi-bar squared distribution and the same size. A simulation study is also conducted in order to compare the usual unrestricted test with the corresponding one of ordered hypotheses. Finally, the results are extended to some special cases. 相似文献
139.
本文导出了考虑外场和束流效应后束流均方根发射度平方变化方程的一般表达式,并就仅考虑外场,仅考虑空间电荷场和仅考虑尾场等三种特殊情况进行了分析。 相似文献
140.