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   2096篇
  免费   150篇
  国内免费   6篇
化学   1551篇
晶体学   7篇
力学   43篇
数学   300篇
物理学   351篇
  2024年   2篇
  2023年   35篇
  2022年   50篇
  2021年   67篇
  2020年   120篇
  2019年   98篇
  2018年   40篇
  2017年   40篇
  2016年   150篇
  2015年   112篇
  2014年   103篇
  2013年   123篇
  2012年   151篇
  2011年   198篇
  2010年   109篇
  2009年   78篇
  2008年   138篇
  2007年   127篇
  2006年   100篇
  2005年   107篇
  2004年   76篇
  2003年   51篇
  2002年   47篇
  2001年   12篇
  2000年   19篇
  1999年   12篇
  1998年   10篇
  1997年   5篇
  1996年   9篇
  1995年   7篇
  1994年   9篇
  1993年   4篇
  1992年   4篇
  1991年   7篇
  1989年   2篇
  1987年   4篇
  1986年   7篇
  1985年   2篇
  1984年   2篇
  1983年   1篇
  1982年   3篇
  1979年   1篇
  1978年   3篇
  1976年   3篇
  1975年   2篇
  1974年   1篇
  1967年   1篇
排序方式: 共有2252条查询结果,搜索用时 15 毫秒
101.
Bridged and unbridged N-heterocyclic carbene (NHC) ligands are metalated with [Ir/Rh(COD)2Cl]2 to give rhodium(I/III) and iridium(I) mono- and biscarbene substituted complexes. All complexes were characterized by spectroscopy, in addition [Ir(COD)(NHC)2][Cl,I] [COD = 1,5-cyclooctadiene, NHC =  1,3-dimethyl- or 1,3-dicyclohexylimidazolin-2-ylidene] (1, 4), and the biscarbene chelate complexes 12 [(η4-1,5-cyclooctadiene)(1,1′-di-n-butyl-3,3′-ethylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] and 14 [(η4-1,5-cyclooctadiene)(1,1′-dimethyl-3,3′-o-xylylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] were characterized by single crystal X-ray analysis. The relative σ-donor/π-acceptor qualities of various NHC ligands were examined and classified in monosubstituted NHC-Rh and NHC-Ir dicarbonyl complexes by means of IR spectroscopy. For the first time, bis(carbene) substituted iridium complexes were used as catalysts in the synthesis of arylboronic acids starting from pinacolborane and arene derivatives.  相似文献   
102.
A study of the reactivity of polyfluorobenzylamines towards the condensation with glyoxal is described. Selected fluorobenzylamines, 3,4-difluorobenzylamine, 3,4,5-trifluorobenzylamine and pentafluorobenzylamine react to give the corresponding hexabenzyl substituted hexaazaisowurtzitanes, (3,4-C6F2H3CH2)6(NCH)6 (1), (3,4,5-C6F3H2CH2)6(NCH)6 (2) and (C6F5CH2)6(NCH)6 (3). An unusual by-product is formed and could be isolated from the condensation with pentafluorobenzylamine. The exact constitution, a novel mixed O/N containing isowurtzitane, (C6F5CH2)5(NCH)5OCH (4), was elucidated by crystal structure determination. Furthermore, the crystal structures of 1 and 3 were determined.  相似文献   
103.
A two‐step synthesis of structurally diverse pyrrole‐containing bicyclic systems is reported. ortho‐Nitro‐haloarenes coupled with vinylic N‐methyliminodiacetic acid (MIDA) boronates generate ortho‐vinyl‐nitroarenes, which undergo a “metal‐free” nitrene insertion, resulting in a new pyrrole ring. This novel synthetic approach has a wide substrate tolerance and it is applicable in the preparation of more complex “drug‐like” molecules. Interestingly, an ortho‐nitro‐allylarene derivative furnished a cyclic β‐aminophosphonate motif.  相似文献   
104.
105.
106.
107.
Herein, we report a regioselective alkenyl electrophile synthesis from unactivated olefins that is based on a direct and regioselective C−H thianthrenation reaction. The selectivity is proposed to arise from an unusual inverse-electron-demand hetero-Diels–Alder reaction. The alkenyl sulfonium salts can serve as electrophiles in palladium- and ruthenium-catalyzed cross-coupling reactions to make alkenyl C−C, C−Cl, C−Br, and C−SCF3 bonds with stereoretention.  相似文献   
108.
109.
110.
The synthesis of [Ti6O4(OiPr)8(O2CPh)8] ( 3 ) and [RuCl(N≡CR)5][RuCl4(N≡CR)2] ( 4a , R = Me; 4b , R = Ph), [Ru(N≡CPh)6][RuCl4(N≡CPh)2] ( 5 ) and [H3O][RuCl4(N≡CMe)2] ( 7a ) is discussed. Crystallization of 5 from CH2Cl2 gave trans-[RuCl2(N≡CPh)4] ( 6 ). The solid-state structures of 3 , 4a , b , 5 , 6 and 7a are reported. Complex 4b forms a 3D network, while 6 displays a 2D structure, due to π-interactions between the benzonitrile ligands. The (spectro)electrochemical behavior of 4a , b and 6 was studied at 25 and –72 °C and the results thereof are compared with [NEt4][RuCl4(N≡CMe)2] ( 7b ) and [RuCl(N≡CPh)5][PF6] ( 8 ). The electrochemical response of the cation and the anion in 4a , b are independent from each other. [RuCl(N≡CR)5]+ possesses one reversible RuII/RuIII process. However, [RuCl4(N≡CMe)2] was shown to be prone to ligand exchange and disproportionation upon formation of either a RuIV and RuII species at 25 °C, while at –72 °C the rapid conversion of the electrochemically formed species is hindered. In situ IR and UV/Vis/NIR studies confirmed the respective disproportionation reaction products of the aforementioned oxidation and reduction, respectively.  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