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   110篇
  免费   4篇
  国内免费   2篇
林业   15篇
农学   2篇
基础科学   3篇
  45篇
综合类   44篇
水产渔业   2篇
畜牧兽医   5篇
  2024年   1篇
  2023年   1篇
  2021年   3篇
  2020年   1篇
  2019年   4篇
  2018年   2篇
  2017年   3篇
  2016年   3篇
  2015年   4篇
  2014年   4篇
  2013年   7篇
  2012年   11篇
  2011年   5篇
  2010年   13篇
  2009年   10篇
  2008年   5篇
  2007年   6篇
  2006年   4篇
  2005年   5篇
  2004年   7篇
  2003年   3篇
  2002年   1篇
  2001年   1篇
  1999年   2篇
  1998年   1篇
  1996年   2篇
  1995年   1篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1987年   1篇
排序方式: 共有116条查询结果,搜索用时 15 毫秒
51.
采用Li-6400便携式光合作用测量系统连接Li-6400-09土壤呼吸室对安太堡露天煤矿排土场土壤呼吸速率进行了测定。结果表明,该地区土壤呼吸日变化比较明显,呈现单峰型曲线,最大值出现在13:00—15:00,与土壤温度最大值同步,稍滞后于空气温度最大值;土壤湿度与土壤呼吸的相关性较差,在一定范围内,土壤呼吸随土壤湿度的升高而升高。  相似文献   
52.
Abstract

This study involves a comprehensive economic analysis of mine water aquaculture. First, the costs and benefits are quantified using standard enterprise budgeting and feasibility techniques. Next, a price analysis is conducted to determine the underlying probability distribution and generate confidence intervals for use in planning purposes. Then, the relationships between mine sites and unemployment, and mine sites and tourism, respectively, are illustrated using a spatial analysis. Finally, the potential economic development impacts of growth in the aquaculture industry on statewide output, income, and employment are estimated. The results have implications for entrepreneurs and the aquaculture and coal industries in Appalachia and other parts of the US where coal mining can be linked to fish farming, water conservation, and recreation.  相似文献   
53.
胡薇  金雷 《排灌机械》2005,23(3):46-48
针对我国矿山抢险排水中存在的问题。分析全贯流式轴流潜水电泵与大型矿用潜水电泵组成的接力排水系统存在的不足。研制开发了充油式混流潜水电泵与大型矿用潜水电泵组成的新型接力排水系统。现场运行的结果表明,改进后的排水系统具有排水能力强、运行可靠性高等优点,解决了地下开采矿井淹后抢险复矿工作中深部大流量排水、有效安全运行的问题。  相似文献   
54.
矿车粘附机理及其清理技术   总被引:5,自引:1,他引:5  
在对粘湿煤与矿车粘附机理及在低温下发生冻粘的机理进行分析的基础上,综述了目前煤矿所采取的防止湿煤粘附,冻粘的方法与技术情况,同时指出了各种方法与技术的优点与不足,并对煤煤矿车防粘防冻技术与方法的发展趋势进行了展望。  相似文献   
55.
以北京首云铁矿尾矿库采矿迹地利用覆盖客土加生态植被毯措施9年来恢复植被为研究对象,采用空间替代时间的方法,对不同恢复年限的植被生态系统碳密度空间格局进行研究,结果表明:随着恢复年限的增加,恢复植被地上部分碳密度呈现先降低再增加的趋势,恢复5年后植被地上部分碳密度趋于稳定;根系碳密度随着恢复年限与地上部分碳密度呈相同的趋势;枯落物碳密度随恢复年限呈增加趋势,恢复6年后碳密度变化趋于稳定;土壤有机碳密度随恢复年限呈现增加趋势,各层有机碳密度均显著低于周边自然植被土壤有机碳密度,周边植被土壤有机碳密度为恢复植被土壤碳密度的2.07~2.87倍,铁矿采矿迹地恢复过程中土壤碳库具有较大的碳汇潜能。  相似文献   
56.
永城市陈四楼煤矿土地复垦适宜性评价研究   总被引:4,自引:1,他引:4  
为了采取指数和法和极限条件法对陈四楼煤矿土地复垦适宜性进行评价。以GIS软件为平台,利用河南省永城市土壤图、地形图、土地利用现状图进行空间叠加分析最终确定4个评价单元。依据研究区的自然、经济、社会现状和相关技术标准,确定了宜农、宜林、宜渔3个复垦方向的评价指标,然后采用指数和法和极限条件法对矿区复垦土地进行适宜性评价。结果表明:评价总面积为73.7 hm2,其中适宜农业种植用地面积为25 hm2,适宜林业种植用地面积为20 hm2,适宜渔业养殖用地面积为28.7 hm2。通过评价研究建立矿区土地复垦适宜性评价等级体系。  相似文献   
57.
Abstract

Four lignite overburdens from a potential lignite mining area of Louisiana were used to evaluate the effect of rates of fertilizer, lime, plant growth and simulated poor drainage conditions on the weathering of these materials. Common bermudagrass (Cynodon dactylon) grown on each overburden material in pots lined with polyethylene bags received 0, 1/2>x, 1x, 2x and 4x the recommended rate of fertilizer which was a combination of N, P and K. Lime was applied to the overburdens based on soil test lime requirement to increase the pH to 6.5.

Enrichment (fertilizers, non‐drained conditions and lime) had a significant effect on the weathering of the overburdens. The pH, EC, organic C, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, Na and Al were significantly affected by one or more of these parameters. Visual observations indicated that fertilizers stimulated root production, which effectively increased the weathering of the overburdens. Lime, applied as CaO, did not increase the pH of the Cow Bayou material substantially, suggesting the presence of pyrite, which was confirmed by X‐ray diffraction analysis. As pyrite oxidized in the Cow Bayou material, soluble salts accumulated on the surface of the material and on the lower parts of the plant. Gypsum and jarosite precipitated as the solution ionic strength of this material increased due to the weathering of the pyrite.

The Prairie Terrace overburden was selected as the best potential topsoil since it had more favorable physical and chemical characteristics which would promote successful reclamation. Reduced materials such as Cow Bayou and Naborton had undesirable physical and chemical properties. Changes in the chemical properties of these materials would be difficult to predict and soil amendments such as lime and gypsum would be needed in significant quantities for successful reclamation. Dolet Hills, a sandy material, had a less desirable texture and would require frequent irrigation and fertilization if it were used as a topsoil substitute.  相似文献   
58.
 Litterfall, leaf litter decomposition and N and P release were studied in four tree species (Dalbergia sissoo, Azadirachta indica, Pongamia pinnata and Shorea robusta) planted on a mine spoil habitat. Annual litterfall varied from 1220 kg ha–1 in the S. robusta stand to 3620 kg ha–1 in the A. indica stand. The fast-growing species A. indica and D. sissoo exhibited higher litter production in comparison to the other two slow-growing species. The total N returned to the soil through litterfall ranged from 8.6 kg ha–1 year–1 in the S. robusta stand to 36.5 kg ha–1 year–1 in the D. sissoo stand. The annual percent leaf litter mass loss was distinctly greater in A. indica (73%) and D. sissoo (69%) in comparison to P. pinatta (59%) and S. robusta (47%). The mean relative decomposition rates of leaf litter material were maximum in the rainy season and minimum in summer. Rainfall and its associated variables exhibited greater control over litter docomposition than temperature. Lignin and water-soluble compounds were better predictors of annual mass loss rates accounting for 90% variability. Mass loss was positively correlated with N and P mineralization rates. Lignin was the best predictor of annual N and P mineralization rates. Nutrient release pattern differed; constant release occurred in A. indica, initial release followed by delayed immobilization and release occurred in D. sissoo and P. pinnata, and initial immobilization followed by gradual release was noticed in S. robusta. A. indica and D. sissoo, showing high litterfall and rapid litter decomposition rate, hold promise for the rehabilitation of nutrient-poor coal mine spoils. On the other hand, S. robusta with less litterfall and a slow decomposition rate may prove disadvantageous. Received: 10 March 1998  相似文献   
59.
矿区废弃地土壤重构与性能恢复研究进展   总被引:8,自引:0,他引:8  
土壤重构是土地复垦研究的核心内容。本文从生物种类与活性、土壤理化性质与矿物学特性、土壤重构新技术的使用等三个方面综述了当前国外进行矿区废弃地土壤重构研究现状;同时从土壤理化性质与土壤养分、土壤微生物及生化特征、土壤剖面重构等三个方面对国内矿区土壤重构研究进展进行了阐述。  相似文献   
60.
设计运用园林绿化技术手段对东曲矿矸石山进行景观改造与生态恢复,因地制宜地将全园划分为以精品园为中心的五个功能分区:办公区、精品园区、苗木生产区、温室大棚生产区、护坡绿化区,并选择抗逆性强的树种进行绿化种植。绿化后的矸石山将有效地抑制其对环境的破坏,并创造出新的绿色环境。  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