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   168156篇
  免费   1936篇
  国内免费   419篇
化学   94125篇
晶体学   2548篇
力学   6420篇
综合类   3篇
数学   17264篇
物理学   50151篇
  2021年   1245篇
  2020年   1501篇
  2019年   1556篇
  2018年   2084篇
  2017年   2079篇
  2016年   3308篇
  2015年   2162篇
  2014年   2988篇
  2013年   7399篇
  2012年   6173篇
  2011年   7255篇
  2010年   4959篇
  2009年   4944篇
  2008年   6875篇
  2007年   6693篇
  2006年   6439篇
  2005年   5911篇
  2004年   5344篇
  2003年   4805篇
  2002年   4631篇
  2001年   5999篇
  2000年   4384篇
  1999年   3397篇
  1998年   2339篇
  1997年   2422篇
  1996年   2369篇
  1995年   2115篇
  1994年   2150篇
  1993年   1923篇
  1992年   2402篇
  1991年   2474篇
  1990年   2303篇
  1989年   2254篇
  1988年   2222篇
  1987年   2227篇
  1986年   2051篇
  1985年   2576篇
  1984年   2591篇
  1983年   2032篇
  1982年   2037篇
  1981年   1886篇
  1980年   1874篇
  1979年   2120篇
  1978年   2187篇
  1977年   2151篇
  1976年   2055篇
  1975年   1939篇
  1974年   1895篇
  1973年   1939篇
  1972年   1273篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
It has been shown by the ESR of spin probes that thionin initially interacts with with negatively charged membranes electrostatically and then passes into the membranes to a depth comparable with the length of the hydrophobic sections of the protein loops.Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Brigham Young University, Provo, Utah, USA. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 594–597, July–August, 1993.  相似文献   
42.
43.
New analytical formulas for the torsionL-tensor are reported, which are used in molecular normal mode analysis calculations for the nonlinear transformation of the force constants from internal coordinates to normal coordinates. The proposed formalism exhibits a relative simplicity as compared to previous reported results. Sample calculations for methanol and hydrazine are presented.  相似文献   
44.
Surface relief formation at holographic recording on amorphous selenium films was demonstrated and investigated. The presence of this optical phase modulation component is essential for ensuring significant, stable and erasable optical recording in a-Se films at 290–320 K temperatures, where conventional photodarkening was known as insignificant and unstable. Photocrystallization can only be observed in super-exposed a-Se films at the given experimental conditions of hologram recording. Erasing behavior of surface relief gratings under heat treatment was also investigated in order to reveal further details of the mechanism. Photoinduced structural transformations within the amorphous phase, connected to local ordering under the condition of light-induced fluidity, are proposed as an explanation for the relief formation and erasing. The observed reversible optical recording process may be useful for the various optoelectronic applications of photoconductive a-Se layers. Received: 12 June 2000 / Accepted: 6 June 2001 / Published online: 30 August 2001  相似文献   
45.
46.
47.
Summary The main purpose of this paper is to introduce the concepts of η-sets, ηζ-sets,η-continuity and ηζ-continuity and to obtain a decomposition of continuity.  相似文献   
48.
The paper mentioned above is a contribution of the authors to Volume 18 (2002) of this journal, see . Recently, J. Domsta pointed out to us that the proof of Theorem 4.2 in that paper contains an error. The purpose of this addendum is to present a correct argument for it.  相似文献   
49.
Electrochemical separation of lead-silver alloys into the constituents by thin-layer electrolysis in molten electrolytes, with bismuth as metal separator, is studied. It is proposed to determine the extent of component recovery by potentiometry.  相似文献   
50.
Data Envelopment Analysis (DEA) offers a piece-wise linear approximation of the production frontier. The approximation tends to be poor if the true frontier is not concave, eg in case of economies of scale or of specialisation. To improve the flexibility of the DEA frontier and to gain in empirical fit, we propose to extend DEA towards a more general piece-wise quadratic approximation, called Quadratic Data Envelopment Analysis (QDEA). We show that QDEA gives statistically consistent estimates for all production frontiers with bounded Hessian eigenvalues. Our Monte-Carlo simulations suggest that QDEA can substantially improve efficiency estimation in finite samples relative to standard DEA models.  相似文献   
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