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   257027篇
  免费   14936篇
  国内免费   1391篇
林业   23868篇
农学   14415篇
基础科学   3202篇
  44343篇
综合类   25549篇
农作物   17503篇
水产渔业   16871篇
畜牧兽医   96906篇
园艺   6600篇
植物保护   24097篇
  2021年   2793篇
  2020年   3132篇
  2019年   3941篇
  2018年   4169篇
  2017年   4649篇
  2016年   4978篇
  2015年   4590篇
  2014年   5930篇
  2013年   16613篇
  2012年   6886篇
  2011年   8870篇
  2010年   7794篇
  2009年   8243篇
  2008年   7981篇
  2007年   7038篇
  2006年   7500篇
  2005年   6791篇
  2004年   6440篇
  2003年   6263篇
  2002年   5597篇
  2001年   5807篇
  2000年   5604篇
  1999年   5196篇
  1998年   4127篇
  1997年   4154篇
  1996年   3907篇
  1995年   4411篇
  1994年   3847篇
  1993年   3552篇
  1992年   4181篇
  1991年   4469篇
  1990年   4156篇
  1989年   4067篇
  1988年   3611篇
  1987年   3698篇
  1986年   3612篇
  1985年   3821篇
  1984年   3646篇
  1983年   3410篇
  1982年   2860篇
  1981年   2762篇
  1980年   2754篇
  1979年   3144篇
  1978年   2854篇
  1977年   2610篇
  1976年   2542篇
  1975年   2326篇
  1974年   2563篇
  1973年   2474篇
  1972年   2202篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Mid-storage hydration-dehydration treatments with medium-vigour lettuce seed very effectively reduced physiological deterioration in storage and ultimately showed better field emergence and final yield. Soaking-drying treatment of high-vigour lettuce seed was not effective. Pre-sowing treatment of medium-vigour lettuce seed, though less effective than mid-storage treatment, gave better field performance, but high-vigour seed did not benefit from the treatment. For carrot, both mid-storage and pre-sowing seed treatments proved beneficial, with the former showing better performance than the latter. Unlike lettuce, well-preserved carrot seed responded positively to the pre-sowing treatment.  相似文献   
22.
Vanilla is a large genus of about 110 species in the orchid family (Orchidaceae), including the species Vanilla planifolia from which commercial vanilla flavoring is derived. Since most species of vanilla are considered rare and endangered there is an urgent need to conserve them through genetic analysis and propagation/conservation studies on this crop.The present study investigated the genetic diversity among nine leafy- and leaf-less Vanilla species employing 30 decamer RAPD primers and 10 ISSR primers. The species under study were diverse and displayed a range of variability (0–66% and 0–81% for RAPD and ISSR, respectively). A total of 154 RAPD polymorphic markers (83.24%, h = 0.378) and 93 ISSR polymorphic markers (86.11%, h = 0.363) were used to generate a genetic similarity matrix followed by the cluster analysis. Specific groupings were revealed by each cluster analysis with slight variation between two different markers. Among the nine species studied, V. planifolia, Vanilla aphylla and Vanilla tahitensis revealed very low level of variation within their collections, thus indicating a narrow genetic base. The large genetic distance of Vanilla andamanica from other species suggests its different origin. A close genetic affinity was observed between the pairs V. planifolia, V. tahitensis and Vanilla albida, V. aphylla. These are the first comparative results for RAPD and ISSR reporting inter-relationship among nine cultivated, wild and hybrid Vanilla species.  相似文献   
23.
24.
以传统栽培为对照,研究畦式好气栽培对水稻根系、群体消长、产量构成因素及产量的影响。结果表明,畦式好气栽培显著提高了整个生育期水稻根系的生物量,与传统栽培相比,增幅达5.46%-11.18%;显著增加了抽穗后10cm以下土层的根系比例和根系活力,提高了根冠比,促进了水稻分蘖的发生,显著提高了水稻有效穗数、结实率和产量,每公顷可比传统栽培增产稻谷637.5kg,增产9.48%。  相似文献   
25.
26.
27.
28.
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   
29.
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   
30.
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