全文获取类型
收费全文 | 147250篇 |
免费 | 1296篇 |
国内免费 | 397篇 |
专业分类
化学 | 80332篇 |
晶体学 | 2389篇 |
力学 | 6069篇 |
综合类 | 3篇 |
数学 | 13596篇 |
物理学 | 46554篇 |
出版年
2021年 | 1031篇 |
2020年 | 1186篇 |
2019年 | 1255篇 |
2018年 | 1638篇 |
2017年 | 1689篇 |
2016年 | 2544篇 |
2015年 | 1561篇 |
2014年 | 2349篇 |
2013年 | 6060篇 |
2012年 | 4860篇 |
2011年 | 5949篇 |
2010年 | 4190篇 |
2009年 | 4214篇 |
2008年 | 5736篇 |
2007年 | 5515篇 |
2006年 | 5390篇 |
2005年 | 4954篇 |
2004年 | 4454篇 |
2003年 | 4119篇 |
2002年 | 4010篇 |
2001年 | 5544篇 |
2000年 | 3975篇 |
1999年 | 3073篇 |
1998年 | 2112篇 |
1997年 | 2208篇 |
1996年 | 2073篇 |
1995年 | 1923篇 |
1994年 | 1920篇 |
1993年 | 1730篇 |
1992年 | 2215篇 |
1991年 | 2301篇 |
1990年 | 2136篇 |
1989年 | 2101篇 |
1988年 | 2077篇 |
1987年 | 2090篇 |
1986年 | 1910篇 |
1985年 | 2374篇 |
1984年 | 2397篇 |
1983年 | 1913篇 |
1982年 | 1919篇 |
1981年 | 1753篇 |
1980年 | 1741篇 |
1979年 | 2027篇 |
1978年 | 2109篇 |
1977年 | 2048篇 |
1976年 | 1977篇 |
1975年 | 1863篇 |
1974年 | 1848篇 |
1973年 | 1879篇 |
1972年 | 1240篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
We study matter-wave solitons in Bose-Einstein condensates of ultracold gaseous atoms with spin degrees of freedom and present a class of exact solutions based on the inverse scattering method. The one-soliton solutions are classified with respect to the spin states. We analyze collisional effects between solitons in the same or different spin state(s), which reveals a very interesting possibility: we can manipulate the spin dynamics by controlling the parameters of colliding solitons. 相似文献
22.
The occurrence and formation of black spots areas in PolyLED devices has been studied by time-of-flight SIMS (TOFSIMS). The composition, shape and position of the black spots is visualised by three-dimensional (3D)-TOFSIMS depth-profiling. It has been established that the formation of non-emissive spots is due to the growth of aluminium oxide clusters at the AlBa/polymer interface. Electron injection in the black spots is lost by the resulting local increase of the resistivity of the cathode. 相似文献
23.
Photoisomerization of provitamin D 3 (7-dehydrocholesterol) in a nematic liquid crystal (ZLI-1695, Merck) is investigated in detail by UV absorption spectroscopy. It is found that dissolution of chiral molecules of provitamin D 3 induces the cholesteric phase in a nematic. The spectral kinetics of photoisomerization in this phase changes significantly from that in an ethanol solution. A sharp nonmonotonic dependence of the increase in accumulation of trans isomer tachysterol in a liquid crystal matrix with a decrease in the induced cholesteric pitch from 2200 to 25 μm is revealed. 相似文献
24.
In this paper, we show that in some cases, no proper covering of a locally compact group topologically generated by left translations
of a topological loop can occur as the group topologically generated by left translations of a topological loop.
__________
Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 22, Algebra
and Geometry, 2004. 相似文献
25.
S. K. Godunov V. T. Zhukov O. B. Feodoritova 《Computational Mathematics and Mathematical Physics》2006,46(6):971-982
An algorithm is constructed for calculating invariant subspaces of symmetric hyperbolic systems arising in electromagnetic, acoustic, and elasticity problems. Discrete approximations are calculated for subspaces that correspond to minimal eigenvalues and smooth eigenfunctions. Difficulties related to the presence of an infinite-dimensional kernel in the differential operator are successfully handled. The efficiency of the algorithm is demonstrated using acoustics equations. 相似文献
26.
L. T. Ashchepkov 《Computational Mathematics and Mathematical Physics》2006,46(7):1168-1175
A general nonlinear programming problem with interval functions is considered. Two reductions of this problem to the deterministic nonlinear programming problem are proposed, and illustrative examples are discussed. 相似文献
27.
Nonlinear Theory of Spectra of Thermally Stimulated Currents in Complex Crystals with Hydrogen Bonds
Tonkonogov M. P. Ismailov Zh. T. Timokhin V. M. Fazylov K. K. Kalitka V. A. Baimukhanov Z. K. 《Russian Physics Journal》2002,45(10):1008-1018
The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field. 相似文献
28.
The equilibrium geometry and hyperfine interaction constants of the nearest and next-to-nearest neighbor atoms are calculated for a negatively charged silicon vacancy in the high-spin state in cubic SiC. The calculations are performed within the cluster approach in terms of the density-functional theory (DFT). It is shown that the results of calculations with the use of a 70-atom cluster are in good agreement with experimental data. A detailed consideration is given to spin polarization in the electron subsystem and the applicability of a simple LCAO model that is commonly used in the interpretation of the electron paramagnetic resonance data for semiconductors. The spin density distribution for the defect under investigation is analyzed in terms of localized orbitals. 相似文献
29.
30.
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