首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   49262篇
  免费   4186篇
  国内免费   4456篇
  2024年   82篇
  2023年   589篇
  2022年   1459篇
  2021年   2549篇
  2020年   1805篇
  2019年   2375篇
  2018年   2193篇
  2017年   1617篇
  2016年   2232篇
  2015年   3136篇
  2014年   3810篇
  2013年   3994篇
  2012年   4601篇
  2011年   4162篇
  2010年   2525篇
  2009年   2296篇
  2008年   2765篇
  2007年   2481篇
  2006年   2020篇
  2005年   1682篇
  2004年   1458篇
  2003年   1368篇
  2002年   1231篇
  2001年   891篇
  2000年   751篇
  1999年   692篇
  1998年   434篇
  1997年   363篇
  1996年   339篇
  1995年   294篇
  1994年   286篇
  1993年   191篇
  1992年   249篇
  1991年   221篇
  1990年   166篇
  1989年   128篇
  1988年   97篇
  1987年   81篇
  1986年   53篇
  1985年   60篇
  1984年   34篇
  1983年   39篇
  1982年   24篇
  1981年   23篇
  1980年   10篇
  1979年   9篇
  1975年   5篇
  1966年   3篇
  1965年   4篇
  1964年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Plant somatic cells have the capability to switch their cell fates from differentiated to undifferentiated status under proper culture conditions, which is designated as totipotency. As a result, plant cells can easily regenerate new tissues or organs from a wide variety of explants. However, the mechanism by which plant cells have such remarkable regeneration ability is still largely unknown. In this study, we used a set of meristem-specific marker genes to analyze the patterns of stem cell differentiation in the processes of somatic embryogenesis as well as shoot or root organogenesis in vitro. Our studies furnish preliminary and important information on the patterns of the de novo stem cell differentiation during various types of in vitro organogenesis.  相似文献   
2.
3.
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   
4.
5.
6.
  相似文献   
7.
8.
9.
Liu  Rui-zhu  Li  Tao  Zhao  Guo-qing 《Neurochemical research》2019,44(5):1090-1100
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.
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号