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   209篇
  免费   11篇
  国内免费   2篇
测绘学   5篇
大气科学   19篇
地球物理   60篇
地质学   98篇
海洋学   8篇
天文学   27篇
自然地理   5篇
  2021年   3篇
  2020年   3篇
  2019年   8篇
  2018年   10篇
  2017年   12篇
  2016年   6篇
  2015年   8篇
  2014年   9篇
  2013年   9篇
  2012年   20篇
  2011年   11篇
  2010年   4篇
  2009年   12篇
  2008年   8篇
  2007年   8篇
  2006年   8篇
  2005年   3篇
  2004年   7篇
  2002年   7篇
  1999年   4篇
  1998年   2篇
  1987年   1篇
  1985年   1篇
  1982年   1篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1952年   1篇
  1951年   1篇
  1950年   1篇
  1948年   1篇
  1932年   1篇
  1929年   3篇
  1928年   5篇
  1927年   1篇
  1926年   2篇
  1925年   1篇
  1924年   1篇
  1923年   1篇
  1922年   2篇
  1921年   3篇
  1920年   3篇
  1918年   5篇
  1916年   2篇
  1915年   3篇
  1914年   1篇
  1913年   3篇
  1912年   4篇
  1911年   1篇
  1910年   3篇
排序方式: 共有222条查询结果,搜索用时 0 毫秒
221.
Groundwater resources in semi-arid areas and especially in the Mediterranean face a growing demand for irrigated agriculture and, to a lesser extent, for domestic uses. Consequently, groundwater reserves are affected and water-table drops are widely observed. This leads to strong constraints on groundwater access for farmers, while managers worry about the future evolution of the water resources. A common problem for building proper groundwater management plans is the difficulty in assessing individual groundwater withdrawals at regional scale. Predicting future trends of these groundwater withdrawals is even more challenging. The basic question is how to assess the water budget variables and their evolution when they are deeply linked to human activities, themselves driven by countless factors (access to natural resources, public policies, market, etc.). This study provides some possible answers by focusing on the assessment of groundwater withdrawals for irrigated agriculture at three sites in North Africa (Morocco, Tunisia and Algeria). Efforts were made to understand the different features that influence irrigation practices, and an adaptive user-oriented methodology was used to monitor groundwater withdrawals. For each site, different key factors affecting the regional groundwater abstraction and its past evolution were identified by involving farmers’ knowledge. Factors such as farmer access to land and groundwater or development of public infrastructures (electrical distribution network) are crucial to decode the results of well inventories and assess the regional groundwater abstraction and its future trend. This leads one to look with caution at the number of wells cited in the literature, which could be oversimplified.  相似文献   
222.
Sustainable urban drainage systems are built along roads and in urban areas to collect urban runoff and avoid flooding, and to filter water pollutants. Sediment collected by runoff is deposited in the stormwater basin and progressively reduces water infiltration efficiency, leading to the clogging of the basin. To help stormwater basin managers and stakeholders better understand and predict clogging rates in order to elaborate maintenance plans and schedules, water transport prediction models are necessary. However,because of the heterogeneous sediment hydrodynamic properties inside the stormwater basin, a twodimensional(2-D) water flow model is required to predict water levels and possible overflow as accurately as possible. Saturated hydraulic conductivity(Ks) and sediment water retention curves were measured in the overall sediment layer of the stormwater basin, in addition to sediment layer thickness and organic matter content(11 sampling points). Sediment depth was used to predict organic matter(OM) content, and the OM was used to predict Ks. Water height in the basin was modeled with the HYDRUS-2 D model by taking into account the sediment hydrodynamic properties distribution. The HYDRUS-2 D model gave a satisfactory representation of the measured data. Scenarios of the hydraulic properties of stormwater basin sediment were tested over time, and hydraulic resistance, R, was calculated to assess the stormwater basin performance. Presently, after 20 years of functioning, the stormwater basin still ensures efficient water infiltration, but the first outflow(Hydraulic resistance,R 24 h)) is expected to appear in the next 5 years, and clogging(R 47 h) in the next 13 years. This 2-D water balance model makes it possible to integrate the hydrodynamic heterogeneity of a stormwater basin. It gives interesting perspectives to better predict 2-D/3-D contaminant transport.  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