全文获取类型
收费全文 | 2705篇 |
免费 | 101篇 |
国内免费 | 244篇 |
出版年
2023年 | 25篇 |
2022年 | 41篇 |
2021年 | 50篇 |
2020年 | 52篇 |
2019年 | 80篇 |
2018年 | 92篇 |
2017年 | 57篇 |
2016年 | 58篇 |
2015年 | 69篇 |
2014年 | 134篇 |
2013年 | 284篇 |
2012年 | 100篇 |
2011年 | 135篇 |
2010年 | 118篇 |
2009年 | 161篇 |
2008年 | 141篇 |
2007年 | 151篇 |
2006年 | 131篇 |
2005年 | 136篇 |
2004年 | 105篇 |
2003年 | 99篇 |
2002年 | 84篇 |
2001年 | 77篇 |
2000年 | 62篇 |
1999年 | 63篇 |
1998年 | 34篇 |
1997年 | 28篇 |
1996年 | 25篇 |
1995年 | 48篇 |
1994年 | 39篇 |
1993年 | 28篇 |
1992年 | 43篇 |
1991年 | 25篇 |
1990年 | 17篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 28篇 |
1986年 | 10篇 |
1985年 | 20篇 |
1984年 | 44篇 |
1983年 | 15篇 |
1982年 | 37篇 |
1981年 | 25篇 |
1980年 | 16篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 8篇 |
1976年 | 12篇 |
1975年 | 2篇 |
1974年 | 2篇 |
排序方式: 共有3050条查询结果,搜索用时 15 毫秒
101.
102.
《Biocatalysis and Biotransformation》2013,31(4):155-160
AbstractPinolenic acid (PLA) enrichment as an ethyl ester from pine nut oil was successfully accomplished in a batch reactor by lipase-catalyzed ethanolysis using Novozym 435 lipase from Candida antarctica as a biocatalyst. PLA is predominantly an sn-3 substituent of the pine nut oil triacylglycerol (TAG), where it accounts for about 39 mol% of the fatty acids esterified at that position. In the presence of ethanol, Novozym 435 exhibited sn-3 regiospecificity with respect to the TAG of pine nut oil. The effect of the molar ratio of reactants on PLA enrichment by ethanolysis was investigated. The molar ratios of pine nut oil to ethanol were varied from 1:20 to 1:100. A fatty acid ethyl ester (FAEE) fraction with higher PLA content was obtained in the early stage of the reaction, although the yield of PLA was small. However, the PLA content of the FAEEs decreased with increasing reaction time, while the yield of PLA increased. The molar ratio of pine nut oil to ethanol that produced the optimum content and yield of PLA in FAEEs was 1:80. 相似文献
103.
Antonia P. De Los Ríos Francisco J. Hernández-Fernández Francisco A. Martínez Manuel Rubio Gloria Víllora 《Biocatalysis and Biotransformation》2013,31(2-4):151-156
Nineteen different 1,3-dialkylimidazolium-based ionic liquids (ILs) were used as reaction media for the synthesis of butyl butyrate by transesterification from vinyl butyrate and 1-butanol catalyzed by Candida antarctica lipase B (CaLB). The reaction was also carried out in hexane as a reference solvent. In all the water-immiscible ILs assayed, the enzymatic activity and selectivity were higher than that obtained in hexane. However, in water-miscible ILs, the activity was lower than in the reference solvent, although they showed >99.99% selectivity. Two solvent properties, hydrophobicity and nucleophilicity, were considered key parameters for analyzing the behavior of CaLB in ILs. In the case of ILs based on the same anion, the synthetic activity was gradually enhanced by increasing cation hydrophobicity. Furthermore, the activity of CaLB was greater in ILs containing anions of lower nucleophilicity. Stability studies indicate that CaLB exhibited greater stability in water-immiscible ILs than in water-miscible ILs. 相似文献
104.
《Biocatalysis and Biotransformation》2013,31(1-4):227-239
Comparative molecular field analysis (CoMFA) was used to derive a quantitative substrate model for the enzymatic resolution of norbornanol esters by the lipase of Candida rugosa. Within these calculations, the steric and electrostatic interactions of both enantiomers and the differences in the corresponding two fields were used for the correlation of the substrate structure with the enantioselectivity of the hydrolysis. Different alignments of the molecules were used to improve the model. 相似文献
105.
《Biocatalysis and Biotransformation》2013,31(6):288-298
AbstractEnzyme incompatibility is a problem in multi-enzyme processes that involve a non-specific protease, such as Alcalase. An example is the one-pot enzymatic synthesis of peptides catalyzed by a lipase and a protease. The incompatibility between lipase B from Candida antarctica (CalB) and Alcalase was studied. To what extent immobilization of both or either CalB or Alcalase onto macroporous beads helps to prevent hydrolysis of CalB by Alcalase was evaluated. The rate of activity loss of native and immobilized CalB in the absence and presence of native and immobilized Alcalase was calculated from the rate of triacetin hydrolysis. Immobilization of both or either CalB or Alcalase onto macroporous beads was found to be effective in largely preventing hydrolysis of CalB by Alcalase. 相似文献
106.
《Biocatalysis and Biotransformation》2013,31(4):222-230
AbstractA lipase-producing bacterium isolated from raw milk was identified as Serratia grimesii based on 16S rRNA sequence analysis. The extracellular lipase was partially purified by ammonium sulfate precipitation and ultrafiltration. Maximal activity was observed at 10°C, the optimum pH was 8.0 and the enzyme was stable at 5–30°C for 1 h. The Km and Vmax values were 1.7 mM and 0.3 mM/min respectively. It was found that the lipase had the highest hydrolytic activity towards sunflower oil and soybean oil. CaCl2 had a stimulatory effect on lipase activity, while EDTA and iodoacetic acid slightly inhibited the lipase activity and the enzyme was strongly inhibited by PMSF. The enzyme was compatible with various non-ionic surfactants as well as sodium cholate and saponin. In addition, the enzyme was relatively stable towards oxidizing agents. This lipase exhibited maximum activity in 35% n-hexane retaining about 2191% activity for 1 h. 相似文献
107.
Epameinondas Xanthakis Sophia Magkouta Heleni Loutrari Haralambos Stamatis Charis Roussos 《Biocatalysis and Biotransformation》2013,31(3):170-178
The monoterpene perillyl alcohol (POH), an intermediate in the plant terpenoid biosynthetic pathway, has well-established tumor chemopreventive and chemotherapeutic potential. We have previously shown that the primary hydroxyl group of POH is essential for its antitumor and anti-angiogenic activities. In the current study we present the enzymatic synthesis of two POH derivatives with different polar and hydrophobic characteristics, namely perillyl glucoside and perillyl glucoside fatty ester, through a two-step modification. Initial glucosylation of POH on its active hydroxyl group with D-(+)-glucose and subsequent esterification of the perillyl glucoside product with vinyl laurate were carried out using almond β-glucosidase and lipase B from Candida antarctica, respectively, in a low-water system. Optimization of enzymatic reactions was performed to achieve the highest possible conversion yields. The antitumor cell proliferation activity against mouse Lewis lung carcinoma cells was retained in both derivatives, although the perillyl glucoside ester showed greater inhibition than perillyl glucoside. Our results underline the feasibility of enzymatically producing novel bioactive analogs of phytochemicals displaying useful physicochemical properties. 相似文献
108.
《Biocatalysis and Biotransformation》2013,31(4):175-180
AbstractPanthenyl esters (panthenyl monoacetate and panthenyl diacetate) were synthesized in high yields (≈100%) by a kinetic reaction control using a commercial immobilized Candida Antarctica lipase B (Novozyme 435) in acetonitrile. The enzyme showed excellent synthetic activity, regioselectivity, and operational stability under the conditions used. 相似文献
109.
Palligarnai T. Vasudevan Ashish A. Palekar Shuo Yan 《Biocatalysis and Biotransformation》2013,31(3):189-199
Crude porcine lipase was purified by continuous rotating annular size-exclusion chromatography. Sephadex G-75 was used as the size-exclusion packing material. Initial studies by this group on a similar unit have been reported [Genest et al. (1998) "Continuous purification of porcine lipase by rotating annular size-exclusion chromatography", Appl. Biochem. Biotechnol. 73, 215-230]. This article presents the results of optimization studies carried out on a modified unit. These modifications resulted in a better performance of the column and a higher throughput. Purification fold values of around 11 were achieved in most runs. The activity recovered was around 99% and the productivity was around 3 mg lipase/mg gel h. 相似文献
110.
《Biocatalysis and Biotransformation》2013,31(2):245-254
AbstractTwo immobilized lipases from Candida antarctica have been compared for the direct esterification of tyrosol with oleic acid in equimolar conditions and in the absence of organic solvent. Candida antarctica lipase B was immobilized on octyl-silica agglomerates and compared with commercial Novozym 435. Reduction of tyrosol particle size to 0.1 mm significantly increased the reaction rate with both immobilized lipases, and reduced pressure improved the final tyrosyl oleate yield up to 95% (w/w) in both cases. Immobilized lipases were recovered and reutilized in three consecutive trials with negligible inactivation. Under optimum conditions, a product mixture comprising more than 95% of tyrosyl oleate (w/w) was attained in less than 2 hours. Finally, the index of antioxidant activity obtained, according to the Rancimat method, indicated that tyrosyl oleate was slightly more effective than tyrosol as an antioxidant in a low polar matrix. 相似文献