全文获取类型
收费全文 | 300024篇 |
免费 | 2680篇 |
国内免费 | 1001篇 |
专业分类
化学 | 145534篇 |
晶体学 | 4826篇 |
力学 | 14814篇 |
综合类 | 38篇 |
数学 | 43166篇 |
物理学 | 95327篇 |
出版年
2018年 | 10559篇 |
2017年 | 11477篇 |
2016年 | 6601篇 |
2015年 | 2740篇 |
2014年 | 2706篇 |
2013年 | 8214篇 |
2012年 | 9978篇 |
2011年 | 19816篇 |
2010年 | 12149篇 |
2009年 | 12114篇 |
2008年 | 17217篇 |
2007年 | 20886篇 |
2006年 | 6279篇 |
2005年 | 12839篇 |
2004年 | 8751篇 |
2003年 | 8001篇 |
2002年 | 5807篇 |
2001年 | 6015篇 |
2000年 | 4748篇 |
1999年 | 3614篇 |
1998年 | 2848篇 |
1997年 | 2855篇 |
1996年 | 2962篇 |
1995年 | 2689篇 |
1994年 | 2517篇 |
1993年 | 2391篇 |
1992年 | 2881篇 |
1991年 | 2765篇 |
1990年 | 2703篇 |
1989年 | 2734篇 |
1988年 | 2684篇 |
1987年 | 2674篇 |
1986年 | 2487篇 |
1985年 | 3361篇 |
1984年 | 3388篇 |
1983年 | 2810篇 |
1982年 | 3003篇 |
1981年 | 2939篇 |
1980年 | 2840篇 |
1979年 | 3003篇 |
1978年 | 3252篇 |
1977年 | 2992篇 |
1976年 | 2956篇 |
1975年 | 2800篇 |
1974年 | 2749篇 |
1973年 | 2792篇 |
1972年 | 1792篇 |
1968年 | 2026篇 |
1967年 | 2165篇 |
1966年 | 1968篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
971.
The Monte Carlo ray-tracing method (MCRT) based on the concept of radiation distribution factor is extended to solve radiative heat transfer problem in turbulent fluctuating media under the optically thin fluctuation approximation. A one-dimensional non-scattering turbulent fluctuating media is considered, in which the mean temperature and absorption coefficient distribution are assumed and the shape of probability density function is given. The distribution of the time-averaged volume radiation heat source is solved by MCRT and direct integration method. It is shown that the results of MCRT based on the concept of radiation distribution factor agree with these of integration solution very well, but results of MCRT based on the concept of radiative transfer coefficient do not agree with these of integration solution. The solution of time-averaged radiative transfer equation by the concept of radiative transfer coefficient should be treated with caution. 相似文献
972.
Using a representation of multichannel quantum defect theory in terms of a quantum Poincaré map for bound Rydberg molecules, we apply Jung's scattering map to derive a generalized quantum map, that includes the continuum. We show that this representation not only simplifies the understanding of the method, but moreover produces considerable numerical advantages. Finally we show under what circumstances the usual semi-classical approximations yield satisfactory results. In particular we see that singularities that cause problems in semi-classics are irrelevant to the quantum map. 相似文献
973.
A. V. Burenin 《Optics and Spectroscopy》2004,97(6):867-875
A noninvariant geometrical group characterizing the internal dynamics of the tetrahydrofuran molecule C4H8O with allowance for the clearly pronounced pseudorotation effect is constructed. On this basis, some qualitative features of the energy spectrum of the molecule following from the analysis of high-resolution spectroscopic data are explained. 相似文献
974.
The kinetics of decay of a phase hologram in a semiconductor CdF2 crystal with bistable In centers is studied. Kinetic constants of the hologram decay are found, and the potential relief of the bistable center is plotted. The resolving power of the crystal is evaluated and recording of a transparency is demonstrated. 相似文献
975.
Processes of electronic excitation energy transfer (EEET) in H2O+D2O solutions within reversed micelles with different degrees of hydration were studied. It is ascertained that the structure of solutions forms a cluster distribution of interacting molecules having a fractal dimensionality. As a result, in regions with a locally high concentration of the dye molecules, an increase in the EEET efficiency is observed. Solubilization by reversed micelles leads to destruction of the cluster structure of the water system, with the dependence of the EEET efficiency on the degree of hydration being nonmonotonic. As the degree of hydration increases, the inhomogeneities of the structure inherent in bulk water are restored. 相似文献
976.
The cross section of absorption of electromagnetic radiation by an inhomogeneous spherical particle is calculated. The general case of an arbitrary value of the ratio of the particle radius to the radius of the dielectric core is considered. The condition of diffuse reflection of electrons from the inner and outer surfaces of the metal layer of the particle is taken as the boundary condition of the problem. The limiting cases are considered and the results obtained are discussed. 相似文献
977.
Computer processing of electronic absorption spectra of rare-earth elements in inorganic laser media
Algorithms and program modules are developed for calculation of the Judd-Ofelt parameters on modern computers. These programs can be used to perform numerical analysis of the energy absorption by rareearth ions in laser media. 相似文献
978.
979.
Using two different types of the laddering equations realized simultaneously by the associated Gegenbauer functions, we show that all quantum states corresponding to the motion of a free particle on AdS
2 and S
2 are splitted into infinite direct sums of infinite-and finite-dimensional Hilbert subspaces which represent Lie algebras u(1, 1) and u(2) with infinite- and finite-fold degeneracies, respectively. In addition, it is shown that the representation bases of Lie algebras with rank 1, i.e., gl(2, C), realize the representation of nonunitary parasupersymmetry algebra of arbitrary order. The realization of the representation of parasupersymmetry algebra by the Hilbert subspaces which describe the motion of a free particle on AdS
2 and S
2 with the dynamical symmetry groups U(1, 1) and U(2) are concluded as well. 相似文献
980.
It is experimentally demonstrated that second-order polarizability gratings preliminarily recorded using bichromatic light in a phosphate glass can be amplified under the action of monochromatic radiation. The amplification effect takes place irrespective of the polarization and direction of propagation of the amplifying radiation and is achieved at various wavelengths. The phenomenon is related to the asymmetry of optical transitions between local centers in an isotropic medium in the presence of electric field. It is theoretically shown that this system may feature the formation of alternating electric field domains with dimensions depending on the grating amplitude. 相似文献