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   1254篇
  免费   107篇
  国内免费   1篇
林业   77篇
农学   31篇
基础科学   4篇
  146篇
综合类   214篇
农作物   57篇
水产渔业   70篇
畜牧兽医   625篇
园艺   18篇
植物保护   120篇
  2021年   26篇
  2020年   28篇
  2019年   24篇
  2018年   25篇
  2017年   25篇
  2016年   32篇
  2015年   25篇
  2014年   31篇
  2013年   45篇
  2012年   54篇
  2011年   74篇
  2010年   37篇
  2009年   35篇
  2008年   63篇
  2007年   55篇
  2006年   49篇
  2005年   50篇
  2004年   36篇
  2003年   37篇
  2002年   35篇
  2001年   14篇
  2000年   25篇
  1999年   16篇
  1998年   9篇
  1997年   14篇
  1996年   12篇
  1995年   11篇
  1994年   8篇
  1993年   9篇
  1992年   14篇
  1991年   19篇
  1990年   22篇
  1989年   26篇
  1988年   16篇
  1987年   19篇
  1986年   13篇
  1985年   11篇
  1984年   13篇
  1983年   21篇
  1981年   13篇
  1980年   13篇
  1979年   14篇
  1978年   15篇
  1977年   12篇
  1976年   16篇
  1975年   10篇
  1974年   10篇
  1973年   14篇
  1972年   15篇
  1967年   7篇
排序方式: 共有1362条查询结果,搜索用时 15 毫秒
31.
32.
A study was designed to evaluate the representativeness and accuracy of data collected on swine birth defects by mailed questionnaire. The study was conducted in the three contiguous counties of Johnson, Lafayette and Pettis in west central Missouri. A personal interview survey and an examination of malformed pigs were used to validate mailed questionnaire data which estimated the frequency and distribution of malformations observed in pigs over a six month period. This period between April and September 1970 was defined as the study period. The results were compared to a previous six month period (April-September 1969), or baseline period, when only the mailed questionnaire was used. The frequency and distribution of the reported malformations by type did not differ significantly (at the p=0.05 level) between the study period (70.4% response) and the baseline period (31.3% response). Evaluation of this and additional data collected during the study suggested that the mailed questionnaire can be used effectively to estimate the frequency and distribution of swine malformations within a defined geographic area.  相似文献   
33.
34.
A cytopathogenic virus isolated from an Iowa farm pig with diarrhea was identified as a member of Group 5 of the porcine enteroviruses. Clinical signs observed in other pigs in the herd were diarrhea, debilitation and gauntness. Morbidity and mortality rates were approximately 50% and 3% respectively.

A Group 5 porcine enterovirus had not been previously isolated in North America according to the Western Hemisphere Committee on Animal Virus Characterization.

  相似文献   
35.
36.
37.
38.
Two serovars of salmonella which are currently of particular importance in both human and animal infections are Salmonella enterica serovars Enteritidis phage type 4 (PT4) and Typhimurium definitive type 104 (DT104). This paper describes the trends in the relationships between the levels of infection of people and a range of farm animal species with these two serovars and explores some of the reasons behind them. In 1996, there was a peak of 520 reports of S Typhimurium DT104 infection in people in Scotland, but the number has decreased every year since, to 96 in 2001. In cattle the incidence of S Typhimurium DT104 also peaked in 1996, with 138 incidents, and it has similarly decreased every year to 2001 when there were 10 reported incidents. Similar declines have been observed in its incidence in sheep and pigs. In people the number of reports of S Enteritidis PT4 peaked in 1997 at 1684 and then declined to 457 in 2001. In chickens, the number of reports of S Enteritidis PT4 peaked in 1998 at 34 incidents, but no incidents were reported in the following three years.  相似文献   
39.
40.
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