全文获取类型
收费全文 | 304736篇 |
免费 | 1789篇 |
国内免费 | 648篇 |
专业分类
化学 | 146357篇 |
晶体学 | 4470篇 |
力学 | 15078篇 |
综合类 | 6篇 |
数学 | 46481篇 |
物理学 | 94781篇 |
出版年
2020年 | 1970篇 |
2019年 | 2265篇 |
2018年 | 10953篇 |
2017年 | 11674篇 |
2016年 | 7997篇 |
2015年 | 3110篇 |
2014年 | 3931篇 |
2013年 | 9369篇 |
2012年 | 10876篇 |
2011年 | 19878篇 |
2010年 | 12514篇 |
2009年 | 12559篇 |
2008年 | 17831篇 |
2007年 | 21218篇 |
2006年 | 7819篇 |
2005年 | 12974篇 |
2004年 | 9268篇 |
2003年 | 8885篇 |
2002年 | 6852篇 |
2001年 | 6097篇 |
2000年 | 4994篇 |
1999年 | 3508篇 |
1998年 | 3054篇 |
1997年 | 3052篇 |
1996年 | 2992篇 |
1995年 | 2426篇 |
1994年 | 2503篇 |
1993年 | 2530篇 |
1992年 | 2666篇 |
1991年 | 2730篇 |
1990年 | 2634篇 |
1989年 | 2617篇 |
1988年 | 2556篇 |
1987年 | 2524篇 |
1986年 | 2436篇 |
1985年 | 3121篇 |
1984年 | 3298篇 |
1983年 | 2652篇 |
1982年 | 2917篇 |
1981年 | 2796篇 |
1980年 | 2592篇 |
1979年 | 2825篇 |
1978年 | 2953篇 |
1977年 | 2889篇 |
1976年 | 2897篇 |
1975年 | 2739篇 |
1974年 | 2714篇 |
1973年 | 2900篇 |
1972年 | 1912篇 |
1967年 | 1868篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
S. N. Molotkov 《JETP Letters》2004,80(8):563-567
A “collective” attack on the key is considered, and its connection with the classical capacity of a quantum communication channel is analyzed. It has been shown that the allowable error probability for legitimate users to which the secure key can be extracted is less than half the value for “translucent” eavesdropping and individual measurements. 相似文献
992.
The properties of high-energy ion beams (beamlets) observed in the boundary layer of the plasma sheet of the Earth’s magnetotail during short time intervals (1–2 min) have been considered. Beamlets are induced by nonlinear impulse accelerating processes occurring in the current sheet of the far regions of the geomagnetic tail. Then, moving toward the Earth along the magnetic field lines, they are detected in the magnetotail (in the plasma sheet boundary layer) and in the high-latitude part of the auroral zone in the form of short bursts of high-energy ions (with energies of several tens of keVs). The size of the localization region of the beamlets in the magnetotail and auroral zone has been determined by the epoch-superposition method, and it has been shown that beamlets are concentrated in a narrow region near the plasma sheet boundary, whose latitude size is no more than 0.8δ. This conclusion corroborates the theoretical prediction that the nonadiabatic resonant acceleration of ions occurs in a spatially localized region near the separatrix separating the open magnetic field lines and closed field lines, which contain the hot and isotropic plasmas of the plasma sheet. Based on the CLUSTER multisatellite measurements, the spatial structure of beamlets is analyzed and it has been found that the Alfvén wave arises due to the excitation of fire-hose instability at the instant of the exit of the ion beam from the current sheet to the high-latitude region of the far tail of the Earth’s magnetosphere. The longitudinal (along the magnetic field) and transverse sizes of a beamlet are estimated. It has been found that the beamlet is a dynamic plasma structure whose longitudinal size is several hundred times larger than its transverse size. 相似文献
993.
N. S. Kazak E. G. Katranji I. A. Utkin A. A. Ryzhevich A. N. Khilo 《Journal of Applied Spectroscopy》2004,71(5):697-701
The phenomenon of self-diffraction of Bessel light beams (BLB) in a nonlinear liquid medium has been studied experimentally and theoretically for the first time. Diffraction maxima which do not correspond to integer orders for an induced periodic structure have been registered. It has been shown that the appearance of these maxima is due to the initial BLB modulation, which can be caused by the departure of the axicon refracting surface from the ideal conical surface, as well as by the imperfection of the form of the Gaussian beam incident on the axicon. 相似文献
994.
Y. Brihaye S. Giller C. Gonera P. Kosinski P. Maslanka 《Czechoslovak Journal of Physics》2004,54(11):1185-1190
The dynamical systems of identical particles admitting quadratic integrals of motion are classified. The relevant integrals are explicitly constructed and their relation to separation of variables in Hamilton-Jacobi equation is clarified. 相似文献
995.
V. G. Domelunksen I. R. Krylov G. A. Polyanskaya M. A. Tsygankov 《Optics and Spectroscopy》2004,97(1):136-140
An interference method for measuring certain parameters of a substance in the vicinity of the critical state is proposed. The essence of the method is to decipher the interference pattern arising upon grazing incidence of a laser beam on a curved liquid-vapor interface. The deciphering allows one to determine the difference between the refractive indices of the two phases and the scaling factor of the wetting meniscus shape. This, in turn, makes it possible to calculate the critical exponents for the temperature dependences of the surface tension and the difference in the densities of the two phases. The ratio of these critical exponents for xenon, measured in the paper, is 3.81±0.03. 相似文献
996.
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
997.
998.
The synthesis of a specific isotopomer, C6D4H(ortho)-H(ortho)D4C6 of biphenyl is reported. The intramolecular dipolar coupling of the protons leads to a well-resolved single-crystal proton
nuclear magnetic resonance (NMR) spectrum and allows one to study the dynamics of the phenyl rings in a unique way. At room
temperature and above, the most conspicuous dynamical mode consists of 180° ring flips. The present data together with previous
measurements of the total flip rate allow us to conclude that the rings flip almost exclusively independently of each other.
Between the incommensurate (IC) phase transition of biphenyl at 38 K andT=250 K, the prominent namical mode consists of oscillatory twists ϕ(t) of the two rings. The data allow us to infer the mean square, (φ2), of these twists. (φ2) is found to grow linearly withT for 50<T<200 K. From the slope of (φ2) vs.T the frequency (the wave number[(v)\tilde]\tilde v) is derived. The result is[(v)\tilde] = 20\tilde v = 20 cm−1. ForT<38 K, the spectra give direct evidence of the IC phase transition and its nature (stripelike rather than quiltlike). The
temperature dependence of the magnitude of the order parameter of the IC phase is obtained. 相似文献
999.
A. E. Nikiforov A. Yu. Zakharov V. A. Chernyshev M. Yu. Ugryumov S. V. Kotomanov 《Physics of the Solid State》2003,45(5):864-867
The structure of the mixed fluorites Ca1−x
SrxF2 and Sr1−x
BaxF2, as well as the structure of the Eu2+ impurity center in these crystals, is calculated within the framework of the virtual-crystal method realized in the shell
model and pair-potential approximation. The phenomenological dependence of the position of the lower level of the 4f
65d configuration of the Eu2+ ion on distance to the Eu2+-ligand is derived. The dependences of the Stokes shift and the Huang-Rhys factor on x are calculated for the yellow luminescence in Sr1−x
BaxF2:Eu2+. The value of x at which the lower level of the 4f
65d configuration of the Eu2+ ion in Sr1−x
BaxF2:Eu2+ falls within the conduction band is found.
__________
Translated from Fizika Tverdogo Tela, Vol. 45, No. 5, 2003, pp. 823–826.
Original Russian Text Copyright ? 2003 by Nikiforov, Zakharov, Chernyshev, Ugryumov, Kotomanov. 相似文献
1000.
Harper equations are derived for a px, py electronic system. Analysis is carried out for extreme points of the quasi-continuous spectrum in the cases when the number of magnetic flux quanta through a unit cell is a rational number and calculations are made for square and triangular lattices as well as for a honeycomb lattice with two nonequivalent atoms. The possibility of application of the results for explaining the fractional Hall effect is considered. 相似文献