全文获取类型
收费全文 | 502586篇 |
免费 | 5154篇 |
国内免费 | 1518篇 |
专业分类
化学 | 263247篇 |
晶体学 | 7726篇 |
力学 | 22463篇 |
综合类 | 11篇 |
数学 | 60833篇 |
物理学 | 154978篇 |
出版年
2021年 | 4342篇 |
2020年 | 4760篇 |
2019年 | 5321篇 |
2018年 | 7270篇 |
2017年 | 7427篇 |
2016年 | 10301篇 |
2015年 | 6006篇 |
2014年 | 9841篇 |
2013年 | 23127篇 |
2012年 | 17687篇 |
2011年 | 21217篇 |
2010年 | 15599篇 |
2009年 | 15398篇 |
2008年 | 19534篇 |
2007年 | 19591篇 |
2006年 | 18160篇 |
2005年 | 16070篇 |
2004年 | 14713篇 |
2003年 | 13135篇 |
2002年 | 13054篇 |
2001年 | 14781篇 |
2000年 | 11202篇 |
1999年 | 8700篇 |
1998年 | 7386篇 |
1997年 | 7256篇 |
1996年 | 6797篇 |
1995年 | 5826篇 |
1994年 | 5849篇 |
1993年 | 5821篇 |
1992年 | 6217篇 |
1991年 | 6500篇 |
1990年 | 6160篇 |
1989年 | 6079篇 |
1988年 | 5840篇 |
1987年 | 5937篇 |
1986年 | 5674篇 |
1985年 | 7248篇 |
1984年 | 7430篇 |
1983年 | 6122篇 |
1982年 | 6413篇 |
1981年 | 6074篇 |
1980年 | 5852篇 |
1979年 | 6306篇 |
1978年 | 6404篇 |
1977年 | 6378篇 |
1976年 | 6358篇 |
1975年 | 5967篇 |
1974年 | 5894篇 |
1973年 | 6093篇 |
1972年 | 4249篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The relativistic four-quark equations are found in the framework of the dispersion relation technique. The behaviour of the low-energy four-particle amplitude is determined by its leading singularities in the pair invariant masses. The approximate solutions of these equations using the method based on the extraction of leading singularities of the amplitudes are obtained. The mass values of lowest exotic mesons are calculated. 相似文献
992.
It is shown that the potential perturbation that shifts a chosen standing wave in space is a block of potential barrier and well for every wave bump between neighbouring knots. The algorithms shifting the range of the primary localization of a chosen bound state in a potential well of finite width are as well applicable to the scattering functions if states of the continuous spectrum are considered as bound states normalized to unity but distributed on an infinite interval with vanishing density. The potential perturbations of the same type on the half-axis concentrate the scattering wave at the origin, thus creating a bound state embedded into the continuous spectrum (zero width resonance). 相似文献
993.
New effects are observed wherein the internal structure of the domain walls in a thin magnetic iron garnet film are modified
by the action of focused laser radiation. A single laser pulse with increasing power gives rise to the following: 1) displacement
of vertical Bloch lines in a domain wall; 2) generation of a pair of vertical Bloch lines on initially line-free walls; and,
3) an irreversible change in shape of a domain wall and the domain structure as a whole. The mechanism leading to the generation
and displacement of Bloch lines is connected with the motion of domain walls which is induced by a local change in the distribution
of demagnetizing fields as a result of a heating-induced decrease of the magnetization in the focal spot of the laser radiation.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 398–402 (25 September 1997) 相似文献
994.
Changes in thin zinc-sulfide films under the action of the γ-radiation of Co60 are studied by investigating electroluminescence spectra of terbium embedded in these films as a luminescent probe. It is
shown that changes in the relation of the intensities of bands, a decrease in their halfwidth and the background component,
and simplification of the spectrum are observed in a short-wave region of the Tb radiation spectrum that corresponds to5D3→7Fj transitions. The same modification of the radiation spectrum is characteristic of ZnS films whose crystalline structure is
ordered in the course of thermal annealing at a temperature of 350°C. Based on the analysis of the data obtained it is inferred
that irradiating the ZnS films with small radiation doses of 104–105 rad leads to the ordering of their crystalline structure due to the elimination of one of the types of structural defects.
Institute of Physics of Semiconductors, National Academy of Sciences of Ukraine, 45, Nauka Ave., Kiev-28, 252650. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 338–341, May–June, 1997. 相似文献
995.
In spherically symmetric systems, in spite of Birkhoff's Theorem, the rates of clocks in vacuum regions on either side of moving mass shells must be continually readjusted to stay in synchrony. This shows up as time-dependence of the metric in terms of the globally meaningful time coordinate. 相似文献
996.
S. Ya. Kotkovskii 《JETP Letters》1997,65(10):768-772
The probability of inclusive semileptonic decay of B mesons is calculated in the constituent-quark model. A compact formula is obtained for the differential decay width of a
B meson in terms of the corresponding decay width of a free b quark and the wave function of the internal motion of the quarks in the B meson. Numerical values of semileptonic-decay widths are obtained for a series of models of the wave function.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 10, 734–737 (25 May 1997) 相似文献
997.
998.
N. P. Venediktov M. Yu. Glyavin V. E. Zapevalov A. N. Kuftin A. S. Postnikova M. V. Yulpatova 《Radiophysics and Quantum Electronics》1997,40(4):336-342
A scheme for automated study of current-voltage characteristics of gyroresonance devices is developed. The effective emission
spread at the cathodes of powerful gyrotrons is studied by analysis of current-voltage characteristics. Experimental data
on the effective emission spread parameter for different modes are given. The permissible emission spread at the cathodes
of powerful gyrotrons is estimated, and the dependence of the electron beam parameters on the cathode emission spread is presented.
A complex measurement technique showing the contribution of different physical mechanisms to the cathode emission spread is
proposed.
Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh
Zavedenii, Radiofizika, Vol. 40, No. 4, pp. 506–516, April, 1997. 相似文献
999.
Vincent S. Smentkowski John T. Yates Jr. Xiaojie Chen William A. Goddard III 《Surface science》1997,370(2-3):209-231
The radiation-induced decomposition of C4F9I and CF3I overlayers at 119 K on diamond (100) surfaces has been shown to be an efficient route to fluorination of the diamond surface. X-ray photoelectron spectroscopy has been used for photoactivation as well as for studying the photodecomposition of the fluoroalkyl iodide molecules, the attachment of the photofragments to the diamond surface, and the thermal decomposition of the fluoroalkyl ligands. Measured chemical shifts agree well with ab initio calculations of both C 1s and F 1s binding energies. It is found that chemisorbed CF3 groups on diamond (100) decompose by 300 K whereas C4F9 groups decompose over the range 300 to 700 K and this reactivity difference is rationalized on steric grounds. Both of these thermal decomposition processes produce surface C---F bonds on the diamond. The surface C---F species thermally decompose over a wide temperature range extending up to 1500 K. Hydrogen passivation of the diamond surface is ineffective in preventing free radical attack from the photodissociated products of the fluoroalkyl iodides; I atoms produced photolytically abstract H from surface C---H bonds to yield hydrogen iodide at 119 K allowing diamond fluorination. The attachment of chemisorbed F species to the diamond (100) surface causes band bending as the surface states are occupied as a result of chemisorption. This results in a shift to higher binding energy of the diamond-related C 1s levels present in the surface and subsurface regions which are sampled by XPS on the diamond. The use of photoactivation of fluoroalkyl iodides for the fluorination of diamond surfaces provides a convenient route compared to other methods involving the action of atomic F, molecular F2, XeF2 and F-containing plasmas. 相似文献
1000.
Processing-induced residual strains in solid cylinders of Nickel 200 were investigated using phase shifting moiré interferometry. Two different experimental approaches were used to study the strains produced during Tungsten-inert gas spot welding. A comparison of results for a ‘hot/fast’ and a ‘cool/slow’ weld demonstrate the capabilities of the general approach. Both experimental methods revealed distinct differences in the residual displacement and strain fields between the two types of welds. 相似文献