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   2901篇
  免费   170篇
  国内免费   84篇
安全科学   448篇
废物处理   34篇
环保管理   1036篇
综合类   613篇
基础理论   362篇
环境理论   44篇
污染及防治   141篇
评价与监测   87篇
社会与环境   261篇
灾害及防治   129篇
  2024年   7篇
  2023年   51篇
  2022年   34篇
  2021年   98篇
  2020年   109篇
  2019年   114篇
  2018年   90篇
  2017年   177篇
  2016年   152篇
  2015年   131篇
  2014年   108篇
  2013年   188篇
  2012年   126篇
  2011年   188篇
  2010年   75篇
  2009年   169篇
  2008年   147篇
  2007年   122篇
  2006年   108篇
  2005年   110篇
  2004年   87篇
  2003年   84篇
  2002年   87篇
  2001年   71篇
  2000年   70篇
  1999年   64篇
  1998年   43篇
  1997年   38篇
  1996年   37篇
  1995年   41篇
  1994年   24篇
  1993年   33篇
  1992年   20篇
  1991年   10篇
  1990年   17篇
  1989年   12篇
  1988年   8篇
  1987年   12篇
  1986年   12篇
  1985年   19篇
  1984年   9篇
  1983年   10篇
  1982年   6篇
  1981年   12篇
  1980年   3篇
  1979年   4篇
  1978年   4篇
  1977年   5篇
  1972年   2篇
  1971年   3篇
排序方式: 共有3155条查询结果,搜索用时 15 毫秒
551.
The objective of this study was to characterize recovered soil fines from construction and demolition (C&D) waste recycling facilities for trace organic pollutants. Over a period of 18 months, five sampling trips were made to 14 C&D waste recycling facilities in Florida. Screened soil fines were collected from older stockpiles and newly generated piles at the sites. The samples were analyzed for the total concentration (mg/kg) of a series of volatile organic compound (VOCs) and semi-volatile organic compounds (semi-VOCs). The synthetic precipitation leaching procedure (SPLP) test was also performed to evaluate the leachability of the trace organic chemicals. During the total analysis only a few volatile organic compounds were commonly found in the samples (trichlorofluoromethane, toluene, 4-isopropyltoluene, trimethylbenzene, xylenes, and methylene chloride). A total of nine VOCs were detected in the leaching test. Toluene showed the highest leachability among the compounds (61.3-92.0%), while trichlorofluoromethane, the most commonly detected compound from both the total and leaching tests, resulted in the lowest leachability (1.4-39.9%). For the semi-VOC analysis, three base-neutral semi-VOC compounds (bis(2-ethylhexyl)phthalate, butyl benzyl phthalate, and di-n-butyl phthalate) and several PAHs (acenaphthene, pyrene, fluoranthene, and phenanthrene) were commonly detected in C&D fines samples. These compounds also leached during the SPLP leaching test (0.1-25%). No acid extractable compounds, pesticides, or PCBs were detected. The results of this study were further investigated to assess risk from land applied recovered soil fines by comparing total and leaching concentrations of recovered soil fines samples to risk-based standards. The results of this indicate that the organic chemicals in recovered soil fines from C&D debris recycling facilities were not of a major concern in terms of human risk and leaching risk to groundwater under reuse and contact scenarios.  相似文献   
552.
ABSTRACT: This study examines water consumption characteristics in Casablanca and analyzes approaches for sustainable water demand management. Research procedures involve the development and estimation of water demand models for the residential/commercial, industrial, and institutional sectors; forecasts of water demand to 2010; and simulation of the effects of a complex of water conservation methods on the forecasted demands. The results indicate that residential/commercial water demand is weakly responsive to price changes (elasticity =?0.448) while institutional water demand is slightly more responsive (elasticity =?0.648). The conservation approaches used in the simulations included public education, plumbing code revisions to require use of water conservation devices, leak detection and repair, pricing policy, metering, and pressure reduction. The results indicate that considerable saving in water use can be attained through a comprehensive water demand management program.  相似文献   
553.
ABSTRACT: This paper describes how a hydrologic model proved to be a valuable tool to help interested parties understand impacts to four threatened and endangered fish species in the Upper Colorado River. In 1994, the Ute Water Conservancy District initiated permitting and design of the Plateau Creek pipeline replacement. The project was considered a major Federal action and therefore subject to the National Environmental Policy Act. Under Section 7 of the Endangered Species Act, the U.S. Fish and Wildlife Service (USFWS) entered the process to develop a Biological Opinion (BO) and determined that the project could potentially impact the endangered fish in the 15‐mile reach of the Colorado River. The Section 7 consultation was directed by a Core Committee comprised of stakeholders in the Upper Colorado River watershed. Hydrologic modeling became the evaluation tool for comparing flow reductions to USFWS target recovery flows and defining make‐up flow requirements to meet those targets. The Colorado River Recovery Implementation Program was designated to provide the make‐up flows. The USFWS released a final BO in December 1997, approving diversions through 2015. An Environmental Impact Statement for the project was completed and the Record of Decision was issued by the Bureau of Land Management in early 1998.  相似文献   
554.
ABSTRACT: Research on the condition of drinking water provision in the United States documents the inequitable financial impact of environmental regulations on small water systems (those serving 3,300 or fewer people). While a variety of federal and state financial assistance programs are available for water systems, few quantitative analyses have evaluated the success of these programs in alleviating the problems of small systems. A case study of the largest aid initiative for water supply infrastructure in Pennsylvania provides the empirical framework through which to analyze government funding opportunities for water systems. This study examines the allocation practices of the Pennsylvania Infrastructure Investment Authority (PENNVEST) to water systems of varying sizes. Utilizing data from PENNVEST applications and the Pennsylvania Department of Environmental Protection, the distribution of PENNVEST award recipients and denied applicants by size characteristics are compared. The study indicates that very small water systems (those serving 500 or fewer) do not apply for or receive funds with the same frequency as their larger counterparts. Understanding the allocation of awards from PENNVEST offers insight into the ability of small communities to access capital for water supply infrastructure.  相似文献   
555.
我国农村可再生能源发展面临生态文明建设、能源安全趋紧、大气污染严重等新的形势变化。作为农业大省,河北省近年来农村可再生能源发展与管理成绩显著,为改善农民生活、保护生态环境、增加能源供应、促进经济社会发展等做出了积极贡献。但新形势下,其农村可再生能源管理也暴露出了思想认识不足、部分法规政策滞后、缺乏宏观科学规划、资金筹措机制单一、后续监督管理不够等问题,需要从加强宣传教育、提高认识水平,完善规章制度、形成法律体系,制定科学规划、明确目标计划,拓宽融资渠道、稳定资金支持、完善服务体系、加强后续管理等方面完善管理与政策,以推进其健康持续发展。  相似文献   
556.
Animals balance feeding and anti-predator behaviors at various temporal scales. When risk is infrequent or brief, prey can postpone feeding in the short term and temporally allocate feeding behavior to less risky periods. If risk is frequent or lengthy, however, prey must eventually resume feeding to avoid fitness consequences. Species may exhibit different behavioral strategies, depending on the fitness tradeoffs that exist in their environment or across their life histories. North Pacific flatfishes that share juvenile rearing habitat exhibit a variety of responses to predation risk, but their response to risk frequency has not been examined. We observed the feeding and anti-predator behaviors of young-of-the-year English sole (Parophrys vetulus), northern rock sole (Lepidopsetta polyxystra), and Pacific halibut (Hippoglossus stenolepis)—three species that exhibit divergent anti-predator strategies—following exposure to three levels of predation risk: no risk, infrequent (two exposures/day), and frequent (five exposures/day). The English sole responded to the frequent risk treatment with higher feeding rates than during infrequent risk, following a pattern of behavioral response that is predicted by the risk allocation hypothesis; rock sole and halibut did not follow the predicted pattern, but this may be due to the limited range of treatments. Our observations of unique anti-predator strategies, along with differences in foraging and species-specific ecologies, suggest divergent trajectories of risk allocation for the three species.  相似文献   
557.
土地政策是影响土地利用及生态环境变化的一个重要的驱动因素。论文分析了“耕地总量动态平衡”政策对中国的耕地变化及其生态环境效应的影响,结果表明,“耕地总量动态平衡”政策对中国耕地的数量变化产生了积极作用,主要表现为:非农建设占用耕地的势头总体上得到遏制,全国及各省(市、区)基本实现耕地占补平衡,促进了农地整理工作的开展。但是,该政策对中国耕地的质量变化的影响却相反,在全国实现耕地占补平衡的情况下,耕地的总体生产能力呈下降趋势,同时,对生态环境产生了一定的负面效应。在此基础上,论文提出了重新审视“耕地总量动态平衡”政策的可行性,以“保护和提高耕地综合生产能力”替代“耕地总量动态平衡”以及根据土地资源区域差异采取不同的具体措施等对该政策加以调整的思路。  相似文献   
558.
Europe’s growing energy deficit and destabilising climate may lead the EU and its constituent member states to change its attitude to population size and growth.  相似文献   
559.
Abstract: For over 10 years, several species of salmon have been identified as either threatened or endangered in the Snake River Basin of Idaho. The United States Bureau of Reclamation, in cooperation with the National Marine Fisheries Service, has proposed a variety of plans to increase stream flows in the Snake River Basin to facilitate movement by juvenile salmon smolts to the ocean. This research examines two of the flow augmentation plans proposed by the Bureau of Reclamation as well as two alternative plans, one founded purely on existing priority‐based water rights and another geared toward minimizing the effects of flow augmentations on farms profitability. Results from a basin‐wide model of agricultural production in the Snake River Basin, the Snake River Agricultural Model, present evidence that (1) older water rights are used towards production of less valuable crops, (2) flow augmentation scenarios have unequal effects on farms profitability across agricultural regions within the basin, and (3) irrigation water is valued from US$4 to US$59 an acre‐foot.  相似文献   
560.
Little research has been performed on the impact of pesticides on earthworms under tropical conditions. Taking into consideration the often-limited resources in tropical countries, simple screening tests are needed. Therefore, it was investigated whether three pesticides relevant for the Brazilian Amazon (benomyl, carbendazim, lambda-cyhalothrin) affect the avoidance behavior of the earthworm Eisenia fetida. The tests were performed for two days according to ISO guideline 17512 but were adapted to tropical conditions (i.e. test substrate, test organism and temperature). The results indicate that this test gives reproducible and reliable results. Toxicity values (NOEC, EC50) are lower than those determined in 14 day-acute mortality tests and are approximately in the same range such as those found in 56 day-chronic reproduction tests with the same earthworm species, which were performed in parallel. Therefore, the use of the earthworm avoidance tests is recommended as a screening tool for the risk assessment of pesticides.  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