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   63篇
  免费   5篇
大气科学   15篇
地球物理   18篇
地质学   22篇
海洋学   5篇
天文学   6篇
自然地理   2篇
  2021年   2篇
  2020年   2篇
  2019年   1篇
  2018年   5篇
  2017年   1篇
  2016年   4篇
  2015年   4篇
  2014年   4篇
  2013年   8篇
  2012年   3篇
  2011年   3篇
  2010年   1篇
  2009年   1篇
  2008年   8篇
  2007年   6篇
  2006年   4篇
  2004年   1篇
  2003年   1篇
  2002年   2篇
  2001年   1篇
  1999年   1篇
  1997年   1篇
  1991年   1篇
  1987年   2篇
  1982年   1篇
排序方式: 共有68条查询结果,搜索用时 109 毫秒
41.
This paper presents a comparison of persistent scatterer interferometry (PSI) monitoring results with in situ displacement measurements at the November 1990 landslide at the Bor?t uranium mill tailing deposit site after heavy rain. Although the landslide did not directly endanger people, site remediation works were undertaken due to the subsequent environmental problems. Additionally, in situ monitoring with benchmarks was established in order to detect the ground motion of the landslide body. PSI campaigning in the ?kofjelo?ko-Cerkljansko area, where the uranium mill tailing is situated, performed for the purpose of measuring displacements of natural targets near the active landslide area, also detected displacements, most probably indicating a creeping process. When comparing the pre- and post-remediation velocities at the benchmarks located on the landslide with persistent scatterers (PSs) located near the landslide, the rates could be regarded as background. The results show that the remediation works in the form of a drainage tunnel were very effective as post-remediation velocities at the landslide closer to the PSs resembled the velocities of the PSs, while the velocities of the landslide mass above the drainage tunnel slowed down, even to below the background velocities. The high correlation values between the movements of the benchmarks and the PSs also confirm that the remediation works were effective as the fluctuations in the displacement values of the landslide were very similar to those of the PSs. Nevertheless, although there are several limitations in comparing the two different datasets, the PSI technique can be complementary to conventional in situ methods.  相似文献   
42.
The water balance of wetlands plays an integral role in their function. Developments adjacent to wetlands can affect their water balance through impacts on groundwater flow and increased discharge in the area, and they can cause lowering of the wetland water table. A 430 km2 area was selected for groundwater modelling to asses the effect of underground mining on the water balance of wetlands in north-eastern Estonia. A nature conservation area (encompassing Selisoo bog) is within 3 km of an underground oil-shale mine. Two future mining scenarios with different areal extents of mining were modeled and compared to the present situation. Results show that the vertical hydraulic conductivity of the subsurface is of critical importance to potential wetland dewatering as a result of mining. Significant impact on the Selisoo bog water balance will be caused by the approaching mine but there will be only minor additional impacts from mining directly below the bog. The major impact will arise before that stage, when the underground mine extension reaches the border of the nature conservation area; since the restriction of activities in this area relates to the ground surface, the conservation area’s border is not sufficiently protective in relation to underground development.  相似文献   
43.
Abstract— A new olivine‐pigeonite ureilite containing abundant diamonds and graphite was found in the United Arab Emirates. This is the first report of a meteorite in this country. The sample is heavily altered, of medium shock level, and has a total weight of 155 g. Bulk rock, olivine (Fo79.8–81.8) and pyroxene (En73.9–75.2, Fs15.5–16.9, Wo8.8–9.5) compositions are typical of ureilites. Olivine rims are reduced with Fo increasing up to Fo96.1–96.8. Metal in these rims is completely altered to Fehydroxide during terrestrial weathering. We studied diamond and graphite using micro‐Raman and in situ synchrotron X‐ray diffraction. The main diamond Raman band (LO = TO mode at ?1332 cm?1) is broadened when compared to well‐ordered diamond single crystals. Full widths at half maximum (FWHM) values scatter around 7 cm?1. These values resemble FWHM values obtained from chemical vapor deposition (CVD) diamond. In situ XRD measurements show that diamonds have large grain sizes, up to >5 μm. Some of the graphite measured is compressed graphite. We explore the possibilities of CVD versus impact shock origin of diamonds and conclude that a shock origin is much more plausible. The broadening of the Raman bands might be explained by prolonged shock pressure resulting in a transitional Raman signal between experimentally shock‐produced and natural diamonds.  相似文献   
44.
This paper presents the effect of land-use changes on land degradation by utilization of remote sensing methods and the Gavrilovi? erosion potential method, due to surface mining activities in the period 2001–2011. Studied area includes the zone of influence of the Rudarski basen Kolubara, which covers the exploitation area of the Kolubara coal basin in the Republic of Serbia. The analysis is based on the processing of Landsat 5 satellite images from 2001 and 2011. In the analysis of satellite images, the supervised classification method was used. The results suggest that the observed spatial–temporal area is exposed to erosion as a result of land-use changes. Preliminary conclusion is that the dominant anthropogenic factor, responsible for changes in land use, is pronounced through the mining activity, industrialization, construction as well as agricultural activities. Very small changes in land use that occurred in the period 2001–2010 have led to relatively small amount of change from the aspect of land degradation. Also, due to the planned exploitation of the mine which included into account the sustainability of ecosystems, primarily through appropriate conservation measures, RB Kolubara is not in danger of a possible erosion processes that could undermine the stability of the basin.  相似文献   
45.
We examine the performance of several methods to estimate meteorological inputs for modelling dispersion in urban areas during convective conditions. Sensible heat flux, surface friction velocity and turbulent velocities are estimated from measurements of mean wind speed and the standard deviation of temperature fluctuations at a single level on a tower at two suburban sites and at one urban site in Riverside, California. These estimates are compared with observations made at these sites during a field study conducted in 2007. The sensible heat flux is overestimated in the urban area, while it is underestimated at a suburban site when temperature fluctuations are used in the free convection formulation to estimate heat flux. The bias in heat flux estimates can be reduced through a correction that depends on stability. It turns out that the bias in heat flux estimates has a minor effect on the prediction of surface friction velocity and turbulent velocities. Estimates of sensible heat flux, surface friction velocity and turbulent velocities are sensitive to estimates of aerodynamic roughness length, and we suggest estimating the aerodynamic roughness length through detailed micrometeorological measurements made during a limited field study. An examination of the impact of the uncertainty in estimating surface micrometeorology on concentrations indicates that, at small distances from a surface release, ground-level concentrations computed using estimates of heat flux and surface friction compare well with the those based on observed values: the bias is small and the 95% confidence interval of the ratio of the two concentrations is 1.7. However, at distances much larger than the Obukhov length, this confidence interval is close to 2.3 because errors in both friction velocity and heat flux affect plume spread. Finally, we show that using measurements of temperature fluctuations in estimating heat flux is an improvement on that based on the surface energy balance, even when net radiation measurements are available.  相似文献   
46.
The human mediated transfer of harmful organisms via shipping, specifically via ballast water transport, leading to the loss of biodiversity, alteration of ecosystems, negative impacts on human health and in some regions economic loss, has raised considerable attention especially in the last decade. Ballast water sampling is very important for biological invasions risk management. The complexity of ballast water sampling is a result of both the variety of organism diversity and behaviour, as well as ship design including availability of ballast water sampling points. Furthermore, ballast water sampling methodology is influenced by the objectives of the sampling study. In the course of research conducted in Slovenia, new sampling equipment for ships' ballast water was developed and tested. In this paper new ballast water sampling methods and equipment together with practical shipboard testing results are presented.  相似文献   
47.
In this work, the charging state of atmospheric nanoparticles was estimated through simultaneous measurements of aerosol size distribution and air ions mobility distribution with the aim to elucidate the formation mechanisms of atmospheric aerosols. The measurements were performed as a part of the QUEST 2 campaign at a boreal forest station in Finland. The overlapping part of the measurement ranges of the particle size spectrometers and air ion mobility spectrometers in the mass diameter interval of 2.6–40 nm was used to assess the percentage of charged particles (charging probability). This parameter was obtained as the slope of the linear regression line on the scatterplot of the measured concentrations of total (neutral + charged) and charged particles for the same diameter interval. Charging probabilities as a function of particle diameter were calculated for different days and were compared with the steady state charging probabilities of the particles in the bipolar ion atmosphere. For the smallest particles detectable by the particle size spectrometers (2.6–5 nm), the high percentages of negatively charged particles were found during the nanometer particle concentration bursts. These values considerably exceeded the values for the steady charging state and it was concluded that negative cluster ions preferably act as condensation nuclei. This effect was found to be the highest in the case of comparatively weak nucleation bursts of nanoparticles, when the rate of the homogeneous nucleation and the concentration of freshly nucleated particles were low. The nucleation burst days were classified according to the concentration of the generated smallest detectable new particles (weak and strong bursts). Approximately the same classification was obtained based on the charge asymmetry on particles with respect to the charge sign (polarity). The probabilities of negative and positive charge on the particles with the diameter of 5–20 nm were found to be nearly equal and they approximately agree with the values corresponding to the steady state charge distribution for negative particles known from lab experiments. It means that the steady charging state was reached during the growing time of particles up to 5 nm. The natural charging state of particles with a diameter between 2.5 and 4.5 nm was estimated by means of a special DMPS setup. Results were found to be in good correlation with the data by the particle size spectrometers and air ion mobility spectrometers.  相似文献   
48.
A petrological, organic geochemical and geochemical study was performed on coal samples from the Soko Mine, Soko Banja basin, Serbia. Ten coal and two carbonaceous clay samples were collected from fresh, working faces in the underground brown coal mine from different parts of the main coal seam. The Lower Miocene, low-rank coal of the Soko Mine is a typical humic coal with huminite concentrations of up to 76.2 vol.%, liptinite less than 14 vol.% and inertinite less than 11 vol.%. Ulminite is the most abundant maceral with variable amounts of densinite and clay minerals. Sporinite and resinite are the most common macerals of the liptinite group. Inertodetrinite is the most abundant maceral of the inertinite group. The mineral-bituminous groundmass identified in some coal samples, and carbonaceous marly clay, indicate sub-aquatic origin and strong bacterial decomposition. The mean random huminite reflectance (ulminite B) for the main coal seam is 0.40 ± 0.05% Rr, which is typical for an immature to early mature stage of organic matter.The extract yields from the coal of the Soko Banja basin ranges from 9413 to 14,096 ppm, in which alkanes constituted 1.0–20.1%, aromatics 1.3–14.7%, asphaltenes 28.1–76.2% and resins 20.2–43.5%. The saturated hydrocarbon fractions included n-C15 to n-C32, with an odd carbon number that predominate in almost all the samples. The contents of n-C27 and n-C29 alkanes are extremely high in some samples, as a contribution of epicuticular waxes from higher plants. Acyclic isoprenoid hydrocarbons are minor constituents in the aliphatic fraction, and the pristane/phytane (Pr/Ph) ratio varies between 0.56 and 3.13, which implies anaerobic to oxic conditions during sedimentation. The most abundant diterpanes were abietane, dehydroabietane and 16α(H)-phyllocladane. In samples from the upper part of the coal seam, diterpanes are the dominant constituents of the alkane fraction. Polycyclic alkanes of the triterpane type are important constituents of alkane fractions. The occurrence of ββ- and αβ-type hopanes from C27 to C31, but without C28, is typical for the Soko Banja coals.The major and trace elements in the coal were analysed using X-ray fluorescence (XRF), and inductively coupled plasma-mass spectrometry (ICP-MS). In comparison with world lignites, using the geometric mean value, the coal from the Soko Banja Basin has a high content of strontium (306.953 mg/kg). Higher values than the world lignites were obtained for Mo (3.614 mg/kg), Ni (8.119 mg/kg), Se (0.884 mg/kg), U (2.642 mg/kg) and W (0.148 mg/kg). Correlation analysis shows inorganic affinity for almost all the major and trace elements, except for S, which has an organic affinity.  相似文献   
49.
50.
A method for sampling estuarine waters and seawater by scuba diving is described. Samples taken from the Krka River Estuary on the eastern Adriatic coast were analysed for mercury content using cold vapour atomic absorption spectrometry (CVAAS). Mercury levels as low as 1 ng dm−3 were determined and these are among the lowest values reported to date. A simple contamination free procedure for the preconditioning of sample containers in the sea was applied. Sampling of water by divers is particularly useful when the intermediate layer in an estuary has to be identified and sampled, as well as for obtaining detailed vertical concentration profiles for mercury and other trace elements.  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