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   530篇
  免费   30篇
  国内免费   53篇
安全科学   40篇
废物处理   3篇
环保管理   154篇
综合类   156篇
基础理论   116篇
污染及防治   23篇
评价与监测   54篇
社会与环境   54篇
灾害及防治   13篇
  2023年   5篇
  2022年   12篇
  2021年   12篇
  2020年   20篇
  2019年   16篇
  2018年   9篇
  2017年   10篇
  2016年   19篇
  2015年   16篇
  2014年   18篇
  2013年   62篇
  2012年   26篇
  2011年   39篇
  2010年   21篇
  2009年   36篇
  2008年   32篇
  2007年   47篇
  2006年   24篇
  2005年   26篇
  2004年   19篇
  2003年   26篇
  2002年   20篇
  2001年   21篇
  2000年   25篇
  1999年   12篇
  1998年   7篇
  1997年   5篇
  1996年   2篇
  1995年   6篇
  1994年   3篇
  1993年   3篇
  1992年   1篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1982年   1篇
  1972年   1篇
排序方式: 共有613条查询结果,搜索用时 296 毫秒
181.
The prediction of the atmospheric concentration of ozoneand of other photochemical pollutants represents one of themajor scientific challenges in the study of urban airquality. To this aim, photochemical models are widelyapplied as support tools for regulatory purposes, but theirresults are known to be affected by several uncertainties,in boundary conditions, geographical and meteorologicaldata and the chemical composition of emission and ambientair as well. Also the mechanism selected to describe theurban chemistry may lead to large differences in the modelresults. In this work, the influence of ambient air composition onthe results of photochemical model has been studied using a simple Lagrangian trajectory model coupled with different chemical sub-models (CB-IV and a simplified version of EMEP). To this aim a parametric sensitivity study of ozone with respect to its precursors' concentration was performed withreference to the same meteorological conditions and by simulatingdifferent scenarios characterized by specific emitted pollutantsconcentration. Rather than analyzing sensitivity by changing initial composition, an analytical local sensitivity concept has been applied; this allowed evaluation the influence of initial concentration on the predicted ozone concentration andto discriminate between VOC-sensitive and NOx-sensitive kineticregimes. Finally, these results have been successfully comparedwith those obtained applying the concept of photochemical indicators (i.e. O3/NOy and H2O2/HNO3 ratios).  相似文献   
182.
ABSTRACT: Fifty‐four Wisconsin wetlands were surveyed in spring 1996 to determine relationships between macroinvertebrate community structure and a suite of 11 environmental attributes. Canonical correspondence analysis (CCA) showed that, after alkalinity, hydroperiod was the next most significant environmental factor influencing macroinvertebrate community structure within the wetlands sampled. CCA and direct gradient biplots were used to identify indicator taxa characteristic of the spring macroinvertebrate communities in persistent and ephemeral wetlands, and taxa characteristic of semi‐terrestrial habitats adjacent to wetlands. Two models were developed to permit the prediction of a wetland's hydroperiod class. One model assigns a range of probabilities that a wetland has a hydroperiod longer or shorter than eight months based on the occurrence or abundance of fairy shrimp, mayflies, scuds, mosquitoes, and phantom midges. A second model predicts that a wetland's hydroperiod is longer or shorter than five months based on the joint occurrences of seven persistent indicator taxa. Data used in both models were derived from a rapid bioassessment of three shoreline D‐frame net sweeps. The use of a coarse level taxonomic identification (primarily order and family) allows the approach to be performed in the field or laboratory. The macroinvertebrate models allow a manager to estimate a wetland's hydroperiod when long term water duration records do not exist. This ability is important to water resource managers because hydroperiod classification (i.e., water permanency) is one criterion used in differentiating wetlands from lakes in Wisconsin and because Wisconsin's legal system affords lakes substantially greater protection than wetlands.  相似文献   
183.
拟破解生态文明测度和评价的现存难题:在指标选取方面,评价目标模糊,指标筛选的主观性强,缺乏结构化方法,导致指标泛化,与一般环境经济评价混淆;在测度标尺方面,无法确定生态文明阈值,对不同文明阶段用同一把尺子去衡量,导致一些非生态文明区域的排名反而靠前;在应用价值方面,综合指标值失去生态经济意义,只是一个抽象的排名数字,导致测度结果不便于理解和运用。为此,依据文明演化的共生理论创立指标-指数耦合链方法,用以导出生态文明测度的阈值和绿值二步指数。依次运用扎根理论法、PSIR及SEM结构模型、足迹家族法、Lotka-Volterra模型等工具,构建从生态文明的指标体系到二步指数的结构化耦合链。全过程始终聚焦生态文明的本质属性——产业与生态的互利共生性:以定性科学属性为出发点,以人与自然复合系统的结构模型为纽带,以生态文明阈值和绿值二步指数定量模型为归宿点。其中,阈值用产业受力指数、生态受力指数和共生度指数3项指数进行衡量,合称为阈值指数;而绿值用1项综合反映区域产业与生态的总量、共生程度和均衡程度的绿值指数进行衡量。据此进行区域生态文明的二步测度。第一步,基于阈值指数的阶段或资格判定:通过产业与生态的共生性,考量被测区域是否进入生态文明门槛,"未入门"区域处于哪一个文明阶段。第二步,基于绿值指数的水平判定:通过产业与生态的互利共生程度,考量"入门"区域的生态文明水平。研究表明,指标-指数耦合链方法不仅可以有效克服单纯指标体系综合法或指数函数法的缺陷和难点,而且能够将两者的长处结合起来。如此,不仅能够避免生态文明测度结果与物质文明"成正比"的弊端,而且能够通过从生态文明二步指数回溯至指标体系的逆向解耦,分析出导致生态文明问题的根本原因,便于提出切中肯綮的对策。  相似文献   
184.
Abstract

Energy management in small to medium enterprises (SMEs) remains undeveloped due to competing priorities and a lack of specialist knowledge. However considerable savings can be demonstrated where companies take the time to investigate their energy use. Savings of over 20% can be achieved through changes to operational and behavioural practice. Additional benefits, such as improved production tracking and improved maintenance, can been seen which add to the value in undertaking an energy monitoring and targeting (M&T) plan. The method described involves the application of a series of ‘virtuous’ cycles of engagement and energy savings that can be applied from the highest factory level right down to a specific machine. The analysis of overall energy use from utility bills and the visualisation of typical machine power profiles aid in understanding the drivers of energy consumption and in engaging management in energy efficiency. The monitoring of specific machines in production highlights the significant consumption of electricity during non-productive times. The development of energy performance indicators is described for product variations which can be useful in tendering for business and selecting optimum production pathways. The approach is illustrated with data from a case study of a precision engineering SME based in Limerick, Ireland.  相似文献   
185.
The design of heating, ventilation and air conditioning systems is still a challenging engineering task which requires experienced and informed decision-making. These systems have a great energy-saving potential at the system level rather than at the level of the individual products of which they are composed. European environmental product policies have been very useful in facilitating a homogeneous rating scheme which can be used to compare the energy performance of different products that provide the same service. This paper proposes a simplified design method which uses the performance of components that are regulated by European product policies to obtain the overall performance of heating systems in residential buildings. It is a flexible method and allows different product configurations to be assessed so as to optimise the system performance during the design phase. The method is tested on a real case study with domestic hot water and space heating systems. The case study shows the potential for improving the heating systems according to the performance levels of its products currently available in the market. Results of the domestic hot water system show that upgrading its storage tank to the maximum energy class (A+) could bring the highest energy savings ( 4162 kWh/y).  相似文献   
186.
Drawing up environmental policy options is a complex activity which involves defining and weighing the merits and risks of various alternative courses of action governments could pursue. In its modern version, this task typically involves formal policy analysis or ‘policy appraisal’, that is, policy work specifically undertaken to generate and evaluate policy options in order to address problems or issues on a policy agenda. Indicators play a powerful but under-investigated role in this process. To shed light on this issue, the paper conducts a case study of the design and evolution of policy indicators in water security policy formulation, examining both their utilization and impact. The paper documents the origins of water security policy indicators; assesses their relevance and influence in policy formulation and identifies the reasons for the emergence of certain preferred indices, despite their having several well-known limitations. In particular, the discussion flags the significance of the political advantages surrounding their ease of use and interpretation, rather than their technical merits, as a key factor affecting the continued utilization and influence of specific indicators in environmental policy and planning.  相似文献   
187.
Sustainability assessments are an increasingly common tool for measuring progress towards sustainable development. Despite their popularity, sustainability assessments and the indicators that compose them are said to have had little impact on the policy arena. In this paper we discuss four attributes that we contend will improve the use of sustainability assessments to guide decision making: non-compartmentalization, site specificity, built-in guidance for target setting, and ability to measure active sustainability. We present a novel assessment tool for wastewater treatment infrastructure that illustrates these attributes. The assessment is composed of two-dimensional indicators we call “burden to capacity” ratios, that reveal and quantify the local value of resources embodied in wastewater and treatment byproducts, and the tradeoffs between designing systems for disposal versus reuse. We apply the sustainability assessment framework to an existing treatment plant in Chengdu, China and discuss the results.  相似文献   
188.
This paper discusses some conceptual fundamentals for the derivation of environmental indicator sets. On the one hand, it defines requirements from environmental politics, environmental management and legislation, reaching from political target hierarchies and sustainable management strategies to holistic protection concepts such as process protection, resource preservation, ecosystem health and ecological integrity. On the other hand, demands from ecosystem theory are described which include the consideration of features such as self-organization, emergence, thermodynamics, gradients and ecological orientors in environmental indicator sets. From that concept, collective and emergent properties are selected and eight holistic ecosystem features are presented that indicate the ecosystemic state as an ensemble. These general indicators of ecosystem integrity are supplemented by variables on structural changes and substance dynamics.  相似文献   
189.
A Landscape Ecology Assessment of the Tensas River Basin   总被引:8,自引:0,他引:8  
A group of landscape ecological indicators were applied to biophysical data masked to the Tensas River Basin. The indicators were used to identify and prioritize sources of nutrients in a Mississippi/Atchafalaya River System sub-basin. Remotely sensed data were used for change detection assessment. With these methods, we were able to look at land use practices over the past twenty years in the Tensas River Basin of Louisiana. A simple land use classification was applied to multispectral scanner (MSS) data from 1972 and 1991. The landscape analysis methods described in this paper will show how to use these methods to assess the impact of human land use practices that are being implemented to improve environmental quality. Landscape assessment methods can be used as a simple, timely, cost effective approach for monitoring, targeting, and modeling ecosystem health in watersheds. Although this study was conducted in the southeast, the methods described in this paper may be applicable to western landscapes.  相似文献   
190.
In discussing issues of landscape change, the complex relationships in the landscape have to be assessed. In participative planning processes, 3D visualisations have a high potential as an aid in understanding and communicating characteristics of landscape conditions by integrating visual and non-visual landscape information. Unclear is, which design and how much interactivity is required for an indicator visualisation that would suit stakeholders best in workshop situations. This paper describes the preparation and application of three different types of integrated 3D visualisations in workshops conducted in the Entlebuch UNESCO Biosphere Reserve (CH). The results reveal that simple representations of a complex issue created by draping thematic maps on the 3D model can make problematic developments visible at a glance; that diagrams linked to the spatial context can help draw attention to problematic relationships not considered beforehand; and that the size of species as indicators of conditions of the landscape's production and biotope function seems to provide a common language for stakeholders with different perspectives. Overall, the of the indicators the functions required to assist in information processing. Further research should focus on testing the effectiveness of the integrated visualisation tools in participative processes for the general public.  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