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   313957篇
  免费   17679篇
  国内免费   8498篇
林业   31254篇
农学   24999篇
基础科学   9117篇
  53972篇
综合类   42673篇
农作物   20286篇
水产渔业   18325篇
畜牧兽医   103172篇
园艺   8379篇
植物保护   27957篇
  2022年   3057篇
  2021年   5064篇
  2020年   5250篇
  2019年   5840篇
  2018年   5474篇
  2017年   6571篇
  2016年   6914篇
  2015年   7155篇
  2014年   8319篇
  2013年   19586篇
  2012年   10389篇
  2011年   12636篇
  2010年   11513篇
  2009年   11647篇
  2008年   11068篇
  2007年   10558篇
  2006年   10808篇
  2005年   9823篇
  2004年   7762篇
  2003年   7369篇
  2002年   6412篇
  2001年   6839篇
  2000年   6980篇
  1999年   6840篇
  1998年   5695篇
  1997年   5480篇
  1996年   5135篇
  1995年   5550篇
  1994年   4861篇
  1993年   4521篇
  1992年   4971篇
  1991年   5095篇
  1990年   4711篇
  1989年   4462篇
  1988年   3949篇
  1987年   3940篇
  1986年   3731篇
  1985年   3873篇
  1984年   3690篇
  1983年   3459篇
  1982年   2894篇
  1981年   2808篇
  1980年   2773篇
  1979年   3152篇
  1978年   2853篇
  1977年   2607篇
  1976年   2542篇
  1975年   2326篇
  1974年   2562篇
  1973年   2473篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
植物健康综合管理系统(IpHM)在保证根系健康生长方面确实起到了作用。这就对种植者提出了挑战。植物营养调节、水分管理、根/冠生长管理的成败取决于是否有健康的根系和成分配比适当的栽培基质。[编者按]  相似文献   
93.
利用SAS估计动物BLUP育种值   总被引:2,自引:0,他引:2  
本文简要介绍了BLUP的数学背景、用于BLUP计算的SAS程序模块使用方法和2个计算BLUP的程序示例。  相似文献   
94.
This study was conducted to evaluate the effects of dietary vitamin K (menadione) on bone quality in cage-raised broilers. Three hundred and sixty male broilers were randomly allotted to one of six treatments, with six replicate pens per treatment and 10 chicks per pen. Broilers were fed one of six diets including a control diet or the control diet plus graded levels of vitamin K (0.5 mg/kg, 2 mg/kg, 8 mg/kg, 32 mg/kg and 128 mg/kg). Water and feed were provided ad libitum during the 7-week experimental period. Results indicated that vitamin K supplementation of broilers diets significantly effected bone quality and feed efficiency. The treatment containing vitamin K at 8 mg/kg improved growth performance (during weeks 6-7) and bone quality (during weeks 0-3). In our study, hydroxyapatite binding capacity of serum osteocalcin (during weeks 0-3), bone breaking strength, bone flexibility, bone ash weight increased linearly (P < 0.05) and bone mineral density, bone mineral content increased quadratically (P < 0.05) with increasing supplementation of vitamin K. In conclusion, to gain optimum bone quality and broiler performance, our studies suggest that the concentration of vitamin K in broilers diets should be 8 mg/kg, 2 mg/kg, and 2 mg/kg, for the starter, grower and finisher phases, respectively. Furthermore, it was shown that the starter period is an important phase for improving bone quality. In addition, this study validated the mechanism of vitamin K effects on bone quality. Vitamin K boosts the carboxylation of osteocalcin and decreases the concentration of serum under-carboxylated osteocalcin enhancing hydroxyapatite binding capacity of serum osteocalcin and improving bone quality.  相似文献   
95.
96.
97.
银川地区羊肝中阿苯达唑(丙硫苯咪唑)残留情况的调查   总被引:1,自引:0,他引:1  
阿苯达唑又称丙硫苯咪唑或丙硫咪唑,有时又称抗蠕敏,是目前国内常用的驱虫效果好、范围广、毒性较低的兽用驱虫药。随着家庭舍饲养羊规模的不断扩大,饲养者为了减少因寄生虫导致的死亡并增加育肥效果,常把阿苯达唑作为育肥前预防驱虫或寄生虫病治疗的首选药,出现了滥用或超剂量使用的现  相似文献   
98.
99.
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   
100.
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   
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