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   149298篇
  免费   8629篇
  国内免费   83篇
林业   5381篇
农学   4353篇
基础科学   1030篇
  16815篇
综合类   25421篇
农作物   5385篇
水产渔业   7308篇
畜牧兽医   80216篇
园艺   1771篇
植物保护   10330篇
  2018年   1871篇
  2017年   2073篇
  2016年   1926篇
  2015年   1734篇
  2014年   2154篇
  2013年   5588篇
  2012年   3957篇
  2011年   4961篇
  2010年   3089篇
  2009年   3196篇
  2008年   4826篇
  2007年   4560篇
  2006年   4425篇
  2005年   4123篇
  2004年   4062篇
  2003年   4064篇
  2002年   4013篇
  2001年   4825篇
  2000年   4637篇
  1999年   3775篇
  1998年   1594篇
  1997年   1629篇
  1996年   1513篇
  1995年   1874篇
  1994年   1680篇
  1993年   1606篇
  1992年   3271篇
  1991年   3387篇
  1990年   3458篇
  1989年   3409篇
  1988年   3132篇
  1987年   3238篇
  1986年   3263篇
  1985年   3152篇
  1984年   2670篇
  1983年   2366篇
  1982年   1604篇
  1981年   1481篇
  1980年   1432篇
  1979年   2316篇
  1978年   1909篇
  1977年   1627篇
  1976年   1441篇
  1975年   1540篇
  1974年   2074篇
  1973年   2086篇
  1972年   2053篇
  1971年   1816篇
  1970年   1712篇
  1969年   1573篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
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   
993.
994.
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   
995.
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   
996.
997.
998.
999.
1000.
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