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   42630篇
  免费   16666篇
  国内免费   6篇
  2023年   90篇
  2022年   241篇
  2021年   722篇
  2020年   2365篇
  2019年   3908篇
  2018年   4065篇
  2017年   4306篇
  2016年   4462篇
  2015年   4699篇
  2014年   4385篇
  2013年   5034篇
  2012年   2969篇
  2011年   2617篇
  2010年   3757篇
  2009年   2468篇
  2008年   1640篇
  2007年   1216篇
  2006年   1180篇
  2005年   1205篇
  2004年   1104篇
  2003年   1071篇
  2002年   1102篇
  2001年   398篇
  2000年   318篇
  1999年   327篇
  1998年   247篇
  1997年   181篇
  1996年   180篇
  1995年   183篇
  1994年   157篇
  1993年   111篇
  1992年   175篇
  1991年   133篇
  1990年   113篇
  1989年   126篇
  1988年   87篇
  1987年   107篇
  1986年   102篇
  1985年   117篇
  1984年   113篇
  1983年   94篇
  1982年   120篇
  1981年   132篇
  1980年   106篇
  1979年   99篇
  1978年   99篇
  1977年   92篇
  1976年   91篇
  1974年   76篇
  1973年   75篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Summary Municipal compost applied to soils in plot experiments with cabbages, lettuces, beans, potatoes and peas in three successive years (25–100 tonnes per hectare) has produced significant enhancement of available soil Cu, Zn and B in each year. Associated significant increases in uptake were as follows: Cu, Zn and B with lettuces and beans, Zn and B with potatoes and B with peas. No significant increases in uptake of any of these elements was obtained in two experiments with cabbages.Compost treatment was associated with severe phytotoxic effects in the experiment with beans and with yield responses in the experiments with peas and potatoes. re]19721116  相似文献   
102.
After observing specimens of Calligonum pumilum Losinsk. and C. juochiangense Y. X. Liou in both the field and in herbarium collections, it was found that the morphological characters of these two species are quite different, especially with respect of the twisted direction of fruit ribs, number of bristle rows along each rib, rigidity and degree of interweaving of bristles, as well as their geographic distribution. Therefore, it is concluded that C. pumilum and C. juochiangense should be accepted as two independent species.  相似文献   
103.
104.
105.
The spatial epidemiology of Bluetongue virus (BTV) at the landscape level relates to the fine‐scale distribution and dispersal capacities of its vectors, midges belonging to the genus Culicoides Latreille (Diptera: Ceratopogonidae). Although many previous researches have carried out Culicoides sampling on farms, little is known of the fine‐scale distribution of Culicoides in the landscape immediately surrounding farms. The aim of this study was to gain a better understanding of Culicoides populations at increasing distances from typical dairy farms in north‐west Europe, through the use of eight Onderstepoort‐type black‐light traps positioned along linear transects departing from farms, going through pastures and entering woodlands. A total of 16 902 Culicoides were collected in autumn 2008 and spring 2009. The majority were females, of which more than 97% were recognized as potential vectors. In pastures, we found decreasing numbers of female Culicoides as a function of the distance to the farm. This pattern was modelled by leptokurtic models, with parameters depending on season and species. By contrast, the low number of male Culicoides caught were homogeneously distributed along the transects. When transects entered woodlands, we found a higher abundance of Culicoides than expected considering the distance of the sampling sites to the farm, although this varied according to species.  相似文献   
106.
107.
108.
109.
110.
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