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   128870篇
  免费   9449篇
  国内免费   45篇
  2023年   701篇
  2022年   1140篇
  2021年   2299篇
  2020年   1786篇
  2019年   2041篇
  2018年   3310篇
  2017年   2974篇
  2016年   4233篇
  2015年   5760篇
  2014年   5925篇
  2013年   7747篇
  2012年   9048篇
  2011年   8378篇
  2010年   5349篇
  2009年   4668篇
  2008年   6375篇
  2007年   6090篇
  2006年   5756篇
  2005年   5515篇
  2004年   5373篇
  2003年   4746篇
  2002年   4098篇
  2001年   3036篇
  2000年   2925篇
  1999年   2470篇
  1998年   1239篇
  1997年   1063篇
  1996年   1092篇
  1995年   926篇
  1994年   837篇
  1993年   793篇
  1992年   1573篇
  1991年   1367篇
  1990年   1263篇
  1989年   1253篇
  1988年   1205篇
  1987年   1120篇
  1986年   1031篇
  1985年   1026篇
  1984年   966篇
  1983年   720篇
  1982年   619篇
  1981年   553篇
  1980年   530篇
  1979年   695篇
  1978年   608篇
  1977年   474篇
  1975年   522篇
  1974年   545篇
  1973年   554篇
排序方式: 共有10000条查询结果,搜索用时 630 毫秒
141.
Comparative mineral and hormonal analyses were made on tissue culture derived truncated leaf syndrome and wild type oil palm seedlings. Mineral analysis confirmed that Boron, Zinc and chlorophyll levels were significantly lower in truncated leaf syndrome leaves than those of wild type. Hormonal analysis also revealed various cytokinin derivatives such as trans-zeatin, trans-zeatin riboside, trans-zeatin O-glucoside and trans-zeatin riboside 5??mono phosphate were significantly higher in truncated leaf syndrome leaves compared to wild type leaves. Brassinolide level was also significantly higher in truncated leaf syndrome leaves than those of the wild type. These observations suggest that the truncated leaf syndrome abnormality could be associated to high cytokinin and brassinosteroid production which affects the uptake of Boron and Zinc.  相似文献   
142.
143.
144.
Bonobos have a reputation as a female-dominated and egalitarian species. We examined the 2 aspects of dominance in 6 captive bonobo groups. Females do not consistently evoke submission from all males in all contexts. Though females occupy the highest-ranking positions in the dominance hierarchy, there are in each group males that obtain rather high ranks and are able to dominate ≥1 female. Thus female dominance is not complete and hierarchies can be better described as nonexclusive female dominance. We studied egalitarianism by measuring linearity and steepness of dominance hierarchies. The hierarchies of all groups are highly linear. Hierarchies among males are steeper than among females. On average, male bonobos are more despotic than females, but females too can have despotic relations, both with other females and with males. Hence one can call bonobos in captivity semidespotic rather than egalitarian.  相似文献   
145.
Forty-five populations of Pentanema corresponding to seven species included in the Pentanema conyzae clade have been studied using AFLP fingerprinting. The results show that allopolyploidization could have been involved in the diversification of this group, specifically in species P. langeanum and P. maletii. Molecular data confirm the presence of P. britannicum in the Iberian Peninsula and key steps are provided to identify the species that are morphologically the most challenging.  相似文献   
146.
147.
Hydrobiologia - In shallow lakes, macrophytes have important effects on food webs, community structure and nutrient dynamics. For this reason they play a significant role in the restoration of...  相似文献   
148.
149.
150.
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