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   394篇
  免费   5篇
  国内免费   3篇
安全科学   6篇
废物处理   19篇
环保管理   53篇
综合类   40篇
基础理论   89篇
环境理论   2篇
污染及防治   133篇
评价与监测   34篇
社会与环境   22篇
灾害及防治   4篇
  2023年   4篇
  2022年   10篇
  2021年   13篇
  2020年   1篇
  2019年   17篇
  2018年   18篇
  2017年   12篇
  2016年   17篇
  2015年   12篇
  2014年   14篇
  2013年   41篇
  2012年   23篇
  2011年   39篇
  2010年   20篇
  2009年   27篇
  2008年   27篇
  2007年   18篇
  2006年   11篇
  2005年   16篇
  2004年   9篇
  2003年   10篇
  2002年   7篇
  2001年   4篇
  2000年   4篇
  1999年   3篇
  1998年   4篇
  1997年   1篇
  1996年   2篇
  1995年   4篇
  1994年   3篇
  1993年   1篇
  1991年   1篇
  1989年   1篇
  1988年   1篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1981年   1篇
  1980年   1篇
  1969年   1篇
  1965年   1篇
排序方式: 共有402条查询结果,搜索用时 62 毫秒
381.
Sulfide generation should be avoided during wastewater transportation. The efficiency of nitrate dosing for the inhibition of sulfide generation was evaluated during reclaimed wastewater transport with two nitrate doses, 2.5 and 5 mg/L nitrate-nitrogen (NO3-N). A calcium nitrate [Ca(NO3)2] solution was injected at the beginning of the 61-km-long gravity pipe, which is part of the Reclaimed Wastewater Reuse System of South Tenerife (Spain). During transportation, after dissolved oxygen depletion, a denitrification process took place. With the 5 mg/L NO3-N dose, nitrate was not completely removed at the end of the pipe, whereas with 2.5 mg/L NO3-N, a complete denitrification was achieved. Sulfide generation was completely inhibited with the 5 mg/L dose. However, with 2.5 mg/L, sulfide generation was not completely inhibited but delayed and minimized to a great extent. Denitrification was stoichiometrically limited by the availability in biodegradable matter. An empirical equation enables one to predict the nitrate concentration.  相似文献   
382.
This article provides a case study of small-scale private sector provision of water supply in Paraguay, where the Government has sought sector policy reforms that would encourage private investment in drinking water supply. Ironically, while the Government has focused almost entirely on garnering the interest of large private international water companies, much smaller local firms have already made significant investments in drinking water services for the poor, all without any participation or encouragement from the Government. Outside Paraguay's two major cities, Asunción and Ciudad del Este, large numbers of aguateros currently provide piped potable water to lower-income people. Though the aguateros have little legal footing — they are in many respects informal and unregulated —they have constructed as much as one third of all the new drinking water connections in these two cities over the past 20 years. The small-scale water systems in Paraguay offer a model of financial, economic, and water-use efficiency. This article asserts that an abundance of groundwater resources, cheap access to electricity for pumping, and a spirit of informal investment, among other variables, has spawned widespread use of this approach. This article documents and analyzes the features of these independent small-scale water providers in Paraguay and the efficiency they bring to the use of water resources in meeting drinking water demands among the poor. It also cautions against policies that may trample on such entrepreneurial spirit in the name of State-managed privatization.  相似文献   
383.
Land-use and land-cover changes have attracted substantial scientific interest in recent years because of their marked influence on hydrological cycles. In developed countries of the Mediterranean basin, the generalized revegetation and forest growth in mountainous areas that occurred during the last five decades are negatively affecting the evolution of water resources in headwaters. In this study, changes in land cover in the Duero River Basin (northern Spain) during the last 50 years were analyzed and their role in hydrological evolution was estimated. For this purpose, step-wise linear regressions were developed to estimate the evolution of runoff as a function of climate (precipitation and temperatures). The results show a significant expansion of forest cover in the headwaters, although it has been more extensive in the mountains to the north of the basin than to the south. River discharges in the headwaters underwent a generalized decline during the study period (1961–2006), but precipitation over the same period did not show an appreciable trend. In the absence of noticeable trends in removal of water for human consumption, our results indicate that revegetation is contributing to the observed hydrological decline. Our hypothesis is confirmed because of the greater divergence in the evolution of precipitation and runoff in the northern headwaters (more forest growth) than in the south headwaters (less forest growth). Results suggest that further increases in forest area will enhance hydrological decline and highlight the importance of integrating land-cover information in water availability assessments in a region where water is a strategic resource.  相似文献   
384.
385.
This study updates and expands the empirical analysis of natural resource scarcity published in 1963 by Harold Barnett and Chandler Morse (“Scarcity and Growth: The Economics of Natural Resource Availability,” Johns Hopkins Press). Unit extraction costs are measured for all extractive products, four major subgroups (agriculture, minerals, forestry, and fishing), and selected individual commodities. The efficacy of the unit cost measure of resource scarcity is addressed and a critique of alternative scarcity indicators is provided. Unit cost appears to be the most practical scarcity index because there are adequate checks against its theoretical shortcomings and data are readily available which contain fewer deficiencies than other indexes. On the basis of the Barnett and Morse definition of relative scarcity, the empirical evidence does not support the need for public actions justified solely on the basis of increasing resource scarcity.  相似文献   
386.
387.
Food and Environmental Virology - Norovirus (NoV) is an important etiological agent of diarrhea in children and adults. In Mexico, NoV screening is not routinely performed. NoV is highly infectious...  相似文献   
388.
The sequential extraction procedures described by Tessier et al., McGrath and Cegarra, and Gimeno-García et al. were compared to investigate trace element (As, Cr, Cu, Pb, and Zn) partitioning patterns and extraction efficiency in three contaminated soils from Mediterranean regions of Spain. Soils were selected from Onda (Castellón) (S1), Aznalcóllar (Sevilla) (S2), and Silla (Valencia) (S3). S1 was a soil contaminated with Pb and Zn after dumping of wastes from the manufacture of ceramic tiles, S2 was polluted accidentally with a highly acid and As-concentrated sludge from mining activities, and S3 was a soil with a high Cr content from tannery sludge disposal. Trace element distribution in the soils—soluble, exchangeable, organically bound, precipitated with carbonates, bound to iron and manganese oxides, and precipitated with sulfides fractions—varied significantly according to the extraction procedure used. In addition, different extraction efficiencies were found for the three sequential extraction procedures compared. Finally, the trace elements studied showed different and specific distribution patterns between the various soil fractions examined.  相似文献   
389.
390.
It is predicted that climate change will drive extinctions of some reptiles and that the number of these extinctions will depend on whether reptiles are able to change their distribution. Whether the latitudinal distribution of reptiles may change in response to increases in temperature is unknown. We used data on reptile distributions collected during the 20th century to analyze whether changes in the distributions of reptiles in Spain are associated with increases in temperature. We controlled for biases in sampling effort and found a mean, statistically significant, northward shift of the northern extent of reptile distributions of about 15.2 km from 1940-1975 to 1991-2005. The southern extent of the distributions did not change significantly. Thus, our results suggest that the latitudinal distributions of reptiles may be changing in response to climate change.  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