全文获取类型
收费全文 | 912篇 |
免费 | 48篇 |
国内免费 | 34篇 |
专业分类
林业 | 123篇 |
农学 | 71篇 |
基础科学 | 27篇 |
167篇 | |
综合类 | 290篇 |
农作物 | 41篇 |
水产渔业 | 71篇 |
畜牧兽医 | 100篇 |
园艺 | 33篇 |
植物保护 | 71篇 |
出版年
2024年 | 8篇 |
2023年 | 16篇 |
2022年 | 18篇 |
2021年 | 32篇 |
2020年 | 21篇 |
2019年 | 34篇 |
2018年 | 25篇 |
2017年 | 32篇 |
2016年 | 26篇 |
2015年 | 43篇 |
2014年 | 55篇 |
2013年 | 77篇 |
2012年 | 43篇 |
2011年 | 74篇 |
2010年 | 55篇 |
2009年 | 68篇 |
2008年 | 66篇 |
2007年 | 61篇 |
2006年 | 39篇 |
2005年 | 37篇 |
2004年 | 32篇 |
2003年 | 12篇 |
2002年 | 24篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 15篇 |
1995年 | 11篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有994条查询结果,搜索用时 31 毫秒
41.
42.
43.
E. T. Craswell A. Sajjapongse D. J. B. Howlett A. J. Dowling 《Agroforestry Systems》1997,38(1-3):121-137
Steeply sloping lands are widespread in the tropics. An estimated 500 million people practice subsistence agriculture in these
marginal areas. Continued population growth has led to the intensified cultivation of large areas of the sloping lands, exacerbating
the problem of soil erosion. Although research shows that alley cropping and other contour agroforestry systems can stabilize
the sloping lands, these systems have not been widely adopted by farmers.
The Framework for Evaluating Sustainable Land Management (FESLM) has been tested in sloping land areas in the Philippines.
Sustainable land management must be productive, stable, viable, and acceptable to farmers, while protecting soil and water
resources. Farms on which contour hedgerow intercropping has been adopted meet the multifaceted requirements of FESLM, whereas
the farmers' current practice does not. Appropriate land management measures for particular locations depend on a complex
suite of social, economic, and biophysical factors, and need to be developed in participation with farmers.
The role of agroforestry in sustainable management of sloping lands is the subject of networks coordinated by the International
Board for Soil Research and Management (IBSRAM) in seven countries in Asia (ASIALAND) and four countries in the Pacific (PACIFICLAND).
We review selected outcomes from a wealth of network data. From these results the following conclusions about the sustainability
of various agroforestry systems for sloping lands can be drawn:
• In the Pacific, soil loss from sloping lands due to water erosion under farmers' current practices is episodic, unpredictable,
and possibly not severe;
• Agroforestry systems that utilize legume shrubs, fruit trees, coffee (Coffea spp.) or rubber (Hevea brasiliensis) provide
useful economic returns, but are not an essential component in terms of soil protection because grass or pineapple (Ananas
comosus) planted on the contour are equally effective in reducing erosion;
• Agricultural intensification will lead to nutrient mining, reduction of aboveground biomass, declining yields, and less
soil protection unless external sources of nutrients are used;
• nitrogen can be effectively supplied using legumes;
• Cash derived from hedgerow trees and/or shrubs may providean incentive for their adoption by farmers, as well as funds to
purchase external inputs such as fertilizers;
• Labor may be a major constraint to the adoption of complex agroforestry systems.
We also discuss the information management systems required to effectively manage and utilize the extensive sets of experimental
and indigenous data being accumulated. We believe such information systems can facilitate technology transfer across and between
regions, and improve the efficiency of research into agroforestry and other land-management approaches.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
44.
Acacia mangium is a very fast growing species belonging to the family Leguminosae that has been introduced in the plantations in Bangladesh for its faster growth and wide range of adaptability. The present study aimed at development of growth and yield prediction models for the species using simultaneous equation method. Models were selected for the species to estimate stand dominant height, stand diameter, stand basal area per hectare and total volume yield per hectare. Paired t-test, 45-degree line test, percent absolute deviation and biological principle of stand development were used for the validation of chosen models. The results suggest that the models derived were statistically and biologically acceptable and could be satisfactorily used for stands of Acacia mangium of ages 4–7 yrs based on a base age of 6 yr. 相似文献
45.
A dendrochronological technique was used to investigate canopy recruitment of beech (Fagus engleriana Seem.) trees in western Hubei Province of Central China by identifying growth releases through gap formation. The results
indicated that 83% and 17% of the canopy trees regenerate in gaps and the understory, respectively. Radial growth analyses
demonstrated that there are three modes for beech regeneration and canopy recruitment: (1) gap origin without suppression;
(2) gap origin with period(s) of suppression; and (3) understory origin. Multiple periods of release and suppression imply
that beech regeneration and canopy recruitment are very sensitive to gap formation. 相似文献
46.
中东欧前社会主义国家森林私有化概况与发展趋势 总被引:2,自引:1,他引:2
概括介绍了中东欧前社会主义国家林权私有化的现状、面临的种种挑战和发展趋势。 相似文献
47.
Seed maturity indices of Populus ciliata were investigated in collections from Sukhatal and Bhowali. Across both seed sources, mean capsule size varied from 68.0±1.5 mm2 to 72.0±0.9 mm2, while mean number of capsules/100 grams varied from 268±8 to 295±12. Mean weight of 100 capsules varied from 25.0±1.4 g to 27.0±1.4 g. Weight of 100 capsules among sources and individual trees differed significantly (P < 0.05), while number of capsules/100 grams and weight of 100 capsules was negatively correlated (r2 = 0.69). As capsules matured moisture content decreased from 83.2±1.1% to 54.3±0.3% at Sukhatal and from 77.7±0.4% to 46.4±0.3% at Bhowali. The optimum germination was at 58–60% moisture content. Maturation was related to capsule colour changes as well as moisture content. These parameters were judged to be good indicators of when to collect P. ciliata seeds. 相似文献
48.
Detection of Novel Reassortant Influenza A (H3N2) and H1N1 2009 Pandemic Viruses in Swine in Hanoi,Vietnam
下载免费PDF全文
![点击此处可从《Zoonoses and public health》网站下载免费的PDF全文](/ch/ext_images/free.gif)
T. D. Dao N. T. Pham B. J. Cowling M. Peyre M. Peiris 《Zoonoses and public health》2015,62(6):429-434
From May to September 2013, monthly samples were collected from swine in a Vietnamese slaughterhouse for influenza virus isolation and serological testing. A(H1N1)pdm09 viruses and a novel H3N2 originating from reassortment between A(H1N1)pdm09 and novel viruses of the North American triple reassortant lineage were isolated. Serological results showed low seroprevalence for the novel H3N2 virus and higher seroprevalence for A(H1N1)pdm09 viruses. In addition, serology suggested that other swine influenza viruses are also circulating in Vietnamese swine. 相似文献
49.
中原崛起与绿色中原建设 总被引:3,自引:0,他引:3
中原崛起对于中部地区崛起、全国区域经济协调发展具有全局意义。实现中原崛起,全面建设小康社会,必须全面贯彻落实科学发展观,加快环境友好型社会建设,发展林业,推进绿色中原建设。针对中原崛起中的生态环境问题,根据河南省经济发展态势、资源禀赋条件、林地利用状况,研究提出了绿色中原建设的目标任务、资源配置和保障措施。 相似文献
50.
云南玉溪市老城中心面临着传统商业衰退以及城市化进程中对中心商业区升级的矛盾,通过引入城市网络的概念,将原本集中布置的商业区延展为一个连续的商业网络,并设计穿越整个地块的开放绿地空间,将保留的历史建筑融合在绿地网络之中,以此保持和发展该地区原有的文化和经济氛围,并形成多元化的土地利用方式。 相似文献