全文获取类型
收费全文 | 10927篇 |
免费 | 1489篇 |
国内免费 | 1744篇 |
专业分类
化学 | 6295篇 |
晶体学 | 68篇 |
力学 | 2464篇 |
综合类 | 122篇 |
数学 | 1325篇 |
物理学 | 3886篇 |
出版年
2024年 | 44篇 |
2023年 | 179篇 |
2022年 | 350篇 |
2021年 | 450篇 |
2020年 | 661篇 |
2019年 | 426篇 |
2018年 | 373篇 |
2017年 | 436篇 |
2016年 | 559篇 |
2015年 | 420篇 |
2014年 | 668篇 |
2013年 | 832篇 |
2012年 | 610篇 |
2011年 | 670篇 |
2010年 | 514篇 |
2009年 | 589篇 |
2008年 | 604篇 |
2007年 | 639篇 |
2006年 | 599篇 |
2005年 | 539篇 |
2004年 | 524篇 |
2003年 | 541篇 |
2002年 | 483篇 |
2001年 | 346篇 |
2000年 | 283篇 |
1999年 | 244篇 |
1998年 | 260篇 |
1997年 | 161篇 |
1996年 | 187篇 |
1995年 | 127篇 |
1994年 | 143篇 |
1993年 | 104篇 |
1992年 | 106篇 |
1991年 | 81篇 |
1990年 | 68篇 |
1989年 | 59篇 |
1988年 | 52篇 |
1987年 | 34篇 |
1986年 | 33篇 |
1985年 | 41篇 |
1984年 | 22篇 |
1983年 | 10篇 |
1982年 | 29篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1971年 | 5篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Gregorio Falqui 《Reports on Mathematical Physics》2002,50(3):395
We formulate and discuss a reduction theorem for Poisson pencils associated with a class of integrable systems, defined on bi-Hamiltonian manifolds, recently studied by Gel'fand and Zakharevich. The reduction procedure is suggested by the bi-Hamiltonian approach to the separation of variables problem. 相似文献
12.
Several a priori tests of a systematic stochastic mode reduction procedure recently devised by the authors [Proc. Natl. Acad. Sci. 96 (1999) 14687; Commun. Pure Appl. Math. 54 (2001) 891] are developed here. In this procedure, reduced stochastic equations for a smaller collections of resolved variables are derived systematically for complex nonlinear systems with many degrees of freedom and a large collection of unresolved variables. While the above approach is mathematically rigorous in the limit when the ratio of correlation times between the resolved and the unresolved variables is arbitrary small, it is shown here on a systematic hierarchy of models that this ratio can be surprisingly big. Typically, the systematic reduced stochastic modeling yields quantitatively realistic dynamics for ratios as large as 1/2. The examples studied here vary from instructive stochastic triad models to prototype complex systems with many degrees of freedom utilizing the truncated Burgers–Hopf equations as a nonlinear heat bath. Systematic quantitative tests for the stochastic modeling procedure are developed here which involve the stationary distribution and the two-time correlations for the second and fourth moments including the resolved variables and the energy in the resolved variables. In an important illustrative example presented here, the nonlinear original system involves 102 degrees of freedom and the reduced stochastic model predicted by the theory for two resolved variables involves both nonlinear interaction and multiplicative noises. Even for large value of the correlation time ratio of the order of 1/2, the reduced stochastic model with two degrees of freedom captures the essentially nonlinear and non-Gaussian statistics of the original nonlinear systems with 102 modes extremely well. Furthermore, it is shown here that the standard regression fitting of the second-order correlations alone fails to reproduce the nonlinear stochastic dynamics in this example. 相似文献
13.
14.
激光二极管反馈干涉的实验观测 总被引:7,自引:2,他引:5
利用LabView软件虚拟示波器和信号源,观测了激光二极管反馈干涉实验现象.实验证明反馈回激光二极管的光的入射方向和入射光强以及信号处理电路的带宽,对反馈干涉信号有很大的影响. 相似文献
15.
L. T. Ashchepkov 《Computational Mathematics and Mathematical Physics》2006,46(7):1168-1175
A general nonlinear programming problem with interval functions is considered. Two reductions of this problem to the deterministic nonlinear programming problem are proposed, and illustrative examples are discussed. 相似文献
16.
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
17.
X-ray diffraction patterns of nanocrystalline Fe-Cu-Nb-Si-B (FINEMET) alloys reveal that bcc α-Fe/α-FeSi crystallites with
the average grain size of 20(5) nm are dispersed in amorphous matrix. Enhanced electron—electron interaction (EEI) and quantum
interference (QI) effects as well as electron-magnon (and/or electron-spin fluctuation) scattering turn out to be the main
mechanisms that govern the temperature dependence of resistivity. Of all the inelastic scattering processes, inelastic electron-phonon
scattering is the most effective mechanism to destroy phase coherence of electron wave functions. The diffusion constant,
density of states at the Fermi level and the inelastic scattering time have been estimated, for the first time, for the alloys
in question
Article presented at the International Symposium on Advances in Superconductivity and Magnetism: Materials, Mechanisms and
Devices, ASMM2D-2001, 25–28 September 2001, Mangalore, India. 相似文献
18.
Weidong Gao Meiqiong Zhan Shuhai Fan Janda Shao Zheng-Xiu Fan 《Applied Surface Science》2005,250(1-4):195-202
The laser-induced damage (LID) behavior of narrow-band interference filters was investigated with a Nd:YAG laser at 1064 nm under single-pulse mode and free-running mode. The absorption measurement of such coatings was performed with surface thermal lensing (STL) technique. The damage morphologies under the two different laser modes were also studied in detail. It was found that all the filters exhibited a pass-band-center-dependent absorption and laser-induced damage threshold (LIDT) behavior, but the damage morphologies were diverse. The explanation was given with the analysis of the electric field distribution and the operational behavior of the irradiation laser. 相似文献
19.
20.
乐毅 《宁波大学学报(理工版)》2004,17(4):437-440
从正交各向异性三维弹性动力学的控制方程出发,在求得四边简支矩形板自由振动频率和位移振型的基础上,构造了受迫振动的位移函数;利用自由振动位移振型的正交性,将控制方程的空间变量和时间变量分离,得到了广义质量、广义力和频率表示的关于时间的2阶常微分方程,从而得到了正交各向异性弹性矩形板在受迫振动下的位移场和应力场.给出了本文方法与薄板理论的算例. 相似文献