全文获取类型
收费全文 | 7552篇 |
免费 | 656篇 |
国内免费 | 4篇 |
专业分类
8212篇 |
出版年
2023年 | 58篇 |
2022年 | 142篇 |
2021年 | 273篇 |
2020年 | 148篇 |
2019年 | 176篇 |
2018年 | 199篇 |
2017年 | 161篇 |
2016年 | 335篇 |
2015年 | 511篇 |
2014年 | 522篇 |
2013年 | 534篇 |
2012年 | 762篇 |
2011年 | 649篇 |
2010年 | 379篇 |
2009年 | 363篇 |
2008年 | 490篇 |
2007年 | 420篇 |
2006年 | 379篇 |
2005年 | 287篇 |
2004年 | 288篇 |
2003年 | 262篇 |
2002年 | 239篇 |
2001年 | 53篇 |
2000年 | 31篇 |
1999年 | 38篇 |
1998年 | 60篇 |
1997年 | 29篇 |
1996年 | 22篇 |
1995年 | 27篇 |
1994年 | 23篇 |
1993年 | 27篇 |
1992年 | 23篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 21篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 15篇 |
1983年 | 24篇 |
1982年 | 8篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 8篇 |
排序方式: 共有8212条查询结果,搜索用时 15 毫秒
991.
Aline Danieli‐Silva Jana Magaly Tesserolli de Souza Ana Julia Donatti Ricardo Pamplona Campos José Vicente‐Silva Leandro Freitas Isabela Galarda Varassin 《Oikos》2012,121(1):35-43
The concept of pollination syndromes has been widely questioned, since plant–pollinator interactions have proved to be more generalist than was previously thought. We examined whether the network of a tropical high‐altitude grassland contained groups of plants and pollinators that interact preferentially with each other. A general binary matrix was created. To assess the robustness of myophily, in all analyses we considered: 1) the whole network, 2) the network after the wasps were removed, and 3) the network after the flies were removed. For each network we evaluated whether: 1) the observed interactions were more related to syndromes than expected by chance, compared to an expected matrix; 2) there was a modular structure; 3) the modules found were more related to syndromes than expected by chance, compared to another expected matrix; 4) the syndromes were equally robust. For this analysis, the general matrix was subdivided into smaller matrices that included each pollination syndrome separately. To test the influence of the functional groups of pollinators and the phylogeny of plants, in addition to the general matrix, we also considered the first expected matrix, a quantitative functional group and a plant phylogeny matrix. The pollination syndromes determined the pattern of interactions in the network: 69% of the total interactions resulted from the functional group of pollinators predicted by the plant syndrome. The network showed greater modularity (13 modules) than expected by chance, mostly consisting of the expected functional groups of pollinators and plant syndromes. The modules were associated with pollination syndromes more than was predicted by chance. Most of the variation in interactions was explained by functional groups of pollinators or by plant syndromes. Plant phylogeny did not account for a significant amount of variation in the interactions. Our findings support the concept of pollination syndromes. However, the interactions were not equally predicted by different pollination syndromes, and the accuracy of the prediction was strongest for ornithophily and melittophily. 相似文献
992.
993.
994.
Park SH Chung PJ Juntawong P Bailey-Serres J Kim YS Jung H Bang SW Kim YK Do Choi Y Kim JK 《Plant physiology》2012,159(3):1111-1124
995.
996.
997.
Sagner A Merkel M Aigouy B Gaebel J Brankatschk M Jülicher F Eaton S 《Current biology : CB》2012,22(14):1296-1301
Epithelial tissues develop planar polarity that is reflected in the global alignment of hairs and cilia with respect to the tissue axes. The planar cell polarity (PCP) proteins form asymmetric and polarized domains across epithelial junctions that are aligned locally between cells and orient these external structures. Although feedback mechanisms can polarize PCP proteins intracellularly and locally align polarity between cells, how global PCP patterns are specified is not understood. It has been proposed that the graded distribution of a biasing factor could guide long-range PCP. However, we recently identified epithelial morphogenesis as a mechanism that can reorganize global PCP patterns; in the Drosophila pupal wing, oriented cell divisions and rearrangements reorient PCP from a margin-oriented pattern to one that points distally. Here, we use quantitative image analysis to study how PCP patterns first emerge in the wing. PCP appears during larval growth and is spatially oriented through the activities of three organizer regions that control disc growth and patterning. Flattening morphogen gradients emanating from these regions does not reduce intracellular polarity but distorts growth and alters specific features of the PCP pattern. Thus, PCP may be guided by morphogenesis rather than morphogen gradients. 相似文献
998.
Julia Schwarzer Ernst Roelof Swartz Emmanuel Vreven Jos Snoeks Fenton Peter David Cotterill Bernhard Misof Ulrich Kurt Schliewen 《Proceedings. Biological sciences / The Royal Society》2012,279(1746):4389-4398
The megadiverse haplochromine cichlid radiations of the East African lakes, famous examples of explosive speciation and adaptive radiation, are according to recent studies, introgressed by different riverine lineages. This study is based on the first comprehensive mitochondrial and nuclear DNA dataset from extensive sampling of riverine haplochromine cichlids. It includes species from the lower River Congo and Angolan (River Kwanza) drainages. Reconstruction of phylogenetic hypotheses revealed the paradox of clearly discordant phylogenetic signals. Closely related mtDNA haplotypes are distributed thousands of kilometres apart and across major African watersheds, whereas some neighbouring species carry drastically divergent mtDNA haplotypes. At shallow and deep phylogenetic layers, strong signals of hybridization are attributed to the complex Late Miocene/Early Pliocene palaeohistory of African rivers. Hybridization of multiple lineages across changing watersheds shaped each of the major haplochromine radiations in lakes Tanganyika, Victoria, Malawi and the Kalahari Palaeolakes, as well as a miniature species flock in the Congo basin (River Fwa). On the basis of our results, introgression occurred not only on a spatially restricted scale, but massively over almost the whole range of the haplochromine distribution. This provides an alternative view on the origin and exceptional high diversity of this enigmatic vertebrate group. 相似文献
999.
1000.