全文获取类型
收费全文 | 605926篇 |
免费 | 6167篇 |
国内免费 | 1746篇 |
专业分类
化学 | 274831篇 |
晶体学 | 8397篇 |
力学 | 25333篇 |
综合类 | 16篇 |
数学 | 64844篇 |
物理学 | 167852篇 |
无线电 | 72566篇 |
出版年
2021年 | 4784篇 |
2020年 | 5292篇 |
2019年 | 5947篇 |
2018年 | 7965篇 |
2017年 | 8000篇 |
2016年 | 11375篇 |
2015年 | 6442篇 |
2014年 | 10905篇 |
2013年 | 25520篇 |
2012年 | 19253篇 |
2011年 | 23289篇 |
2010年 | 17384篇 |
2009年 | 18103篇 |
2008年 | 22863篇 |
2007年 | 23631篇 |
2006年 | 22021篇 |
2005年 | 19701篇 |
2004年 | 18248篇 |
2003年 | 16545篇 |
2002年 | 16389篇 |
2001年 | 18265篇 |
2000年 | 14558篇 |
1999年 | 11632篇 |
1998年 | 10295篇 |
1997年 | 10130篇 |
1996年 | 9397篇 |
1995年 | 8527篇 |
1994年 | 8548篇 |
1993年 | 8149篇 |
1992年 | 8870篇 |
1991年 | 8972篇 |
1990年 | 8601篇 |
1989年 | 8196篇 |
1988年 | 7909篇 |
1987年 | 7429篇 |
1986年 | 7006篇 |
1985年 | 8897篇 |
1984年 | 9176篇 |
1983年 | 7682篇 |
1982年 | 7745篇 |
1981年 | 7413篇 |
1980年 | 7281篇 |
1979年 | 7451篇 |
1978年 | 7783篇 |
1977年 | 7640篇 |
1976年 | 7641篇 |
1975年 | 7096篇 |
1974年 | 7137篇 |
1973年 | 7330篇 |
1972年 | 5235篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
We prove that a random change of variable in general improves convergence properties of the Fourier expansions, and we give
a precise quantitative estimate of the phenomenon.
Submitted: December 1997, final version: May 1998 相似文献
992.
993.
Mass distributions of fragments in the low-energy fission of nuclei from 187Ir to 213At have been analysed. This analysis has shown that shell effects in symmetric-mode fragment mass yields from the fission of pre-actinide nuclei could be described if one assumes the existence of two strongly deformed neutron shells in the arising fragments with neutron numbers N1 ≈ 52 and N2 ≈ 68. A new method has been proposed for quantitatively describing the mass distributions of the symmetric fission mode for pre-actinides with A ≈ 180–220. 相似文献
994.
We show that an electron confined to a single finite parabolic quantum well in crossed electric and magnetic fields can behave as a double quantum well system. The magnetic field is parallel to the heterostructure layers and the electric field is perpendicular to those. For a suitable choice of both fields and quantum well width, the electron can be confined to a double quantum well effective potential that is very similar to the electronic potential model for diatomic molecules. The double quantum well spectrum is calculated using a numerical algorithm based on semiclassical methods. A physical interpretation of this quantum system is given based on the analogy to the electrons bound to diatomic molecules. 相似文献
995.
Space time-index plots for probing dynamical nonstationarity 总被引:3,自引:0,他引:3
We propose a simple method to efficiently probe dynamical nonstationarity in observed time series. In a space time-index plot, the density distributions as a function of normalized time-index are V-shaped due to nonstationarity. We show that this method is workable for short data sets and typical examples are illustrated. 相似文献
996.
We show that, contrary to earlier reports, application of the one-parameter variational technique to the classical (image) model for H in front of an Al surface leads to energy shifts for the ground state which are very close to those obtained numerically with a more sophisticated model of the system. 相似文献
997.
998.
999.
1000.
We review data on methods for synthesis, chemical and pharmacological properties of pyrido[1,2-a)pyrimidines.Scientific-Research Institute of Pharmacology of the Russian Academy of Medical Sciences, All-Union Science Center for Biologically Active Substances, Staraya Kupavna, 124432. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 579–596, May, 1994. Original article submitted March 3, 1994. 相似文献