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排序方式: 共有166条查询结果,搜索用时 15 毫秒
51.
Abstract. Multi-channel seismic data obtained from the Nankai accretionary prism and forearc basin system has been studied to elucidate the migration and accumulation process of gas to the BGHS and examine the distribution pattern of BSRs and characteristic reflections associated with them.
BSRs are distributed widely in the Nankai accretionary prism and associated forearc basins (33,000 km2 ) and 90 % of them have migration and recycling origins. The widest distribution of the BSRs can be seen at the prism. A correlation between the BSR distributions and prism size shows that the BSRs tend to be more well-developed in a prism of large size. This suggests that a large prism may produce much amount of gas-bearing fluids that migrate to the BGHS and form the BSRs (tectonic control), hi the forearc basins, the BSRs are identified at topographic highs, anticlines and basin margins (structural control).
The upward migration of gas-bearing fluids is carried out through permeable sand layers and as a result, the distribution of BSRs is confined to alternating beds of sand and mud facies (sedimentary control). However, if there is enough time for upward migration and accumulation of gas to the BGHS, the BSRs can be generated widely in low-permeable mud facies (time control).
Those results imply that structural, tectonic, sedimentary and time controls are primary factors to decide the distribution of BSRs in the Nankai Trough area. 相似文献
BSRs are distributed widely in the Nankai accretionary prism and associated forearc basins (33,000 km
The upward migration of gas-bearing fluids is carried out through permeable sand layers and as a result, the distribution of BSRs is confined to alternating beds of sand and mud facies (sedimentary control). However, if there is enough time for upward migration and accumulation of gas to the BGHS, the BSRs can be generated widely in low-permeable mud facies (time control).
Those results imply that structural, tectonic, sedimentary and time controls are primary factors to decide the distribution of BSRs in the Nankai Trough area. 相似文献
52.
Due to a continual rainfall, a flowslide occurred in Yamashina area, Kanazawa City, Japan on November 8, 2002 in the Tertiary
mudstone area. The sliding mass was fully fluidized during the motion and moved downward the slope for a long distance. On
December 31, 2003, slope failure was triggered by intensive rainfall and snowmelt water at the same site again, and resulted
in the second occurrence of flowslide. The total displacement of the slope was recorded with an extensometer. Through field
investigation, the difference of the sliding mechanism between the two flowslides was examined. 相似文献
53.
Yasuhiro Umeda 《Tectonophysics》1985,118(3-4)
The source processes of large shallow earthquakes are investigated based on the various field phenomena and on the seismograms recorded at short focal distances. The results from coseismic and postseismic field surveys in some source regions strongly show that there must be a particular region characterized by a large dislocation, large acceleration and extremely low aftershock activity. This specific region seems to have a relatively small dimension compared with the length of the main fault.The predominant short-period waves on the strong-motion seismograms are concentrated within the short intervals at the initial parts of P and S waves. This fact also suggests that the rupture elements generating the predominant short-period waves are not distributed over the entire surface of a single main fault but are concentrated in a small region.We call this confined small region in the source area “earthquake core”. The earthquake core is formed a little later than the start of smoothing dislocation and it may be located at some distance from the starting point of rupture. 相似文献
54.
Geochemistry of Late Permian to Early Triassic pelagic cherts from southwest Japan: implications for an oceanic redox change 总被引:4,自引:0,他引:4
Major, trace, and rare earth element abundances were determined for the southwestern Japanese pelagic chert sequence from the early Late Permian to early Early Triassic to investigate a redox change in deep-sea pelagic environments before and at the Permo-Triassic boundary (PTB) (251 Ma). The sequence was primarily deposited in the deep-sea of the superocean Panthalassa, and then was accreted to Japan in the Middle Jurassic. A remarkable lithostratigraphic change from red chert to siliceous∼carbonaceous claystone through gray chert is observed in this sequence. Constituent elements for these sedimentary rocks are essentially derived from two sources: (1) an ancient seawater via biogenic (mainly radiolarian), hydrothermal, and authigenic materials and (2) an average shale-like terrigenous material. The present measurement demonstrates significant stratigraphic changes of the Ce/Cenon-ter* value (estimated Ce anomaly value of non-terrigenous component, recalculated by subtraction of terrigenous REEs from bulk REEs) and the (Mn/TE)sample/(Mn/TE)PAAS value (excess Mn component other than terrigenous one; TE=terrigenous elements including Ti, Al, Nb, Hf, Th; PAAS=Post-Archean Average Australian Shale) in the Permian chert. The Ce/Cenon-ter* values increase from <0.2 to 1 and the (Mn/TE)sample/(Mn/TE)PAAS values decrease up-section, suggesting that the redox condition of deep-sea open-ocean changed from oxic to suboxic in an interval of approximately 10 Myr. The (∑Fe/TE)sample/(∑Fe/TE)PAAS and (Mn/TE)sample/(Mn/TE)PAAS values of carbonaceous claystone near or at the PTB are less than unity, suggesting that reductive dissolution of iron and manganese occurred under an anoxic condition. This supports the idea of the PTB oceanic anoxia in the superocean Panthalassa. The present data suggest that the anoxic condition prevailed in the deep-sea pelagic regions for an extremely long period, much more than 10 Myr, from the middle Late Permian to early Early Triassic. This long-term development of widespread oceanic anoxia may have been linked to the greatest mass extinction of the Phanerozoic. 相似文献
55.
56.
Masahito Shigemitsu Yutaka W. Watanabe Yasuhiro Yamanaka Hajime Kawakami Makio C. Honda 《Journal of Oceanography》2010,66(5):697-708
We used time-series sediment trap data for four major components, organic matter and ballast minerals (CaCO3, opal, and lithogenic matter) from 150, 540, and 1000 m in the western subarctic Pacific (WSAP), where opal is the predominant
mineral in sinking particles, to develop four simple models for settling particles, including the “ballast model”. The ballast
model is based on the concept that most of the organic matter “rain” in the deep sea is carried by the minerals. These four
models are designed to simultaneously reproduce the flux of each major component of settling particles at 540 and 1000 m by
using the data for each component at 150 m as initial values. Among the four models, the ballast model, which considers the
sinking velocity increase with depth, was identified as the best using the Akaike information criterion as a measure of the
model fit to data. This model successfully reproduced the flux of organic matter at 540 and 1000 m, indicating that the ballast
model concept works well in the shallow zone of the WSAP on a seasonal timescale. This also suggests that ballast minerals
not only physically protect the organic matter from degradation during the settling process but also enhance the sinking velocity
and reduce the degree of decomposition. 相似文献
57.
58.
59.
Hironori Iwai Yasuhiro Murayama Shoken Ishii Kohei Mizutani Yuichi Ohno Taichiro Hashiguchi 《Boundary-Layer Meteorology》2011,141(1):117-142
To study the wind field within the atmospheric boundary layer over the Tokyo metropolitan area, Doppler lidar observations
were made 45 km north of Sagami Bay and 30 km west of Tokyo Bay, from 14 May to 15 June 2008. Doppler lidar on 27 May 2008
observed the vertical and horizontal wind structure of a well-developed sea-breeze front (SBF) penetrating from Sagami Bay.
At the SBF, a strong updraft (maximum w approximately equal to 5 m s−1) was formed with a horizontal scale of about 500 m and vertical scale of 2 km. The spatial relationship between the strong
updraft over the nose of the SBF and prefrontal thermal suggests that the strong updraft was triggered by interaction between
the SBF and the thermal. After the updraft commenced, a collocated ceilometer observed an intense aerosol backscatter up to
2 km above ground level. The observational results suggest that the near-surface denser aerosols trapped in the head region
of the SBF escaped from the nose of the SBF and were then vertically transported up to the mixing height by the strong updraft
at the SBF. This implies that these phenomena occurred not continuously but intermittently. The interaction situations between
the SBF and prefrontal thermal can affect the wind structure at the SBF and the regional air quality. 相似文献
60.
At Syowa Station (69.0°S, 39.6°E), located on East Ongul Island near the continent of Antarctica, atmospheric electric-field observations started in 1968 and had been carried out intermittently. An improved electric-field mill at Syowa Station had and obtained better-quality atmospheric electric-field data from February 2005 to January 2006. After a 1-year interruption, the observations resumed in January 2007.The atmospheric electric-field data from Syowa Station are often contaminated due to local disturbances caused by near-ground meteorological phenomena. We examined correlations between the atmospheric electric field and near-ground weather from February 2005 to January 2006 and from February 2007 to January 2008, and proposed a criterion to extract “fair-weather” electric-field data based on wind speed and cloud coverage data. The diurnal variation of fair-weather data in January followed the shape of the so-called Carnegie curve. Fair-weather data obtained during a substorm showed some correspondence between the atmospheric electric field and variations in the geomagnetic field. This newly developed extraction method may enable the use of atmospheric electric-field data for studying the solar terrestrial environment. 相似文献