全文获取类型
收费全文 | 424068篇 |
免费 | 3178篇 |
国内免费 | 1018篇 |
专业分类
化学 | 220753篇 |
晶体学 | 6805篇 |
力学 | 20673篇 |
综合类 | 18篇 |
数学 | 49064篇 |
物理学 | 130951篇 |
出版年
2020年 | 3598篇 |
2019年 | 4244篇 |
2018年 | 5918篇 |
2017年 | 5946篇 |
2016年 | 8260篇 |
2015年 | 4536篇 |
2014年 | 7675篇 |
2013年 | 17594篇 |
2012年 | 13396篇 |
2011年 | 16178篇 |
2010年 | 12082篇 |
2009年 | 12025篇 |
2008年 | 15182篇 |
2007年 | 15315篇 |
2006年 | 13928篇 |
2005年 | 12490篇 |
2004年 | 11673篇 |
2003年 | 10606篇 |
2002年 | 10504篇 |
2001年 | 11581篇 |
2000年 | 8847篇 |
1999年 | 6831篇 |
1998年 | 5943篇 |
1997年 | 6023篇 |
1996年 | 5557篇 |
1995年 | 5074篇 |
1994年 | 5277篇 |
1993年 | 4959篇 |
1992年 | 5651篇 |
1991年 | 5694篇 |
1990年 | 5558篇 |
1989年 | 5472篇 |
1988年 | 5499篇 |
1987年 | 5383篇 |
1986年 | 5135篇 |
1985年 | 6716篇 |
1984年 | 7057篇 |
1983年 | 5880篇 |
1982年 | 5949篇 |
1981年 | 5876篇 |
1980年 | 5660篇 |
1979年 | 5936篇 |
1978年 | 6231篇 |
1977年 | 6291篇 |
1976年 | 6315篇 |
1975年 | 5863篇 |
1974年 | 5872篇 |
1973年 | 6117篇 |
1972年 | 4424篇 |
1971年 | 3860篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Forces along Equidistant Particle Paths 总被引:1,自引:1,他引:0
Two particles on the sphere leave the equator moving due south and travel at a constant and equal speed along a geodesic colliding
at the south pole. An observer who is unaware of the curvature of the space will conclude that there is an attractive force
acting between the particles. On the other hand, if particles travel at the same speed (initially parallel) along geodesics
in the hyperbolic plane, then the particle paths diverge. Imagine two particles in the hyperbolic plane that are bound together
at a constant distance with their center of mass traveling along a geodesic path at a constant velocity, then the force due
to the curvature of the space acts to break the bond and increases as a quadratic function of the velocity. We consider this
problem for the sphere and the hyperbolic plane and we give the exact formula for the apparent force between the particles.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
172.
P. Murzyn C. R. Pidgeon P. J. Phillips J. -P. Wells N. T. Gordon T. Ashley J. H. Jefferson T. M. Burke J. Giess M. Merrick B. N. Murdin C. D. Maxey 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):220
We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τs300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τs is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τs in non-degenerate lightly n-type Hg0.78Cd0.22Te of approximately the same band gap as InSb, and find that τs varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τs, imply that the Elliott–Yafet model dominates in these materials. 相似文献
173.
We report a comprehensive analyzes of the Fourier transform infrared (FTIR) absorption and Raman scattering data on the structural and vibrational properties of dilute ternary GaAs1−xNx,[GaP1−xNx] (x<0.03) alloys grown on GaAs [GaP] by metal organic chemical vapor deposition (MOCVD) and solid source molecular beam epitaxy (MBE). By using realistic total energy and lattice dynamical calculations, the origin of experimentally observed N-induced vibrational features are characterized. Useful information is obtained about the structural stability, vibrational frequencies, lattice relaxations and compositional disorder in GaNAs (GaNP) alloys. At lower composition (x<0.015) most of the N atoms occupy the As [P] sublattice {NAs[NP]}—they prefer moving out of their substitutional sites to more energetically favorable locations at higher x. Our results for the N-isotopic shifts of local mode frequencies compare favorably well with the existing FTIR data. 相似文献
174.
G. Borges 《Acta Physica Hungarica A》2004,21(2-4):341-347
We present preliminary results on J/? production in Pb-Pb collisions at 158 GeV/nucleon, obtained in the analysis of the most recent data sample collected by NA50 experiment in year 2000. The results are compared with an updated absorption curve deduced from new high statistics protonnucleus data. The measurements reported here confirm the anomalous J/? suppression already observed by NA50 from previously collected data samples. 相似文献
175.
N. E. Pukhaeva 《Physics of Atomic Nuclei》2004,67(1):115-129
Preliminary results are reported on the two-particle correlation function R(Q) in hadronic Z decays, fully hadronic WW decays, and mixed hadronic-leptonic WW decays using data collected by the DELPHI detector at LEP at energies between 189 and 206 GeV. Evidence for Bose-Einstein correlations was observed in all three cases. The event mixing technique was used to determine correlations between particles arisingfrom different W bosons in fully hadronic WW decays. An excess of like-sign particle pairs with low four-momentum difference in fully hadronic WW events is observed, consistent with the effect expected from correlations between identical particles from different W bosons. 相似文献
176.
A. V. Turik A. I. Chernobabov G. S. Radchenko S. A. Turik 《Physics of the Solid State》2004,46(12):2213-2216
Effective complex piezoelectric and dielectric constants of disordered heterogeneous systems, such as statistical mixtures consisting of spheroidal particles of the same orientation but with random distribution in space, are studied. It is found for the first time that, in such systems, there exists giant piezoelectric enhancement accompanied by giant relaxation of piezoelectric coefficients and permittivity. The piezoelectric and dielectric spectra differ considerably from the Debye spectra and have a Cole-Cole character. The dependence of the effects considered on the aspect ratios of the spheroids is investigated. The physical mechanisms responsible for the anomalous behavior of the piezoelectric coefficients and permittivity are considered. 相似文献
177.
O. P. Bobrov S. N. Laptev H. Neuhäuser V. A. Khonik K. Csach 《Physics of the Solid State》2004,46(10):1863-1867
Isochronous relaxation of tensile stresses is measured in a bulk Pd40Cu30Ni10P20 metallic glass in the initial state and after certain thermal treatments. The results of measurements are used to find the energy spectrum of irreversible structural relaxation, from which the temperature dependence of shear viscosity is then calculated. This dependence is also found independently from measurements of creep in the same glass. The calculated viscosity is shown to agree well with the experimental data. 相似文献
178.
V. V. Dvorkin N. N. Dzbanovskii A. F. Pal’ N. V. Suetin A. Yu. Yur’ev P. Ya. Detkov 《Physics of the Solid State》2004,46(4):729-732
A suspension of ultrafine-dispersed nanodiamond was used for introducing (in particular, selectively) high-density centers of diamond nucleation on various substrates. High-quality doped diamond films to be used as electrochemistry electrodes were deposited from the gas phase in a microwave discharge on certain substrates treated using ultrafine-dispersed nanodiamond. A uniform distribution of nucleation centers with concentrations greater than 1010 cm-2 on silicon substrates was obtained. Electrochemical current-potential curves were measured for continuous films. Diamond meshes of different transparency were grown using selective nucleation. Successful production of high-quality doped diamond meshes gives grounds to consider them the most promising electrodes for use in electrochemistry. 相似文献
179.
G. Busiello R. V. Saburova V. G. Sushkova G. P. Chugunova 《Physics of the Solid State》2004,46(2):316-325
The ageing effect is studied analytically in a disordered quantum system interacting with its surroundings and subjected to an external ac magnetic field. Energy dissipation is due to the interaction of the system with a set of independent harmonic oscillators, imitating a quantum thermal bath. Dynamic equations for the autocorrelation function and linear-response function are derived using the method of closed-path integrals. The effect of an external field is studied on the correlation function and response in the spin-glass and paramagnetic phases. Both functions are found to depend on the spin interaction strength. 相似文献
180.
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