全文获取类型
收费全文 | 56792篇 |
免费 | 3417篇 |
国内免费 | 855篇 |
专业分类
化学 | 37222篇 |
晶体学 | 325篇 |
力学 | 2020篇 |
综合类 | 47篇 |
数学 | 8451篇 |
物理学 | 12999篇 |
出版年
2023年 | 526篇 |
2022年 | 539篇 |
2021年 | 766篇 |
2020年 | 991篇 |
2019年 | 943篇 |
2018年 | 1265篇 |
2017年 | 1049篇 |
2016年 | 1884篇 |
2015年 | 1777篇 |
2014年 | 1865篇 |
2013年 | 3532篇 |
2012年 | 4116篇 |
2011年 | 4165篇 |
2010年 | 2600篇 |
2009年 | 2193篇 |
2008年 | 3497篇 |
2007年 | 3414篇 |
2006年 | 3067篇 |
2005年 | 2910篇 |
2004年 | 2503篇 |
2003年 | 2011篇 |
2002年 | 1780篇 |
2001年 | 1113篇 |
2000年 | 902篇 |
1999年 | 696篇 |
1998年 | 554篇 |
1997年 | 517篇 |
1996年 | 611篇 |
1995年 | 407篇 |
1994年 | 460篇 |
1993年 | 441篇 |
1992年 | 432篇 |
1991年 | 383篇 |
1990年 | 370篇 |
1989年 | 346篇 |
1988年 | 279篇 |
1987年 | 276篇 |
1986年 | 250篇 |
1985年 | 402篇 |
1984年 | 362篇 |
1983年 | 255篇 |
1982年 | 337篇 |
1981年 | 323篇 |
1980年 | 288篇 |
1979年 | 277篇 |
1978年 | 268篇 |
1976年 | 273篇 |
1975年 | 248篇 |
1974年 | 258篇 |
1973年 | 244篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Sauer, Shelah, Vapnik and Chervonenkis proved that if a set system on n vertices contains many sets, then the set system has full trace on a large set. Although the restriction on the size of the
groundset cannot be lifted, Frankl and Pach found a trace structure that is guaranteed to occur in uniform set systems even
if we do not bound the size of the groundset. In this note we shall give three sequences of structures such that every set
system consisting of sufficiently many sets contains at least one of these structures with many sets. 相似文献
82.
The present paper determines the form of automorphisms of $\[{E_2}(R)\]$ and $\[G{E_2}(R)\]$ over commutative rings provided 2, 3 and 5 are units. 相似文献
83.
In this Note, we present a result concerning the non existence of linear monotone schema with fixed stencil on regular meshes for some linear parabolic equation in two dimensions. The parabolic equations of interest arise from non isotropic diffusion modelling. A corollary is that no linear monotone 9 points-schemes can be designed for the one-dimensional heat equation emerged in the plane with an arbitrary direction of diffusion. Some applications of this result are provided: for the Fokker–Planck–Lorentz model for electrons in the context of plasma physics; all linear monotone scheme for the one-dimensional hyperbolic heat equation treated as a two-dimensional problem are not consistent in the diffusion limit for an arbitrary direction of propagation. We also examine the case of the Landau equation. To cite this article: C. Buet, S. Cordier, C. R. Acad. Sci. Paris, Ser. I 340 (2005). 相似文献
84.
Let Ψ(x,y) (resp. Ψm(x,y)) denote the number of integers not exceeding x that are y-friable, i.e. have no prime factor exceeding y (resp. and are coprime to m). Evaluating the ratio Ψm(x/d,y)/Ψ(x,y) for 1≤slantd≤slantx, m≥slant 1, x≥slant y≥slant 2, turns out to be a crucial step for estimating arithmetic sums over friable integers. Here, it is crucial to obtain formulae with a very wide range of validity. In this paper, several uniform estimates are provided for the aforementioned ratio, which supersede all previously known results. Applications are given to averages of various arithmetic functions over friable integers which in turn improve corresponding results from the literature. The technique employed rests mainly on the saddle-point method, which is an efficient and specific tool for the required design.2000 Mathematics Subject Classification: Primary—11N25; Secondary—11K65, 11N37 相似文献
85.
86.
ZHU Yabin ZHOU Yueliang LIU Zhen WANG Shufang CHEN Zhenghao U Huibin YANG Guozhen XlAO Ling Ren Hongtao JIAO Yulei Zheng Minghui 《中国科学G辑(英文版)》2004,47(2):165-172
The irreversibility field (Hirr) of Y-based superconductor is much higher than that of Bi-based superconductor. Y-based superconductor is capable of maintaining stable electrical currents in high magnetic field and electric field, so it is a better suited mate-rial for electric-current applications. Commonly, the Y-based tapes comprise a YBCO thick film deposited on a flexible substrate, typically with an intermediate buffer layer, and an overcoat of noble metal. In this process, the interm… 相似文献
87.
This paper is devoted to a detailed theoretical study of an ion pair SN2 reaction LiNCO+CH3F in the gas phase and in solution at the level of MP2(full)/6-31+G**//HF/6-31+G**. Two possible reaction mechanisms, inversion and retention, are discussed. There are eight possible reaction pathways. The inversion mechanism is more favorable no matter in the gas phase or in solution based on analyses of the transition structures. Methyl isocyanate should form preferentially in the gas phase and more stable methyl cyanate is the main product in solution. The retardation of the reaction in solvents was attributed to the difference in solvation in the separated reactants and in the transition state. 相似文献
88.
We prove that the generalized random walks associated to a root system R in and a nonnegative multiplicity function k defined on R, converge in distribution (if suitably normalized) to a Markov process with càdlàg trajectories and infinitesimal generator a differential-difference operator on which generalizes the usual Laplacian. To cite this article: L. Gallardo, L. Godefroy, C. R. Acad. Sci. Paris, Ser. I 338 (2004). 相似文献
89.
The concept of super hamiltonian semigroup is introduced. As a result, the structure theorems obtained by A. Cherubini and A. Varisco on quasi commutative semi-groups and quasi hamiltonian semigroups respectively are extended to super hamiltonian semigroups. 相似文献
90.