全文获取类型
收费全文 | 502篇 |
免费 | 64篇 |
国内免费 | 2篇 |
专业分类
568篇 |
出版年
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 17篇 |
2014年 | 17篇 |
2013年 | 21篇 |
2012年 | 27篇 |
2011年 | 21篇 |
2010年 | 25篇 |
2009年 | 13篇 |
2008年 | 30篇 |
2007年 | 12篇 |
2006年 | 22篇 |
2005年 | 23篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 21篇 |
2000年 | 18篇 |
1999年 | 12篇 |
1998年 | 14篇 |
1997年 | 12篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 13篇 |
1991年 | 18篇 |
1990年 | 5篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 17篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1972年 | 5篇 |
1969年 | 3篇 |
排序方式: 共有568条查询结果,搜索用时 15 毫秒
41.
42.
Hentschel U Schmid M Wagner M Fieseler L Gernert C Hacker J 《FEMS microbiology ecology》2001,35(3):305-312
The aim of this study was to isolate bacteria with antimicrobial activities from the marine sponges Aplysina aerophoba and Aplysina cavernicola. The obtained 27 isolates could be subdivided into eight phylogenetically different clusters based on comparative sequence analysis of their 16S rDNA genes. The sponge isolates were affiliated with the low (Bacillus) and high G+C Gram-positive bacteria (Arthobacter, Micrococcus), as well as the alpha-Proteobacteria (unknown isolate) and gamma-Proteobacteria (Vibrio, Pseudoalteromonas). One novel Bacillus species was identified and two species were closely related to previously uncharacterized strains. Isolates with antimicrobial activity were numerically most abundant in the genera Pseudoalteromonas and the alpha-Proteobacteria. The sponge isolates show antimicrobial activities against Gram-positive and Gram-negative reference strains but not against the fungus Candida albicans. A general pattern was observed in that Gram-positive bacteria inhibited Gram-positive strains while Gram-negative bacteria inhibited Gram-negative isolates. Antimicrobial activities were also found against clinical isolates, i.e. multi-resistant Staphylococcus aureus and Staphylococcus epidermidis strains isolated from hospital patients. The high recovery of strains with antimicrobial activity suggests that marine sponges represent an ecological niche which harbors a hitherto largely uncharacterized microbial diversity and, concomitantly, a yet untapped metabolic potential. 相似文献
43.
Traditionally, symbiotic and pathogenic interactions were considered different manifestations of the bacteria-host interaction. However, the molecular mechanisms that mediate communication between and cellular modulation of the involved partners are quite similar. With this review we aim to contribute to a reduction of the traditional gap between symbiosis and pathogenesis research. 相似文献
44.
45.
Evolutionary distances for protein-coding sequences: modeling site- specific residue frequencies 总被引:13,自引:8,他引:5
Estimation of evolutionary distances from coding sequences must take into
account protein-level selection to avoid relative underestimation of longer
evolutionary distances. Current modeling of selection via site-to-site rate
heterogeneity generally neglects another aspect of selection, namely
position-specific amino acid frequencies. These frequencies determine the
maximum dissimilarity expected for highly diverged but functionally and
structurally conserved sequences, and hence are crucial for estimating long
distances. We introduce a codon- level model of coding sequence evolution
in which position-specific amino acid frequencies are free parameters. In
our implementation, these are estimated from an alignment using methods
described previously. We use simulations to demonstrate the importance and
feasibility of modeling such behavior; our model produces linear distance
estimates over a wide range of distances, while several alternative models
underestimate long distances relative to short distances. Site-to-site
differences in rates, as well as synonymous/nonsynonymous and
first/second/third-codon-position differences, arise as a natural
consequence of the site-to-site differences in amino acid frequencies.
相似文献
46.
47.
BUALUANG FAIYUE MOHAMMED J. AL‐AZZAWI TIMOTHY J. FLOWERS 《Plant, cell & environment》2010,33(5):702-716
Although an apoplastic pathway (the so‐called bypass flow) is implicated in the uptake of Na+ by rice growing in saline conditions, the point of entry of this flow into roots remains to be elucidated. We investigated the role of lateral roots in bypass flow using the tracer trisodium‐8‐hydroxy‐1,3,6‐pyrenetrisulphonic acid (PTS) and the rice cv. IR36. PTS was identified in the vascular tissue of lateral roots using both epifluorescence microscopy and confocal laser scanning microscopy. Cryo‐scanning electron microscopy and epifluorescence microscopy of sections stained with berberine‐aniline blue revealed that the exodermis is absent in the lateral roots. We conclude that PTS can move freely through the cortical layers of lateral roots, enter the stele and be transported to the shoot via the transpiration stream. 相似文献
48.
Response of the elm leaf beetle to host plants induced by oviposition and feeding: the infestation rate matters 总被引:5,自引:0,他引:5
T. Meiners N.K. Hacker P. Anderson & M. Hilker 《Entomologia Experimentalis et Applicata》2005,115(1):171-177
We investigated by olfactometry and feeding‐ and oviposition‐choice‐tests how the highly specialised elm leaf beetle, Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), responds to conspecifically induced defences in the field elm Ulmus minor Miller (Ulmaceae). While egg deposition of the beetle induced elms to release volatiles attractive to the egg parasitoid Oomyzus gallerucae Fonscolombe (Hymenoptera: Eulophidae), feeding alone did not. In the present study, females of the elm leaf beetle showed preferences for the odours of twigs induced by low egg deposition and feeding over odours from uninfested twigs. In contrast, heavy infestation rendered elm odours less attractive to the beetles. Feeding and oviposition bioassays revealed an oviposition preference for leaves from uninfested twigs when compared to locally infested leaves. However, beetles preferred to feed upon systemically induced leaves compared to uninfested ones. The different preferences of the elm leaf beetle during host plant approach might be explained by a strategy that accounts for both gaining access to high quality nutrition and avoiding competition or parasitism. 相似文献
49.
The expansion of the biologics pipeline depends on the identification of candidate proteins for clinical trials. Speed is one of the critical issues, and the rapid production of high quality, research-grade material for preclinical studies by transient gene expression (TGE) is addressing this factor in an impressive way: following DNA transfection, the production phase for TGE is usually 2-10 days. Recombinant proteins (r-proteins) produced by TGE can therefore enter the drug development and screening process in a very short time--weeks. With "classical" approaches to protein expression from mammalian cells, it takes months to establish a productive host cell line. This article summarizes efforts in industry and academia to use TGE to produce tens to hundreds of milligrams of r-proteins for either fundamental research or preclinical studies. 相似文献
50.
Defining the cause of skewed X-chromosome inactivation in X-linked mental retardation by use of a mouse model 总被引:1,自引:0,他引:1 下载免费PDF全文
Muers MR Sharpe JA Garrick D Sloane-Stanley J Nolan PM Hacker T Wood WG Higgs DR Gibbons RJ 《American journal of human genetics》2007,80(6):1138-1149
Extreme skewing of X-chromosome inactivation (XCI) is rare in the normal female population but is observed frequently in carriers of some X-linked mutations. Recently, it has been shown that various forms of X-linked mental retardation (XLMR) have a strong association with skewed XCI in female carriers, but the mechanisms underlying this skewing are unknown. ATR-X syndrome, caused by mutations in a ubiquitously expressed, chromatin-associated protein, provides a clear example of XLMR in which phenotypically normal female carriers virtually all have highly skewed XCI biased against the X chromosome that harbors the mutant allele. Here, we have used a mouse model to understand the processes causing skewed XCI. In female mice heterozygous for a null Atrx allele, we found that XCI is balanced early in embryogenesis but becomes skewed over the course of development, because of selection favoring cells expressing the wild-type Atrx allele. Unexpectedly, selection does not appear to be the result of general cellular-viability defects in Atrx-deficient cells, since it is restricted to specific stages of development and is not ongoing throughout the life of the animal. Instead, there is evidence that selection results from independent tissue-specific effects. This illustrates an important mechanism by which skewed XCI may occur in carriers of XLMR and provides insight into the normal role of ATRX in regulating cell fate. 相似文献