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141.
142.
Abermann Jakob Eckerstorfer Markus Malnes Eirik Hansen Birger Ulf 《Natural Hazards》2019,97(2):517-534
Natural Hazards - On 11 April 2016 we observed high slushflow and wet snow avalanche activity at the environmental monitoring station Kobbefjord in W-Greenland. Snow avalanches released as a result... 相似文献
143.
Morphology, distribution and formation of relict marginal moraines in the Swedish mountains 总被引:2,自引:0,他引:2
Relict marginal moraines are commonly used landforms in palaeoglaciological reconstructions. In the Swedish mountains, a large number of relict marginal moraines of variable morphology and origin occur. In this study, we have mapped 234 relict marginal moraines distributed all along the Swedish mountains and classified them into four morphological classes: cirque‐and‐valley moraines, valley‐side moraines, complex moraines and cross‐valley moraines. Of these, 46 moraines have been reclassified or are here mapped for the first time. A vast majority of the relict moraines are shown to have formed during deglaciation of an ice‐sheet, rather than by local mountain glaciers as suggested in earlier studies. The relict marginal moraines generally indicate that deglaciation throughout the mountains was characterised by a retreating ice‐sheet, successively damming glacial lakes, and downwasting around mountains. The general lack of moraines indicating valley and cirque glaciers during deglaciation suggests that climatic conditions were unfavourable for local glaciation during the last phase of the Weichselian. This interpretation contrasts with some earlier studies that have reconstructed the formation of local glaciers in the higher parts of the Swedish mountains during deglaciation. 相似文献
144.
Addi Bischoff Mike Komnik Jakob Storz Jasper Berndt 《Meteoritics & planetary science》2023,58(9):1260-1273
The lunar regolith breccia Dhofar 1769, which was found in 2012 as a single 125 g piece in the Zufar desert area of Oman, contains a relatively large, dark-colored impact melt breccia embedded in a fine-grained clastic matrix. The internal texture of the fragment indicates the repeated melt breccia formation on the lunar surface, their repeated brecciation, and mixing in second, third, and fourth generations of brecciated rock types. The chemical and mineralogical data reveal the incorporation of a feldspar-rich subophitic crystalline melt within a feldspar-rich microporphyritic crystalline melt breccia. This lithic paragenesis itself is embedded within a mafic, crystalline melt breccia. The entire breccia with the three different impact melts has been finally incorporated into the whole rock breccia. The three impact melts are mixtures of different source rocks and impact projectiles, based on the obtained minor and trace element compositions (in particular of Ni and the rare earth elements [REE]) of the impact melt lithologies. For all processes of impact melt formation, additional steps of their brecciation and re-lithification require a minimum number of seven impact processes. 相似文献
145.
High-quality seismic data document a Maastrichtian-Paleocene rift episode on the Vøring margin lasting for 20 m.y. prior to continental breakup. The rift structures are well imaged in the Fenris Graben and Gjallar Ridge region in the western Vøring Basin, and are characterized by low-angle detachment faults with variable fault geometries from south to north. The structural restoration has facilitated the division of pre- and syn-rift sediments across the extensional terrain, which is subsequently used to evaluate mode and mechanism for the lithospheric deformation. Extension estimates based on the structural restoration, subsidence analysis and crustal thickness evaluations yield stretching factors ranging between 1.5 to 2.3 across the main fault zone just landward of the early Tertiary flood basalts. The structural restoration also shows that a middle crustal dome structure, observed beneath the low-angle faults, can be explained by extensional unroofing. Thus, the dome structure may represent a possible metamorphic core complex. Calculations of the effects on vertical motion, assuming uniform and two-layer differential stretching models combined with the arrival of the Iceland mantle plume during rifting, indicate that the uniform extension model may account for both observed early rift subsidence and subsequent late rift uplift and erosion. Although the differential model can not be excluded, it implies early rift uplift which is not compatible with our seismic interpretation. The direct and indirect effects of the Iceland mantle plume may have caused as much as 1.2 km of late rift uplift. Comparison of the volcanic Vøring margin and the non-volcanic West Iberian margin shows similarities in terms of structural style as well as in mode and distribution of extension. 相似文献
146.
In this paper, a time series from 1999 to 2007 of absolute total electron content (TEC) values has been computed and analyzed
using singular value decomposition (SVD). The data set has been computed using a Kalman Filter and is based on dual frequency
GPS data from three reference stations in Denmark located in the midlatitude region. The station separation between the three
stations is 132–208 km (the time series of the TEC can be freely downloaded at ). For each year, a SVD has been performed on the TEC time series in order to identify the three time varying (daily, yearly,
and 11 yearly) characteristics of the ionosphere. The applied SVD analysis provides a new method for separating the daily
from the yearly components. The first singular value is very dominant (approximately six times larger than the second singular
value), and this singular value corresponds clearly to the variation of the daily cycle over the year. The second singular
value corresponds to variations of the width of the daily peak over the year, and the third singular value shows a clear yearly
variation of the daily signal with peaks around the equinoxes. The singular values for each year show a very strong correlation
with the sunspot number for all the singular values. The correlation coefficients for the first 5 sets of singular values
are all above 0.96. Based on the SVD analysis yearly models of the TEC in the ionosphere can be recomposed and illustrate
the three time varying characteristics of the ionosphere very clearly. By prediction of the yearly mean sunspot number, future
yearly models can also be predicted. These can serve as a priori information for a real time space weather service providing
information of the current status of the ionosphere. They will improve the Kalman filter processing making it more robust,
but can also be used as starting values in the initialization phase in case of gaps in the data stream. Furthermore, the models
can be used to detect variations from the normal local ionospheric activity. 相似文献
147.