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   211篇
  免费   33篇
  国内免费   66篇
化学   308篇
晶体学   1篇
物理学   1篇
  2023年   2篇
  2022年   4篇
  2021年   3篇
  2020年   6篇
  2019年   7篇
  2018年   4篇
  2017年   2篇
  2016年   9篇
  2015年   9篇
  2014年   13篇
  2013年   19篇
  2012年   18篇
  2011年   13篇
  2010年   19篇
  2009年   10篇
  2008年   25篇
  2007年   12篇
  2006年   15篇
  2005年   19篇
  2004年   18篇
  2003年   15篇
  2002年   4篇
  2001年   7篇
  2000年   2篇
  1999年   8篇
  1998年   2篇
  1997年   7篇
  1996年   8篇
  1995年   13篇
  1994年   5篇
  1993年   5篇
  1992年   1篇
  1991年   2篇
  1989年   1篇
  1984年   1篇
  1983年   2篇
排序方式: 共有310条查询结果,搜索用时 15 毫秒
91.
92.
以聚乙二醇(PEG)为反应介质,考察了水溶性铑膦络合物RhCl(CO)(TPPTS)2 (TPPTS为间-三苯基膦三磺酸钠)对长链烯烃氢甲酰化反应的催化性能. 结果表明,添加适量的水于PEG中对催化剂活性有重要影响. 以PEG-400-H2O为溶剂的催化体系对 1-十二烯氢甲酰化反应的催化活性较高,在100 ℃, 5 0 MPa的优化条件下, 1-十二烯的转化率可达到92 6%, 生成醛的选择性为95 8%. 反应完成后,含水溶性铑膦络合物的PEG-水溶液与含产物的有机相分离方便,易于实现催化剂的循环使用,催化剂重复使用8次,未观察到活性和选择性下降.  相似文献   
93.
Specific features of the behavior of the supramolecular metal complex catalysts based on calixarenes, cyclodextrins, and dendrimers in the reactions of hydroformylation, Wacker oxidation, hydroxylation of aromatics, 2-naphthol coupling, and oxidative coupling of styrenes and benzene were studied. The factors affecting the catalytic activity and selectivity are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 766–778, April, 2008.  相似文献   
94.
A new class of cationic alpha-cyclodextrins bearing 2-hydroxy-3-trimethylammoniopropyl groups has been synthesised. We investigated their efficiency as mass-transfer promoters in a biphasic hydroformylation reaction catalysed by a rhodium trisulfonated triphenylphosphine system. These cationic alpha-cyclodextrins greatly increased the reaction rate, the chemoselectivity, and, surprisingly, the linear-to-branched aldehyde ratio. We attributed this unexpected enhancement of the linear-to-branched aldehyde ratio to the in situ formation of new catalytic supramolecular species obtained by ion-exchange between the catalyst ligand and the cationic alpha-cyclodextrins.  相似文献   
95.
96.
97.
1-辛烯在Co/CNTs催化剂上的氢甲酰化研究: 钌的促进作用   总被引:1,自引:0,他引:1  
采用等体积浸渍法制备了碳纳米管负载的钴及钴-钌双金属催化剂,并以1-辛烯的氢甲酰化反应为探针,研究了所制催化剂的催化性能;用TEM、XRD、TPR、TG技术对催化剂的形貌、物相结构、还原行为和热稳定性进行了研究。结果表明,金属钌能够促进金属钴在碳纳米管上的均匀担载,并有助于金属钴的还原,降低了催化剂的还原温度。1-辛烯的氢甲酰化反应结果表明,少量钌的加入,可明显提高反应的转化率和C9-醛的选择性;在双金属催化剂中,金属催化剂的粒径更小,分布更均匀,钌的加入对钴金属催化剂有促进作用。  相似文献   
98.
A comprehensive theoretical investigation into the mechanism of 1‐phenyl‐1‐(4‐pyridyl)ethene hydroformylation, using a rhodium catalyst employing a nonlocal density functional method (B3LYP), was carried out. The calculated results show that it is strongly exothermic by >90 kJ/mol of the whole catalytic cycle, and the rate‐limited step is H2 oxidative addition. The regioselectivity originates from olefin insertion into the Rh? H bond. The predominant product is the regiospecifically 3‐phenyl‐3‐(4‐pyridal)propanal determined both thermodynamically and kinetically. These are in agreement with practicality experimental studies. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006  相似文献   
99.
DFT calculations were carried out to study the full catalytic cycle for the hydroformylation of propene, catalyzed by the heterobimetallic model catalyst trans‐Pt(H)(PH3)2(SnCl3). Before the study of the full catalytic cycle, the performance of six pure GGA, one GGA with inclusion of dispersion corrections, four hybrid‐GGA, and three meta‐GGA exchange correlation functional to describe a model reaction promoted by Pt‐Sn catalyst were assessed. It is shown that the BP86 and GPW91 functionals, using extended basis set, provides reliable energetic results when compared with the CCSD(T) calculations. All intermediates and transition states along the elementary steps of the entire catalytic cycle were located and the energies involved in the catalytic cycle calculated using BP86 functional. The solvent effects along the entire catalytic cycle were evaluated using the polarizable continuum model. In contrast with the rhodium catalysts, the regioselectivity of the hydroformylation is set at the carbonylation step. The hydrogenolysis is the rate determining step of the entire cycle, with the activation energy of ~21 kcal mol?1 in agreement with the experimental value of ~25 kcal mol?1. The trans effect of the SnCl ligand seems to be pronounced only in the first step of the catalytic cycle, facilitating the insertion of the olefin into the Pt? H bond trans to it. The analysis of the stationary points obtained along each elementary step of the catalytic cycle is carried out separately and discussed. The BP86/cc‐pVTZ/SBKJC results shows that the pathway leading to the linear aldehyde is preferred, being in agreement with the experimental findings. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010  相似文献   
100.
Rh/L和Rh-Zn/L分子筛催化剂上乙烯的氢甲酰化反应   总被引:2,自引:0,他引:2  
Rh/L和Rh-Zn/L分子筛催化剂上乙烯的氢甲酰化反应董永治,徐奕德,刘安明,李大明,黄林(中国科学院大连化学物理研究所催化基础国家重点实验室,大连116023)关键词Rh/L分子筛催化剂,Rh-Zn/L分子筛催化剂,氢甲酰化反应,乙烯近年来,氢甲...  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