全文获取类型
收费全文 | 40945篇 |
免费 | 3206篇 |
国内免费 | 3732篇 |
出版年
2024年 | 80篇 |
2023年 | 558篇 |
2022年 | 1339篇 |
2021年 | 2332篇 |
2020年 | 1609篇 |
2019年 | 2095篇 |
2018年 | 1858篇 |
2017年 | 1336篇 |
2016年 | 1886篇 |
2015年 | 2648篇 |
2014年 | 3160篇 |
2013年 | 3349篇 |
2012年 | 3791篇 |
2011年 | 3378篇 |
2010年 | 1999篇 |
2009年 | 1826篇 |
2008年 | 2177篇 |
2007年 | 1845篇 |
2006年 | 1573篇 |
2005年 | 1267篇 |
2004年 | 1095篇 |
2003年 | 966篇 |
2002年 | 789篇 |
2001年 | 675篇 |
2000年 | 627篇 |
1999年 | 580篇 |
1998年 | 374篇 |
1997年 | 346篇 |
1996年 | 319篇 |
1995年 | 313篇 |
1994年 | 275篇 |
1993年 | 196篇 |
1992年 | 249篇 |
1991年 | 218篇 |
1990年 | 162篇 |
1989年 | 141篇 |
1988年 | 106篇 |
1987年 | 89篇 |
1986年 | 55篇 |
1985年 | 64篇 |
1984年 | 37篇 |
1983年 | 41篇 |
1982年 | 24篇 |
1981年 | 21篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1965年 | 1篇 |
1950年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
1.
2.
The functioning of the vertebrate eye depends on its absolute size, which is presumably adapted to specific needs. Eye size variation in lidless and spectacled colubrid snakes was investigated, including 839 specimens belonging to 49 genera, 66 species and subspecies. Variations of adult eye diameters (EDs) in both absolute and relative terms between species were correlated with parameters reflecting behavioral ecology. In absolute terms, eye of arboreal species was larger than in terrestrial and semiaquatic species. For diurnal species, EDs of terrestrial species do not differ from semiaquatic species; for nocturnal species the ED of terrestrial species is larger than fossorial species but not different from semiaquatic species. In relative terms, ED did not differ significantly by habitat for diurnal species. Although the ED of terrestrial species is larger than fossorial species there were no differences for nocturnal species between semiaquatic and fossorial snakes. In contrast to other vertebrates studied to date, colubrid EDs in absolute and relative terms are larger in diurnal than in nocturnal species. These observations suggest that among colubrid snakes, eye size variation reflects adaptation to specific habitats, foraging strategies and daily activities, independently of phylogeny. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc. 相似文献
3.
Plants of four isolines of soyabean [Glycine max(L.) Merrill]Clark, vizL71-920 (maturity genecomplemente1e2e3 ), L80-5914 (E1e2e3), Clark(e1E2E3), and L65-3366 (E1E2E3), were grown inshort (12.25 h d - 1natural light) and long days (12.25 h d- 1natural light supplemented with 2.75 h d - 1low-irradianceartificial light) from first flowering to maturity in a polythenetunnel maintained at 30/24°C (day/night). Whereas therewere few differences among the isolines grown in short days,in long days the dominant alleles increased crop duration, biomassand seed yield substantially. Increases in biological and economicyield were not solely a consequence of longer crop duration:the dominant alleles also increased crop growth rate and radiationuse efficiency in long days (from 1.3 g MJ - 1total radiationine1e2e3 to 2.8 g MJ - 1inE1E2E3 ). Greater radiation use efficiencyresulted from a relatively longer leaf area duration, betterdistribution and orientation of a larger mass of leaves withinthe canopy, and smaller partitioning of assimilates to reproductivestructures. The work reveals the substantial effects of thethree lociE1 / e1, E2/ e2and E3/e3 on the response of plantgrowth, as well as development, to environment. Their relevanceto crop adaptation is discussed. Copyright 2000 Annals of BotanyCompany Glycine max(L.) Merrill, soyabean, maturity genes, flowering, phenology, growth, yield 相似文献
4.
5.
6.
7.
8.
<正>Aristolochic acids, mutational signature, and hepatocellular carcinoma Aristolochic acids (AA) are the etiologic agents of aristolochic acid nephropathy (AAN) and contribute to the global prevalence of chronic kidney disease and urothelial cancer (Grollman et al., 2007). DNA adducts formed by AA generate a unique AT transversions mutation spectrum at 相似文献
9.
Neurochemical Research - Inhalation anesthetic isoflurane may cause an increased risk of cognitive impairment. Previous studies have indicated that this cognitive decline is associated with... 相似文献
10.
D. R. Gustafsson L. Lei K. Luo X. Chu X. Zhao Q. Zhang F. Zou 《Medical and veterinary entomology》2019,33(3):407-419
In total, 366 birds representing 55 species in 24 families and eight orders, were examined for chewing lice (Phthiraptera: Amblycera, Ischnocera) in two high‐altitude localities in Yunnan Province, China. In Ailaoshan, almost all of the birds examined were resident passeriforms, of which 36% were parasitized by chewing lice. In Jinshanyakou, most birds were on migration, and included both passerine and non‐passerine birds. Of the passerine birds caught in Jinshanyakou, only one bird (0.7%) was parasitized by chewing lice. The prevalence of Myrsidea and Brueelia‐complex lice on birds caught in Ailaoshan was higher than in previous reports. Of the chewing lice identifiable to species level, three represent new records for China: Actornithophilus hoplopteri (Mjöberg, 1910), Maculinirmus ljosalfar Gustafsson & Bush, 2017 and Quadraceps sinensis Timmermann, 1954. In total, 17 new host records are included, of which we describe two as new species in the Brueelia‐complex: Guimaraesiella (Cicchinella) ailaoshanensis sp. nov. ex Schoeniparus dubius dubius (Hume, 1874) and G. (C.) montisodalis sp. nov. ex Fulvetta manipurensis tonkinensis Delacour & Jabouille, 1930. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:9FC3D8EE‐2CED‐4DBE‐A1DB‐471B71260D27 . 相似文献