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   621862篇
  免费   5349篇
  国内免费   1669篇
化学   305812篇
晶体学   8436篇
力学   32631篇
综合类   17篇
数学   100993篇
物理学   180991篇
  2021年   5346篇
  2020年   5878篇
  2019年   6594篇
  2018年   18506篇
  2017年   18367篇
  2016年   18088篇
  2015年   7698篇
  2014年   11457篇
  2013年   25280篇
  2012年   23403篇
  2011年   32984篇
  2010年   22506篇
  2009年   22562篇
  2008年   28025篇
  2007年   29817篇
  2006年   20050篇
  2005年   18892篇
  2004年   17725篇
  2003年   16481篇
  2002年   15386篇
  2001年   15308篇
  2000年   11916篇
  1999年   9151篇
  1998年   7940篇
  1997年   7737篇
  1996年   7354篇
  1995年   6532篇
  1994年   6488篇
  1993年   6313篇
  1992年   6608篇
  1991年   7043篇
  1990年   6723篇
  1989年   6629篇
  1988年   6463篇
  1987年   6275篇
  1986年   6006篇
  1985年   7585篇
  1984年   7911篇
  1983年   6649篇
  1982年   6934篇
  1981年   6441篇
  1980年   6108篇
  1979年   6615篇
  1978年   6835篇
  1977年   6700篇
  1976年   6665篇
  1975年   6370篇
  1974年   6181篇
  1973年   6510篇
  1972年   4752篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
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   
52.
53.
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   
54.
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   
55.
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   
56.
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   
57.
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   
58.
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   
59.
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   
60.
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