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   151020篇
  免费   8352篇
  国内免费   73篇
林业   6723篇
农学   5145篇
基础科学   977篇
  18935篇
综合类   26788篇
农作物   6319篇
水产渔业   7394篇
畜牧兽医   74638篇
园艺   2284篇
植物保护   10242篇
  2018年   2848篇
  2017年   3093篇
  2016年   2420篇
  2015年   1810篇
  2014年   2136篇
  2013年   5562篇
  2012年   4243篇
  2011年   5574篇
  2010年   4109篇
  2009年   3906篇
  2008年   5291篇
  2007年   5312篇
  2006年   4176篇
  2005年   4058篇
  2004年   3814篇
  2003年   3955篇
  2002年   3652篇
  2001年   4493篇
  2000年   4315篇
  1999年   3492篇
  1998年   1520篇
  1997年   1484篇
  1996年   1319篇
  1995年   1634篇
  1994年   1423篇
  1993年   1451篇
  1992年   2935篇
  1991年   3045篇
  1990年   2965篇
  1989年   3029篇
  1988年   2754篇
  1987年   2786篇
  1986年   2926篇
  1985年   2792篇
  1984年   2298篇
  1983年   2028篇
  1982年   1442篇
  1979年   2073篇
  1978年   1631篇
  1977年   1480篇
  1976年   1401篇
  1975年   1510篇
  1974年   1861篇
  1973年   1928篇
  1972年   1844篇
  1971年   1757篇
  1970年   1660篇
  1969年   1574篇
  1968年   1280篇
  1967年   1409篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Mean selenium and vitamin E (alpha-tocopherol) concentrations in the liver, myocardium and skeletal muscle of nine goat kids with nutritional myodegeneration (NMD) were significantly lower than those in a group of nine kids dying from other causes. Each of the 18 kids was from a different property in the southern half of the North Island. The polyunsaturated fatty acid composition of the liver, myocardium and skeletal muscle was not significantly different between the two groups, but the overall level of peroxidisable polyunsaturated fatty acids appeared high in both groups. A further 21 kids with confirmed NMD and live 'controls', submitted as routine cases to Palmerston North Animal Health Laboratory, were included with the above 18 kids in a comparison of liver selenium and alpha-tocopherol concentrations. Kids with NMD had liver selenium concentrations ranging from 170-1100 (mean = 380) nmol/kg and alpha-tocopherol from 0.7-11.0 (mean =2.2) micromol/kg. In control kids, the liver selenium concentration ranged from 530-4300 (mean = 1220) nmol/kg and a-tocopherol from 1.7-14.0 (mean = 5.6) pmollkg. Although these ranges overlapped, the results suggest that liver selenium concentrations <500 nmol/kg and alpha-tocopherol concentrations <2.5 micromol/kg should be regarded as deficient. Liver selenium concentrations from 500-1100 nmol/kg and alpha-tocopherol concentrations from 2.5-10 micromol/kg should be considered marginal. Goat kids appear to require more selenium than lambs or calves which may explain the higher prevalence of NMD in kids. In some cases, however, the disease is associated with low alpha-tocopherol suggesting that supplementation with selenium alone may not always be sufficient.  相似文献   
992.
For various anamnestic reasons the cervical vertebral column of 78 horses was examined radiologically. Statistical comparisons showed that male "warmbloods" were more frequently affected than was expected. Our horses were older than comparable animals in the international literature. Independently of their history the radiologic diagnosis of "cervical spondylarthrosis" was established in 56 horses. Arthrosis and other conditions were clinically manifested by spinal ataxia (44 horses) or mechanical impairment of the neck's mobility (21 horses). 10 of the arthrotic patients had synovial cysts causing compression of the spinal cord. 79 percent of all dorsal intervertebral arthrotic joints were found in the caudal column (C6/7 to C7/Th1). With 38 percent, C6/7 was the most frequently affected joint. Clinical and radiological findings could be compared with patho-anatomic results in 29 horses. The correlation was satisfactory.  相似文献   
993.
A total of 763 fecal or intestinal samples from diarrheic calves and piglets were examined for viral content by immunofluorescence, electron microscopy or cell culture. Routine fluorescent antibody and cultural tests detected rotavirus (n=126), coronavirus (n=80) and bovine viral diarrhea virus (n=13). Electron microscopy detected rotaviruses (n=24) and coronaviruses (n=17) not identified by standard fluorescent antibody tests. Other viruses detected by electron microscopy included Breda virus-like particles (n=49), astroviruses (n=1), caliciviruses (n=1), rhabdoviruses (n=1), parvoviruses (n=2), enteroviruses (n=3), togavirus-like particles (n=2), and “chained” particles (n=5). Mixtures of several of the viruses were detected in a number of fecal samples.

The survey emphasized the value of electron microscopy as a broad-spectrum diagnostic tool.

  相似文献   
994.
995.
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