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   147773篇
  免费   8374篇
  国内免费   85篇
林业   5539篇
农学   4431篇
基础科学   1043篇
  17236篇
综合类   25740篇
农作物   5517篇
水产渔业   7509篇
畜牧兽医   76900篇
园艺   1845篇
植物保护   10472篇
  2018年   1833篇
  2017年   2022篇
  2016年   1922篇
  2015年   1664篇
  2014年   2051篇
  2013年   5500篇
  2012年   3909篇
  2011年   4935篇
  2010年   3026篇
  2009年   3057篇
  2008年   4817篇
  2007年   4625篇
  2006年   4503篇
  2005年   4186篇
  2004年   4078篇
  2003年   4075篇
  2002年   4007篇
  2001年   4724篇
  2000年   4571篇
  1999年   3726篇
  1998年   1498篇
  1997年   1529篇
  1996年   1425篇
  1995年   1772篇
  1994年   1601篇
  1993年   1526篇
  1992年   3176篇
  1991年   3301篇
  1990年   3349篇
  1989年   3342篇
  1988年   3065篇
  1987年   3150篇
  1986年   3236篇
  1985年   3108篇
  1984年   2622篇
  1983年   2327篇
  1982年   1590篇
  1981年   1489篇
  1980年   1443篇
  1979年   2320篇
  1978年   1920篇
  1977年   1633篇
  1976年   1445篇
  1975年   1551篇
  1974年   2088篇
  1973年   2092篇
  1972年   2056篇
  1971年   1818篇
  1970年   1713篇
  1969年   1574篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
A 3 year old Boxer dog was presented with a history of syncope and an irregular heart heat. An arrhythmia characterised by ventricular premature contractions was detected and was thought to cause the syncopal episodes. On the basis of the age, breed and the characteristic electrocardiographic findings, a diagnosis of Boxer Cardiomyopathy was made. The dog was treated with procainamide 500 mg every 8 hours to control the arrythmia and there were no further syncopal episodes in the subsequent 13 months.  相似文献   
992.
A total of 763 fecal or intestinal samples from diarrheic calves and piglets were examined for viral content by immunofluorescence, electron microscopy or cell culture. Routine fluorescent antibody and cultural tests detected rotavirus (n=126), coronavirus (n=80) and bovine viral diarrhea virus (n=13). Electron microscopy detected rotaviruses (n=24) and coronaviruses (n=17) not identified by standard fluorescent antibody tests. Other viruses detected by electron microscopy included Breda virus-like particles (n=49), astroviruses (n=1), caliciviruses (n=1), rhabdoviruses (n=1), parvoviruses (n=2), enteroviruses (n=3), togavirus-like particles (n=2), and “chained” particles (n=5). Mixtures of several of the viruses were detected in a number of fecal samples.

The survey emphasized the value of electron microscopy as a broad-spectrum diagnostic tool.

  相似文献   
993.
994.
Outbreaks of budgerigar fledgling disease (BFD) occurred in three budgerigar aviaries in Ontario. Acute death in seven to ten-day-old nestlings and feather abnormalities in birds over three weeks of age were common findings. Ascites, hepatomegaly and hydropericardium were prominent gross lesions. Histologically, basophilic intranuclear inclusions were seen in many tissues. A severe drop in hatchability occurred in one aviary—a finding not previously reported with BFD. Interruption of breeding controlled the disease in aviary 1, but failed in two consecutive attempts in aviary 2. A third outbreak occurred in aviary 2 after depopulation and restocking. In aviary 3, the spread of disease was very rapid; 90% of the nestlings died within a few weeks. A papovavirus similar to a previously described isolate was recovered in this outbreak.  相似文献   
995.
996.
997.
998.
999.
1000.
Congenital aortic stenosis usually affects the subvalvular region, and occurs mainly in Newfoundland, Golden Retriever, German Shepherd, and Boxer dogs. The disorder is inherited as a dominant trait with variable penetrance in Newfoundland dogs.

The prevalence of subaortic stenosis-like heart murmurs in Golden Retriever dogs appears to be very much greater than previously suspected.

Most cases of aortic stenosis represent mild lesions, are detected as incidental findings, and result in no loss of longevity or quality of life. Moderate or severe stenosis may result in exertional weakness, syncope, or sudden death. Signs of congestive heart failure are rare unless mitral valve insufficiency is present.

Generally, electrocardiography and radiography are unrevealing in this disorder. Doppler echocardiography may be the best diagnostic tool to detect even mild cases of aortic stenosis.

At present, therapy is limited due to the technical expertise and expense required. The prognosis depends on the severity of the lesion.

  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