全文获取类型
收费全文 | 285篇 |
免费 | 3篇 |
国内免费 | 9篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 14篇 |
2013年 | 21篇 |
2012年 | 4篇 |
2011年 | 18篇 |
2010年 | 7篇 |
2009年 | 23篇 |
2008年 | 21篇 |
2007年 | 20篇 |
2006年 | 17篇 |
2005年 | 27篇 |
2004年 | 16篇 |
2003年 | 13篇 |
2002年 | 12篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1983年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有297条查询结果,搜索用时 15 毫秒
291.
Joo Valdir Comasseto Leandro Helgueira Andrade lvaro Takeo Omori Leonardo Fernandes Assis Andr Luiz Meleiro Porto 《Journal of Molecular Catalysis .B, Enzymatic》2004,29(1-6):55-61
The enantioselective deracemization of a number of p-substituted aryl ethanols and the reduction of p-substituted acetophenones were carried out with whole fungal cells of Aspergillus terreus CCT 4083, A. terreus CCT 3320 and Rhizopus oryzae CCT 4964 giving the corresponding alcohols in enantiomeric excesses up to >99%. 相似文献
292.
A novel electrochemical sensor based on 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanocrystals (TOCNCs) and l-cystines (l-Cys) modified Au electrode (TOCNC/l-Cys/Au) has been fabricated for detection and discrimination of the enantiomers of phenylalanine (Phe), leucine (Leu), and valine (Val). The three amino acids are in connection with metabolism diseases. The TOCNC/l-Cys/Au electrode exhibited obvious peak current difference for the amino acid enantiomers by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The TOCNCs on the electrode surface expressed different interactions with d- and l-amino acids, so the electrochemical recognitions of the three amino acid enantiomers were achieved. TOCNCs were characterized by Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM). The modified electrodes were characterized by SEM and electrochemical techniques. According to DPV, peak currents of the two enantiomers decreased linearly with their concentrations. Furthermore, satisfactory results were obtained when this electrode was applied to measure the d- and l-Phe mixture. The experimental results show that TOCNCs are suitable material for chiral sensor. The contrast of serum sample of healthy people and patients with type 2 diabetes also was proposed, and significant difference was exhibited on the modified electrode. This work is significant for the screening, diagnosis, and treatment of multiple metabolic diseases. 相似文献
293.
Stephen J. Sowerby Wolfgang M. Heckl George B. Petersen 《Journal of molecular evolution》1996,43(5):419-424
Scanning tunneling microscopy was used to investigate the structure of the two-dimensional adsorbate formed by molecular self-assembly
of the purine base, adenine, on the surfaces of the naturally occurring mineral molybdenite and the synthetic crystal highly
oriented pyrolytic graphite. Although formed from adenine, which is achiral, the observed adsorbate surface structures were
enantiomorphic on molybdenite. This phenomenon suggests a mechanism for the introduction of a localized chiral symmetry break
by the spontaneous crystallization of these prebiotically available molecules on inorganic surfaces and may have some role
in the origin of biomolecular optical asymmetry. The possibility that purine-pyrimidine arrays assembled on naturally occurring
mineral surfaces might act as possible templates for biomolecular assembly is discussed.
Correspondence to: G.B. Petersen 相似文献
294.
An aldo-keto reductase gene (klakr) from Kluyveromyces lactis XP1461 was cloned and heterologously expressed in Escherichia coli. The aldo-keto reductase KlAKR was purified and found to be NADH-dependent with a molecular weight of approximately 36 kDa. It is active and stable at 30 °C and pH 7.0. The maximal reaction rate (vmax), apparent Michaelis–Menten constant (Km) for NADH and t-butyl 6-cyano-(5R)-hydroxy-3-oxohexanoate (1a) and catalytic number (kcat) were calculated as 7.63 U mg−1, 0.204 mM, 4.42 mM and 697.4 min−1, respectively. Moreover, the KlAKR has broad substrate specificity to a range of aldehydes, ketones and keto-esters, producing chiral alcohol with e.e. or d.e. >99% for the majority of test substrates. 相似文献
295.
G. A. Gusev K. Kobayashi E. V. Moiseenko N. G. Poluhina T. Saito Tao Ye V. A. Tsarev Jianhua Xu Yan Huang Guobin Zhang 《Origins of life and evolution of the biosphere》2008,38(6):509-515
Results of the second stage of the RAMBAS (RAdiation Mechanism of Biomolecular ASymmetry) experiment on investigation of the
radiation mechanism of the influence on chiral molecules are presented. Optical activity of samples of racemic mixtures of
amino acids with heavy metals was compared prior to and after irradiation by electron flux from a radioactive source. It is
found that the irradiation results in asymmetric degradation of both complexes and amino acids and in production of chiral
asymmetry of the samples under study. These results confirm the conclusions inferred from the first stage of the RAMBAS experiment
and could be important for the solution of the origin-of-life and biological homochirality problems. 相似文献
296.
Toshiyuki Itoh Yumiko Takagi Hiroshi Tsukube 《Journal of Molecular Catalysis .B, Enzymatic》1997,3(6):214-270
The optically active building blocks for organic synthesis: tertiary carbinols, antitumor lignan, liquid crystals, 1,3-diene and biscyclopropyl compounds were synthesized through lipase-catalyzed reaction. This paper discusses ways in which organic chemists can expand the applicability of lipase-catalyzed reactions for use in designing a synthetic strategy. Several excellent examples are described in which lipase-catalyzed reactions were involved as the key steps. Because lipase-catalyzed reactions often offer insufficient enantioselectivity, a new method to enhance the enantioselectivity of a lipase-catalyzed reaction was demonstrated. Thiacrown ether technology was typically used to synthesize new optically active ,-difluoro-γ-lactone. 相似文献
297.
Hongbin Henriksson Jerry Ståhlberg Roland Isaksson Göran Pettersson 《FEBS letters》1996,390(3):339-344
The cellulases cellobiohydrolase 1 (CBH 1) and endoglucanase 1 (EG 1) from the fungus Trichoderma reesei are closely related with 40% sequence identity and very similar in structure. In CBH 1 the active site is enclosed by long loops and some antiparallel β-strands forming a 40 Å long tunnel, whereas in EG 1 part of those loops are missing so that the enzyme has a more common active site groove. Both enzymes were immobilized on silica and these materials were used as chiral stationary phases for chromatographic separation of the enantiomers of two chiral drugs, propranolol and alprenolol. The CBH 1 phase showed much better resolution than did the EG 1 phase, suggesting that the tunnel structure of the protein may play an important role in the chiral separation. The chiral compounds were found to be competitive inhibitors of both enzymes when p-nitrophenyl lactoside (pNPL) was used as substrate. (S)-enantiomers showed stronger inhibitory effects and also longer retention time on the stationary phases than the (R)-enantiomers. The consistency between kinetic data and retention on the stationary phases clearly shows that the enzymatically active sites of CBH 1 and EG 1 are involved in chiral recognition. 相似文献