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   591篇
  免费   35篇
  国内免费   11篇
安全科学   26篇
废物处理   22篇
环保管理   148篇
综合类   75篇
基础理论   171篇
环境理论   1篇
污染及防治   139篇
评价与监测   24篇
社会与环境   28篇
灾害及防治   3篇
  2023年   10篇
  2022年   6篇
  2021年   17篇
  2020年   13篇
  2019年   17篇
  2018年   22篇
  2017年   19篇
  2016年   44篇
  2015年   22篇
  2014年   25篇
  2013年   52篇
  2012年   35篇
  2011年   41篇
  2010年   25篇
  2009年   19篇
  2008年   33篇
  2007年   17篇
  2006年   25篇
  2005年   18篇
  2004年   21篇
  2003年   21篇
  2002年   20篇
  2001年   21篇
  2000年   6篇
  1999年   6篇
  1998年   2篇
  1997年   4篇
  1996年   5篇
  1995年   3篇
  1994年   1篇
  1993年   2篇
  1992年   9篇
  1991年   4篇
  1990年   5篇
  1989年   1篇
  1988年   5篇
  1987年   4篇
  1986年   4篇
  1985年   1篇
  1984年   5篇
  1983年   6篇
  1982年   5篇
  1981年   3篇
  1980年   4篇
  1979年   5篇
  1978年   1篇
  1976年   1篇
  1974年   1篇
  1968年   1篇
排序方式: 共有637条查询结果,搜索用时 11 毫秒
51.
Ground and surface water selenium (Se) contamination is problematic throughout the world, leading to harmful impacts on aquatic life, wildlife, livestock, and humans. A groundwater reactive transport model was applied to a regional‐scale irrigated groundwater system in the Lower Arkansas River Basin in southeastern Colorado to identify management practices that remediate Se contamination. The system has levels of surface water and groundwater Se concentrations exceeding the respective chronic standard and guidelines. We evaluate potential solutions by combining the transport model with an assessment of the cost to employ those practices. We use a framework common in economics and engineering fields alike, the Pareto frontier, to show the impact of four different best management practices on the tradeoffs between Se and cost objectives. We then extend that analysis to include institutional constraints that affect the economic feasibility associated with each practice. Results indicate that although water‐reducing strategies have the greatest impact on Se, they are the hardest for farmers to implement given constraints common to western water rights institutions. Therefore, our analysis shows that estimating economic and environmental tradeoffs, as is typically done with a Pareto frontier, will not provide an accurate picture of choices available to farmers where institutional constraints should also be considered.  相似文献   
52.
Given the unique biogeochemical, physical, and hydrologic services provided by floodplain wetlands, proper management of river systems should include an understanding of how floodplain modifications influence wetland ecosystems. The construction of levees can reduce river–floodplain connectivity, yet it is unclear how levees affect wetlands within floodplains, let alone the cumulative impacts within an entire watershed. This paper explores spatial relationships between levee and floodplain wetland systems in the Wabash Basin, United States. We used a hydrogeomorphic floodplain delineation technique to map floodplain extents and identify wetlands that may be hydrologically connected to river networks. We then spatially examined the relationship between levee presence, wetland area, and other river network attributes within discrete subbasins. Our results show that cumulative wetland area is relatively constant in subbasins that contain levees, regardless of maximum stream order within the subbasin. In subbasins that do not contain levees, cumulative wetland area increases with maximum stream order. However, we found that wetland distributions around levees can be complex, and further studies on the influence of levees on wetland habitat may need to consider finer resolution spatial scales.  相似文献   
53.
Declines in salmon stocks and general watershed health in Washington State, USA, have led to an increase in stream restoration and enhancement projects initiated throughout the state. The increasing number of projects has also raised questions regarding the monitoring of these efforts. Project managers receiving hydraulic project approvals (HPAs) were surveyed to determine whether monitoring was taking place on their projects. About half the project managers surveyed reported the collection of baseline data and the use of biological, physical, chemical, or other water quality measures for their projects. Of those who reported collection of monitoring data, only 18% indicated that monitoring was required. Respondents were also asked to rank the importance of various project goals on a Likert scale. Project managers with projects focusing on “engineering” goals (e.g., roadbed stabilization) were less likely than other project managers to collect baseline monitoring data. Project managers with projects focusing on “restoration/ecological” or “fisheries” goals were more likely than other project managers to collect monitoring measures. Although monitoring appears to be taking place in slightly more than half of the projects surveyed, the nature of the data collected varies widely across projects, and in most cases the monitoring effort is voluntary. This suggests that project sponsors, funders, and managers must consider the issues involved in requiring appropriate monitoring, establishing standardized monitoring guidelines, the time frames in which to monitor, providing other incentives for conducting monitoring, and ensuring adequate funding for monitoring efforts.  相似文献   
54.
Snow is an important component of the hydrologic cycle for many regions worldwide. In addition to vital water resources, snowmelt can be important for forest ecosystem dynamics and flood risk. However, standard design events in the United States lack a design snowmelt event, including only precipitation events, though snowmelt has been shown to be larger than rainfall. In this article, we present a method using hourly snow water equivalent data to develop and test a function for representing the diurnal pattern of snowmelt. A two‐parameter beta distribution function is modified for the purposes of this study and found to fit the pattern of snowmelt well with a root mean squared error of 0.008. Soil moisture sensors were additionally utilized to assess the timing of the snowmelt water outflow from the base of the snowpack that supports the shape of the function, but suggests that the timing of losses recorded on snow pillows lag as much as 3 h. Further testing of the function showed the shape of the function to be accurate. The methods developed and tested in this paper can be applied for design purposes comparing snowmelt and rainfall events or to improve hydrological models investigating processes such as streamflow or groundwater recharge.  相似文献   
55.
Geographic information systems and remote sensing technologies have become an important tool for visualizing conservation management and developing solutions to problems associated with conservation. When multiple organizations separately develop spatial data representations of protected areas, implicit error arises due to variation between data sets. We used boundary data produced by three conservation organizations (International Union for the Conservation of Nature, World Resource Institute, and Uganda Wildlife Authority), for seven Ugandan parks, to study variation in the size represented and the location of boundaries. We found variation in the extent of overlapping total area encompassed by the three data sources, ranging from miniscule (0.4 %) differences to quite large ones (9.0 %). To underscore how protected area boundary discrepancies may have implications to protected area management, we used a landcover classification, defining crop, shrub, forest, savanna, and grassland. The total area in the different landcover classes varied most in smaller protected areas (those less than 329 km2), with forest and cropland area estimates varying up to 65 %. The discrepancies introduced by boundary errors could, in this hypothetical case, generate erroneous findings and could have a significant impact on conservation, such as local-scale management for encroachment and larger-scale assessments of deforestation.  相似文献   
56.
57.
ABSTRACT: Recent research that couples climate change scenarios based on general circulation models (GCM) with Great Lakes hydrologic models has indicated that average water levels are projected to decline in the future. This paper outlines a methodology to assess the potential impact of declining water levels on Great Lakes waterfront communities, using the Lake Huron shoreline at Goderich, Ontario, as an example. The methodology utilizes a geographic information system (GIS) to combine topographic and bathymetric datasets. A digital elevation surface is used to model projected shoreline change for 2050 using water level scenarios. An arbitrary scenario, based on a 1 m decline from February 2001 lake levels, is also modeled. By creating a series of shoreline scenarios, a range of impact and cost scenarios are generated for the Goderich Harbor and adjacent marinas. Additional harbor and marina dredging could cost as much as CDN $7.6 million. Lake freighters may experience a 30 percent loss in vessel capacity. The methodology is used to provide initial estimates of the potential impacts of climate change that can be readily updated as more robust climate change scenarios become available and is adaptable for use in other Great Lakes coastal communities.  相似文献   
58.
Co-management has gained prominence due to the sustained interest in participatory forms of natural resource management. While theoretical development posed an initial challenge, it has become an integral part of the co-management literature. This paper comprehensively explores co-management theory. It begins with an investigation of theory itself. The major elements of theory (concepts, variables and relational propositions) are described and a typology of theoretical statements (formats) is conceptualized. Co-management theory is subsequently charted according to the four schemes (modelling, propositional, analytical and meta-theoretical) which make up the typology. Given the maturing nature of the co-management literature and the absence of any meta-theoretical schemes, we examine the central and underlying assumption of co-operation through the science of sociobiology. Reciprocal altruism is pursued to explain why non-kin co-operate, and is adapted to elucidate the potentials and pitfalls of co-management. This meta-theory enriches understanding of co-management, provides guidance to the other theoretical schemes, and offers a foundational basis upon which construction of subtle predications is possible.  相似文献   
59.
Eutrophication, harmful algal blooms, and human health impacts are critical environmental challenges resulting from excess nitrogen and phosphorus in surface waters. Yet we have limited information regarding how wetland characteristics mediate water quality across watershed scales. We developed a large, novel set of spatial variables characterizing hydrological flowpaths from wetlands to streams, that is, “wetland hydrological transport variables,” to explore how wetlands statistically explain the variability in total nitrogen (TN) and total phosphorus (TP) concentrations across the Upper Mississippi River Basin (UMRB) in the United States. We found that wetland flowpath variables improved landscape-to-aquatic nutrient multilinear regression models (from R2 = 0.89 to 0.91 for TN; R2 = 0.53 to 0.84 for TP) and provided insights into potential processes governing how wetlands influence watershed-scale TN and TP concentrations. Specifically, flowpath variables describing flow-attenuating environments, for example, subsurface transport compared to overland flowpaths, were related to lower TN and TP concentrations. Frequent hydrological connections from wetlands to streams were also linked to low TP concentrations, which likely suggests a nutrient source limitation in some areas of the UMRB. Consideration of wetland flowpaths could inform management and conservation activities designed to reduce nutrient export to downstream waters.  相似文献   
60.
A cost-of-illness framework was applied to health and income data to quantify the health burden from illnesses associated with exposure to polluted recreational marine waters. Using data on illness severity due to exposure to polluted coastal water and estimates of mean annual salaries and medical costs (adjusted to 2001 values) for residents of Orange County, California, we estimated that the economic burden per gastrointestinal illness (GI) amounts to 36.58 dollars, the burden per acute respiratory disease is 76.76 dollars, the burden per ear ailment is 37.86 dollars, and the burden per eye ailment is 27.31 dollars. These costs can become a substantial public health burden when millions of exposures per year to polluted coastal waters result in hundreds of thousands of illnesses. For example, exposures to polluted waters at Orange County's Newport and Huntington Beaches were estimated to generate an average of 36,778 GI episodes per year. At this GI illness rate, one can also expect that approximately 38,000 more illness episodes occurred per year of other types, including respiratory, eye, and ear infections. The combination of excess illnesses associated with coastal water pollution resulted in a cumulative public health burden of 3.3 million dollars per year for these two beaches. This paper introduces a public health cost variable that can be applied in cost-benefit analyses when evaluating pollution abatement strategies.  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