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   327906篇
  免费   18302篇
  国内免费   4916篇
林业   28860篇
农学   20113篇
基础科学   6215篇
  51161篇
综合类   45539篇
农作物   19667篇
水产渔业   18882篇
畜牧兽医   125155篇
园艺   7750篇
植物保护   27782篇
  2021年   4083篇
  2020年   4255篇
  2019年   5069篇
  2018年   4992篇
  2017年   5713篇
  2016年   6049篇
  2015年   6042篇
  2014年   7272篇
  2013年   18372篇
  2012年   9424篇
  2011年   11723篇
  2010年   9900篇
  2009年   10392篇
  2008年   10759篇
  2007年   9949篇
  2006年   10405篇
  2005年   9630篇
  2004年   8338篇
  2003年   7930篇
  2002年   7291篇
  2001年   8204篇
  2000年   7970篇
  1999年   7651篇
  1998年   5304篇
  1997年   5219篇
  1996年   4921篇
  1995年   5445篇
  1994年   4842篇
  1993年   4516篇
  1992年   5838篇
  1991年   6005篇
  1990年   5705篇
  1989年   5588篇
  1988年   5027篇
  1987年   4986篇
  1986年   4976篇
  1985年   5058篇
  1984年   4564篇
  1983年   4205篇
  1982年   3347篇
  1981年   3211篇
  1980年   3146篇
  1979年   3973篇
  1978年   3486篇
  1977年   3158篇
  1976年   2859篇
  1974年   3311篇
  1973年   3304篇
  1972年   3047篇
  1971年   2863篇
排序方式: 共有10000条查询结果,搜索用时 480 毫秒
201.
202.
Ohne Zusammenfassung Mit 2 Abbildungen  相似文献   
203.
204.
Isolated dog neutrophils exposed to known chemotactic factors assumed a bipolar configuration in suspension. This response was initiated within 2 minutes with a gradual return to spherical shape. The rate of return to sphere was positively correlated with the dose of stimulant. Dog neutrophils exposed to N-formylmethionyl-leucyl-phenylalanine (fMLP) did not adapt to bipolar conformation and did not bind radiolabeled fMLP. These findings are consistent with other species (pig and cow) that also did not respond to fMLP.  相似文献   
205.
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   
206.
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   
207.
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   
208.
在大田生产条件下 ,采用随机区组设计 ,从农艺性状、经济性状、生理生化特性等方面对台优、新台糖22、新台糖25和粤糖93/159四个引进甘蔗品种进行生长发育特性研究。结果表明 :新台糖22蔗茎产量和含糖量最高 ,分别比台优、新台糖25增产26 65%、34 93%和21 8%、34 8% ,差异达到5 %显著或1 %极显著水平 ;其次是粤糖93/159 ,分别比台优、新台糖25增产21 82 %、29 77%和19 88 %、32 66% ,差异达到5%显著水平 ;新台糖22与台优、粤糖93/159与新台糖25之间的蔗茎产量差异和含糖量差异不显著。对研究项目进行综合评定 ,评价值高低排序为 :新台糖22>粤糖93/159>台优>新台糖25。  相似文献   
209.
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   
210.
Twenty stifles (10 dogs) were studied for a period of 1 year after various lesions of the cranial cruciate ligament and medial meniscus were produced surgicaoy. Through serial arthroscopic evaluations, degenerative processes In stifles with a "torn" cranial cruciate ligament were documented. Intra-articular changes were minimal after partial meniscectomy and were severe after total meniscectomy. Multiple arthroscopies caused no demonstrable changes.  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