全文获取类型
收费全文 | 372662篇 |
免费 | 7232篇 |
国内免费 | 5606篇 |
专业分类
化学 | 188015篇 |
晶体学 | 5024篇 |
力学 | 20034篇 |
综合类 | 328篇 |
数学 | 65239篇 |
物理学 | 106860篇 |
出版年
2022年 | 2779篇 |
2021年 | 3605篇 |
2020年 | 3997篇 |
2019年 | 4433篇 |
2018年 | 15457篇 |
2017年 | 15123篇 |
2016年 | 12903篇 |
2015年 | 5325篇 |
2014年 | 7114篇 |
2013年 | 13766篇 |
2012年 | 14883篇 |
2011年 | 22955篇 |
2010年 | 15043篇 |
2009年 | 15311篇 |
2008年 | 18222篇 |
2007年 | 20012篇 |
2006年 | 11052篇 |
2005年 | 11007篇 |
2004年 | 10140篇 |
2003年 | 9771篇 |
2002年 | 8844篇 |
2001年 | 8306篇 |
2000年 | 6645篇 |
1999年 | 5029篇 |
1998年 | 4526篇 |
1997年 | 4304篇 |
1996年 | 4125篇 |
1995年 | 3388篇 |
1994年 | 3513篇 |
1993年 | 3503篇 |
1992年 | 3567篇 |
1991年 | 3687篇 |
1990年 | 3566篇 |
1989年 | 3489篇 |
1988年 | 3313篇 |
1987年 | 3243篇 |
1986年 | 3165篇 |
1985年 | 3855篇 |
1984年 | 4034篇 |
1983年 | 3289篇 |
1982年 | 3533篇 |
1981年 | 3317篇 |
1980年 | 3095篇 |
1979年 | 3401篇 |
1978年 | 3551篇 |
1977年 | 3551篇 |
1976年 | 3597篇 |
1975年 | 3390篇 |
1974年 | 3379篇 |
1973年 | 3536篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
E. K. Bashkirov 《Laser Physics》2006,16(8):1218-1226
An exact solution is found for the collective model of two identical two-level atoms that resonantly interact with a two-mode quantum electromagnetic field in an ideal cavity via two-photon nondegenerate transitions. In the case under study, at the initial moment, both field modes are in the coherent state and atoms are in the excited state. The time dependences of the atomic probabilities, the mean number of photons in the modes, and the statistics and squeezing of the photon modes are studied based on the exact solution. 相似文献
92.
93.
In a two-dimensional array of magnetic moments with planar magnetization and relatively weak anisotropy in the basal plane, a stepwise phase transition is induced by an external magnetic field parallel to the easy axis of the system. This transition is similar to the spin flop phase transition in weakly anisotropic Heisenberg antiferromagnets with the significant difference that it is accompanied by the rearrangement of the sublattice structure of the magnet; i.e., it can be interpreted as a topological transition. The transition should manifest itself for arrays of submicron magnetic particles (magnetic dots) on nonmagnetic substrates, which have recently become the object of intensive research. 相似文献
94.
Yu. M. Smirnov 《Journal of Applied Spectroscopy》2006,73(6):785-791
Dissociative excitation of the lead atom in e-PbI2 collisions has been studied experimentally. 27 excitation cross sections were measured for an energy of the exciting electrons
equal to 100 eV. Nine optical excitation functions were recorded with variation of the electron energy in the range 0–100
eV. The most probable reaction channels for low electron energies are discussed, as well as the ratio of the dissociative
excitation cross sections for the lead atom in e-PbI2 and e-PbCl2 collisions.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 701–706, November–December, 2006. 相似文献
95.
K. E. Mochalov O. A. Ustinova S. A. Strel’tsov S. L. Grokhovskii A. L. Zhuze I. R. Nabiev A. V. Sukhanova V. A. Oleinikov 《Optics and Spectroscopy》2002,93(4):493-500
Topotecan (TPT), a water-soluble derivative of camptothecin (inhibitor of human DNA topoiomerase I), has found wide application in cancer chemotherapy. The central problem in using topotecan is the presence of lactone rings in its molecules, which undergo hydrolysis at a physiological pH yielding an inactive and even toxic form of the drug. The analysis of Raman spectra of TPT in H2O and D2O solutions made it possible to assign the spectral bands to the vibrations of particular molecular groups. Spectral features indicative of the opening of the lactone rings of the TPT molecules, deprotonation of the hydroxyl groups in their quinoline fragments, and of possible participation of the hydroxyl and carbonyl groups in H bonding are found. The data obtained are necessary to study the molecular mechanisms of TPT-DNA interaction and the formation of ternary complexes between TPT, DNA, and DNA topoisomerase I. 相似文献
96.
G. E. Volovik 《JETP Letters》2002,76(5):240-244
An analogue of a black hole can be realized in the low-temperature laboratory. The horizon can be constructed for “relativistic” ripplons (surface waves) living on the brane. The brane is represented by the interface between two superfluid liquids, 3He-A and 3He-B, sliding along each other without friction. A similar experimental arrangement was recently used for the observation and investigation of the Kelvin-Helmholtz type of instability in superfluids [1]. The shear-flow instability in superfluids is characterized by two critical velocities. The lowest threshold measured in recent experiments [1] corresponds to the appearance of the ergoregion for ripplons. In the modified geometry, this will give rise to the black-hole event horizon in the effective metric experienced by ripplons. In the region behind the horizon, the brane vacuum is unstable due to interaction with the higher-dimensional world of bulk superfluids. The time of the development of instability can be made very long at low temperature. This will allow us to reach and investigate the second critical velocity—the proper Kelvin-Helmholtz instability threshold. The latter corresponds to the singularity inside the black hole, where the determinant of the effective metric becomes infinite. 相似文献
97.
The existence of linear nonstationary optical resonances in a diatomic nanostructural object with a dipole-dipole atomic interaction has been proved. A new solution to the joint system of modified Bloch optical equations and nonlocal field equations is obtained for time intervals much shorter than the times of phase and energy relaxation. Formulas for effective polarizabilities of the object’s atoms, which have a set of dimensional resonances, are derived. The frequencies of these resonances significantly differ from the eigenfrequencies of the object’s atoms, and their properties depend on the interatomic distance, light-pulse duration, initial atomic inversions, and the orientation of the object’s axis relative to the direction of incidence of the external light wave. 相似文献
98.
99.
We use the adiabatic hyperspheric expansion and the Faddeev decomposition of the wave function with only s-waves. We derive for a fixed hyperradius an integro-differential equation for the angular eigenvalue and wave function. The
correlations lower the interaction energy for N = 20 by about a factor of 5.
Received October 22, 2001; accepted for publication November 5, 2001 相似文献
100.
An implicit quasi-monotone second-order accurate method is proposed for analyzing the spiral Couette flow of a rarefied gas between coaxial cylinders. The basic advantages of the method over the conventional method of stationry iterations are that the former is conservative with respect to the collision integral, has a simple software implementation for any types of boundary conditions, and applies to a wide range of Knudsen numbers. 相似文献