全文获取类型
收费全文 | 2444篇 |
免费 | 284篇 |
国内免费 | 3篇 |
出版年
2021年 | 27篇 |
2018年 | 23篇 |
2017年 | 22篇 |
2016年 | 27篇 |
2015年 | 43篇 |
2014年 | 63篇 |
2013年 | 68篇 |
2012年 | 91篇 |
2011年 | 119篇 |
2010年 | 63篇 |
2009年 | 59篇 |
2008年 | 75篇 |
2007年 | 84篇 |
2006年 | 63篇 |
2005年 | 80篇 |
2004年 | 77篇 |
2003年 | 76篇 |
2002年 | 76篇 |
2001年 | 82篇 |
2000年 | 72篇 |
1999年 | 74篇 |
1998年 | 40篇 |
1997年 | 36篇 |
1996年 | 37篇 |
1995年 | 31篇 |
1994年 | 29篇 |
1993年 | 39篇 |
1992年 | 57篇 |
1991年 | 63篇 |
1990年 | 63篇 |
1989年 | 62篇 |
1988年 | 43篇 |
1987年 | 53篇 |
1986年 | 31篇 |
1985年 | 45篇 |
1984年 | 30篇 |
1983年 | 38篇 |
1982年 | 32篇 |
1981年 | 27篇 |
1979年 | 45篇 |
1978年 | 35篇 |
1977年 | 36篇 |
1976年 | 36篇 |
1975年 | 20篇 |
1974年 | 35篇 |
1973年 | 33篇 |
1972年 | 32篇 |
1971年 | 25篇 |
1969年 | 22篇 |
1967年 | 24篇 |
排序方式: 共有2731条查询结果,搜索用时 15 毫秒
971.
T. Armstrong Bowes 《BMJ (Clinical research ed.)》1897,2(1912):463-464
972.
973.
974.
975.
976.
977.
The flowering of Myristica insipida R. Br. was studied in two rain forest communities in northern Queensland. This dioecious, subcanopy tree had a male-biased sex ratio at both study sites. In the lowland population the male-bias could be attributed to males (trees producing staminate flowers) starting to flower at a smaller average size than females (trees producing pistillate flowers). There were no intersexual differences in spacing or distribution within the study sites. Males trees flowered earlier, flowered longer, and produced over twice as many flowers as females during the study season. Although the onset of flowering was rather variable, 18–22 days following heavy rains, most trees had a synchronous period of maximum flowering. Pollination manipulations determined that there was no fruit development without pollination, and that increasing pollen loads resulted in increased fruit set with diminishing effect. Taking into account the sex-ratios and intersexual differences in flower production, the pollen-ovule ratio was calculated to be 16,000–19,000. Male trees were found to expend more energy on flowering than female trees. Open-pollination resulted in 1.0% of female flowers setting fruit. The much greater cost of fruit production resulted in females expending 421% more energy on reproduction than males. Fruit and seed production were judged to be pollination-limited. Nonetheless, this species exhibited several characteristics that are predicted if dioecy evolved by means of sexual selection. 相似文献
978.
979.
980.
Function of the ypt2 gene in the exocytic pathway of Schizosaccharomyces pombe. 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Molecular biology of the cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The ypt2 gene of the fission yeast Schizosaccharomyces pombe encodes a member of the ypt/rab family of small GTP-binding proteins, related in sequence to Sec4p of Saccharomyces cerevisiae but closer to mammalian rab8. We have introduced a mutation into the gene corresponding to a mutation identified in ypt1, in which a conserved valine residue was altered to asparagine. The mutated ypt2 gene was introduced into the S. pombe genome by gene replacement. The resulting strain was temperature-sensitive for growth. Normal growth was restored by introduction of a plasmid-borne wild-type ypt2 cDNA or by cDNA for rab8 but not by various other rab or ypt sequences. At restrictive temperature the mutant cells accumulated the secretory protein acid phosphatase in a form that appeared to be fully glycosylated and acquired a population of vesicles detectable by electron microscopy. Thus the ypt2 protein, and by inference rab8, appear to function in the last stage of the secretory pathway. 相似文献