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   136326篇
  免费   7352篇
  国内免费   126篇
林业   5995篇
农学   4195篇
基础科学   862篇
  15922篇
综合类   24692篇
农作物   5312篇
水产渔业   6444篇
畜牧兽医   70344篇
园艺   1636篇
植物保护   8402篇
  2018年   1919篇
  2017年   2094篇
  2016年   1879篇
  2015年   1630篇
  2014年   2089篇
  2013年   4783篇
  2012年   3717篇
  2011年   4512篇
  2010年   2951篇
  2009年   3122篇
  2008年   4649篇
  2007年   4273篇
  2006年   4138篇
  2005年   3828篇
  2004年   3843篇
  2003年   3898篇
  2002年   3601篇
  2001年   4242篇
  2000年   4266篇
  1999年   3382篇
  1998年   1495篇
  1997年   1390篇
  1996年   1368篇
  1995年   1515篇
  1994年   1405篇
  1993年   1372篇
  1992年   2765篇
  1991年   2947篇
  1990年   2959篇
  1989年   2850篇
  1988年   2657篇
  1987年   2619篇
  1986年   2693篇
  1985年   2615篇
  1984年   2104篇
  1983年   1915篇
  1979年   1962篇
  1978年   1562篇
  1977年   1370篇
  1976年   1243篇
  1975年   1390篇
  1974年   1659篇
  1973年   1706篇
  1972年   1704篇
  1971年   1616篇
  1970年   1582篇
  1969年   1536篇
  1968年   1304篇
  1967年   1373篇
  1966年   1271篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
Morbidity (greater than or equal to 1 disease condition) for pups sold from 3 pet stores from January 1987 through December 1988 ranged from 54 to 68%. In 1 store, morbidity was higher for store pups, compared with pups originating from private parties, for such disease conditions as "kennel cough," diarrhea, and several species of gastrointestinal parasites. In-store mortality ranged from 5 to 9.5% of pups arriving for sale.  相似文献   
992.
The ovaries of two infertile cows of high breeding value were recovered after slaughter, and a total of 222 oocytes were obtained. Of these, 156 were classified as of good or fair quality and were subjected to in vitro maturation, in vitro fertilisation (using frozen semen from three bulls of high breeding value) and in vitro culture procedures. After eight days, 27 embryos were obtained, of which 13 were transferred fresh, and 14 were frozen. Three recipients of fresh embryos became pregnant; two calved and one aborted at four months. One of eight recipients of frozen-thawed embryos became pregnant but aborted at three months.  相似文献   
993.
‘Simultaneous’ urethral pressure profilometry using microtip pressure transducer catheters was evaluated as an aid to the diagnosis of urethral sphincter mechanism incompetence by means of comparisons between 50 continent and 50 incontinent anaesthetised bitches. Highly significant differences were detected and the technique was found to have considerable potential as a diagnostic aid.  相似文献   
994.
995.
996.
Host range of avian influenza virus in free-living birds   总被引:17,自引:0,他引:17  
Isolation of avian influenza virus (AIV) has been reported from 12 orders and 88 species of free-living birds. Most isolations are reported from species in the orders Anseriformes and Charadriiformes and it is recognized that species in Anseriformes represent important reservoirs of AIV. Morbidity and mortality among free-living birds attributable to AIV infection are rare, but differences in prevalence of AIV occur within and between avian species. Seasonal variation has been reported from free-living and sentinel ducks with peak AIV infection occurring in late summer and early fall. Prevalence of AIV is age-related, with highest isolation rates reported from juvenile birds. Differences in susceptibility to AIV infection among species have been demonstrated under experimental conditions. The dynamics and epidemiology of species-related variation in populations of free-living birds require further study.  相似文献   
997.
The use of electron microscopy to assist in the rapid diagnosis of virus diseases of veterinary importance is reviewed. Electron microscopy can be used to assist the laboratory diagnosis of a virus disease at two stages during the investigation; either by demonstrating virus in clinical material or by identifying isolates from tissue culture or similar systems. Direct electron microscopy and immunoelectron microscopy are particularly useful for rapid diagnosis. The advantages of electron microscopy lie in speed and flexibility, and the disadvantages in the high particle concentration needed and the presumptive nature of a diagnosis.  相似文献   
998.
Four groups of BTV free Frisian and cross bred calves were used to determine the length of viraemia following infection with different doses of BTV-8 Italian isolate. The first group of five animals was infected with 10 TCID50 of BTV-8, the second group of four animals with 103 TCID50 and the third group, which also included four animals, was infected with 106 TCID50. A placebo containing uninfected tissue culture medium was given to the four animals of the fourth group. The viraemia was evaluated by real time RT-PCR and virus isolation. In all infected groups, virus isolation was able to detect infectious virus up to 39 days post infection (dpi) while RT-PCR was positive up to 151–157 dpi. Infectious dose did influence neither the length nor the pattern of BTV-8 viraemia and confirmed that real time RT-PCR remains positive although no circulating virus is detectable in the peripheral circulation.  相似文献   
999.
The short-term neurologic and long-term leptomeningeal effects of repeated subarachnoid administration of metrizamide at concentrations of 170 mg I/ml and 300 mg I/ml were investigated in dogs. After two months, arachnoid fibrosis of varying degrees was present in all dogs that had received metrizamide at the higher concentration. The higher concentration of met-rizamide was more epileptogenic than the concentration of 170 mg I/ml. The presence of subarachnoid hemorrhage was not considered to play a role in the development of the arachnoid fibrosis. Veterinary Radiology Vol. 21, No. 2, 1980; pp 78–81.  相似文献   
1000.
Temporomandibular dysplasia was found in six American Cocker Spaniels related to each other. Clinical signs and diagnosis are described.  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