全文获取类型
收费全文 | 4047篇 |
免费 | 382篇 |
国内免费 | 76篇 |
专业分类
化学 | 120篇 |
晶体学 | 10篇 |
力学 | 1355篇 |
综合类 | 20篇 |
数学 | 841篇 |
物理学 | 2159篇 |
出版年
2024年 | 14篇 |
2023年 | 42篇 |
2022年 | 39篇 |
2021年 | 66篇 |
2020年 | 150篇 |
2019年 | 133篇 |
2018年 | 93篇 |
2017年 | 110篇 |
2016年 | 96篇 |
2015年 | 124篇 |
2014年 | 199篇 |
2013年 | 238篇 |
2012年 | 151篇 |
2011年 | 242篇 |
2010年 | 180篇 |
2009年 | 226篇 |
2008年 | 274篇 |
2007年 | 234篇 |
2006年 | 225篇 |
2005年 | 180篇 |
2004年 | 173篇 |
2003年 | 176篇 |
2002年 | 154篇 |
2001年 | 111篇 |
2000年 | 109篇 |
1999年 | 82篇 |
1998年 | 92篇 |
1997年 | 75篇 |
1996年 | 65篇 |
1995年 | 56篇 |
1994年 | 43篇 |
1993年 | 45篇 |
1992年 | 41篇 |
1991年 | 51篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1988年 | 22篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 26篇 |
1984年 | 18篇 |
1983年 | 6篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 6篇 |
1971年 | 2篇 |
排序方式: 共有4505条查询结果,搜索用时 515 毫秒
11.
Solitary waves and their bifurcations of KdV like equation with higher order nonlinearity 总被引:3,自引:1,他引:2
We investigate the KdV like equation with higher order nonlinearity ut + a(1 +bun)unux + uxxx = 0with n ≥ 1, a, b ∈ R and α≠ 0. The bifurcations and explicit expressions of solitary wave solutions for theequation are discussed by using the bifurcation method and qualitative theory of dynamical systems. Thebifurcation diagrams, existence and number of the solitary waves are given. 相似文献
12.
Guofen Yu Yuanci Gao Shenggang Liu Wenxiang Wang Jin Wu 《International Journal of Infrared and Millimeter Waves》2002,23(8):1261-1269
Analysis of the field distributions in a single biological cell under electromagnetic wave is given. With Debye approximation, the dielectric relaxation of each part of the cell, including the extracellular and cellular media, the cell membrane and the nuclear membrane, was taken into account. Making use of some typical parameters for a cell, the voltage across nuclear and cytoplasma membranes under electromagnetic waves are calculated up to millimeter wave frequency range. The calculated result indicates that it is unlikely to generate electroporation by present available millimeter wave sources. 相似文献
13.
An analytical solution of a linearized problem of the emission of periodic internal waves by part of a plane which oscillates with a small amplitude in an arbitrary direction in a viscous exponentially stratified fluid is constructed. Solutions of the dispersion equation are given for all positions of the emitting surface (arbitrary, vertical, horizontal, and critical when one of the beam propagation directions is collinear with the emitting surface). The possibility of transition to the case of a uniform fluid, which is important for applications, is analyzed. 相似文献
14.
We obtain expressions for the energy spectrum widths of Rayleigh waves corresponding to their deformational coupling to Fermi and Boltzmann electrons in a two-dimensional layer near the surface of a semibounded solid. We evaluate the nonequilibrium energy of Rayleigh waves that depends on these widths and is caused by the same coupling to the corresponding hot electrons. We show that this energy is independent of the degeneracy degree of the electrons and is given by the mean energy of free Rayleigh waves heated up to temperature of the electrons. We find conditions under which the thermodynamics is determined by this nonequilibrium energy of Rayleigh waves in films of a certain thickness with Fermi electrons near the surface and by the equilibrium energy of bulk phonons in thicker samples. All the results are obtained using the Keldysh diagram technique applied to the case of semibounded media. 相似文献
15.
LIN Chang ZHANG Xiu-Lian 《理论物理通讯》2005,44(2):247-251
The nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation is analytically investigated by using the formally variable separation approach. New analytical solutions for the governing equation of this system have been obtained for dust acoustic waves in a dust plasma for the first time. We derive exact analytical expressions for the general case of the nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation. 相似文献
16.
A group representation of radiation propagation in an anisotropic medium is developed. The system of wave equations for electromagnetic potentials, obtained from the Maxwell equations with account for the constitutive equations, has been factorized. It is shown that the linear differential operator of the factorized system is orthogonal in transparent crystals and unitary in gyrotropic ones and is represented through the momentum operator. On the basis of the commutation relations for the components of this operator, the eigenvalue problem has been solved and the expression for the change in the radiant energy in the crystal in the form of spherical waves has been obtained. The dependences of the ray and phase velocities and the polarization vectors of waves on the birefringence anisotropy and gyrotropy as well as on the angular momentum, displacement current, and bound charge determining them have been analyzed. It has been established that in the general case of gyrotropic crystals where the nonreciprocity phenomenon takes place and in magnetoelectrics Maxwell equations are represented in a form similar to the Dirac equations and the electromagnetic radiation is correctly described by means of bispinors and is quantized as fermions. 相似文献
17.
A brief account of applications of polarized inelastic neutron scattering in condensed matter research is given. We show that
full polarization analysis is the only tool allowing to discriminate unambiguously between different magnetic modes in various
magnetic materials. We show by means of recent results in the Heisenberg ferromagnet EuS that the effects of dipolar interactions
can be studied on a microscopic scale. Moreover, we have found for the first time indications for the divergence of the longitudinal
fluctuations belowT
c. In the itinerant antiferromagnet chromium we demonstrate that the dynamics of the longitudinal and transverse excitations
are very different, resolving a long standing puzzle concerning the slope of their dispersion. Finally, we show that a measurement
of the polarization-dependent part of the cross section of non-centrosymmetric MnSi proves directly that the chirality of
the magnetic fluctuations is left-handed. 相似文献
18.
ZHANG WenlingDepartment of Mathematics Physics National Natural Science Foundation of China Beijing China 《中国科学A辑(英文版)》2004,(6)
We use qualitative analysis and numerical simulation to study peaked traveling wave solutions of CH-γ and CH equations. General expressions of peakon and periodic cusp wave solutions are obtained. Some previous results become our special cases. 相似文献
19.
20.
着重研究了多孔介质BISQ模型中慢纵波的基本特性.给出了BISQ模型下慢纵波速度 和衰减的低频近似公式.与Biot理论对比,BISQ模型中慢纵波的衰减随频率降低急剧增大, 且随喷射流长度的减小而增加;相速度随喷射流长度的减小而增加,其低频极限值不是零; 孔隙流体位移与固相骨架位移之比的幅值随喷射流长度的增加而减小,其相位特点与Biot模 型预测的不同;在流体与孔隙介质的边界上可产生更大的渗流.为对比,同时也给出快纵波 的行为.依据BISQ模型可推断:非黏滞流体饱和孔隙介质中不存在喷射流机理;BISQ模型中
关键词:
多孔介质
喷射流
慢纵波
动力协调 相似文献