全文获取类型
收费全文 | 233130篇 |
免费 | 1996篇 |
国内免费 | 803篇 |
专业分类
化学 | 116875篇 |
晶体学 | 3997篇 |
力学 | 10757篇 |
综合类 | 1篇 |
数学 | 25540篇 |
物理学 | 78759篇 |
出版年
2020年 | 1794篇 |
2019年 | 2045篇 |
2018年 | 2719篇 |
2017年 | 2653篇 |
2016年 | 3913篇 |
2015年 | 2391篇 |
2014年 | 3970篇 |
2013年 | 10082篇 |
2012年 | 7529篇 |
2011年 | 9396篇 |
2010年 | 6687篇 |
2009年 | 6631篇 |
2008年 | 8707篇 |
2007年 | 8738篇 |
2006年 | 8278篇 |
2005年 | 7501篇 |
2004年 | 6923篇 |
2003年 | 6118篇 |
2002年 | 6065篇 |
2001年 | 7094篇 |
2000年 | 5375篇 |
1999年 | 4236篇 |
1998年 | 3564篇 |
1997年 | 3473篇 |
1996年 | 3294篇 |
1995年 | 3009篇 |
1994年 | 2951篇 |
1993年 | 3043篇 |
1992年 | 3153篇 |
1991年 | 3333篇 |
1990年 | 3085篇 |
1989年 | 3027篇 |
1988年 | 3066篇 |
1987年 | 2956篇 |
1986年 | 2805篇 |
1985年 | 3809篇 |
1984年 | 4005篇 |
1983年 | 3198篇 |
1982年 | 3413篇 |
1981年 | 3337篇 |
1980年 | 3234篇 |
1979年 | 3335篇 |
1978年 | 3422篇 |
1977年 | 3353篇 |
1976年 | 3449篇 |
1975年 | 3143篇 |
1974年 | 3151篇 |
1973年 | 3195篇 |
1972年 | 2235篇 |
1971年 | 1849篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
973.
B. D. Symeopoulos P. G. Koutsoukos 《Journal of Radioanalytical and Nuclear Chemistry》1993,173(1):23-36
The formation of barium sulfate in aqueous media causes problems of insoluble scale formation. On the other hand, the coprecipitation of uranium and transuranium elements with barium sulfate has been suggested for the determination of these elements in environmental monitoring processes. Therefore, the study of barium sulfate crystal growth is required. The investigations done so far suffer from the low sensitivity of the analytical methods used. In the present work we have overcome this problem by using131Ba for the preparation of supersaturated solutions. Thus kinetics parameters such as induction time and precipitation rates were measured. The polynuclear mechanism was found to be operative at high and the spiral growth at low supersaturations. 相似文献
974.
975.
A. I. Golovashkin N. V. Anshukova L. I. Ivanova O. T. Maljuchkov A. P. Rusakov 《Czechoslovak Journal of Physics》1996,46(3):1191-1192
On the basis of new experimental studies of specific heat, magnetic properties and thermal expansion, it was shown that dielectric-metal phase transitions were the consequence of delocalization of the heavy holes located on metalapical oxygen bonds in the high-Tc oxide systems. The ordered arrays of such holes (CDW) results in the dielectric gaps in electron spectrum and anomalous negative thermal expansion. The free carriers introduced by doping can couple through excitations of these localized holes, (local bosons). The high-Tc superconductivity will possess anomalous Hc2(T) dependence and γ-type specific heat jump at Tc. This local bosons model is the basis for explanation of the obtained experimental data. 相似文献
976.
Triorganotin(IV) and triorganolead(IV) derivatives of the types Me3Sn(SCZ) and Ph3Pb(SCZ) (where SCZ? is the anion of a semicarbanzone ligand) have been synthesized by substitution reactions of trimethyltin chloride and triphenyl-lead chloride with semicarbazones derived from heterocyclic ketones. The resulting complexes have been characterized by elemental analyses, molecualr weight determinations and conductivity measurements. The mode of bonding has been established on the basis of infrared and 1H, 13C and 119Sn NMR spectroscopic studies. Some respresentative complexes have also been evaluated for their antimicrobial effects on different species of pathogenic fungi and bacteria; the results of these investigations have been reported in the present paper. 相似文献
977.
We describe the dynamics of phase separation and transition processes, in binary mesomorphic mixtures with the help of a system of two coupled partial derivative equations. We emphasize, both analytically and numerically, that, depending on the regions of the phase diagram, the dynamical behaviour may result either from a two step process (first the phase transition, then the phase separation) or from a process showing salient features of the Cahn-Hilliard spinodal decomposition (bicontinuous periodic networks in the transient stages). The dynamics of evolution of the domain patterns are illustrated with the help of numerical simulations in which homeotropic and planar anchorages are visualized. 相似文献
978.
979.
980.
We introduce a new class of experiments which provide graphic insights into the propagation of acoustic waves in anisotropic media. Simply stated, we have devised a means of observing the expanding acoustic wavefront from a point disturbance in a solid. The data may be viewed as a movie or a series of snapshots. The observed wavefronts represent the group-velocity surfaces of acoustic waves, which reflect the basic elastic anisotropy of the solid. The technique has been applied to coherent acoustic waves with frequencies in the megahertz range (at ambient temperatures) and to incoherent heat pulses in the hundred-gigahertz range (at liquid-helium temperatures). In this article, we first provide a pedagogical introduction to wave propagation in elastically anisotropic media, reviewing some early methods for visualizing acoustic waves. Next, we describe the “acoustic wavefront imaging” method and give representative results in crystals and composite materials. Finally, we show how this method relates to recent advances in phonon imaging and internal diffraction of ultrasound. 相似文献