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   254386篇
  免费   15153篇
  国内免费   652篇
林业   23666篇
农学   14035篇
基础科学   2972篇
  43529篇
综合类   22607篇
农作物   17197篇
水产渔业   16776篇
畜牧兽医   99192篇
园艺   6302篇
植物保护   23915篇
  2021年   2464篇
  2020年   2868篇
  2019年   3666篇
  2018年   4185篇
  2017年   4527篇
  2016年   4858篇
  2015年   4325篇
  2014年   5670篇
  2013年   16264篇
  2012年   6317篇
  2011年   8339篇
  2010年   7493篇
  2009年   8078篇
  2008年   7732篇
  2007年   6827篇
  2006年   7335篇
  2005年   6548篇
  2004年   6399篇
  2003年   6103篇
  2002年   5439篇
  2001年   6035篇
  2000年   5755篇
  1999年   5320篇
  1998年   4165篇
  1997年   4190篇
  1996年   3917篇
  1995年   4477篇
  1994年   3933篇
  1993年   3612篇
  1992年   4375篇
  1991年   4452篇
  1990年   4298篇
  1989年   4136篇
  1988年   3659篇
  1987年   3659篇
  1986年   3652篇
  1985年   3921篇
  1984年   3672篇
  1983年   3483篇
  1982年   2838篇
  1981年   2760篇
  1980年   2760篇
  1979年   3340篇
  1978年   2937篇
  1977年   2764篇
  1976年   2631篇
  1975年   2485篇
  1974年   2560篇
  1973年   2572篇
  1972年   2258篇
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
141.
142.
143.
144.
145.
146.
Ohne Zusammenfassung Mit 2 Abbildungen  相似文献   
147.
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   
148.
149.
Over 54,600 ha of table grapes (Vitis vinifera), mainly cvs. ‘Thompson Seedless’, ‘Flame Seedless’ and ‘Redglobe’, are planted in Chile. Almost the entire production is exported to the USA, Europe, Asia, or one of several Latin American countries, which typically requires 15–40 d of maritime transportation. During this period, several physical, physiological, and pathological factors cause table grape deterioration. Because berry size is the main quality factor in international markets, farmers often overuse the growth regulators, gibberellic acid (GA3) and forchlorfenuron (CPPU), in an effort to increase berry size. We examined the effect of preharvest growth regulators on seedless (‘Thompson Seedless’, and ‘Ruby Seedless’) and seeded (‘Redglobe’) table grape cultivars during cold (0 °C) storage plus a shelf life period of 3 d at 20 °C. The overuse of GA3, eight instead of two GA3 applications on Thompson Seedless, and the use of one GA3 application on Redglobe and ‘Ruby Seedless’, increased berry pedicel thickness and lowered cuticle content but induced shatter and predisposed grapes to gray mold caused by Botrytis cinerea. In contrast, CPPU increased berry pedicel thickness and cuticle content but did not increase shatter or gray mold incidence. Clusters that were subjected to overuse of combined GA3 and CPPU were highly sensitive to shatter, had the thickest pedicel, and developed a high gray mold incidence during cold storage. Hairline, a fine cracking developed during cold storage, was induced on ‘Thompson Seedless’ and ‘Ruby Seedless’ by growth regulators, but no hairline occurred on ‘Redglobe’ table grapes. Therefore, berry quality during cold storage is greatly influenced by growth regulator management in the vineyard.  相似文献   
150.
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   
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