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   41278篇
  免费   3189篇
  国内免费   2908篇
  2024年   51篇
  2023年   544篇
  2022年   1237篇
  2021年   2267篇
  2020年   1503篇
  2019年   2000篇
  2018年   1886篇
  2017年   1281篇
  2016年   1869篇
  2015年   2598篇
  2014年   3095篇
  2013年   3402篇
  2012年   3804篇
  2011年   3383篇
  2010年   2022篇
  2009年   1834篇
  2008年   2112篇
  2007年   1888篇
  2006年   1572篇
  2005年   1256篇
  2004年   1042篇
  2003年   926篇
  2002年   725篇
  2001年   684篇
  2000年   623篇
  1999年   592篇
  1998年   363篇
  1997年   373篇
  1996年   355篇
  1995年   316篇
  1994年   303篇
  1993年   198篇
  1992年   272篇
  1991年   228篇
  1990年   167篇
  1989年   141篇
  1988年   118篇
  1987年   94篇
  1986年   57篇
  1985年   66篇
  1984年   36篇
  1983年   39篇
  1982年   18篇
  1981年   20篇
  1980年   8篇
  1979年   6篇
  1965年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 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.
4.
Comment on: Rokavec M, et al. Mol Cell 2012; 45:777-89.  相似文献   
5.
6.
7.
  相似文献   
8.
Due to the fact that the flood data series of small drainage basins is relatively short, available data are often not sufficient for flood risk analysis. This presents the problem of risk analysis using very small data samples. One method that can be applied is to regard the available small samples as fuzzy information and optimize them using information diffusion technology to yield analytical results with greater reliability. In this article a risk analysis method based on information diffusion theory is applied to create a new flood risk analysis model. Application of the model is illustrated taking the Jinhuajiang and Qujiang drainage basins as examples. This is a new attempt at applying information diffusion theory in flood risk analysis. Computations based on this analytical flood risk model can yield an estimated flood damage value that is relatively accurate. This study indicates that the aforementioned model exhibits fairly stable analytical results, even when using a small set of sample data. The results also indicate that information diffusion technology is highly capable of extracting useful information and therefore improves system recognition accuracy. This method can be easily applied and the analytical results produced are easy to understand. Results are accurate enough to act as a guide in disaster situations.  相似文献   
9.
10.
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   
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