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41.
Increased Carbon Sink in Temperate and Boreal Forests   总被引:6,自引:0,他引:6  
An intense search is under way to identify the `missing sink' in the world carbon budget of perhaps 2 Pg year–1 (petagrams, or billiontonnes) of carbon, but its location and mechanism have proved elusive. Here we use a new forest inventory data set to estimate the carbon sink and the carbon pool of woody biomass in 55 countries that account for nearly all temperate or boreal forests and approximately half the world's total forest area. In each country there was a net accumulation of biomass; together, the carbon sink of woody biomass was 0.88 Pg year–1 during the 1990swith estimated uncertainty from 0.71 to 1.1 Pg year–1. Thisestimate, already about half of the missing sink, would probably be even larger if carbon accumulation in soil and detritus were also accounted for, but we are unable to quantify that additional sink. The sink is twice that estimated for the woody biomass of these forests a decade ago due to higher estimates for tree growth throughout the region and decreased timber harvests in Russia. In contrast, the new data indicate a carbon pool that is smaller than earlier estimates because of improved data for Russia and Australia.  相似文献   
42.
The Finnish coastal fishery of Atlantic salmon (Salmo salar) in the northern Baltic Sea is regulated using multi-annual, pre-fixed, opening dates of harvests that aim to enhance spawning escapement of early migrating wild salmon. Such an inflexible management regime does not set regulations that track varying run sizes of salmon. We introduce an array of computational intelligence techniques to estimate and forecast coastal run size and escapement of salmon into three spawning rivers in the northern Baltic Sea. Our results indicated that the present management pattern, driven largely by regional fisheries policy, contrasts greatly with a “run-size driven” (i.e. abundance-based) management approach. Introducing run-size driven management, i.e. setting regulations annually by tracking preseason forecasts, would better ensure adequate escapement and at the same time allow the maintenance of coastal catch at sustainable level. Setting regulations annually would allow effective harvesting in years when the run is high, and would effectively restrict harvests when the run is low.  相似文献   
43.
The lithostratigraphy of pre‐Late Weichselian sediments and OSL‐dating results from four localities in the Suupohja area of western Finland, adjacent to the centre of the former Scandinavian glaciations, are presented. The studied sections expose glacifluvial, quiet‐water, littoral and aeolian deposits overlain by Middle and/or Late Weichselian tills. Litho‐ and biostratigraphical results together with seven OSL age determinations on buried glacifluvial sediment at Rävåsen (94±15 ka) and on till‐covered littoral and aeolian sediments at Risåsen, Rävåsen, Jätinmäki and Kiviharju (79±10 to 54±8 ka), accompanied by previous datings and interpretations, suggest that the glacifluvial sediments at Risåsen were deposited at the end of the Saalian Stage (MIS 6) and those at Risåsen were deposited possibly in the Early Weichselian Substage (MIS 5d?). Palaeosol horizons and ice‐wedge casts together with the dated littoral and aeolian sediments between the Harrinkangas Formation (Saalian) and the overlying till(s) indicate that western Finland was ice‐free during most of the Weichselian time. Littoral deposits, dated to the Middle Weichselian (MIS 4–3), occur at altitudes of 50–90 m a.s.l., which indicates significant glacio‐isostatic depression. The depression resulted from expansion of the ice sheet in the west of Finland at that time.  相似文献   
44.
45.
Recent efforts to project vegetationresponses to climatic warming have emphasized thetight linkages between climate and vegetationdistribution. Here we provide several examplesindicating that the direct effects of climatic warmingon boreal vegetation can be qualitatively differentthan the indirect effects mediated by climaticresponses of herbivores. These herbivore-mediatedvegetation responses to climatic warming will likelyvary regionally. In southern Fennoscandia, we projectthat the climatically induced changes in animalpopulations should enhance the density of spruce atthe expense of pine and broadleafed trees. In northernFennoscandia we project reduced herbivory onbroadleafed trees and increased herbivory on pine,leading to an increase in broadleafed trees and spruceand a reduction in pine. Climatic warming in interiorAlaska may reduce herbivory on broadleafed trees andincrease herbivory on evergreen spruce, thusreinforcing the impact of increased fire frequency.  相似文献   
46.
Pekka Tuisku 《Lithos》1991,27(4):279-300
The amphibolite facies, iron-rich metapelites (garnet-staurolite mica schists) of the early Proterozoic Puolankajärvi Formation are intercalated with metamorphosed basic rocks which vary from iron-rich amphibolites to magnesium-rich layered sills and serpentinites. Garnet-cummingtonite-hornblende assemblages are abundant at the contacts of the metapelites with amphibolites, while garnet-chlorite, garnet-gedrite±chlorite, garnet-gedrite-cummingtonite±chlorite and chlorite-cummingtonite-hornblende assemblages occur at their contacts with the layered magnesium-rich sill.

The bulk composition profiles of these contacts, normalised with respect to chromium and/or aluminium, show conspicuous enrichment in Fe, S, Ga and Co and depletion in Si, K, Ba and Rb. Some elements (e.g. Mg, Mn, Ni, P, Zr and Hf) are depleted or enriched in only small amounts, while others (e.g. Ca, Na, Sr and the rare earth elements) may show both enrichment and depletion in the course of a profile.

Although early infiltration during the hydration of metabasites and tectonic reworking may have produced some interaction of the basites with the pelites, the major metasomatic event is considered to have bile elements. The composition of the metapelites, for example, approached that of magnesium-rich ultramafites through potassium depletion, while the ultramafites became markedly enriched in iron. To conserve the volume, silica was depleted from the contact which underwent iron enrichment.  相似文献   

47.
A battery of biochemical biomarkers and the SigmaPCB concentration in adult female perch (Perca fluviatilis) verified an aquatic pollution gradient with the city of Stockholm (Sweden) as a point source of anthropogenic substances. The investigation included both an upstream gradient, 46 km westwards through Lake M?laren, and a downstream gradient, 84 km eastwards through the Stockholm archipelago. Besides the main gradient from Stockholm, there were strong indications of pollution coming from the Baltic Sea. The results indicated a severe pollution situation in central Stockholm, with poor health status of the perch, characterised by increased specific EROD activity in the liver, increased liver EROD somatic index, decreased AChE activity in the muscle, increased amount of DNA adducts in the liver, and a high concentration of biliary 1-pyrenol. In addition, laboratory exposure to common EROD inducers elicited an abnormal response, suggestive of chronic intoxication.  相似文献   
48.
Esker aquifers are common groundwater bodies in Europe. Management of these aquifers should take account of the sustainability of groundwater-dependent ecosystems and land use in an integrated way. An unconfined esker aquifer in northern Finland was modelled with MODFLOW to determine how groundwater resources are impacted by the surrounding peatland drainage scheme and to simulate scenarios for possible drainage restoration. The impacts of groundwater abstraction and climate change were also simulated. A calibration-constrained Monte Carlo method was used to provide information on the uncertainties associated with model predictions. The results suggest that peatland drainage in the vicinity of eskers can have a significant role in lowering the water table, even though climate variability may mask these impacts. Drainage restoration by filling the ditches might have positive impacts on the aquifer water levels. Comparison of water-table changes caused by peatland drainage with the changes brought by water abstraction and climate variability helped to quantify impacts of different land-use scenarios and facilitated discussion with the local stakeholders. Based on this study, more attention should be devoted to peatland drainage schemes in integrated groundwater management of esker aquifers.  相似文献   
49.
Energetic particle precipitation couples the solar wind to the Earth's atmosphere and indirectly to Earth's climate. Ionisation and dissociation increases, due to particle precipitation, create odd nitrogen (NOx) and odd hydrogen (HOX) in the upper atmosphere, which can affect ozone chemistry. The long-lived NOx can be transported downwards into the stratosphere, particularly during the polar winter. Thus, the impact of NOx is determined by both the initial ionisation production, which is a function of the particle flux and energy spectrum, as well as transport rates. In this paper, we use the Sodankylä Ion and Neurtal Chemistry (SIC) model to simulate the production of NOx from examples of the most representative particle flux and energy spectra available today of solar proton events (SPE), auroral energy electrons, and relativistic electron precipitation (REP). Large SPEs are found to produce higher initial NOx concentrations than long-lived REP events, which themselves produce higher initial NOx levels than auroral electron precipitation. Only REP microburst events were found to be insignificant in terms of generating NOx. We show that the Global Ozone Monitoring by Occultation of Stars (GOMOS) observations from the Arctic winter 2003–2004 are consistent with NOx generation by a combination of SPE, auroral altitude precipitation, and long-lived REP events.  相似文献   
50.
We have studied the structure of chaos in three-body dynamics using the concept of intermittency, implying that violent states of a system alternate in time with quasi-regular states producing together a non-stationary and evolving pattern of unpredictable behaviour. Computer simulations are produced to demonstrate explicitly sporadic short violent bursts in quasi-regular hierarchical states of the systems. This is seen both in orbits and in the long time series generated by the system. The time series prove to be similar in shape to what is observed in various physical experiments with laboratory chaotic systems when they reveal the so-called type-III intermittency. The new effective methods of time series analysis enable us to discover a strange attractor with a fractal dimension slightly above 2. This shows that three-body dynamics has the same intrinsic qualitative structure and quantitative measure of chaos as the widely known chaotic system, the Lorenz attractor.  相似文献   
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