全文获取类型
收费全文 | 356685篇 |
免费 | 7171篇 |
国内免费 | 4931篇 |
专业分类
化学 | 172881篇 |
晶体学 | 5303篇 |
力学 | 20794篇 |
综合类 | 325篇 |
数学 | 50810篇 |
物理学 | 118674篇 |
出版年
2021年 | 4607篇 |
2020年 | 5140篇 |
2019年 | 5920篇 |
2018年 | 7910篇 |
2017年 | 7950篇 |
2016年 | 10040篇 |
2015年 | 5377篇 |
2014年 | 9264篇 |
2013年 | 15453篇 |
2012年 | 13756篇 |
2011年 | 15496篇 |
2010年 | 12762篇 |
2009年 | 12867篇 |
2008年 | 14344篇 |
2007年 | 13871篇 |
2006年 | 12519篇 |
2005年 | 10808篇 |
2004年 | 10263篇 |
2003年 | 9415篇 |
2002年 | 9740篇 |
2001年 | 9215篇 |
2000年 | 7293篇 |
1999年 | 5599篇 |
1998年 | 5281篇 |
1997年 | 4962篇 |
1996年 | 4568篇 |
1995年 | 4004篇 |
1994年 | 4099篇 |
1993年 | 4081篇 |
1992年 | 4002篇 |
1991年 | 4403篇 |
1990年 | 4386篇 |
1989年 | 4314篇 |
1988年 | 4031篇 |
1987年 | 4083篇 |
1986年 | 3747篇 |
1985年 | 4310篇 |
1984年 | 4516篇 |
1983年 | 3892篇 |
1982年 | 4058篇 |
1981年 | 3699篇 |
1980年 | 3456篇 |
1979年 | 3998篇 |
1978年 | 4075篇 |
1977年 | 4204篇 |
1976年 | 4362篇 |
1975年 | 4059篇 |
1974年 | 3963篇 |
1973年 | 4085篇 |
1972年 | 3544篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The European Physical Journal C - The CMS experiment&;nbsp;[1] uses a general purpose detector designed for detecting the diverse signatures associated with Higgs production and new physics... 相似文献
992.
V. B. Philippov N. Ya. Kirpichnikova A. S. Kirpichnikova 《Journal of Mathematical Sciences》2003,117(2):4028-4033
The problem on the diffraction of the electromagnetic plane wave on a small obstacle included in a layer is investigated. The obstacle is assumed to be an elliptic cylinder whose diameter and focal distance are small in comparison with the length of the incident wave. It is proved that the small obstacle radiates as a point source, and its amplitude is proportional to the area of the cross-section and the jumps of the dielectric and magnetic constants on the interfaces. Bibliography: 5 titles. 相似文献
993.
Pyroelectric effect in lead-magnoniobate-based solid solutions 总被引:1,自引:0,他引:1
E. P. Smirnova S. E. Aleksandrov K. A. Sotnikov A. A. Kapralov A. V. Sotnikov 《Physics of the Solid State》2003,45(7):1305-1309
A coordinated study of the dielectric, electrostriction, and pyroelectric properties of the lead-magnoniobate-based ceramic solid solutions 0.9PbMg1/3Nb2/3O3-0.1PbTiO3 and 0.55PbMg1/3Nb2/3O3-0.45PbSc1/2Nb1/2O3 conducted at the relaxor transition temperatures is reported. Electromechanical coupling stimulated by the giant electrostriction effect is shown to play an essential part in the pyroelectric effect. 相似文献
994.
The electrodynamic properties of coaxial two-dimensional Bragg resonators with two-dimensional distributed feedback are analyzed. These resonators are made of coaxial waveguide sections with doubly periodic corrugation, which provides coupling and mutual scattering of four partial waves. Two of them propagate along the waveguide, while the other two propagate in the transverse (azimuthal) direction. It is shown that the high azimuthal index selectivity of two-dimensional Bragg resonators may be related to a qualitative difference in topology of the dispersion characteristics of azimuth-symmetric and asymmetric normal waves propagating in infinite waveguides of such a geometry. For the finite-length systems used as two-dimensional Bragg resonators, the eigenmode spectrum is found for two types of boundary conditions that correspond to the limiting cases of perfectly matched (open) systems and, conversely, of systems closed for the extraction of transverse electromagnetic fluxes. Perimeter-to-length ratios of the resonator at which the Q factor of the fundamental azimuth-symmetric mode is greater than those of the other modes are determined. The applicability domain of the geometrical approach, which was earlier applied to two-dimensional Bragg resonators, is discussed. 相似文献
995.
Mathematical Notes - It is shown in this paper that ${h\left( r \right)}$ is a smoothly varying function of order ? if and only if the function $\rho \left( r \right) = \left( {\ln h\left(... 相似文献
996.
A direct central collision of two identical bodies of revolution is studied. A nonstationary mixed boundary-value problem with an unknown moving boundary is formulated. Its solution is represented by a series in term of Bessel functions. An infinite system of Volterra equations of the second kind for the unknown expansion coefficients is derived by satisfying the boundary conditions. The basic characteristics of the collision process are determined depending on the curvature of the frontal surface of the bodies 相似文献
997.
1,3-Diarylpropynones were cleanly converted to the corresponding 3-arylindenones in various superacidic media. This new, simple, one-pot reaction proved to be efficient (yields up to 95%) and very fast (reaction time less than 30 min). 相似文献
998.
The equilibrium conversion of nitriles in the reaction of cyanoalkylphosphonates with methanol in the presence of sodium methylate, as determined by potentiometric titration with perchloric acid in nitromethane, varies from 58 to 17.7%. The practical yields of imidates were evaluated by a preparative procedure of isolation of purified imidates from the reaction mixtures (56-14%). Because of the low conversions of nitriles, the reaction is expedient to use only for preparing alkyl (dialkoxyphosphoryl)acetimidates. 相似文献
999.
A simple method of determining ultra-trace Au in natural water was presented by using graphite furnace atomic absorption spectrophotometry (GFAAS) after in situ enrichment with thiol cotton fiber (TCF). The sample solution was adjusted to pH 1.5-2.0 with HCl, then the water sample was passed through a column packed with 0.10-0.20 g TCF and the flow rate was controlled at 20-40 ml min−1. The effects of interferences, such as complexing and oxidizing agents and other elements adsorbed on TCF were overcome by chemical treatments prior to the desorption of Au. The adsorbed Au was adsorbed with 2.0 ml hot acid, then it was extracted with 1.00 ml methyl isobutylketone (MIBK). For a 5 l water sample, the detection limit of Au is 0.02 ng l−1. The relative standard deviation (R.S.D.) for the determination of 1.44 ng l−1 Au was 9.4%.The method was applied to determine ultra-trace Au both in suspended phase and soluble phase in natural water, the concentrations of total Au in natural water samples range from 0.51 to 67.82 ng l−1. The recovery of added 0.50-6.00 ng l−1 Au was 80-95%. The method is useful in prospecting for Au deposits by means of hydrogeochemical methods. The enrichment is carried out in the field, and then the determination of Au is completed later in the laboratory. 相似文献
1000.
Faitel'son E. A. Korkhov V. P. Aniskevich A. N. Starkova O. A. 《Mechanics of Composite Materials》2004,40(1):57-66
The results of a complex study of structural changes in a cured Norpol 440 polyester resin under the action of damp environment and mechanical loading are presented. A considerable effect of absorbed moisture on the structure and some characteristics of the material is revealed by using thermophysical methods and X-ray diffractometry. The joint effect of moisture and mechanical stress is estimated by investigating the creep in stationary and nonstationary moisture conditions. The anisotropy of the material structure formed during creep is evaluated from the results of dilatometric measurements. It is found that the degree of anisotropy of the material after creep accompanied by moisture sorption is higher than that after creep in the conditions of moisture equilibrium with atmosphere. It is established that the aftercure and relaxation of the residual creep deformation come to an end at heating to 80-85°C. At a further rise in temperature and repeated heating, changes in the material structure are not observed. 相似文献