全文获取类型
收费全文 | 204251篇 |
免费 | 1715篇 |
国内免费 | 594篇 |
专业分类
化学 | 102414篇 |
晶体学 | 3340篇 |
力学 | 9287篇 |
综合类 | 5篇 |
数学 | 22486篇 |
物理学 | 69028篇 |
出版年
2021年 | 1660篇 |
2020年 | 1798篇 |
2019年 | 2004篇 |
2018年 | 2703篇 |
2017年 | 2602篇 |
2016年 | 3769篇 |
2015年 | 2305篇 |
2014年 | 3616篇 |
2013年 | 9094篇 |
2012年 | 7240篇 |
2011年 | 8740篇 |
2010年 | 6048篇 |
2009年 | 5911篇 |
2008年 | 7922篇 |
2007年 | 8090篇 |
2006年 | 7731篇 |
2005年 | 6896篇 |
2004年 | 6427篇 |
2003年 | 5655篇 |
2002年 | 5494篇 |
2001年 | 6426篇 |
2000年 | 4932篇 |
1999年 | 3795篇 |
1998年 | 3038篇 |
1997年 | 3048篇 |
1996年 | 2791篇 |
1995年 | 2613篇 |
1994年 | 2462篇 |
1993年 | 2338篇 |
1992年 | 2691篇 |
1991年 | 2671篇 |
1990年 | 2600篇 |
1989年 | 2397篇 |
1988年 | 2449篇 |
1987年 | 2448篇 |
1986年 | 2279篇 |
1985年 | 2961篇 |
1984年 | 3220篇 |
1983年 | 2631篇 |
1982年 | 2806篇 |
1981年 | 2775篇 |
1980年 | 2642篇 |
1979年 | 2729篇 |
1978年 | 2821篇 |
1977年 | 2823篇 |
1976年 | 2887篇 |
1975年 | 2670篇 |
1974年 | 2645篇 |
1973年 | 2777篇 |
1972年 | 1763篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
P. Murzyn C. R. Pidgeon P. J. Phillips J. -P. Wells N. T. Gordon T. Ashley J. H. Jefferson T. M. Burke J. Giess M. Merrick B. N. Murdin C. D. Maxey 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):220
We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τs300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τs is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τs in non-degenerate lightly n-type Hg0.78Cd0.22Te of approximately the same band gap as InSb, and find that τs varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τs, imply that the Elliott–Yafet model dominates in these materials. 相似文献
93.
It is found that, when a bismuth crystal is subjected simultaneously to concentrated loading and a dc magnetic field, the magnetoplastic effect manifests itself as an abrupt decrease in the average length of wedge twins on the (111) cleavage plane (and, hence, as a decrease in the total twinned volume of the crystal) as a threshold value of the magnetic field is reached. However, the magnetic field stimulates glide deformation, which is indicated by an increase in the size of dislocation rosettes. The microhardness of a crystal varies smoothly and tends to increase with increasing magnetic field. The last phenomenon is accounted for by hardening of the crystal under the indenter in the presence of a magnetic field, because several slip systems become operative. 相似文献
94.
The exact solution of the problem of ion transport current in an electrolyte in the presence of a conjugate flow of solvent
is obtained in the framework of the one-dimensional Gurevich-Kharkats diffusion-migration model; the conditions for the existence
of the solution are analyzed. 相似文献
95.
Stimulated Raman scattering (SRS) in a long-distance fiber-optic communication line with wavelength-division multiplexing (WDM) is studied theoretically at a high power of the signal transmitted. A new criterion for determining the SRS threshold is used to calculate the critical input power versus the number of optical channels and frequency separation between them. The theoretical model is verified experimentally. SRS interaction between two channels in a communication line with an SRS amplifier for which the optical waveguide of the line serves as a nonlinear medium is measured. 相似文献
96.
97.
98.
99.
100.
A plane acoustic layer bounded by elastic membranes is considered. Dispersion relations for symmetric and antisymmetric waves are derived. The limit behavior of dispersion curves is investigated for wave numbers tending to zero and to infinity. With the use of the resulting asymptotic expansions, the two-point Pade approximations are constructed. The orthogonality relations for eigenmodes are presented. 相似文献