全文获取类型
收费全文 | 394篇 |
免费 | 24篇 |
国内免费 | 31篇 |
专业分类
化学 | 414篇 |
综合类 | 14篇 |
数学 | 1篇 |
物理学 | 20篇 |
出版年
2023年 | 3篇 |
2022年 | 10篇 |
2021年 | 26篇 |
2020年 | 8篇 |
2019年 | 13篇 |
2018年 | 5篇 |
2017年 | 14篇 |
2016年 | 10篇 |
2015年 | 16篇 |
2014年 | 8篇 |
2013年 | 13篇 |
2012年 | 36篇 |
2011年 | 18篇 |
2010年 | 16篇 |
2009年 | 15篇 |
2008年 | 22篇 |
2007年 | 21篇 |
2006年 | 14篇 |
2005年 | 20篇 |
2004年 | 15篇 |
2003年 | 21篇 |
2002年 | 16篇 |
2001年 | 14篇 |
2000年 | 13篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 16篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有449条查询结果,搜索用时 15 毫秒
81.
Kenichi Murata Masato Suzuki Nobuhumi Nakamura Hiroyuki Ohno 《Electrochemistry communications》2009,11(8):1623-1626
The direct electron transfer reaction of fructose dehydrogenase (FDH) from Gluconobacter sp. on alkanethiol-modified silver nanoparticles (AgNPs) was examined using cyclic voltammetry and surface-enhanced resonance Raman scattering (SERRS). Using cyclic voltammetry, catalytic oxidation currents (based on the direct electron transfer reaction of FDH) were observed from a potential of approximately −100 mV (vs. Ag/AgCl, 3 M NaCl) in the presence of d-fructose, without a mediator. A comparison of the SERRS spectra and the resonance Raman spectra of FDH in solution indicated that the heme c site retained its six-coordinated low-spin heme after immobilization. Moreover, SERRS also demonstrated that the heme c of the adsorbed FDH was the electron transfer site within the enzyme. 相似文献
82.
Leonard Stoica Tautgirdas Ruzgas Lo Gorton 《Bioelectrochemistry (Amsterdam, Netherlands)》2009,76(1-2):42
The reaction mechanism of cellobiose dehydrogenase (CDH) from Phanerochaete chrysosporium, adsorbed on graphite electrodes, was investigated by following its catalytic reaction with cellobiose registered in both direct and mediated electron transfer modes between the enzyme and the electrode. A wall-jet flow through amperometric cell housing the CDH-modified graphite electrode was connected to a single line flow injection system. In the present study, it is proven that cellobiose, at concentrations higher than 200 μM, competes for the reduced state of the FAD cofactor and it slows down the transfer of electrons to any 2e−/H+ acceptors or further to the heme cofactor, via the internal electron transfer pathway. Based on and proven by electrochemical results, a kinetic model of substrate inhibition is proposed and supported by the agreement between simulation of plots and experimental data. The implications of this kinetic model, called pseudo-ping-pong mechanism, on the possible functions CDH are also discussed. The enzyme exhibits catalytic activity also for lactose, but in contrast to cellobiose, this sugar does not inhibit the enzyme. This suggests that even if some other substrates are coincidentally oxidized by CDH, however, they do not trigger all the possible natural functions of the enzyme. In this respect, cellobiose is regarded as the natural substrate of CDH. 相似文献
83.
Summary Human 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) catalyzes the interconversion of cortisone into active cortisol. 11βHSD1 inhibition is a tempting target for the treatment of a host of human disorders that might benefit from blockade of glucocorticoid action, such as obesity, metabolic syndrome, and diabetes type 2. Here, we report an in silico screening study aimed at identifying new selective inhibitors of human 11βHSD1 enzyme. In the first step, homology modeling was employed to build the 3D structure of 11βHSD1. Further, molecular docking was used to validate the predicted model by showing that it was able to discriminate between known 11βHSD1 inhibitors or substrates and non-inhibitors. The homology model was found to reproduce closely the crystal structure that became publicly available in the final stages of this work. Finally, we carried out structure-based virtual screening experiments on both the homology model and the crystallographic structure with a database of 114’000 natural molecules. Among these, 15 molecules were consistently selected as inhibitors based on both the model and crystal structures of the enzyme, implying a good quality for the homology model. Among these putative 11βHSD1 inhibitors, two were flavonone derivatives that have already been shown to be potent inhibitors of the enzyme. 相似文献
84.
85.
A new electrogenerated chemiluminescence biosensor was fabricated by immobilizing ECL reagent Ru(bpy)32+ and alcohol dehydrogenase in sol-gel/chitosan/poly(sodium 4-styrene sulfonate) (PSS) organically modified composite material. The component PSS was used to immobilize ECL reagent Ru(bpy)32+ by ion-exchange, while the addition of chitosan was to prevent the cracking of conventional sol-gel-derived glasses and provide biocompatible microenvironment for alcohol dehydrogenase. Such biosensor combined enzymatic selectivity with the sensitivity of ECL detection for quantification of enzyme substrate and it was much simpler than previous double-layer design. The detection limit was 9.3 × 10−6 M for alcohol (S/N = 3) with a linear range from 2.79 × 10−5 to 5.78 × 10−2 M. With ECL detection, the biosensor exhibited wide linear range, high sensitivity and good stability. 相似文献
86.
Tairan Wang Ran Wei Yingting Feng Lijun Jin Yunpeng Jia Duxia Yang Zuonan Liang Mengge Han Xia Li Chenze Lu Xiangxian Ying 《Molecules (Basel, Switzerland)》2021,26(16)
The importance of yeast old yellow enzymes is increasingly recognized for direct asymmetric reduction of (E/Z)-citral to (R)-citronellal. As one of the most performing old yellow enzymes, the enzyme OYE3 from Saccharomyces cerevisiae S288C exhibited complementary enantioselectivity for the reduction of (E)-citral and (Z)-citral, resulting in lower e.e. value of (R)-citronellal in the reduction of (E/Z)-citral. To develop a novel approach for the direct synthesis of enantio-pure (R)-citronellal from the reduction of (E/Z)-citral, the enzyme OYE3 was firstly modified by semi-rational design to improve its (R)-enantioselectivity. The OYE3 variants W116A and S296F showed strict (R)-enantioselectivity in the reduction of (E)-citral, and significantly reversed the (S)-enantioselectivity in the reduction of (Z)-citral. Next, the double substitution of OYE3 led to the unique variant S296F/W116G, which exhibited strict (R)-enantioselectivity in the reduction of (E)-citral and (E/Z)-citral, but was not active on (Z)-citral. Relying on its capability discriminating (E)-citral and (Z)-citral, a new cascade reaction catalyzed by the OYE3 variant S296F/W116G and glucose dehydrogenase was developed, providing the enantio-pure (R)-citronellal and the retained (Z)-citral after complete reduction of (E)-citral. 相似文献
87.
Preparative isolation and analysis of alcohol dehydrogenase inhibitors from Glycyrrhiza uralensis root using ultrafiltration combined with high‐performance liquid chromatography and high‐speed countercurrent chromatography 下载免费PDF全文
A simple, rapid, and effective assay based on ultrafiltration combined with high‐performance liquid chromatography and high‐speed countercurrent chromatography was developed for screening and purifying alcohol dehydrogenase inhibitors from Glycyrrhiza uralensis root extract. Experiments were carried out to optimize binding conditions including alcohol dehydrogenase concentration, incubation time, temperature, and pH. By comparing the chromatograms, three compounds were found possessing alcohol dehydrogenase binding activity in Glycyrrhiza uralensis root. Under the target‐guidance of ultrafiltration combined with the high‐performance liquid chromatography experiment, liquiritin ( 1 ), isoliquiritin ( 2 ), and liquiritigenin ( 3 ) were separated by high‐speed countercurrent chromatography using ethyl acetate/methanol/water (5:1:4) as the solvent system. The alcohol dehydrogenase inhibitory activities of these three isolated compounds were assessed; compound 2 showed strongest inhibitory activity with an IC50 of 8.95 μM. The results of the present study indicated that the combinative method using ultrafiltration, high‐performance liquid chromatography and high‐speed countercurrent chromatography could be widely applied for the rapid screening and isolation of enzyme inhibitors from complex mixtures. 相似文献
88.
Abrahamson MJ Vázquez-Figueroa E Woodall NB Moore JC Bommarius AS 《Angewandte Chemie (International ed. in English)》2012,51(16):3969-3972
A leucine dehydrogenase has been successfully altered through several rounds of protein engineering to an enantioselective amine dehydrogenase. Instead of the wild-type α-keto acid, the new amine dehydrogenase now accepts the analogous ketone, methyl isobutyl ketone (MIBK), which corresponds to exchange of the carboxy group by a methyl group to produce chiral (R)-1,3-dimethylbutylamine. 相似文献
89.
90.
《Analytical letters》2012,45(2):65-73
Abstract 5′nucleotidase activity was measured by a coupled optical assay in which adenosine, liberated by action of the primary enzyme, released ammonia which in turn formed L-glutamate from 2-oxoglutarate and NADH. Oxidation of the latter is monitored at 340 nm. Greater activity was obtained when triethanolamine buffer, pH 7.2, and Mn++ were substituted for tris buffer, pH 7.9, and Mg++. The concentration of substrate, 5′AMP, was altered to 1 mmole/liter and that of β-glycerophosphate to 50 mmoles/liter to achieve optimal activity of true nucleotidase and suppression of 5′AMP-hydrolysis by non-specific phosphatases. 相似文献