全文获取类型
收费全文 | 414298篇 |
免费 | 9057篇 |
国内免费 | 5543篇 |
专业分类
化学 | 211111篇 |
晶体学 | 6365篇 |
力学 | 21186篇 |
综合类 | 329篇 |
数学 | 51117篇 |
物理学 | 138790篇 |
出版年
2022年 | 3802篇 |
2021年 | 4842篇 |
2020年 | 5237篇 |
2019年 | 5752篇 |
2018年 | 7973篇 |
2017年 | 8117篇 |
2016年 | 10324篇 |
2015年 | 6417篇 |
2014年 | 10020篇 |
2013年 | 20117篇 |
2012年 | 17278篇 |
2011年 | 19535篇 |
2010年 | 14576篇 |
2009年 | 14568篇 |
2008年 | 16859篇 |
2007年 | 16518篇 |
2006年 | 15209篇 |
2005年 | 15665篇 |
2004年 | 14663篇 |
2003年 | 12133篇 |
2002年 | 10976篇 |
2001年 | 12394篇 |
2000年 | 9230篇 |
1999年 | 7281篇 |
1998年 | 6245篇 |
1997年 | 5872篇 |
1996年 | 5522篇 |
1995年 | 4741篇 |
1994年 | 4765篇 |
1993年 | 4553篇 |
1992年 | 4891篇 |
1991年 | 5133篇 |
1990年 | 4911篇 |
1989年 | 4744篇 |
1988年 | 4415篇 |
1987年 | 4528篇 |
1986年 | 4322篇 |
1985年 | 5276篇 |
1984年 | 5316篇 |
1983年 | 4445篇 |
1982年 | 4489篇 |
1981年 | 4174篇 |
1980年 | 4100篇 |
1979年 | 4448篇 |
1978年 | 4423篇 |
1977年 | 4418篇 |
1976年 | 4442篇 |
1975年 | 4192篇 |
1974年 | 4210篇 |
1973年 | 4223篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Field emission projector studies of fullerene coatings deposited on tungsten tip field emitters reveal specific ordered patterns in the form of doublets, quadruplets, rings, disks, and other forms in the emitter images. The ways in which these types of ordered emission patterns arise and their relation to C60 microformations have been established. Possible causes of the emergence of the ordered emission images are analyzed on the basis of published data and experimental results obtained. A modification of the model of field emission from the surface of microformations taking into account internal reflection of the electronic waves from the formation boundaries has been proposed. 相似文献
992.
W. Kockelmann M. Hofmann O. Moze S.J. Kennedy K.H.J. Buschow 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):25-32
The element distributions and the magnetic ordering behaviour of compounds RNi10Si2 (R
=
Tb, Dy, Ho, Er, Tm) have been studied by neutron powder diffraction down to temperatures of 1.6 K. The compounds crystallize
in an ordered variant of the ThMn12 structure type in the tetragonal space group P4/nmm. An ordered 1:1 distribution of Ni and Si on sites 4d and 4e, respectively,
corresponds to a modulation vector [0, 0, 1] with respect to the space group I4/mmm of the ThMn12 structure. TbNi10Si2 orders antiferromagnetically below T
N
= 4.5 K with a magnetic propagation vector of [0, 0, 1/2]. The magnetic Tb moments, 8.97(2) /Tb atom at 1.6 K, are aligned along the c-axis. The Ni sites in TbNi10Si2 do not carry any ordered magnetic moments. The compounds with R
=
Dy, Ho, Er, and Tm are paramagnetic down to 1.6 K and 3.0 K, respectively.
Received 10 July 2002 / Received in final form 12 September 2002 Published online 29 October 2002 相似文献
993.
A self-consistent model of the development of dendrites and partial discharges in a dielectric solid under a variable voltage
is suggested. Dendrites originate at sites with the enhanced local field strength and also where the dielectric is broken
down under the action of partial discharges. The numerical simulation is used to quantitatively describe the space-time dynamics
of the dendrites and partial discharges in epoxy resin for the tip-plane electrode configuration. The simulated data are compared
with electrical measurements of partial discharges and with optical images of dendrite growth under the same conditions. 相似文献
994.
M. W. Brenner K. A. Gridnev S. E. Belov W. Ershov E. Indola 《Physics of Atomic Nuclei》2002,65(4):612-615
The interaction of α particles above 5 MeV with a 2s-1d target is dominated by resonances. It cannot be described only in terms of a mean-field one-body potential. An analysis of the elastic α-particle scattering by 28Si encourages the comprehension of the resonance states to be mainly fragments of a mixed-parity band. In the present article, the angular distributions of particles scattered by 32S are analyzed in terms of such bands. The analysis of new data from an experiment made at Florida State University reveals the existence of states that do not belong to the above bands. This follows from a coupled-channel analysis of the elastic and inelastic (2+) cross sections. An α-particle structure at the nuclear surface is suggested. 相似文献
995.
996.
Switching kinetics of uniaxial ferroelastic ferroelectrics (FFs) in external electric and stress fields is studied using classical theory of nucleation and growth. The stage in which the polarization and deformation reversal involves the main body of the FF and the final stage (Ostwald ripening) of the FF switching are studied with allowance for the change in the repolarization and redeformation during the phase transition. The time dependences of the repolarization and redeformation are found, and equations are derived from which the polarization current and the deformation flux, as well as their time dependence, can be calculated. The calculated main characteristics of the FF switching are compared with the experimental data for switching of Rochelle salt single crystals. 相似文献
997.
A. S. Shlapakovskii 《Technical Physics》1997,42(5):516-521
A coaxial waveguide partially filled with a dielectric as the slow-wave structure of a dielectric Cherenkov maser is investigated.
The dispersion of the fundamental mode of this waveguide is very weak at phase velocities close to the velocity of light,
and for this reason a very wide gain bandwidth is possible under conditions of an interaction with a relativistic electron
beam. The dispersion equation for an infinitely thin tubular beam in a coaxial waveguide with a dielectric liner adjoining
either the outer or inner conducting surface is derived. The gain bandwidth as a function of the parameters of the electron
beam and the slow-wave system are investigated on the basis of numerical solution of the dispersion equation, and a comparison
with similar dependences for the conventional configuration of a dielectric Cherenkov maser is made. The structural features
of the coaxial configuration which enable novel approaches to the problems of matching the microwave signal at the entrance
and exit of the system are discussed.
Zh. Tekh. Fiz. 67, 66–72 (May 1997) 相似文献
998.
S. Moss de Oliveira P. M. C. de Oliveira F. C. de Sá Barreto 《Journal of statistical physics》1995,78(5-6):1619-1627
Using the finite-size scaling renormalization group, we obtain the two-dimensional flow diagram of the Blume-Capel model forS=1 andS=3/2. In the first case our results are similar to those of mean-field theory, which predicts the existence of first- and second-order transitions with a tricritical point. In the second case, however, our results are different. While we obtain in theS=1 case a phase diagram presenting a multicritical point, the mean-field approach predicts only a second-order transition and a critical endpoint. 相似文献
999.
G. Carelli N. Ioli A. Messina A. Moretti S. Schepis F. Strumia 《International Journal of Infrared and Millimeter Waves》1998,19(9):1191-1199
We measured the dependence of the reflectivity of InSb crystals upon temperature in the submillimeter region using monochromatic radiation from an optically pumped far infrared (FIR) laser. The measures allowed us to determine the value of the electron effective mass at low temperatures with radiations of different frequencies. Our measurements extend the results obtained recently on pure crystals with magneto-optical methods to the low temperatures region where only old measures were available. 相似文献
1000.
DAndrea A. Tomassini N. Ferrari L. Righini M. Selci S. Bruni M. R. Simeoni G. 《Il Nuovo Cimento D》1995,17(11):1423-1427
Il Nuovo Cimento D - Normalized reflection spectra in GaInAs/GaAs quantum wells are shown for two sets of samples with different alloy concentration (x=9% and 18.5%) and well thickness ranging from... 相似文献