全文获取类型
收费全文 | 2132篇 |
免费 | 171篇 |
专业分类
2303篇 |
出版年
2023年 | 17篇 |
2022年 | 34篇 |
2021年 | 58篇 |
2020年 | 39篇 |
2019年 | 51篇 |
2018年 | 40篇 |
2017年 | 53篇 |
2016年 | 67篇 |
2015年 | 102篇 |
2014年 | 130篇 |
2013年 | 162篇 |
2012年 | 202篇 |
2011年 | 197篇 |
2010年 | 104篇 |
2009年 | 92篇 |
2008年 | 120篇 |
2007年 | 140篇 |
2006年 | 132篇 |
2005年 | 108篇 |
2004年 | 102篇 |
2003年 | 79篇 |
2002年 | 75篇 |
2001年 | 22篇 |
2000年 | 14篇 |
1999年 | 21篇 |
1998年 | 33篇 |
1997年 | 18篇 |
1996年 | 5篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1962年 | 1篇 |
1936年 | 1篇 |
1929年 | 1篇 |
1928年 | 1篇 |
1926年 | 1篇 |
1925年 | 1篇 |
排序方式: 共有2303条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
5.
6.
7.
Parthenogenesis in Tubificidae 总被引:2,自引:2,他引:0
Tamara L. Poddubnaya 《Hydrobiologia》1984,115(1):97-99
The ability of tubificids to reproduce parthenogenetically following or in place of bisexual reproduction has been proved. During parthenogenesis the spermatogenesis ceases at an early stage of sexual cell development, which, together with some peculiarities of the structure of the sexual system, rules out the possibility of self-fertilization in the worms. For two years of cultivation the life cycles of 3 parthenogenetic generations in Tubifex tubifex and 2 in Limnodrilus hoffmeisteri were traced. 相似文献
8.
9.
Summary We have improved zygote recovery 11–1,000 fold by optimizing the physiology of gamete release and mating inAcetabularia acetabulum. Gamete release was affected by agar purity, concentration, and volume/gametangial pair. Cold pre-treatment of gametangia (14–30 d at 10°C in the dark) synchronized subsequent gamete release at 21°C in the light. Cold pre-treatment was nearly twice as effective in synchronizing subsequent gamete release when intact, gametangia-bearing caps rather than isolated gametangia were pretreated. Synchronizing gamete release doubled mating efficiency. In a wild-type laboratory strain ofA. acetabulum, there were 1,561±207 gametes/gametangium which had half-lives of 14.5 d in 0.1% seawater-agar. We recovered 48–93% of the expected numbers of zygotes from a mass mating of 8 to 1,226 gametangia and 11–128% of the expected numbers of zygotes from mating single gametangial pairs: the large range in the calculated mating efficiency may be attributable to the variation in the numbers of gametes made per gametangium. Zygote recovery from single gametangial pairs was highly dependent on the volume of mating matrix. In addition, most zygotes recovered were unattached to any other zygotes in the subsequent generation (> 95% single cells from matings of 1–500 gametangial pairs). Our improvements in mating conditions and zygote recovery (1) have facilitated cell manipulation and culture ofA. acetabulum in the laboratory; and (2) have made controlled crosses for selection and genetic analysis of mutants feasible. These advances have removed a major barrier to genetic analysis of development inAcetabularia.Abbreviations LB
Luria-Bertani bacteriological broth
- SE
standard error of the mean
- Tg
agar gelling temperatures
- DAPI
4,6-diamidino-2-phenylindole 相似文献
10.
Michael A. Poss Joyce A. Reid Charles A. Free W. Lynn Rogers Helen Weber Denis E. Ryono Tamara Dejneka Jack M. DeForrest Thomas L. Waldron Russell J. Brittain Harold N. Weller Maria P. Cimarusti Edward W. Petrillo 《Bioorganic & medicinal chemistry letters》1993,3(12):2739-2744
The syntheses and pharmacological activity of a series of diol sulfonamides which function as inhibitors of human renin are described. The most potent compound in this series, compound 20 (SQ 33,800), is a subnanomolar inhibitor of human renin (IC50 = 0.35 × 10−9 M). 相似文献