全文获取类型
收费全文 | 91129篇 |
免费 | 5774篇 |
国内免费 | 625篇 |
专业分类
林业 | 4168篇 |
农学 | 2840篇 |
基础科学 | 711篇 |
11865篇 | |
综合类 | 16927篇 |
农作物 | 3416篇 |
水产渔业 | 4364篇 |
畜牧兽医 | 46044篇 |
园艺 | 1383篇 |
植物保护 | 5810篇 |
出版年
2021年 | 915篇 |
2020年 | 983篇 |
2019年 | 1090篇 |
2018年 | 1763篇 |
2017年 | 1987篇 |
2016年 | 1748篇 |
2015年 | 1617篇 |
2014年 | 1837篇 |
2013年 | 3426篇 |
2012年 | 3603篇 |
2011年 | 4133篇 |
2010年 | 2651篇 |
2009年 | 2455篇 |
2008年 | 3654篇 |
2007年 | 3519篇 |
2006年 | 3090篇 |
2005年 | 3024篇 |
2004年 | 2714篇 |
2003年 | 2728篇 |
2002年 | 2514篇 |
2001年 | 2677篇 |
2000年 | 2700篇 |
1999年 | 2098篇 |
1998年 | 841篇 |
1997年 | 750篇 |
1995年 | 787篇 |
1994年 | 692篇 |
1993年 | 691篇 |
1992年 | 1589篇 |
1991年 | 1771篇 |
1990年 | 1687篇 |
1989年 | 1628篇 |
1988年 | 1512篇 |
1987年 | 1559篇 |
1986年 | 1610篇 |
1985年 | 1436篇 |
1984年 | 1218篇 |
1983年 | 1036篇 |
1982年 | 692篇 |
1979年 | 1085篇 |
1978年 | 845篇 |
1976年 | 725篇 |
1975年 | 757篇 |
1974年 | 1024篇 |
1973年 | 1000篇 |
1972年 | 969篇 |
1971年 | 897篇 |
1970年 | 870篇 |
1969年 | 820篇 |
1967年 | 713篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
对于玉米育种而言,新组合的科学评价至关重要。以西南区55个玉米新组合为研究材料,对其产量等15个农艺性状进行灰色关联度分析、主成分分析和聚类分析。结果表明:不同玉米新组合农艺性状与产量的关联度大小依次为单株粒重>穗粗>籽粒含水量>百粒重>空杆率>穗行数>出籽率>穗长>倒折率>行粒数>茎粗>株高>穗位高>秃尖长。以产量最高组合1703为理想品种,综合评价表现较优的组合有成单388、绵1308、川单1751和荣玉1756。通过主成分分析将14个性状降为9个主成分,可解释表型变异的91.11%。依据主成分综合评价模型,可将所有组合分为6类,其中,川单1751、青青711、恩1010、成单388、绵1308、青青733和1703表现最优。聚类分析结果则将所有材料分为5类,结果与主成分分析法得出的结论基本一致。结果表明,玉米新组合绵1308、成单388、川单1751和1703表现最优。 相似文献
992.
993.
994.
995.
Can additional N fertiliser ameliorate the elevated CO2‐induced depression in grain and tissue N concentrations of wheat on a high soil N background?
下载免费PDF全文
![点击此处可从《Journal of Agronomy and Crop Science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M. Tausz R. M. Norton S. Tausz‐Posch M. Löw S. Seneweera G. O'Leary R. Armstrong G. J. Fitzgerald 《Journal of Agronomy and Crop Science》2017,203(6):574-583
Elevated CO2 stimulates crop yields but leads to lower tissue and grain nitrogen concentrations [N], raising concerns about grain quality in cereals. To test whether N fertiliser application above optimum growth requirements can alleviate the decline in tissue [N], wheat was grown in a Free Air CO2 Enrichment facility in a low‐rainfall cropping system on high soil N. Crops were grown with and without addition of 50–60 kg N/ha in 12 growing environments created by supplemental irrigation and two sowing dates over 3 years. Elevated CO2 increased yield and biomass (on average by 25%) and decreased biomass [N] (3%–9%) and grain [N] (5%). Nitrogen uptake was greater (20%) in crops grown under elevated CO2. Additional N supply had no effect on yield and biomass, confirming high soil N. Small increases in [N] with N addition were insufficient to offset declines in grain [N] under elevated CO2. Instead, N application increased the [N] in straw and decreased N harvest index. The results suggest that conventional addition of N does not mitigate grain [N] depression under elevated CO2, and lend support to hypotheses that link decreases in crop [N] with biochemical limitations rather than N supply. 相似文献
996.
Veterinary Research Communications - 相似文献
998.
Physiological Response of Multiple Contrasting Rice (Oryza sativa L.) Cultivars to Suboptimal Temperatures
下载免费PDF全文
![点击此处可从《Journal of Agronomy and Crop Science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M. M. Rachoski A. Vidal O. A. Ruiz A. B. Menéndez A. A. Rodríguez 《Journal of Agronomy and Crop Science》2015,201(2):117-127
The physiological response of multiple rice cultivars, eighteen initially and eight cultivars later on, to suboptimal temperatures (ST) conditions was investigated in laboratory and outdoor experimental conditions. Treatment with ST decreased growth in different extents according to the cultivar and affected the PSII performance, determined by chlorophyll fluorescence fast‐transient test, and stomatal conductance, regardless the experimental condition. Two groups of cultivars could be distinguished on the base of their growth and physiological parameters. The group of cultivars presenting higher growths displayed optimal JIP values, and higher instantaneous water use efficiency (WUEi), due to a lower Gs under ST, unlike cultivars showing lower growth values, which presented worse JIP values and could not adjust their Gs and hence their WUEi. In this work, we detected at least two cultivars with superior tolerance to ST than the cold tolerant referent Koshihikari. These cultivars could be used as parents or tolerance donors in breeding for new crop varieties. On other hand, positive and significant correlations between data obtained from laboratory and outdoor experiments suggest that laboratory measurements of most of the above mentioned parameters would be useful to predict the response of rice cultivars to ST outdoor. 相似文献
999.
Y. L. Loko A. Adjatin A. Dansi R. Vodouhè A. Sanni 《Genetic Resources and Crop Evolution》2015,62(8):1181-1192
1000.
Carlos Yanes‐Roca Mayra E. Toledo‐Cuevas Lizbeth J. Sánchez Ana Born‐Torrijos Nicole Rhody Kevan L. Main 《Journal of the World Aquaculture Society》2018,49(3):612-624
Black snook, Centropomus nigrescens, have been identified as a promising candidate for aquaculture although, like many of the Centropomid species, high mortality associated with early larval stages presents a significant bottleneck to their commercialization. The digestive capacity of black snook larvae throughout the first 37 d after hatch (d.a.h.) was evaluated by quantifying digestive enzyme activities using biochemical techniques. Results showed that black snook larvae have alkaline proteases at hatching, which are known to be important during the first days of feeding for digestion. Toward the end of the study, acid proteases concentration increased (37 d.a.h.). Enzymes for lipid digestion, pancreatic lipase and bile salt‐activated lipase, were already present in the larvae before exogenous feeding commenced, and their activity increased with age and growth (length). Intracellular digestion, measured as the activity of leucine‐alanine peptidase, was high early on (5 d.a.h.) and decreased as development progressed (next 32 d). In contrast, alkaline phosphatase activity was lowest at first feeding and subsequently increased with age. Overall patterns in enzyme activity suggest the possibility of live feed weaning before 32 d.a.h. if artificial diets can be properly balanced. 相似文献