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   244708篇
  免费   14867篇
  国内免费   665篇
林业   23474篇
农学   13938篇
基础科学   2941篇
  42233篇
综合类   21501篇
农作物   17230篇
水产渔业   16566篇
畜牧兽医   92415篇
园艺   6287篇
植物保护   23655篇
  2021年   2472篇
  2020年   2839篇
  2019年   3635篇
  2018年   3989篇
  2017年   4313篇
  2016年   4744篇
  2015年   4274篇
  2014年   5635篇
  2013年   16216篇
  2012年   5961篇
  2011年   7835篇
  2010年   7256篇
  2009年   7853篇
  2008年   7187篇
  2007年   6193篇
  2006年   6850篇
  2005年   6030篇
  2004年   5925篇
  2003年   5737篇
  2002年   5064篇
  2001年   5558篇
  2000年   5183篇
  1999年   5004篇
  1998年   4101篇
  1997年   4166篇
  1996年   3902篇
  1995年   4473篇
  1994年   3858篇
  1993年   3544篇
  1992年   4086篇
  1991年   4315篇
  1990年   3962篇
  1989年   3978篇
  1988年   3515篇
  1987年   3497篇
  1986年   3461篇
  1985年   3808篇
  1984年   3549篇
  1983年   3400篇
  1982年   2821篇
  1981年   2733篇
  1980年   2730篇
  1979年   3135篇
  1978年   2797篇
  1977年   2644篇
  1976年   2484篇
  1975年   2316篇
  1974年   2510篇
  1973年   2419篇
  1972年   2187篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
65.
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   
66.
67.
68.
69.
Rostral and caudal rhinoscopy in dogs and cats facilitates the investigation of the nasal cavity and accurate biopsy. Rostral rhinoscopy can be performed by rigid endoscopes; caudal rhinoscopy requires flexible endoscopes. Deep anaesthesia or additional analgesia with local anaesthesia is necessary. The nasal cavity is assessed by its form, colour, surface of the mucous membrane, hyperemia, plaques, lesions, and the secretion is assessed by its quantity, colour and viscosity. Foreign bodies and neoplasia must also be looked for. Case reports with abnormal findings are described.  相似文献   
70.
Bluetongue virus infection in sheep and cattle during fetal development causes neuropathology. Two strains of bluetongue virus serotype 11 designated as UC-2 and UC-8 have different virulence patterns in newborn mice. These viruses have distinctly different electropherotype patterns on polyacrylamide gel electrophoresis indicating a genetic difference in these two viruses of the same serotype. Four bovine fetuses each were inoculated intramuscularly with either UC-2 or UC-8, and one fetus was inoculated with placebo. The inoculation was made intramuscularly through the uterine wall at 120 days' gestation, and the bovine fetuses were recovered by cesarean section 12 or 20 days after inoculation. Fetal blood was collected for virus isolation and serology. Virus was reisolated from brain, blood, lung and liver. Both strains, UC-2 and UC-8, cause severe lesions in the 120 day fetuses. The encephalomalacic lesions occurred earlier and were more severe in fetuses inoculated with UC-8 as compared to those inoculated with UC-2. The subtle differences observed in the fetuses inoculated with the two different strains suggest that there is a difference in pathogenic potential of the two viruses. These differences do not appear to be completely dependent upon the host species.  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