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   148865篇
  免费   7970篇
  国内免费   82篇
林业   6219篇
农学   4368篇
基础科学   933篇
  16664篇
综合类   28330篇
农作物   5714篇
水产渔业   6758篇
畜牧兽医   77247篇
园艺   1768篇
植物保护   8916篇
  2018年   1860篇
  2017年   1982篇
  2016年   1859篇
  2015年   1668篇
  2014年   1891篇
  2013年   5655篇
  2012年   3758篇
  2011年   4628篇
  2010年   3019篇
  2009年   2968篇
  2008年   4557篇
  2007年   4284篇
  2006年   4024篇
  2005年   3790篇
  2004年   3835篇
  2003年   3817篇
  2002年   3705篇
  2001年   4510篇
  2000年   4529篇
  1999年   3488篇
  1998年   1499篇
  1997年   1520篇
  1995年   1718篇
  1994年   1587篇
  1993年   1537篇
  1992年   3167篇
  1991年   3445篇
  1990年   3332篇
  1989年   3389篇
  1988年   3087篇
  1987年   3084篇
  1986年   3281篇
  1985年   3192篇
  1984年   2601篇
  1983年   2420篇
  1982年   1574篇
  1981年   1501篇
  1979年   2373篇
  1978年   1943篇
  1977年   1655篇
  1976年   1641篇
  1975年   1690篇
  1974年   2155篇
  1973年   2186篇
  1972年   2147篇
  1971年   2025篇
  1970年   1947篇
  1969年   1793篇
  1968年   1501篇
  1967年   1571篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Test and corrective management was applied in one dairy herd (130 milking cows) to control bovine leukemia virus infection. It consisted of: raising uninfected calves in order to establish a pool of uninfected replacement heifers, preventing transmission of bovine leukemia virus through transfer of blood from animal to animal and closing the herd. Regular herd testing was combined with selected changes in herd management. These procedures have been followed since January 1979. Prevalence of antibodies (as determined by gel-immunodiffusion) has declined markedly since the program was implemented.  相似文献   
982.
983.
Dogs were successfully isolated for a period of either 52 or 64 weeks following vaccination with an inactivated, adjuvanted canine parvovirus-2 vaccine. Antibody persisted in all ten vaccinated dogs, although in one case by 52 weeks postvaccination only virus neutralizing antibody, and not hemagglutination-inhibiting antibody, could be detected. Sentinel unvaccinated dogs housed alongside the vaccinated dogs throughout the study remained free of canine parvovirus-2 antibody until challenged. Upon oral challenge with canine parvovirus-2 infected material all unvaccinated dogs developed one or more signs of canine parvovirus-2 disease, shed virus and developed antibody. None of the vaccinated dogs became overtly sick. Of the five vaccinated dogs challenged 52 weeks after vaccination, three shed virus and one showed a significant rise in antibody. At 64 weeks after vaccination only one of the five challenged dogs shed virus and showed a boost in antibody titer.  相似文献   
984.
985.
986.
A herd of 180 beef cows was synchronized with prostaglandin and bred by artifical insemination for five successive years. Factors influencing the success or failure of estrus synchronizing programs were identified, including the management of nutrition, postpartum interval, cow age and artificial insemination technology. Specific recommendations on the management of prostaglandin-controlled breeding programs resulted in improving the pregnancy rates from 33% in year 1 to 67% in year 5. Improved management and close veterinary supervision were shown to improve the success of an estrus synchronization program.  相似文献   
987.
A condition resembling chronic malignant catarrhal fever was seen in a 9-month-old pet sika hind (Cervus nippon). From an initial acute depression, pyrexia, and anorexia, the condition progressed to include hypopyon, keratitis, lethargy, loss of condition, sloughing of one hoof and eventually death after seven weeks. There were multiple, 5 to 8mm diameter dark-red nodules throughout the mesenteries and mediastinum, along abdominal organ ligaments, and about the uterus and kidneys. Histopathology showed the nodules to be organising vascular thrombi. Concurrent perivascular mononuclear infiltrations and intravascular thrombi in many tissues confirmed that the condition was malignant catarrhal fever.  相似文献   
988.
989.
Lymphosarcoma in a six year old male Doberman pinscher was accompanied by hypercalcemia, generalized osteolysis and renal calcification. Tumor involvement of bone marrow was extensive. The possible pathogenesis of hypercalcemia was thought to be the result of a locally active bone-resorbing factor secreted by the tumor cells.  相似文献   
990.
Year end tax planning   总被引:1,自引:1,他引:0       下载免费PDF全文
  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