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151.
Tadashi Shimamura Shohei Yanagita Kazuo Yamakoshi Kenichi Nogami Okio Arai Yuji Tazawa Koichi Kobayashi 《Earth and Planetary Science Letters》1979,42(3):379-382
Isotopic compositions of potassium and calcium in individual magnetic spherules were determined. No significant anomaly was observed for potassium within twice the statistical error (2σ), although for calcium isotopes enrichments of46Ca,44Ca and42Ca were observed in one spherule. The relative excess of46Ca,44Ca and42Ca in the spherule agrees with the relative yield of spallogenic calcium isotopes observed in iron meteorites. This fact indicates that the enrichment in the calcium isotopes was caused by cosmic ray irradiation of the spherule in outer space. 相似文献
152.
Tsutomu Sueishi Takaharu Sato Naoto Kawai Kazuo Kobayashi 《Physics of the Earth and Planetary Interiors》1979,19(1):1-11
Two short geomagnetic episodes in the middle Matuyama epoch have been identified within thin (4.3-mm) sections of two deep-sea calcareous sediment cores taken in the western equatorial Pacific. Both cores are correlated by magnetostratigraphic and micropaleontological methods. Magnetic stability and paleomagnetic reliability are tested by alternating field demagnetization of natural remanent magnetization as well as by the ratios of intensities of anhysteretic remanent magnetization to those of saturation isothermal remanent magnetization. One episode is dated to be 1.06 m.y. BP. The other is identified to be about 1.94 m.y. BP, which is presumably in agreement with the Reunion event. Both episodes seem to be accompanied by conspicuous drops in field intensity. Possible correlation of field intensity with biological productivity in the ocean is also postulated from the present paleomagnetic results. 相似文献
153.
Partition coefficients for trace amounts of trivalent ions between artificial single crystals of Mg2SiO4 grown by the Czochralski method and the coexisting melt have been determined by neutron activation analysis. They are found to vary greatly with the amount of visible imperfections in the crystal and slightly with the concentration of the ions in the melt. Plots of the partition coefficients against ionic radius of the trace ions give a pattern which agrees qualitatively with that found in a natural olivine phenocryst-groundmass pair. 相似文献
154.
Daisuke Takahashi Kazuo Kido Yoshinori Nishida Naoto Kobayashi Naoyuki Higaki Hideo Miyake 《Continental Shelf Research》2007
We conducted hydrographic observations in 2002 to investigate the anticyclonic eddy that emerges every summer in Funka Bay, Hokkaido, Japan, and elucidate dynamical structure and wind-driven upwelling within the eddy. The anticyclonic eddy has a vertical scale of 32 m and is characterized by a strong baroclinic flow and a sharp pycnocline with a concave isopycnal structure. The sharp pycnocline occurs below a warm and relatively low-salinity water termed summer Funka Bay water (FS), which is formed by heating from solar radiation and dilution from river discharge in summertime Funka Bay. Flow of the anticyclonic eddy rotates as a rigid body at each layer, and the horizontal scale and rotation period of the eddy in the surface layer are about 15 km and 2.2 days, respectively. The dynamical balance of the anticyclonic eddy is well explained by the gradient flow balance. The contribution of centrifugal force to the gradient flow balance is about 27%. Therefore, the effect of the nonlinear term associated with centrifugal force cannot be neglected in considering the dynamics of the anticyclonic eddy in summertime Funka Bay. In addition, upwelling of subsurface water was observed in the surface layer of the central part of the eddy. The formation mechanism of this upwelling is consistent with interaction between horizontal uniform wind and the eddy. This upwelling is driven by upward Ekman pumping velocity related to the horizontal divergence of Ekman transport. In summertime Funka Bay, there are two wind effects that affect the anticyclonic eddy: a decay effect of the upwelling of subsurface water resulting from horizontal uniform wind (mainly northwesterly wind), and a maintenance or spin-up effect of horizontal non-uniform wind (mainly southerly–southeasterly seasonal wind) with negative wind stress curl. 相似文献
155.
Salient facts on the vertical movement now in action in Japan are summarized and briefly discussed with reference to the fundamental structure of her geology to show some relations between the living and fossil mountains. 相似文献
156.
Meteorological observation by a helicopter was carried out to investigate the structure of sea breezes over the coastal area of Tosa Bay in Shikoku island, Japan. Several groups of wave trains were found over the sea during a flight made on 25 November 1992. Not only the terrain barrier but the remaining cold air pools formed in valleys hindered further advance of the sea breeze inland, so that the presence of such wave trains may appear to be due to the effect of the secondary flow which supplies moister and cooler air from behind the sea breeze front. 相似文献
157.
158.
The role of meso-scale eddies in mixed layer deepening and mode water formation in the western North Pacific 总被引:3,自引:1,他引:2
Shinya Kouketsu Hiroyuki Tomita Eitarou Oka Shigeki Hosoda Taiyo Kobayashi Kanako Sato 《Journal of Oceanography》2012,68(1):63-77
Distributions of mixed layer depths around the centers of anti-cyclonic and cyclonic eddies in the North Pacific Ocean were
composited by using satellite-derived sea surface height anomaly data and Argo profiling float data. The composite distributions
showed that in late winter, deeper mixed layers were more (less) frequently observed inside the cores of the anti-cyclonic
(cyclonic) eddies than outside. This relationship was the clearest in the region of 140°E–160°W and 35°N–40°N, where the temperature
and salinity of the deep mixed layers were similar to those of the lighter variety of central mode water (L-CMW). A simple
one-dimensional bulk mixed layer model showed that both strong sea-surface heat and momentum fluxes and weak preexisting stratification
contributed to formation of the deep mixed layer. These conditions were associated with the anti-cyclonic eddies, suggesting
that these eddies are important in the formation of mode waters, particularly L-CMW. 相似文献
159.
Variations of water properties in surface and intermediate layers along 32°S in the southern Indian Ocean were examined using
a 50-year (1960–2010) time series reproduced from historical hydrographic and Argo data by using optimum interpolation. Salinity
in the 26.7–27.3σθ density layer decreased significantly over the whole section, at a maximum rate of 0.02 decade−1 at 26.8–26.9σθ, for the 50-year average. Three deoxygenating cores were identified east of 75°E, and the increasing rate of apparent oxygen
utilization in the most prominent core (26.9–27.0σθ) exceeded 0.05 ml l−1 decade−1. The pycnostad core of Subantarctic Mode Water (SAMW) and the salinity minimum of Antarctic Intermediate Water shifted slightly
toward the lighter layers. Comparisons with trans-Indian Ocean survey data from 1936 suggest that the tendencies found in
the time series began before 1960. Interestingly, cores of many prominent trends were located just offshore of Australia at
26.7–27.0σθ, which is in the SAMW density range. Spectrum analysis revealed that two oscillation components with time scales of about
40 and 10 years were dominant in the subsurface layers. Our results are fairly consistent with, and thus support, the oceanic
responses in the southern Indian Ocean to anthropogenic climate change predicted by model studies. 相似文献
160.
Redistribution and export of contaminated sediment within eastern Fukushima Prefecture due to typhoon flooding 下载免费PDF全文
Akihiro Kitamura Hiroshi Kurikami Kazuyuki Sakuma Alex Malins Masahiko Okumura Masahiko Machida Koji Mori Kazuhiro Tada Yasuhiro Tawara Takamaru Kobayashi Takafumi Yoshida Hiroyuki Tosaka 《地球表面变化过程与地形》2016,41(12):1708-1726
Tropical cyclones expose river basins to heavy rainfall and flooding, and cause substantial soil erosion and sediment transport. There is heightened interest in the effects of typhoon floods on river basins in northeast Japan, as the migration of radiocaesium‐bearing soils contaminated by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident will affect future radiation levels. The five main catchments surrounding FDNPP are the Odaka, Ukedo, Maeda, Kuma and Tomioka basins, but little quantitative modelling has been undertaken to identify the sediment redistribution patterns and controlling processes across these basins. Here we address this issue and report catchment‐scale modelling of the five basins using the GETFLOWS simulation code. The three‐dimensional (3D) models of the basins incorporated details of the geology, soil type, land cover, and used data from meteorological records as inputs. The simulation results were checked against field monitoring data for water flow rates, suspended sediment concentrations and accumulated sediment erosion and deposition. The results show that the majority of annual sediment migration in the basins occurs over storm periods, thus making typhoons the main vectors for redistribution. The Ukedo and Tomioka basins are the most important basins in the region in terms of overall sediment transport, followed by the other three basins each with similar discharge amounts. Erosion is strongly correlated with the underlying geology and the surface topography in the study area. A low permeability Pliocene Dainenji formation in the coastal area causes high surface water flow rates and soil erosion. Conversely, erosion is lower in an area with high permeability granite basement rocks between the Hatagawa and Futaba faults in the centre of the study area. Land cover is also a factor controlling differences in erosion and transport rates between forested areas in the west of the study area and predominantly agricultural areas towards the east. The largest sediment depositions occur in the Ogaki and Takigawa Dams, at the confluence of the Takase and Ukedo Rivers, and at the Ukedo River mouth. Having clarified the sediment redistribution patterns and controlling processes, these results can assist the ongoing task of monitoring radioactive caesium redistribution within Fukushima Prefecture, and contribute to the design and implementation of measures to protect health and the environment. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献