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   159341篇
  免费   9231篇
  国内免费   133篇
林业   6747篇
农学   4961篇
基础科学   1106篇
  19994篇
综合类   26274篇
农作物   6088篇
水产渔业   8388篇
畜牧兽医   81434篇
园艺   2099篇
植物保护   11614篇
  2019年   1518篇
  2018年   2400篇
  2017年   2578篇
  2016年   2457篇
  2015年   2097篇
  2014年   2537篇
  2013年   6220篇
  2012年   4820篇
  2011年   5747篇
  2010年   3496篇
  2009年   3454篇
  2008年   5507篇
  2007年   5251篇
  2006年   4985篇
  2005年   4695篇
  2004年   4557篇
  2003年   4477篇
  2002年   4387篇
  2001年   5004篇
  2000年   4808篇
  1999年   3912篇
  1998年   1539篇
  1997年   1569篇
  1995年   1807篇
  1994年   1625篇
  1993年   1540篇
  1992年   3228篇
  1991年   3337篇
  1990年   3380篇
  1989年   3380篇
  1988年   3114篇
  1987年   3187篇
  1986年   3279篇
  1985年   3136篇
  1984年   2643篇
  1983年   2350篇
  1982年   1601篇
  1981年   1494篇
  1980年   1452篇
  1979年   2352篇
  1978年   1934篇
  1977年   1645篇
  1976年   1462篇
  1975年   1557篇
  1974年   2101篇
  1973年   2119篇
  1972年   2086篇
  1971年   1838篇
  1970年   1738篇
  1969年   1598篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
951.
952.
R. J. HANCE 《Weed Research》1969,9(2):108-113
Summary. Model adsorbents were prepared by treating cellulose phosphate powder with a series of alkyltrimethylammonium compounds in which the size of the alkyl group was varied from C8to C18. The adsorption of linuron, atrazine and EPTC by these materials was found to increase logarithmically with increasing chain length. The extent of the adsorption was large compared with the adsorption of these herbicides by a humic acid and by a preparation made by removing the bulk of the inorganic constituents of a peat soil with a mixture of HCl and HF. Since soil organic matter is thought to contain alkyl groups, it is concluded that the possible influence of such groups should be considered in any discussion of the mechanisms involved in the adsorption of organic molecules by soils.
Adsorption du linuron, de I'atrazine de l'EPTC par des adsorbants de la série aliphatique et des préparations organiques de sol  相似文献   
953.
954.
Summary. Entry of ioxynil-14C into portions of leaves was greater with mustard than with barley or pea and was unrelated to stomatal density. Measurement of ioxynil content of sprayed plants showed that by increasing the concentration of ioxynil and adding a surfactant, almost as much ioxynil could be made to enter barley as entered mustard from a lower concentration without surfactant. Auto radiographs showed that a limited amount of 14C was translocated to a small extent in plants following localized application of ioxynil-14C. An experiment comparing leaf removal by cutting with destruction of equivalent leaf areas by ioxynil treatment suggested a greater translocated effect of ioxynil with mustard than with pea or barley. Les principes de la phytotoxicité différentielle du 4-hydroxy-3,5-di-iodobetZonitrile II. Absorption et migration  相似文献   
955.
Summary. The adsorption of simazine from, and subsequent desorption into, 0–01 M calcium chloride solution was investigated using twenty-three Rothamsted soil samples from sites differing greatly in cropping history and manurial treatment. Organic carbon content was the only factor related to the ability of the soils to sorb simazine; this accounted for 90% or more of the variation between soils Equilibrium was attained during adsorption in from fewer than 2 to more than 24 hr. Equilibrium during desorption was only occasionally attained within 24 hr. Differences between theoretically predicted and measured concentrations of simazine in solution following desorption were least for soils that attained equilibrium fastest during adsorption. Differences in adsorption and desorption kinetics between soils could not be related to soil pH, organic carbon content or cropping and manuring history. Comparisons of unlimed and limed soils suggested that no simnazine was lost by acid hydrolysis during the experiments.
Adsorption et désorption de la simazine par quelques sols de Rothamsted  相似文献   
956.
957.
958.
959.
960.
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