全文获取类型
收费全文 | 528054篇 |
免费 | 4747篇 |
国内免费 | 1281篇 |
专业分类
化学 | 269060篇 |
晶体学 | 7645篇 |
力学 | 25993篇 |
综合类 | 17篇 |
数学 | 67787篇 |
物理学 | 163580篇 |
出版年
2021年 | 5028篇 |
2020年 | 5479篇 |
2019年 | 6224篇 |
2018年 | 8419篇 |
2017年 | 8565篇 |
2016年 | 11628篇 |
2015年 | 6177篇 |
2014年 | 10439篇 |
2013年 | 23489篇 |
2012年 | 18336篇 |
2011年 | 21790篇 |
2010年 | 16420篇 |
2009年 | 16281篇 |
2008年 | 20656篇 |
2007年 | 20510篇 |
2006年 | 18613篇 |
2005年 | 16620篇 |
2004年 | 15468篇 |
2003年 | 13955篇 |
2002年 | 13847篇 |
2001年 | 14729篇 |
2000年 | 11343篇 |
1999年 | 8753篇 |
1998年 | 7600篇 |
1997年 | 7470篇 |
1996年 | 6928篇 |
1995年 | 6257篇 |
1994年 | 6264篇 |
1993年 | 6017篇 |
1992年 | 6375篇 |
1991年 | 6865篇 |
1990年 | 6577篇 |
1989年 | 6486篇 |
1988年 | 6321篇 |
1987年 | 6132篇 |
1986年 | 5871篇 |
1985年 | 7408篇 |
1984年 | 7769篇 |
1983年 | 6532篇 |
1982年 | 6817篇 |
1981年 | 6326篇 |
1980年 | 6003篇 |
1979年 | 6505篇 |
1978年 | 6741篇 |
1977年 | 6629篇 |
1976年 | 6587篇 |
1975年 | 6302篇 |
1974年 | 6129篇 |
1973年 | 6424篇 |
1972年 | 4706篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
The exact solution of the problem of ion transport current in an electrolyte in the presence of a conjugate flow of solvent
is obtained in the framework of the one-dimensional Gurevich-Kharkats diffusion-migration model; the conditions for the existence
of the solution are analyzed. 相似文献
922.
Spatial parameters of the X-ray radiation produced by a high-voltage nanosecond discharge evolving in air under atmospheric
pressure in the rod (cathode)-plane electrode system with a 10-cm electrode spacing are studied experimentally. A ∼170-ns
voltage pulse with an amplitude of ∼200 kV and 10-ns rise time is applied to the cathode. The photoelectronic method is used
to study, under the same conditions, the integrated (over the gap) characteristics of the radiation, in particular, the duration
of its generation. It is found that, when the size of the X-ray source is not smaller than that of the discharge region of
diffusive luminescence, radiation from the cathode region of the gap is primarily observed (i.e., from the region where the
electric field distribution is sharply inhomogeneous). The X-ray generation is usually observed after the bridging of the
discharge gap, the X-ray pulse having a rise time of ∼3 ns, a duration of ∼10 ns, and an effective radiation energy of ∼6
keV. 相似文献
923.
Interaction between an rf electromagnetic field and the Fe/Cr superlattice placed in a rectangular waveguide so that a high-frequency
current passes in the plane of superlattice layers is considered. The transmission coefficient versus the magnetic field strength
is found at centimeter waves, and a correlation between this dependence and the field dependence of the dc magnetoresistance
is established. It is shown that a change in the transmission coefficient may greatly exceed the giant magnetoresistance of
the superlattice. The frequency dependence of the microwave measurements has an oscillatory character. The oscillation frequencies
are analyzed in terms of wavelet transformation. Two types of oscillation periods are found to exist, one of which corresponds
to the resonance of waves traveling in the superlattice along the direction parallel to the narrow wall of the waveguide. 相似文献
924.
P. D. Kim I. A. Turpanov S. V. Stolyar R. S. Iskhakov V. I. Yushkov A. Ya. Beten’kova L. A. Li E. V. Bondareva T. N. Isaeva M. M. Karpenko 《Technical Physics》2004,49(4):431-434
The crystal structure and hysteretic magnetic properties of equiatomic single-crystal CoPt films applied on MgO substrates
by magnetron sputtering, as well as modification of these properties by thermal annealing, are studied. Heat-treated films
of thickness in the range 2<d≤16 nm exhibit perpendicular magnetic anisotropy. A correlation between the crystalline anisotropy constant of the CoPt films
and the order parameter of the LI0 superstructure in these alloys is found. The effect of a single-crystalline MgO substrate on the structure and magnetic properties
of equiatomic CoPt films is revealed. 相似文献
925.
V. L. Bychkov L. P. Grachev I. I. Esakov A. A. Ravaev K. V. Khodataev 《Technical Physics》2004,49(7):833-838
A longitudinal dc electric discharge in a submerged high-pressure supersonic air jet is described. Photographs of the discharge
are provided. The experimental voltage across the discharge gap and the discharge current are given for two resistances of
the resistor that limits the discharge current over a certain range of the discharge channel length along the air flow. The
current-voltage discharge characteristic is provided at a constant discharge length. The main discharge characteristics are
obtained from a comparison of the experimental and theoretical results calculated on the basis of the simplest model. 相似文献
926.
A. S. Baranov 《Technical Physics》2004,49(8):1081-1083
A concise proof is given for the expansion of the reciprocal distance between two points in spheroidal harmonics. The proof
is given for an oblate and a prolate spheroid. 相似文献
927.
The translational nonequilibrium zone in a shock wave is considered for a gas consisting of light particles and a small addition
of heavy particles. The gas is taken to be two-dimensional, and long-range forces are assumed to be absent. In the framework
of this approximation, a program for molecular dynamics simulation of the gas is developed. It is applied to calculate a particle
distribution function in the shock wave, to analyze the time evolution of the distribution function, and to study its dependence
on the gas composition. 相似文献
928.
O. I. Kotov L. B. Liokumovich S. I. Markov A. V. Medvedev A. V. Khlybov 《Technical Physics》2004,49(1):71-75
Mechanisms of polarization modulation in a single-mode fiber that modulate the phase difference between polarization modes without affecting their amplitudes are considered. A coefficient that characterizes the efficiency of cylindrical piezoceramic modulators and is independent of their resonant properties is introduced. Analytical expressions for this coefficient for different modulation mechanisms are derived. The lateral pressure on the fiber is shown to provide the highest efficiency. For isotropic fibers, a modulator with a squeezing covering, which increases significantly its efficiency, is studied. For anisotropic fibers, the most appropriate way of phase difference modulation is longitudinal extension, in which case the birefringence axes do not have to be matched. In most cases, the measured and predicted efficiencies are in good correspondence. 相似文献
929.
Stimulated Raman scattering (SRS) in a long-distance fiber-optic communication line with wavelength-division multiplexing (WDM) is studied theoretically at a high power of the signal transmitted. A new criterion for determining the SRS threshold is used to calculate the critical input power versus the number of optical channels and frequency separation between them. The theoretical model is verified experimentally. SRS interaction between two channels in a communication line with an SRS amplifier for which the optical waveguide of the line serves as a nonlinear medium is measured. 相似文献
930.