全文获取类型
收费全文 | 3341篇 |
免费 | 129篇 |
国内免费 | 442篇 |
专业分类
林业 | 45篇 |
农学 | 948篇 |
基础科学 | 52篇 |
252篇 | |
综合类 | 1448篇 |
农作物 | 705篇 |
水产渔业 | 31篇 |
畜牧兽医 | 191篇 |
园艺 | 81篇 |
植物保护 | 159篇 |
出版年
2024年 | 10篇 |
2023年 | 27篇 |
2022年 | 78篇 |
2021年 | 106篇 |
2020年 | 122篇 |
2019年 | 106篇 |
2018年 | 67篇 |
2017年 | 114篇 |
2016年 | 158篇 |
2015年 | 110篇 |
2014年 | 161篇 |
2013年 | 212篇 |
2012年 | 283篇 |
2011年 | 240篇 |
2010年 | 184篇 |
2009年 | 202篇 |
2008年 | 228篇 |
2007年 | 188篇 |
2006年 | 183篇 |
2005年 | 137篇 |
2004年 | 115篇 |
2003年 | 109篇 |
2002年 | 98篇 |
2001年 | 85篇 |
2000年 | 70篇 |
1999年 | 65篇 |
1998年 | 51篇 |
1997年 | 59篇 |
1996年 | 50篇 |
1995年 | 49篇 |
1994年 | 31篇 |
1993年 | 51篇 |
1992年 | 34篇 |
1991年 | 26篇 |
1990年 | 31篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1962年 | 3篇 |
1955年 | 1篇 |
排序方式: 共有3912条查询结果,搜索用时 62 毫秒
61.
62.
63.
64.
水稻籼粳杂种一代生育期的表现 总被引:3,自引:1,他引:3
采用生育期不同的籼型野败恢复系和保持系与典型粳稻和籼粳中间型亲本配制成80份籼粳杂种一代组合,用亚种肉品种间杂交为对照,研究了籼粳稻杂种一代生育期的表现。结果表明,以籼粳亚种间杂种一代生育期优势最强,一般都超过双亲平均值;品种间杂种一代生育期优势最弱,接近中亲值;籼或使型亲本配籼粳中间型亲本,杂种一代生育期优势介于上述两类型组合之间。籼粳杂交由于双亲的不同,组合间F1生育期优势差异很大,有的组合甚至出现负向优势.这种生育期优势差异既受双亲本身生育期的迟早所支配,如杂种一代生育期长短排列顺序为中籼/晚粳>中籼/早或中粳>早籼或早熟中籼/晚粳>早籼或早熟中籼/早或中粳;又受籼型亲本所含的野败恢、保遗传基因所制约,凡用籼型野败恢复系配制的籼粳杂种一代其生育期优势明显减弱,并与双亲籼、粳遗传距离的大小有关,杂种一代生育期优势随双亲籼、便遗传距离的扩大而增强。 相似文献
65.
66.
百日草自交系花粉萌发条件及花粉活力研究 总被引:1,自引:0,他引:1
研究了不同培养基、采集时间、贮藏温度和湿度等因素对百日草花粉离体培养萌发效果的影响。结果表明:花粉萌发较适宜的培养基为ME3 16%PEG4000 12%蔗糖;上午10:00采集花粉萌发率要显著地高于下午3:00采集的;在4℃湿润条件下贮藏18 h,J6花粉生活力下降较小,而在室温干燥条件下几乎失去活力;相对湿度在66%以下时极不利于花粉保存;11个百日草自交系花粉离体萌发率差异显著。 相似文献
67.
配电网起着输送和分配电能的作用,线路损耗给供电企业造成很大的成本投入,降低能源的利用率。分析配电网线路损耗的原因,提出降低线路损耗的具体措施,以期为配电网节能降耗、安全运行提供参考。 相似文献
68.
69.
Sampson Agyin-Birikorang George A. O’Connor John E. Erickson 《Journal of plant nutrition》2013,36(12):1881-1900
Commercial fertilizer (particularly nitrogen) costs account for a substantial portion of the total production costs of cellulosic biomass and can be a major obstacle to biofuel production. In a series of greenhouse studies, we evaluated the feasibility of co-applying Gibberellins (GA) and reduced nitrogen (N) rates to produce a bioenergy crop less expensively. In a preliminary study, we determined the minimum combined application rates of GA and N required for efficient biomass (sweet sorghum, Sorghum bicolor) production. Co-application of 75 kg ha?1 (one-half of the recommended N rate for sorghum) and a modest GA rate of 3 g ha?1 optimized dry matter yield (DMY) and N and phosphorus (P) uptake efficiencies, resulting in a reduction of N and P leaching. Organic nutrient sources such as manures and biosolids can be substituted for commercial N fertilizers (and incidentally supply P) to further reduce the cost of nutrient supply for biomass production. Based on the results of the preliminary study, we conducted a second greenhouse study using sweet sorghum as a test bioenergy crop. We co-applied organic sources of N (manure and biosolids) at 75 and 150 kg PAN ha?1 (representing 50 and 100% N rate respectively) with 3 g GA ha?1. In each batch of experiment, the crop was grown for 8 wk on Immokalee fine sand of minimal native fertility. After harvest, sufficient water was applied to soil in each pot to yield ~1.5 L (~0.75 pore volume) of leachate, and analyzed for total N and soluble reactive P (SRP). The reduced (50%) N application rate, together with GA, optimized biomass production. Application of GA at 3 g ha?1, and the organic sources of N at 50% of the recommended N rate, decreased nutrient cost of producing the bioenergy biomass by ~$375 ha?1 (>90% of total nutrient cost), and could reduce offsite N and P losses from vulnerable soils. 相似文献
70.
Dohan Mariam Soma Delwendé Innocent Kiba Nana Ewusi-Mensah Zacharia Gnankambary François Lompo Michel Papoaba Sedogo 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2018,68(5):401-411
Low phosphorus availability in cultivated soils limits sustainable crop production in sub‐Saharan Africa. This study aimed at evaluating the effect of long‐term application of different types of organic amendments on soil P forms, P use efficiency and sorghum yields. A long term experiment established in 1980 at Saria in Burkina Faso, comparing the effects of manure, compost and sorghum straw was used. Manure and compost significantly increased organic P and resin‐P by about 35% and 64%, respectively after 10 and 32 years of sorghum cultivation, and HCl‐P after 32 years of cultivation compared to the control. Manure significantly increased NaHCO3-Pi and NaOH-Pi by 63% and 26%, respectively compared to the control. Sorghum straw had little effect on measured soil P forms. Manure and compost were the best in increasing sorghum grain yield, which effect were strongly correlated to soil pH, carbon and nitrogen. The partial factors productivities of P resulting from the application of studied organic amendments were similar and low, but significantly higher than that of the control treatment. Organic amendments with high P content, maintaining soil carbon and pH could be used to improve soil P availability, sorghum yield and reduce the demand for mineral phosphorus fertilizers. 相似文献