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   269篇
  免费   28篇
  国内免费   16篇
电工技术   11篇
综合类   21篇
化学工业   10篇
金属工艺   2篇
建筑科学   101篇
矿业工程   4篇
能源动力   5篇
轻工业   2篇
水利工程   138篇
石油天然气   6篇
无线电   1篇
一般工业技术   5篇
冶金工业   1篇
自动化技术   6篇
  2023年   4篇
  2022年   5篇
  2021年   12篇
  2020年   9篇
  2019年   12篇
  2018年   10篇
  2017年   17篇
  2016年   5篇
  2015年   16篇
  2014年   11篇
  2013年   21篇
  2012年   13篇
  2011年   18篇
  2010年   16篇
  2009年   13篇
  2008年   15篇
  2007年   17篇
  2006年   20篇
  2005年   14篇
  2004年   8篇
  2003年   9篇
  2002年   5篇
  2001年   2篇
  2000年   9篇
  1999年   2篇
  1998年   4篇
  1997年   4篇
  1996年   2篇
  1995年   5篇
  1994年   3篇
  1993年   3篇
  1992年   5篇
  1991年   1篇
  1990年   1篇
  1988年   1篇
  1985年   1篇
排序方式: 共有313条查询结果,搜索用时 15 毫秒
81.
王升 《山西建筑》2010,36(8):363-365
鉴于小流域暴雨径流为铁路桥涵孔径的设计依据,直接关系桥梁的运营安全,对形态法与地方公式、铁三院法的结果进行综合分析及比较,确定合理的小流域径流公式,以期提高小流域暴雨径流计算的精度。  相似文献   
82.
In recent years, remotely sensed image datasets with ground resolutions below 10 cm have seen widening applications in fluvial sciences with the development of methods for image based measurements of bathymetry, grain sizes and habitat types. However, given that these datasets typically contain hundreds or thousands of images, one of their key limitations is the need to georeference this large volume of imagery. Automated registration of remotely sensed imagery based on pattern matching algorithms has been the focus of much publication in other disciplines and there are now methods capable of automatically registering a newly sensed image to a pre‐existing reference image. Based on such strategies, this paper presents an automated georeferencing tool specifically designed for fluvial remote sensing which uses a simple and well established pattern matching algorithm. This new method allows for very large image databases to be automatically georeferenced without the recourse to ground control points from the field and thus requiring minimal labour. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
83.
高婷 《山西建筑》2006,32(15):161-162
基于理想沉淀池相关理论,分析了平流式沉淀池的工作情况,研究了提高其处理能力和处理效率的方法,提出了沿途集水可以提高沉淀池的水力负荷,但一定程度地降低了处理效率,表明了通过中途集水实现沉淀池挖潜是可行的。  相似文献   
84.
通过对潜江市气象、施药方式等方面调查,应用SoilFug模型预测农药的分布、归宿,结果表明农药的大部分是通过降解作用而从环境中除去的,挥发和径流的比例很小.应用模型计算了全年降雨径流中农药浓度,以峰值浓度和平均浓度分别进行安全用量估算(kg/ha):甲草胺1.8~13.8、丁草胺14.55~30、甲胺磷1.95~5.1、乐果2.25~4.2、敌敌畏2.85~7.0,甲基对硫磷0.53~1.2、对硫磷2.25~4.05,甲基对硫磷对环境的风险最大。  相似文献   
85.
设计洪水是水利水电工程设计的重要参数, 对于无实测水文资料的设计断面设计洪水计算通常会移用其上下 游或邻近流域的水文站设计洪水成果。通过水文推理公式对设计洪峰流量与集水面积的变化关系进行推导分析, 再通过西南地区不同流域的众多实测设计洪水成果进行统计分析, 归纳总结了西南地区洪峰流量随集水面积的变 化关系及其变化规律。  相似文献   
86.
滨江流域GPS降水预报系统的研究与实现   总被引:1,自引:0,他引:1  
 利用试验区建立的GPS水汽监测网获得的近乎实时的水汽数据,采用模块开发和系统集成方式,研制了流域GPS降水预报系统。介绍了系统的体系结构、主要功能、运行情况及开发的关键技术。叙述了流域降水预报的各种预报方法,并建立了基于遗传算法的降水预报神经网络模型(GA-BP网络模型)。结果表明,GPS水汽可为降水预报提高精度;GA-BP网络是一种精度较高的降水预报模型,可提高预测精度,增长有效预见期。该系统能根据流域GPS观测数据、高空数据、卫星云图,数值产品等数据,实现不同数据源的信息处理和不同时效的降水预报制作,为洪水预警预报和防洪决策服务。  相似文献   
87.
Assessment of urban energy use may proceed by a number of methods. Here we derive an energy account from local statistics, and compare them with an input output (IO) analysis as applied to Melbourne, Australia. These approaches highlight different aspects of urban energy use and comparable outputs are presented together to assess consistency, to identify complementarities and discuss the insight each approach brings to understanding urban energy. The IO method captures the direct and embodied primary energy requirements of local household expenditure (235.8 GJ/capita/year) while the regional assessment more directly accounts for local production activity (258.1 GJ/capita/year). The parity of these results is unexpected for a developed city with a strong tertiary sector. Sectoral detail reveals differences between the primary energy required by Melbourne's economic structure and that ultimately required through the full supply chain relating to household expenditure. This is accompanied by an IO analysis of the geography of Melbourne's ‘energy catchment’. It is suggested that the IO consumption and regional production approaches have particular relevance to policies aimed at consumption behaviour and economic (re)structuring, respectively. Their complementarity further suggests that a combined analysis would be valuable in understanding urban energy futures and economic transitions elsewhere.  相似文献   
88.
The effects of long‐term atmospheric deposition of pollutant elements on the trans‐surface causative relationships at three lake sites having different catchment characteristics were investigated in this study. The selected determinants included lake productivity, bottom sediment quality, and a suite of microbial variables (microbial biomass (Cmic); basal respiration; substrate‐induced respiration; bacterial:fungal ratio; metabolic quotient; and alkaline phosphatase and FDAase activities) measured at the land–water interface, in relation to atmospheric deposition of phosphate; nitrate; ammonium; sulphate; calcium; and magnesium. The results indicated significant between‐site differences (P < 0.001) in the atmospheric deposition of phosphate (0.21–1.96 kg.h?1.year?1); nitrate (2.77–28.05 kg.h?1.year?1); ammonium (0.58–11.60 kg.h?1.year?1); sulphate (5.64–32.15 kg.h?1.year?1); calcium (4.50–30.00 kg.h?1.year?1); and magnesium (1.50–12.15 kg.h?1.year?1), as well as a consistently increasing input of these ions across time. The catchment vegetation had important effects on microbial variables that, in turn, affected lake productivity. Interfaces of woodland lake were found to be rich in phenolics, supporting low Cmic and activities. Except for alkaline phosphatase, which declined over time, atmospheric deposition of pollutant elements increased the Cmic and activities at the land–water interface. The time lag correlation analysis indicated the Cmic and lake productivity relationships were significantly altered by atmospherically driven nitrogen and phosphorus inputs, with a time lag of 2–3 years. Despite being supportive, aerial nutrient inputs appeared to have a destabilizing effect on both, microbial biomass and lake productivity variables. These observations indicate that if present atmospheric deposition trends of pollutant elements continue, it will modify the cross‐domain causative relationships of inland lentic systems over the long term. These study results are relevant for the formulation of strategies for managing freshwater tropical lakes.  相似文献   
89.
The presence of a wide areal extent of small‐sized village reservoirs offers a considerable potential for the development of culture‐based fisheries (CBFs) in Sri Lanka. To this end, this study uses geographical information systems (GISs) and remote sensing (RS) techniques to determine the morphometric and biological characteristics most useful for classifying non‐perennial reservoirs for CBF development and for assessing the influence of catchment land‐use patterns on potential CBF yields. The reservoir shorelines at full water supply level were mapped with a Global Positioning System to determine shoreline length and reservoir areal extent. The ratio of shoreline length to reservoir extent, which was reported to be a powerful predictor variable of CBF yields, could be reliably quantified using RS techniques. The areal extent of reservoirs, quantified with RS techniques (RS extent), was used to estimate the ratio of forest cover plus scrubland cover to RS extent and was found to be significantly related to the CBF yield (R2 = 0.400; P < 0.05). The results of this study indicated that morphometric characteristics and catchment land‐use patterns, which might be viewed as indices of biological productivity, can be quantified using RS and GIS techniques.  相似文献   
90.
基于典型次洪泥沙动力学过程的岔巴沟流域水沙关系分析   总被引:1,自引:0,他引:1  
为准确把握岔巴沟流域径流泥沙变化趋势并分析其原因,以岔巴沟流域1970—2016年98场洪水输沙过程为研究对象,通过分析不同年代次洪输沙量,阐明了次洪水输沙动力学过程。结果表明:岔巴沟流域近50 a来次洪输沙滞回曲线模式主要表现为顺时针型、逆时针型、8字型、复杂型4种,4种模式中逆时针型所占比例和次洪输沙量最大,顺时针型所占比例最小,但平均洪峰流量和平均输沙峰值最高,复杂型洪水平均持续时间最长。不同年代次洪输沙频率表现为1980—1989年间洪水输沙滞回曲线以逆时针型为主,其次为复杂型洪水,2006年以来逆时针型和复杂型洪水数量大幅减少,8字型洪水数量增多; 出现这种现象可能是由于岔巴沟流域自20世纪70年代以来开展小流域综合治理,各种水土保持措施在1970—1989年间产生较强的作用,但2000年后,由于长期使用后产生淤满和损坏等状况,效力逐渐降低,对岔巴沟流域整体的水沙输移模式产生影响。  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