全文获取类型
收费全文 | 25747篇 |
免费 | 714篇 |
国内免费 | 950篇 |
专业分类
化学 | 5355篇 |
晶体学 | 875篇 |
力学 | 485篇 |
综合类 | 76篇 |
数学 | 17561篇 |
物理学 | 3059篇 |
出版年
2023年 | 94篇 |
2022年 | 227篇 |
2021年 | 186篇 |
2020年 | 199篇 |
2019年 | 571篇 |
2018年 | 602篇 |
2017年 | 404篇 |
2016年 | 375篇 |
2015年 | 395篇 |
2014年 | 776篇 |
2013年 | 1761篇 |
2012年 | 801篇 |
2011年 | 1754篇 |
2010年 | 1713篇 |
2009年 | 1806篇 |
2008年 | 1990篇 |
2007年 | 1964篇 |
2006年 | 1557篇 |
2005年 | 1095篇 |
2004年 | 1039篇 |
2003年 | 833篇 |
2002年 | 706篇 |
2001年 | 566篇 |
2000年 | 503篇 |
1999年 | 514篇 |
1998年 | 436篇 |
1997年 | 398篇 |
1996年 | 462篇 |
1995年 | 471篇 |
1994年 | 455篇 |
1993年 | 390篇 |
1992年 | 318篇 |
1991年 | 209篇 |
1990年 | 184篇 |
1989年 | 170篇 |
1988年 | 123篇 |
1987年 | 128篇 |
1986年 | 141篇 |
1985年 | 194篇 |
1984年 | 137篇 |
1983年 | 82篇 |
1982年 | 121篇 |
1981年 | 112篇 |
1980年 | 91篇 |
1979年 | 60篇 |
1978年 | 87篇 |
1977年 | 69篇 |
1976年 | 56篇 |
1975年 | 26篇 |
1974年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The graph-theoretic operation of rooted subtree prune and regraft is increasingly being used as a tool for understanding and modelling reticulation events in evolutionary biology. In this paper, we show that computing the rooted subtree prune and regraft distance between two rooted binary phylogenetic trees on the same label set is NP-hard. This resolves a longstanding open problem. Furthermore, we show that this distance is fixed parameter tractable when parameterised by the distance between the two trees.Received March 16, 2004 相似文献
22.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
23.
Andrei K. Lerner 《Archiv der Mathematik》2005,85(6):538-543
We show that the Hardy-Littlewood maximal operator and a class of Calderón-Zygmund singular integrals satisfy the strong type
modular inequality in variable Lp spaces if and only if the variable exponent p(x) ∼ const.
Received: 15 September 2004 相似文献
24.
Nonlocal vertex algebras generated by formal vertex operators 总被引:2,自引:0,他引:2
Haisheng Li 《Selecta Mathematica, New Series》2005,11(3-4):349-397
This is the first paper in a series to study vertex algebra-like objects arising from infinite-dimensional quantum groups
(quantum affine algebras and Yangians). In this paper we lay the foundations for this study. For any vector space W, we study what we call quasi compatible subsets of Hom (W,W((x))) and we prove that any maximal quasi compatible subspace has a natural nonlocal (namely noncommutative) vertex algebra
structure with W as a natural faithful quasi module in a certain sense, and that any quasi compatible subset generates a nonlocal vertex algebra
with W as a quasi module. In particular, taking W to be a highest weight module for a quantum affine algebra we obtain a nonlocal vertex algebra with W as a quasi module. We also formulate and study a notion of quantum vertex algebra and we give general constructions of nonlocal
vertex algebras, quantum vertex algebras and their modules. 相似文献
25.
26.
27.
Dmitri I. Panyushev 《Advances in Mathematics》2004,186(2):307-316
We study Abelian ideals of a Borel subalgebra consisting of long roots. It is shown that methods of Cellini and Papi can be extended to this situation. A uniform expression for the number of long Abelian ideals is given. We also show that there is a one-to-one correspondence between the long Abelian ideals and B-stable commutative subalgebras in the little adjoint representation of the Langlands dual Lie algebra. 相似文献
28.
U.S. NaziaA.K.M.A. Islam 《Solid State Communications》2003,125(1):37-40
The Eliashberg spectral density function is constructed for the superconducting compound BaxK1−xBiO3 with x=0.5, 0.6, 0.7. The functions, besides yielding some prominent structures, show widely spreading spectra that inhibit lattice instability by yielding not too large values of λ(<1.32). The resulting spectral functions show similar shape as other results, where available, and also successfully reproduce the observed critical temperature, isotope exponent, gap ratio and several other parameters. 相似文献
29.
In this paper we relate the operators in the operator representations of a generalized Nevanlinna function N(z) and of the function −N(z)−1 under the assumption that z=∞ is the only (generalized) pole of nonpositive type. The results are applied to the Q-function for S and H and the Q-function for S and H∞, where H is a self-adjoint operator in a Pontryagin space with a cyclic element w, H∞ is the self-adjoint relation obtained from H and w via a rank one perturbation at infinite coupling, and S is the symmetric operator given by S=H∩H∞. 相似文献
30.
The existence of an attractor for a 2D-Navier-Stokes system with delay is proved. The theory of pullback attractors is successfully applied to obtain the results since the abstract functional framework considered turns out to be nonautonomous. However, on some occasions, the attractors may attract not only in the pullback sense but in the forward one as well. Also, this formulation allows to treat, in a unified way, terms containing various classes of delay features (constant, variable, distributed delays, etc.). As a consequence, some results for the autonomous model are deduced as particular cases of our general formulation. 相似文献