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   325175篇
  免费   17559篇
  国内免费   671篇
林业   24985篇
农学   14319篇
基础科学   3009篇
  47924篇
综合类   42940篇
农作物   17850篇
水产渔业   18536篇
畜牧兽医   141420篇
园艺   6536篇
植物保护   25886篇
  2019年   3762篇
  2018年   4541篇
  2017年   4965篇
  2016年   5157篇
  2015年   4581篇
  2014年   5967篇
  2013年   16604篇
  2012年   8421篇
  2011年   10815篇
  2010年   8333篇
  2009年   8687篇
  2008年   10093篇
  2007年   9300篇
  2006年   9558篇
  2005年   8788篇
  2004年   8642篇
  2003年   8425篇
  2002年   7623篇
  2001年   8926篇
  2000年   8655篇
  1999年   7459篇
  1998年   4407篇
  1997年   4460篇
  1996年   4205篇
  1995年   4869篇
  1994年   4331篇
  1993年   3981篇
  1992年   6118篇
  1991年   6448篇
  1990年   6284篇
  1989年   6249篇
  1988年   5611篇
  1987年   5675篇
  1986年   5724篇
  1985年   5766篇
  1984年   5016篇
  1983年   4653篇
  1982年   3518篇
  1981年   3322篇
  1980年   3219篇
  1979年   4361篇
  1978年   3734篇
  1977年   3304篇
  1976年   3186篇
  1975年   3123篇
  1974年   3586篇
  1973年   3698篇
  1972年   3426篇
  1971年   3310篇
  1970年   3210篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
172.
173.
174.
175.
The parasympathetic and sympathetic divisions of the autonomic nervous system are involved in homeostatic control of a wide variety of ocular functions, including accommodation, pupillomotor control, lacrimation, eyelid position, and aqueous humor production. Familiarity with the functional anatomy of the autonomic nervous system is paramount to the understanding and application of the large number of autonomic drugs used in veterinary ophthalmology. The cholinergic and adrenergic agents discussed in this article are commonly employed to facilitate routine ophthalmic examination, in the diagnosis of autonomic dysfunction, and in the treatment of a variety of ocular diseases.  相似文献   
176.
177.
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   
178.
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   
179.
Des informations sur la biologie et la diffusion des principaux insectes nuisibles aux eucalyptus en Italie sont données, ainsi que sur l'importance de leurs dégats et sur les méthodes de lutte les plus couramment employées. En plus des quelques espèces polyphages, qui peuvent causer des dégats sporadiques, les phytophages vivant exclusivement aux dépens d'Eucalyptus spp. en Italie sont Phoracantha semipunctata, Gonipterus scutellatus et Ctenarytaina eucalypti. La première espèce est nuisible aux eucalyptus cultivès pour la production du bois et est répandue en Italie centrale et méridionale, en Sicile et en Sardaigne, alors que les deux autres espèces endommagent surtout les eucalyptus destinés aux marchés de fleurs (fleurs et rameaux) et ne sont prèsentes qu'en Ligurie occidentale. La lutte contre P. semipunctata est conduite par des interventions d'ordre sylvicultural, consistant essentiellement è recéper des peuplements sérieusement attaqués; le parasite oophage Patasson nitens, importé d'Afrique du Sud, permet de controler G. scutellatus alors que les larves de plusieurs syrphes prédatrices agissent efficacement contre C. eucalypti.  相似文献   
180.
Disseminated Aspergillus terreus infection was diagnosed in ten previously healthy adult dogs--nine German shepherds and one dalmatian. The disease was characterized by the presence of multiple granulomas and infarcts in a wide range of organs. The kidney, spleen, and skeletal system were most commonly and severely affected. Fungal hyphae were demonstrated in large numbers within granulomas and thrombi, and A. terreus was readily isolated by culture. This disseminated mycosis appears unique; in this series of cases there was no apparent predisposing factor, portal of entry, or primary focus for dissemination of the infection.  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