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   54篇
  免费   2篇
测绘学   3篇
大气科学   6篇
地球物理   15篇
地质学   17篇
海洋学   5篇
天文学   7篇
自然地理   3篇
  2023年   1篇
  2021年   1篇
  2020年   1篇
  2018年   3篇
  2017年   2篇
  2016年   2篇
  2015年   1篇
  2014年   4篇
  2012年   1篇
  2011年   2篇
  2010年   2篇
  2009年   4篇
  2008年   1篇
  2007年   2篇
  2006年   7篇
  2004年   2篇
  2003年   2篇
  2002年   1篇
  2001年   2篇
  1999年   2篇
  1998年   1篇
  1994年   1篇
  1991年   2篇
  1986年   1篇
  1985年   3篇
  1984年   3篇
  1983年   1篇
  1977年   1篇
排序方式: 共有56条查询结果,搜索用时 250 毫秒
11.
During field campaigns of the BEEP project (Biological Effects of Environmental Pollution in Marine Coastal Ecosystems) in 2001-2002, metabolites of polycyclic aromatic hydrocarbons (PAHs) were determined in bile samples from three fish species, flounder (Platichthys flesus), perch (Perca fluviatilis) and eelpout (Zoarces viviparus), from four separate areas in the Baltic Sea. Two determination methods were applied: fixed wavelength fluorescence (FF) for pyrene-type metabolites and high-performance liquid chromatography with fluorescence detection (HPLC). There was a good correlation between the FF method and 1-OH pyrene determined by HPLC. Normalisation of the FF data for absorbance at 380 nm or bile protein concentrations greatly increased variance in one third and decreased it in two thirds of the cases and resulted in a loss of significant differences (protein normalisation) between the sampling stations, but normalisation of the HPLC data had little effect on the results. The biliary PAH metabolite content was usually higher in males than in females. In perch and eelpout the biliary PAH contents were at similar levels, whereas in flounder the levels were lower. The sampling areas arranged in decreasing order of biliary PAH contents were: Wismar Bay > Gulf of Gdansk > Lithuanian coast > Kvadofj?rden (reference area). It is concluded that FF with un-normalised data is a reliable and simple method for monitoring purposes and only one sex of a selected species should be used.  相似文献   
12.
Measurements of clustering in large-scale imaging surveys that make use of photometric redshifts depend on the uncertainties in the redshift determination. We have used light-cone simulations to show how the deprojection method successfully recovers the real-space correlation function when applied to mock photometric redshift surveys. We study how the errors in the redshift determination affect the quality of the recovered two-point correlation function. Considering the expected errors associated with the planned photometric redshift surveys, we conclude that this method provides information on the clustering of matter useful for the estimation of cosmological parameters that depend on the large-scale distribution of galaxies.  相似文献   
13.
14.
Soil moisture has a pronounced effect on earth surface processes. Global soil moisture is strongly driven by climate, whereas at finer scales, the role of non‐climatic drivers becomes more important. We provide insights into the significance of soil and land surface properties in landscape‐scale soil moisture variation by utilizing high‐resolution light detection and ranging (LiDAR) data and extensive field investigations. The data consist of 1200 study plots located in a high‐latitude landscape of mountain tundra in north‐western Finland. We measured the plots three times during growing season 2016 with a hand‐held time‐domain reflectometry sensor. To model soil moisture and its temporal variation, we used four statistical modelling methods: generalized linear models, generalized additive models, boosted regression trees, and random forests. The model fit of the soil moisture models were R2 = 0.60 and root mean square error (RMSE) 8.04 VWC% on average, while the temporal variation models showed a lower fit of R2 = 0.25 and RMSE 13.11 CV%. The predictive performances for the former were R2 = 0.47 and RMSE 9.34 VWC%, and for the latter R2 = 0.01 and RMSE 15.29 CV%. Results were similar across the modelling methods, demonstrating a consistent pattern. Soil moisture and its temporal variation showed strong heterogeneity over short distances; therefore, soil moisture modelling benefits from high‐resolution predictors, such as LiDAR based variables. In the soil moisture models, the strongest predictor was SAGA (System for Automated Geoscientific Analyses) wetness index (SWI), based on a 1 m2 digital terrain model derived from LiDAR data, which outperformed soil predictors. Thus, our study supports the use of LiDAR based SWI in explaining fine‐scale soil moisture variation. In the temporal variation models, the strongest predictor was the field‐quantified organic layer depth variable. Our results show that spatial soil moisture predictions can be based on soil and land surface properties, yet the temporal models require further investigation. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   
15.
The cyclic nature of glaciations and related postglacial faulting represents a risk for the deep geological disposal of spent nuclear fuel in areas likely to be affected by future glaciations. Seismic history was therefore studied by means of detecting geomorphological structures on airborne laser scanning digital elevation models and underground by excavating in an esker and trenching across a postglacial fault located in northern Fennoscandia. OLS dating and assessing the geomorphological structures was used for timing of the seismic history. The results suggest that the faulting of different segments in the Pasmajärvi complex is due to at least two late Weichselian events, which probably occurred both subglacially and postglacially. The most reliable input for the moment magnitude estimates was vertical slip profiles, and therefore these estimates (MW ≈ 6.4–6.9) are suggested. © 2020 John Wiley & Sons, Ltd.  相似文献   
16.
New radiocarbon dates from Finnish subfossil mammoth material (Mammuthus sp.), transported by glacial ice, range in age from ca. 32000 to ca. 22500 yr BP. These results suggest that there was a larger ice-free area in Fennoscandia during the Middle Weichselian than previously assumed. In addition, two dates are also presented for bones found in clay with a different transport history. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   
17.
The characteristics of groundwater systems and groundwater contamination in Finland, Norway and Iceland are presented, as they relate to outbreaks of disease. Disparities among the Nordic countries in the approach to providing safe drinking water from groundwater are discussed, and recommendations are given for the future. Groundwater recharge is typically high in autumn or winter months or after snowmelt in the coldest regions. Most inland aquifers are unconfined and therefore vulnerable to pollution, but they are often without much anthropogenic influence and the water quality is good. In coastal zones, previously emplaced marine sediments may confine and protect aquifers to some extent. However, the water quality in these aquifers is highly variable, as the coastal regions are also most influenced by agriculture, sea-water intrusion and urban settlements resulting in challenging conditions for water abstraction and supply. Groundwater is typically extracted from Quaternary deposits for small and medium municipalities, from bedrock for single households, and from surface water for the largest cities, except for Iceland, which relies almost entirely on groundwater for public supply. Managed aquifer recharge, with or without prior water treatment, is widely used in Finland to extend present groundwater resources. Especially at small utilities, groundwater is often supplied without treatment. Despite generally good water quality, microbial contamination has occurred, principally by norovirus and Campylobacter, with larger outbreaks resulting from sewage contamination, cross-connections into drinking water supplies, heavy rainfall events, and ingress of polluted surface water to groundwater.  相似文献   
18.
Cross-flooding ducts are used to equalize asymmetric flooding and, thus, to decrease the heel angle of a ship in an emergency. The present design guidelines for cross-flooding arrangements involve uncertainties associated with the effect of variable structural factors. In this study, scale model experiments were carried out to determine discharge coefficients of a typical cross-duct, with a focus on the effect of structural components such as the girders, stiffeners, and web frame. Flow conditions and configuration of the components were varied in the experiments. The structural stiffeners in the cross-duct were found to notably increase the discharge coefficient whereas the effects of the web frame and the inclination of the duct at an angle of 7° were negligible. The experimentally obtained discharge coefficient values for the cross-duct were considerably lower than the corresponding values computed according to the generally used guidelines of the IMO Resolution MSC.245(83). This indicates that the geometrical properties of the girders in the cross-ducts need to be properly addressed to avoid overestimating the discharge coefficients. Overall, the experimental results formed an indispensable dataset for the validation and further development of CFD approaches.  相似文献   
19.
As a result of global changes, shifts of alpine tree lines towards higher elevations have been recorded, but the role of the spatial variability of the snowpack and zonal‐pattern soil‐nutrient regimes is poorly understood. Norway spruce (Picea abies (L.) Karst) is best suited to fertile soils, and hence we applied soil physical‐chemical and snow measurements and the age chronology of Norway spruce along an elevational gradient (380–557 m a.s.l.) to address a vertical soil zonality hypothesis on mafic Lommoltunturi fell in Finnish Lapland. With regard to increasing elevation, we found an increase in soil NTOT, CTOT and Al, but a decrease in soil Ca, Mg and Ca:Al ratio as well as in electrical conductivity (EC). In addition, the snowpack was significantly thicker in low‐elevation forest than in the tree line and open tundra. In the 1840s, spruce established on low‐elevation soils with a Ca:Al ratio of 2.2. Starting from the 1920s a significant shift of spruce occurred such that it took 60 years to expand the tree line by 55 m in elevation. The spruce tree line has advanced, and the age distribution indicates new colonization of spruce in closed forest up to tundra. The poor soil Ca:Al ratio of 0.02 on tundra apparently is a constraint for spruce. Spruce forest is young (<165 years), and hence we argue that spruce has expanded onto formerly tree‐free sites of this mafic fell. This paper demonstrates that vertical soil zonality is a potential driver for the diffuse tree line of Picea abies on mafic Fennoscandian fells.  相似文献   
20.
During the EU project BEEP a battery of biomarkers was applied in flounder (Platichthys flesus) and the blue mussel (Mytilus edulis) collected at three locations off the Lithuanian coast (Baltic Sea) in June and September 2001 and 2002. The elevated biomarker responses in specimens sampled in September 2001 were apparently related to the extensive dredging activities in the Klaipeda port area and subsequent dumping of contaminated sediments. High concentrations of organic pollutants (organochlorines and PBDEs) were also measured in the tissues of both indicator species. In addition, response levels of genotoxicity, cytotoxicity, immunotoxicity as well as concentrations of PAH metabolites in the bile of flounder showed elevations in 2002 after an oil spill in the Būtinge oil terminal in November 2001. In flounder, biomarker measurements 10 months after the spill indicated recovery processes but in mussels a high level of genotoxicity could still be observed 22 months later. The present study illustrates the usefulness of the multi-biomarker approach in the detection of biological effects of pollution in this region of the Baltic Sea.  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