全文获取类型
收费全文 | 1760篇 |
免费 | 175篇 |
国内免费 | 197篇 |
出版年
2024年 | 6篇 |
2023年 | 40篇 |
2022年 | 61篇 |
2021年 | 81篇 |
2020年 | 99篇 |
2019年 | 85篇 |
2018年 | 81篇 |
2017年 | 53篇 |
2016年 | 70篇 |
2015年 | 72篇 |
2014年 | 80篇 |
2013年 | 127篇 |
2012年 | 59篇 |
2011年 | 82篇 |
2010年 | 67篇 |
2009年 | 95篇 |
2008年 | 84篇 |
2007年 | 104篇 |
2006年 | 101篇 |
2005年 | 75篇 |
2004年 | 65篇 |
2003年 | 70篇 |
2002年 | 60篇 |
2001年 | 40篇 |
2000年 | 48篇 |
1999年 | 29篇 |
1998年 | 21篇 |
1997年 | 23篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 23篇 |
1983年 | 7篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 13篇 |
1973年 | 4篇 |
排序方式: 共有2132条查询结果,搜索用时 62 毫秒
1.
S. Usha 《Journal of biomolecular structure & dynamics》2013,31(7):1474-1492
We have analyzed the nonbonded interactions of the structurally similar moieties, adenine and guanine forming complexes with proteins. The results comprise (a) the amino acid–ligand atom preferences, (b) solvent accessibility of ligand atoms before and after complex formation with proteins, and (c) preferred amino acid residue atoms involved in the interactions. We have observed that the amino acid preferences involved in the hydrogen bonding interactions vary for adenine and guanine. The structural variation between the purine atoms is clearly reflected by their burial tendency in the solvent environment. Correlation of the mean amino acid preference values show the variation that exists between adenine and guanine preferences of all the amino acid residues. All our observations provide evidence for the discriminating nature of the proteins in recognizing adenine and guanine. 相似文献
2.
H. Chen L. Wang C.X. Su G.H. Gong P. Wang Z.L. Yu 《Letters in applied microbiology》2008,47(3):180-186
Aims: Antibiotics from Bacillus subtilis JA show strong pathogen inhibition ability, which has potential market application; yet, the composition of these antibiotics has not been elucidated. The aim of this paper is to isolate and identify these antibiotics.
Methods and Results: The antagonistic activity of JA was tested in vitro ; it exhibited strong inhibition against some important phytopathogens and postharvest pathogens. Crude antibiotic production was extracted with methanol from the precipitate by adding 6 mol l−1 HCl to the bacillus-free culture broth. The crude extract was run on Diamonsil C18 column (5 μ m, 250 × 4·6 mm) in HPLC system to separate the antibiotics. Major antibiotics were classified into three lipopeptide families according to electrospray ionization–mass spectrometry analysis. Subsequently, the classification of antibiotics was confirmed with typical collision-induced dissociation fragments.
Conclusions: Three kinds of antibiotics were isolated from B. subtilis JA and were identified to the lipopeptide families, surfactin, iturin and fengycin. These compounds could function as biocontrol agents against a large spectrum of pathogens.
Significance and Impact of the Study: This study provided a reliable and rapid method for isolation and structural characterization of lipopeptide antibiotics from B. subtilis . 相似文献
Methods and Results: The antagonistic activity of JA was tested in vitro ; it exhibited strong inhibition against some important phytopathogens and postharvest pathogens. Crude antibiotic production was extracted with methanol from the precipitate by adding 6 mol l
Conclusions: Three kinds of antibiotics were isolated from B. subtilis JA and were identified to the lipopeptide families, surfactin, iturin and fengycin. These compounds could function as biocontrol agents against a large spectrum of pathogens.
Significance and Impact of the Study: This study provided a reliable and rapid method for isolation and structural characterization of lipopeptide antibiotics from B. subtilis . 相似文献
3.
4.
Ding-Kwo Chang Shu-Fang Cheng Chi-Hui Lin EricAssen B. Kantchev Cheng-Wei Wu 《生物化学与生物物理学报:生物膜》2005,1712(1):37-51
Two glutamic acid-rich fusion peptide analogs of influenza hemagglutinin were synthesized to study the organization of the charged peptides in the membranous media. Fluorescence and gel electrophoresis experiments suggested a loose association between the monomers in the vesicles. A model was built which showed that a positional difference of 3, 7 and 4, 8 results in the exposure of Glu3 and Glu7 side chains to the apolar lipidic core. Supportive results include: first, pKa values of two pH units higher than reference value in aqueous medium for Glu3 and Glu7 CγH, whereas the deviation of pKa from the reference value for Glu4 and Glu8 CγH is substantially smaller; second, Hill coefficients of titration shift of these protons indicate anti-cooperativity for Glu3 and Glu7 side chain protons but less so for Glu4 and Glu8, implying a strong electrostatic interaction between Glu3 and Glu7 possibly resulting from their localization in an apolar environment; third, positive and larger titration shift for NH of Glu3 is observed compared to that of Glu4, suggesting stronger hydrogen bond between the NH and the carboxylic group of Glu3 than that of Glu4, consistent with higher degree of exposure to hydrophobic medium for the side chain of Glu3. 相似文献
5.
Michael A. Borowitzka 《Journal of applied phycology》1995,7(1):3-15
In the last decade the screening of microalgae, especially the cyanobacteria (blue-green algae), for antibiotics and pharmacologically
active compounds has received ever increasing interest. A large number of antibiotic compounds, many with novel structures,
have been isolated and characterised. Similarly many cyanobacteria have been shown to produce antiviral and antineoplastic
compounds. A range of pharmacological activities have also been observed with extracts of microalgae, however the active principles
are as yet unknown in most cases. Several of the bioactive compounds may find application in human or veterinary medicine
or in agriculture. Others should find application as research tools or as structural models for the development of new drugs.
The microalgae are particularly attractive as natural sources of bioactive molecules since these algae have the potential
to produce these compounds in culture which enables the production of structurally complex molecules which are difficult or
impossible to produce by chemical synthesis. 相似文献
6.
7.
8.
The nucleoside antibiotic, 3′-azido-3′-deoxythymidine, or simply, azidothymidine has shown great promise in inhibiting the
human immuno deficiency virus and in reducing mortality among AIDS patients. Conformational properties of azidothymidine have
been investigated by quantum-mechanical PCILO method and compared with those of the parent nucleoside, thymidine. The results
indicate great similarity between them and this similarity is remarkably striking in the situations that prevail in aqueous
solution. This result has important biological significance in explaining the drug action of azidothymidine. 相似文献
9.
The α -toxin (phospholipase C) of Clostridium perfringens has been reported to contain catalytically essential zinc ions We report here that histidine residues are essential for the co-ordination of these ion(s). Incubation of alpha toxin with diethylpyrocarbonate, a histidine modifying reagent, did not result in the loss of phospholipase C activity unless the protein was first incubated with EDTA, suggesting that zinc ions normally protect the susceptible histidine residues. When the amino acid sequences of three phospholipase C's were aligned, essential zinc binding histidine residues in the non-toxic B. cereus phospholipase C were found in similar positions in the toxic C. perfringens enzyme and the weakly toxic C. bifermentans phospholipase C. 相似文献
10.