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   737篇
  免费   57篇
  国内免费   243篇
安全科学   44篇
废物处理   11篇
环保管理   51篇
综合类   453篇
基础理论   191篇
污染及防治   134篇
评价与监测   116篇
社会与环境   34篇
灾害及防治   3篇
  2024年   1篇
  2023年   24篇
  2022年   31篇
  2021年   32篇
  2020年   34篇
  2019年   33篇
  2018年   28篇
  2017年   31篇
  2016年   46篇
  2015年   30篇
  2014年   34篇
  2013年   78篇
  2012年   45篇
  2011年   63篇
  2010年   44篇
  2009年   37篇
  2008年   54篇
  2007年   42篇
  2006年   36篇
  2005年   32篇
  2004年   32篇
  2003年   24篇
  2002年   30篇
  2001年   22篇
  2000年   25篇
  1999年   21篇
  1998年   26篇
  1997年   10篇
  1996年   16篇
  1995年   16篇
  1994年   12篇
  1993年   14篇
  1992年   11篇
  1991年   2篇
  1990年   10篇
  1989年   4篇
  1986年   1篇
  1984年   1篇
  1982年   2篇
  1976年   2篇
  1972年   1篇
排序方式: 共有1037条查询结果,搜索用时 756 毫秒
741.
Pollution of hazardous elements in roof runoff has been a potential danger to aquatic ecosystem as documented in previous studies. In this study, concentrations of lead (Pb), zinc (Zn), arsenic (As), and cadmium (Cd) in roof runoff were measured for short-term rainfall events. The concentrations of the selected elements varied to a high degree during the rainfall period, and the well-known first-flush phenomenon was not observed due to the short-term rainfall patterns. Based on event mean concentrations (EMCs) and fluxes, the elemental pollution may be ranked as Zn >> Pb > As > Cd. The average levels of Pb and Zn exceeded the fourth class value and fifth class value of the environmental quality standards for surface water in China. The relative high pollution could be caused by atmospheric deposition and the erosion of crust steel appurtenance installed above the rooftop. Furthermore, elements in particulate form dominated the roof runoff pollution, and the ratios of elements in particulate form to total amounts were 0.6 (As), 0.9 (Pb), 0.7 (Cd), and 0.5 (Zn). This study cleared the pollution characteristics of hazardous elements in short-term storm water roof runoff; it was useful for the selection of best management practices.  相似文献   
742.
Trace elements were determined in fish and oysters from Sepetiba Bay, Brazil, by total reflection Xray fluorescence using synchrotron radiation (SRTXRF). Cr, Mn, Fe, Ni, Cu, Zn and Se were determined in fish muscles and organs and in oyster soft tissue. SRTXRF was shown to be a good tool for the analysis of trace elements from biological tissue samples. Overall, the levels of the analysed metals were higher in oysters than in the fish samples. Metals were not uniformly distributed throughout the body of the analysed fish. The detected concentrations of Cr, Zn and Se were very high in some samples, surpassing the maximum limits established by Brazilian legislation.  相似文献   
743.
744.
利用2012年12月在青岛采集的31个总悬浮颗粒物(TSP)样品,分析其中11种微量元素的总浓度和溶解态浓度,讨论了沙尘负载、气溶胶来源、酸过程及天气条件对微量元素溶解度的影响.结果表明,Fe和Al的溶解度<5%,Pb、Ba、Bi的为10%左右,Cu、V、Cd、Mn的为20%~30%,Zn和As的约为40%.随着沙尘负载量的增加,气溶胶中微量元素溶解度呈规律性递减.气团后向轨迹聚类分析和正矩阵因子分析(PMF)结果显示,受人为源影响的气溶胶中微量元素溶解度明显高于受沙尘源影响的,受二次生成源和海洋源影响的的气溶胶中微量元素溶解度明显高于受土壤源影响的.大气酸过程是造成这些差异的主要原因.相关性分析表明,SO42-、NO3-和有机酸等酸组分均对微量元素溶解度有一定影响.霾天时气溶胶中微量元素溶解度明显低于雾天的,其原因为酸组分在较高的相对湿度下更能促进微量元素溶解度的提高.  相似文献   
745.
南京市霾天气与主要气象条件的相关分析   总被引:4,自引:0,他引:4  
利用天气学原理,分析研究2012~2014年南京市霾天气的主要地面天气形势、气象要素以及PM2.5与PM10浓度的相互关系.结果表明,2012~2014年南京市霾天气以轻度和轻微霾为主,且冬季最多,夏季最少;相对湿度在50%~80%之间有利于霾的发生,尤其是70%≤RH<80%时;有87.6%的霾发生在风速≤4m/s的情况下,并且主要来自东北偏东到东南风向区域.最利于南京霾天气形成的主要天气形势是均压场、高压控制和高压后部,而低压槽、副高控制和台风影响时霾发生较少.PM2.5在PM10中所占比例与霾强度呈正比.通过对南京市气象条件与霾的关系,及后向轨迹HYSPLIT4模式的聚类分析显示,结合南京市霾天气时的风向统计,影响南京霾发生的污染源主要有本地源、南京市东南地区的近距离污染源和华北地区的远距离污染源.  相似文献   
746.
Anaerobic processes for treatment of low and high strength wastewaters and solid wastes constitute the core method in the natural biological mineralization (NBM) treatment concept. When adequately combined with the complementary NBM-systems and modern clean water saving practices in wastewater collection and transport, they represent a feasible route to sustainable environmental protection (EPsus), in essence even towards a more sustainable society. Despite the development and implementation of modern high rate Anaerobic Wastewater Treatment (AnWT-) systems and complementary innovative NBM-processes, the considerable progress made since the seventies in fundamental insights in microbiology, biochemistry and process technology, still numerous challenging improvements in the NBM-field can be realized. This contribution is mainly based on the insights attained from wide ranging literature evaluations and the results of experimental research conducted by numerous PhD students who participated in our group over the last four decades. An attempt is made here to identify major facets on which an improved insight can, and consequently should, be obtained in order to accomplish more optimal operation and design of various types of Anaerobic Degradation (AnDeg-) processes.  相似文献   
747.
土壤中腐殖酸对外源农用稀土生物可利用性的影响   总被引:10,自引:0,他引:10  
采用盆栽实验方法,研究了腐殖酸对稀土元素在土壤-植物体系中的迁移、富集和生物可利用性的影响,结果表明,在试验土壤红壤中,稀土元素主要富集在小麦根部,加入低浓度的腐殖酸后,促进了小麦对稀土元素的吸收:而高浓度的腐殖酸则抑制小麦对稀土元素的吸收,腐殖酸浓度过高时,对小麦生长产生毒害作用,同时发现,小麦中叶绿素含量与小麦中稀土含量存在相关关系。  相似文献   
748.
Gangba sheep are known for having typical sensory characteristics attributed to free range conditions and grazing on wild plants. The genuine Gangba mutton was selected as the experimental group, and the commercial Tibetan mutton was selected as the control group, the nutritive composition of basic chemical components, amino acids and fatty acids in mutton were investigated to correlate its unique meat quality and eating satisfaction. The results showed that fatty acids were significantly higher (P<0.05) in Gangba mutton than in commercial mutton, and the higher content of flavoring amino acids (glutamic acid and aspartame) were primarily responsible for the taste attributes umami of meat juices. Moreover, the trace elements analysis in mutton and grazing factors (forage, water source and soil) were conducted, to explain the source of essential trace elements in mutton. The concentrations of essential trace elements show that the Gangba mutton was a valuable source for highly available Cu and Zn in human nutrition, and well managed with few detected of toxicity metal. The concentrations of essential trace elements in mutton are closely related to the trace elements in environmental grazing factors. In conclusion, the congenital grazing conditions (a highly mineralized water resource, natural forages and clean soils) were shown to contribute to the unique meat characteristics of Gangba sheep.  相似文献   
749.
Objective: Guardrail heights play a crucial role in the way that errant vehicles interact with roadside barriers. Low rail heights increase the propensity of vehicle rollover and override, whereas excessively tall rails promote underride. Further, rail mounting heights and post embedment depths may be altered by variations in roadside terrain. An increased guardrail height may be desirable to accommodate construction tolerances, soil erosion, frost heave, and future roadway overlays. This study aimed to investigate and identify a maximum safe installation height for the Midwest Guardrail System that would be robust and remain crashworthy before and after pavement overlays.

Methods: A research investigation was performed to evaluate the safety performance of increased mounting heights for the standard 787-mm (31-in.)-tall Midwest Guardrail System (MGS) through crash testing and computer simulation. Two full-scale crash tests with small passenger cars were performed on the MGS with top-rail mounting heights of 864 and 914 mm (34 and 36 in.). Test results were then used to calibrate computer simulation models.

Results: In the first test, a small car impacted the MGS with 864-mm (34-in.) rail height at 102 km/h (63.6 mph) and 25.0° and was successfully redirected. In the second test, another small car impacted the MGS with a 914-mm (36-in.) rail height at 103 km/h (64.1 mph) and 25.6° and was successful. Both system heights satisfied the Manual for Assessing Safety Hardware (MASH) Test Level 3 (TL-3) evaluation criteria. Test results were then used to calibrate computer simulation models. A mounting height of 36 in. was determined to be the maximum guardrail height that would safely contain and redirect small car vehicles. Simulations confirmed that taller guardrail heights (i.e., 37 in.) would likely result in small car underride. In addition, simulation results indicated that passenger vehicle models were successfully contained by the 34- and 36-in.-tall MGS installed on approach slopes as steep as 6:1.

Conclusions: A mounting height of 914 mm (36 in.) was determined to be the maximum guardrail height that would safely contain and redirect 1100C vehicles and not allow underride or excessive vehicle snag on support posts. Recommendations were also provided regarding the safety performance of the MGS with increased height.  相似文献   

750.
The aim of this study was to identify possible relationships between biochemical- superoxide dismutase (SOD), glutathione peroxidase (GPx), thiobarbituric acid reactive substances (TBARS) of mussels (Mytilus galloprovincialis) and chemical (Hg, Cd, Pb, Cr, Cu, Zn, Mn and Fe) contaminants from relatively clean area (Middle Bay) and heavily polluted area (Inner Bay) of the Izmir Bay. Sampling of mussels was performed in the beginning of May 2004. Mussel digestive glands have been used for biochemical assays. Trace metal content was determined by atomic absorption spectrophotometer using standard procedures. Metal contents in mussels collected at polluted site increased compared to the middle part of the bay. While there was a positive correlation between metals and SOD enzyme activity, there was a negative correlation between metals and GPx enzyme activity. An increase was observed in SOD enzyme activity and a decrease of GPx enzyme activity at the inner part of the bay.  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