全文获取类型
收费全文 | 60329篇 |
免费 | 4933篇 |
国内免费 | 31篇 |
专业分类
65293篇 |
出版年
2022年 | 413篇 |
2021年 | 854篇 |
2020年 | 528篇 |
2019年 | 638篇 |
2018年 | 831篇 |
2017年 | 771篇 |
2016年 | 1357篇 |
2015年 | 2392篇 |
2014年 | 2512篇 |
2013年 | 3334篇 |
2012年 | 4236篇 |
2011年 | 4243篇 |
2010年 | 2755篇 |
2009年 | 2440篇 |
2008年 | 3531篇 |
2007年 | 3590篇 |
2006年 | 3391篇 |
2005年 | 3418篇 |
2004年 | 3355篇 |
2003年 | 3148篇 |
2002年 | 3116篇 |
2001年 | 711篇 |
2000年 | 531篇 |
1999年 | 729篇 |
1998年 | 865篇 |
1997年 | 597篇 |
1996年 | 602篇 |
1995年 | 591篇 |
1994年 | 572篇 |
1993年 | 596篇 |
1992年 | 535篇 |
1991年 | 463篇 |
1990年 | 389篇 |
1989年 | 405篇 |
1988年 | 402篇 |
1987年 | 338篇 |
1986年 | 340篇 |
1985年 | 395篇 |
1984年 | 444篇 |
1983年 | 374篇 |
1982年 | 459篇 |
1981年 | 409篇 |
1980年 | 363篇 |
1979年 | 240篇 |
1978年 | 293篇 |
1977年 | 285篇 |
1976年 | 231篇 |
1975年 | 216篇 |
1974年 | 236篇 |
1973年 | 220篇 |
排序方式: 共有10000条查询结果,搜索用时 8 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.
8.
Peter J Stephens 《BMJ (Clinical research ed.)》2005,330(7506):1508-1509
9.
10.
Charles L. Nunn Peter H. Thrall Kelly Stewart Alexander H. Harcourt 《Evolutionary ecology》2008,22(4):519-543
Emerging infectious diseases threaten a wide diversity of animals, and important questions remain concerning disease emergence
in socially structured populations. We developed a spatially explicit simulation model to investigate whether—and under what
conditions—disease-related mortality can impact rates of pathogen spread in populations of polygynous groups. Specifically,
we investigated whether pathogen-mediated dispersal (PMD) can occur when females disperse after the resident male dies from
disease, thus carrying infections to new groups. We also examined the effects of incubation period and virulence, host mortality
and rates of background dispersal, and we used the model to investigate the spread of the virus responsible for Ebola hemorrhagic
fever, which currently is devastating African ape populations. Output was analyzed using regression trees, which enable exploration
of hierarchical and non-linear relationships. Analyses revealed that the incidence of disease in single-male (polygynous)
groups was significantly greater for those groups containing an average of more than six females, while the total number of
infected hosts in the population was most sensitive to the number of females per group. Thus, as expected, PMD occurs in polygynous
groups and its effects increase as harem size (the number of females) increases. Simulation output further indicated that
population-level effects of Ebola are likely to differ among multi-male–multi-female chimpanzees and polygynous gorillas,
with larger overall numbers of chimpanzees infected, but more gorilla groups becoming infected due to increased dispersal
when the resident male dies. Collectively, our results highlight the importance of social system on the spread of disease
in wild mammals. 相似文献