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   588342篇
  免费   4229篇
  国内免费   1310篇
化学   287232篇
晶体学   8315篇
力学   30856篇
综合类   17篇
数学   85539篇
物理学   181922篇
  2021年   5055篇
  2020年   5502篇
  2019年   6255篇
  2018年   13056篇
  2017年   13455篇
  2016年   13947篇
  2015年   6627篇
  2014年   10572篇
  2013年   23688篇
  2012年   21014篇
  2011年   29271篇
  2010年   20644篇
  2009年   20659篇
  2008年   26935篇
  2007年   29022篇
  2006年   18875篇
  2005年   20187篇
  2004年   17307篇
  2003年   16184篇
  2002年   14904篇
  2001年   14881篇
  2000年   11634篇
  1999年   8810篇
  1998年   7649篇
  1997年   7515篇
  1996年   7134篇
  1995年   6406篇
  1994年   6397篇
  1993年   6156篇
  1992年   6505篇
  1991年   6975篇
  1990年   6683篇
  1989年   6609篇
  1988年   6450篇
  1987年   6257篇
  1986年   5988篇
  1985年   7546篇
  1984年   7926篇
  1983年   6655篇
  1982年   6953篇
  1981年   6465篇
  1980年   6135篇
  1979年   6646篇
  1978年   6887篇
  1977年   6697篇
  1976年   6687篇
  1975年   6369篇
  1974年   6205篇
  1973年   6555篇
  1972年   4757篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
The phsicochemical indices and the fatty-acid and triacylglycerol compositions of cottonseed and palm oils, of cottonseed oil hydrogenate, and of compositions based on them have been determined with the aid of IR and UV spectroscopies, GLC analysis, and chemical transformations. The compositions and amounts of the main classes of lipids in the initial oils and the hydrogenate have been studied. It has been found that in the process of hydrogenation the amount of oxygenated components falls. The work was conducted with the financial support of the Uzbek Fund for Fundamental Investigations.  相似文献   
53.
Institute of Botany, Academy of Sciences of the Republic of Azerbaidzhan, Baku. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 291–292, March–April, 1994.  相似文献   
54.
55.
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   
56.
The synthesis of benzazepine analogues of the opium alkaloid noscapine ( 1 ) is described. The benzazepines 2 and 3 were prepared starting from nornarceine ethyl ester ( 4 ; readily available from 1 ) in several steps. X-Ray analysis of compound 2 revealed that it is not a diastereosisomer mixture but a racemate of the threo-form and thus has the same configuration as 1 .  相似文献   
57.
The applicability of differential electrolytic potentiometry as a detection system in flow injection analysis is investigated. A computer-controlled injector which delivers precise volumes of sample solutions in a reproducible manner was developed. Conditions such as current density employed, the concentrations of the solutions used and the flow rate were optimized. Chloride in water was determined by means of this system. The relation between chloride concentration and the measured signal was found to be Nernstian for solutions of concentrations above 6 μg ml−1 chloride. For solutions below this concentration, the relation is linear.  相似文献   
58.
An estimate of the factors which influence the rate of growth of filamentary silicon crystals in a standard chloride system using a quartz reactor with hot walls is given. It is shown that a diffusion form of crystallization is observed under the conditions investigated.Voronezh State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 22–26, October, 1995.  相似文献   
59.
The characterization of the clusters formed on alkaline hydrolysis of [PdCl4]2– was performed using17O,23Na,35Cl,133Cs NMR and UV spectroscopy. The chemical composition of the clusters was found to be [Pd(OH)2] n ·nNaCl. No mononuclear oxo- or hydroxocomplexes were detected. The spatial structure of the clusters is stabilized by alkali metal cations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 675–679, April, 1993.  相似文献   
60.
Oxidation of the title compounds yields, besides the reported isoimides 3 and/or the amides 4 , also the imides 5 . The observed product dichotomy is considered as the result of an intramolecular nucleophilic attack on the aroyl group, of the pressumed zwitterionic intermediate 2 , by O or N present in the ambident N-aroylimine site of 2 . The results of AM1 calculations agree with the product studies and both permit the formulation of a set of rules correlating structure and selectivity.  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