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   21篇
  免费   0篇
  国内免费   5篇
大气科学   1篇
地球物理   3篇
地质学   19篇
海洋学   1篇
自然地理   2篇
  2023年   1篇
  2022年   1篇
  2021年   2篇
  2020年   2篇
  2019年   1篇
  2018年   3篇
  2017年   2篇
  2015年   1篇
  2014年   3篇
  2013年   5篇
  2012年   1篇
  2011年   1篇
  2009年   1篇
  2004年   1篇
  1993年   1篇
排序方式: 共有26条查询结果,搜索用时 359 毫秒
11.
12.
The present study investigates the hydrogeochemistry and contamination of Varamin deep aquifer located in the southeast of Tehran province, Iran. The study also evaluates groundwater suitability for irrigation uses. The hydrogeochemical study was conducted by collecting and analyzing 154 groundwater samples seasonally during 2014. Based on evolutionary sequence of Chebotarev, the aquifer is in the stage of SO4 + HCO3 in the north half of the plain and it has evolved into SO4 + Cl in the south half. The unusual increase in TDS and Cl? toward the western boundaries of the aquifer indicates some anomalies. These anomalies have originated from discharge of untreated wastewater of Tehran city in these areas. The studied aquifer contains four dominant groundwater types including Na–Ca–SO4 (55%), Na–Ca–HCO3 (22%), Na–Cl (13%) and Ca–Cl (10%). The spatial distributions of Na–Cl and Ca–Cl water types coincide with observed anomalies. Ionic relationships of SO4 2? versus Cl? and Na+ versus Cl? confirm that water–rock interaction and anthropogenic contribution are main sources of these ions in the groundwater. The main processes governing the chemistry of the groundwater are the dissolution of calcite, dolomite and gypsum along the flow path, and direct ion exchange. Reverse ion exchange controls the groundwater chemistry in the areas contaminated with untreated wastewater. Based on Na% and SAR, 10.3 and 27% of water samples are unsuitable for irrigation purposes, respectively. Regarding residual sodium carbonate, there is no treat for crop yields. Only 6% of water samples represent magnesium adsorption ratios more than 50% which are harmful and unsuitable for irrigation.  相似文献   
13.
Karst areas have much higher ecological vulnerability and are easy to be contaminated by polycyclic aromatic hydrocarbons (PAHs), which are introduced as health risk pollutants. PAHs ratios were used to understand the sources and transport behavior of PAHs conducted in the karst Nanshan Underground River, China. Water, sediments from the underground river and water, sediments, soil from the surface were collected monthly in 2011 and 2012. Abundant PAHs were found both in the underground river and in the surface system. The detected ΣPAHs concentrations varied from 353 to 13,203 ng L?1 in the groundwaters and content from 169 to 12,038 ng g?1 in the sediments of the underground river. The ratios of anthracene to anthracene, plus phenanthrene and fluoranthene to fluoranthene, plus pyrene indicated that PAHs were delivered in the groundwaters from combusted grass, wood, and coal, while in the sediments were a mixture of non-combusted petroleum, grass, wood, coal and combusted grass, wood, coal. The similarities in sources between an underground river and surface system indicated that farmlands play a major role for the transport of PAHs and contamination in the underground river. Karst features are liable for the transport behavior.  相似文献   
14.
为查明重庆老龙洞地下河流域有机氯农药的污染情况及其特征和来源,通过气相色谱-微池电子捕获检测器(GC-μ ECD)检测水体OCPs含量.结果表明研究区水样中受到了有机氯农药不同程度的污染.α-HCH是研究区水体HCHs主要成分,HCHs的残留主要来自于大气长距离传输.DDTs的主要成分各采样点不尽相同.DDTs的输入为历史上工业DDTs的使用且在水体中其主要以好氧转化为主.与国内外河流相比较,老龙洞地下河流域水体有机氯农药含量处于较高水平.  相似文献   
15.
Abstract Karst areas have much higher ecological vulnerability and are easy to be contaminated by polychlorinated biphenyls(PCBs) which are introduced as health risk pollutants.PCBs concentrations were used to understand the transport behavior of PCBs conducted in the karst Nanshan Underground River,China.Water and sediments from the underground river water,and sediments and soil from the surface of the corresponding watershed were collected monthly in 2011 and 2012 and PCBs were analyzed.Seasonal variations were found in concentrations of PCBs both in the waters and sediments.PCBs concentrations varied from 0.3 to 29.9 ng·L-1 in the groundwater,while from 0.1 to 366.1 ng·g-1 in the underground sediments.Correlations were found in concentrations of PCBs in waters and sediments between the underground river and surface systems which indicate that the surface systems play a major role for the transport of PCBs and contamination in the underground river systems.Karst features are liable for the transport behavior.The underground river waters transport PCBs at mean 3 g·day-1.  相似文献   
16.
Earth dam site selection is one of the most important problems in water resources management. It depends on a set of qualitative and quantitative criteria, and they may even be in conflict with each other. This study aims to develop a multicriteria decision-making approach to locate the dam site and construct a multipurpose earth dam in Harsin City at the western part of Iran. For this purpose, firstly, the influential criteria for locating the earth dam site were determined using a comprehensive literature review and the experts’ opinions. Then, some watersheds in the surrounding areas of Iran’s Harsin City were studied and four feasible sites proposed. In the final stage, these sites, in order to construct a multipurpose earth dam, were prioritized using the analytic hierarchy process approach and the most optimal site was selected.  相似文献   
17.
Current study deals with investigating the effects of both time factor and the selection of a constitutive model type on predicting deformations of an excavation braced by nailing using two and three-dimensional finite element analyses. In addition, the effects of stress path and the type of defined initial conditions of the analytical model on deformations of the floor and walls of the excavation are also studied. Time factor, in the form of earth materials’ creep, can largely be entered into calculation of deformations of excavations by conducting viscoelastic and viscoplastic analyses. On the other hand, there hasn’t been done a comprehensive study regarding the creep behavior of excavations through comparing the results of two-dimensional and three-dimensional numerical analyses so far. The results showed that it’s largely possible to approach the actual deformation behavior of an excavation by considering the constitutive model of soft soil creep, SSC model, in the numerical plastic analyses. The effects of stress path on the deformation behavior of the excavation walls and excavation floor are investigated by using OCR stress ratio and POP stress difference; These two factors, both of which are also analogous, represent a boundary value for swelling behavior of the excavation floor and an increasing rate for the deformation behavior of the excavation walls since the increase in OCR or POP is equal to the increase in the soil lateral pressure coefficient at rest.  相似文献   
18.
Soil aquifer treatment (SAT) is an effective indirect technique for wastewater reuse. The present study aims at assessing the soil capacity in arid region of Varamin on natural attenuation of inorganic constituents of municipal treated wastewater of Tehran City. In order to simulate SAT pond, four columns of 30 cm in height and 4 cm in diameter were filled with sandy loam soil taken from artificial recharge pond in Varamin plain. These columns were recharged by secondary treated wastewater from Shahre-Rey treatment plant under the plan of 12-h wetting and drying cycles. During the experiment, 50 pore volume passed through each column. The pH, EC, TDS, SAL, SAR, major ions, nitrate, phosphate and trace elements were measured in influent and effluent samples. The concentration of Na+, Ca2+, Mg2+, Cl? and SO42? increased in effluent samples due to a washout process and dissolution of minerals. The soil could only attenuate NO3?, K+, Rb and PO43? with the percentage of 18.4, 24.6, 67.7 and 83.6, respectively. The soil of studied area is rich in Cr, Ni, Sr, Pb, Cu, Zn, Ba and Rb. The concentrations of all mentioned trace elements, with the exception of Rb, have increased in the effluent samples with respect to influent. Also, the quality indices of TDS, SAL and SAR have increased 10.6, 25.2 and 8.7%, respectively, in effluent. Soil column samples, at the end of experiment, contain high amounts of major and trace elements. Consequently, there is a potential risk for groundwater contamination in long-term recharge.  相似文献   
19.

Coal mining has serious impacts on local environment, including damage to the land and soil by subsidence, damage to ground-water systems through the fracturing and subsiding of overlying rocks, contamination of surface waters with acid mine drainage, and pollution of the atmosphere by release of toxic gases. The damage to ground water and its consequent impacts on the regional environment is the core of research of the coal mining from the perspective of environment protection. The present paper focuses on the changes of surface vegetation coverage, the pollutants released from pit coal power plants, and the damages to the ground aquifers induced by mining activities in arid Eastern Junggar coalfield of China. At first, the authors investigated the changes of surface vegetation coverage, since mining began in the 2000s using Landsat data. Results show that the low surface vegetation coverage (grade 1 plus grade 2) in the southern part of the region decreased from 11.62?×?108 m2 in 2003 to 9.57?×?108 m2 in 2017 (?17.6%), while it increased from 11.58?×?108 m2 in 2003 to 12.70?×?108 m2 in 2017 (+?9.7%) in the eastern part. The high surface vegetation coverage (grade 3 plus grade 4) in the southern part increased from 1.94?×?108 m2 in 2003 to 4.00?×?108 m2 in 2017 (+?106.2%), while it decreased from 4.39?×?108 m2 in 2003 to 3.26?×?108 m2 in 2017 (?25.74%) in the eastern part. The data of annual precipitation during the same period in this area show that the changes of surface vegetation coverage have less relationship with the annual precipitation, which indicates that the mining activities is probably the major factor for that. Second, a statistic of air pollutants generated from pit coal power plants was made based on data of references. Results show that the estimated gaseous pollutant emissions increased as 865.23 tons of smoke particles, 5940.73 tons of SO2, and 7584.48 tons of NO2 in 2013, which increased rapidly with 9.73 times the smoke particle, 21.69 times the SO2, and 9.24 times the NO2 than that of 2007. And then, the physical and numerical simulation of the damage of mining activities to aquifers was made to show the permeability of the reference points of overlying aquifers varies associated with mining activities. Results show that the porous rock matrix permeability has a negative relationship with fluctuation during mining, while the fracture permeability shows a positive one. Finally, a case investigation in southern area surrounding this coalfield was illustrated. Result shows that the local ground-water level decreased by 16 m difference from the altitude level of?+?774 m in 2003 to?+?758 m in 2013. Data and results from this study presented the already and the potential pollutions and damages to local environment induced by the mining activities in this region.

  相似文献   
20.
为查明重庆老龙洞地下河流域有机氯农药的污染情况及其特征和来源,通过气相色谱-微池电子捕获检测器(GC-μECD)检测水体OCPs含量。结果表明研究区水样中受到了有机氯农药不同程度的污染。α-HCH是研究区水体HCHs主要成分,HCHs的残留主要来自于大气长距离传输。DDTs的主要成分各采样点不尽相同。DDTs的输入为历史上工业DDTs的使用且在水体中其主要以好氧转化为主。与国内外河流相比较,老龙洞地下河流域水体有机氯农药含量处于较高水平。  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