全文获取类型
收费全文 | 431575篇 |
免费 | 3775篇 |
国内免费 | 1193篇 |
专业分类
化学 | 234487篇 |
晶体学 | 6825篇 |
力学 | 18849篇 |
综合类 | 13篇 |
数学 | 46252篇 |
物理学 | 130117篇 |
出版年
2018年 | 4193篇 |
2017年 | 4157篇 |
2016年 | 6436篇 |
2015年 | 4146篇 |
2014年 | 6361篇 |
2013年 | 17425篇 |
2012年 | 12519篇 |
2011年 | 15431篇 |
2010年 | 10846篇 |
2009年 | 10625篇 |
2008年 | 14311篇 |
2007年 | 14639篇 |
2006年 | 13789篇 |
2005年 | 12479篇 |
2004年 | 11423篇 |
2003年 | 10391篇 |
2002年 | 10219篇 |
2001年 | 12050篇 |
2000年 | 9289篇 |
1999年 | 7291篇 |
1998年 | 6117篇 |
1997年 | 6148篇 |
1996年 | 5873篇 |
1995年 | 5460篇 |
1994年 | 5472篇 |
1993年 | 5122篇 |
1992年 | 6011篇 |
1991年 | 5882篇 |
1990年 | 5782篇 |
1989年 | 5670篇 |
1988年 | 5739篇 |
1987年 | 5625篇 |
1986年 | 5299篇 |
1985年 | 7060篇 |
1984年 | 7310篇 |
1983年 | 6079篇 |
1982年 | 6375篇 |
1981年 | 6278篇 |
1980年 | 6144篇 |
1979年 | 6318篇 |
1978年 | 6776篇 |
1977年 | 6539篇 |
1976年 | 6552篇 |
1975年 | 6134篇 |
1974年 | 6165篇 |
1973年 | 6292篇 |
1972年 | 4381篇 |
1971年 | 3647篇 |
1968年 | 3783篇 |
1967年 | 3977篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
In this Note, we study a 2×2 system of evolution equations with some codimension 3 crossing. We derive two conditions of non-degeneracy. We focus on one of them and reduce our system to some Landau–Zener's type system. Using this reduction, we describe the energy transfer at the crossing by Landau–Zener formula for 2-scales semi-classical measures. To cite this article: C. Fermanian Kammerer, P. Gérard, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 915–920. 相似文献
102.
The structural evolution in amorphous silicon and germanium thin films has been investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis. The results established that the structure of as-deposited semiconductor films is of a high density of nanocrystallites embedded in the amorphous matrix. In addition, from ACF analysis, the structure of a-Ge is more ordered than that of a-Si. The density of embedded nanocrystallites in amorphous films was found to diminish with annealing temperature first, then to increase. The conclusions also corroborate well with the results of diminished medium-range order in annealed amorphous films determined previously by a variable coherence microscopy method. 相似文献
103.
We investigate the linear stability of the Bickley jet in the framework of the beta-plane approximation. Because singular inviscid neutral modes exist in the retrograde case , it is necessary to add viscosity to interpret them. One of these modes was found in closed form by Howard and Drazin [1] . However, its critical point is at the center of the jet and it was therefore not possible for these authors to ascertain the relationship of this mode to the stability problem or to discuss how to continue the eigenfunction across the singularity.
The viscous critical layer problem associated with this singularity is considerably more difficult than the usual one (which leads to integrals of the Airy function) because and, consequently, a second-order turning point is involved. Our analysis shows that the Howard–Drazin mode is degenerate in the domain where it is valid as a limit of the viscous problem (wavenumber α2 ≤ 9/2 ), that is, it corresponds to both an odd and an even mode. This conclusion is confirmed by direct numerical solution of the Orr–Sommerfeld equation which shows, in addition, that viscosity is destabilizing along portions of the stability boundary. For a retrograde jet, instability is found to occur beyond the inviscid critical value of β, that is, in the region where the flow would be stable according to the Rayleigh–Kuo condition. 相似文献
The viscous critical layer problem associated with this singularity is considerably more difficult than the usual one (which leads to integrals of the Airy function) because and, consequently, a second-order turning point is involved. Our analysis shows that the Howard–Drazin mode is degenerate in the domain where it is valid as a limit of the viscous problem (wavenumber α
104.
105.
The buffer extracts (3S) of sclerotia of Sclerotinia sclerotiorum IFO 9395 contained mitogenic substance(s) to murine splenocytes (Shinohara et al. Chem. Pharm. Bull., 38, 2219 (1990)). Although the native 3S was slightly mitogenic, heating of 3S induced significant mitogenic activity. To isolate the mitogen, we separated 3S by ion-exchange and gel filtration chromatographies. The isolated mitogen, named sclerogen, has a molecular mass of 32 kilodaltons (kDa) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and the isoelectric point (pI) of 5.9 by chromatofocusing. Sclerogen was significantly mitogenic in vitro against murine splenocytes after heat denaturation, and also showed the augmentation of the primary mixed lymphocyte reaction (MLR) in vitro. However, sclerogen did not show the activation of an alternative pathway of complement and hemagglutination activity. These results suggest that sclerogen is a unique mitogen which differs from lectins and shows mitogenicity after heat denaturation. 相似文献
106.
A fast-frequency modulated (FM) diode laser has been optically narrowed using the technique of resonant optical feedback, to provide linewidths in each FM mode of ≈ 200 kHz peak-to-peak. With a drive frequency of 50 MHz and modulation index of 0.2, the FM laser has been used for the first time to obtain Doppler-free FM spectra of the Rb D1 line at 795 nm. The potential use of this system for laser frequency stabilisation is discussed. 相似文献
107.
Under idealized conditions, electroconvection in a nematic liquid crystal sets in at a well-defined threshold of the driving ac voltage. Fluctuating convection rolls of a small amplitude below that threshold have been observed recently. The measurement of the amplitude of these fluctuations is described in detail in this paper. It is based on averaging the light intensity signals using the structure function and a quantitative analysis of the light deflection. 相似文献
108.
109.