首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1480383篇
  免费   30497篇
  国内免费   8336篇
化学   758083篇
晶体学   21118篇
力学   78122篇
综合类   155篇
数学   253289篇
物理学   408449篇
  2021年   13784篇
  2020年   16182篇
  2019年   16360篇
  2018年   17145篇
  2017年   15802篇
  2016年   30249篇
  2015年   21569篇
  2014年   30996篇
  2013年   75336篇
  2012年   45805篇
  2011年   48976篇
  2010年   42341篇
  2009年   43478篇
  2008年   45751篇
  2007年   43267篇
  2006年   43916篇
  2005年   38948篇
  2004年   37843篇
  2003年   34135篇
  2002年   34257篇
  2001年   35158篇
  2000年   28874篇
  1999年   24535篇
  1998年   21929篇
  1997年   21784篇
  1996年   21585篇
  1995年   19566篇
  1994年   19071篇
  1993年   18629篇
  1992年   19429篇
  1991年   19527篇
  1990年   18718篇
  1989年   18710篇
  1988年   18262篇
  1987年   18181篇
  1986年   17207篇
  1985年   23517篇
  1984年   24455篇
  1983年   20456篇
  1982年   21980篇
  1981年   21176篇
  1980年   20547篇
  1979年   21075篇
  1978年   22113篇
  1977年   21826篇
  1976年   21594篇
  1975年   20302篇
  1974年   20014篇
  1973年   20386篇
  1972年   14867篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
973.
Alloys of the systems Fe–Al (mixable over the whole concentration range) and Fe–Mg (insoluble with each other) were produced by implantation of Fe ions into Al and Mg, respectively. The implantation energy was 200 keV and the ion doses ranged from 1 × 1014 to 9 × 1017cm-2The obtained implantation profiles were determined by Auger electron spectroscopy depth profiling. Maximum iron concentrations reached were up to 60 at.% for implantation into Al and 94 at.% for implantation into Mg. Phase analysis of the implanted layers was performed by conversion electron Mössbauer spectroscopy and X‐ray diffraction. For implantation into Mg, two different kinds of Mössbauer spectra were obtained: at low doses paramagnetic doublets indicating at least two different iron sites and at high doses a dominant ferromagnetic six‐line‐pattern with a small paramagnetic fraction. The X‐ray diffraction pattern concluded that in the latter case a dilated αiron lattice is formed. For implantation into Al, the Mössbauer spectra were doublet structures very similar to those obtained at amorphous Fe–Al alloys produced by rapid quenching methods. They also indicated at least two different main iron environments. For the highest implanted sample a ferromagnetic six‐line‐pattern with magnetic field values close to those of Fe3Al appeared.  相似文献   
974.
975.
We report on the first observation and studies of a weak delocalizing logarithmic temperature dependence of the conductivity, which causes the conductivity of the 2D metal to increase as T decreases down to 16 mK. The prefactor of the logarithmic dependence is found to decrease gradually with density, to vanish at a critical density n c , 2∼2×1012 cm−2, and then to have the opposite sign at n>n c ,2. The second critical density sets the upper limit on the existence region of the 2D metal, whereas the conductivity at the critical point, G c ,2∼120e 2/h, sets an upper (low-temperature) limit on its conductivity. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 497–501 (25 September 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.  相似文献   
976.
Some corollaries of the Hirzebruch-Thom signature theorem are discussed. The multiplicativity of the signature and the naturalness of the Pontryagin classes for coverings in the case of ℚ-homology manifolds is proved. A geometric proof of Hirzebruch’s well-known “functional equation” for the virtual signature is outlined. Bibliography: 25 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 231, 1995, pp. 197–209. Translated by N. Yu. Netsvetaev.  相似文献   
977.
New lower bounds for probabilities of large deviations of tests and estimators are proposed. These bounds cover the cases of moderate and Cramér-type large deviations. Bibliography: 12 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 216, 1994, pp. 52–61. Translated by the author.  相似文献   
978.
Summary. We generalise and apply a refinement indicator of the type originally designed by Mackenzie, Süli and Warnecke in [15] and [16] for linear Friedrichs systems to the Euler equations of inviscid, compressible fluid flow. The Euler equations are symmetrized by means of entropy variables and locally linearized about a constant state to obtain a symmetric hyperbolic system to which an a posteriori error analysis of the type introduced in [15] can be applied. We discuss the details of the implementation of the refinement indicator into the DLR--Code which is based on a finite volume method of box type on an unstructured grid and present numerical results. Received May 15, 1995 / Revised version received April 17, 1996  相似文献   
979.
980.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号