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   56879篇
  免费   3594篇
  国内免费   280篇
林业   3350篇
农学   2120篇
基础科学   404篇
  9596篇
综合类   6578篇
农作物   2224篇
水产渔业   3218篇
畜牧兽医   27892篇
园艺   844篇
植物保护   4527篇
  2021年   737篇
  2020年   774篇
  2019年   700篇
  2018年   1568篇
  2017年   1670篇
  2016年   1545篇
  2015年   1211篇
  2014年   1518篇
  2013年   2882篇
  2012年   2676篇
  2011年   2745篇
  2010年   1730篇
  2009年   1656篇
  2008年   2517篇
  2007年   2319篇
  2006年   2057篇
  2005年   1915篇
  2004年   1778篇
  2003年   1730篇
  2002年   1487篇
  2001年   1677篇
  2000年   1617篇
  1999年   1284篇
  1998年   486篇
  1997年   498篇
  1996年   422篇
  1995年   470篇
  1992年   838篇
  1991年   937篇
  1990年   843篇
  1989年   892篇
  1988年   810篇
  1987年   768篇
  1986年   811篇
  1985年   722篇
  1984年   578篇
  1983年   511篇
  1979年   681篇
  1978年   539篇
  1977年   449篇
  1976年   428篇
  1975年   450篇
  1974年   571篇
  1973年   556篇
  1972年   550篇
  1971年   438篇
  1970年   416篇
  1969年   453篇
  1968年   400篇
  1967年   404篇
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
171.
A yearling Rambouillet ram with an asymmetrical scrotum was examined for potential breeding soundness prior to use in a synchronized mating program in a purebred flock of 20 ewes. Initial sperm cell evaluation revealed 78% knobbed acrosomes associated with few other abnormalities of the head and midpiece. Use of the ram resulted in no conception in one group of ten synchronized ewes. One month later, the proportion of sperm cells with knobbed acrosomes was 80%.  相似文献   
172.
173.
A retrospective morbidity and mortality study was carried out on 125 case records of cattle involving xylazine/halothane anesthesia at the Ontario Veterinary College, Guelph between May 1979 and February 1983.  相似文献   
174.

An osteosarcoma of the femoral diaphysis associated with the presence of a bone plate in a dog  相似文献   

175.
The known information on hymenopterous parasites of Nitidulidae was consolidated in this article. Species of parasites, nitidulid hosts and, where possible, plant host of the nitidulids are provided along with citations to sources of information. Thirty-three species of hymenopterous parasites are recorded in nine different families. Since nomenclature of several of the parasites has changed, it was updated with the assistance of specialists.  相似文献   
176.
Clinical hypocalcaemia was associated with single doses of three oi more days; supply of zinc oxide to dairy cows for facial eczema control. Experimental hand dosing of a single dose of zinc oxide (40 and 120 mg Zn/kg b wt) to Jersey cows caused a significant drop in serum calcium concentration at 24 h followed by a rise to concentrations higher than controls at subsequent samplings over four days. At the highest zinc dose rate, 78% of serum calcium values were equal to or lower than the lowest control value at 24 h post dosing. Serum magnesium concentrations had a reciprocal relationship to the calcium levels at all samplings. Serum zinc concentrations were most elevated over the 48 h post dosing, returning to normal levels at the fifth day. Following the highest zinc dose milk yields were reduced by approximately 1.5 kg milk/cow/day for 48 h. Similar results were obtained when cows grazed pasture on which large amounts of zinc oxide had been sprayed.  相似文献   
177.
From October 1983 to July 1984, the north hemisphere of Venus, from latitude 30 degrees to latitude 90 degrees , was mapped by means of the radar imagers and altimeters of the spacecraft Venera 15 and Venera 16. This report presents the results of the radar mapping of the Maxwell Montes region, one of the most interesting features of Venus' surface. A radar mosaic map and contour map have been compiled.  相似文献   
178.
Of 131 cases of Corynebacterium equi infection in horses submitted for necropsy to the Ontario Veterinary College or Veterinary Laboratory Services, OMAF, Guelph, Ontario from 1958 to 1984, 115 were diagnosed as suppurative pneumonia, and of these 55 had associated ulcerative enterocolitis. Only five animals had intestinal involvement without pulmonary lesions. The remaining 11 cases included arthritis/cellulitis, skin abscesses and submandibular lymphadenitis. While the lung, intestine and associated lymph nodes yielded C. equi most frequently, in 21% of cases C. equi was also cultured from parenchymatous organs (spleen, liver or kidney) or blood. Corynebacterium equi infection accounted for 10% of all foals submitted for postmortem examination and 45% of all foals with pneumonia. Affected foals were one to four months of age. Submissions occurred between the months of May and August with a peak during July. There was a significantly greater prevalence of C. equi infection in Standardbreds when compared with other breeds. Of foals in this study, 36% were from farms which had had other horses succumb to this disease. Of the foals with pulmonary involvement, 21% did not have fever or clinical signs referable to the respiratory or gastrointestinal systems, findings which indicated that a large percentage of cases were subclinical.  相似文献   
179.
180.
P & P practice     
  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