全文获取类型
收费全文 | 353篇 |
免费 | 32篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 3篇 |
综合类 | 27篇 |
化学工业 | 17篇 |
金属工艺 | 1篇 |
建筑科学 | 46篇 |
矿业工程 | 8篇 |
能源动力 | 7篇 |
轻工业 | 36篇 |
水利工程 | 218篇 |
石油天然气 | 4篇 |
无线电 | 1篇 |
一般工业技术 | 3篇 |
冶金工业 | 3篇 |
原子能技术 | 1篇 |
自动化技术 | 26篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 18篇 |
2021年 | 13篇 |
2020年 | 16篇 |
2019年 | 9篇 |
2018年 | 16篇 |
2017年 | 9篇 |
2016年 | 19篇 |
2015年 | 8篇 |
2014年 | 17篇 |
2013年 | 15篇 |
2012年 | 25篇 |
2011年 | 17篇 |
2010年 | 26篇 |
2009年 | 17篇 |
2008年 | 18篇 |
2007年 | 19篇 |
2006年 | 15篇 |
2005年 | 15篇 |
2004年 | 11篇 |
2003年 | 15篇 |
2002年 | 7篇 |
2001年 | 15篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有401条查询结果,搜索用时 15 毫秒
31.
Slurry transportation is an economic haulage system in oil sands and coal-mining operations characterized by long haulage distances and rugged terrain. In such conditions, the ton-km-hr limits are exceeded creating extreme tire wear and high maintenance costs. Steep haul grades and rugged terrain also cause mechanical wear and tear, which decrease haulage equipment economic life. Hydraulic transportation is a proven and viable technology for slurry transportation in such conditions. Currently, stationary pipeline transportation is being used in transporting minerals in many mines. There is an increasing demand to create slurrified minerals at the mining faces to be transported to the processing plant. However, stationary pipelines are not capable for dealing with the rapidly changing configuration of the mining faces. In this paper, the authors develop the ground articulating pipeline (GAP) technology to address this problem. The GAP system consists of pipelines connected together with flexible joints in each pipe section, which allows deflection to avoid torsional stresses from the adjoining frames. This flexible arrangement accommodates the horizontal and vertical displacements of the mobile system as it follows the hydraulic shovels in the excavation process. The mechanics of the GAP system, as well as the production–economic function, are formulated and simulated over an extended period using data and information from Syncrude’s North Mine. The results show that the GAP system is technically and economically viable for productivity between 6,300 and 6,500 tons per hour. The simulated head loss for the GAP system is 15.66 m per 400 m, which compares with 20 m per 400 m for the existing stationary system at Syncrude. The pressure gradient-radius curves are asymptotic to the pipe boundaries, which indicates steep axial pressure gradient in these areas. 相似文献
32.
33.
通过评价黄河流域河湖生态环境演变特征,探究其存在的问题,分析黄河流域河湖生态环境复苏目标与总体格局,探讨并提出黄河流域河湖生态环境复苏的实现路径.结果表明,黄河流域河湖生态环境系统正在由无序发展向有序发展转变.针对黄河流域河湖生态环境复苏面临的河湖生态环境脆弱、区域地下水超采、流域水土流失等主要问题,应从强化河湖监管、... 相似文献
34.
以典型干旱区草型湖泊乌梁素海湿地为研究区,在实地调查和试验的基础上,依据资源经济学和生态经济学的理论和方法,针对乌梁素海湿地资源的特点,对乌梁素海湿地的价值进行了货币化评估.评估结果表明,乌梁素海湿地的总价值为28.24亿元,其中直接实物产品价值为7 164.70万元,直接非实物服务价值为18 193.43万元,间接价值为81 960.58万元,目前非使用类价值为17.51亿元.只有合理开发乌梁素海湿地资源,保护好这一对区域环境具有重要意义的干旱区湿地生态系统,才能实现乌梁素海湿地资源的可持续利用,保证湖区经济的可持续发展. 相似文献
35.
Review of the natural conditions and anthropogenic threats to the Ethiopian Rift Valley rivers and lakes
下载免费PDF全文
![点击此处可从《Lakes & Reservoirs: Research and Management》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This review article considers the lakes found within the Ethiopian Rift Valley system and the rivers draining from the highlands towards them. The Ethiopian Rift Valley system extends in a north‐east–south‐west direction, bisecting the Ethiopian highlands. They differ in sizes and hydrological and hydrogeological settings. The lakes support a variety of flora and fauna, mainly fishes, reptiles, birds and mammals. The lakes and their feeder rivers, however, are currently being subjected to more human use pressure than previously experienced, attributable mainly to water abstractions for irrigation, household water supply and industrial activities in the catchments. Soil erosion, primarily attributable to the lack of soil conservation practices on farm lands, overgrazing and deforestation, along with unregulated irrigation practices, are generating large quantities of silt reaching the lakes. Improper utilization of water and land resources in the catchments, along with population growth and climate change impacts, is escalating the threats to the health of the lake and river ecosystems. As a result, some of the lakes exhibited reduced water levels and increased salinity. This article reviews the major environmental changes happening to these lakes and their feeder rivers. Visits were made to the area to update previous information while also consolidating the trends of change in the aquatic systems and the watersheds attributed to intense development practices. 相似文献
36.
37.
长江中游通江湖泊的调蓄能力与整个区域的水安全密切相关。在对洞庭湖、鄱阳湖(下称“两湖”)调蓄机理探讨的基础上,揭示了两湖泊调蓄的临界状态及临界条件,分析了三峡水库蓄水期两湖泊调蓄能力的变化。研究结果表明:洞庭湖与鄱阳湖具有相同的调蓄机理,其调蓄能力变化受入湖流量和长江干流顶托的双重影响,湖泊调蓄过程表现为入湖与出湖水量的动态调整,湖泊调蓄量不断向0趋近。三峡水库运用后,两湖泊9—10月份调蓄能力下降明显,与2003—2007年相比,2008—2014年两湖汛后调蓄水量的减小更大。 相似文献
38.
Human interventions that limit channel mobility such as bank stabilization are frequent in riparian zones in urban or agricultural environments. This is potentially problematic because channel mobility is an important geomorphological and ecological agent that structures natural instream and riparian ecosystems. This study aims to (1) quantify the relationship between mobility and three types of habitat‐related features, namely bars, oxbow lakes and log jams, for a 54‐km‐long reach of the Yamaska Sud‐Est River (Quebec, Canada), which runs from the forested Appalachian Mountains to the agricultural St‐Lawrence lowlands, and (2) evaluate the impact of human interventions and geomorphological characteristics on these three features. Channel mobility was measured from historical aerial photos for the period 1950–2009. A combination of high‐resolution aerial photos, LiDAR digital elevation model, and field observations was used to measure and map sediment bars, oxbow lakes and log jams, as well as several geomorphological characteristics (channel width, slope, sinuosity and floodplain width). A strong link between the mobility and the presence of habitat features is revealed, but local geomorphological contexts result in different mobility patterns responsible for specific habitats. Floodplain to channel width ratio appears as the best geomorphological factor predicting habitat diversity. Human intervention, mostly through bank stabilization, also appears to be a key factor limiting mobility and its related habitats. These results highlight the importance of defining a protected mobility corridor along rivers where geomorphic processes such as bank erosion can freely occur, as it is an essential process that should be integrated in land use planning and river management. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
39.
40.
2003 年夏和 2004 年夏对中国长江中下游地区的 30 个浅水湖泊的浮游植物类群进行调查。为了研究不同氮磷比(TN/TP)对浮游植物组成的影响,将浮游2003 年夏和 2004 年夏对中国长江中下游地区的 30 个浅水湖泊的浮游植物类群进行调查。为了研究不同氮磷比(TN/TP)对浮游植物组成的影响,将浮游植物的六个门,分别在 TN/TP>30、12<TN/TP<30、TN/TP<12 三个区间随总磷的变化规律进行研究。当 TN/TP 从高水平(>30)降到中等水平(12~30)时,除蓝藻门外的其他五个浮游植物门的斜率均随总磷的升高而增加。但是当 TN/TP从中等水平(12~30)降到低水平(<12)时,除绿藻和隐藻门外,其他浮游植物门的斜率均随总磷的升高呈下降趋势。当 TN/TP 从高水平(>30)降到降至低水平(<12)时,蓝藻门的斜率不断降低,说明蓝藻在较高 TN/TP 有更好的生长潜力。同样发现,绿藻和隐藻门则随 TN/TP 的降低有更好的生长潜力。当 TN/TP 在高水平(>30)和低水平(<12)时,硅藻、甲藻和裸藻门的斜率均发生下降,说明这三个门的藻类在 TN/TP 为中等水平(12~30)的环境中有更好的生长潜力。 相似文献