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   350篇
  免费   38篇
  国内免费   109篇
大气科学   11篇
地球物理   82篇
地质学   301篇
海洋学   57篇
天文学   2篇
综合类   27篇
自然地理   17篇
  2024年   1篇
  2023年   4篇
  2022年   11篇
  2021年   17篇
  2020年   13篇
  2019年   9篇
  2018年   13篇
  2017年   8篇
  2016年   13篇
  2015年   17篇
  2014年   16篇
  2013年   24篇
  2012年   18篇
  2011年   22篇
  2010年   21篇
  2009年   13篇
  2008年   29篇
  2007年   21篇
  2006年   50篇
  2005年   27篇
  2004年   20篇
  2003年   10篇
  2002年   16篇
  2001年   9篇
  2000年   12篇
  1999年   13篇
  1998年   9篇
  1997年   18篇
  1996年   4篇
  1995年   2篇
  1994年   4篇
  1993年   6篇
  1992年   4篇
  1991年   3篇
  1990年   7篇
  1989年   2篇
  1988年   2篇
  1986年   2篇
  1985年   2篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
排序方式: 共有497条查询结果,搜索用时 31 毫秒
471.
1Introduction Thebiogeochemicalcycleofmercuryinaqueous systemisthekeyfactorleadingtotheexpansionof mercurypollutiononaglobalscaleandthesafetyof fishconsumers.Dissolvedgaseousmercury(DGM)e vasionisconsideredasoneofthemostimportantmer curysourcesforatmosphere.Atthesametime,this procedurewillreducetheHgburdeninthewatercol umnandmaythusdecreasemethylmercuryproduction andaccumulationinfish(Nriagu,1994).TheBaihua ReservoirissituatedinGuizhouProvince,andithas sufferedseriousmercurycontaminationfr…  相似文献   
472.
In this study, we applied synchrotron radiation X-ray fluorescence technique (SR-XRF) to investigate the heavy metals including Hg and Pb in a few single strands of pinnule of the outermost wing feather of snow petrel (Pagodroma Nivea) collected in the Antarctic. The microscopic distributions of Hg and Pb along with the strand of pinnule show significant variation and the types of distribution are different for pinules, suggesting that external contamination may have an important impact on the levels of Hg and Pb, rather than reflecting levels in the blood during feather formation. This should be taken into account in future monitoring studies. The sources of Hg and Pb detected in the feather were also discussed. Using feathers of snow petrel to investigate the springtime mercury depletion events (MDEs) in the Antarctic were proposed.  相似文献   
473.
Small-scale mercury smelting activities with indigenous method are always extensive in the Wuchuan area, northeastern Guizhou Province, China. Because of the simple processes without any environmental protection, a large amount of mercury vapor released to the ambient air during the processing of cinnabar roasting. So the health of the workers may be negatively affected through inhalation of the mercury-polluted air. Mercury, creatinine and β2-MG contents in urine among the workers in the study areas and the residents in the control site (Changshun County) were determined to discuss the health impact of mercury vapor exposure to the workers in the study areas. Health examinations also were carded out to identify clinical symptoms of mercury poisoning for the smelting workers. Results indicated that the geometric mean value of urinary mercury for the smelting workers was g/g Cr μg/g Cr (N=22), significantly higher than 1.24 μg/g (N=54) for residents in the control site. β2-MG as a renal biomarker can be used to study human nephrotoxicity at an early stage and it is most useful to define effects for assessing re-absorption function to indicate tubular injury. The results showed a serious adverse effect on renal system for the smelting workers due to mercury exposure. Several workers have already manifested some clinical symptoms of lightly chronic mercury poisoning and the symptoms include finger and eyelid lightly tremor, gingivitis and blue mercury line in mouth. The study illuminated that the workers in gaged in indigenous mercury smelting in the Wuchuan area were seriously exposed to mercury vapor,  相似文献   
474.
475.
476.
477.
Mercury is an important pollutant in lakes. Methylmercury (MeHg), the most toxic mercury species, which can be formed from inorganic mercury in lakes, can be bioaccumulated into high concentration in food chain and result in a potential threat to human beings. Sediments play an important role for the Hg biogeochemistry in the aquatic systems: Mercury methylation has been shown to be fastest in the surfacial sediments, where the microbial activity is highest. The formation of MeHg in lakes suggests that sediments and/or near-shore wetlands can be the sources of MeHg in aquatic environments. The Baihua Reservoir, located in the suburb of Guiyang, was impounded in 1966. From the 1970s to the 1990s, Guizhou Organic Chemical Plant which used inorganic mercury as catalyst to produce acetic acid, was responsible for the discharge of waste water with high mercury content.  相似文献   
478.
《中国地球化学学报》2006,25(B08):242-243
In direct continuation with the acquired knowledge of ecosystem approach for the presence of mercury in the Amazon, we have launched in 2001 the NSERC-supported pan-Canadian COMERN project. This Collaborative Mercury Research Network addresses the urgent need for the development of a framework enabling researchers, political stakeholders, and communities concerned by the mercury question to evolve towards an interdisciplinary association capable of synergistically combining our knowledge on Hg into an original synthesis. We are presenting a simple integrated indicator representative of the specific susceptibility of an ecosystem to Hg bioaccumulation and subsequent transfer to humans. This indicator includes three concepts: (1) the sensitivity to bioaccumulation, induced and influenced by factors such as the Hg loading, the different transport and methylation processes, and human activities; (2) the vulnerability of the populations exposed to Hg through consumption of local and market fish; and (3) the adaptability of the ecosystem and the people living into it, an evaluation of its resilience, or its capacity to recover and/or to cope with the contamination, taking into account the social and political resources within the communities impacted.  相似文献   
479.
Half a millennium mercury production at Idrija is reflected in increased mercury contents in all environmental segments. The bulk of roasting residues from the middle of the 19th century to 1977 was discharged directly into the Idrijca River, and the material was carried at high waters to the Soca River and farther into the Adriatic Sea. It has been estimated that 45500 tons of mercury were emitted into the environment during the operating period of the mine, which ceased production in 1994. In the lower reaches of the Idrijca the riverine deposits with high mercury contents have been, and will be in the future a source of mercury polluted sediment. Stream sediments were monitored at the same locations along the Idrijca and Soca rivers (70 kin) every 5 years since 1991 (1991-2005). Grain size distribution was determined by dry sieving and fractions for geochemical analysis were prepared (〈0.04 and 〈0.125 mm). Soils on river terraces were sampled at 5 localities in the lower course of Idrijca. At two locations of the terrace profiles the samples of averaged meadow forage and plantain (Plantago lanceolata) were collected within a 50-meters radius. We found that there was no decrease in mercury concentration in active river sediments during the last 20 years. Upstream from the Idrija Town the mercury concentrations in active river sediments vary from 1 to 10 mg/kg (average 3.3 mg/kg). From Idrija to Spodnja Idrija the mercury concentrations increase extremely and vary greatly (32-4,121 mg/kg, the average is 734 mg/kg). From Spodnja ldrija to the Idrijca-Soca confluence is the average 218 mg/kg, and 57 mg/kg downstream in the Soca River sediments.  相似文献   
480.
The Podljubelj mercury mine lies in the NW part of Slovenia. The ore is of hydrothermal-vein type. The ore deposit was exploited between the years 1557 and 1902. Total production of the mine was 110000 tons of ore (360 tons of Hg). A smelter located close to the mine had been in operation since 1855. The waste material from the mine and the smelter was dumped in close vicinity of the mine. Total quantity of the waste has been estimated at 170000 tons. In order to establish environmental impacts, soil and stream sediment samples were investigated. Soil samples were collected at two different depths (horizons A and B) in a 100 m grid within an 88 ha area. In the vast area also 11 samples of stream sediments were considered. Heavy metals were determined by means of cold vapor atomic absorption spectrometry CV-AAS after aqua regia digestion. Based on the chemical analyses of samples, the estimated mercury mean for soils is 3.67 mg/kg (0.35-244 mg/kg) for horizon A and 1.39 mg/kg (0.17-71.7 mg/kg) for horizon B. The estimated mercury mean for stream sediments is 0.64 mg/kg (0.065-1.36 mg/kg). The concentrations of mercury in soils generally decrease with depth and distance from the mine. The highest content of Hg was determined in a sample taken in the immediate vicinity of the smelter (719 mg/kg). The results have shown that on the 9 ha of the study area, the contents of Hg in soils exceeded the officially set limit value for soils (10 mg/kg). High contents of Hg in soil around the abandoned smelter are a consequence of former atmospheric emissions and technological losses. High contents of Hg were also found in the mine and smelter waste dump. At the edges of the study area and in the samples of stream sediments, Hg concentrations are low.  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