全文获取类型
收费全文 | 1210篇 |
免费 | 141篇 |
国内免费 | 1篇 |
专业分类
1352篇 |
出版年
2021年 | 14篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 15篇 |
2017年 | 15篇 |
2016年 | 20篇 |
2015年 | 44篇 |
2014年 | 45篇 |
2013年 | 49篇 |
2012年 | 76篇 |
2011年 | 70篇 |
2010年 | 57篇 |
2009年 | 44篇 |
2008年 | 53篇 |
2007年 | 76篇 |
2006年 | 56篇 |
2005年 | 78篇 |
2004年 | 74篇 |
2003年 | 80篇 |
2002年 | 61篇 |
2001年 | 21篇 |
2000年 | 27篇 |
1999年 | 31篇 |
1998年 | 11篇 |
1997年 | 17篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 15篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1976年 | 8篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1972年 | 8篇 |
1970年 | 6篇 |
1964年 | 5篇 |
1953年 | 6篇 |
排序方式: 共有1352条查询结果,搜索用时 15 毫秒
101.
102.
Biological and molecular characterizations of Toxoplasma gondii strains obtained from southern sea otters (Enhydra lutris nereis) 总被引:2,自引:0,他引:2
Cole RA Lindsay DS Howe DK Roderick CL Dubey JP Thomas NJ Baeten LA 《The Journal of parasitology》2000,86(3):526-530
Toxoplasma gondii was isolated from brain or heart tissue from 15 southern sea otters (Enhydra lutris nereis) in cell cultures. These strains were used to infect mice that developed antibodies to T. gondii as detected in the modified direct agglutination test and had T. gondii tissue cysts in their brains at necropsy. Mouse brains containing tissue cysts from 4 of the strains were fed to 4 cats. Two of the cats excreted T. gondii oocysts in their feces that were infectious for mice. Molecular analyses of 13 strains indicated that they were all type II strains, but that they were genetically distinct from one another. 相似文献
103.
Mostoslavsky R Chua KF Lombard DB Pang WW Fischer MR Gellon L Liu P Mostoslavsky G Franco S Murphy MM Mills KD Patel P Hsu JT Hong AL Ford E Cheng HL Kennedy C Nunez N Bronson R Frendewey D Auerbach W Valenzuela D Karow M Hottiger MO Hursting S Barrett JC Guarente L Mulligan R Demple B Yancopoulos GD Alt FW 《Cell》2006,124(2):315-329
The Sir2 histone deacetylase functions as a chromatin silencer to regulate recombination, genomic stability, and aging in budding yeast. Seven mammalian Sir2 homologs have been identified (SIRT1-SIRT7), and it has been speculated that some may have similar functions to Sir2. Here, we demonstrate that SIRT6 is a nuclear, chromatin-associated protein that promotes resistance to DNA damage and suppresses genomic instability in mouse cells, in association with a role in base excision repair (BER). SIRT6-deficient mice are small and at 2-3 weeks of age develop abnormalities that include profound lymphopenia, loss of subcutaneous fat, lordokyphosis, and severe metabolic defects, eventually dying at about 4 weeks. We conclude that one function of SIRT6 is to promote normal DNA repair, and that SIRT6 loss leads to abnormalities in mice that overlap with aging-associated degenerative processes. 相似文献
104.
Mycoplasma pneumoniae and Mycoplasma salivarium: Electron Microscopy of Colony Growth in Agar 总被引:1,自引:3,他引:1 下载免费PDF全文
Colonies of Mycoplasma pneumoniae and Mycoplasma salivarium grown in PPLO agar were examined by light and electron microscopy. The main objective of the investigation was to attempt in situ fixation and minimize tonic changes in the organisms. Microscopy revealed that both organisms grew both in and upon the agar. The agar and surface growths of M. pneumoniae exhibited similar profiles, whereas those of M. salivarium differed strikingly. Both organisms are highly pleomorphic, but their matrix was denser and appeared more intact than in previously reported profiles. Cells which resemble the commonly reported mycoplasma were occasionally observed. The significance of these discrepant profiles remains unanswered. It is suggested that they may represent aged or osmotically damaged cells. 相似文献
105.
106.
Modise T Ryder C Mane SP Bandara AB Jensen RV Inzana TJ 《Journal of bacteriology》2012,194(10):2775-2776
We report the complete genome sequences of TI0902, a highly virulent type A1 strain, and TIGB03, a related, attenuated chemical mutant strain. Compared to the wild type, the mutant strain had 45 point mutations and a 75.9-kb duplicated region that had not been previously observed in Francisella species. 相似文献
107.
Calcium signalling: dynamics,homeostasis and remodelling 总被引:1,自引:0,他引:1
Ca2+ is a highly versatile intracellular signal that operates over a wide temporal range to regulate many different cellular processes. An extensive Ca2+-signalling toolkit is used to assemble signalling systems with very different spatial and temporal dynamics. Rapid highly localized Ca2+ spikes regulate fast responses, whereas slower responses are controlled by repetitive global Ca2+ transients or intracellular Ca2+ waves. Ca2+ has a direct role in controlling the expression patterns of its signalling systems that are constantly being remodelled in both health and disease. 相似文献
108.
Mackie RI Rycyk M Ruemmler RL Aminov RI Wikelski M 《Physiological and biochemical zoology : PBZ》2004,77(1):127-138
Herbivorous lizards are potentially capable of high digestive efficiency, but the presence of an indigenous microbial population has been implied from measurements of activity rather than directly studied. This study is the first to provide direct biochemical and microbiological evidence for fermentative digestion in free-living land iguanas (Conolophus pallidus) and marine iguanas (Amblyrhynchus cristatus) from the Galapagos archipelago. In marine iguanas, the stomach and large capacious colon contained ca. 32% and 60%, respectively, of the weight of total gut content. Total volatile fatty acid concentration was ca. 150 and 180 mM, respectively, for marine and land iguanas. Molar proportions of acetate, propionate, and butyrate (80.3%, 9.5%, and 3.5%) in land iguana fecal samples were similar to those for marine iguanas. Examination of fecal samples using confocal and transmission electron microscopy, as well as cultivable counts, revealed a dense and diverse population of bacteria, with spores prominent. Total culturable counts of anaerobes (2.22x10(8) g(-1) wet weight of fecal material) outnumbered aerobes on average by a factor of ca. 700. Combined, these results strongly support the contention that these unique herbivorous lizards are largely dependent on the presence and metabolic activities of a resident bacterial population in order to hydrolyze and ferment plant polymers that are indigestible to the host. 相似文献
109.
Roderick C. Slieker Matthias S. Roost Liesbeth van Iperen H. Eka D. Suchiman Elmar W. Tobi Fran?oise Carlotti Eelco J. P. de Koning P. Eline Slagboom Bastiaan T. Heijmans Susana M. Chuva de Sousa Lopes 《PLoS genetics》2015,11(10)
Remodelling the methylome is a hallmark of mammalian development and cell differentiation. However, current knowledge of DNA methylation dynamics in human tissue specification and organ development largely stems from the extrapolation of studies in vitro and animal models. Here, we report on the DNA methylation landscape using the 450k array of four human tissues (amnion, muscle, adrenal and pancreas) during the first and second trimester of gestation (9,18 and 22 weeks). We show that a tissue-specific signature, constituted by tissue-specific hypomethylated CpG sites, was already present at 9 weeks of gestation (W9). Furthermore, we report large-scale remodelling of DNA methylation from W9 to W22. Gain of DNA methylation preferentially occurred near genes involved in general developmental processes, whereas loss of DNA methylation mapped to genes with tissue-specific functions. Dynamic DNA methylation was associated with enhancers, but not promoters. Comparison of our data with external fetal adrenal, brain and liver revealed striking similarities in the trajectory of DNA methylation during fetal development. The analysis of gene expression data indicated that dynamic DNA methylation was associated with the progressive repression of developmental programs and the activation of genes involved in tissue-specific processes. The DNA methylation landscape of human fetal development provides insight into regulatory elements that guide tissue specification and lead to organ functionality. 相似文献
110.
Rita Barallon Steven R. Bauer John Butler Amanda Capes-Davis Wilhelm G. Dirks Eugene Elmore Manohar Furtado Margaret C. Kline Arihiro Kohara Georgyi V. Los Roderick A. F. MacLeod John R. W. Masters Mark Nardone Roland M. Nardone Raymond W. Nims Paul J. Price Yvonne A. Reid Jaiprakash Shewale Gregory Sykes Anton F. Steuer Douglas R. Storts Jim Thomson Zenobia Taraporewala Christine Alston-Roberts Liz Kerrigan 《In vitro cellular & developmental biology. Animal》2010,46(9):727-732
Cell misidentification and cross-contamination have plagued biomedical research for as long as cells have been employed as research tools. Examples of misidentified cell lines continue to surface to this day. Efforts to eradicate the problem by raising awareness of the issue and by asking scientists voluntarily to take appropriate actions have not been successful. Unambiguous cell authentication is an essential step in the scientific process and should be an inherent consideration during peer review of papers submitted for publication or during review of grants submitted for funding. In order to facilitate proper identity testing, accurate, reliable, inexpensive, and standardized methods for authentication of cells and cell lines must be made available. To this end, an international team of scientists is, at this time, preparing a consensus standard on the authentication of human cells using short tandem repeat (STR) profiling. This standard, which will be submitted for review and approval as an American National Standard by the American National Standards Institute, will provide investigators guidance on the use of STR profiling for authenticating human cell lines. Such guidance will include methodological detail on the preparation of the DNA sample, the appropriate numbers and types of loci to be evaluated, and the interpretation and quality control of the results. Associated with the standard itself will be the establishment and maintenance of a public STR profile database under the auspices of the National Center for Biotechnology Information. The consensus standard is anticipated to be adopted by granting agencies and scientific journals as appropriate methodology for authenticating human cell lines, stem cells, and tissues. 相似文献