全文获取类型
收费全文 | 270116篇 |
免费 | 2233篇 |
国内免费 | 987篇 |
专业分类
化学 | 130817篇 |
晶体学 | 4021篇 |
力学 | 14347篇 |
综合类 | 4篇 |
数学 | 49525篇 |
物理学 | 74622篇 |
出版年
2018年 | 11471篇 |
2017年 | 11239篇 |
2016年 | 8192篇 |
2015年 | 2489篇 |
2014年 | 2654篇 |
2013年 | 8086篇 |
2012年 | 8856篇 |
2011年 | 16762篇 |
2010年 | 9879篇 |
2009年 | 10186篇 |
2008年 | 12326篇 |
2007年 | 14587篇 |
2006年 | 6090篇 |
2005年 | 6641篇 |
2004年 | 6406篇 |
2003年 | 6301篇 |
2002年 | 5240篇 |
2001年 | 5997篇 |
2000年 | 4644篇 |
1999年 | 3644篇 |
1998年 | 2912篇 |
1997年 | 2905篇 |
1996年 | 2908篇 |
1995年 | 2626篇 |
1994年 | 2463篇 |
1993年 | 2374篇 |
1992年 | 2830篇 |
1991年 | 2720篇 |
1990年 | 2658篇 |
1989年 | 2694篇 |
1988年 | 2635篇 |
1987年 | 2641篇 |
1986年 | 2455篇 |
1985年 | 3311篇 |
1984年 | 3324篇 |
1983年 | 2748篇 |
1982年 | 2948篇 |
1981年 | 2881篇 |
1980年 | 2797篇 |
1979年 | 2936篇 |
1978年 | 3170篇 |
1977年 | 2976篇 |
1976年 | 2908篇 |
1975年 | 2767篇 |
1974年 | 2711篇 |
1973年 | 2739篇 |
1972年 | 1776篇 |
1968年 | 1939篇 |
1967年 | 2140篇 |
1966年 | 1937篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Elliott H. Lieb Israel M. Sigal Barry Simon Walter Thirring 《Communications in Mathematical Physics》1988,116(4):635-644
LetN(Z) denote the number of electrons which a nucleus of chargeZ can bind in non-relativistic quantum mechanics (assuming that electrons are fermions). We prove thatN(Z)/Z1 asZ.Research partially supported by the NSERC under Grant NA7901 and by the USNSF under Grants DMS-8416049 and PHY 85-15288-A01 相似文献
972.
During ageing the Al-2·0 at. %Zn-1·0 at. % Mg alloy at elevated temperatures the width of the precipitation free zone (PFZ) at both sides of the grain boundaries (GB) is identical with that free of quenched-in dislocation loops (DL). After sufficiently long ageing a band of precipitates is growing inside the former PFZ and the DLs in the midgrain regions act as sites for the heterogeneous nucleation of the-phase. Two precipitation processes significantly affect the mechanical properties. TEM correlates grain boundary precipitate density and morphology with grain boundary misorientation. 相似文献
973.
We study a one-dimensional model for fracture, identifying fractured areas with intervals on which a stress field exceeds a threshold value. When is a diffusion process, the cumulative numberN(l) of fractured areas whose length is greater thanl obeys a power lawCl
–p
asl0 with probability one. The exponentp and the constantC are determined. The exponentp agrees with the Hausdorff dimension of the end points of fractured areas, i.e.,
–1(). Even if is self-similar with parameterH>0, i.e.,(cx)– is equivalent toc
H
{(x)–} for anyc>0, the exponentp does not depend solely onH;p=H, where(0, 1/H) is another parameter characterizing. Non-diffusion processes are given whereN(l) does not follow a power law. 相似文献
974.
975.
976.
H. Ghafoori-Shiraz 《Optical and Quantum Electronics》1988,20(6):493-500
The coupling efficiency between semiconductor laser diodes (LDs) and single-mode fibres (SMFs) can be improved by matching their respective modes. This may be achieved by constructing a conical microlens on the end of an Al-coated vapour-axial deposition (VAD) SMF. A simple process to etch an SMF end selectively to produce such a conical microlens is described.A minimum coupling loss of 3 dB has been obtained using 1.3-m InGaAsP/InP buried heterostructure LDs. Experimental results on coupling efficiency and loss penalty due to lateral misalignment are also reported. This conical microlens is easy to manufacture and reproduce. 相似文献
977.
Dupieux P Alard JP Augerat J Babinet R Bastid N Brochard F Charmensat P De Marco N Fanet H Fodor Z Fraysse L Girard J Gorodetzky P Gosset J Laspalles C Lemaire MC L'Hôte D Lucas B Marroncle J Montarou G Parizet MJ Poitou J Qassoud D Racca C Schimmerling W 《Physics letters. [Part B]》1988,200(1-2):17-21
Proton-proton small angle correlations have been measured in neon-nucleus collisions, using the 4 pi detector Diogene, at 400 and 800 MeV per nucleon incident energies. Values of the size of the emitting region are obtained by comparison with the Koonin formula, taking into account the biases of the apparatus. The dependence of the density on target mass and incident energy is also analysed. 相似文献
978.
Two different 6-quark resonating group models of the deuteron are investigated to study the off-shell property of theN-N interaction. In the first model the quarks interact by a central one-gluon-exchange potential plus confinement potential. The meson-exchange contribution to then-p potential is simulated by a central GaussianN-N potential. In the second model the quarks interact by one-gluon-and one-pion-exchange potentials (central and noncentral) plus confinement potential. A small additional -exchange potential between neutron and proton binds the deuteron at the correct energy.Several off-shell variants of the two resonating group models are compared with each other by analyzing their elastic electron scattering cross sections. It is found that the standard renormalized version of the resonating group model yields potentials and wave functions that may be considered physical within the limitations of the model. Unitary off-shell transformations, which modify potentials and wave functions in any sizeable way, lead to a disagreement between the charge distribution predicted by the model via analysis of electron scattering and the charge distribution following from the microscopic quark distribution.Both of the 6-quark models support a soft repulsive core of the tripletn-p potential with a core height of around 900 MeV. 相似文献
979.
K. Kawahta T. Tetsuka J. Fujita M. Nagatsu H. Ohnishi S. Okajima T. Iwasaki 《International Journal of Infrared and Millimeter Waves》1988,9(7):655-665
A 4-channel HCN laser scattering system has been developed and applied to the JIPP T-IIU tokamak. Main aim of this system is to study microturbulence excited in the plasma, especially in the high power ICRF heating experiment. The observed density fluctuations are in a frequency range of the electron diamagnetic drift wave and have broad frequency spectra. The main part of the wavenumber is found to satisfy the condition of
. In the heating experiments, deterioration of the energy confinement time is observed, and the density fluctuation level increases with the increase of the heating power. 相似文献
980.
Brown coal from two areas in New Zealand was treated with acids (HF and HCl) to remove the clays. Iron was then introduced into the “cleaned” coal by ion exchange. Mössbauer spectra of the untreated coal, the low temperature ash of the coal, “cleaned” coal and ion-exchanged coal were analysed. From these spectra we conclude that a pair of lines with QS~1 mm s?1 and IS~0.45 mm s?1 is probably due to organically bonded iron. 相似文献