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   59149篇
  免费   3339篇
  国内免费   37篇
林业   3064篇
农学   2220篇
基础科学   353篇
  7485篇
综合类   6909篇
农作物   2113篇
水产渔业   3208篇
畜牧兽医   33115篇
园艺   739篇
植物保护   3319篇
  2019年   503篇
  2018年   958篇
  2017年   1042篇
  2016年   1009篇
  2015年   870篇
  2014年   1019篇
  2013年   2338篇
  2012年   1819篇
  2011年   2210篇
  2010年   1443篇
  2009年   1381篇
  2008年   2047篇
  2007年   2052篇
  2006年   1948篇
  2005年   1799篇
  2004年   1695篇
  2003年   1680篇
  2002年   1549篇
  2001年   2347篇
  2000年   2196篇
  1999年   1733篇
  1998年   687篇
  1997年   624篇
  1996年   609篇
  1995年   675篇
  1994年   576篇
  1993年   562篇
  1992年   1270篇
  1991年   1401篇
  1990年   1461篇
  1989年   1340篇
  1988年   1246篇
  1987年   1238篇
  1986年   1174篇
  1985年   1116篇
  1984年   920篇
  1983年   734篇
  1982年   527篇
  1979年   796篇
  1978年   618篇
  1977年   470篇
  1976年   528篇
  1975年   509篇
  1974年   631篇
  1973年   613篇
  1972年   638篇
  1971年   611篇
  1970年   591篇
  1969年   539篇
  1967年   510篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
Serum samples from 224 Norwegian cats were analyzed for the presence of feline leukemia virus (FeLV) p27 common core antigen, and for antibodies to feline immunodeficiency virus (FIV). Ninety specimens originated from the serum bank at the central referral clinic at the Norwegian College of Veterinary Medicine, which had been collected during the years 1983-1989; 67 sera were submitted from veterinarian practitioners; while 67 sera originated from cats presented for euthanasia. The cats were classified into one "healthy" and one "sick" group. Only 2.2% of sick cats and 1.2% of healthy cats showed FeLV antigenemia, a finding which is lower than which has been reported from many other countries. The prevalence of FIV antibodies was 10.1% in sick cats and 5.9% in healthy cats. Antibodies to FIV was most prevalent in male cats (14.7%) than in female cats (2.1%), and more prevalent among domestic cats (12.0%) compared to pedigree cats (2.4%). Antibodies to FIV in the cats demonstrated increasing prevalence with increasing age. It may be concluded that FeLV causes minor problems in Norwegian cats, while FIV is present in a similar prevalence to what is reported from other countries.  相似文献   
154.
155.
156.
157.
158.
159.
160.
The cellularity of subcutaneous adipose tissue of 108 male castrated pigs (German Landrace) was investigated. The tissue was taken bioptically under anesthetic conditions. The outer and the inner layer of backfat were examined separately, fresh unfixed tissue slices floating in Ringer solution were subjected to microscopic measurements of adipocyte diameters. The animals were kept in feeding experiments, 3 and 2 sectors respectively of growing period were examined (40 kg; 66 kg, 88 kg body mass) divided into 6 and 4 feeding levels respectively for 21 days (0.4; 0.6/0.8; 1.0; 1.2; 1.4 MJ metabolic energy per kg body mass0.75 per day). The inner layer of backfat showed bigger fat cells compared to the outer layer. The average fat cell size was greater for the older and heavier than for the younger animals. The gradation of food administration resulted not in a straight parallel rise in fat cell size but in an effective consequence with respect to the distribution frequency of the dates: The higher the food energy level, the more the accumulation of small fat cells from 10 til 30 microns diameter. These cell fractions succeeded in being signified as typical and important closed population. Other authors also had described these particular cells, i.e. "fat cell clusters" and "VSFC" (= very small fat cells) respectively. An external use of the dates for computer simulation programs resulted in success and manifested the independently gained conclusions. The examinations were performed by support of different branches of literature and the results had to be discussed in front of a wide background of known connections.(ABSTRACT TRUNCATED AT 250 WORDS)  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