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   243篇
  免费   7篇
  国内免费   19篇
安全科学   13篇
废物处理   7篇
环保管理   43篇
综合类   59篇
基础理论   74篇
环境理论   1篇
污染及防治   48篇
评价与监测   13篇
社会与环境   5篇
灾害及防治   6篇
  2023年   7篇
  2022年   5篇
  2021年   8篇
  2020年   5篇
  2019年   8篇
  2018年   6篇
  2017年   13篇
  2016年   12篇
  2015年   11篇
  2014年   11篇
  2013年   17篇
  2012年   16篇
  2011年   19篇
  2010年   15篇
  2009年   20篇
  2008年   13篇
  2007年   5篇
  2006年   17篇
  2005年   8篇
  2004年   12篇
  2003年   7篇
  2002年   5篇
  2001年   7篇
  1998年   1篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1991年   1篇
  1988年   2篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1979年   1篇
  1961年   3篇
  1959年   1篇
排序方式: 共有269条查询结果,搜索用时 15 毫秒
21.
Environmental agencies across the United States have searched for adequate methods to assess anthropogenic impacts on the environment. Biological assessments, which compare the taxonomic composition of an aquatic assemblage to relevant biocriteria, have surfaced as an effective method to assess the ecological integrity of US waterbodies. In this study, bioassessment data were collected and analyzed in conjunction with physical habitat and chemical stressor data for streams and rivers within the San Diego basin from 1998 through 2005. Physical stressors such as sediment loading, riparian destruction, and in-stream habitat homogenization affect many locations in the region. However, physical habitat measures alone were found to frequently overestimate the biological integrity of streams in the region. Many sites within the San Diego Basin, although unaffected by physical stressors, continue to exhibit low biological integrity scores. Sites with low biological integrity tend to possess higher specific conductance and salinity compared to sites with high biological integrity. We suggest that one possible reason for these differences is the source water used for municipal purposes.  相似文献   
22.
Ammonia (NH(3)) emissions from animal systems have become a primary concern for all of livestock production. The purpose of this research was to establish the relationship of nitrogen (N) emissions to specific components of swine production systems and to determine accurate NH(3) emission factors appropriate for the regional climate, geography, and production systems. Micrometeorological instrumentation and gas sensors were placed over two lagoons in North Carolina during 1997-1999 to obtain information for determining ammonia emissions over extended periods and without interfering with the surrounding climate. Ammonia emissions varied diurnally and seasonally and were related to lagoon ammonium concentration, acidity, temperature, and wind turbulence. Conversion of significant quantities of ammonium NH(4)(+) to dinitrogen gas (N(2)) were measured in all lagoons with the emission rate largely dependent on NH(4)(+) concentration. Lagoon NH(4)(+) conversion to N(2) accounted for the largest loss component of the N entering the farm (43% as N(2)); however, small amounts of N(2)O were emitted from the lagoon (0.1%) and from field applications (0.05%) when effluent was applied nearby. In disagreement with previous and current estimates of NH(3) emissions from confined animal feeding operation (CAFO) systems, and invalidating current assumptions that most or all emissions are in the form of NH(3), we found much smaller NH(3) emissions from animal housing (7%), lagoons (8%), and fields (2%) using independent measurements of N transformation and transport. Nitrogen input and output in the production system were evaluated, and 95% of input N was accounted for as output N from the system.  相似文献   
23.
Why, despite a recent surge in the UK in “sustainable communities” policy discourse, do so many community-led sustainability initiatives remain fragmented, marginal and disconnected from local government strategies? How can community- and government-led sustainability initiatives be better integrated such that they add significantly to a denser matrix and cluster of sustainable places? These questions, we argue, lie at the heart of current sustainable place-making debates. With particular reference to two spatial scales of analysis and action, the small town of Stroud, England and the city of Cardiff, Wales, we explore the twin processes of disconnection and connection between community sustainability activists and local state actors. We conclude that whilst there will always remain a need for community groups to protect the freedom which comes from acting independently, for community activists and policy-makers alike, there are nevertheless a series of mutual benefits to be had from co-production. However, in setting out these benefits we also emphasise the dual need for local government to play a much more nuanced, integrative and facilitatory role, in addition to, but separate from, its more traditional regulatory role.  相似文献   
24.
Recognition and avoidance of conspecifics based on chemical cues could reduce the risk of aggressive interactions between males. Success in agonistics encounters with unfamiliar males should be lower than with previously known familiar males. Then, males should avoid the chemicals from unfamiliar males with respect to those from familiar males. However, boldness and size could affect the outcome of encounters between males and, consequently, the response to chemical cues of conspecific males. We compared the time spent by male turtles Mauremys leprosa in water pools with chemical stimuli from unfamiliar or familiar males or with their own chemical stimuli. We also performed a behavioral test to estimate boldness of turtles in an antipredatory situation. Turtles avoided the chemicals from unfamiliar males respect to familiar ones and their own odors, but their responses depended on boldness and size of the tested turtle. Bold turtles avoided water with chemicals of unfamiliar males, but not with chemicals of familiar males, whereas shy turtles avoided chemicals of both familiar and unfamiliar males. On the other hand, large males avoided the odor from unfamiliar males, but small males did not avoid water with the odor from other males. Results suggest that male M. leprosa can detect chemicals released to water from conspecific males and discriminate between familiar and unfamiliar males. However, responses to these chemicals depended on boldness and body size of the responding turtle because these factors may affect intrasexual competition.  相似文献   
25.
26.
The main purpose of a water distribution system (WDS) is to deliver safe water of desirable quality, quantity and continuity to consumers. However, in many cases, a WDS fails to fulfill its goal owing to structural and associated hydraulic failures and/or water quality failures. The impact of these failures can be reduced significantly if preventive actions are taken based on their potential of occurrences or if a failure occurs and is detected within a minimum period of time after its occurrence. The aim of this research was to develop a forensic system for WDS failures. As part of the proposed forensic analysis, a framework has been developed, which investigates structural and associated hydraulic failures as well as water quality failures and integrates all failure investigation under a single platform. Under this framework, four different models have been developed to evaluate and identify structural and associated hydraulic failures and water quality failures. If a failure is detected in the system, the framework is capable of identifying the most probable location of the failure. To investigate the effectiveness of the proposed framework, the developed models have been tested and implemented in different WDSs.  相似文献   
27.
ABSTRACT

While local governance is widely acknowledged as an important element in the pursuit of sustainability, local action alone is insufficient to produce lasting change. One recent solution to this quandary has been the production of certification frameworks that encourage sustainable development at the neighbourhood scale by providing local actors with standardised definitions of sustainable practices. While these frameworks facilitate the spread of sustainable development strategies between local communities, there are significant contrasts between their approaches to encouraging local sustainable development that simultaneously fulfils global objectives. This article explores these contrasts through two neighbourhood-scale sustainability certification frameworks: LEED for Neighborhood Development (LEED-ND) and the EcoDistricts Protocol. Analysis of these frameworks in the context of two centrally-located neighbourhoods in Portland, Oregon, reveals substantial contrasts between the two frameworks in terms of the relative flexibility of their sustainability metrics, the time frame over which decisions regarding sustainable development are made, and community involvement in the process of pursuing specific objectives. Furthermore, it suggests that greater flexibility in the application of standards, continuous governance, and greater community involvement lead to more dynamic and holistic forms of sustainability that evolve as both local community needs and broader understandings of sustainability change over time.  相似文献   
28.
ABSTRACT: Thames Water is one of ten regional Water Authorities established in 1974 to manage all water services in England and Wales. This paper looks back at water reorganization and reviews the achievements and highlights of the last three years. Constitutionally, Water authorities are a combination of a nationalized industry and local authority. This has advantages and disadvantages. Freedom of action, particularly in financial matters, is constrained by Government and official agencies. A severe pollution of the upper Thames and the drought of 1976 tested Thames Water's ability to deal with emergencies. Thames Water does not have an operational monopoly. Private Water Companies supply one third of the water demand and local authorities manage nearly all the sewers. But Thames Water's control over planning and investment ensures that the river basin is managed in a coordinated fashion. Tariff structure changes have led the Authority to bill all its consumers direct. The Thames is a small but intensively used river and vigilance is needed to maintain water quality. Thames Water is proud of the restoration of the tidal Thames from a typical grossly polluted metropolitan estuary to its present excellent condition. The British Government intends to establish a national water industry strategic planning organization but at the same time they affirm that there can be no departure from the principle of integrated river basin management.  相似文献   
29.
Warner, Richard C., Carmen T. Agouridis, Page T. Vingralek, and Alex W. Fogle, 2010. Reclaimed Mineland Curve Number Response to Temporal Distribution of Rainfall. Journal of the American Water Resources Association (JAWRA) 46(4): 724-732. DOI: 10.1111/j.1752-1688.2010.00444.x Abstract: The curve number (CN) method is a common technique to estimate runoff volume, and it is widely used in coal mining operations such as those in the Appalachian region of Kentucky. However, very little CN data are available for watersheds disturbed by surface mining and then reclaimed using traditional techniques. Furthermore, as the CN method does not readily account for variations in infiltration rates due to varying rainfall distributions, the selection of a single CN value to encompass all temporal rainfall distributions could lead engineers to substantially under- or over-size water detention structures used in mining operations or other land uses such as development. Using rainfall and runoff data from a surface coal mine located in the Cumberland Plateau of eastern Kentucky, CNs were computed for conventionally reclaimed lands. The effects of temporal rainfall distributions on CNs was also examined by classifying storms as intense, steady, multi-interval intense, or multi-interval steady. Results indicate that CNs for such reclaimed lands ranged from 62 to 94 with a mean value of 85. Temporal rainfall distributions were also shown to significantly affect CN values with intense storms having significantly higher CNs than multi-interval storms. These results indicate that a period of recovery is present between rainfall bursts of a multi-interval storm that allows depressional storage and infiltration rates to rebound.  相似文献   
30.
The yellow-legged clearwing (YLC) Synanthedon vespiformis (Lepidoptera: Sesiidae) occurs in the Mediterranean and central Europe. It is polyphagous, boring into the woody parts of broadleaf species including forest trees as well as various Rosaceae species. S. vespiformis has been reported as an economically important pest causing severe injury to stone fruit plantations. Many attractants for sesiid species were discovered by random field screening using 2,13- and 3,13-octadecadienyl alcohols, acetates and aldehydes, including one for S. vespiformis; and about 20 sex pheromones of sesiids have been identified so far. In the present study we identified the natural composition of the sex pheromone of YLC laboratory reared females as a blend of E3,Z13- and Z3,Z13-octadecadienyl acetates, at a ratio of 4:1. We developed an efficient lure for monitoring the pest. Pheromone funnel traps with rubber septa, impregnated with 1 mg pheromone blend, efficiently captured males for 10 weeks. Suspension of Shin-Etsu? ropes containing a 2:1 blend of E3,Z13-18:Ac and Z3,Z13-18:Ac at 13.74 mg/ha/h, resulted in shutdown of trap catches in the treated plots and closely situated neighboring plots indicating that mating disruption is feasible.  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