全文获取类型
收费全文 | 245097篇 |
免费 | 1472篇 |
国内免费 | 416篇 |
专业分类
化学 | 112518篇 |
晶体学 | 3815篇 |
力学 | 12990篇 |
综合类 | 3篇 |
数学 | 38003篇 |
物理学 | 79656篇 |
出版年
2021年 | 1024篇 |
2020年 | 1181篇 |
2019年 | 1251篇 |
2018年 | 10470篇 |
2017年 | 11333篇 |
2016年 | 6594篇 |
2015年 | 2410篇 |
2014年 | 2477篇 |
2013年 | 6159篇 |
2012年 | 9148篇 |
2011年 | 18481篇 |
2010年 | 11349篇 |
2009年 | 11421篇 |
2008年 | 16249篇 |
2007年 | 19688篇 |
2006年 | 5570篇 |
2005年 | 11731篇 |
2004年 | 7926篇 |
2003年 | 7548篇 |
2002年 | 5451篇 |
2001年 | 5711篇 |
2000年 | 4287篇 |
1999年 | 3117篇 |
1998年 | 2157篇 |
1997年 | 2224篇 |
1996年 | 2250篇 |
1995年 | 2022篇 |
1994年 | 2002篇 |
1993年 | 1806篇 |
1992年 | 2281篇 |
1991年 | 2372篇 |
1990年 | 2212篇 |
1989年 | 2179篇 |
1988年 | 2171篇 |
1987年 | 2175篇 |
1986年 | 1990篇 |
1985年 | 2464篇 |
1984年 | 2496篇 |
1983年 | 1996篇 |
1982年 | 2002篇 |
1981年 | 1844篇 |
1980年 | 1830篇 |
1979年 | 2136篇 |
1978年 | 2221篇 |
1977年 | 2080篇 |
1976年 | 2042篇 |
1975年 | 1912篇 |
1974年 | 1895篇 |
1973年 | 1969篇 |
1972年 | 1272篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
891.
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
892.
893.
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
894.
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
895.
The diffraction of a plane wave incident on a thick hologram at the first and second Bragg angles in the process of nonlinear recording is analyzed using the coupled-wave equations. It is shown that, in this case, the two-wave approximation with the use of effective modulation amplitudes of the refractive index, n 1ef and n 2ef, can be applied. Analytical dependences of n 1ef and n 2ef on the modulation amplitudes of the refractive index n 1 and n 2 at the fundamental and doubled spatial frequencies are obtained and the criteria of their applicability are determined. The dependences found are used to calculate the parameters of gratings recorded in a photopolymeric material. 相似文献
896.
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
897.
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
898.
899.
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
900.
The process of muon (pion) pair production with small invariant mass in electron-positron high-energy annihilation, accompanied by emission of a hard photon at large angles, is considered. We find that the Drell-Yan picture for the differential cross section is valid in the charge-even experimental setup. Radiative corrections both for the electron block and for the final-state block are taken into account. 相似文献