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171.
172.
Active skarn formation beneath Lascar Volcano, northern Chile: a petrographic and geochemical study of xenoliths in eruption products 总被引:4,自引:0,他引:4
S. J. MATTHEWS R. A. MARQUILLAS A. J. KEMP F. K. GRANGE & M. C. GARDEWEG 《Journal of Metamorphic Geology》1996,14(4):509-530
Calcsilicate xenoliths occur in large numbers in some lavas and pyroclastic flows of Lascar Volcano. Their whole-rock major element and REE compositions indicate that the protolith was the Upper Cretaceous Yacoraite Formation, which crops out extensively in NW Argentina. The whole-rock major element compositions of the xenoliths fall into specific groups suggesting a strong geochemical zonation in the skarn zone. Three geochemical zones have been identified; (1) an outer metamorphic zone rich in wollastonite; (2) a middle zone rich in pyroxene and garnet; (3) an inner zone rich in pyroxene and magnetite. The two innermost zones have developed from the wollastonite zone by infiltration of metasomatic fluids rich in Fe, Mn, Mg, Ti and Al. Whole-rock REE patterns have not changed significantly during prograde metamorphism and metasomatism, indicating REE immobility in the altering fluids. Retrograde alteration by acid-sulphate fluids produced anhydrite skarns and secondary calcite and wilkeite veins in the wollastonite zone. The carbon and oxygen isotopic compositions of this calcite indicate that it formed by Rayleigh crystallization from a low-temperature (<200 °C) fluid containing dissolved H2 CO3 . The calculated δ18 O of the water in this fluid suggests a magmatic origin whereas the calculated δ13 C of the dissolved carbonate is consistent with derivation from rocks of the Yacoraite Formation at 350 °C. It is suggested that the magmatic acid-sulphate fluid was responsible for leaching carbonate from the surrounding carbonate rocks and redepositing it in the skarn zone. REEs were mobilized during the retrograde acid-sulphate and acid-carbonate alteration. A negative Ce anomaly associated with this carbonate and sulphate indicates high oxygen fugacities in the mineralizing fluids. 相似文献
173.
Esperanza Muñoz-Salinas C. S. Renschler D. Palacios L. M. Namikawa 《Natural Hazards》2008,45(2):309-320
In contrast to dramatic flow regime changes by less frequent large-scale volcanic eruptions, those caused by more frequent
small-scale processes in volcanic landscapes may also drastically change the direction and dynamics of flow in a drainage
system formed solely by fluvial processes. During such periods of channel morphology change, it is necessary to frequently
update channel flow parameters to assess preventive measures for civil protection purposes. Often aerial photography is impracticable,
since parts of the channels are covered by dense vegetation, while total station and laser topographic surveys are often too
slow and costly, particularly during a high frequency of events. This article introduces and validates a new methodology for
updating the representation of channel morphology in Digital Elevation Models (DEM) used specifically for assessing the dangers
of frequently occurring lahars along gorges in volcanic landscapes during eruptive and non-eruptive periods. The updating
of channel cross-sections was achieved by inserting more detailed representative profiles of homogeneous channel sectors in
DEMs derived from existing less detailed topographic maps. The channel profiles were surveyed along the thalweg in equidistant
points according to Universal Transverse Mercator (UTM) (x,y) coordinates and elevation derived from the existing DEM. The
proposed technique was applied at Tenenepanco-Huiloac Gorge on Popocatépetl volcano, Mexico, in an area affected by major
lahars during the volcano’s most recent eruptive period from 1994 to 2005. The proposed method can reduce the cost and person-hours
of a regular channel topographic survey dramatically and the enhanced DEM can determine volume parameters and flood zones
associated with the 1 July 1997 and 21 January 2001 lahars, respectively. In addition, the updated DEM with better channel
representation allowed a more realistic fluid flow and lahar simulation with the process-based TITAN2D model. 相似文献
174.
We determine detailed 3-D Vp and Vs structures of the crust and uppermost mantle beneath the Kyushu Island, southwest Japan, using a large number of arrival times from local earthquakes. From the obtained Vp and Vs models, we further calculate Poisson’s ratio images beneath the study area. By using this large data set, we successfully image the 3-D seismic velocity and Poisson’s ratio structures beneath Kyushu down to a depth of 150 km with a more reliable spatial resolution than previous studies. Our results show very clear low Vp and low Vs anomalies in the crust and uppermost mantle beneath the northern volcanoes, such as Abu, Kujyu and Unzen. Low-velocity anomalies are seen in the mantle beneath most other volcanoes. In contrast, there are no significant low-velocity anomalies in the crust or in the upper mantle between Aso and Kirishima. The subducting Philippine Sea slab is imaged generally as a high-velocity anomaly down to a depth of 150 km with some patches of normal to low seismic wave velocities. The Poisson’s ratio is almost normal beneath most volcanoes. The crustal seismicity is distributed in both the high- and low-velocity zones, but most distinctly in the low Poisson’s ratio zone. A high Poisson’s ratio region is found in the forearc crustal wedge above the slab in the junction area with Shikoku and Honshu; this high Poisson’s ratio could be caused by fluid-filled cracks induced by dehydration from the Philippine Sea slab. The Poisson’s ratio is normal to low in the forearc mantle in middle-south Kyushu. This is consistent with the absence of low-frequency tremors, and may indicate that dehydration from the subducting crust is not vigorous in this region. 相似文献
175.
Both the 34 value and the total S content of products from Vulture Volcano, Italy are mainly controlled by the separation of S gases, predominantly SO2, from high f
O2magmas containing S predominantly as SO
2-
4
. The addition of evaporites to such magmas appears to be a relatively uncommon and limited phenomenon. The total S content of the most primitive product of Vulture Volcano (5600 mg/kg) is very high. The high 34S value of 4 indicates an origin through the partial melting of a mantle containing high S, enriched in 34S of unknown origin. 相似文献
176.
The passage of the Earth through dense clumps of dark matter, the presence of which is predicted by certain cosmologies, would produce large quantities of heat in the interior of this planet through the capture and subsequent annihilation of dark matter particles. This heat would lead to large-scale volcanism which could in turn have caused mass extinctions. The periodicity of such volcanic outbursts agrees with the frequency of paleontological mass extinctions as well as the observed periodicity in the occurrence of the largest flood basalt provinces on the globe. 相似文献
177.
Kuju Volcano lies near Aso Caldera at the center of Kyushu Island, western Japan. After a few hundred years of dormancy,
a phreatic explosion accompanied by a small ash eruption occurred on 11 October 1995. This study was undertaken to determine
the subsurface seismic velocity structure associated with the active magmatic regime in the Kuju volcanic region. The three-dimensional,
upper crustal, P-wave velocity structure beneath Kuju Volcano was determined using methods for the simultaneous inversion
of P-wave arrival times from local earthquakes in and around the Kuju volcanic region for velocities and hypocentral parameters.
Results reveal two shallower low-velocity anomalies located in the northern and southern parts of Kuju Volcano, consistent
with the presence of significant negative Bouguer gravity anomalies. In addition, a high-velocity anomaly is located approximately
5 km northwest of Mt. Kuju, one of the domes in Kuju Volcano. Beneath this high-velocity anomaly, a low-velocity anomaly is
present. This velocity structure suggests a magmatic regime that has a lid consisting of cooled solid material overlying a
chamber of partially molten material.
Received: 23 September 1997 / Accepted: 20 June 1998 相似文献
178.
火山与地震的共性特征及有关问题讨论 总被引:4,自引:1,他引:3
对火山与地震及其伴随现象进行了对比分析,发现二者除外在形式不同外,在分布范围、深部构造及其它方面具有明显的共性特征.讨论了火山与地震具有共性特征的原因,认为它们都与岩浆活动有关.因此,内陆地震的发生有可能是地壳内岩浆上涌的直接结果 相似文献
179.
At a glance of its stratighraphy, the Taftan Volcano can be classified as three groups: pre-, syn- and post-volcanic deposits. The pre-volcanic deposits consist mostly of flysch facies and colored mélange complex. The syn-volcanic deposits are mainly the product of the Taftan Volcano which is mostly composed of pyroclastic and lava flows from the main body of this volcano. The post-volcanic deposits are mostly epiclastic and reworked materials from the Taftan Volcano due to its erosion and weathering. Major and trace elements, and Sr/Rb isotopic compositions determined on whole-rock samples from the Taftan Volcano showed that the volcano was formed at the continental margin. The whole-rock isotopic composition of the Taftan Volcano showed a feature of strong enrichment with ^87Sr/^86Sr=0.705326-0.705921. Geochronological samples of the Tartan Volcano determined by the ^40K/^40Ar method gave an age range of 6.95±0.72 to 0.71±0.03 Ma. The rare-earth element patterns are characterized by high LREE and nearly strongly linear patterns for MREE to HREE, suggesting that distinctive minerals such as olivine and pyroxene crystallized in the early magmatic stage and then were involved in reaction between the lower crust and residual magma. The integrated isotope and trace element systematics and tectonic structure beneath the Taftan Volcano suggested the lower-crust assimilation by the primary magma. The primary magma had generated from a heterogeneous mantle source and a secondary petrogenetical process. This magma could have been affected by the subduction of the Oman Sea undemeath the continental Eurasia plate. 相似文献
180.
在“九五”科技重点项目“中国若干近代火山潜在喷发危险及其监测研究”项目起动之际,作者对于火山喷发危险的监测研究中的CT技术者进行调研,本文总结了这方面的研究3方法和思路,并介绍了中国在这方面的部分成果,展望今后的研究动向。 相似文献