全文获取类型
收费全文 | 9039篇 |
免费 | 843篇 |
国内免费 | 4篇 |
出版年
2024年 | 10篇 |
2023年 | 43篇 |
2022年 | 90篇 |
2021年 | 164篇 |
2020年 | 122篇 |
2019年 | 165篇 |
2018年 | 163篇 |
2017年 | 162篇 |
2016年 | 254篇 |
2015年 | 492篇 |
2014年 | 481篇 |
2013年 | 539篇 |
2012年 | 783篇 |
2011年 | 751篇 |
2010年 | 418篇 |
2009年 | 405篇 |
2008年 | 593篇 |
2007年 | 546篇 |
2006年 | 537篇 |
2005年 | 537篇 |
2004年 | 508篇 |
2003年 | 450篇 |
2002年 | 391篇 |
2001年 | 130篇 |
2000年 | 86篇 |
1999年 | 111篇 |
1998年 | 103篇 |
1997年 | 76篇 |
1996年 | 66篇 |
1995年 | 58篇 |
1994年 | 67篇 |
1993年 | 35篇 |
1992年 | 57篇 |
1991年 | 49篇 |
1990年 | 41篇 |
1989年 | 33篇 |
1988年 | 39篇 |
1987年 | 25篇 |
1986年 | 24篇 |
1985年 | 26篇 |
1984年 | 35篇 |
1983年 | 26篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1980年 | 14篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1975年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有9886条查询结果,搜索用时 109 毫秒
201.
202.
Wouter L. W. Hazenbos Kimberly K. Kajihara Richard Vandlen J. Hiroshi Morisaki Sophie M. Lehar Mark J. Kwakkenbos Tim Beaumont Arjen Q. Bakker Qui Phung Lee R. Swem Satish Ramakrishnan Janice Kim Min Xu Ishita M. Shah Binh An Diep Tao Sai Andrew Sebrell Yana Khalfin Angela Oh Chris Koth S. Jack Lin Byoung-Chul Lee Magnus Strandh Klaus Koefoed Peter S. Andersen Hergen Spits Eric J. Brown Man-Wah Tan Sanjeev Mariathasan 《PLoS pathogens》2013,9(10)
Infection of host tissues by Staphylococcus aureus and S. epidermidis requires an unusual family of staphylococcal adhesive proteins that contain long stretches of serine-aspartate dipeptide-repeats (SDR). The prototype member of this family is clumping factor A (ClfA), a key virulence factor that mediates adhesion to host tissues by binding to extracellular matrix proteins such as fibrinogen. However, the biological siginificance of the SDR-domain and its implication for pathogenesis remain poorly understood. Here, we identified two novel bacterial glycosyltransferases, SdgA and SdgB, which modify all SDR-proteins in these two bacterial species. Genetic and biochemical data demonstrated that these two glycosyltransferases directly bind and covalently link N-acetylglucosamine (GlcNAc) moieties to the SDR-domain in a step-wise manner, with SdgB appending the sugar residues proximal to the target Ser-Asp repeats, followed by additional modification by SdgA. GlcNAc-modification of SDR-proteins by SdgB creates an immunodominant epitope for highly opsonic human antibodies, which represent up to 1% of total human IgG. Deletion of these glycosyltransferases renders SDR-proteins vulnerable to proteolysis by human neutrophil-derived cathepsin G. Thus, SdgA and SdgB glycosylate staphylococcal SDR-proteins, which protects them against host proteolytic activity, and yet generates major eptopes for the human anti-staphylococcal antibody response, which may represent an ongoing competition between host and pathogen. 相似文献
203.
Yu S. Zhou Sheila Webb Laura Lettice Steve Tardif Fiona Kilanowski Christine Tyrrell Heather MacPherson Fiona Semple Peter Tennant Tina Baker Alan Hart Paul Devenney Paul Perry Tracey Davey Perdita Barran Chris L. Barratt Julia R. Dorin 《PLoS genetics》2013,9(10)
β-defensin peptides are a family of antimicrobial peptides present at mucosal surfaces, with the main site of expression under normal conditions in the male reproductive tract. Although they kill microbes in vitro and interact with immune cells, the precise role of these genes in vivo remains uncertain. We show here that homozygous deletion of a cluster of nine β-defensin genes (DefbΔ9) in the mouse results in male sterility. The sperm derived from the mutants have reduced motility and increased fragility. Epididymal sperm isolated from the cauda should require capacitation to induce the acrosome reaction but sperm from the mutants demonstrate precocious capacitation and increased spontaneous acrosome reaction compared to wild-types but have reduced ability to bind the zona pellucida of oocytes. Ultrastructural examination reveals a defect in microtubule structure of the axoneme with increased disintegration in mutant derived sperm present in the epididymis cauda region, but not in caput region or testes. Consistent with premature acrosome reaction, sperm from mutant animals have significantly increased intracellular calcium content. Thus we demonstrate in vivo that β-defensins are essential for successful sperm maturation, and their disruption leads to alteration in intracellular calcium, inappropriate spontaneous acrosome reaction and profound male infertility. 相似文献
204.
Samantha Wilkinson Zen H. Lu Hendrik-Jan Megens Alan L. Archibald Chris Haley Ian J. Jackson Martien A. M. Groenen Richard P. M. A. Crooijmans Rob Ogden Pamela Wiener 《PLoS genetics》2013,9(4)
Following domestication, livestock breeds have experienced intense selection pressures for the development of desirable traits. This has resulted in a large diversity of breeds that display variation in many phenotypic traits, such as coat colour, muscle composition, early maturity, growth rate, body size, reproduction, and behaviour. To better understand the relationship between genomic composition and phenotypic diversity arising from breed development, the genomes of 13 traditional and commercial European pig breeds were scanned for signatures of diversifying selection using the Porcine60K SNP chip, applying a between-population (differentiation) approach. Signatures of diversifying selection between breeds were found in genomic regions associated with traits related to breed standard criteria, such as coat colour and ear morphology. Amino acid differences in the EDNRB gene appear to be associated with one of these signatures, and variation in the KITLG gene may be associated with another. Other selection signals were found in genomic regions including QTLs and genes associated with production traits such as reproduction, growth, and fat deposition. Some selection signatures were associated with regions showing evidence of introgression from Asian breeds. When the European breeds were compared with wild boar, genomic regions with high levels of differentiation harboured genes related to bone formation, growth, and fat deposition. 相似文献
205.
Margaret C. Stanley Helen W. Nathan Lara K. Phillips Sarah J. Knight Josie A. Galbraith Chris J. Winks Darren F. Ward 《Arthropod-Plant Interactions》2013,7(1):59-67
The direct and indirect interactions of invasive ants with plants, insect herbivores, and Hemiptera are complex. While ant and Hemiptera interactions with native plants have been well studied, the effects of invasive ant–scale insect mutualisms on the reproductive output of invasive weeds have not. The study system consisted of Argentine ants (Linepithema humile), boneseed (Chrysanthemoides monilifera monilifera), and sap-sucking scale insects (Hemiptera: Saissetia oleae and Parasaissetia nigra), all of which are invasive in New Zealand. We examined the direct and indirect effects of Argentine ants on scale insects and other invertebrates (especially herbivores) and on plant reproductive output. Argentine ants spent one-third of their time specifically associated with scale insects in tending behaviours. The invertebrate community was significantly different between uninfested and infested plants, with fewer predators and herbivores on ant-infested plants. Herbivore damage was significantly reduced on plants with Argentine ants, but sooty mould colonisation was greater where ants were present. Herbivore damage increased when ants were excluded from plants. Boneseed plants infested with Argentine ants produced significantly more fruits than plants without ants. The increase in reproductive output in the presence of ants may be due to increased pollination as the result of pollinators being forced to relocate frequently to avoid attack by ants, resulting in an increase in pollen transfer and higher fruit/seed set. The consequences of Argentine ant invasion can be varied; not only does their invasion have consequences for maintaining biodiversity, ant invasion may also affect weed and pest management strategies. 相似文献
206.
207.
Idrish Ali Patrick O'Brien Gaurav Kumar Thomas Zheng Nigel C. Jones Didier Pinault Chris French Margaret J. Morris Michael R. Salzberg Terence J. O'Brien 《PloS one》2013,8(6)
Early life stress results in an enduring vulnerability to kindling-induced epileptogenesis in rats, but the underlying mechanisms are not well understood. Recent studies indicate the involvement of thalamocortical neuronal circuits in the progression of kindling epileptogenesis. Therefore, we sought to determine in vivo the effects of early life stress and amygdala kindling on the firing pattern of hippocampus as well as thalamic and cortical neurons. Eight week old male Wistar rats, previously exposed to maternal separation (MS) early life stress or early handling (EH), underwent amygdala kindling (or sham kindling). Once fully kindled, in vivo juxtacellular recordings in hippocampal, thalamic and cortical regions were performed under neuroleptic analgesia. In the thalamic reticular nucleus cells both kindling and MS independently lowered firing frequency and enhanced burst firing. Further, burst firing in the thalamic reticular nucleus was significantly increased in kindled MS rats compared to kindled EH rats (p<0.05). In addition, MS enhanced burst firing of hippocampal pyramidal neurons. Following a stimulation-induced seizure, somatosensory cortical neurons exhibited a more pronounced increase in burst firing in MS rats than in EH rats. These data demonstrate changes in firing patterns in thalamocortical and hippocampal regions resulting from both MS and amygdala kindling, which may reflect cellular changes underlying the enhanced vulnerability to kindling in rats that have been exposed to early life stress. 相似文献
208.
Aylwyn Scally Bryndis Yngvadottir Yali Xue Qasim Ayub Richard Durbin Chris Tyler-Smith 《PloS one》2013,8(6)
All non-human great apes are endangered in the wild, and it is therefore important to gain an understanding of their demography and genetic diversity. Whole genome assembly projects have provided an invaluable foundation for understanding genetics in all four genera, but to date genetic studies of multiple individuals within great ape species have largely been confined to mitochondrial DNA and a small number of other loci. Here, we present a genome-wide survey of genetic variation in gorillas using a reduced representation sequencing approach, focusing on the two lowland subspecies. We identify 3,006,670 polymorphic sites in 14 individuals: 12 western lowland gorillas (Gorilla gorilla gorilla) and 2 eastern lowland gorillas (Gorilla beringei graueri). We find that the two species are genetically distinct, based on levels of heterozygosity and patterns of allele sharing. Focusing on the western lowland population, we observe evidence for population substructure, and a deficit of rare genetic variants suggesting a recent episode of population contraction. In western lowland gorillas, there is an elevation of variation towards telomeres and centromeres on the chromosomal scale. On a finer scale, we find substantial variation in genetic diversity, including a marked reduction close to the major histocompatibility locus, perhaps indicative of recent strong selection there. These findings suggest that despite their maintaining an overall level of genetic diversity equal to or greater than that of humans, population decline, perhaps associated with disease, has been a significant factor in recent and long-term pressures on wild gorilla populations. 相似文献
209.
210.
Chun-Ho Yun Hiram G. Bezerra Tung-Hsin Wu Fei-Shih Yang Chuan-Chuan Liu Yih-Jer Wu Jen-Yuan Kuo Chung-Lieh Hung Jason Jeun-Shenn Lee Charles Jia-Yin Hou Hung-I Yeh Chris T. Longenecker Ricardo C. Cury 《PloS one》2013,8(4)