全文获取类型
收费全文 | 85916篇 |
免费 | 7583篇 |
国内免费 | 42篇 |
出版年
2023年 | 281篇 |
2022年 | 705篇 |
2021年 | 1548篇 |
2020年 | 879篇 |
2019年 | 1108篇 |
2018年 | 1439篇 |
2017年 | 1241篇 |
2016年 | 2136篇 |
2015年 | 3630篇 |
2014年 | 4048篇 |
2013年 | 4812篇 |
2012年 | 6536篇 |
2011年 | 6483篇 |
2010年 | 4170篇 |
2009年 | 3798篇 |
2008年 | 5430篇 |
2007年 | 5433篇 |
2006年 | 5233篇 |
2005年 | 5032篇 |
2004年 | 4893篇 |
2003年 | 4669篇 |
2002年 | 4402篇 |
2001年 | 862篇 |
2000年 | 625篇 |
1999年 | 961篇 |
1998年 | 1232篇 |
1997年 | 823篇 |
1996年 | 743篇 |
1995年 | 653篇 |
1994年 | 617篇 |
1993年 | 666篇 |
1992年 | 558篇 |
1991年 | 522篇 |
1990年 | 465篇 |
1989年 | 400篇 |
1988年 | 420篇 |
1987年 | 344篇 |
1986年 | 318篇 |
1985年 | 403篇 |
1984年 | 520篇 |
1983年 | 405篇 |
1982年 | 502篇 |
1981年 | 486篇 |
1980年 | 414篇 |
1979年 | 295篇 |
1978年 | 323篇 |
1977年 | 282篇 |
1976年 | 264篇 |
1975年 | 204篇 |
1974年 | 241篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Ivonne J. Garzn‐Ordua Shaun L. Winterton Yunlan Jiang Laura C.V. Breitkreuz Peter Duelli Michael S. Engel Norman D. Penny Catherine A. Tauber Atsushi Mochizuki Xingyue Liu 《Systematic Entomology》2019,44(3):499-513
We present a time‐calibrated phylogeny of the charismatic green lacewings (Neuroptera: Chrysopidae). Previous phylogenetic studies on the family using DNA sequences have suffered from sparse taxon sampling and/or limited amounts of data. Here we combine all available previously published DNA sequence data and add to it new DNA sequences generated for this study. We analysed these data in a supermatrix using Bayesian and maximum likelihood methods and provide a phylogenetic hypothesis for the family that recovers strong support for the monophyly of all subfamilies and resolves relationships among a large proportion of chrysopine genera. Chrysopinae tribes Leucochrysini and Belonopterygini were recovered as monophyletic sister clades, while the species‐rich tribe Chrysopini was rendered paraphyletic by Ankylopterygini. Relationships among the subfamilies were resolved, although with relatively low statistical support, and the topology varied based on the method of analysis. Greatest support was found for Apochrysinae as sister to Nothochrysinae and Chrysopinae, which is in contrast to traditional concepts that place Nothochrysinae as sister to the rest of the family. Divergence estimates suggest that the stem groups to the various subfamilies diverged during the Triassic‐Jurassic, and that stem groups of the chrysopine tribes diverged during the Cretaceous. 相似文献
22.
Michael Kopelman 《BMJ (Clinical research ed.)》1984,288(6411):150-151
23.
Silvio Antoniak Erica M. Sparkenbaugh Michael Tencati Mauricio Rojas Nigel Mackman Rafal Pawlinski 《PloS one》2013,8(11)
Heart failure is a major clinical problem worldwide. Previous studies have demonstrated an important role for G protein-coupled receptors, including protease-activated receptors (PARs), in the pathology of heart hypertrophy and failure. Activation of PAR-2 on cardiomyocytes has been shown to induce hypertrophic growth in vitro. PAR-2 also contributes to myocardial infarction and heart remodeling after ischemia/reperfusion injury. In this study, we found that PAR-2 induced hypertrophic growth of cultured rat neonatal cardiomyocytes in a MEK1/2 and p38 dependent manner. In addition, PAR-2 activation on mouse cardiomyocytes increased expression of the pro-fibrotic chemokine MCP-1. Furthermore, cardiomyocyte-specific overexpression of PAR-2 in mice induced heart hypertrophy, cardiac fibrosis, inflammation and heart failure. Finally, in a mouse model of myocardial infarction induced by permanent ligation of the left anterior descending coronary artery, PAR-2 deficiency attenuated heart remodeling and improved heart function independently of its contribution to the size of the initial infarct. Taken together, our data indicate that PAR-2 signaling contributes to the pathogenesis of hypertrophy and heart failure. 相似文献
24.
Michael Lenhard 《Current biology : CB》2012,22(19):R838-R840
25.
26.
27.
The cost of interspecific competition in two gerbil species 总被引:5,自引:1,他引:4
28.
29.
Michael R. Seringhaus 《The Yale journal of biology and medicine》2002,75(4):239-Aug;75(4):239
30.
Sandra L. Almeyda Zambrano Eben N. Broadbent Sam Shanee Noga Shanee Anneke Deluycker Michael Steinberg Scott A. Ford Alma Hernndez Jaramillo Robin Fernandez‐Hilario Carolina Lagos Castillo Angelica M. Almeyda Zambrano 《American journal of primatology》2019,81(8)
Habitat loss is one of the main threats to wildlife. Therefore, knowledge of habitat use and preference is essential for the design of conservation strategies and identification of priority sites for the protection of endangered species. The yellow‐tailed woolly monkey (Lagothrix flavicauda Humboldt, 1812), categorized as Critically Endangered on the IUCN Red List, is endemic to montane forests in northern Peru where its habitat is greatly threatened. We assessed how habitat use and preference in L. flavicauda are linked to forest structure and composition. The study took place near La Esperanza, in the Amazonas region, Peru. Our objective was to identify characteristics of habitat most utilized by L. flavicauda to provide information that will be useful for the selection of priority sites for conservation measures. Using presence records collected from May 2013 to February 2014 for one group of L. flavicauda, we classified the study site into three different use zones: low‐use, medium‐use, and high‐use. We assessed forest structure and composition for all use zones using 0.1 ha Gentry vegetation transects. Results show high levels of variation in plant species composition across the three use zones. Plants used as food resources had considerably greater density, dominance, and ecological importance in high‐use zones. High‐use zones presented similar structure to medium‐ and low‐use zones; thus it remains difficult to assess the influence of forest structure on habitat preference. We recommend focusing conservation efforts on areas with a similar floristic composition to the high‐use zones recorded in this study and suggest utilizing key alimentation species for reforestation efforts. 相似文献