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   231篇
  免费   21篇
  国内免费   18篇
安全科学   32篇
废物处理   1篇
环保管理   36篇
综合类   85篇
基础理论   51篇
污染及防治   10篇
评价与监测   18篇
社会与环境   13篇
灾害及防治   24篇
  2023年   4篇
  2022年   4篇
  2021年   13篇
  2020年   10篇
  2019年   8篇
  2018年   6篇
  2017年   8篇
  2016年   7篇
  2015年   5篇
  2014年   5篇
  2013年   8篇
  2012年   13篇
  2011年   22篇
  2010年   10篇
  2009年   20篇
  2008年   8篇
  2007年   17篇
  2006年   5篇
  2005年   11篇
  2004年   11篇
  2003年   7篇
  2002年   2篇
  2001年   10篇
  2000年   6篇
  1999年   6篇
  1998年   6篇
  1997年   3篇
  1996年   7篇
  1995年   5篇
  1994年   4篇
  1993年   1篇
  1992年   3篇
  1991年   3篇
  1990年   2篇
  1989年   3篇
  1988年   5篇
  1987年   1篇
  1978年   1篇
排序方式: 共有270条查询结果,搜索用时 15 毫秒
31.
综述了车辆事故紧急呼救技术的原理,从车辆事故检测识别技术、移动车辆定位技术、无线通信技术和地理信息系统几方面概述车辆事故紧急呼救技术的研究内容。进一步介绍车辆事故紧急呼救技术的国内外研究和应用现状,并从车辆事故识别技术、地图匹配及组合导航、集群通信及通信网络几方面总结并指出车辆事故紧急呼救技术的关键技术和难点。展望了车辆事故紧急呼救技术的发展趋势,并就我国发展车辆事故呼救技术的可行性和发展方向进行探讨。  相似文献   
32.
To document environmental impact predictions for land development, as required by United States government regulatory agencies, vegetation studies are conducted using a variety of methods. Density measurement (stem counts) is one method that is frequently used. However, density measurement of shrub and herbaceous vegetation is time-consuming and costly. As an alternative, the Braun-Blanquet cover-abundance scale was used to analyze vegetation in several ecological studies. Results from one of these studies show that the Braun-Blanquet method requires only one third to one fifth the field time required for the density method. Furthermore, cover-abundance ratings are better suited than density values to elucidate graphically species-environment relationships. For extensive surveys this method provides sufficiently accurate baseline data to allow environmental impact assessment as required by regulatory agencies.  相似文献   
33.
The EU Flood Directive 2007/60 requires the assessment and delineation of flood risk maps. The latter should provide the required knowledge for the development of flood risk management plans (FRMPs), that should deal with all features of risk management: e.g. preparation, protection and prevention, comprising also the phase of the flood forecasting and warning systems, in addition to the emergency management. The risk maps, delineated through the expert-drive qualitative (EDQ) approach currently adopted in several European countries, such as Italy, fail to represent the information base that needed by stakeholders for selecting the suitable objectives and designing the appropriate mitigation actions for flood risk management. In the EDQ approach, the flood hazard and the potential damage degree maps are combined by means of a matrix to obtain a qualitative flood risk map. However, the performance of the risk matrix is not usually rigorous validated and, therefore, presents limits, such as subjective and not careful explained interpretation of rating and poor resolution, (due to range compression), that can produce errors in comparative ranking of risk areas. In this context, this paper proposes the FloodRisk approach that aims to improve the efficacy of flood risk map overcoming the limits of EDQ approach in supplying the knowledge base that allow to analyze costs and benefits of potential mitigation measures. However, the proposed approach is also able to involve the citizens in the flood management process, enhancing their awareness. An application of FloodRisk procedure is showed on a pilot case in “Serio” Valley, (North Italy), and its strengths and limits, in terms of additional efforts required in its application compared with EDQ procedure, have been discussed focusing on the efficacy of the outcomes provided for the fulfillment of FRMPs. The results have demonstrated the ability of FloodRisk, respect to EDQ approach, to distinguish successfully different levels of vulnerability of exposure elements, thanks to the use of asset value and depth-damage curves, that allows a suitably evaluation of the effectiveness of risk mitigation strategies. In this light, a successfully application of a cost-benefit analysis of FloodRisk approach on a portfolio of alternative mitigation actions, (i.e. structural and non-structural measurements), has been demonstrated on the proposed study case. However, FloodRisk requires additional information, e.g. water depths assessment and assets values, and it needs a proper analysis and communication of the uncertainty in its results. Although they still exist limitations that impede, at present, the FloodRisk application without an adequate understanding and a critical consideration of the hazard, exposure and vulnerability characteristics of the study area, considerations are supplied on how the utilization of this approach can be maximized in the light of the next flood risk maps revision due by December 2019.  相似文献   
34.
The structure and advancement of woody vegetation was studied in a semi-arid rangeland of southern Ethiopia under three land-use systems (communal land, a government ranch and a traditional grazing reserve enclosure) and along a distance gradient (near, middle and far) from water sources. A total of 54 woody plant species were identified. Based on the subjective opinions of the pastoralists, 85% of the identified woody plants have forage values to livestock. Cadaba farinsoa, Ormocarpum trichocarpum, Rhus natalensis, Acacia brevispica, Cordia gharaf and Hibiscus sparseaculeatus were reported to have fair to good palatability. Tree equivalent (TE) density of all woody plants combined was greater (P <0.01) in the government ranch (1) 188 TE ha(-1)) and the communal land (1083 TE ha(-1)) than in the traditional grazing reserve (419 TE ha(-1)), whereas this did not vary significantly (P >0.05) along the distance gradient from water. The most important encroaching woody plant species in the study areas were in descending order: Commiphora africana, Acacia drepanolobium, A. brevispica, Acacia. tortilis, Grewia tembensis and Lannea floccosa. The density of individual encroaching woody plant species along the distance gradient from water was not consistent. All encroaching woody species had the highest TE density in the communal land. The prevalence of these species followed the pattern of intensity of use within the communal grazing area. Most of the woody species had the highest abundance in the height class >0-2m regardless of land use and distance gradient from water. This study investigated the advance of severe woody encroachment in the communal and government sites as well as along the distance gradient from water. Some of the important contributing factors that can be suggested are heavy grazing pressure (in both the communal and government sites), expansion of cultivation and reduced mobility of livestock due to settlement of the pastoralists in the communal land.  相似文献   
35.
The main aim of this article is to demonstrate a method of complex landscape analysis in order to estimate the landscape suitability for the construction of surface-flow wetlands (SFW) for wastewater treatment. This is a multilevel suitability analysis from a more general regional (landscape) assessment based on a map of landscape types (1:100,000) toward a detailed analysis based on aerial orthophotos and detailed soil maps (1:10,000). The assessment scheme consists of landscape classification according to the physical-chemical properties of landscape factors (soil conditions, landforms, hydrogeology, expert decisions concerning landscape values, and suitability analysis). The partial suitability values of SFWs are derived by summarizing expert values for landscape factors (each ranging from -1 to +1). By multiplying the summarized partial suitability values with nature protection values (ranging from 0 to 1), we obtain the final suitability value for each landscape type. Any kind of nature protection area has been considered nonsuitable and excluded at regional-level analysis. The results of the regional analysis demonstrate that suitability is distributed relatively equally over the study area. The high suitability potential (classified as "very suitable") is relatively evenly distributed in lowland regions throughout the country. The share of "very suitable" and "suitable" areas in different counties varies from 5 to 23% and 7 to 49%, respectively. The detailed analysis based on aerial orthophotos showed that areas suitable for SFWs can also be found within the areas determined to be unsuitable based on the less detailed map of landscape types, whereas differences are much greater between settlements chosen for the detailed suitability analysis.  相似文献   
36.
In partnership with the US Department of Energy’s Office of Industrial Technology, Whyco Technologies, Inc., has developed an innovative perforated plating barrel used in the plating of metal parts. This new technology employs a thin-walled construction, differing from the traditional thick-wall design required to provide adequate structural integrity. The thicker walls lowered the efficiency of transferring plating solution into and out of the barrel and diminished the electrical current pushed through the holes and onto the parts being plated. By machining pockets out of the traditional thick-walled perforated structure, Whyco produced a ‘honeycomb’ of staggered cells, allowing for the greatest number of holes per open area while maintaining structural integrity. Hydrodynamic pumping occurs during barrel rotation to create greater solution transfer than in traditional barrels. The Whyco barrel has higher current density plating, which leads to faster plating cycles, reduced bath concentration, and better plating of difficult chemistries such as in alloys. This new technology has helped the company reduce energy use by 16%, eliminate more than 480 tons/year of solid waste, and reduce wastewater by more than 17 000 gallons/day. The resulting cost savings total more than $500 000 annually. The company has manufactured and sold more than 275 of these barrels to other electroplating companies that are reporting up to a 40% increase in plating productivity and similar energy and environmental impacts.  相似文献   
37.
坡度图在滑坡研究中的应用   总被引:2,自引:0,他引:2  
王念秦 《灾害学》1991,6(3):66-70
本文阐述了坡度图的概念和作用;详细介绍了坡度尺、坡度图的作法、以及坡度图在兰州地区的应用结果;简要分析了斜坡坡度与滑坡的关系。  相似文献   
38.
The increasing production and usage of chlorinated paraffins(CPs) correspondently increase the amount of CPs that experience thermal processes. Our previous study revealed that a significant amount of medium-chain chlorinated paraffins(MCCPs), short-chain chlorinated paraffins(SCCPs) as well as aromatic and chlorinated polycyclic aromatic hydrocarbons(Cl-PAHs) were formed synergistically during the thermal decomposition of CP-52(a class of CP products).However, the transformation mechanisms of CP-52 to these compounds are still not very clear.This article presents a mechanistic analysis on the decomposition of CP-52 experimentally and theoretically. It was found that CP-52 initially undergoes dehydrochlorination and carbon chain cleavage and it transformed into chlorinated and unsaturated hydrocarbons. Cyclization and aromatization were the most accessible pathways at low temperatures(200–400°C), both of which produce mostly aromatic hydrocarbons. As the temperature exceeds 400°C, the hydrocarbons could decompose into small molecules, and the subsequent radical-induced reactions become the predominant pathways, leading to the formation of Cl-PAHs. The decomposition of CP-52 was investigated by using density functional theory and calculations demonstrating the feasibility and rationality of PCB and PCN formation from chlorobenzene. The results improve the understanding of the transformation processes from CP-52 to SCCPs and Cl-PAHs as well as provide data for reducing their emissions during thermal-related processes.  相似文献   
39.
国土空间规划体系构建工作已经全面展开,清晰详实的现状图和数据是摸清自然资源家底的重要基础,也是编制国土空间规划的重要支撑。而当前国土空间现状数据的用地分类标准、数据精度和应用目标等尚不统一。基于遥感影像、地理国情和互联网POI等多源数据进行国土空间现状一张图研究,综合现有用地分类标准和数据精度,构建青岛市国土空间规划现状一张图。在此基础上,探讨国土空间规划一张图应用方向,包括青岛市“三生空间”和资源环境研判分析,以及城镇建设适宜性、生态服务功能重要性和农业生产适宜性分析等内容。国土空间规划现状一张图的构建,对于明确资源利用上限与环境质量底线,规范国土空间规划数据,以及支撑国土空间规划编制和管理具有重要作用。  相似文献   
40.
Molecular mechanics, molecular dynamics and quantum mechanical tools have been used to explore the conformational space of (+)(3S,4S)-multifidene bioactive compounds. All the computations have been performed in the absence and presence of the solvent, simulated by the explicit introduction of a number of water molecules or by the polarized continuum model (PCM). Three conformational minima, both in vacuo and in water (simulated by PCM tool), have been confirmed at ab initio level of theory (B3LYP and MP2). All minima lie in a very narrow range of energy, and the interconversion between them is possible with a small amount of energy expense.  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