全文获取类型
收费全文 | 4488篇 |
免费 | 807篇 |
国内免费 | 314篇 |
专业分类
化学 | 607篇 |
晶体学 | 33篇 |
力学 | 1012篇 |
综合类 | 79篇 |
数学 | 1278篇 |
物理学 | 2600篇 |
出版年
2024年 | 4篇 |
2023年 | 39篇 |
2022年 | 62篇 |
2021年 | 104篇 |
2020年 | 82篇 |
2019年 | 103篇 |
2018年 | 111篇 |
2017年 | 139篇 |
2016年 | 159篇 |
2015年 | 130篇 |
2014年 | 224篇 |
2013年 | 269篇 |
2012年 | 223篇 |
2011年 | 294篇 |
2010年 | 237篇 |
2009年 | 325篇 |
2008年 | 322篇 |
2007年 | 334篇 |
2006年 | 262篇 |
2005年 | 254篇 |
2004年 | 217篇 |
2003年 | 252篇 |
2002年 | 231篇 |
2001年 | 153篇 |
2000年 | 147篇 |
1999年 | 136篇 |
1998年 | 126篇 |
1997年 | 104篇 |
1996年 | 74篇 |
1995年 | 78篇 |
1994年 | 73篇 |
1993年 | 41篇 |
1992年 | 45篇 |
1991年 | 35篇 |
1990年 | 28篇 |
1989年 | 37篇 |
1988年 | 18篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 5篇 |
排序方式: 共有5609条查询结果,搜索用时 156 毫秒
1.
We propose a conjecture on the relative twist formula of l-adic sheaves, which can be viewed as a generalization of Kato—Saito's conjecture. We verify this conjecture under some transversal assumptions. We also define a relative cohomological characteristic class and prove that its formation is compatible with proper push-forward. A conjectural relation is also given between the relative twist formula and the relative cohomological characteristic class. 相似文献
2.
We give a sheaf theoretic interpretation of Potts models with external magnetic field, in terms of constructible sheaves and their Euler characteristics. We show that the polynomial countability question for the hypersurfaces defined by the vanishing of the partition function is affected by changes in the magnetic field: elementary examples suffice to see non-polynomially countable cases that become polynomially countable after a perturbation of the magnetic field. The same recursive formula for the Grothendieck classes, under edge-doubling operations, holds as in the case without magnetic field, but the closed formulae for specific examples like banana graphs differ in the presence of magnetic field. We give examples of computation of the Euler characteristic with compact support, for the set of real zeros, and find a similar exponential growth with the size of the graph. This can be viewed as a measure of topological and algorithmic complexity. We also consider the computational complexity question for evaluations of the polynomial, and show both tractable and NP-hard examples, using dynamic programming. 相似文献
3.
左手介质椭圆光波导基模传播特性 总被引:1,自引:0,他引:1
在椭圆柱坐标系中,采用分离变量方法,得出了左手介质椭圆光波导本征方程的近似解,通过数值计算,分析了椭圆波导偏心率、左手介质的电容率、磁导率对椭圆光波导基模传播特性的影响,并将左介质光波导与右手介质光波导基模特性进行对比,得出左手介质光波导的基模特性与右手介质光波导基模特性差别不大的结论. 相似文献
4.
M. Gorkunov M. Lapine E. Shamonina K.H. Ringhofer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):263-269
Effective magnetic properties of a composite meta-material consisting of periodically arranged circular conductive elements
are studied theoretically. A general expression for the effective bulk permeability is obtained with mutual effects and lattice
ordering being taken into account. The resonance frequency of the permeability is found to be strongly dependent on the size
and shape of the unit cell. Frequency dispersion of the permeability is studied with special attention paid to the frequency
range, where negative values of the permeability are possible. Corresponding recommendations for optimisation of the meta-materials
with negative permeability are made. The results are confirmed by numerical simulations of the finite structure behaviour
in an external magnetic field.
Received 19 April 2002 Published online 31 July 2002 相似文献
5.
6.
P. E. Cladis 《Journal of statistical physics》1991,62(5-6):899-925
We first discuss nonlinear aspects of phase transition theory applied to a particular liquid crystal phase transition. A simple derivation is given to show how two coupled Goldstone modes (one appearing as gauge fluctuations of the ordered phase) can force a phase transition, against all expectations, to take place discontinuously (theory of Halperin, Lubensky, and Ma)-but the discontinuity may be immeasurably small. Then, we describe a new dynamical test of phase transition order, developed by Cladiset al., that turns out to be more sensitive than x-ray diffraction and adiabatic calorimetry. Quantitative data found by this new method are in excellent agreement with the measurements of adiabatic calorimetry and x-ray diffraction as well as expectations implicit in the predictions of HLM.This is the text of an after-banquet talk given at the CNLS Workshop on the Dynamics of Concentrated Systems. 相似文献
7.
It is long known that the Fokker-Planck equation with prescribed constant coefficients of diffusion and linear friction describes
the ensemble average of the stochastic evolutions in velocity space of a Brownian test particle immersed in a heat bath of
fixed temperature. Apparently, it is not so well known that the same partial differential equation, but now with constant
coefficients which are functionals of the solution itself rather than being prescribed, describes the kinetic evolution (in
the N→∞ limit) of an
isolated
N-particle system with certain stochastic interactions. Here we discuss in detail this recently discovered interpretation.
An erratum to this article can be found at 相似文献
8.
利用解析和数值方法研究了在具有横向折射率周期性调制的克尔型非线性介质中光学格子孤子的传输,得到了孤子参数的演化方程以及格子孤子的形成和稳定传输的条件.结果表明:当光束的入射角小于某临界角度时,光束可被类似波导形式的路径俘获而稳定传输,该临界角随折射率调制周期、调制深度的增加而增大,且光束越窄临界值越大.此外,线性空间啁啾虽然对光束传输的中心位置没有任何影响,但会导致光束发散从而破坏格子孤子的形成和稳定传输,对此提出了采用特定功率取值来补偿啁啾作用从而形成格子孤子的方案.
关键词:
光孤子
光学格子
光传输
矩方法 相似文献
9.
10.
In this study, the nonlinear dynamic responses of a string are simulated using the Cellular Automata method based on the reflection rule. In the case of nonlinear systems, the velocity of wave propagation is not constant and depends on the amplitude. A new treatment of the dynamic time step is proposed for the Cellular Automata method considering the effect of the propagation velocity. As numerical examples, first, the dynamic responses of a string with linear characteristic are simulated using the Cellular Automata method. A typical resonance curve can be obtained. Second, the dynamic responses of a string with nonlinear characteristic are simulated using the proposed method. Some characteristic types of vibration can be obtained. It is concluded that the linear and nonlinear dynamic responses of a string may be obtained by simulation using the Cellular Automata method. 相似文献