全文获取类型
收费全文 | 6009篇 |
免费 | 582篇 |
国内免费 | 3篇 |
出版年
2022年 | 80篇 |
2021年 | 152篇 |
2020年 | 64篇 |
2019年 | 107篇 |
2018年 | 95篇 |
2017年 | 84篇 |
2016年 | 159篇 |
2015年 | 291篇 |
2014年 | 273篇 |
2013年 | 329篇 |
2012年 | 414篇 |
2011年 | 338篇 |
2010年 | 231篇 |
2009年 | 175篇 |
2008年 | 235篇 |
2007年 | 233篇 |
2006年 | 234篇 |
2005年 | 223篇 |
2004年 | 194篇 |
2003年 | 208篇 |
2002年 | 182篇 |
2001年 | 97篇 |
2000年 | 119篇 |
1999年 | 92篇 |
1998年 | 59篇 |
1997年 | 54篇 |
1996年 | 58篇 |
1995年 | 44篇 |
1992年 | 87篇 |
1991年 | 69篇 |
1990年 | 105篇 |
1989年 | 66篇 |
1988年 | 77篇 |
1987年 | 59篇 |
1986年 | 67篇 |
1985年 | 84篇 |
1984年 | 70篇 |
1983年 | 63篇 |
1982年 | 59篇 |
1981年 | 53篇 |
1980年 | 55篇 |
1979年 | 46篇 |
1978年 | 53篇 |
1977年 | 50篇 |
1976年 | 46篇 |
1975年 | 40篇 |
1974年 | 51篇 |
1973年 | 50篇 |
1972年 | 48篇 |
1970年 | 48篇 |
排序方式: 共有6594条查询结果,搜索用时 19 毫秒
1.
2.
Charlotte Gray 《CMAJ》1984,130(6):769-772
3.
4.
Matthias Schlichting Pamela Menegazzi Charlotte Helfrich-F?rster 《Proceedings. Biological sciences / The Royal Society》2015,282(1815)
Circadian clocks are thought to be essential for timing the daily activity of animals, and consequently increase fitness. This view was recently challenged for clock-less fruit flies and mice that exhibited astonishingly normal activity rhythms under outdoor conditions. Compensatory mechanisms appear to enable even clock mutants to live a normal life in nature. Here, we show that gradual daily increases/decreases of light in the laboratory suffice to provoke normally timed sharp morning (M) and evening (E) activity peaks in clock-less flies. We also show that the compound eyes, but not Cryptochrome (CRY), mediate the precise timing of M and E peaks under natural-like conditions, as CRY-less flies do and eyeless flies do not show these sharp peaks independently of a functional clock. Nevertheless, the circadian clock appears critical for anticipating dusk, as well as for inhibiting sharp activity peaks during midnight. Clock-less flies only increase E activity after dusk and not before the beginning of dusk, and respond strongly to twilight exposure in the middle of the night. Furthermore, the circadian clock responds to natural-like light cycles, by slightly broadening Timeless (TIM) abundance in the clock neurons, and this effect is mediated by CRY. 相似文献
5.
6.
7.
8.
A rapid method for cloning and sequencing variable-region genes of expressed immunoglobulins 总被引:9,自引:0,他引:9
A rapid procedure is described for cloning immunoglobulin V region genes from cells that express them. cDNA is synthesized from mRNA template using primers homologous to the immunoglobulin constant-region genes. Blunt-ended, double-stranded cDNA is obtained by sequential addition of enzymes to a single tube. The cDNA is inserted directly into the M13 vector, which is screened by plaque lifting for the presence of specific inserts. Screening probes can be generated from 32P-labeled single-stranded cDNAs generated from primers different from those used for cloning, or alternatively, from previously cloned V or C gene segments. The ease of cloning a cDNA V region is directly related to the abundance of Ig-specific mRNA within the cell of interest. This method minimizes the number of steps and the time needed to obtain accurate and complete sequences of any expressed Ig V region gene. 相似文献
9.
Metabolism of palmitate in cultured rat Sertoli cells 总被引:1,自引:0,他引:1
Isolated rat Sertoli cells were incubated in the presence of [1-14C]palmitate at a cell concentration of 1.54 +/- 0.31 mg protein/flask (n = 7). The oxidation of palmitate was concentration dependent and maximal oxidation was obtained at 0.35 mM-palmitate. At a saturating concentration of palmitate the oxidation was linear for at least 6 h. About 65% of the total amount of palmitate oxidized during 5 h at 0.52 mM-palmitate (109 +/- 44 nmol/flask, n = 5) was recovered as CO2 and the rest as acid-soluble compounds. Almost all radioactive acid-soluble compounds which were secreted by the Sertoli cells were shown to be 3-hydroxybutyrate and acetoacetate. The palmitate recovery in cellular lipids and triacylglycerols was 9.4 +/- 5.1 nmol/flask (n = 5) and 3.5 +/- 2.8 nmol/flask (n = 5) respectively. Addition of glucose had no significant effect on palmitate oxidation but caused a 9-fold increase in esterification of palmitate into triacylglycerols. We conclude that cultured rat Sertoli cells can oxidize palmitate to CO2 and ketone bodies and that fatty acids appear to be a major energy substrate for these cells. 相似文献
10.