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   36433篇
  免费   9608篇
  国内免费   1410篇
化学   41895篇
晶体学   340篇
力学   470篇
数学   2351篇
物理学   2395篇
  2023年   24篇
  2022年   15篇
  2021年   169篇
  2020年   1258篇
  2019年   2607篇
  2018年   1029篇
  2017年   668篇
  2016年   3406篇
  2015年   3553篇
  2014年   3460篇
  2013年   4109篇
  2012年   3027篇
  2011年   2230篇
  2010年   2859篇
  2009年   2843篇
  2008年   2431篇
  2007年   1848篇
  2006年   1559篇
  2005年   1708篇
  2004年   1520篇
  2003年   1369篇
  2002年   2081篇
  2001年   1390篇
  2000年   1320篇
  1999年   377篇
  1998年   54篇
  1997年   61篇
  1996年   47篇
  1995年   23篇
  1994年   32篇
  1993年   25篇
  1992年   21篇
  1991年   18篇
  1990年   20篇
  1989年   16篇
  1988年   16篇
  1987年   9篇
  1986年   15篇
  1985年   27篇
  1984年   27篇
  1982年   23篇
  1981年   14篇
  1980年   21篇
  1979年   15篇
  1978年   11篇
  1977年   17篇
  1976年   9篇
  1975年   8篇
  1974年   11篇
  1973年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The title compound, hexadecacarbonylbis{μ3‐[(diphenylphosphanyl)methanediidyl]sulfanido}‐μ4‐disulfido(2−)‐hexairon(4 FeFe), [Fe6(C13H10PS)2(S2)(CO)16], contains two inversion‐related [Fe3(Ph2PCS)(CO)8] subclusters linked by an equatorial disulfide bond [S—S = 2.1490 (9) Å]. Each Ph2PCS3− ligand is coordinated to a triiron core in a μ3‐κP2C2S fashion.  相似文献   
992.
A new and versatile, crown ether appended, chiral supergelator has been designed and synthesized based on the bis‐urea motif. The introduction of a stereogenic center improved its gelation ability significantly relative to its achiral analogue. This low‐molecular‐weight gelator forms supramolecular gels in a variety of organic solvents. It is sensitive to multiple chemical stimuli and the sol–gel phase transitions can be reversibly triggered by host–guest interactions. The gel can be used to trap enzymes and release them on demand by chemical stimuli. It stabilizes the microparticles in Pickering emulsions so that enzyme‐catalyzed organic reactions can take place in the polar phase inside the microparticles, the organic reactants diffusing through the biphasic interface from the surrounding organic phase. Because of the higher interface area between the organic and polar phases, enzyme activity is enhanced in comparison with simple biphasic systems.  相似文献   
993.
994.
995.
Low‐temperature generation of P‐nitroxyl phosphane 2 (Ph2POTEMP), which was obtained by the reaction of Ph2PH ( 1 ) with two equivalents of TEMPO, is presented. Upon warming, phosphane 2 decomposed to give P‐nitroxyl phosphane P‐oxide 3 (Ph2P(O)OTEMP) as one of the final products. This facile synthetic protocol also enabled access to P‐sulfide and P‐borane derivatives 7 and 13 , respectively, by using Ph2P(S)H ( 6 ) or Ph2P(BH3)H ( 11 ) and TEMPO. Phosphane sulfide 7 revealed a rearrangement to phosphane oxide 8 (Ph2P(O)STEMP) in CDCl3 at ambient temperature, whereas in THF, thermal decomposition of sulfide 7 yielded salt 10 ([TEMP‐H2][Ph2P(S)O]). As well as EPR and detailed NMR kinetic studies, indepth theoretical studies provided an insight into the reaction pathways and spin‐density distributions of the reactive intermediates.  相似文献   
996.
997.
The motivation behind the present work is to synthesize some nonionic surfactants containing heterocyclic nucleus with intermediate fatty compounds for improving their surfactants properties. 2‐Cyano‐N‐octadecylacetamide was utilized as key intermediate for the synthesis of some new thiazole, pyrazole, oxazole, pyrimidine, 1,3‐dithiolane, thiophene, coumarin, oxazine and pyridazine derivatives. The newly synthesized compounds undergo propoxylation using propylene oxide to afford nonionic surface active agents. The antimicrobial and surface activities were evaluated and characterized through investigations of their spreading behavior in monolayer on water.  相似文献   
998.
999.
1000.
Cu ( II ) supported on poly(8‐hydroxyquinoline‐p‐styrenesulfonate) (Cu ( II )@PHQSS) was prepared and fully characterized by the different techniques including fourier transform infrared spectroscopy (FT‐IR), 1H NMR, 13C NMR, thermal gravimetric analysis (TGA), differential thermal gravimetric (DTG), differential thermal analysis (DTA), scanning electron microscope (SEM) and energy dispersive X‐ray analysis (EDS). Afterward, the Cu ( II )@PHQSS as nanostructured catalyst was used as catalyst for the synthesis of hexahydroquinolines.  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