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   2991篇
  免费   94篇
  国内免费   14篇
化学   2402篇
晶体学   28篇
力学   30篇
数学   205篇
物理学   434篇
  2023年   18篇
  2022年   16篇
  2021年   22篇
  2020年   42篇
  2019年   42篇
  2018年   29篇
  2017年   25篇
  2016年   59篇
  2015年   58篇
  2014年   93篇
  2013年   189篇
  2012年   151篇
  2011年   181篇
  2010年   125篇
  2009年   108篇
  2008年   185篇
  2007年   167篇
  2006年   188篇
  2005年   189篇
  2004年   172篇
  2003年   140篇
  2002年   149篇
  2001年   47篇
  2000年   43篇
  1999年   26篇
  1998年   38篇
  1997年   30篇
  1996年   27篇
  1995年   17篇
  1994年   30篇
  1993年   17篇
  1992年   25篇
  1991年   16篇
  1989年   11篇
  1988年   16篇
  1986年   14篇
  1985年   34篇
  1984年   47篇
  1983年   27篇
  1982年   40篇
  1981年   44篇
  1980年   27篇
  1979年   26篇
  1978年   17篇
  1977年   22篇
  1976年   19篇
  1975年   17篇
  1974年   17篇
  1973年   14篇
  1972年   9篇
排序方式: 共有3099条查询结果,搜索用时 15 毫秒
61.
62.
Numerical Algorithms - In this paper, we propose an infeasible arc-search interior-point algorithm for solving nonlinear programming problems. Most algorithms based on interior-point methods are...  相似文献   
63.
64.
A bioassay-directed fractionation of the cytotoxic constituents of the Japanese sea hare Dolabella auricularia resulted in the isolation of two 35-membered depsipeptides dolastatin G (1) and nordolastatin G (2), which showed cytotoxicity against HeLa S(3) cells with IC(50) values of 1.0 and 5.3 &mgr;g/mL, respectively. The gross structures of these substances were established by spectroscopic analysis including 2D NMR techniques. The absolute stereostructure of 1 was determined by chiral HPLC analysis of amino acid components obtained from acid hydrolysis of 1 and by the enantioselective syntheses of two degradation products arising from polyketide portions. Nordolastatin G (2) is a congener that has the same absolute stereochemistry as that of 1.  相似文献   
65.
66.
In the presence of palladium complexes as catalysts, fluorinated disilanes add to 1,3-dienes, metehyl vinyl ketone and p-benzoquinone to give mainly 1,4-addition products.  相似文献   
67.
Polyoxime-urethanes have been synthesized from dioximes and diisocyanates, and their structures have been ascertained by elemental analysis and infrared spectroscopy. They can be represented by the general formula: These polymer films were photolyzed by using a high-pressure 100-W mercury lamp, and the rate of decomposition of the N? O bond was determined by use of ultraviolet and infrared spectra, or comparing the photochemical behavior with that of corresponding model compounds. Upon irradiating these polymers in the presence or absence of sensitizers or a hydrogen donor, there were obtained photolyzed polymers of low molecular weight, of which the molecular weights were estimated by observing the viscosity changes. To deduce the mechanism of photodegradation of polyoxime-urethane, photolysis of benzophenone oxime-phenyl urethane was investigated as a model compound.  相似文献   
68.
Reductive S-monoacylation of lipoamide with some carboxylic acids and tri-n-butylphosphine was carried out in acetonitrile to obtain the corresponding S-monoacylated compounds in excellent yield. This method was applied to the preparation of S-monoacylated dihydrolipoyl polymer with a neighboring thiol group. The acyl transfer from the polymer to cyclohexylamine was enhanced as much as 64 times by adding silver perchlorate.  相似文献   
69.
The proposed structures of patellamides B and C, cytotoxic lipophilic cyclic peptides from a marine tunicate, have been revised on the basis of the spectral data of their partial hydrolysates, and their revised structures have been synthetically confirmed by the use of diphenyl phosphorazidate(DPPA) and diethyl phosphorocyanidate(DEPC).  相似文献   
70.
A novel [2.2]metacyclophane in which two benzene rings are linked together with a carbon-carbon double bond and a disilane unit was prepared. Photolysis of the cyclophane in the presence of oxygen afforded the 4,5-dihydro-4,5-disilapyrene derivative via a transannular dehydrogenation reaction.  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