全文获取类型
收费全文 | 351834篇 |
免费 | 3978篇 |
国内免费 | 1089篇 |
专业分类
化学 | 190577篇 |
晶体学 | 6057篇 |
力学 | 14499篇 |
综合类 | 7篇 |
数学 | 37504篇 |
物理学 | 108257篇 |
出版年
2019年 | 2791篇 |
2018年 | 3273篇 |
2017年 | 3336篇 |
2016年 | 5437篇 |
2015年 | 3580篇 |
2014年 | 5578篇 |
2013年 | 15364篇 |
2012年 | 10699篇 |
2011年 | 13143篇 |
2010年 | 9194篇 |
2009年 | 9140篇 |
2008年 | 12066篇 |
2007年 | 12039篇 |
2006年 | 11393篇 |
2005年 | 10346篇 |
2004年 | 9539篇 |
2003年 | 8519篇 |
2002年 | 8330篇 |
2001年 | 10197篇 |
2000年 | 7765篇 |
1999年 | 6115篇 |
1998年 | 4910篇 |
1997年 | 4854篇 |
1996年 | 4699篇 |
1995年 | 4388篇 |
1994年 | 4287篇 |
1993年 | 4125篇 |
1992年 | 4843篇 |
1991年 | 4633篇 |
1990年 | 4563篇 |
1989年 | 4551篇 |
1988年 | 4481篇 |
1987年 | 4513篇 |
1986年 | 4196篇 |
1985年 | 5652篇 |
1984年 | 5729篇 |
1983年 | 4851篇 |
1982年 | 5115篇 |
1981年 | 4916篇 |
1980年 | 4822篇 |
1979年 | 5088篇 |
1978年 | 5356篇 |
1977年 | 5145篇 |
1976年 | 5065篇 |
1975年 | 4879篇 |
1974年 | 4834篇 |
1973年 | 5007篇 |
1972年 | 3278篇 |
1968年 | 3049篇 |
1967年 | 3189篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
We complete our previous(1, 2) demonstration that there is a family of new solutions to the photon and Dirac equations using spatial and temporal circles and four-vector behaviour of the Dirac bispinor. We analyse one solution for a bound state, which is equivalent to the attractive two-body interaction between a charged point particle and a second, which remains at rest. We show this yields energy and angular momentum eigenvalues that are identical to those found by the usual method of solving of the Dirac equation,(4) including fine structure. We complete our previous derivation(2) of QED from a set of rules for the two-body interaction and generalise these. We show that QED may be decomposed into a two-body interaction at every point in spacetime. 相似文献
942.
Using two different types of the laddering equations realized simultaneously by the associated Gegenbauer functions, we show that all quantum states corresponding to the motion of a free particle on AdS
2 and S
2 are splitted into infinite direct sums of infinite-and finite-dimensional Hilbert subspaces which represent Lie algebras u(1, 1) and u(2) with infinite- and finite-fold degeneracies, respectively. In addition, it is shown that the representation bases of Lie algebras with rank 1, i.e., gl(2, C), realize the representation of nonunitary parasupersymmetry algebra of arbitrary order. The realization of the representation of parasupersymmetry algebra by the Hilbert subspaces which describe the motion of a free particle on AdS
2 and S
2 with the dynamical symmetry groups U(1, 1) and U(2) are concluded as well. 相似文献
943.
944.
The process of muon (pion) pair production with small invariant mass in electron-positron high-energy annihilation, accompanied by emission of a hard photon at large angles, is considered. We find that the Drell-Yan picture for the differential cross section is valid in the charge-even experimental setup. Radiative corrections both for the electron block and for the final-state block are taken into account. 相似文献
945.
A scheme of nuclear excitation by the ionic X-ray lines in laser plasma using two femtosecond laser pulses is proposed. The first pulse produces plasma with a given degree of ionization, allowing the X-ray line energies of the target ions to be tuned to resonance with the nuclear transition, while the second pulse generates hot electrons that are necessary for X-ray generation. 相似文献
946.
The influence of the parameter of amplitude-phase coupling for nonlinear amplification on the phase-frequency characteristics of an injection laser in the regime of pumping current modulation has been investigated theoretically. The parameter is defined as the coefficient of proportionality between changes in the real and imaginary parts of the refractive index during variation of the density of photons in the cavity. The substantial dependence of the coefficient of phase modulation on the parameter of the amplitude-phase coupling for nonlinear amplification at small modulation frequencies is shown. A technique to determine the indicated parameter based on the frequency dependence of the ratio between the coefficients of phase and amplitude modulation is suggested. 相似文献
947.
948.
L. J. Qin X. L. Meng Ch. L. Du L. Zhu B. Ch. Xu H. Zh. Xu F. Y. Jiang Z. Sh. Shao 《Optics & Laser Technology》2004,36(1):47-50
We have demonstrated a passively Q-switched operation of Nd:GdVO4 laser in which a GaAs crystal is used as the saturable absorber for the first time as far as we know. A maximum average output power of 1.64 W was obtained at an incident pump power of 12 W, the corresponding optical conversion efficiency and peak power were 13.7% and 116.8 W, respectively. The maximum peak energy obtained in the experiment by 50% transmission couple was 19 μJ. 相似文献
949.
Experimental data are obtained on the dynamics of conduction-electron relaxation at the stage preceding the melting of a silicon surface layer. The energy of a quantum of probe radiation is smaller than the band gap, making it possible to obtain information about the electron-phonon relaxation processes for an electron concentration of ~ 1021 cm?3 in the conduction band. 相似文献
950.
Capacity Constrained Transit Assignment with Common Lines 总被引:1,自引:0,他引:1
Fumitaka Kurauchi Michael G. H. Bell Jan-Dirk Schmöcker 《Journal of Mathematical Modelling and Algorithms》2003,2(4):309-327
This paper proposes the use of absorbing Markov chains to solve the capacity constrained transit network loading problem taking
common lines into account. The approach handles congested transit networks, where some passengers will not be able to board
because of the absence of sufficient space. The model also handles the common lines problem, where choice of route depends
on frequency of arrivals. The mathematical formulation of the problem is presented together with a numerical example.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献