全文获取类型
收费全文 | 637篇 |
免费 | 81篇 |
国内免费 | 308篇 |
专业分类
安全科学 | 28篇 |
废物处理 | 25篇 |
环保管理 | 46篇 |
综合类 | 572篇 |
基础理论 | 162篇 |
环境理论 | 1篇 |
污染及防治 | 62篇 |
评价与监测 | 88篇 |
社会与环境 | 38篇 |
灾害及防治 | 4篇 |
出版年
2024年 | 4篇 |
2023年 | 24篇 |
2022年 | 42篇 |
2021年 | 44篇 |
2020年 | 33篇 |
2019年 | 43篇 |
2018年 | 43篇 |
2017年 | 41篇 |
2016年 | 38篇 |
2015年 | 52篇 |
2014年 | 47篇 |
2013年 | 71篇 |
2012年 | 51篇 |
2011年 | 46篇 |
2010年 | 38篇 |
2009年 | 36篇 |
2008年 | 43篇 |
2007年 | 46篇 |
2006年 | 40篇 |
2005年 | 34篇 |
2004年 | 28篇 |
2003年 | 26篇 |
2002年 | 19篇 |
2001年 | 11篇 |
2000年 | 26篇 |
1999年 | 16篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 20篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1985年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1026条查询结果,搜索用时 984 毫秒
511.
The control of exposure to welding fumes is of increasing importance in promoting a healthy, safe and productive work environment. This article describes the effects of shielding gas composition on the amount and composition of welding fumes produced during gas metal arc welding (GMAW). The amount of fumes generated during welding was measured for steady current over a range of wire-feed speeds and arc voltages using the standard procedures contained in ANSI/AWS F1.2 [American Welding Society. ANSI/AWS F1.2. Laboratory method for measuring fume generation rates and total fume emission of welding and allied processes. Miami, Florida; 1992]. Results of these measurements show that the fume formation rates (FFRs) increase with CO2 and O2 in the shielding gas mixture. The lowest FFRs were obtained with the mixtures of Ar?+?2%CO2 and Ar?+?3%CO2?+?1%O2. The highest FFRs were obtained with the mixtures of Ar?+?18%CO2 and Ar?+?5%CO2?+?4%O2. The welding fumes contains mainly iron, manganese, silicon, titanium and sodium under oxide forms. The fume cluster particles have dimensions between 0.5 and 2?µm. The FFR was found to be governed by the transfer modes of molten metal, i.e. the current intensity and arc voltage, as well as by the shielding gas mixtures composition. Thus these parameters have to be taken into consideration before designing a welding process. Whenever possible, users of GMAW should use the lowest current intensity. However, when this is not possible, due to the constraints of process productivity, welders should use higher currents, but with Ar?+?2%CO2 and Ar?+?3%CO2?+?1%O2 shielding mixtures, which will lead to smaller fume emissions. 相似文献
512.
Adsorption rates of Sb(V) ions on an activated alumina (AA) were analyzed by batchwise experiments, while the continuous adsorption, desorption, regeneration of AA, and multiple reuse cycles were studied by flow column tests. The adsorption rates increased quickly with the increases of shaking speed and operation temperature. The adsorbed Sb(V) ions were desorbed easily by a 50 mM NaOH solution, and a 41–90 times concentrated Sb(V) solution was yielded correspondingly. AA was effectively regenerated by desorption operation and ca. 93% of the initial adsorption capacity was retained after six times adsorption/desorption cycles. 相似文献
513.
Total suspended particles (TSP) and metal concentrations were determined in Salvador, Bahia, Brazil at two sites: a residential area and a residential‐commercial‐industrial neighborhood. The determined metals associated with atmospheric aerosols include Al, Ca, Cr, Cd, Fe, Mg, Mn, V, Zn and Na. Factor analysis was employed to identify the major atmospheric deposition sources. At one site the data were best represented by two sources: resuspended soil + marine aerosol and vehicular emissions, which represents 93% of the total system variance. In the second one the data were best represented by three sources: resuspended soil, metallurgy and building construction, which represents 79% of the total system variance. 相似文献
514.
The relationship between the rainwater composition on two consecutive rain days was analyzed. Logrono, a remote station in the North of Spain was chosen for the analyses. The concentration of the major ions in the rainwater of the first rain day is linearly related to the concentration of the second rain day except for those ions whose source is the soil (Ca2+ and Mg2+). These ions are related to SO4 2? and NO3 ? in the first rain day, but not in the second. 相似文献
515.
焦化废水中有机物的识别、污染特性及其在废水处理过程中的降解 总被引:5,自引:0,他引:5
采用液-液萃取辅以硅胶、氧化铝净化的方法,并结合GC/MS分析技术,系统分析了焦化废水中有机物的组成.在焦化废水中检测到15类558种有机物.根据有机物的分子结构、废水中的含量、毒性及环境效应,筛选出焦化废水中的特征性有机污染物,以区别于其它工业废水,可作为追溯环境中污染物来源的依据.经物理、生物和化学处理后,焦化废水中大部分有机物被去除,其中,对去除率的主要贡献是生物处理阶段.为了更好地考察生物处理阶段对有机污染物的去除特征,选定酚类、多环芳烃和喹啉类物质作为研究对象,分析了3类特征性污染物在A/O2工艺各单元中的去除状况及组成变化特征. 相似文献
516.
This research examined the antecedents of organizational citizenship behavior helping norms in teams, specifically with regard to how members' personality, values, beliefs, and helping behavior predict the emergence of helping norms in newly formed project teams. We drew from theory on emergent phenomena and team composition research to propose and test a compilation model of how helping norms are influenced by having at least one member with particularly low (minimum) or high (maximum) levels of attributes that may influence helping‐norm development (i.e., conscientiousness, agreeableness, other‐oriented values, personal helping beliefs). We further examined the extent to which members' helping behaviors, as rated by peers, predicted helping norms and whether these behaviors mediated the relationship between individual attributes and helping norms. The results of a longitudinal study of 47 student project teams revealed that teams' minimums on agreeableness, other‐oriented values, and personal helping beliefs had direct relationships with helping‐norm emergence, and the effects of agreeableness were mediated through mean helping behavior. By contrast, teams' maximums on these attributes showed no relationships with helping norms, and only a team maximum on agreeableness was associated with teams' mean helping behavior. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
517.
518.
北京冬季一次重污染过程的污染特征及成因分析 总被引:9,自引:0,他引:9
为了研究北京冬季重污染过程的污染特征及形成原因,选取2013年1月9~15日一次典型重污染过程,对污染期间气象要素、大气颗粒物组分特征和天气背景场进行综合研究.结果表明,此次大气重污染过程中PM10和PM2.5平均质量浓度分别为347.7μg/m3和222.4μg/m3,均超过环境空气质量标准(GB3095-2012)中规定的日均二级浓度限值.重污染时段PM2.5中NH4+、NO3-和SO42-质量浓度之和占PM2.5质量浓度的44.0%,OC/EC的平均比值为5.44,说明二次无机离子和有机物对此次污染过程中PM2.5贡献较大.稳定的大气环流背景场、高湿度低风速的地面气象条件和低而厚的逆温层导致北京地区大气层结稳定,加上北京三面环山的特殊地形结构,是造成此次大气重污染过程的主要原因. 相似文献
519.
对不同质量浓度的NH3-N在水平潜流人工湿地内的去除过程进行考察,并且对比分析了去除率和硝化强度,利用PCR-DGGE技术研究了ρ(NH3-N)及植物种植等因素对人工湿地中AOB(氨氧化细菌)群落结构的影响. 结果表明:在水力停留时间为2.5d的情况下,模拟低污染水ρ(NH3-N)分别为0.6~0.7和4.5~5.0mg/L时,芦苇湿地对TN的去除率分别为81.9%和62.2%. 较高的ρ(NH3-N)和种植芦苇有利于提高湿地硝化强度和AOB群落多样性. 系统运行50d时,处理高ρ(NH3-N)和低ρ(NH3-N)低污染水的芦苇湿地的硝化强度分别为0.164和0.103mg/(kg·h);AOB群落Shannon-Weaver多样性指数(系统运行90d时)分别为2.32和1.75. 处理高ρ(NH3-N)的低污染水时,空白湿地和芦苇湿地的硝化强度分别为0.082和0.164mg/(kg·h);AOB群落Shannon-Weaver多样性指数(系统运行90d时)从1.95增至2.32. 相似文献
520.
土壤、土地利用多样性及其与相关景观指数的关联分析 总被引:1,自引:0,他引:1
土壤作为人类赖以生存的物质基础,与土地利用之间存在密切联系,土壤类型及属性的差异很大程度上决定了土地利用的方式,同时土地利用方式的不同也间接地改变着土壤类型、性质及功能多样性的格局。在人地矛盾、人与自然矛盾不断加剧的今天,研究土地和土壤的空间分布格局变化及两者之间的交互关系具有重要意义。利用土壤多样性理论和景观生态学原理综合分析土壤、土地利用类型的空间分布格局,并借助空间网格的概念量化分析土壤和土地利用类型的空间分布情况。以河南省中南部样区为研究对象,利用仙农熵变形公式计算了1 km×1 km、3 km×3 km、5 km×5 km 3种网格尺度下的土壤和土地利用的空间分布多样性和各县市的土壤和土地利用构成组分多样性,运用ArcGIS探讨了多样性指数与景观指数之间的关联性,综合评价研究区的土壤类型空间分布与土地利用空间分布格局的相互性。研究表明:同一种土壤和土地利用类型的空间分布多样性指数在异网格尺度下具有相似的分异规律;土地利用与土壤类型的构成组分多样性之间不具有明显的相关性,土壤类型均匀分布的地区,土地利用类型不一定会均匀分布,而两者的平均斑块面积之间具有明显的相关性,土壤斑块的大小对土地利用斑块的大小影响较大,土壤类型的空间分布特征在一定程度上,将影响土地利用的空间分布格局和变化过程;土壤类型的面积指数、平均斑块面积指数分别与土壤空间分布多样性之间具有较好的相关性,相关系数分别为r2=0.990、r2=0.599。而土地利用的面积指数、平均斑块面积指数与土地利用空间分布多样性指数之间的相关性较差,相关系数分别为r2=0.437、r2=0.034。土壤的平均斑块形状指数与多样性指数之间存在一定正相关关系,相关系数为r2=0.612;但土地利用的形状指数与多样性之 相似文献