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   90篇
  免费   6篇
  国内免费   1篇
测绘学   1篇
大气科学   15篇
地球物理   11篇
地质学   28篇
海洋学   6篇
天文学   20篇
自然地理   16篇
  2018年   1篇
  2017年   3篇
  2016年   3篇
  2015年   3篇
  2014年   4篇
  2013年   2篇
  2012年   2篇
  2011年   3篇
  2010年   4篇
  2009年   5篇
  2008年   3篇
  2007年   5篇
  2006年   5篇
  2005年   5篇
  2004年   11篇
  2003年   4篇
  2002年   5篇
  2001年   2篇
  2000年   6篇
  1998年   2篇
  1997年   4篇
  1996年   3篇
  1995年   1篇
  1993年   2篇
  1991年   2篇
  1990年   1篇
  1988年   1篇
  1987年   1篇
  1984年   1篇
  1980年   1篇
  1973年   1篇
  1972年   1篇
排序方式: 共有97条查询结果,搜索用时 31 毫秒
71.
72.
The geochemical baselines of nickel and chromium were studied from the data produced by the Barents Ecogeochemistry project, a large international regional geochemical mapping exercise. The project surveyed major and trace element distributions in stream water, organic and mineralogically-modified soil horizons, and terrestrial moss in the northwestern part of Russia and in Finland. Other materials were collected during the pilot phase and later from thirty special sites. The results on respective materials by XRF, ICP-MS and ICP-AES showed that both geological and anthropogenic factors have an influence on the geochemical baseline concentrations of Ni and Cr in organic soil and stream water. The main explanation of the observed distribution patterns in terrestrial moss is human activity, but geological factors can also affect the baselines. The variation of geochemical baselines in the mineral-rich soil horizon depends only on variations in bedrock. The mineralogy of samples mainly controls the leachability properties of soil samples.  相似文献   
73.
74.
Hair nickel, mercury, cadmium, lead and chromium concentrations were measured from still-born ringed seal pups and from other ringed seal groups from Lake Saimaa in Finland. Nickel concentration was significantly higher in the hair samples of still-born pups as compared to live-born pups and to adult seals. There was assumed to be some connection between the stillbirth of the pups and nickel concentration of the hair. Mercury concentration of the natal hair of pups was significantly higher than the mercury concentration of the first adult hair but no clear connection between stillbirth and mercury pollution was observed. No differences were observed in cadmium, lead and chromium concentrations of the hair of still-born and other ringed seal groups.  相似文献   
75.
Stream water composition, measured weekly for 8–9 months in 1994 in three arctic catchments on and around the Kola Peninsula (Russia, Finland and Norway), is presented in the form of time-series. In all three catchments, snowmelt causes a major dilution of the stream water, as reflected by marked dips in electrical conductance. In the most polluted catchment (C2), the snowmelt flood (the major hydrological event at these latitudes) is reflected in the stream water by a pH dip and a pulse in technogenic heavy metals (Cu, Ni, etc.), Al and S. This results from melting of the snow laden with heavy metals and sulphate, and from leaching of the topsoil layer. In the most pristine catchment (C8), snowmelt causes no heavy metal pulse (remote location) but yields an increase in stream water Al (acidic lithology/overburden). In the intermediate catchment (C5), very subdued heavy metal and S increases are noticeable in the stream water, whilst its pH increases steadily until summer (basic lithology). Some elements (Cl, S) may be mobilised out of the snowpack before its complete thawing and reach the stream 1–2 weeks ahead of the heavy metals. The substrate (soil, overburden and bedrock) of a catchment controls to a large extent its ability to buffer acid inputs.  相似文献   
76.
The pH, electrical conductance and concentration of six anions and 33 cations were determined in stream waters sampled in 1994 from eight arctic catchments on and adjacent to the Kola Peninsula (Russia, Finland and Norway). The catchments are located at various distances (5–300 km) from the major industrial emissions centres of Monchegorsk, Nikel and Zapoljarniy in Russia. The source of the elements can be (1) natural, marine (sea spray), (2) natural, geogenic (blowing soil/dust, till, bedrock), and/or (3) anthropogenic, industrial (emissions from smelters, dust from mining, etc.), each source showing a distinct signature. The median concentration of many contaminants can vary by up to three orders of magnitude from polluted to remote locations, and the concentration ranges observed in different catchments often do not overlap. This implies that contamination falls sharply with distance from source, but is quite profound and lasting close to the emission centres. Elevated trace metal contents in the most polluted streams indicates that deposited contaminants are transferred to the aquatic ecosystem, and eventually can reach the ocean.  相似文献   
77.
Laboratory measurements of soil samples are necessary to assess the effect of mineralogy, grain size distribution, moisture content, and electrolyte composition on the resistivity spectrum of soil material. Laboratory results are also required for the interpretation of field data. Induced polarization phenomena in glacial soils are poorly understood and so far no convenient laboratory techniques are available for its measurement. Coarse grain size and the need to measure unsaturated samples and to monitor the homogeneity of the sample require a sample holder–electrode construction that differs from those presented in Clay mineral Studies. This study presents a spectral induced polarization laboratory system that is suitable for measuring fine- and coarse-grained and both saturated and unsaturated soil samples. The noise caused by the electrode–electrolyte interface is studied in detail. It is shown that easy-to-use platinum or acid-free steel potential electrodes are convenient over a broad frequency band ranging from 0.016Hz up to more than 1000 Hz. The laboratory experiments and comparisons between laboratory and field results also indicate that sampling and sample packing procedures have only a minor influence on the phase spectrum of glacial soils.  相似文献   
78.
GHG mitigation of agricultural peatlands requires coherent policies   总被引:1,自引:0,他引:1  
As soon as peat soil is drained for agricultural production, the peat starts to degrade, which causes emissions to the atmosphere. In countries with large peatland areas, the GHG mitigation potential related to management of these soils is often estimated as the highest amongst the measures available in agriculture. Although the facts are well known, the policies leading to diminished emissions are often difficult to implement. We have analysed the reasons why the mitigation potential is not fully utilized and what could be done better in national implementation of climate policies. Four cases are used to illustrate the necessary steps to reach mitigation targets: determining the amount and properties of peat soils, estimating the potential, costs and feasibility of the mitigation measures, and selecting and implementing the best measures. A common feature for all of the cases was that national and international climate policies have increased the public interest in GHG emissions from peat soils and increased the pressure for mitigation. Basically the same factors restrict the implementation of mitigation measures in all countries with significant peat soil areas. The most important of these is lack of policy coherence, e.g. ignoring climate policies when planning land use or agricultural policies. We conclude that GHG mitigation is achieved only if other policies, especially national regulations and strategies, are in line with climate policies.

Policy relevance

Agricultural peat soils could be used to help reach GHG mitigation goals in many countries, but the full potential of mitigation of peat soils is not used. Although peatland cultivation inevitably leads to loss of the whole peat layer and high emissions, there are few incentives or regulation to effectively minimize these losses. This article discusses the possibilities to reduce GHG emissions from agricultural peat soils, with specific emphasis on the barriers of implementing mitigation measures nationally. The lessons learned from the selected cases emphasize the role of all policy makers and their cooperation in planning coherent policies for achieving the goals determined by climate policies.  相似文献   

79.
In the southern coastal area of Finland, many studies exist on shore displacements related to the higher Ancylus Lake and Litorina Sea altitudes. However, the late- Holocene shore displacement history is much less known and the shore displacement models are based on interpolations. Kruunuvuorenlampi, a small lake located at an altitude of 8.6 m a.s.l., was studied to test the reliability of the interpolated models. The cores revealed an unusual bottom lithostratigraphy, with a coarse gravel and sand layer sandwiched between the lower marine clays and upper shallow-water clay-gyttja. Analysis of diatoms, pollen and loss-on-ignition, together with radiocarbon datings, were carried out to determine and date the isolation event of the lake. The results show that the lake was isolated ca. 2400 14C years BP and that the coarse grained layer was deposited prior to the isolation. The reconstruction of the emergence of the lake basin area suggests that the coarse grained layer originated from strong wave erosion of the shores before the isolation. This interpretation is supported by the presence of a wave-washed boulder belt on the NE slope of the basin. The isolation of Kruunuvuorenlampi lies exactly on the interpolated shore displacement model of the 30 m Litorina isobase. This placement suggests that no significant transgressions took place between the Litorina transgression and the isolation of Kruunuvuorenlampi.  相似文献   
80.
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