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   390557篇
  免费   4936篇
  国内免费   1789篇
化学   211295篇
晶体学   5878篇
力学   15756篇
综合类   64篇
数学   47282篇
物理学   117007篇
  2020年   3315篇
  2019年   3457篇
  2018年   4485篇
  2017年   4577篇
  2016年   7093篇
  2015年   4703篇
  2014年   6950篇
  2013年   17074篇
  2012年   13542篇
  2011年   16445篇
  2010年   11480篇
  2009年   11195篇
  2008年   15554篇
  2007年   15501篇
  2006年   14550篇
  2005年   13149篇
  2004年   11799篇
  2003年   10415篇
  2002年   10258篇
  2001年   11312篇
  2000年   8629篇
  1999年   6435篇
  1998年   5413篇
  1997年   5297篇
  1996年   5254篇
  1995年   4705篇
  1994年   4783篇
  1993年   4663篇
  1992年   5079篇
  1991年   5010篇
  1990年   4812篇
  1989年   4637篇
  1988年   4578篇
  1987年   4505篇
  1986年   4369篇
  1985年   5820篇
  1984年   5935篇
  1983年   5103篇
  1982年   5419篇
  1981年   5076篇
  1980年   4831篇
  1979年   5110篇
  1978年   5345篇
  1977年   5313篇
  1976年   5327篇
  1975年   4966篇
  1974年   5063篇
  1973年   5271篇
  1972年   3795篇
  1971年   3064篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Selective monoaddition of carbonodithioate anions to divinyl sulfoxide gives rise to O-alkyl S-[2-(vinylsulfinyl)ethyl] carbonodithioates [ROC(S)SK, R = Et, Bu; 42–50°C, 6 h, NaHCO3, aqueous benzene].  相似文献   
992.
Copolymers of 1-vinyl-1,2,4-triazole and 5-vinyltetrazole with 1,1,5-trihydrooctafluoropentyl methacrylate and 1,1,7-trihydrododecafluoroheptyl methacrylate were prepared under the conditions of radical initiation. These copolymers were used for modification of the surface of a glassy carbon electrode, and the effect of the modification on the electrochemical behavior of the electrode in anodic oxidation of dopamine and NO was studied. The possibility of enhancing the selectivity of the electrochemical sensor for monitoring NO in biological media was demonstrated.  相似文献   
993.
Hybrid organoinorganic composites insoluble in water and organic solvents were prepared by the hydrolysis of tetraethoxysilane in the presence of poly-1-vinylpyrazole, poly-1-vinylimidazole, and poly-4-vinylpyridine. The composition of the composites was determined by the nature of the polymeric nitrogen base and hydrolysis conditions. The composites synthesized showed high sorption activity in the extraction of the [PdCl4]2?, [PtCl6]2?, and [AuCl4]? ions from hydrochloric acid solutions.  相似文献   
994.
The influence exerted by addition of -hydroxynaphthoic acid and combined additive Hg + Pb + -hydroxynaphthoic acid on the corrosion and self-discharge of a porous zinc electrode in alkali solution was studied.  相似文献   
995.
Our recently developed in-cell NMR procedure now enables one to observe protein conformations inside living cells. Optimization of the technique demonstrates that distinguishing the signals produced by a single protein species depends critically on protein overexpression levels and the correlation time in the cytoplasm. Less relevant is the selective incorporation of (15)N. Poorly expressed proteins, insoluble proteins, and proteins that cannot tumble freely due to associations within the cell cannot yet be observed. We show in-cell NMR spectra of bacterial NmerA and human calmodulin and discuss limitations of the technique as well as prospects for future applications.  相似文献   
996.
The comparison of thermal and calorimetric properties of metal derivatives of 6-aminopicolinic acid (APH) is presented. The salts and complexes of APH with Cr(III), Cd(II), Cu(II), Ni(II), Pb(II), Co(II)and Ag(I) have been studied by TG-DTA and DSC methods up to 1200°C in a nitrogen atmosphere. Decomposition processes are proposed. The decarboxylation, deamination and carbonation of the organic fragments of molecules take place. The compounds decompose to metal or to metal oxides. The values of the transition enthalpy were determinated. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
997.
This review summarizes recent developments in the field of enantioseparations in capillary electromigration techniques using nonaqueous background electrolytes. The more established and rather intensively reviewed field of nonaqueous chiral capillary electrophoresis (NAQ-CE) is covered in less detail whereas more attention is paid to the relatively new field of nonaqueous capillary electrochromatography (NAQ-CEC).  相似文献   
998.
The influence exerted by the particle size and the distribution of sol impurities in the initial graphite, and also by pyrite additives, on the properties of residual graphite hydrosulfates synthesized by oxidation in the CrO3-H2SO4 system was studied.  相似文献   
999.
1000.
The composition and structure of films formed in etching of nickel in a Ni(NO3)2 solution in the presence of Cl- and NO2 - ions was studied.  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