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   271539篇
  免费   15822篇
  国内免费   663篇
林业   23988篇
农学   14065篇
基础科学   2969篇
  44078篇
综合类   29883篇
农作物   17214篇
水产渔业   17096篇
畜牧兽医   108098篇
园艺   6333篇
植物保护   24300篇
  2020年   2890篇
  2019年   3682篇
  2018年   4099篇
  2017年   4524篇
  2016年   4889篇
  2015年   4377篇
  2014年   5718篇
  2013年   16341篇
  2012年   6659篇
  2011年   8608篇
  2010年   7494篇
  2009年   8072篇
  2008年   8014篇
  2007年   7140篇
  2006年   7619篇
  2005年   6970篇
  2004年   6709篇
  2003年   6579篇
  2002年   5912篇
  2001年   6489篇
  2000年   6158篇
  1999年   5699篇
  1998年   4203篇
  1997年   4259篇
  1996年   3962篇
  1995年   4589篇
  1994年   3981篇
  1993年   3702篇
  1992年   4616篇
  1991年   4815篇
  1990年   4574篇
  1989年   4532篇
  1988年   4085篇
  1987年   4147篇
  1986年   4128篇
  1985年   4363篇
  1984年   4030篇
  1983年   3699篇
  1982年   3010篇
  1981年   2892篇
  1980年   2834篇
  1979年   3522篇
  1978年   3128篇
  1977年   2910篇
  1976年   2729篇
  1975年   2647篇
  1974年   2941篇
  1973年   2895篇
  1972年   2663篇
  1971年   2609篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Two serological tests (indirect immunofluorescence and enzyme-linked immunosorbent assay) were developed for the detection of fetal antibody to Chlamydia psittaci. Fetal blood and thoracic fluid from 126 field cases of suspected ovine chlamydial abortion were examined using both tests. Placenta and fetal tissues (lung, liver, and kidney) from the same animals were also examined by the following conventional diagnostic methods: isolation in McCoy cells, detection of chlamydial lipopolysaccharide (LPS), modified Ziehl-Nielsen staining, and direct fluorescent antibody staining of chlamydia in frozen cryostat sections. Seventy cases were positive by fetal serology, and of these, 68 were also positive by isolation and/or LPS detection. The remaining 56 cases had negative fetal serology, and of these, 39 were positive by isolation and/or LPS detection. Results indicate that fetal serology, although less sensitive than either isolation in McCoy cells or detection of chlamydial LPS antigen, may be of particular use when placenta is not available.  相似文献   
103.
104.
    
Ohne Zusammenfassung  相似文献   
105.
106.
107.
108.
109.
The medical records of 38 horses with puncture wounds of the navicular bursa were reviewed. Only 12 horses had a satisfactory outcome (breeding or riding). Of the remaining 26 horses, 19 were euthanized, five were sold due to persistent severe lameness, one died, and one was lost to long-term follow-up. Different combinations of conservative management prior to surgical debridement and drainage of the navicular bursa were unsuccessful in resolving the condition. Horses that were treated surgically within 1 week of the injury and had a hind leg affected had the best chance of a satisfactory outcome. Additional wound debridement was necessary in 15 horses after initial surgical treatment. The most common complications encountered were navicular bone osteomyelitis and sepsis of the deep digital flexor tendon. Thirteen of 14 horses that had rupture of the deep digital flexor tendon and subluxation of the distal interphalangeal joint had an unsatisfactory outcome. One mare subsequently developed ankylosis of the distal interphalangeal joint and was a useful brood mare. Two horses that had biaxial palmar digital neurectomy because of persistent lameness were later euthanized because of navicular bone fracture and rupture of the deep digital flexor tendon. Results from limited numbers of bacterial cultures and antibiotic sensitivities suggest that penicillin and an aminoglycoside antibiotic should be used as initial antibiotic therapy. Immediate surgical debridement and appropriate antibiotic treatment are recommended as the minimum therapy for penetrating wounds of the navicular bursa in horses.  相似文献   
110.
GRAY  S. J.; PRICE  COLIN 《Forestry》1990,63(2):161-175
Traditional forest economics deals with regularly-ordered activities.For many reasons, however, choices must often be made amongconflicting operational priorities. In these circumstances,maximizing net discounted revenue per hectare does not maximizeglobal profit. Priorities for action should be chosen in orderof urgency index ratio, defined as the cost of delaying an operationdivided by the units of limited resource needed to undertakethe operation. Forest managers tend to use informal and sometimesconflicting rules to assign priorities among uses of limitedresources. These priorities often differ from those indicatedby urgency index ratio. Urgency index ratio can be determinedby simple calculations based on readily-available data. Theconcept can be extended to include multiple constraints.  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