全文获取类型
收费全文 | 772220篇 |
免费 | 10093篇 |
国内免费 | 2605篇 |
专业分类
化学 | 412376篇 |
晶体学 | 10874篇 |
力学 | 35132篇 |
综合类 | 37篇 |
数学 | 101898篇 |
物理学 | 224601篇 |
出版年
2021年 | 5796篇 |
2020年 | 6657篇 |
2019年 | 7204篇 |
2018年 | 10299篇 |
2017年 | 10264篇 |
2016年 | 14768篇 |
2015年 | 9962篇 |
2014年 | 14121篇 |
2013年 | 34845篇 |
2012年 | 29094篇 |
2011年 | 34276篇 |
2010年 | 23423篇 |
2009年 | 22769篇 |
2008年 | 30175篇 |
2007年 | 30263篇 |
2006年 | 28162篇 |
2005年 | 28698篇 |
2004年 | 26143篇 |
2003年 | 22256篇 |
2002年 | 20385篇 |
2001年 | 21297篇 |
2000年 | 16484篇 |
1999年 | 12960篇 |
1998年 | 10854篇 |
1997年 | 10606篇 |
1996年 | 10387篇 |
1995年 | 9295篇 |
1994年 | 9228篇 |
1993年 | 8832篇 |
1992年 | 10015篇 |
1991年 | 9955篇 |
1990年 | 9549篇 |
1989年 | 9206篇 |
1988年 | 9301篇 |
1987年 | 9071篇 |
1986年 | 8585篇 |
1985年 | 11405篇 |
1984年 | 11752篇 |
1983年 | 9596篇 |
1982年 | 9932篇 |
1981年 | 9741篇 |
1980年 | 9340篇 |
1979年 | 9691篇 |
1978年 | 10098篇 |
1977年 | 9880篇 |
1976年 | 9952篇 |
1975年 | 9238篇 |
1974年 | 9276篇 |
1973年 | 9474篇 |
1972年 | 6535篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
We show that an electron confined to a single finite parabolic quantum well in crossed electric and magnetic fields can behave as a double quantum well system. The magnetic field is parallel to the heterostructure layers and the electric field is perpendicular to those. For a suitable choice of both fields and quantum well width, the electron can be confined to a double quantum well effective potential that is very similar to the electronic potential model for diatomic molecules. The double quantum well spectrum is calculated using a numerical algorithm based on semiclassical methods. A physical interpretation of this quantum system is given based on the analogy to the electrons bound to diatomic molecules. 相似文献
952.
Space time-index plots for probing dynamical nonstationarity 总被引:3,自引:0,他引:3
We propose a simple method to efficiently probe dynamical nonstationarity in observed time series. In a space time-index plot, the density distributions as a function of normalized time-index are V-shaped due to nonstationarity. We show that this method is workable for short data sets and typical examples are illustrated. 相似文献
953.
954.
High resolution finite difference schemes for solving the nonlinear model Boltzmann equations are presented for the computations of rarefied gas flows. The discrete ordinate method is first applied to remove the velocity space dependency of the distribution function which renders the model Boltzmann equation in phase space to a set of hyperbolic conservation laws with source terms in physical space. Then a high order essentially nonoscillatory method due to Harten et al. (J. Comput. Phys. 71, 231, 1987) is adapted and extended to solve them. Explicit methods using operator splitting and implicit methods using the lower-upper factorization are described to treat multidimensional problems. The methods are tested for both steady and unsteady rarefied gas flows to illustrate its potential use. The computed results using model Boltzmann equations are found to compare well both with those using the direct simulation Monte Carlo results in the transitional regime flows and those with the continuum Navier-Stokes calculations in near continuum regime flows. 相似文献
955.
In this paper we show that the Boltzmann weights of the three-dimensional Baxter-Bazhanov model give representations of the braid group if some suitable spectral limits are taken. In the trigonometric case we classify all possible spectral limits which produce braid group representations. Furthermore, we prove that for some of them we get cyclotomic invariants of links and for others we obtain tangle invariants generalizing the cyclotomic ones. 相似文献
956.
957.
958.
L. M. Mironovich 《Chemistry of Heterocyclic Compounds》1994,30(9):1092-1094
3-Hydrazino-6-tert-butyl-1,2,4-triazolo[3,4,c]-1,2,4-triazin-5-one was synthesized by the reaction of a substituted 4-(N,N-dimethylcarbamoyl)-3-thioxo-1,2,4-triazine with hydrazine. The spectral characteristics and the proposed reaction mechanism are discussed.The Sumy State University, Sumy 244007. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1258–1260, September, 1994. Original article submitted September 14, 1994. 相似文献
959.
960.
V. G. Lapin 《Radiophysics and Quantum Electronics》1995,38(3-4):195-198
It is shown that the nonstable character of nonlinear interaction of a system of waves similar to that resulting from double stimulated Brillouin scattering is retained upon the oblique incidence of a powerful electromagnetic wave on a layer of supercritical plasma. In this case we have nonlinear back reflection from a layer of supercritical plasma. The threshold intensity of the pump wave is greater than that in the case of subcritical plasma for TE polarization waves but can markedly decrease for waves polarized in the incidence plane. Instability is possible only for a layer of finite thickness.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 3–4, pp. 298–303, March–April, 1995. 相似文献