全文获取类型
收费全文 | 65769篇 |
免费 | 5350篇 |
国内免费 | 32篇 |
专业分类
71151篇 |
出版年
2022年 | 447篇 |
2021年 | 918篇 |
2020年 | 577篇 |
2019年 | 684篇 |
2018年 | 905篇 |
2017年 | 838篇 |
2016年 | 1465篇 |
2015年 | 2564篇 |
2014年 | 2758篇 |
2013年 | 3652篇 |
2012年 | 4560篇 |
2011年 | 4603篇 |
2010年 | 2994篇 |
2009年 | 2679篇 |
2008年 | 3844篇 |
2007年 | 3932篇 |
2006年 | 3715篇 |
2005年 | 3739篇 |
2004年 | 3638篇 |
2003年 | 3421篇 |
2002年 | 3404篇 |
2001年 | 772篇 |
2000年 | 586篇 |
1999年 | 808篇 |
1998年 | 965篇 |
1997年 | 677篇 |
1996年 | 672篇 |
1995年 | 643篇 |
1994年 | 629篇 |
1993年 | 655篇 |
1992年 | 582篇 |
1991年 | 517篇 |
1990年 | 428篇 |
1989年 | 460篇 |
1988年 | 445篇 |
1987年 | 368篇 |
1986年 | 380篇 |
1985年 | 426篇 |
1984年 | 475篇 |
1983年 | 398篇 |
1982年 | 510篇 |
1981年 | 441篇 |
1980年 | 396篇 |
1979年 | 262篇 |
1978年 | 308篇 |
1977年 | 306篇 |
1976年 | 246篇 |
1975年 | 237篇 |
1974年 | 251篇 |
1973年 | 227篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
This paper is concerned with gene survival in a population which may increase without density dependence according to a generalization of the Moran model for haploid individuals. A selective advantage to one allele and the possibility of differential reproductive rates are allowed. Simple conditions are given for ultimate homozygosity to be certain and for the possibility of ultimate polymorphism. The results complement and extend those of Heyde (1981, 1982). 相似文献
2.
3.
4.
5.
6.
Peter Buchwald 《Theoretical biology & medical modelling》2009,6(1):5-13
Background
The function and viability of cultured, transplanted, or encapsulated pancreatic islets is often limited by hypoxia because these islets have lost their vasculature during the isolation process and have to rely on gradient-driven passive diffusion, which cannot provide adequate oxygen transport. Pancreatic islets (islets of Langerhans) are particularly susceptible due to their relatively large size, large metabolic demand, and increased sensitivity to hypoxia. Here, finite element method (FEM) based multiphysics models are explored to describe oxygen transport and cell viability in avascular islets both in static and in moving culture media. 相似文献7.
James F. Richards Kulgite Lit Roland Fuca Catherine Bourgeault 《Biochemical and biophysical research communications》1981,99(4):1461-1467
Several species of ornithine decarboxylase were separated by chromatography of rat thymus and kidney extracts on DEAE-Sepharose CL-6B. One major and one minor species were absent from thymus of rats two hours after hormone treatment but otherwise, the elution profile was identical to thymus from control animals. The elution patterns of ODC activity in kidneys of rats treated 2.5 or 5 hours before sacrifice with dexamethasone differ from that of control kidney and from each other. Enzyme from kidneys early after hormone treatment is eluted earlier than enzyme from control tissue, while at 5 hours, the enzyme is eluted much later than in the control. This suggests that the hormone-induced activity is subsequently modified. 相似文献
8.
9.
R.J. Ulvik I. Romslo F. Roland R.R. Crichton 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,677(1):50-56
Mitochondria mobilize iron from ferritin by a mechanism that depends on external FMN. With rat liver mitochondria, the rate of mobilization of iron is higher from rat liver ferritin than from horse spleen ferritin. With horse liver mitochondria, the rate of iron mobilization is higher from horse spleen ferritin than from rat liver ferritin. The results are explained by a higher affinity between mitochondria and ferritins of the same species. The mobilization of iron increases with the iron content of the ferritin and then levels off. A maximum is reached with ferritins containing about 1 200 iron atoms per molecule. The results represent further evidence that ferritin may function as a direct iron donor to the mitochondria. 相似文献
10.