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   94篇
  免费   1篇
  国内免费   2篇
安全科学   3篇
废物处理   4篇
环保管理   10篇
综合类   29篇
基础理论   16篇
污染及防治   22篇
评价与监测   1篇
社会与环境   10篇
灾害及防治   2篇
  2021年   2篇
  2019年   3篇
  2018年   1篇
  2017年   5篇
  2016年   5篇
  2014年   4篇
  2013年   3篇
  2012年   7篇
  2011年   8篇
  2009年   3篇
  2008年   1篇
  2007年   6篇
  2006年   7篇
  2004年   3篇
  2003年   3篇
  2002年   4篇
  1999年   1篇
  1998年   2篇
  1997年   1篇
  1995年   1篇
  1992年   3篇
  1988年   1篇
  1986年   1篇
  1985年   2篇
  1984年   1篇
  1983年   2篇
  1980年   2篇
  1967年   1篇
  1965年   2篇
  1964年   1篇
  1963年   1篇
  1955年   1篇
  1954年   1篇
  1953年   1篇
  1943年   1篇
  1941年   1篇
  1937年   1篇
  1933年   2篇
  1921年   2篇
排序方式: 共有97条查询结果,搜索用时 15 毫秒
1.
The provision of ecosystem services is a prominent rationale for urban greening, and there is a prevailing mantra that ‘trees are good’. However, understanding how urban trees contribute to sustainability must also consider disservices. In this perspective article, we discuss recent research on ecosystem disservices of urban trees, including infrastructure conflicts, health and safety impacts, aesthetic issues, and environmentally detrimental consequences, as well as management costs related to ecological disturbances and risk management. We also discuss tradeoffs regarding species selection and local conservation concerns, as well as the central role of human perception in the interpretation of ecosystem services and disservices, particularly the uncritical assertion that ‘everybody loves trees’. Urban forestry decision-making that fails to account for disservices can have unintended negative consequences for communities. Further research is needed regarding life cycle assessments, stakeholder decision-making, return-on-investment, and framings of services and disservices in urban forestry.  相似文献   
2.
Seepage from Hg mine wastes and calcines contains high concentrations of mercury (Hg). Hg pollution is a major environmental problem in areas with abandoned mercury mines and retorting units. This study evaluates factors, especially the hydrological and sedimentary variables, governing temporal and spatial variation in levels and state of mercury in streams impacted by Hg contaminated runo . Samples were taken during di erent flow regimes in theWanshan Hg mining area in Guizhou Province, China. In its headwaters the sampled streams/rivers pass by several mine wastes and calcines with high concentration of Hg. Seepage causes serious Hg contamination to the downstream area. Concentrations of Hg in water samples showed significant seasonal variations. Periods of higher flow showed high concentrations of total Hg (THg) in water due to more particles being re-suspended and transported. The concentrations of major anions (e.g., Cl??, F??, NO3?? and SO4 2??) were lower during higher flow due to dilution. Due to both sedimentation of particles and dilution from tributaries the concentration of THg decreased from 2100 ng/L to background levels (< 50 ng/L) within 10 km distance downstream. Sedimentation is the main reason for the fast decrease of the concentration, it accounts for 69% and 60% for higher flow and lower flow regimes respectively in the upper part of the stream. Speciation calculation of the dissolved Hg fraction (DHg) (using Visual MINTEQ) showed that Hg(OH)2 associated with dissolved organic matter is the main form of Hg in dissolved phase in surface waters in Wanshan (over 95%).  相似文献   
3.
Regional Environmental Change - This study investigates the historical development of the southwest coastal region of Bangladesh through the lens of human-delta co-evolutionary system. The change...  相似文献   
4.
5.
6.
7.
Dissolved organic sulfur (DOS) is an important fraction for sulfur mobilization in ecosystem. In this work stream waters were sampled in 25 forested sites in southern China to study the dissolved sulfur fractions. Dissolved sulfur was fractionated into dissolved organic sulfur (DOS) and inorganic sulfate (SO42-) for 95 stream water samples. The results showed that the concentration of DOS ranged from 0 to 13.1 mg/L (average 1.3 mg/L) in all the streams. High concentrations of DOS in stream waters were found in the sites with high concentrations of sulfate. DOS constituted less than 60.1% of dissolved sulfur (average 17.9%). Statistical analysis showed that DOS concentration was correlated with SO42- in streams waters and total sulfur in surface layer soils. The results also showed that DOS concentration in stream waters had a seasonal variation, but no trends were found with it. The implication was that the long term sulfur deposition had led the increase of the concentration and fraction of DOS in stream waters in acid rain prevailing regions  相似文献   
8.
Changes to natural organic compounds by acid deposition and subsequent effects on Al mobilization are not well understood. The HUMEX catchment-scale acidification experiment in western Norway offers a unique possibility for an integrated assessment of these interactions. In this report, the soil and soil water chemical data from the HUMEX site, from before and after the onset of experimental acidification, are used to characterize the catchment. Changes in soil water chemistry are discussed and controls on dissolved organic carbon are addressed in relation to Al mobilization. Decreases in the concentration of dissolved organic carbon (DOC) and organic Al fractions were found in soil water after the treatment started. These changes were related to an increase in soil water sulphate concentrations. The sulphate levels showed a significant increase (on a 95% level) in four of ten soil horizons while nitrate remained nearly unchanged. In organic soils, where the dissolved organic carbon content was high, the major control for monomeric aluminum concentration appeared to be the amount of exchangeable aluminum in the soil. In mineral soils, the gibbsite dissolution may govern inorganic Al concentrations in soil water, though substantial undersaturation was found when DOC was high.  相似文献   
9.
10.
Summary Whirligig beetles aggregate in the daytime into dense single-and multispecies groups (rafts) of hundreds or thousands of individuals. On the 22km shoreline of Lake Itasca in northern Minnesota, these aggregations were on the average 0.8 km apart, and they were usually found day after day in the same ocations.Most beetles apparently do not home to the aggregation of their origin after dispersing at night because (a) the species composition of some aggregations changed greatly, and (b) paint-marked beetles (Dineutus horni) moved overnight from one aggregation as far as 4km, joining 11 of the 14 large (>300 beetles) D. horni groups on the lake.Throughout the night, the largest concentrations of beetles remained within 100m of the diurnal aggregation sites. Beetles reconvened into the compact rafts before daybreak, in part by following each other in sometimes long single files or trains. Their forward motion stopped after they joined large number of other beetles. We infer that following behavior enables those individuals that have dispersed from their original aggregations (during their nocturnal foraging) to find and join other aggregations before daylight.Naive fish ate the beetles despite their noxious secretions. However, fish living near rafting sites and feeding on insects on the water surface in daylight should soon learn to avoid the beetles. The rafting sites would then become safe places. We observed fish attacking only those beetles that had been either dispersed from their rafts or released into open water away from raft sites in the daytime. We speculate that the evolutionary significance of the aggregation behavior is related to predator (fish) avoidance.  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