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排序方式: 共有37条查询结果,搜索用时 15 毫秒
1.
Boninite is an unusual, plagioclase-free magnesian andesite, occurring as vesicular pillow lavas and hyaloclastites, accompanied by andesites and dacites in Chichi-jima, Bonin Islands. The Bonin Islands belong to the Izu-Mariana arc and consist of dominant volcanic rocks and subordinate sedimentary rocks of late Oligocene-early Miocene age. The chemistry of boninite is characterized by high contents of MgO. Cr and Ni similar to primitive basalts, but apparently in ill accord with its relatively high SiO2 content of ? 55%. The relation of SiO2 to total FeO/MgO ratio indicates that boninite belongs to the cale-alkalic rock suite. The mineralogy of boninite consists of olivine (Fo87-90), orthopyroxene (En87-90), clinopyroxene (Wo38-35En37-44Fs25-21), hydrous glass and Cr-spinel, Experimental studies show that the magma of boninite composition could be in equilibrium with upper mantle peridotite at pressures less than 17 kb and temperatures of 1200–1050°C under high PH2O. It is suggested that boninite is a sea-floor quenched product (900°C) of a direct partial melt of the upper mantle. Related andesites and dacites are considered to be probably fractional crystallization products from the same magma. 相似文献
2.
Jiro Koyama Chie Imakado Seiichi Uno Takako Kuroda Shouichi Hara Takahiro Majima Hideyuki Shirota Nathaniel C. Añasco 《Marine pollution bulletin》2014
To assess risks of chemically-dispersed oil to marine organisms, oil concentrations in the water were simulated using a hypothetical spill accident in Tokyo Bay. Simulated oil concentrations were then compared with the short-term no-observed effect concentration (NOEC), 0.01 mg/L, obtained through toxicity tests using marine diatoms, amphipod and fish. Area of oil concentrations higher than the NOEC were compared with respect to use and non-use of dispersant. Results of the simulation show relatively faster dispersion near the mouth of the bay compared to its inner sections which is basically related to its stronger water currents. Interestingly, in the inner bay, a large area of chemically-dispersed oil has concentrations higher than the NOEC. It seems emulsifying oil by dispersant increases oil concentrations, which could lead to higher toxicity to aquatic organisms. When stronger winds occur, however, the difference in toxic areas between use and non-use of dispersant is quite small. 相似文献
3.
Kazuhiro?AokiEmail author Manabu?Shimizu Hiroshi?Kuroda Toshifumi?Yamatogi Naoya?Ishida Shigeru?Kitahara Keiji?Hirano 《Journal of Oceanography》2016,72(5):811-816
In both 2009 and 2010, massive Chattonella blooms occurred in Tachibana Bay. Observation results show that high cell densities of Chattonella were distributed in the central area of Tachibana Bay with low salinity water. Model results indicate that the low salinity water originated from the Ariake Sea and intruded into Tachibana Bay during the northerly or weak winds. It is suggested that low salinity water was mainly discharged from the northern area of the Ariake Sea. Northerly wind enhanced the horizontal advection of the low salinity water intruding into Tachibana Bay originating from the northern area of the Ariake Sea. 相似文献
4.
Hiroshi Kuroda Manabu Shimizu Yuuichi Hirota Hideki Akiyama 《Journal of Oceanography》2007,63(5):849-862
Through analysis of monthly in situ hydrographic, tide gauge, altimetry and Kuroshio axis data for the years 1993–2001, the intraannual variability of sea level
around Tosa Bay, Japan, with periods of 2–12 months is examined together with the intraannual variability of the Kuroshio
south of the bay. It is shown that the intraannual variation of steric height on the slope in Tosa Bay can account for that
of sea level at the coast around the bay as well as on this slope. It is found that the steric height (or sea level) variation
on the slope in this bay is mainly controlled by the subsurface thermal variation correlated with the Kuroshio variation off
Cape Ashizuri, the western edge of Tosa Bay. That is, when the nearshore Kuroshio velocity south of the cape is intensified
[weakened] concurrently with the northward [southward] displacement of the current axis, temperature in an entire water column
decreases [increases] simultaneously, mainly due to the upward [downward] displacement of isotherms, coincident with that
of the main thermocline. It follows that the steric height (or sea level) decreases [increases]. 相似文献
5.
M. R. Ramesh Kumar S. M. Pednekar M. Katsumata M. K. Antony Y. Kuroda A. S. Unnikrishnan 《Theoretical and Applied Climatology》2006,85(1-2):117-122
Summary The diurnal cycle of rainfall over the eastern equatorial Indian Ocean was studied for the period 23rd October 2001 to 31st October 2003 using hourly data from the Triton buoy positioned at 1.5° S and 90° E. An analysis of the active and weak spells
of rainfall for different seasons revealed peaks in the late evening hours in Winter, Summer and Fall and in early morning
hours (in Spring) in 2002. The active spell of rainfall peaked in the afternoon hours, during Winter, Spring and Summer in
2003, which agrees with the previous results of Janowiak et al. (1994). An analysis of rainfall events showed that Fall 2002
had a maximum number of rainfall events (90) and minimum (60) were observed in Spring 2003. Further it was found that the
majority of rain events (>60%) were less than 3 hours in duration throughout the study period. The longer duration rainfall
events (i.e. rain events greater than 6 hour duration) contributed significantly to Spring 2002 (20% of the total rainfall)
and Winter 2003 (21% of the total rainfall). Harmonic analysis of the hourly rainfall data for different seasons revealed
that diurnal harmonic explains more than 80% of the variance for all seasons. Furthermore, the diurnal harmonic has a maximum
amplitude for all seasons except summer, where the semidiurnal and six hourly harmonics are significant. 相似文献
6.
Junichiro Kuroda Hidetoshi Hara Katsumi Ueno Thasinee Charoentitirat Teruyuki Maruoka Takashi Miyazaki Akira Miyahigashi Stefano Lugli 《Island Arc》2017,26(2)
In this paper we present petrographic and geochemical data of sulfate mineral deposits in northeast Nakhon Sawan, central Thailand, and provide new constraints on their age. The deposits are made up mainly of strongly deformed nodular and massive gypsum in the upper part, and less deformed layered anhydrite in the lower part. They are intruded by andesitic dikes that contain Middle Triassic zircons (ca 240 Ma). These dikes are probably part of the regional magmatic activity of the Sukhothai Arc during the Early to Middle Triassic. Sulfur (δ34S) and strontium (87Sr/86Sr) isotopic compositions of the sulfates range from 15.86 ‰ to 16.26 ‰ and from 0.70810 to 0.70817, respectively. Comparisons with the Phanerozoic seawater isotopic evolution curve indicate that those values are best explained by precipitation of the sulfates from Carboniferous seawater, in particular seawater of late Mississippian age (ca 326 Ma), and this would be consistent with previous studies of calcareous fossils in the limestones that crop out around this site. Our interpretation is that evaporitic gypsum was originally precipitated from hypersaline seawater on a shallow lagoon or shelf on the Khao Khwang Platform during the Serpukhovian, and that this gypsum changed to anhydrite during early burial. The anhydrite was then cut by andesitic dikes during the Middle Triassic, and more recently the upper part of which was rehydrated during exhumation to form secondary gypsum near the surface. 相似文献
7.
Hiroshi Kuroda Manabu Shimizu Yuuichi Hirota Daisuke Ambe Hideki Akiyama 《Journal of Oceanography》2008,64(1):81-91
In order to specify a vertical thermal structure related to surface current variation on the continental slope in Tosa Bay,
Japan, we analyzed monthly regular hydrographic measurements in the years 1991–2004. Subsurface temperature below 200 m on
the slope was found to vary synchronously with the vertical displacement of the main thermocline around 200 m. It is shown
that the vertical-averaged temperature below 200 m is significantly correlated with an along-isobath/southwestward surface
current velocity on the slope. This correlation indicates that when a strong (weak) southwestward surface current is observed,
temperature below 200 m decreases (increases) simultaneously, that is, isotherms below the 200 m are displaced upward (downward)
together with the main thermocline. Moreover, when the strong southwestward flow is detected, across-isobath isotherms around
200 m slope upward toward the offshore direction. Furthermore, it is suggested that as the Kuroshio axis moves offshore south
of the bay, the southwestward flow tends to be weakened by the combined effect of other Kuroshio parameters such as transport
and stream width as well as the Kuroshio axis position. As a result, it is inferred that the correlation between the surface
current and subsurface temperature can be interpreted in terms of the formation and decay of an anticlockwise circulation
interacting with a cold eddy. 相似文献
8.
Using known compositions of primordial and spallation xenon components in several meteorites, the neutron produced Xe128n has been resolved. For obtaining the value for spallation produced (Xe128/Xe130)c, the meteorites with low iodine content and high spallation contribution are considered. Using these data, the neutron densities in several meteorites due to cosmic-ray exposure are calculated and their significance is qualitatively discussed. 相似文献
9.
K. Kuroda T. Irifune T. Inoue N. Nishiyama M. Miyashita K. Funakoshi W. Utsumi 《Physics and Chemistry of Minerals》2000,27(8):523-532
Determination of the phase boundary between ilmenite and perovskite structures in MgSiO3 has been made at pressures between 18 and 24 GPa and temperatures up to 2000 °C by in situ X-ray diffraction measurements
using synchrotron radiation and quench experiments. It was difficult to precisely define the phase boundary by the present
in situ X-ray observations, because the grain growth of ilmenite hindered the estimation of relative abundances of these phases.
Moreover, the slow reaction kinetics between these two phases made it difficult to determine the phase boundary by changing
pressure and temperature conditions during in situ X-ray diffraction measurements. Nevertheless, the phase boundary was well
constrained by quench method with a pressure calibration based on the spinel-postspinel boundary of Mg2SiO4 determined by in situ X-ray experiments. This yielded the ilmenite-perovskite phase boundary of P (GPa) = 25.0 (±0.2) – 0.003
T (°C) for a temperature range of 1200–1800 °C, which is generally consistent with the results of the present in situ X-ray
diffraction measurements within the uncertainty of ∼±0.5 GPa. The phase boundary thus determined between ilmenite and perovskite
phases in MgSiO3 is slightly (∼0.5 GPa) lower than that of the spinel-postspinel transformation in Mg2SiO4.
Received: 19 May 1999 / Accepted: 21 March 2000 相似文献
10.
Yoshifumi Kuroda 《Journal of Oceanography》2000,56(1):103-116
The variability of the New Guinea Coastal Current (NGCC) and New Guinea Coastal Undercurrent (NGCUC) were examined from one year time series of current data from ADCP moorings at 2°S, 142°E and 2.5°S, 142°E. Change in the hydrographic structure induced by monsoonal wind forcing was also examined from hydrographic data along the 142°E covering consecutively two winter seasons and two summer seasons. The westward NGCUC was observed to persist year around. The annual mean depth of the current core was 220 m, the mean speed of the zonal component was 54 cm/s with a standard deviation of 15 cm/s at the 2.5°S site. Velocity fluctuations at 20–30 day period were observed year around. Seasonal reversal of the surface intensified NGCC was clearly observed. In the boreal summer characterized by the southeasterly monsoon, westward currents of over 60 cm/s were dominant in the surface layer. The warm, low-salinity layer thickened at this time and sloped down toward the New Guinea coast from the equator. This surface water accumulation may be caused by onshore Ekman drift at the New Guinea coast, combined with weak Ekman upwelling at the equator. In the boreal winter, an eastward surface current developed to 100 cm/s extending down to 100 m depth in response to the northwesterly monsoonal winds. Coastal upwelling was indicated in this season and the surface water accumulated at the equator due to Ekman convergence. Shipboard ADCP data indicated that the NGCUC intensified in boreal summer as the width and depth of the NGCUC increased. 相似文献