全文获取类型
收费全文 | 463422篇 |
免费 | 3420篇 |
国内免费 | 926篇 |
专业分类
化学 | 220394篇 |
晶体学 | 7229篇 |
力学 | 24824篇 |
综合类 | 18篇 |
数学 | 63323篇 |
物理学 | 151980篇 |
出版年
2021年 | 4196篇 |
2020年 | 4636篇 |
2019年 | 5493篇 |
2018年 | 7914篇 |
2017年 | 8095篇 |
2016年 | 10640篇 |
2015年 | 5420篇 |
2014年 | 9662篇 |
2013年 | 19714篇 |
2012年 | 16005篇 |
2011年 | 18850篇 |
2010年 | 14811篇 |
2009年 | 14899篇 |
2008年 | 17840篇 |
2007年 | 17790篇 |
2006年 | 16356篇 |
2005年 | 14320篇 |
2004年 | 13590篇 |
2003年 | 12274篇 |
2002年 | 12394篇 |
2001年 | 12887篇 |
2000年 | 10233篇 |
1999年 | 7660篇 |
1998年 | 6853篇 |
1997年 | 6709篇 |
1996年 | 6042篇 |
1995年 | 5514篇 |
1994年 | 5423篇 |
1993年 | 5301篇 |
1992年 | 5664篇 |
1991年 | 6023篇 |
1990年 | 5929篇 |
1989年 | 5713篇 |
1988年 | 5561篇 |
1987年 | 5628篇 |
1986年 | 5190篇 |
1985年 | 6341篇 |
1984年 | 6788篇 |
1983年 | 5702篇 |
1982年 | 6085篇 |
1981年 | 5755篇 |
1980年 | 5411篇 |
1979年 | 5938篇 |
1978年 | 6109篇 |
1977年 | 6198篇 |
1976年 | 6353篇 |
1975年 | 5879篇 |
1974年 | 5719篇 |
1973年 | 6005篇 |
1972年 | 4583篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
J.T. Devaraju B.H. Sharmila S. Asokan K.V. Acharya 《Applied Physics A: Materials Science & Processing》2002,75(4):515-518
The electrical switching behaviour of As45Te55-xInx (5≤x≤15) and As50Te50-xInx (2.5≤x≤11.5) has been studied over a wide range of compositions. These glasses are found to exhibit threshold switching.
The composition dependence of switching voltage (Vt) has been found to exhibit a change in slope and a local minimum at compositions x=10 and 12.5 for As45Te55-xInx and x=7.5 and 10.8 for As50Te50-xInx, respectively. The slope change in Vt verses x and the local minimum have been identified using two network topological effects, namely the rigidity percolation
threshold and the chemical threshold.
Received: 23 August 2001 / Accepted: 27 August 2001 / Published online: 11 February 2002 相似文献
962.
R. Martínez-Snchez J. A. Matutes-Aquino O. Ayala-Valenzuela S. D. De la Torre 《Physica B: Condensed Matter》2002,320(1-4):285-287
An amorphous phase containing traces of non-transformed Co and Ti powders was obtained by mechanical alloying nominal compositions of Co67Ti33 and Co50Ti50 in a high-energy ball-mill. These alloys were prepared from elemental powders of Co and Ti. The heat treatment of Co67Ti33 at 573, 873 and 1173 K crystallized nanoparticles of Co2Ti and Co3Ti compounds, while the same treatments conducted on Co50Ti50 resulted in the formation of Co2Ti and CoTi nanoparticles. The saturation magnetizations reached a maximum value in the amorphous state and they decreased when the temperatures of the heat treatment rose. Demagnetizing interparticle interaction effects were estimated through hysteresis loops and initial magnetization curves using the Fourier technique. 相似文献
963.
Yu. G. Abov A. D. Gul'ko F. S. Dzheparov S. V. Stepanov S. S. Trostin 《Physics of Atomic Nuclei》2002,65(11):1999-2008
The nuclear magnetic resonance in beta-active nuclei 8Li at the doubled Larmor frequency in LiF polycrystals is studied before and after treating these polycrystals with an external pressure. A quantitative approach is proposed that makes it possible to calculate the parameters of the resonance line-shape function versus the dislocation structure of crystallites. Data suggesting that the samples under investigation that were subjected to a treatment with an external pressure develop dislocations whose Burgers vectors are parallel are obtained. 相似文献
964.
A classification has been obtained for spaces which admit complete sets of motion integrals of the (3.1)-type and are spatially homogeneous. The metrics and Killing vectors have been found in explicit form for all types of these spaces. A classification by Bianchi is given for the spaces obtained. 相似文献
965.
M. Gutowski I. Dabkowska J. Rak S. Xu J.M. Nilles D. Radisic K.H. Bowen Jr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):431-439
The photoelectron spectra (PES) of anions of uracil-glycine and uracil-phenylalanine complexes reveal broad features with
maxima at 1.8 and 2.0 eV. The results of ab initio density functional B3LYP and second order M?ller-Plesset theory calculations indicate that the excess electron occupies a
π* orbital localized on uracil. The excess electron attachment to the complex can induce a barrier-free proton transfer (BFPT)
from the carboxylic group of glycine to the O8 atom of uracil. As a result, the four most stable structures of the anion of
uracil-glycine complex can be characterized as the neutral radical of hydrogenated uracil solvated by the anion of deprotonated
glycine. The similarity between the PES spectra for the uracil complexes with glycine and phenylalanine suggests that the
BFPT is also operative in the case of the latter anionic species. The BFPT to the O8 atom of uracil may be related to the
damage of nucleic acid bases by low energy electrons because the O8 atom is involved in a hydrogen bond with adenine in the
standard Watson-Crick pairing scheme.
Received 6 April 2002 Published online 13 September 2002 相似文献
966.
An electrostatic interaction between two separate, grounded, uncharged, perfectly conducting spheres of different radii in a uniform electrostatic field is investigated. It is shown that at a small center-to-center distance of the spheres, the force of the polarization interaction between the spheres depends appreciably more weakly on that distance in comparison to the force of the electrostatic interaction of two elementary dipoles as it should be in view of the interaction between two like polarization charges. 相似文献
967.
The Fokker–Planck-type kinetic equation is constructed with the help of the evolution equation for the transverse energy of channelized particles, which in its turn is derived beyond the framework of perturbation theory proceeding from the condition of nonconcervation of the adiabatic invariant. 相似文献
968.
969.
D.A. Garanin E.M. Chudnovsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):3-7
We compute the width and shape of the EPR and tunneling resonances due to dislocations in Mn12 acetate crystals. Uncorrelated dislocations produce the Gaussian shape of resonances while dislocations bound in pairs produce
the Lorentzian shape. We stress that the uniaxial spin Hamiltonian together with crystal defects can explain the totality
of experimental data on Mn12.
Received 2 August 2001 / Received in final form 15 March 2002 Published online 17 September 2002 相似文献
970.
Atomic-force microscopy was used to study the surface topography of SiGe structures grown by epitaxial deposition of Ge on profiled Si(111) substrates under electromigration conditions. Systems of highly ordered germanium nanosized islands with dimensions of 10–20 nm and a density of 6×1010 cm?2 were obtained. It is shown that the geometrical parameters of self-organizing nanoislands can be controlled by a proper choice of the growth and postgrowth annealing conditions for these structures. 相似文献