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   234741篇
  免费   4659篇
  国内免费   4069篇
化学   134240篇
晶体学   3482篇
力学   9437篇
综合类   268篇
数学   25819篇
物理学   70223篇
  2021年   1984篇
  2020年   2253篇
  2019年   2437篇
  2018年   2962篇
  2017年   3056篇
  2016年   4271篇
  2015年   3116篇
  2014年   4400篇
  2013年   10029篇
  2012年   8951篇
  2011年   10735篇
  2010年   7674篇
  2009年   7396篇
  2008年   9845篇
  2007年   9870篇
  2006年   9236篇
  2005年   8465篇
  2004年   7491篇
  2003年   6562篇
  2002年   6454篇
  2001年   7116篇
  2000年   5398篇
  1999年   3935篇
  1998年   3230篇
  1997年   3140篇
  1996年   3140篇
  1995年   2736篇
  1994年   2826篇
  1993年   2661篇
  1992年   2889篇
  1991年   2953篇
  1990年   2767篇
  1989年   2641篇
  1988年   2594篇
  1987年   2515篇
  1986年   2548篇
  1985年   3323篇
  1984年   3376篇
  1983年   2819篇
  1982年   3052篇
  1981年   2816篇
  1980年   2612篇
  1979年   2795篇
  1978年   2997篇
  1977年   3033篇
  1976年   3060篇
  1975年   2794篇
  1974年   2907篇
  1973年   2959篇
  1972年   2318篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
21.
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   
22.
Blumberg  L. M. 《Chromatographia》1994,39(11-12):719-728
Chromatographia - Previously [11], the theoretical limit ofresolution in one class of chromatographic conditions was found and its proof was briefly outlined. Here, the theoretical limits...  相似文献   
23.
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   
24.
In this paper, an application of the Riquer-Thomas-Janet theory is described for the problem of transforming a system of partial differential equations into a passive form, i.e., to a special form which contains explicitly both the equations of the initial system and all their nontrivial differential consequences. This special representation of a system markedly facilitates the subsequent integration of the corresponding differential equations. In this paper, the modern approach to the indicated problem is presented. This is the approach adopted in the Knuth-Bendix procedure [13] for critical-pair/completion and then Buchberger's algorithm for completion of polynomial ideal bases [13] (or, alternatively, for the construction of Groebner bases for ideals in a differential operator ring [14]). The algorithm of reduction to the passive form for linear system of partial differential equations and its implementation in the algorithmic language REFAL, as well as the capabilities of the corresponding program, are outlined. Examples illustrating the power and efficiency of the system are presented.  相似文献   
25.
26.
The article surveys the main results of the statistical approach to the solution of ill-posed problems of mathematical physics, in application to specific ill-posed inverse problems in geophysics.Invited paper presented at the International Seminar on Mathematical Foundations of the Interpretation of Geophysical Fields, Moscow, May–June 1972.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 79, pp. 67–81, 1978.  相似文献   
27.
A masked lithium homoenolate, generated by tellurium/lithium exchange, was reacted with epoxides. The lithium compound was also converted into other organometallics such as Grignard, and cuprates and the reactivity of those organometallics with epoxides was evaluated. The same building block was employed in the synthesis of (+/−)-frontalin.  相似文献   
28.
A test for a function to be a solution of an elliptic PDE is given in terms of extensions, as solutions, from the boundaries inside the domains belonging to an isotopic family. It generalizes a result of Ehrenpreis for spheres moved along a straight line.

  相似文献   

29.
30.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 3, pp. 438–444, March, 1991.  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