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   13001篇
  免费   393篇
  国内免费   1280篇
安全科学   349篇
废物处理   915篇
环保管理   1518篇
综合类   3240篇
基础理论   3591篇
环境理论   1篇
污染及防治   2544篇
评价与监测   1210篇
社会与环境   1121篇
灾害及防治   185篇
  2024年   14篇
  2023年   99篇
  2022年   207篇
  2021年   235篇
  2020年   223篇
  2019年   144篇
  2018年   1634篇
  2017年   1569篇
  2016年   1352篇
  2015年   355篇
  2014年   291篇
  2013年   346篇
  2012年   753篇
  2011年   1611篇
  2010年   924篇
  2009年   817篇
  2008年   1120篇
  2007年   1438篇
  2006年   193篇
  2005年   176篇
  2004年   157篇
  2003年   193篇
  2002年   217篇
  2001年   103篇
  2000年   128篇
  1999年   74篇
  1998年   61篇
  1997年   46篇
  1996年   36篇
  1995年   33篇
  1994年   24篇
  1993年   19篇
  1992年   26篇
  1991年   6篇
  1990年   13篇
  1989年   3篇
  1988年   2篇
  1987年   1篇
  1986年   2篇
  1984年   13篇
  1983年   9篇
  1982年   2篇
  1981年   2篇
  1979年   1篇
  1935年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
It has been recognized that the involvement of local community is essential to ensure the sustainability of A/R CDM (afforestation/reforestation clean development mechanism) project. This study verifies if the risks of non-permanence and leakage are addressed in a registered small scale A/R CDM project in Vietnam. Workshops, interviews, and a questionnaire survey of local villagers revealed that the project has caused a shortage of land for conventional activities such as grazing, fuel wood collection and shifting cultivation, and consequently posed the risks of project non-permanence and leakage. It is suggested that participation of all stakeholders in the community to the A/R CDM project beyond existing land tenure and adequate carbon benefit sharing according to the level of contribution to the project are required to reduce the risk of non permanence. To ensure the participation, the community should have capability such as consensus building and collective action. Leakage would be minimized if the community has alternative measures to the conventional activities before starting the project. We argue that it is necessary to first develop a community’s capabilities in the readiness phase of any A/R CDM project in order to reduce the risks for the project sustainability, and that new sources of funding are needed for this purpose.  相似文献   
942.
Indentifying common priorities in shared natural resource systems constitutes an important platform for implementing adaptation and a major step in sharing a common responsibility in addressing climate change. Predominated by discourses on REDD + (Reduced Emissions from Deforestation and Forest Degradation and conservation, sustainable management of forests and enhancement of forest carbon stocks in developing countries) with little emphasis on adaptation there is a risk of lack of policy measures in addressing climate change in the Congo Basin. Forest products and ecosystem services provide security portfolios for the predominantly rural communities, and play major roles in national development programmes in both revenue and employment opportunities. Thus, raising the profile of forests in the policy arena especially in the twin roles of addressing climate change in mitigation and adaptation and achieving resilient development is crucial. Within the framework of the Congo Basin Forests and Climate Change Adaptation project (COFCCA) project, science policy dialogue was conducted to identify and prioritize forest based sectors vulnerable to climate change but important to household livelihoods and national development. The goal of the prioritization process was for the development of intervention in forest as measures for climate change adaptation in Central Africa. Participants constituted a wide range of stakeholders (government, Non Governmental Organizations, research institutions, universities, community leaders, private sectors etc.) as representatives from three countries directly involved in the project: Cameroon, Central African Republic and Democratic Republic of Congo. Building on national priorities, four forest related sectors were identified as common priorities at the regional level for focus on climate change adaptation. These sectors included: (1) energy with emphasis on fuel wood and Charcoal; (2) Water principally quality, quantity, accessibility, etc.; (3) Food with emphasis on Non Timber Forest Products, and (4) Health linked to healthcare products (medicinal plants). Using these prioritized sectors, the project focused on addressing the impacts of climate change on local communities and the development of adaptation strategies in the three pilot countries of the Congo Basin region. The four sectors constitute the key for development in the region and equally considered as priority sectors in the poverty reduction papers. Focused research on these sectors can help to inject the role of forests in national and local development and their potentials contributions to climate change adaptation in national and public discourses. Mainstreaming forest for climate change adaptation into national development planning is the key to improve policy coherence and effectiveness in forest management in the region.  相似文献   
943.
Water quality evaluation based on improved fuzzy matter-element method   总被引:1,自引:0,他引:1  
For natural water, method of water quality evaluation based on improved fuzzy matter-element evaluation method is presented. Two important parts are improved, the weights determining and fuzzy membership functions. The coefficient of variation of each indicator is used to determine the weight instead of traditional calculating superscales method. On the other hand, fuzzy matter-elements are constructed, and normal membership degrees are used instead of traditional trapezoidal ones. The composite fuzzy matter-elements with associated coefficient are constructed through associated transformation. The levels of natural water quality are determined according to the principle of maximum correlation. The improved fuzzy matter-element evaluation method is applied to evaluate water quality of the Luokou mainstream estuary at the first ten weeks in 2011 with the coefficient of variation method determining the weights. Water quality of Luokou mainstream estuary is dropping from level I to level II. The results of the improved evaluation method are basically the same as the official water quality. The variation coefficient method can reduce the workload, and overcome the adverse effects from abnormal values, compared with the traditional calculating superscales method. The results of improved fuzzy matter-element evaluation method are more credible than the ones of the traditional evaluation method. The improved evaluation method can use information of monitoring data more scientifically and comprehensively, and broaden a new evaluation method for water quality assessment.  相似文献   
944.
滇池底泥的砷污染现及其吸附特性   总被引:1,自引:0,他引:1       下载免费PDF全文
本文详细调查分析了滇池底泥中砷污染现状并进行了评价,同时研究了滇池底泥对砷的吸附特性以及底泥中砷的不同形态及其含量特征。   相似文献   
945.
催化裂化是石油炼厂从重质油生产汽油的主要过程之一,是石化炼油中的核心部分,也是环境监理关注的重点.以某石化公司油品质量升级改造项目为例,对新建350万吨/年催化裂化装置的环境监理开展深入研究,为国内深入开展类似项目的环境监理工作、出台环境监理技术规范提供有益的参考.  相似文献   
946.
顾丽军  杨毅  刘敏  聂明华  李涛  侯立军 《环境科学》2013,34(11):4195-4203
利用切向流超滤技术(CFUF)分离出长江口滨岸及近海水体中的胶体,并对其稳定性和物质组成进行了定量分析.结果表明,XP和WSK胶体的尺寸和Zeta-电位随pH的升高而减小,XP、WSK胶体的等电点分别出现在pH<2、pH=3.8;所采水样的胶体有机碳(COC,M r1×103~1μm)浓度为7.7~35.7μmol·L-1,占总溶解有机碳(DOC)的7.1%~41.7%;三维荧光光谱(3DEEM)分析发现研究区出现类色氨酸荧光峰、类紫外富里酸荧光峰和类腐殖质荧光峰;胶体态Na、Mg、K、Ca、Co、Cr、Cu、Fe、Li、Mn、Ni平均分别占溶解态的0.33%、5.7%、0.975%、1%、7.2%、7%、11.9%、15.7%、5.5%、10.5%、11.3%.Co、Cr、Cu、Fe、Li、Mn、Ni与COC的结合能力大于Na、Mg、K、Ca.相关分析表明,胶体的尺寸、DOC、真溶解有机碳(UOC)与盐度呈负相关,COC与盐度无线性关系,胶体态痕量金属(Co、Cr、Cu、Fe、Li、Mn、Ni)总浓度与COC呈线性关系.  相似文献   
947.
考察了在常温常压条件下,等离子体分别协同SiO2、Al2O3、NiO/Al2O3降解甲苯的性能,并从材料的介电常数、对甲苯的吸附性及臭氧分解能力等角度分析了不同活性表现的原因,同时,采用原位红外技术研究了甲苯降解过程中催化剂表面吸附物种的变化.结果表明,当甲苯浓度为100 ppm,气体流量为100 mL·min-1时,一定范围内,甲苯降解率随着能量密度、介电常数、吸附性及臭氧分解能力的提高而提高.甲苯在催化剂表面的吸附对其降解途径有十分重要的影响:在放电区域中加入SiO2,甲苯仍然在气相中完成降解;而存在Al2O3 及NiO/Al2O3时,甲苯氧化成苯甲酸的过程主要发生在催化剂表面,是甲苯催化降解的关键步骤,苯甲酸在活性位点的积累将降低催化剂的反应活性.  相似文献   
948.
太阳是地球表层环境的主要能量来源,大量地质记录表明太阳辐射量变化引起地球环境的剧烈变化。人类能源消费是将地质历史时期储存的能量在较短时间内以热能形式释放出来,其实质相当于额外增加了太阳辐射量。本文以太阳辐射变化为纽带,将当前世界能源消费总量与引起地球环境剧烈变化的太阳辐射变化量(△TSI)进行比较,发现当前人类能源消费总量已约占十到百年尺度地球表面接收太阳辐射变化量的1/2,如果以地球陆地面积计算,当前人类释放的化石太阳能已与太阳辐射十年尺度变化量相当。如果太阳辐射变化可以直接引起气候变化,那么,当前由于人类能源消费而快速释放的热能也可能直接引起地球(尤其是陆地)的增温。提出地表能量平衡的“贮水池效应”,除了考虑温室气体变化引起的能量向系统外逃逸效率高低变化外,还应考虑能量输入增减对地表能量平衡的作用。  相似文献   
949.
The photocatalytic degradation kinetics of carbofuran was optimized by central composite design based on response surface methodology for the first time. Three variables, TiO2 concentration, initial pH value and the concentration of carbofuran, were selected to determine the dependence of degradation efficiencies on independent variables. Response surface methodology modeling results indicated that the degradation efficiency of carbofuran was highly affected by the initial pH value and the concentration of carbofuran. Then nine degradation intermediates were detected by HPLC/MS/MS. The Frontier Electron Densities of carbofuran were calculated to predict the active sites on carbofuran attacked by hydroxyl radicals and photoholes. Point charges were used to elucidate the chemisorption pattern on TiO2 catalysts during the photocatalytic process. By combining the experimental results and calculation data, the photocatalytic degradation pathways of carbofuran were proposed, including the addition of hydroxyl radicals and the cleavage of the carbamate side chain.  相似文献   
950.
应用IVE模型计算上海市机动车污染物排放   总被引:30,自引:7,他引:30  
为了解上海市机动车污染现状,建立上海市机动车源排放清单,分别选择上海市中心城区、商业区和收入相对较低区域中的主干道、快速道和次干道3种共9条典型道路,开展机动车技术水平参数、比功率(VSP)分布状况、启动状况等测试,并在此基础上将International Vehicle E-mission(IVE)模型本地化.调查结果表明,上海市区实际道路上轻型客车、出租车、公交巴士、卡车和摩托车(包含助动车)分别占道路总车流量的41.0%、30.8%、15.6%、6.9%和5.7%;从技术组成看,约85%的轻型客车和97%的出租车均安装有三元催化装置,约30%的公交巴士和90%的卡车没有达到欧Ⅰ标准;机动车的VSP分布主要集中在-2.9~1.2 kw·t-1.模式计算结果表明,2004年上海市机动车CO、VOC、NOx和PM排放量分别为57.06×104t、7.75×104t、9.20×104t和0.26×104t;20%的高排放车对总排放量的贡献占到25%~45%;启动过程中排放的CO、VOC和PM占总排放量的15%~25%,NOx仅占总排放量的4.5%.  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