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   142811篇
  免费   7467篇
  国内免费   82篇
林业   6480篇
农学   4239篇
基础科学   890篇
  15991篇
综合类   28462篇
农作物   5694篇
水产渔业   6404篇
畜牧兽医   72112篇
园艺   1645篇
植物保护   8443篇
  2018年   1722篇
  2017年   1886篇
  2016年   1761篇
  2015年   1551篇
  2014年   1845篇
  2013年   5200篇
  2012年   3620篇
  2011年   4386篇
  2010年   2866篇
  2009年   2906篇
  2008年   4351篇
  2007年   4120篇
  2006年   3922篇
  2005年   3700篇
  2004年   3746篇
  2003年   3695篇
  2002年   3565篇
  2001年   4333篇
  2000年   4304篇
  1999年   3302篇
  1998年   1403篇
  1997年   1422篇
  1995年   1609篇
  1994年   1501篇
  1993年   1464篇
  1992年   2984篇
  1991年   3157篇
  1990年   3058篇
  1989年   3122篇
  1988年   2852篇
  1987年   2976篇
  1986年   3099篇
  1985年   3022篇
  1984年   2435篇
  1983年   2239篇
  1982年   1483篇
  1981年   1399篇
  1979年   2218篇
  1978年   1821篇
  1977年   1503篇
  1976年   1471篇
  1975年   1549篇
  1974年   2025篇
  1973年   2040篇
  1972年   2050篇
  1971年   1992篇
  1970年   1820篇
  1969年   1712篇
  1968年   1358篇
  1967年   1486篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
171.
172.
The rate of the frog or guinea pig heart preparation was not significantly influenced by the H-ion concentration when this was kept within limits which allowed the heart to continue beating. The theory that the H-ion concentration is intimately concerned with the origination of the heart beat is not supported by the results of this investigation.  相似文献   
173.
174.
175.
176.
177.
178.
179.
Intrajugular injection of a purified E. coli lipopolysaccharide induced a biphasic fever in sheep after a latent period of 12 to 20 min. The changes in the blood flow from the liver and from the viscera drained by the portal vein were: (a) in the latent period, decreases in total hepatic blood flow (THF) due to decreased portal venous blood flow (PVF); (b) during the first febrile phase, increases in THF due to increased hepatic arterial blood flow and, (c) in the second febrile phase, increases in THF due to decreased PVF. Although there were large variations in the oxygen supply to the viscera drained by the portal vein and to the liver, there were relatively small or no changes in their oxygen consumption.  相似文献   
180.
Abstract. Slurry from farm animals may contaminate water supplies, rivers and bathing waters with faecal coliforms, such as Escherichia coli . Where animals harbour the O157 strain the hazard to human health is particularly high, but both the hazard level, and the low incidence and sporadic nature of the excretion of E. coli O157 make it difficult to study this strain under field conditions. The survival of total E. coli and of E. coli O157 were compared in the laboratory for two soils under controlled temperature and moisture. E. coli O157 die-off rate was the same as or quicker than for total E. coli . This result meant that field experiments studying the fate of total E. coli should give a satisfactory evaluation of the risk of water contamination by the O157 strain. In four field experiments at three sites, slurry containing total E. coli numbers of 2.2 × 104 to 5.7 × 105 colony forming units per mL (c.f.u. mL–1) was applied to drained field plots. Field die-off was faster than expected from laboratory experiments, especially in one experiment where two weeks dry weather followed application. In all but this experiment, the first drain flow events after slurry application led to very high E. coli concentrations in the drains (103 to 104 c.f.u. mL–1). E. coli O157 was present in the slurry used for two of the experiments (33 c.f.u. per 100 mL in each case). However the proportion of E.coli O157 was very low (about 1 in 105) and it was not detected in the drainage water. After the first week E. coli drainage water numbers decreased rapidly but they were 1–10 c.f.u. mL–1 for much of the sampling period after slurry application (1–3 months).  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