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   142534篇
  免费   8321篇
  国内免费   1090篇
林业   6346篇
农学   5070篇
基础科学   1466篇
  17395篇
综合类   27223篇
农作物   5380篇
水产渔业   6827篇
畜牧兽医   71176篇
园艺   2147篇
植物保护   8915篇
  2021年   1260篇
  2020年   1329篇
  2019年   1622篇
  2018年   2197篇
  2017年   2590篇
  2016年   2305篇
  2015年   2204篇
  2014年   2551篇
  2013年   5307篇
  2012年   4653篇
  2011年   5591篇
  2010年   3865篇
  2009年   3711篇
  2008年   5284篇
  2007年   4934篇
  2006年   4598篇
  2005年   4365篇
  2004年   4047篇
  2003年   4086篇
  2002年   3868篇
  2001年   4354篇
  2000年   4389篇
  1999年   3494篇
  1998年   1590篇
  1997年   1419篇
  1996年   1351篇
  1995年   1484篇
  1994年   1401篇
  1993年   1324篇
  1992年   2762篇
  1991年   2953篇
  1990年   2981篇
  1989年   2822篇
  1988年   2649篇
  1987年   2627篇
  1986年   2679篇
  1985年   2495篇
  1984年   2123篇
  1983年   1881篇
  1979年   1885篇
  1978年   1511篇
  1977年   1304篇
  1976年   1293篇
  1975年   1361篇
  1974年   1674篇
  1973年   1689篇
  1972年   1637篇
  1971年   1525篇
  1970年   1472篇
  1969年   1450篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
93.
94.
95.
Observations on transplacental infection with bluetongue virus in sheep   总被引:1,自引:0,他引:1  
Twenty-four ewes were inoculated with 1 of 2 strains of bluetongue virus type 4 at 40, 60, or 80 days of gestation. Two ewes aborted, 2 ewes died, and 1 was killed during the experiment, but their fetuses were recovered. At term, 2 mummified fetuses, 4 dead lambs, and 17 clinically healthy lambs were produced by 12 sheep, and the remaining 7 sheep were barren. Porencephaly and cerebellar dysgenesis were found in term lambs born to sheep inoculated at 40 and 60 days of gestation. Radiographic examination of 12 fetuses showed developmental ages far less than their chronologic age; 8 fetuses had skeletal growth-retardation lines, which were also observed in the dead lambs. A systemic lymphoreticular hyperplasia was observed in the dead lambs and in all lambs at 12 weeks of age; in 4 of the latter, granulomatous reactions were present in the liver and kidney. Lungs of the full-term lambs were reduced in weight and showed poor alveolar development and mononuclear cell infiltration, which persisted in the 12-week-old lambs. It was concluded that bluetongue virus is capable of causing not only gross abnormalities of the CNS, but also generalized growth retardation and fetal lymphoreticular hyperplasia.  相似文献   
96.
Antigens in the extracellular protein (ECP) complexes of Bacteroides nodosus, isolated from sheep with either benign or virulent footrot, were studied by immunoelectrophoresis (IEP). Rabbit antisera against ECP from virulent and benign strains, were used in homologous and heterologous crossed IEP. Four precipitin peaks unique to the virulent strain, and five peaks unique to the benign strain were identified. In an attempt to characterize the different antigens in ECP, rabbit antisera were raised against an outer membrane protein (OMP, mol. wt. 35 000 daltons), pili and various proteases of virulent and benign strains of B. nodosus. No precipitin band was observed when ECP from both B. nodosus strains were reacted against anti-OMP and anti-pilus antisera. However, single precipitin bands unique to one protease from the benign strain and one protease from the virulent strain were identified. The results suggest that specific antigens other than proteases or pili are important in determining whether a B. nodosus isolate is virulent or benign.  相似文献   
97.
A brief discussion of those aspects of neonatal physiology that pertain to anesthetic risk and selection of anesthetic techniques is followed by discussion of suggested techniques for anesthetic management in healthy foals. Preoperative preparation and management of foals with selected serious surgical conditions are also considered.  相似文献   
98.
Periodontal disease. Etiology and pathogenesis   总被引:1,自引:0,他引:1  
Periodontal disease is the number-one cause of the early loss of teeth in dogs and cats. Some of the factors in the adult animal that play a major role in the development of periodontal diseases are discussed in this article, including overcrowding, malocclusions, diet, developmental defects, and metabolic and systemic disease.  相似文献   
99.
Crystalluria results from oversaturation of urine with crystallogenic substance. However, oversaturation may occur as a result of in vitro as well as in vivo events. The microscopic appearance of crystals only represents a tentative identification of their composition because variable conditions associated with their formation, growth, and dissolution may alter their appearance. Definitive identification is dependent on physical methods such as optical crystallography, x-ray diffraction, and electron microscopic analysis.  相似文献   
100.
A steam-dryer, designed and manufactured in Sweden, was evaluated for destroying Bursaphelenchus xylophilus in pine chips from southern USA. In a trial, pine chips were treated at different temperature and pressure regimes for 5 or 10min. The lowest time/temperature/pressure combination was to increase the vessel temperature from 85 to 104°C in 5 min at low pressure. Samples of pine chips were assayed for nematodes in laboratories in USA, Sweden, and Finland. No nematodes of any species were recovered from any of the treated pine-chip samples. Large and heterogeneous pieces of wood in the treated samples were also nematode-free. The apparatus was a prototype capable of handling about 400 kg h-1. The final version would have to be able to process 100-200 th-1.  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