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   24134篇
  免费   2184篇
  国内免费   19篇
  2023年   90篇
  2022年   177篇
  2021年   395篇
  2020年   203篇
  2019年   277篇
  2018年   375篇
  2017年   309篇
  2016年   538篇
  2015年   982篇
  2014年   1089篇
  2013年   1427篇
  2012年   1673篇
  2011年   1719篇
  2010年   1124篇
  2009年   957篇
  2008年   1417篇
  2007年   1479篇
  2006年   1385篇
  2005年   1343篇
  2004年   1307篇
  2003年   1251篇
  2002年   1239篇
  2001年   246篇
  2000年   185篇
  1999年   280篇
  1998年   353篇
  1997年   251篇
  1996年   215篇
  1995年   215篇
  1994年   218篇
  1993年   214篇
  1992年   175篇
  1991年   155篇
  1990年   175篇
  1989年   158篇
  1988年   154篇
  1987年   142篇
  1986年   124篇
  1985年   131篇
  1984年   156篇
  1983年   153篇
  1982年   170篇
  1981年   156篇
  1980年   138篇
  1979年   101篇
  1978年   109篇
  1977年   100篇
  1976年   85篇
  1974年   84篇
  1973年   75篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
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   
12.
13.
14.
15.
Chlorokybus atmophyticus has a sarcinoid growth habit and produces scale-covered zoospores. Flagella are laterally inserted and attached internally to a multilayered structure characteristic of the Charophyceae. There are two kinds of pyrenoid in each cell, a feature previously observed in only one scaly green flagellate. C. atmophyticus demonstrates that the sarcinoid growth habit arose independently at least twice in the green algae and cannot be used to define taxonomic groups unless combined with other criteria. It is further concluded that C. atmophyticus should be classified in a separate family Chlorokybaceae and a separate order Chloroky bales.  相似文献   
16.
17.
Wives and Warriors: Women and the Military in the United States and Canada. Laurie Weinstein and Christie C. White. eds. Westport, CT: Bergin and Garvey, 1997. 252 pp.  相似文献   
18.
19.
20.
The in vivo effects of dexamethasone administration on liver and extrahepatic tissue carnitine concentrations were assessed in 48-h-starved rats. In heart and kidney, but not in liver, dexamethasone significantly increased total carnitine concentration. Acute (2.5 h) treatment with 2-tetradecylglycidate (TDG), a specific inhibitor of carnitine palmitoyl transferase 1, not only increased total hepatic carnitine concentrations, but also permitted an effect of dexamethasone (a further increase in hepatic carnitine concentration). The results are discussed in terms of acute (substrate-mediated) and chronic (hormonal) control of carnitine turnover.  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