全文获取类型
收费全文 | 256009篇 |
免费 | 1093篇 |
国内免费 | 636篇 |
专业分类
化学 | 112995篇 |
晶体学 | 3411篇 |
力学 | 16019篇 |
综合类 | 7篇 |
数学 | 52517篇 |
物理学 | 72789篇 |
出版年
2019年 | 2289篇 |
2018年 | 13676篇 |
2017年 | 13598篇 |
2016年 | 10128篇 |
2015年 | 2674篇 |
2014年 | 3860篇 |
2013年 | 7331篇 |
2012年 | 9214篇 |
2011年 | 16891篇 |
2010年 | 11034篇 |
2009年 | 11578篇 |
2008年 | 12823篇 |
2007年 | 14894篇 |
2006年 | 5810篇 |
2005年 | 6225篇 |
2004年 | 6287篇 |
2003年 | 6298篇 |
2002年 | 5496篇 |
2001年 | 5229篇 |
2000年 | 3969篇 |
1999年 | 2959篇 |
1998年 | 2780篇 |
1997年 | 2592篇 |
1996年 | 2447篇 |
1995年 | 2162篇 |
1994年 | 2079篇 |
1993年 | 2130篇 |
1992年 | 2125篇 |
1991年 | 2441篇 |
1990年 | 2362篇 |
1989年 | 2442篇 |
1988年 | 2320篇 |
1987年 | 2351篇 |
1986年 | 2182篇 |
1985年 | 2702篇 |
1984年 | 2712篇 |
1983年 | 2352篇 |
1982年 | 2412篇 |
1981年 | 2312篇 |
1980年 | 2122篇 |
1979年 | 2437篇 |
1978年 | 2581篇 |
1977年 | 2657篇 |
1976年 | 2745篇 |
1975年 | 2551篇 |
1974年 | 2478篇 |
1973年 | 2659篇 |
1972年 | 2169篇 |
1971年 | 1981篇 |
1970年 | 1850篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Mutual–temporal coherence of the supercontinuum (SC) generation has been experimentally investigated using a diffraction grating based interferometer. A broadband SC generation was produced in a pyrex glass plate with a 1.6-μm coherence length at 550-nm center wavelength. The degree of mutual coherence of 0.34 was measured for a wavefront shift for zero and first diffraction orders of half of the beam diameter. A design of SC source with the capability of manipulating the amplitudes and phases of optical frequency components within the SC pulse is presented for coherence applications. 相似文献
62.
The conditions for obtaining a high efficiency of energy exchange upon two-wave interactions in dynamic holograms are found by analysis and numerical simulation of a system of nonlinear equations. Use of an asymmetric scheme of beam interaction in a medium with two nonlinearities, one of which determines the amplitude and relaxation time of a grating and the other of which provides phase modulation of the interacting beams, is proposed. It is shown that such a scheme in combination with the specific properties of a medium makes it possible to radically reduce the requirements for the nonlinearity of a medium and the intensity of a light flux in limiting systems, as well as to significantly decrease the time of the transition process. As a result, it becomes possible to attain an efficiency of energy transfer higher than 90% and to increase the corresponding attenuation of a high-power beam by almost two orders of magnitude, which is of interest for optical limiting of intense light fluxes. 相似文献
63.
JETP Letters - The problem of storing ultracold neutrons over a plane magnetic mirror in the presence of gravity is considered. For neutrons with a definite polarization, the sum of the magnetic... 相似文献
64.
The results of experimental investigations on thermal nonequilibrium ionization in CO2: N2: He mixtures are presented. Measurements of electron density, ne, in vibrationally excited nitrogen were made in a supersonic flow with different CO2 contents as well as in a CO2: N2: He = 1 : 5 : 4 mixture laser gas. The mixtures were heated in a shock tube and expanded through a supersonic nozzle. Furthermore, supersonic mixing of N2 and CO2 + He was used in some experiments. The measured values of ne in the plenum chamber and in the supersonic nozzle are reported, and the processes responsible for nonequilibrium ionization in a laser-active medium are discussed. 相似文献
65.
66.
Dimitar I. Pushkarov 《Central European Journal of Physics》2004,2(3):420-455
Basic ideas and results which characterize quantum diffusion of defects in quantum crystals like solid helium as a new phenomenon
are presented. Quantum effects in such media lead to a delocalization of point defects (vacancies, impurities etc.) and they
turn into quasiparticles of a new type—defectons, which are characterized not by their position in the crystal lattice but
by their quasimomentum and dispersion law. Defecton-defecton and defecton-phonon scattering are considered and an interpolation
formula for the diffusion coefficient valid in all interesting temperature and concentration regions is presented. A comparison
with the experimental data is made. Some alternative points of view are discussed in detail and the inconsistency of the Kisvarsanyi-Sullivan
theory is shown. 相似文献
67.
68.
I. Morgenstern 《Zeitschrift für Physik B Condensed Matter》1987,67(2):265-270
I present an abstraction of the Hopfield-model for neural networks which is suitable for physical chip design using commerically available two-dimensional gate arrays. It can be shown that ±1-bonds combined with a dilution of about 80–90% of the original Hopfield-connections still lead to a comparable performance of the network. Furthermore the learning capability of the chips is discussed. Future extensions concerning programmable designs are outlined. The impact on aspects of brain research is discussed. 相似文献
69.
D. N. Karimov E. A. Krivandina Z. I. Zhmurova B. P. Sobolev V. A. Bezhanov S. P. Chernov G. M. Shapochkin 《Crystallography Reports》2006,51(6):1009-1015
Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca1?x R xF2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region. 相似文献
70.