全文获取类型
收费全文 | 1212篇 |
免费 | 167篇 |
专业分类
1379篇 |
出版年
2021年 | 13篇 |
2017年 | 15篇 |
2016年 | 15篇 |
2015年 | 26篇 |
2014年 | 36篇 |
2013年 | 55篇 |
2012年 | 46篇 |
2011年 | 49篇 |
2010年 | 42篇 |
2009年 | 37篇 |
2008年 | 35篇 |
2007年 | 38篇 |
2006年 | 47篇 |
2005年 | 44篇 |
2004年 | 39篇 |
2003年 | 39篇 |
2002年 | 46篇 |
2001年 | 33篇 |
2000年 | 40篇 |
1999年 | 30篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 17篇 |
1991年 | 35篇 |
1990年 | 28篇 |
1989年 | 31篇 |
1988年 | 18篇 |
1987年 | 33篇 |
1986年 | 24篇 |
1985年 | 16篇 |
1984年 | 20篇 |
1983年 | 43篇 |
1982年 | 24篇 |
1980年 | 10篇 |
1979年 | 20篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1976年 | 17篇 |
1975年 | 20篇 |
1974年 | 14篇 |
1973年 | 16篇 |
1972年 | 9篇 |
1971年 | 12篇 |
1970年 | 11篇 |
1969年 | 11篇 |
1967年 | 9篇 |
1966年 | 10篇 |
排序方式: 共有1379条查询结果,搜索用时 15 毫秒
1.
Frank H. T. Rhodes 《Journal of the history of biology》1987,20(2):139-157
Conclusion The major tenets of the recent hypothesis of punctuated equilibrium are explicit in Darwin's writing. His notes from 1837–1838 contain references to stasis and rapid change. In the first edition of the Origin (1859), Darwin described the importance of isolation of local varieties in the process of speciation. His views on the tempo of speciation were influenced by Hugh Falconer and also, perhaps, by Edward Suess (1831–1914). It is paradoxical that, although both topics were recorded in his unpublished notes of 1837–1838, the second was not explicitly and fully discussed until the fourth edition of the Origin (1866). While no wholly satisfactory explanation of this paradox suggests itself, it seems probable that Falconer's work on the persistence of fossil species of elephant helped Darwin to see the wider significance of the tempo of evolution for his general theory. 相似文献
2.
3.
4.
Human T cell responses to the Epstein-Barr nuclear antigen-1 (EBNA-1) as evaluated by synthetic peptides 总被引:1,自引:0,他引:1
A panel of synthetic peptides derived from Epstein-Barr virus (EBV) nuclear antigen 1 (EB-NA-1) was used to examine human T cell responses to this antigen. In six of seven normal persons with past EBV infection, T cell precursors specific for five peptides (P27, amino acid residues 83-101;P62, 148-166;E31, 353-367;E41, 368-381; and E11, 461-474) were detectable. The precursor frequencies were in the range of 1:20,000 to less than 1:100,000 peripheral blood mononuclear cells as determined by limiting dilution analyses. Only two of these peptides were predicted as alpha-helices; all peptides were glycine-rich. Four other peptides were not reactive in the seven individuals tested. T cell responses were not detectable in donors without prior EBV infection. Infectious mononucleosis patients investigated 4-6 weeks after diagnosis had likewise no detectable peptide-specific T cell precursors. Thus, it appears that T cells recognizing peptides from EBNA-1 arise and persist in people with past EBV infection. 相似文献
5.
6.
Summary Anthraquinones produced by suspension cultures of Cinchona ledgeriana are released into the medium, which becomes saturated with products late in the growth cycle. When a high affinity polymeric adsorbent, such as the macro-reticular Amberlite XAD-7, is added to the culture the concentration of anthraquinone in the medium is maintained at a low level and production may be stimulated 15-fold, yielding up to 20 mg/1/day. More than 90% of the product is released from the cells. For maximal yields it is shown that both the amount of adsorbent used and the time after sub-culture at which it is added to the system are critical. The value of such a method for product recovery from immobilised cells is discussed. 相似文献
7.
8.
9.
A yeast-Escherichia coli shuttle vector containing the M13 origin of replication has been constructed. This vector allows selection and replication in both Saccharomyces cerevisiae and E. coli, as well as single-stranded packaging from E. coli upon infection with a helper phage. The presence of a polylinker with various unique restriction sites facilitates the cloning of desired genes. 相似文献
10.