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   2243篇
  免费   126篇
  国内免费   7篇
化学   1839篇
晶体学   15篇
力学   30篇
数学   288篇
物理学   204篇
  2023年   31篇
  2022年   50篇
  2021年   84篇
  2020年   94篇
  2019年   68篇
  2018年   35篇
  2017年   43篇
  2016年   85篇
  2015年   93篇
  2014年   89篇
  2013年   123篇
  2012年   163篇
  2011年   202篇
  2010年   116篇
  2009年   92篇
  2008年   147篇
  2007年   120篇
  2006年   107篇
  2005年   86篇
  2004年   83篇
  2003年   56篇
  2002年   40篇
  2001年   19篇
  2000年   12篇
  1999年   13篇
  1998年   13篇
  1997年   9篇
  1996年   15篇
  1995年   7篇
  1994年   12篇
  1993年   15篇
  1992年   10篇
  1991年   11篇
  1990年   8篇
  1988年   12篇
  1987年   8篇
  1986年   10篇
  1985年   22篇
  1984年   21篇
  1983年   6篇
  1982年   28篇
  1981年   18篇
  1980年   15篇
  1979年   11篇
  1978年   7篇
  1977年   6篇
  1976年   14篇
  1975年   5篇
  1974年   5篇
  1973年   9篇
排序方式: 共有2376条查询结果,搜索用时 671 毫秒
971.
It is proved that the integral is additive on simple summable functions of a generalized measure space.  相似文献   
972.
973.
The crystal and molecular structures of [Mn(mep)2- (NCS)2] ({ {mep}}=4-methoxy-2-(5-methoxy-3-methyl-1H-pyrazol-1-yl)-6-methylpyrimidine) have been determined by X-ray crystallography. The crystal structure of the title compound is built up of isolated [Mn(mep)2(NCS)2] molecules with the stereochemistry of a distorted octahedron for the MnN6 chromophore. The e.p.r. (Q-band) data are in agreement with the structural data.  相似文献   
974.
Identified π±,K ±, p and -p transverse momentum spectra at mid-rapidity in √sNN = 130 GeV Au-Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleonsN part similarly for all particle species. The multiplicity densities scale faster thanN part. TheK ± andp ±yields per participant increase faster than the π± yields. We combine the PHENIX neutral and charged pion measurement and find that in central collisions forp T >-2 GeV/c,-p andp yields are comparable to or even exceed the pion yields.  相似文献   
975.
976.
A general continuous review production planning problem with stochastic demand is considered. Conditions under which the stochastic problem may be correctly solved using an equivalent deterministic problem are developed. This deterministic problem is known to have the same solution as the stochastic problem. Moreover, conditions are established under which the deterministic equivalent problem differs from a commonly used deterministic approximation to the problem only in the interest rate used in discounting. Thus, solving the stochastic problem is no more difficult than solving a commonly used approximation of the problem.  相似文献   
977.
The factors governing the competitiun between 1,2-and 1,3-eliminations have been studied and the results obtained have been applied to a biomimetic synthesis of chrysanthemol.  相似文献   
978.
979.
980.
A facile two-step stereospecific synthesis of the protein farnesyltransferase inhibitor chaetomellic acid A (1) and its analogues was developed. Addition of organocuprates derived from Grignard reagents (e.g. tetradecylmagnesium chloride and CuBr.Me(2)S) to dimethyl acetylenedicarboxylate (DMAD) in tetrahydrofuran containing hexamethylphosphoramide was followed by capture of the resulting copper enolates with a variety of electrophiles (e.g. methyl iodide) to give dimethyl cis-butenedioate derivatives 4-11. Hydrolysis with lithium hydroxide generated the corresponding lithium carboxylates, which readily closed to 2,3-disubstituted maleic anhydrides 17-20 upon acid treatment. Compound 16, an analogue wherein the tetradecyl group of 1 is replaced by a farnesyl moiety, is 7-fold more potent than 1 as an inhibitor of protein farnesyltransferase from yeast and displays a 100:1 selectivity for this enzyme relative to yeast protein geranylgeranyltransferase. In contrast, analogue 15, which contains a geranylgeranyl side chain, shows ca. 10:1 selectivity for the latter enzyme.  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