全文获取类型
收费全文 | 3176篇 |
免费 | 68篇 |
国内免费 | 26篇 |
专业分类
3270篇 |
出版年
2023年 | 7篇 |
2022年 | 33篇 |
2021年 | 44篇 |
2020年 | 16篇 |
2019年 | 8篇 |
2018年 | 11篇 |
2017年 | 13篇 |
2016年 | 246篇 |
2015年 | 941篇 |
2014年 | 1287篇 |
2013年 | 58篇 |
2012年 | 45篇 |
2011年 | 30篇 |
2010年 | 58篇 |
2009年 | 37篇 |
2008年 | 25篇 |
2007年 | 15篇 |
2006年 | 14篇 |
2005年 | 42篇 |
2004年 | 55篇 |
2003年 | 19篇 |
2002年 | 25篇 |
2001年 | 31篇 |
2000年 | 17篇 |
1999年 | 18篇 |
1998年 | 8篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 18篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 15篇 |
1988年 | 6篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1973年 | 3篇 |
1967年 | 2篇 |
1966年 | 3篇 |
1964年 | 2篇 |
1960年 | 2篇 |
1957年 | 6篇 |
1956年 | 2篇 |
1955年 | 2篇 |
1954年 | 2篇 |
1943年 | 2篇 |
1925年 | 2篇 |
排序方式: 共有3270条查询结果,搜索用时 0 毫秒
101.
人胚胎干细胞程序降温保存的实验研究 总被引:1,自引:0,他引:1
本文采用升降式程序降温仪对人胚胎于细胞进行了程序降温保存,并探讨和比较了降温速率、置核温度、保护剂和投入液氮前温度对冻存复苏后胚胎干细胞的存活率、活力及分化特性的影响。结果表明:采用Me_2SO 血清 DMEM(体积比为1∶3∶6)的保护剂,从0℃开始,以0.5℃/min的速率对细胞悬液降温;至-10℃时对其进行置核,并于-35℃时将其快速投入液氮中保存,复温后效果最佳。冻存复温后细胞存活率可达81.8%,复苏后的胚胎干细胞形态和集落生长方式都与冻前的生长形态相同,且胚胎干细胞标志之一碱性磷酸酶(AKP)反应阳性,同时染色体组型仍正常。 相似文献
102.
103.
104.
105.
106.
107.
108.
109.
Luc Villandre David A. Stephens Aurelie Labbe Huldrych F. Günthard Roger Kouyos Tanja Stadler The Swiss HIV Cohort Study 《PloS one》2016,11(2)
Background
Transmission patterns of sexually-transmitted infections (STIs) could relate to the structure of the underlying sexual contact network, whose features are therefore of interest to clinicians. Conventionally, we represent sexual contacts in a population with a graph, that can reveal the existence of communities. Phylogenetic methods help infer the history of an epidemic and incidentally, may help detecting communities. In particular, phylogenetic analyses of HIV-1 epidemics among men who have sex with men (MSM) have revealed the existence of large transmission clusters, possibly resulting from within-community transmissions. Past studies have explored the association between contact networks and phylogenies, including transmission clusters, producing conflicting conclusions about whether network features significantly affect observed transmission history. As far as we know however, none of them thoroughly investigated the role of communities, defined with respect to the network graph, in the observation of clusters.Methods
The present study investigates, through simulations, community detection from phylogenies. We simulate a large number of epidemics over both unweighted and weighted, undirected random interconnected-islands networks, with islands corresponding to communities. We use weighting to modulate distance between islands. We translate each epidemic into a phylogeny, that lets us partition our samples of infected subjects into transmission clusters, based on several common definitions from the literature. We measure similarity between subjects’ island membership indices and transmission cluster membership indices with the adjusted Rand index.Results and Conclusion
Analyses reveal modest mean correspondence between communities in graphs and phylogenetic transmission clusters. We conclude that common methods often have limited success in detecting contact network communities from phylogenies. The rarely-fulfilled requirement that network communities correspond to clades in the phylogeny is their main drawback. Understanding the link between transmission clusters and communities in sexual contact networks could help inform policymaking to curb HIV incidence in MSMs. 相似文献110.