全文获取类型
收费全文 | 3491篇 |
免费 | 410篇 |
国内免费 | 1篇 |
出版年
2021年 | 36篇 |
2020年 | 27篇 |
2019年 | 38篇 |
2018年 | 29篇 |
2017年 | 35篇 |
2016年 | 68篇 |
2015年 | 104篇 |
2014年 | 134篇 |
2013年 | 138篇 |
2012年 | 169篇 |
2011年 | 193篇 |
2010年 | 88篇 |
2009年 | 87篇 |
2008年 | 127篇 |
2007年 | 141篇 |
2006年 | 137篇 |
2005年 | 117篇 |
2004年 | 126篇 |
2003年 | 121篇 |
2002年 | 108篇 |
2001年 | 136篇 |
2000年 | 117篇 |
1999年 | 101篇 |
1998年 | 41篇 |
1997年 | 47篇 |
1996年 | 41篇 |
1995年 | 42篇 |
1994年 | 27篇 |
1993年 | 31篇 |
1992年 | 91篇 |
1991年 | 84篇 |
1990年 | 49篇 |
1989年 | 77篇 |
1988年 | 58篇 |
1987年 | 68篇 |
1986年 | 38篇 |
1985年 | 45篇 |
1984年 | 48篇 |
1983年 | 41篇 |
1982年 | 28篇 |
1981年 | 36篇 |
1979年 | 36篇 |
1978年 | 41篇 |
1977年 | 38篇 |
1976年 | 41篇 |
1975年 | 37篇 |
1974年 | 40篇 |
1973年 | 27篇 |
1972年 | 49篇 |
1971年 | 35篇 |
排序方式: 共有3902条查询结果,搜索用时 19 毫秒
1.
J. Jordan Price Scott M. Lanyon Kevin E. Omland 《Proceedings. Biological sciences / The Royal Society》2009,276(1664):1971-1980
Birds in which both sexes produce complex songs are thought to be more common in the tropics than in temperate areas, where typically only males sing. Yet the role of phylogeny in this apparent relationship between female song and latitude has never been examined. Here, we reconstruct evolutionary changes in female song and breeding latitude in the New World blackbirds (Icteridae), a family with both temperate and tropical representatives. We provide strong evidence that members of this group have moved repeatedly from tropical to temperate breeding ranges and, furthermore, that these range shifts were associated with losses of female song more often than expected by chance. This historical perspective suggests that male-biased song production in many temperate species is the result not of sexual selection for complex song in males but of selection against such songs in females. Our results provide new insights into the differences we see today between tropical and temperate songbirds, and suggest that the role of sexual selection in the evolution of bird song might not be as simple as we think. 相似文献
2.
3.
Alkes L. Price Nick Patterson Dustin C. Hancks Simon Myers David Reich Vivian G. Cheung Richard S. Spielman 《PLoS genetics》2008,4(12)
Variation in gene expression is a fundamental aspect of human phenotypic variation. Several recent studies have analyzed gene expression levels in populations of different continental ancestry and reported population differences at a large number of genes. However, these differences could largely be due to non-genetic (e.g., environmental) effects. Here, we analyze gene expression levels in African American cell lines, which differ from previously analyzed cell lines in that individuals from this population inherit variable proportions of two continental ancestries. We first relate gene expression levels in individual African Americans to their genome-wide proportion of European ancestry. The results provide strong evidence of a genetic contribution to expression differences between European and African populations, validating previous findings. Second, we infer local ancestry (0, 1, or 2 European chromosomes) at each location in the genome and investigate the effects of ancestry proximal to the expressed gene (cis) versus ancestry elsewhere in the genome (trans). Both effects are highly significant, and we estimate that 12±3% of all heritable variation in human gene expression is due to cis variants. 相似文献
4.
5.
The seven currently recognized species of Geranium endemic to the Hawaiian Islands are unusual in their shrubby or arborescent habit and unlobed, parallel-veined leaves rather than the palmately cleft or lobed leaves and herbaceous habit typical of the genus. Their placement within the genus and their biogeographic source have been obscured by this morphological distictiveness and the limited resolution of relationships on the basis of morphology in the very speciose subgenus Geranium. Phylogenetic analysis of rbcL gene sequences provides strong support for the monophyly of the Hawaiian group, and indicates that the Hawaiian clade is deeply nested within section Geranium rather than comprising a separate section. The continental relatives studied to date with the greatest similarity in sequence to the Hawaiian group are native to the Americas rather than Asia or the Pacific. The Hawaiian species are extremely similar to one another in rbcL sequence, while the tree topology obtained is consistent with a basal position for Geranium arboreum within the group. 相似文献
6.
7.
8.
9.
10.