全文获取类型
收费全文 | 84024篇 |
免费 | 4942篇 |
国内免费 | 2753篇 |
专业分类
化学 | 49173篇 |
晶体学 | 775篇 |
力学 | 3393篇 |
综合类 | 202篇 |
数学 | 15511篇 |
物理学 | 22665篇 |
出版年
2023年 | 703篇 |
2022年 | 995篇 |
2021年 | 1252篇 |
2020年 | 1442篇 |
2019年 | 1393篇 |
2018年 | 2534篇 |
2017年 | 2771篇 |
2016年 | 2988篇 |
2015年 | 2567篇 |
2014年 | 2667篇 |
2013年 | 4424篇 |
2012年 | 7116篇 |
2011年 | 6715篇 |
2010年 | 4442篇 |
2009年 | 3907篇 |
2008年 | 4118篇 |
2007年 | 4008篇 |
2006年 | 3597篇 |
2005年 | 6915篇 |
2004年 | 5951篇 |
2003年 | 3960篇 |
2002年 | 2068篇 |
2001年 | 1470篇 |
2000年 | 1181篇 |
1999年 | 1113篇 |
1998年 | 871篇 |
1997年 | 750篇 |
1996年 | 893篇 |
1995年 | 698篇 |
1994年 | 697篇 |
1993年 | 622篇 |
1992年 | 713篇 |
1991年 | 578篇 |
1990年 | 472篇 |
1989年 | 384篇 |
1988年 | 367篇 |
1987年 | 302篇 |
1986年 | 282篇 |
1985年 | 335篇 |
1984年 | 261篇 |
1983年 | 212篇 |
1982年 | 200篇 |
1981年 | 177篇 |
1980年 | 143篇 |
1979年 | 163篇 |
1978年 | 139篇 |
1977年 | 126篇 |
1976年 | 177篇 |
1975年 | 136篇 |
1973年 | 149篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Newton-Leibniz integration rule only applies to commuting functions of continuum variables, while operators made of Dirac’s symbols (ket versus bra, e.g., |q〉〈q| of continuous parameter q) in quantum mechanics are usually not commutative. Therefore, integrations over the operators of type |〉〈| cannot be directly performed by Newton-Leibniz rule. We invented an innovative technique of integration within an ordered product (IWOP) of operators that made the integration of non-commutative operators possible. The IWOP technique thus bridges this mathematical gap between classical mechanics and quantum mechanics, and further reveals the beauty and elegance of Dirac’s symbolic method and transformation theory. Various applications of the IWOP technique, including constructing the entangled state representations and their applications, are presented. 相似文献
92.
93.
94.
Soliton interaction under the influence of higher-order effects 总被引:6,自引:0,他引:6
In this paper, we present exact N-soliton solution by employing simple, straightforward Darboux transformation based on the Lax pair for Hirota equation, a higher-order nonlinear Schrödinger (HNLS) equation. As examples, one- and two-soliton solutions in explicit forms are given and their properties are also analyzed. A bound solution without interaction will be theoretically predicted if one can adjust frequency shift for each soliton appropriately. Further, we obtain the approximate eigenvalues by employing two-soliton solution and discuss analytically the interaction between neighboring solitons under the influence of the higher-order effects. It is shown that the combined effects of the higher-order effects can restrain the interaction between neighboring solitons to some extent. The results are proved by directly solving HNLS equation numerically. 相似文献
95.
A simple model consisting of two electronic levels and one vibrational mode (phonon) was theoretically studied. The electronic-vibrational interaction was linear in the vibrational displacement. The vibrational mode was taken in the harmonic approximation and was attached to the thermal bath formed by the ambient environment. The kinetic constants of the vibrational dissipation were of the second order in the vibrational-bath coupling and were taken in the Markovian limit. Although, depending on the parameters of the model, different curves of the non-radiative vibration-induced excited state decay were obtained, in general, three time intervals, corresponding to different physical behaviour, were found. In the short-time interval, small oscillations superimposed on the excited state decay were observed. They were determined by the vibrational frequency and influenced by electronic-vibrational coupling. In the middle-time interval, almost quasi-exponential decay was detected; its rate constant increased with stronger electronic-vibrational interaction and speed of vibrational relaxation. In the long-time interval, the decay was very slow and, under special conditions, even an asymptotic non-zero excited state population was observed. Its value increased with the strength of the off-diagonal electron-vibrational coupling. Links of the parameters of the model with quantum chemical terms were estimated. 相似文献
96.
We investigate an operator renormalization group method to extract and describe the relevant degrees of freedom in the evolution of partial differential equations. The proposed renormalization group approach is formulated as an analytical method providing the fundamental concepts of a numerical algorithm applicable to various dynamical systems. We examine dynamical scaling characteristics in the short-time and the long-time evolution regime providing only a reduced number of degrees of freedom to the evolution process. 相似文献
97.
By using two sections of erbium doped fiber and a fiber optical reflector, a novel, highly efficient L bandamplifier is demonstrated with significantly power-conversion-efficiency enhancement and the gain increasing of as much as 13 dB. 相似文献
98.
Jerónimo Rodríguez 《Comptes Rendus Mathematique》2004,339(6):445-450
In the present Note we introduce an extension of the conservative space–time mesh refinement method presented by Fouquet et al. We also propose a post-treatment of the solution that reduces the spurious phenomena due to the non-conformity between the time meshes. A reinterpretation of the equations in terms of new unknowns leads to a new scheme with second order consistent coupling equations. Numerical experiments in 2D and a plane wave analysis for the 1D model show that the method is second order accurate for an arbitrary refinement. To cite this article: J. Rodríguez, C. R. Acad. Sci. Paris, Ser. I 339 (2004). 相似文献
99.
We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure. 相似文献
100.