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   82448篇
  免费   3889篇
  国内免费   65篇
林业   4297篇
农学   2566篇
基础科学   439篇
  8755篇
综合类   15798篇
农作物   3562篇
水产渔业   3768篇
畜牧兽医   41093篇
园艺   1081篇
植物保护   5043篇
  2018年   968篇
  2017年   1099篇
  2016年   1019篇
  2015年   1000篇
  2014年   1147篇
  2013年   2735篇
  2012年   2094篇
  2011年   2351篇
  2010年   1461篇
  2009年   1350篇
  2008年   2090篇
  2007年   2116篇
  2006年   1931篇
  2005年   2559篇
  2004年   2375篇
  2003年   2208篇
  2002年   1793篇
  2001年   2309篇
  2000年   2247篇
  1999年   1945篇
  1998年   705篇
  1997年   699篇
  1995年   816篇
  1993年   700篇
  1992年   1563篇
  1991年   1656篇
  1990年   1771篇
  1989年   1747篇
  1988年   1637篇
  1987年   1549篇
  1986年   1616篇
  1985年   1589篇
  1984年   1310篇
  1983年   1190篇
  1982年   790篇
  1981年   727篇
  1979年   1337篇
  1978年   1052篇
  1977年   906篇
  1976年   857篇
  1975年   1004篇
  1974年   1275篇
  1973年   1316篇
  1972年   1336篇
  1971年   1246篇
  1970年   1146篇
  1969年   1086篇
  1968年   944篇
  1967年   1009篇
  1966年   915篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Above ground production of a typical Cortaderia pilosa dominant sward in the Falkland Islands was estimated over one growing season by summing significant positive increments in DM production of various sward components and by sequential cutting to ground level. The standing crop was characterized by a high proportion of standing dead matter at all times of the year. Net herbage production was estimated as 2200 kg ha-1 and 1440 kg ha-1 by the 'difference' and "sequential culling" techniques, respectively. The pattern of leaf growth was determined on another site by regular linear measurements of a population of physiologically similar C. pilosa leaves. There was very little early season growth and most of the DM was produced in a short period in the middle part of the growing season. The poor early season growth was attributed to adverse climatic conditions. A significant increase in green matter digestibility in October and November was masked by the low digestibility and high contribution to the overall DM by the standing dead component of the herbage.
The implications of these findings are briefly discussed in relation to the increased utilization of C. pilosa by improved pasture management, including burning and possibly reseeding areas with improved species. Tissue turnover studies combined with more knowledge of sheep nutrition cycles would enable grazing systems to be developed on a sounder basis than previously.  相似文献   
102.
103.
104.
105.
106.
107.
108.
109.
The vulvar labia of ewes naturally infected with ureaplasma were significantly more swollen and red than those of uninfected ewes. Similar changes were observed following experimental infection of previously uninfected ewes. These differences, although statistically significant, were not sufficiently marked to be useful in diagnosing infection by clinical examination.  相似文献   
110.
Faecal samples from 434 calves under 1 year of age (307 diarrhoeal and 127 normal) were collected from three dairy farms and one village in selected areas of Bangladesh. The samples were tested by an enzyme-linked immunosorbent assay (ELISA) to detect the presence of rotavirus antigen. Of 402 dairy calves tested, 28 (7.0%) were positive, of which 21 (7.2%) were from diarrhoeic calves and 7 (6.3%) from non-diarrhoeic calves. Rotavirus infection varied from farm to farm (2.7–9.2%) and there was no positive response from any of the 32 village calves. Rotavirus was most commonly found in calves of 1 week of age or less (up to 22.2% in one group) but was not found in any calves later than 6 months of age. More than 80% of rotavirus-positive samples from diarrhoeic calves exhibited a titre of 128 or more (geometric mean 345±4.5), whereas non-diarrhoeal calves had titres less than or equal to 128 (geometric mean=29±1.9), suggesting that rotavirus infection in calves in Bangladesh was mostly associated with diarrhoea.  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