全文获取类型
收费全文 | 1379520篇 |
免费 | 29667篇 |
国内免费 | 7799篇 |
专业分类
化学 | 695846篇 |
晶体学 | 20474篇 |
力学 | 75673篇 |
综合类 | 106篇 |
数学 | 244278篇 |
物理学 | 380609篇 |
出版年
2021年 | 13561篇 |
2020年 | 15965篇 |
2019年 | 16098篇 |
2018年 | 14023篇 |
2016年 | 28548篇 |
2015年 | 20935篇 |
2014年 | 30520篇 |
2013年 | 74469篇 |
2012年 | 40203篇 |
2011年 | 39143篇 |
2010年 | 38488篇 |
2009年 | 40454篇 |
2008年 | 37653篇 |
2007年 | 33780篇 |
2006年 | 38386篇 |
2005年 | 31461篇 |
2004年 | 32120篇 |
2003年 | 29877篇 |
2002年 | 30630篇 |
2001年 | 30761篇 |
2000年 | 26131篇 |
1999年 | 23143篇 |
1998年 | 21255篇 |
1997年 | 21148篇 |
1996年 | 21209篇 |
1995年 | 19267篇 |
1994年 | 18716篇 |
1993年 | 18298篇 |
1992年 | 18566篇 |
1991年 | 18782篇 |
1990年 | 18001篇 |
1989年 | 18033篇 |
1988年 | 17634篇 |
1987年 | 17563篇 |
1986年 | 16512篇 |
1985年 | 22868篇 |
1984年 | 23981篇 |
1983年 | 20098篇 |
1982年 | 21720篇 |
1981年 | 20958篇 |
1980年 | 20286篇 |
1979年 | 20600篇 |
1978年 | 21802篇 |
1977年 | 21422篇 |
1976年 | 21133篇 |
1975年 | 19840篇 |
1974年 | 19494篇 |
1973年 | 19905篇 |
1972年 | 14425篇 |
1967年 | 12654篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
991.
An analysis of events in the tunneling junction shows that the interaction of one-electron processes in a many-electron system may be a source of scale-invariant low-frequency fluctuations of conductivity (the interaction consists in that the quantum probability of an electron transition depends on fast random changes in the environment in the course of the transition, including the changes caused by analogous transitions). The theory relates flicker fluctuations in the tunneling conductivity to the discrete character of the spectrum of electron states and explains the nonlinearity of the noise-current characteristic observed in nanocomposites. 相似文献
992.
993.
M.V. Kossov 《The European Physical Journal A - Hadrons and Nuclei》2002,14(3):377-392
Photonuclear interaction cross-sections from the GEANT4 database are approximated for all nuclei and all energies (from the
hadron production threshold to about 40 TeV). The approximation methods in the giant-dipole resonance region, nucleon resonance
region, and high-energy region are improved with respect to existing approximations. As an application of the approximation
for photonuclear cross-sections, an improved method of calculating electronuclear cross-sections is developed. The interaction
cross-section of virtual photons with nuclei at high Q2 are approximated and a simple algorithm for describing the electronuclear reactions, including high-Q2 scattering, is proposed.
Received: 22 February 2002 / Accepted: 6 May 2002 相似文献
994.
The electrodynamic properties of granular high-temperature superconducting media are studied. Relations for the surface resistance and impedance of a high-temperature superconducting medium are derived. The temperature and frequency dependence of the phase velocity and group velocity and depth of penetration of the electromagnetic field into the Josephson medium are calculated. The possibility of using high-temperature superconducting films as high-efficiency shields is shown. The shielding properties are improved appreciably with increase in the critical current density of the high-temperature superconducting film. The shield thickness is several microns or several fractions of a micron for a critical current density of >107 A/m2. The results obtained can be used in designing superhigh-frequency shields, microstrip lines, and other devices based on high-temperature superconducting Josephson media. 相似文献
995.
D. P. Kouzov 《Journal of Mathematical Sciences》2002,108(5):721-735
A condition for regularization of boundary-contact integrals in two-dimensional problems of acoustics is considered. With an example of the simplest boundary-contact problem of acoustics, it is shown that a known sufficient condition for regularization is also a necessary one. The study of analytic properties of the transition admittance of an infinite plate that is in contact with a medium is conducted in order to obtain this statement. The considerations are carried out in general terms. The results obtained may be used in arbitrary models of plate theory, and they also may be adapted to boundary-contact problems of another physical nature. Bibliography: 9 titles. 相似文献
996.
Timinskas A. Cheshunene A. Kurtinaitene M. Skominas V. 《Russian Journal of Applied Chemistry》2002,75(6):911-914
Conditions under which anodized aluminum is treated first in a dilute solution of phosphoric acid and then in a fluoroborate immersion solution in order to deposit a multilayer system of cobalt and copper in the pores in the oxide were studied. 相似文献
997.
James K. Freericks Elliott H. Lieb Daniel Ueltschi 《Communications in Mathematical Physics》2002,227(2):243-279
The Falicov–Kimball model is a simple quantum lattice model that describes light and heavy electrons interacting with an
on-site repulsion; alternatively, it is a model of itinerant electrons and fixed nuclei. It can be seen as a simplification
of the Hubbard model; by neglecting the kinetic (hopping) energy of the spin up particles, one gets the Falicov–Kimball model.
We show that away from half-filling, i.e. if the sum of the densities of both kinds of particles differs from 1, the particles
segregate at zero temperature and for large enough repulsion. In the language of the Hubbard model, this means creating two
regions with a positive and a negative magnetization.
Our key mathematical results are lower and upper bounds for the sum of the lowest eigenvalues of the discrete Laplace operator
in an arbitrary domain, with Dirichlet boundary conditions. The lower bound consists of a bulk term, independent of the shape
of the domain, and of a term proportional to the boundary. Therefore, one lowers the kinetic energy of the itinerant particles
by choosing a domain with a small boundary. For the Falicov- Kimball model, this corresponds to having a single “compact”
domain that has no heavy particles.
Received: 21 June 2001 / Accepted: 4 January 2002 相似文献
998.
A.R. DegheidyM.T. Attia M. Sallah 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,74(3):285-297
The time-independent radiative transfer problem in a scattering and absorbing planar random medium with general boundary conditions and internal energy source is considered. The medium is assumed to consist of two randomly mixed immiscible fluids, with the mixing statistics described as a two-state homogeneous Markov process. The problem is solved in terms of the solution of the corresponding free-source problem with simple boundary conditions which is solved using Pomraning-Eddington approximation in the deterministic case. A formalism, developed to treat radiative transfer in statistical mixtures, is used to obtain the ensemble-averaged solution. The average partial heat fluxes are calculated in terms of the albedoes of the source-free problem. Results are obtained for isotropic and anisotropic scattering for specular and diffused reflecting boundaries. 相似文献
999.
L.V. Zolotukhina Ye.V. ZabolotskayaYe.V. Arkhipova M.G. Zuev 《Journal of Physics and Chemistry of Solids》2002,63(3):415-418
Phase equilibria in the Sc2O3-V2O5-Nb2O5-Ta2O5 system and properties of ScNb2−2xTa2xVO9 phases were studied by X-ray phase analysis, optical and radio spectroscopy. A continuous series of solid solutions was shown to exist at 0≤x≤1. V(IV) centers with different crystallographic surrounding were detected for all the considered compositions. A correlation between the number of V(IV) ions and the width of the forbidden gap in the solid solutions was found. 相似文献
1000.
We prove that the diffusion semigroups generated by the second order differential ultraspherical (Gegenbauer) operator are pseudomeasure operators. 相似文献