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   1394篇
  免费   29篇
  国内免费   17篇
安全科学   88篇
废物处理   49篇
环保管理   342篇
综合类   136篇
基础理论   366篇
环境理论   3篇
污染及防治   279篇
评价与监测   105篇
社会与环境   64篇
灾害及防治   8篇
  2023年   18篇
  2022年   27篇
  2021年   34篇
  2020年   25篇
  2019年   16篇
  2018年   31篇
  2017年   40篇
  2016年   47篇
  2015年   35篇
  2014年   42篇
  2013年   110篇
  2012年   60篇
  2011年   87篇
  2010年   62篇
  2009年   58篇
  2008年   73篇
  2007年   84篇
  2006年   78篇
  2005年   55篇
  2004年   50篇
  2003年   57篇
  2002年   40篇
  2001年   22篇
  2000年   16篇
  1999年   22篇
  1998年   21篇
  1997年   17篇
  1996年   24篇
  1995年   24篇
  1994年   20篇
  1993年   16篇
  1992年   13篇
  1991年   10篇
  1990年   11篇
  1989年   11篇
  1988年   8篇
  1987年   7篇
  1986年   6篇
  1985年   5篇
  1984年   9篇
  1983年   4篇
  1982年   9篇
  1981年   5篇
  1979年   4篇
  1978年   6篇
  1975年   2篇
  1974年   3篇
  1973年   2篇
  1938年   2篇
  1931年   2篇
排序方式: 共有1440条查询结果,搜索用时 15 毫秒
931.
Contribution from Fourth World Wilderness Congress-Acid Rain Symposium, Denver (Estes Park), Colorado, September 11–18, 1987.  相似文献   
932.

The presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in wastewater has been reported as a result of fecal shedding of infected individuals. In this study, the occurrence of SARS-CoV-2 RNA was explored in primary-treated wastewater from two municipal wastewater treatment plants in Quintana Roo, Mexico, along with groundwater from sinkholes, a household well, and submarine groundwater discharges. Physicochemical variables were obtained in situ, and coliphage densities were determined. Three virus concentration methods based on adsorption-elution and sequential filtration were used followed by RNA isolation. Quantification of SARS-CoV-2 was done by RT-qPCR using the CDC 2020 assay, 2019-nCoV_N1 and 2019-nCoV_N2. The Pepper mild mottle virus, one of the most abundant RNA viruses in wastewater was quantified by RT-qPCR and compared to SARS-CoV-2 concentrations. The use of three combined virus concentration methods together with two qPCR assays allowed the detection of SARS-CoV-2 RNA in 58% of the wastewater samples analyzed, whereas none of the groundwater samples were positive for SARS-CoV-2 RNA. Concentrations of SARS-CoV-2 in wastewater were from 1.8 × 103 to 7.5 × 103 genome copies per liter (GC l−1), using the N1 RT-qPCR assay, and from 2.4 × 102 to 5.9 × 103 GC l−1 using the N2 RT-qPCR assay. Based on PMMoV prevalence detected in all wastewater and groundwater samples tested, the three viral concentration methods used could be successfully applied for SARS-CoV-2 RNA detection in further studies. This study represents the first detection of SARS-CoV-2 RNA in wastewater in southeast Mexico and provides a baseline for developing a wastewater-based epidemiology approach in the area.

  相似文献   
933.
Surface water and air volatile organic compound (VOC) data from 10 U.S. Geological Survey monitoring sites were used to evaluate the potential for direct transport of VOCs from the atmosphere to urban streams. Analytical results of 87 VOC compounds were screened by evaluating the occurrence and detection levels in both water and air, and equilibrium concentrations in water (Cws) based on the measured air concentrations. Four compounds (acetone, methyl tertiary butyl ether, toluene, and m‐ & p‐xylene) were detected in more than 20% of water samples, in more than 10% of air samples, and more than 10% of detections in air were greater than long‐term method detection levels (LTMDL) in water. Benzene was detected in more than 20% of water samples and in more than 10% of air samples. Two percent of benzene detections in air were greater than one‐half the LTMDL in water. Six compounds (chloroform, p‐isopropyltoluene, methylene chloride, perchloroethene, 1,1,1‐trichloroethane, and trichloroethene) were detected in more than 20% of water samples and in more than 10% of air samples. Five VOCs, toluene, m‐ & p‐xylene, methyl tert‐butyl ether (MTBE), acetone, and benzene were identified as having sufficiently high concentrations in the atmosphere to be a source to urban streams. MTBE, acetone, and benzene exhibited behavior that was consistent with equilibrium concentrations in the atmosphere.  相似文献   
934.
It is generally believed that forest cover in North Korea has undergone a substantial decrease since 1980, while in South Korea, forest cover has remained relatively static during that same period of time. The United Nations Food and Agriculture Organization (FAO) Forest Resources Assessments—based on the reported forest inventories from North and South Korea—suggest a major forest cover decrease in North Korea, but only a slight decrease in South Korea during the last 30 years. In this study, we seek to check and validate those assessments by comparing them to independently derived forest cover maps compiled for three time intervals between 1990 and 2010, as well as to provide a spatially explicit view of forest cover change in the Korean Peninsula since the 1990s. We extracted tree cover data for the Korean Peninsula from existing global datasets derived from satellite imagery. Our estimates, while qualitatively supporting the FAO results, show that North Korea has lost a large number of densely forested areas, and thus in this sense has suffered heavier forest loss than the FAO assessment suggests. Given the limited time interval studied in our assessment, the overall forest loss from North Korea during the whole span of time since 1980 may have been even heavier than in our estimate. For South Korea, our results indicate that the forest cover has remained relatively stable at the national level, but that important variability in forest cover evolution exists at the regional level: While the northern and western provinces show an overall decrease in forested areas, large areas in the southeastern part of the country have increased their forest cover.  相似文献   
935.
Increasing demand for global food production is leading to greater use of irrigation to supplement rainfall and enable more intensive use of land. Minimizing adverse impacts of this intensification on surface water and groundwater resources is of critical importance for the achievement of sustainable land use. In this paper we examine the linkages between irrigation runoff and resulting changes in quality of receiving surface waters and groundwaters in Australia and New Zealand. Case studies are used to illustrate impacts under different irrigation techniques (notably flood and sprinkler systems) and land uses, particularly where irrigation has led to intensification of land use. For flood irrigation, changes in surface water contaminant concentrations are directly influenced by the amount of runoff, and the intensity and kind of land use. Mitigation for flood irrigation is best achieved by optimizing irrigation efficiency. For sprinkler irrigation, leaching to groundwater is the main transport path for contaminants, notably nitrate. Mitigation measures for sprinkler irrigation should take into account irrigation efficiency and the proximity of intensive land uses to sensitive waters. Relating contaminant concentrations in receiving groundwaters to their dominant causes is often complicated by uncertainty about the subsurface flow paths and the possible pollutant sources, viz. drainage from irrigated land. This highlights the need for identification of the patterns and dynamics of surface and subsurface waters to identify such sources of contaminants and minimize their impacts on the receiving environments.  相似文献   
936.
Since wetland construction projects are becoming more commonplace, meaningful follow-up studies are needed to evaluate how these systems change over time. To that end, the objective of our study was to examine the temporal changes in plant community composition and water chemistry in two constructed wetlands. We investigated two wetland sites that were constructed in 2003 in northern Otsego County, NY, a county that is largely dominated by agriculture. Site 1 was previously an active cow pasture and site 2 was previously a wet meadow surrounded by agricultural fields. No active plant introduction was made during the construction; however, both sites were located in areas with many remnant wetlands and were connected to through-flowing streams. In 2004 (Year 1) and 2010 (Year 7), the plant community composition and nitrogen retention were assessed. We found that both sites experienced site-wide declines in plant species richness, including the loss of upland and facultative upland species and the unanticipated loss of facultative wetland and some obligate species. We propose that high water levels, which, at their maximum depth were >1.5 m deeper than in Year 1, maintained by landowners in the years after the initial survey, may have been responsible for the unexpected loss of wetland species. We also found that site 1 exhibited considerable nitrogen retention in both Year 1 and Year 7; however, N concentrations were low at site 2 in both years.  相似文献   
937.
Public lands occupied by feral horses in North America are frequently managed for multiple uses with land use conflict occurring among feral horses, livestock, wildlife, and native grassland conservation. The factors affecting habitat use by horses is critical to understand where conflict may be greatest. We related horse presence and abundance to landscape attributes in a GIS to examine habitat preferences using 98 field plots sampled within a portion of the Rocky Mountain Forest Reserve of SW Alberta, Canada. Horse abundance was greatest in grassland and cut block habitats, and lowest in conifer and mixedwood forest. Resource selection probability functions and count models of faecal abundance indicated that horses preferred areas closer to water, with reduced topographic ruggedness, situated farther from forests, and located farther away from primary roads and trails frequented by recreationalists, but closer to small linear features (i.e. cut lines) that may be used as beneficial travel corridors. Horse presence and abundance were closely related to cattle presence during summer, suggesting that both herbivores utilise the same habitats. Estimates of forage biomass removal (44 %) by mid-July were near maximum acceptable levels. In contrast to horse-cattle associations, horses were negatively associated with wild ungulate abundance, although the mechanism behind this remains unclear and warrants further investigation. Our results indicate that feral horses in SW Alberta exhibit complex habitat selection patterns during spring and summer, including overlap in use with livestock. This finding highlights the need to assess and manage herbivore populations consistent with rangeland carrying capacity and the maintenance of range health.  相似文献   
938.
The government of Canada ratified the Kyoto Protocol on 17 December 2002, but over 100 Canadian municipalities had joined the International Council for Local Environmental Intitatives' (ICLEI) Cities for Climate Protection (CCP) campaign up to a decade earlier. A low-cost home energy rating system (HERS) evaluation and individualized energy plan was provided to 420 households in Kitchener, Ontario, from September 2000 to August 2001. To assess the impact of the energy efficiency program, natural gas consumption in the year prior to the evaluation was compared with that in the year following. Overall, a 5% reduction was achieved, but individual responses varied widely. Situational and psychological factors were evaluated for three groups of households: the conservers, the consumers and the steady middle group. Conservers (30% of households) had higher initial energy consumption levels and achieved two-thirds of the potential savings identified by the energy evaluation. Consumers (12% of households) had higher ownership rates of high-efficiency furnaces and water heaters and demonstrated the rebound effect of increased demand for energy services following the evaluation. Low-income groups were the most likely to behave as conservers (42%) while high-income groups were the least likely to be conservers (13%) and the most likely to be consumers. Local programs need to be inclusive of all income groups to increase participation and implementation rates by systematically reducing barriers (financial, knowledge, trust) or increasing incentives (financial, regulatory or social) if the desired goal (e.g. Kyoto target) is to be achieved.  相似文献   
939.
Collaborative Modeling for Decision Support integrates collaborative modeling with participatory processes to inform natural resources decisions. Practitioners and advocates claim that the approach will lead to better water management, balancing interests more effectively and reducing the likelihood of costly legal delays. These claims are easy to make, but the benefits will only be realized if the process is conducted effectively. To provide guidance for how to conduct an effective collaborative modeling process, a task committee cosponsored by the Environmental Water Resources Institute (EWRI) of the American Society of Civil Engineers and by the U.S. Army Corps of Engineers' Institute for Water Resources developed a set of Principles and Best Practices for anyone who might convene or conduct collaborative modeling processes. The guidance is intended for both conflict resolution professionals and modelers, and our goal is to integrate these two fields in a way that will improve water resources planning and decision making. Here, the set of eight principles is presented along with a selection of associated best practices, illustrated by two different case examples. The complete document is available at: http://www.computeraideddisputeresolution.us/bestpractices/ .  相似文献   
940.

The release of carbon dioxide from the burning of fossil fuels is believed to be responsible for climate change. In the UK, road transport emits 22% of the total output of carbon dioxide. This study applies the ecological footprint to Merseyside to ascertain the global environmental impact of passenger transport (expressed in hectares). Results show that car travel has a footprint of 704 000 hectares, which is 87% of the total footprint. It is demonstrated in scenarios that Policy initiatives involving the Local Transport Plan will cause the footprint to increase. It is also shown that individual behaviour could be influenced when highlighting the impacts of different modes of transport along the same route. By using the ecological footprint in educational programmes, the effect can be shown of carbon emissions and land appropriation on the 'school run'; these issues could be promoted alongside others such as health, safety, congestion, global equity and fairness.  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