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   208505篇
  免费   13564篇
  国内免费   698篇
林业   22814篇
农学   13846篇
基础科学   2942篇
  40129篇
综合类   11025篇
农作物   16988篇
水产渔业   15687篇
畜牧兽医   70723篇
园艺   6138篇
植物保护   22475篇
  2021年   2409篇
  2020年   2799篇
  2019年   3596篇
  2018年   3674篇
  2017年   4012篇
  2016年   4577篇
  2015年   4191篇
  2014年   5532篇
  2013年   16063篇
  2012年   4942篇
  2011年   6489篇
  2010年   6787篇
  2009年   7474篇
  2008年   5968篇
  2007年   4923篇
  2006年   5750篇
  2005年   5017篇
  2004年   4886篇
  2003年   4671篇
  2002年   4033篇
  2001年   4467篇
  2000年   4145篇
  1999年   4235篇
  1998年   3964篇
  1997年   4042篇
  1996年   3769篇
  1995年   4289篇
  1994年   3674篇
  1993年   3369篇
  1992年   3276篇
  1991年   3431篇
  1990年   3082篇
  1989年   3032篇
  1988年   2663篇
  1987年   2750篇
  1986年   2570篇
  1985年   2939篇
  1984年   2931篇
  1983年   2837篇
  1982年   2526篇
  1981年   2473篇
  1980年   2478篇
  1979年   2428篇
  1978年   2311篇
  1977年   2203篇
  1976年   2051篇
  1975年   1804篇
  1974年   1823篇
  1973年   1734篇
  1971年   1488篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
The effect of three herbicides, diclofop-methyl (DM), imazamethabenz-methyl (IM) and fenoxaprop-ethyl (FE), was investigated at the recommended rate (×) and double the recommended rate (2×) in a durum wheat crop. FE had the smallest effect on root system characteristics, while IM had the greatest effect. For all herbicides, the double rate treatment gave a greater statistical reduction than the single rate for root system characteristics. FE had the smallest effect on the activity of aerobic microorganisms, while DM gave the greatest reduction, 10 days after application, and all three herbicides reduced earthworm abundance. DM gave the smallest reduction in the number of tillers and in plant height, while the double rate of IM gave the greatest reduction. For all three herbicides, double the recommended rate resulted in a significant reduction in the weight of 1000 seeds, while no statistically significant deviations were noted at the recommended rate. Finally, the use of all three herbicides resulted in significantly lower statistical yields compared to the sample (control plot), although there were no significant statistical differences among them, for either recommended or double recommended rates.  相似文献   
122.
糖槭叶枯病 Phyllosticta negundinis病菌孢子放散开始期和高峰期与每年的温、湿度变化有关。病害发生严重程度与降雨量关系密切 ,降雨早且量大时病害严重。病菌以分生孢子器和分生孢子在病叶上越冬 ,通过气流传播成为翌年初侵染源。喷洒 70 %甲基托布津可湿性粉剂 10 0 0倍液和 75%百菌清可湿性粉剂 80 0倍液均能收到较好的效果  相似文献   
123.
124.
125.
Lactate Kinetics in veterinary Critical Care: A Review   总被引:3,自引:0,他引:3  
Elevation in blood lactate concentration, with or without accompanying metabolic acidosis, is a hallmark finding in patients with circulatory compromise, and is also consistently noted in other conditions affecting critically ill or injured individuals. Little is reported in a veterinary literature regarding lactate measurement in the emergency and critical care setting, despite impressive reports of the clinical usefulness of lactate measurement in people. The purpose of this article is to review lactate kinetics and the clinical utility of lactate measurement. Limitations to lactate evaluation will also be discussed.  相似文献   
126.
Results are given of a survey on the occurrence of pathotypes (races) of Synchytrium endobioticum (potato wart) in both parts of re-unified Germany. An assortment of six differential cultivars appears to be sufficient to distinguish between the seven presently important German wart pathotypes. A total of ten pathotypes was recorded. Two West and two East German pathotypes seem to be identical, based on the results obtained with presently available cultivars. In contrast to pathotype 1 (common race) which prior to 1945 was distributed over the whole German territory, the 'new' pathotypes seem to prefer the central and south German mountain areas.  相似文献   
127.
合成了14个含有 N-莰-2-基的磷酰胺和硫代磷酰胺类化合物,用红外、核磁及元素分析确定其结构,并探讨了~(31)Pδ值的规律性变化。初步生物试验表明,磷酰胺类化合物对水稻发芽具有明显的抑制作用,其中化合物Ⅱ1的活性大于对照药剂抗倒胺但低于多效唑。  相似文献   
128.
129.
130.
Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils.  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