全文获取类型
收费全文 | 1525篇 |
免费 | 148篇 |
出版年
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 28篇 |
2020年 | 17篇 |
2019年 | 12篇 |
2018年 | 24篇 |
2017年 | 19篇 |
2016年 | 35篇 |
2015年 | 57篇 |
2014年 | 67篇 |
2013年 | 83篇 |
2012年 | 87篇 |
2011年 | 106篇 |
2010年 | 56篇 |
2009年 | 62篇 |
2008年 | 77篇 |
2007年 | 73篇 |
2006年 | 82篇 |
2005年 | 65篇 |
2004年 | 66篇 |
2003年 | 53篇 |
2002年 | 57篇 |
2001年 | 28篇 |
2000年 | 28篇 |
1999年 | 18篇 |
1998年 | 31篇 |
1997年 | 16篇 |
1996年 | 19篇 |
1995年 | 18篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 17篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 23篇 |
1987年 | 11篇 |
1986年 | 21篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1974年 | 8篇 |
1969年 | 10篇 |
排序方式: 共有1673条查询结果,搜索用时 0 毫秒
51.
The feeding behavior and ecology ofPan paniscus was studied over a seven-month period in Equateur, Republic of Zaïre, during 1974–1975. Additional data were gathered during four weeks in 1979.Pan paniscus was found to be primarily frugivorous but bonobo foods also consist of leaves, flowers, pith, invertebrates and small mammals. 相似文献
52.
Addition of the arginine analogue, canavanine, to cultures of nitrogen-fixing Anabaena cylindrica at the onset of akinete formation, resulted in the development of akinetes randomly distributed within the filament, in addition to those adjacent to heterocysts. The total frequency of akinetes increased up to five-fold. A feature of akinetes is their increased content of cyanophycin granules (an arginine-aspartic acid polymer) and addition of canavanine to cultures at an earlier stage resulted in entire filaments becoming agranular and containing agranular akinetes. The effects on akinete pattern appeared to be specific for canavanine since other amino acid analogues, although increasing the frequency of akinetes (approximately two-fold), had no effect on their position relative to heterocysts. In ammonia-grown, stationary phase cultures of A. cylindrica, akinetes were observed adjacent to proheterocysts and in positions more than 20 cells from any heterocyst. These observations indicate that nitrogen fixation and heterocysts are not essential for akinete formation in A. cylindrica, although the availability of a source of fixed nitrogen does appear to be a requirement.These results suggest that during exponential growth some aspect of the physiology of vegetative cells suppresses their development into akinetes and that the role of the heterocyst may not be one of direct stimulation of adjacent vegetative cells to form akinetes, but the removal or negation of the inhibition within them. A model for akinete formation and the involvement of canavanine is given. 相似文献
53.
54.
Asclepias welshii, restricted to the Coral Pink Sand Dunes of southern Utah, is described and illustrated. Its relationship to other species of seriesRoseae is discussed. 相似文献
55.
J. Edson Pontes James M. Pierce Jr. Byung-Kil Choe Noel R. Rose 《In vitro cellular & developmental biology. Plant》1979,15(7):469-472
Summary Studies of acid phosphates produced by cell lines MA 160 and EB 33 demonstrated immunochemically their prostatic origin. MA
160 and EB 33, rather than being HeLa contaminants, may be hybrids of prostatic epithelial and HeLa cells or true prostatic
cell lines with chromosomal changes common to all long-term cultivated cell lines.
This research was supported by NIH (Cancer) Research Grants Nos. 18748 and 16426; and Detroit General Hospital Research Corporation. 相似文献
56.
Noel H. Holmgren 《Brittonia》1978,30(2):182-194
The mountains of Costa Rica and western Panama constitute a natural floristic region that is inhabited by six species ofCastilleja.Castilleja talamancensis, C. lentii andC. tayloriorum are described as new. The remaining three areC. arvensis,C. irasuensis andC. quirosii. All butC. arvensis are endemic to the area. The six species are keyed, described, illustrated, mapped and documented with literature and specimen citations. 相似文献
57.
Galactokinase Mutants of Chinese Hamster Somatic Cells Resistant to 2-Deoxygalactose 总被引:6,自引:0,他引:6
下载免费PDF全文
![点击此处可从《Genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The growth of Chinese hamster somatic cells was inhibited by 0.2 mg/cc of 2-deoxygalactose. Mutants partially or fully resistant to 2-deoxygalactose were isolated in a single-step or two-step selection. Some of them did not grow as well as the wild type; one of them which lacked galactokinase(EC.2.7.1.6) activity did not grow at all in galactose medium. The galactokinase kinetic properties (Vmax & kmax of the other mutants and of the wild type were different. Therefore resistance resulted either from the possible absence of galactokinase synthesis or from a structural mutation, possible a missence mutation, in the galactokinase gene.- A simple diagnostic test for juvenile cataract is proposed. 相似文献
58.
Noel W. Preston 《BMJ (Clinical research ed.)》1965,2(5452):11-13
59.
60.