全文获取类型
收费全文 | 262篇 |
免费 | 15篇 |
国内免费 | 2篇 |
学科分类
工业技术 | 279篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 30篇 |
2015年 | 18篇 |
2014年 | 15篇 |
2013年 | 18篇 |
2012年 | 22篇 |
2011年 | 19篇 |
2010年 | 19篇 |
2009年 | 34篇 |
2008年 | 21篇 |
2007年 | 14篇 |
2006年 | 10篇 |
2005年 | 12篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1994年 | 1篇 |
1992年 | 1篇 |
排序方式: 共有279条查询结果,搜索用时 15 毫秒
191.
Chun‐Sheng Chang Chin‐Shuo Hsu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(5):537-544
Lipase‐catalyzed enantioselective esterification between (R,S)‐ketoprofen and alkanediol in organic solvents was developed to produce (S)‐ketoprofen hydroxyalkyl esters. The acyl acceptor of 1,6‐hexanediol for the resolution of (R,S)‐ketoprofen yielded only the enantioselectivity (the enantiomeric ratio of initial rate for (S)‐ketoprofen to that of (R)‐ketoprofen) VS/VR = 8, when crude Lipase MY originating from Candida rugosa was used. However, isopropanol‐dried immobilized lipases (IPA‐dried IM‐lipase) effectively enhanced the enantioselectivity to greater than 20 in the esterification of (R,S)‐ketoprofen when 1,4‐butanediol, 1,5‐pentanediol or 1,6‐hexanediol was employed. IPA‐dried IM‐lipase and isooctane were selected to use for optimally immobilized lipase and reaction medium, respectively. The IPA‐dried IM‐lipase exhibited the highest enantioselectivity, E = 26.7, to the (S)‐enantiomer with 1,5‐pentanediol and the best enzyme activity to the (S)‐enantiomer with 1,4‐butanediol. The finding indicates that the carbon chain length of the alkanediol strongly affected the enzyme activity and enantioselectivity of lipase‐catalyzed esterification. A maximum enantioselectivity of 37 at 27 °C was generated by IPA‐dried IM‐lipase for the enantioselective esterification of racemic ketoprofen with 1,4‐butanediol. IPA‐dried IM‐lipase can effectively increase the enantioselectivity of lipase. Copyright © 2005 Society of Chemical Industry 相似文献
192.
193.
194.
195.
The influence of solvent on the kinetics of enantioselective hydrogenation of ethyl pyruvate by Pt/Al2O3/dihydrocinchonidine is reported. In a non‐polar solvent, toluene, the reaction is approximately zero order in substrate at
constant hydrogen pressure, while under the same conditions and at the same substrate concentration, in the polar solvents
ethanol and propylene carbonate the reaction shows a first‐order substrate concentration dependence. Fits to a Michaelis–Menten
rate expression show that these differences are the expression of the relative magnitudes of the adsorption term in the rate
expression, which in turn reflects the influence of the solvent on the adsorption–desorption processes which take place at
the catalyst surface.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
196.
《分离科学与技术》2012,47(17):2630-2641
Optical resolution of racemic mixtures of arginine and alanine was performed by chiral selective nanofiltration membrane. The chiral selective layer of the membrane was prepared by interfacial polymerization of metaphenylenediamine, trimesoyl chloride, and S (-)-2-acetoxypropionyl chloride (S-2-actoxpcl) in situ on the top of polysulfone ultrafiltration membrane. S-2-actoxpcl consists of a chiral carbon atom that has an induced chiral environment in the membrane. The membranes were characterized by FTIR, scanning electron microscopy, and atomic force microscopy to establish a structure-performance relationship. The optical resolution was performed on the membrane testing module and the effect of process parameters was determined. The results indicated that the incorporation of S-2-actoxpcl made membrane chiral selective hence membranes performed optical resolution. The resolution capacity increased by increasing S-2-actoxpcl in polymerizing solution up to 0.03% but any increase beyond 0.03% reduces the resolution capacity. More than 92% enantiomeric excess of D enantiomer was observed in the permeate of the membrane which was prepared from 0.07% trimesoyl chloride and 0.03% S-2-actoxpcl. The membrane prepared without the chain terminator exhibited less volumetric flux but more solute rejection compared to those prepared with the chain terminator. The flux of the membrane increases as the amount of the chain terminator in the reaction increases. 相似文献
197.
198.
Makoto Kamezawa Hojun Tachibana Takehiko Ohtani Yoshinobu Naoshima 《Journal of chemical ecology》1994,20(5):1057-1061
The two chiral pheromone acetates, (S)-2-tridecanyl acetate and (S)-2-pentadecanyl acetate, were synthesized with an enantiomeric excess (e.e.) of almost 100% byPseudomonas cepacia lipase-catalyzed hydrolysis of their corresponding racemic acetates in an acetone-water solvent system. 相似文献
199.
We describe here a strategy to improve the expression efficiency and enantioselectivity of Aspergillus niger epoxide hydrolase (ANEH) by directed evolution. Based on a blue‐colony screening system using the LacZα (β‐galactosidase α peptide) complementation solubility reporter, several ANEH variants out of 15 000 transformants from a random‐mutagenesis library were identified that show improved recombinant expression in E. coli. Among them, Pro221Ser was subsequently used as a template for iterative saturation mutagenesis (ISM) at sites around the ANEH binding pocket. Following four rounds of ISM, a highly enantioselective mutant was identified that catalyzes the hydrolytic kinetic resolution of racemic glycidyl phenyl ether with a selectivity factor of E=160 in favor of the (S)‐diol compared to WT ANEH characterized by E=4.6. Expression of this mutant is 50 times higher than that of WT ANEH. It also serves as an excellent stereoselective catalyst in the hydrolytic kinetic resolution and desymmetrization of several other structurally diverse epoxides. 相似文献
200.
Min Woo Ha Heejin Lee Hye Yeong Yi Yohan Park Sori Kim Suckchang Hong Myungmo Lee Mi‐hyun Kim Taek‐Soo Kim Hyeung‐geun Park 《Advanced Synthesis \u0026amp; Catalysis》2013,355(4):637-642
A new enantioselective α‐benzylation and α‐allylation of α‐tert‐butoxycarbonyllactones was devloped. α‐Benzylation and α‐allylation of α‐tert‐butoxycarbonylbutyrolactone and α‐tert‐butoxycarbonylvalerolactone under phase‐transfer catalytic conditions (50% cesium hydroxide, toluene, −60 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐NAS bromide (1 mol%) afforded the corresponding α‐substituted α‐tert‐butoxycarbonyllactones in very high chemical yields (up to 99%) and optical yields (up to 99% ee). The synthetic potential of this method has been successfully demonstrated by the asymmetric synthesis of unnatural α‐quaternary homoserines, 3‐alkyl‐3‐carboxypyrrolidine and 3‐alkyl‐3‐carboxypiperidine. 相似文献