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   672069篇
  免费   5652篇
  国内免费   1962篇
化学   340672篇
晶体学   10035篇
力学   33418篇
综合类   18篇
数学   87776篇
物理学   207764篇
  2021年   5848篇
  2020年   6409篇
  2019年   7287篇
  2018年   9709篇
  2017年   9753篇
  2016年   13620篇
  2015年   7639篇
  2014年   12704篇
  2013年   30029篇
  2012年   22919篇
  2011年   27519篇
  2010年   20260篇
  2009年   20207篇
  2008年   25721篇
  2007年   25655篇
  2006年   23545篇
  2005年   21132篇
  2004年   19597篇
  2003年   17566篇
  2002年   17485篇
  2001年   18862篇
  2000年   14587篇
  1999年   11426篇
  1998年   9808篇
  1997年   9591篇
  1996年   9058篇
  1995年   8213篇
  1994年   8178篇
  1993年   7987篇
  1992年   8465篇
  1991年   8934篇
  1990年   8516篇
  1989年   8383篇
  1988年   8260篇
  1987年   8023篇
  1986年   7614篇
  1985年   9941篇
  1984年   10397篇
  1983年   8613篇
  1982年   9012篇
  1981年   8601篇
  1980年   8211篇
  1979年   8731篇
  1978年   8989篇
  1977年   8868篇
  1976年   8849篇
  1975年   8366篇
  1974年   8254篇
  1973年   8556篇
  1972年   6204篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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   
62.
Addition of functionalized zinc-copper reagents to the title complexes proceeds in a highly diastereoselective fashion to afford dienol complexes. The relative configurations of adducts 3d were determined by single X-ray diffraction analysis.  相似文献   
63.
Skarping  G.  Dalene  M.  Brunmark  P. 《Chromatographia》1994,39(9-10):619-623
Chromatographia - An LC-MS method is described for the determination of 4,4′-MDA (4,4′-methylene dianiline) in hydrolysed urine as a biomarker for exposure to 4,4′-MDI...  相似文献   
64.
Alumaa  P.  Pentšuk  J. 《Chromatographia》1994,38(9-10):566-570
Chromatographia - A theoretical model is used to predict retention times of divalent metal cations in single-column ion chromatography using one or more ligands in the eluent. Stability constants...  相似文献   
65.
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   
66.
A set of exact conditions is compiled for the purpose of developing and testing approximations for the exchange-correlation energy as a functional of the electron density. Special emphasis is placed upon recently developed density-scaling relationships. Commonly used generalized gradient approximations are compared against several of these conditions. A direct tabular comparison of these functionals (not of calculated properties) with one another is also made. © 1994 John Wiley & Sons, Inc.  相似文献   
67.
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   
68.
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   
69.
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   
70.
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