全文获取类型
收费全文 | 211篇 |
免费 | 33篇 |
国内免费 | 66篇 |
专业分类
化学 | 308篇 |
晶体学 | 1篇 |
物理学 | 1篇 |
出版年
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
101.
Carbó JJ Lledós A Vogt D Bo C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(5):1457-1467
The origin of stereoinduction by chiral aminophosphane phosphinite (AMPP) ligands in asymmetric hydroformylation was investigated with a theoretical approach. The roles of the stereogenic center at the aminophosphane phosphorus atom (NP*) and of the chirality of the backbone were analyzed by considering three experimentally tested cases: 1) P-stereogenic yielding high ee, 2) P-nonstereogenic yielding low ee, and 3) P-stereogenic yielding low ee. We succeeded in reproducing the experimentally observed trends for the three studied AMPP ligands. Our results indicated that alkene insertion into the rhodium-hydride bond is the selectivity-determining step, and not alkene coordination. Additional calculations on model systems revealed that the different nonbonding weak-type interactions of styrene with the substituents of the NP* stereogenic center in an axial position is responsible for stereodifferentiation. The chirality of the AMPP backbone plays a secondary role. The rationalization of the stereochemical outcome is not straightforward, because two competitive equatorial/axial reaction paths, showing opposite asymmetric induction, must be considered. Construction of stereochemical models and evaluation of stereoinduction for novel ligand systems suggested that two prerequisites are required to improve the performance of AMPP-type ligands in asymmetric hydroformylation: 1) combination of stereorecognition and stereohindrance by substituents at the NP* atom, and 2) more rigid backbones. 相似文献
102.
Zhao B Peng X Wang Z Xia C Ding K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(26):7847-7857
A new class of C(2)-symmetric chiral bidentate phosphonite ligands has been synthesized in moderate to good yields from readily available starting materials. Application of these air-stable chiral phosphonites in the Rh(I)-catalyzed asymmetric hydroformylation of styrene derivatives, vinyl acetate, and allyl cyanide afforded the corresponding chiral aldehydes with high regio- and enantioselectivities under mild reaction conditions. The modular nature of the ligands allows fine-tuning of the selectivities through judicious modifications of the substituents on the ligand backbone. X-ray structural analysis of the catalyst precursor suggested that the steric hindrance caused by the protruding remote substituents of the ligands into the vicinity of the metal center might be an important factor for the enantio-control of the reaction, whereas the sense of asymmetric induction can be rationalized on the basis of a trigonal-bipyramidal transition state diagram. 相似文献
103.
The main results obtained by studying hydroformylation of olefins on polymeric rhodium-containing catalysts are reviewed. Different types of N-containing polymeric ligands capable of hydroformylating under conditions of heterogeneous catalysis are considered. Possibilities of using water-soluble polymers containing quaternary ammonium groups are shown. The data on the influence of a polymeric matrix on the catalytic properties of the rhodium catalyst of olefin hydroformylation are presented.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2346–2351, November, 2004. 相似文献
104.
Hydroformylation of 1-hexene in the presence of rhodium complexes immobilized on polyorganosiloxanes
N. V. Kolesnichenko G. V. Terekhova A. T. Teleshev E. I. Alekseeva E. V. Slivinsky 《Russian Chemical Bulletin》1997,46(6):1107-1109
It was demonstrated that the catalyst system based on acacRh(CO)2 and polyorgano-siloxanes exhibits high activity and stability in hydroformylation of 1-hexene. The effects of the nature
of the oligomer, the ratio of oligomers, and the oligomer: rhodium ratio in the polymer on the synthesis and catalytic properties
of the system were studied.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1155–1157, June, 1997. 相似文献
105.
106.
Hejun Zhu Yunjie Ding Fu Yang Li Yan Jianmin Xiong Hongmei Yin Liwu LinNatural Gas Utilization Applied Catalysis Laboratory Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian China 《天然气化学杂志》2004,(2)
A novel TPPTS-Rh/SiO2 catalyst, prepared by directly modifying a heterogeneous high-surface-area Rh/SiO2 catalyst with water-soluble TPPTS ligands, could decrease the resistance of mass transfer in water/oil biphasic media for the hydroformylation of higher olefins. The catalytic performance for hydroformylation on this biphasic TPPTS-Rh/SiO2 catalyst system was higher than those of the traditional biphasic HRhCO(TPPTS)3 systems, owing to the chemical bonds between the highly dispersed Rh metal particles and the TPPTS ligands. The catalyst system is applicable for hydroformylation of higher olefins such as 1-dodecene. 相似文献
107.
新型复合负载金属-支撑水相催化剂 总被引:1,自引:0,他引:1
朱何俊 丁云杰 严丽 熊建民 李学民 张连忠 林培滋 黄世煜 林励吾 ZHU Hejun DING Yunjie YAN Li XIONG Jianmin Li Xuemin ZHANG Lianzhong LIN Peizi Huang Shiyu LIN Liwu 《催化学报》2003,24(2):81-82
复合催化剂SAP/Rh-SiO2中匀相组分和多相组分具有协同作用。本文主要考察V助剂对Rh-V/SiO2多相催化剂和SAP/Rh-V-SiO2复合催化剂1-己烯氢甲酰化性能的影响。实验结果表明:加入助剂V之后,Rh-V/SiO2催化剂的活性(147.2h-1)比Rh/SiO2催化剂的活性(20.8h-1)有很大提高,而复合SAP/Rh-V-SiO2催化剂的活性(594h-1)比SAP/Rh-SiO2催化剂的活性(370.5h-1)提高很多。V有很强的储氢作用,在Rh-V/SiO2催化剂上更容易发生氢溢流,因此该类复合催化剂的作用机理可能是多相催化剂上产生的H和CO溢流等活性物种溢流至烯烃配位的匀相催化剂活性上发生反应,从而促进复合催化剂活性的提高。 相似文献
108.
IntroductionFormorethanonedecade,catalyticchemistshavemadenotableachievementsindevelopingthepreparativeapproachestoheterogenizedmolecularcatalystsandhighlydispersedmetalcatalystsfromorganometalliccompoundsandclusters,throughtheexplorationinsurfaceorganome… 相似文献
109.
合成了四个从葡萄糖及半乳糖衍生的手性芳基双膦配体,制备了手性双膦-铑(Ⅰ)配合物催化剂,并将其用于苯乙烯不对称氢甲酰化反应中.结果表明,葡萄糖骨架手性中心与联萘基之间有协同作用,对映体过量值和转化率受配体C-4骨架立体中心的绝对构型影响,而产物的绝对构型则主要由联萘单元控制;配体4-双{[(S)-1,1′-联萘基-2,2′-双基]-磷}-苯基-3,6-脱水-β-D-葡萄糖的吡喃糖苷基和联萘基的匹配组合,给出41%的对映体选择性和74∶26(异构/正构)区域选择性. 相似文献
110.
Imre Tth Cornelis J. Elsevier Johannes G. de Vries Jzsef Bakos Wilberth J.J. Smeets Anthony L. Spek 《Journal of organometallic chemistry》1997,540(1-2):15-25
Unlike bis(diphenyl)phosphine derivatives in general, (2S,4S)-pentane-2,4-diyl-bis(5H-dibenzo[b]phosphindole), S,S-BDBPP, gives a trans oligomeric compound [PtCl2(S,S-BDBPP)]n, 1, in reaction with dichloro-Pt precursors such as PtCl2(PhCN)2, PtCl2(CH3CN)2 and PtCl2(COD) at room temperature. Compound 1, which could be readily isolated, slowly rearranges in solutions at room temperature to the expected cis-monomer PtCl2(S,S-BDBPP), 3. Heating or the presence of PtCl2(COD) accelerates the transformation of compound 1 to 3. SnCl2 adducts of both compounds, trans-[PtCl(SnCl3)(S,S-BDBPP)]n, 2, and cis-PtCl(SnCl3)(S,S-BDBPP), 4, as well as the known cis-PtCl(SnCl3)(S,S-BDPP), 5, (S,S-BDPP = (2S,4S)-2,4-bis(diphenylphosphino)pentane) have been tested as catalysts in the asymmetric hydroformylation of p-isobutylstyrene. The phenyl analog 5 provides up to 75% e.e. but moderate yields to chiral 2-(4-isobutylphenyl)-2-propanal. Compared to this, the regioselectivity to the branched aldehyde is remarkably increased; however, the enantioselectivity is drastically decreased by the use of both dibenzophosphole derivatives 2 and 4. The similarities in the selectivities provided by 2 and 4 indicate that the trans oligomer 2 transforms to the cis-monomer 4 during the catalytic process. X-ray crystal structure determination of compound 3 shows a half-chair conformation for the chelate ring with a symmetric arrangement of dibenzophosphole groups. Besides a preference for the latter achiral conformation, the planar structure of the dibenzophosphole groups can also be considered as reason for the moderate enantioselectivities provided by 4. 相似文献