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31.
Lunar breccias of low metamorphic grade offer a unique opportunity to investigate the magnetic properties of dispersed fine grained iron. These rocks exhibit a pronounced time dependent magnetization whose acquisition and decay are well explained by Ne´el's single domain theory. The effect is due to iron grains in the range of 120A?to 150A?in diameter which covers the transition from superparamagnetic to stable single domain behavior. 相似文献
32.
Dendrochronology for the last 1400 years in eastern Tibet 总被引:11,自引:0,他引:11
Achim Bräuning 《GeoJournal》1994,34(1):75-95
Twentyfour tree-ring chronologies of various tree-species(Picea, Abies, Larix, Juniperus) from sites near the upper timberline in eastern Tibet were established, the longest one dating back to 620 A.D. A new classification of pointer intervals is presented, distinguishing between different kinds of signatures in a tree-ring series and amount of growth change in relation to the previous year. The various types of signatures can be related to meteorological events like cold winters and summers, summer drought or to recreation reactions after years of reduced growth. The distribution pattern and type of pointer intervals combined with ring width variation enables the detection of periods of favourable or unfavourable growth conditions with regard to climate history. Based on far-distance correlations and signature analysis regions of similar tree-growth are mapped out. 相似文献
33.
Dr. Achim Hirschberg Helmut G. F. Winkler 《Contributions to Mineralogy and Petrology》1968,18(1):17-42
The stability relations between cordierite and almandite in rocks, having a composition of CaO poor argillaceous rocks, were experimentally investigated. The starting material consisted of a mixture of chlorite, muscovite, and quartz. Systems with widely varying Fe2+/Fe2++Mg ratios were investigated by using two different chlorites, thuringite or ripidolite, in the starting mixture. Cordierite is formed according to the following reaction: $${\text{Chlorite + muscovite + quartz}} \rightleftharpoons {\text{cordierite + biotite + Al}}_{\text{2}} {\text{SiO}}_{\text{5}} + {\text{H}}_{\text{2}} {\text{O}}$$ . At low pressures this reaction characterizes the facies boundary between the albite-epidotehornfels facies and the hornblende-hornfels facies, at medium pressures the beginning of the cordierite-amphibolite facies. Experiments were carried out reversibly and gave the following equilibrium data: 505±10°C at 500 bars H2O pressure, 513±10°C at 1000 bars H2O pressure, 527±10°C at 2000 bars H2O pressure, and 557±10°C at 4000 bars H2O pressure. These equilibrium data are valid for the Fe-rich starting material, using thuringite as the chlorite, as well as for the Mg-rich starting mixture with ripidolite. At 6000 bars the equilibrium temperature for the Mg-rich mixture is 587±10°C. In the Fe-rich mixture almandite was formed instead of cordierite at 6000 bars. The following reaction was observed: $${\text{Thuringite + muscovite + quartz}} \rightleftharpoons {\text{almandite + biotite + Al}}_{\text{2}} {\text{SiO}}_{\text{5}} {\text{ + H}}_{\text{2}} {\text{O}}$$ . Experiments with the Fe-rich mixture, containing Fe2+/Fe2++Mg in the ratio 8∶10, yielded three stability fields in a P,T-diagram (Fig.1):
- Above 600°C/5.25 kb and 700°C/6.5 kb almandite+biotite+Al2SiO5 coexist stably, cordierite being unstable.
- The field, in which almandite, biotite and Al2SiO5 are stable together with cordierite, is restricted by two curves, passing through the following points:
- 625°C/5.5 kb and 700°C/6.5 kb,
- 625°C/5.5 kb and 700°C/4.0 kb.
- At conditions below curves 1 and 2b, cordierite, biotite, and Al2SiO5 are formed, but no garnet.
34.
35.
36.
Tree ring inferred summer temperature variations over the last millennium in western Himalaya, India 总被引:1,自引:1,他引:0
We report the first millennium-long reconstruction of mean summer (May–June–July–August) temperature extending back to AD 940 derived from tree-ring width data of Himalayan pencil juniper (Juniperus polycarpos C. Koch) from the monsoon-shadow zone in the western Himalaya, India. Centennial-scale variations in the reconstruction reveal periods of protracted warmth encompassing the 11–15th centuries. A decreasing trend in mean summer temperature occurred since the 15th century with the 18–19th centuries being the coldest interval of the last millennium, coinciding with the expansion of glaciers in the western Himalaya. Since the late 19th century summer temperatures increased again. However, current warming may be underestimated due to a weakening in tree growth-temperature relationship noticeable in the latter part of the 20th century. Mean summer temperature over the western Himalaya shows a positive correlation with summer monsoon intensity over north central India. Low-frequency variations in mean summer temperature anomalies over northwestern India are consistent with tree-ring inferred aridity in western North America. These far-distance linkages reported here for the first time underscore the utility of long-term temperature records from the western Himalayan region in understanding global-scale climatic patterns. 相似文献
37.
Achim G. Reisdorf Andreas Wetzel Rudolf Schlatter Peter Jordan 《Swiss Journal of Geoscience》2011,104(1):97-146
The deposits of the Early Jurassic in northern Switzerland accumulated in the relatively slowly subsiding transition zone
between the southwestern part of the Swabian basin and the eastern part of the Paris basin under fully marine conditions.
Terrigenous fine-grained deposits dominate, but calcarenitic and phosphorit-rich strata are intercalated. The total thickness
varies between 25 and 50 m. In the eastern and central parts of N Switzerland, sediments Sinemurian in age constitute about
90% of the total thickness. To the West, however, in the Mont Terri area, Pliensbachian and Toarcian deposits form 70% of
the total thickness. Stratigraphic gaps occur on a local to regional scale throughout N Switzerland. Such hiatus comprise
a subzone to a stage in time. With respect to lithology and fossil content, the Early Jurassic deposits in northern Switzerland
are similar to those in SW Germany. Nonetheless, an exact stratigraphic correlation is hardly possible, particulary in the
southern and southwestern Folded Jura where distinct facies changes occur over short distances. Revised existing and new litho-
and biostratigraphic data form the base to refine the stratigraphic subdivision of the deposits that have been informally
called “Lias”. The name Staffelegg Formation is suggested and defined as the mapping unit for the Early Jurassic. The Staffelegg
Formation is introduced for Early Jurassic sediments in northern Switzerland between the Doubs River and Mt. Weissenstein
in the west and the Randen Hills located north of the city of Schaffhausen in the east. The Staffelegg Formation starts within
the Planorbis zone of the Hettangian. The upper boundary to the overlying Aalenian Opalinus-Ton is diachronous. The lithostratigraphic
names previously in use have been replaced by new ones, in accordance within the rules of lithostratigraphic nomenclature.
The Staffelegg Formation comprises 11 members and 9 beds. Several of these beds are important correlation horizons in terms
of allostratigraphy. Some of them correspond to strata or erosional unconformities encountered in the Swabian realm, some
of them can be correlated with strata in the Paris basin. The facies transition to the Paris basin is expressed by introduction
of a corresponding lithostratigraphic unit. 相似文献
38.
Achim A. Beylich Else Kolstrup Tage Thyrsted Niklas Linde Laust B. Pedersen Lars Dynesius 《Geomorphology》2004,57(3-4):303-319
In Latnjavagge, a 9-km2 drainage basin with homogeneous lithology in periglacial northern Swedish Lapland, water balance, water chemistry and radio magnetotelluric geophysical investigations along selected profiles were integrated with assessment of regolith thickness as well as of ground frost conditions within the basin. In combination with direct field observations, the geophysical profiles demonstrated presence of relatively thin regolith in most of the investigated area, yet in some parts, the bedrock was located deeper and locally was not detected at 40-m depth. TDS values of the water were generally very low. The areas that contributed with the lowest ion concentrations were cold and had a thin regolith, whereas there were higher concentrations in water that drained radiation exposed slopes with earlier thaw and thicker regolith. The low resistivities found along the profiles in the geophysical investigations in combination with the relatively higher TDS values found in related runoff and subsurface water samples showed that larger volumes of ice-rich frozen ground were not found along the investigated profiles in late August. 相似文献
39.
Qin-Bo Cheng Christian Reinhardt-Imjela Xi Chen Achim Schulte Xiang Ji Fu-Lin Li 《水文科学杂志》2013,58(8):1460-1476
ABSTRACTA new physics-based rainfall–runoff method of the Soil and Water Assessment Tool (SWAT) was developed, which integrates a water balance (WB) approach with the variable source area (WB-VSA). This approach was further compared with four methods—soil-water-dependent curve number (CN-Soil), evaporation-dependent curve number (CN-ET), Green and Ampt equation (G&A) and WB—in a monsoonal watershed, Eastern China. The regional sensitivity analysis shows that volumetric efficiency coefficient (VE) with river discharges is sensitive to the most parameters of all approaches. The results of model calibration against VE demonstrate that WB-VSA is the most accurate owing to its reflection of the spatial variation of runoff generation as affected by topography and soil properties. Other methods can also mimic baseflow well, but the G&A and CN-ET simulate floods much worse than the saturation excess runoff approaches (WB-VSA, WB and CN-Soil). Meanwhile, CN-Soil as an empirical method fails to simulate groundwater levels. By contrast, WB-VSA captures them best.
Editor M.C. Acreman; Associate editor S. Kanae 相似文献
40.
Sebastian B. Hammerschmidt Earl E. Davis Andre Hüpers Achim Kopf 《Geo-Marine Letters》2013,33(5):405-418
Along the Nankai Trough megasplay fault off SE Japan, the effect of fluid migration on subduction-related seismogenesis and tsunamigenesis remains unresolved. To investigate the existence and role of fluid flow, a SmartPlug borehole observatory was installed at Site C0010 of the Integrated Ocean Drilling Program NanTroSEIZE Kumano transect, where a shallow branch of the fault was intersected and in situ fluid pressure monitored from August 2009 to November 2010. The tidal signal in the formation showed no phase shift relative to seafloor loading. The attenuation of 0.73 reflects the loading efficiency accurately, and enabled calculation of a formation compressibility of 1.0×10–9 Pa–1 and a hydraulic diffusivity (HD) of 1.5×10–5 m2 s–1. A similar HD is predicted by a tidal response model based on SmartPlug pressure data. By contrast, permeability measurements on intact samples from Site C0004 SE along-strike the splay fault and from Site C0006 in the frontal thrust zone were found to be similar and one magnitude smaller respectively, despite having a higher porosity. This is explained by the presence of fractures, which are covered by the larger scale of in situ measurements at Site C0010. Consequently, HD can be set to be at least 10–5 m2 s–1 for the splay fault and 10–6 m2 s–1 for the frontal thrust fault zone. Considering recent publications makes fluid flow at the splay fault unlikely, despite the presence of fractures. If the influence of fractures is limited, then processes leading to fault weakening may be enhanced. 相似文献