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91.
In 1981 a magnetic and bathymetric survey was carried out over Explorer Seamount located approximately between 48°50′ and
49°30′N and 130°40′ and 131°30′W. During the cruise four pillow fragments were dredged from peaks in this area. Based on the
observed magnetic data, it was identified that the main peak of Explorer Seamount should be of the Bruhnes age while the magnetic
high in the NW of study area would be Gauss. This would yield a spreading rate of about 2 cm per year for the Matuyama epoch.
The results of intensities of remanence measured from the pillow fragments indicate that the ages are less than 106 years. Similarly the Curie temperature is consistent with ages of around 106 years. An attempt was made to model the observed magnetic field using a series of uniformly magnetized NE-SW trending blocks
of alternating polarity. Agreement between the model and observed results is satisfied. Oxidation ratios calculated from measured
samples suggest that the main peak of Explorer Seamount is not far from the present day ridge axis, which agrees with the
younger interpretation from the magnetic profiles.
The results mentioned above strongly, but not conclusively, favour an interpretation in which the southeastern peak of Explorer
Seamount is of the Bruhnes age and the recent spreading is at Explorer trench, then the Sovanco Fracture Zone should be thought
of as a complex triangular area between the northern end of Juan de Fuca Ridge and Explorer Seamount rather than as a simple
transform fault as defined conventionally. 相似文献
92.
93.
A Weichselian Late Pleniglacial fluvio-aeolian deposit has been investigated in the southern Netherlands. Three main structural lineaments have been distinguished: (1) very small, vertical platy structures (microjoints), in a parallel and a columnar configuration; (2) large joints and normal faults with minor displacement (‘Grubbenvorst type’), arranged in a conjugate fault-system; (3) large joints and normal faults (‘wedge-type’), located adjacent to ice-wedge casts. Since clay is absent, the occurrence of the vertical platy structures cannot be attributed to desiccation cracking. The vertical platy structures are interpreted as the result of thermal contraction cracking of a relatively thin layer, due to a sudden temperature drop. The large joints and normal faults of the Grubbenvorst type are the result of failure of the sediment due to the melting of the permafrost in the Late Pleniglacial, just before the formation of the Beuningen Gravel Bed. In other areas large periglacial convolutions have been formed during the same period. The normal faults and joints of the wedge type are more generally known. They are the result of failure of the sediment adjacent to a melting ice wedge. 相似文献
94.
95.
On cumulus mergers 总被引:1,自引:0,他引:1
96.
Importance of inherited rift margin structures in the early North Alpine Foreland Basin, Switzerland 总被引:1,自引:0,他引:1
The earliest evolution of the North Alpine Foreland Basin in Switzerland was characterized by deposition in small, structurally partitioned sub-basins during the Late Cretaceous and Early Tertiary, rather than in a single, large foredeep. These sub-basins, which were probably located between old rift margin fault-blocks reactivated during Alpine compression, were incorporated into the thrust wedge during thin-skinned deformation. In eastern Switzerland, the most external sub-basins with respect to the orogenic wedge (North Helvetic Flysch and Blattengrat units) have at their base an unconformity attributed to flexural forebulge erosion. More internal sub-basins (Sardona and Prättigau units) contain a conformable succession from the underlying passive margin stage and are dominated by deep-water sedimentation. In western Switzerland, both external sub-basins, now found in the Helvetic Diablerets and Wildhorn nappes, and deep-water internal sub-basins (Höchst-Meilleret Flysch, Neisen Flysch, Tarentaise Flysch) preserve a well-developed basal unconformity. Comparison of the eastern and western Swiss transects shows important intrabasinal lateral variations to be present. The western Swiss area was a topographic high for much of the Late Cretaceous and Early Tertiary; this is demonstrated by the increased chronostratigraphic gap at the karstified basal unconformity surface in western Switzerland. The strata onlapping this unconformity young to the west, suggesting that drowning of the emergent area was delayed compared with the east. In addition, reactivation and uplift of the rift margin structures occurred earlier in western Switzerland compared with eastern Switzerland. There is therefore strong evidence for lateral topographic gradients in the early foreland basin caused by differential amounts of tectonic reactivation of rift margin structures. In the early foreland basin-fill, these lateral variations are as important in determining depositional patterns as strike-normal changes across the basin. 相似文献
97.
98.
Saha Ajoy Ramya V. L. Jesna P. K. Mol S. Sibina Panikkar Preetha Vijaykumar M. E. Sarkar U. K. Das B. K. 《Natural Resources Research》2021,30(2):1367-1394
Natural Resources Research - Freshwater has a significant role in determining the ecological environment, public health and socio-economic development. This study analyzed the spatio-temporal... 相似文献
99.
Paul Bushby and Joanne Mason take a look at the workings of the Sun's dynamo, from the development of physical theory through current ideas and methods, to the possibilities for future understanding of this enigmatic magnetic engine. 相似文献