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41.
The tsunami of 26th December 2004 severely affected Yemen’s Socotra Island with a death at a distance of 4,600 km from the
epicenter of the Magnitude 9.0 earthquake. Yemen allowed a detailed assessment of the far-field impact of a tsunami in the
main propagation direction. The UNESCO mission surveyed 12 impacted towns on the north and south shores covering from the
east to the west tip of Socotra. The international team members were on the ground in Yemen from 11 to 19 October 2006. The
team measured tsunami run-up heights and inundation distances based on the location of watermarks on buildings and eyewitness
accounts. Maximum run-up heights were typically on the order of 2–6 m. Each measurement was located by means of global positioning
systems (GPS) and photographed. Numerous eyewitness interviews were recorded on video. The tsunami impact on Socotra is compared
with other locations along the shores of the Indian Ocean. 相似文献
42.
The present paper reports on a study of the interaction of a current-free monochromatic surface wave field with a wave-free uniform current field in a three-dimensional flow frame. The wave and the current fields are not necessarily collinear with each other. The formulation of the wave-current field is done under the assumption of irrotational and inviscid flow. We have developed the three dimensional expressions describing the characteristics of the combined flow in terms of mass, momentum and energy transport conservation. These equations are found efficient to describe the sought-for combined wave-current field. The parameters describing the wave-current field after the interaction are the surface disturbance amplitude and length, mean water depth, mean current-like parameter and direction of the combined flow, which would be calculated from a set of equations that satisfy conservation of mean mass, momentum and energy flux and a dispersion relation on the free surface before and after the interaction. The results are shown in terms of relative changes in wave heights and lengths, current-like parameters and final directions obtained for the combined wave-current field with respect to current-free wave and wave-free current pre-interaction parameters. 相似文献
43.
44.
45.
Measurements are taken of the mantle magnitudeM
m
, developed and introduced in previous papers, in the case of the 1960 Chilean and 1964 Alaskan earthquakes, by far the largest events ever recorded instrumentally. We show that theM
m
algorithm recovers the seismic moment of these gigantic earthquakes with an accuracy (typically 0.2 to 0.3 units of magnitude, or a factor of 1.5 to 2 on the seismic moment) comparable to that achieved on modern, digital, datasets. In particular, this study proves that the mantle magnitudeM
m
does not saturate for large events, as do standard magnitude scales, but rather keeps growing with seismic moment, even for the very largest earthquakes. We further prove that the algorithm can be applied in unfavorable experimental conditions, such as instruments with poor response at mantle periods, seismograms clipped due to limited recording dynamics, or even on microbarograph records of air coupled Rayleigh waves.In addition, we show that it is feasible to use acoustic-gravity air waves generated by those very largest earthquakes, to obtain an estimate of the seismic moment of the event along the general philosophy of the magnitude concept: a single-station measurement ignoring the details of the earthquake's focal mechanism and exact depth. 相似文献
46.
Emile A. Okal 《Earth and Planetary Science Letters》1981,52(2):397-409
We present a comprehensive study of the seismicity of the Antarctic plate for the period 1925–1980. The total seismic energy released during this period in the interior of the plate, 3.2 × 1022 ergs, is compared to figures for the African plate, of similar kinematics and size, and to the neighboring Nazca plate. We conclude that Antarctic seismicity is comparable to that of other plates, thus refuting the claim that a surrounding ring of spreading ridges hampers transmission of tectonic stress and leaves it stress-free, and clearly showing the importance of ridge-push as a driving mechanism for the plates. In the souteastern Pacific Basin, it is shown that the line of maximum age in the plate, which is the locus of previous positions of the triple junction, is a line of preferential stress release, along with more conventional features, e.g. fracture zones. In the Indian Ocean, we study a 1973 earthquake northeast of Kerguelen (Ms = 5.5): its depth (45 km), tensional mechanism, and low stress suggest that it represents a magmatic process related to the nearby hotspot, and possibly involving the pipeline structure proposed by Morgan. 相似文献
47.
Emile A. Okal 《Earth and Planetary Science Letters》1980,46(2):306-310
Body- and surface-wave data from a magnitude Ms = 6.4 event in the Bellingshausen Sea are used to infer a thrust fault mechanism, with compressional stress directed parallel to the vector of relative motion between Antarctica and the Pacific plate at the nearby ridge. The solution would not, on the other hand, be compatible with stress fields involving absolute plate motion, such as asthenospheric drag. 相似文献
48.
Emile A. Okal 《Physics of the Earth and Planetary Interiors》1976,12(4):319-328
Long-period records of multiple Love waves from the 1957 earthquake in Mongolia (MS = 8.0) at Pasadena are analysed and compared to synthetic seismograms, generated by the method of Kanamori. A fit in the time domain shows that the records are not consistent with the previous solution, achieved through a frequency-domain analysis of directivity by Ben-Menahem and Toksöz. The solution asks for a shorter rupture of 270 km at a velocity of 3.5 km/s. The focal parameters are constrained by updating all the reported first motion and are found to be: strike = 103°, dip = 53°, slip = 32°. A seismic moment of 1.8 · 1028 dyn · cm is obtained. These figures are also consistent with a time-domain analysis of Love waves at Palisades and Strasbourg, and of Rayleigh waves at Pasadena, with a directivity study of Love waves at Pasadena, and with static deformation and isoseismal data. A discussion is given of the relation between moment, magnitude and rupture area, and a comparison is made with other events in the same region: it is concluded that this earthquake does not exhibit an “intra-plate” behavior, but rather compares better with “inter-plate” events, such as the great Assam earthquake. 相似文献
49.
Emile Novel 《Aquatic Sciences - Research Across Boundaries》1969,31(1):150-156
Résumé L'auteur a étudié, dans des conditions expérimentales définies, la vitesse de sédimentation des bactéries appartenant à l'espèceEscherichia coli dans l'eau du Léman, puisée dans le Petit-lac.
Théoriquement la durée de chute est de 16 heures et 40 minutes pour un mètre. L'on voit ainsi que pour atteindre le fond du
Léman en sa plus grande profondeur un colibacille mettrait 256 jours et 18 heures si rien ne venait entraver sa descente.
Zusammenfassung Unter definierten Versuchsbedingungen wurde die Sedimentationsgeschwindigkeit von Bakterien der ArtEscherichia coli aus dem Genfersee (Lac Léman) studiert, und zwar mit Material aus dem Petit Lac. Theoretisch betr?gt die Sinkzeit pro Meter 16 h 40 min. Daraus geht hervor, dass ein Colibazillus, sofern er unbehindert absinken kann, 256 h 18 min ben?tigt, um den Grund des Genfersees an seiner tiefsten Stelle zu erreichen.相似文献
50.
Emile Novel 《Aquatic Sciences - Research Across Boundaries》1965,27(2):238-249
Conclusions Si l'on examine les chiffres, aussi bien du point de vue qualitatif (recherche des coliformes) que du point de vue quantitatif
(nombre total des germes) de la période 1957 à 19621), on remarque une aggravation sensible de la situation bactériologique ces dernières années et, notamment surtout, en 1961
et 1962.
Summary The examination of the figures with regard to the qualitative point of view (coliforms) as well as to the quantitative one (total number of germs) for the period of 1957 to 19621) reveals an aggravation of the bacterial situation in the last years and, especially, in 1961 and 1962.
Zusammenfassung Bei der Prüfung der Zahlen, sowohl in qualitativer (Colibakterien) als auch in quantitativer Hinsicht (Total der vorhandenen Keime) wird für die Zeit von 1957 bis 19621) eine merkliche Verschlechterung der bakteriologischen Verh?ltnisse festgestellt. Dies gilt besonders für die letzten Jahre, vor allem aber für 1961 und 1962.相似文献