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71.
Abstract— Two unusual dark clasts found in the Vigarano CV3 chondrite were examined using an optical microscope and a scanning electron microscope (SEM). Both clasts lack chondrules, Ca-Al-rich inclusions, and coarse-grained mineral fragments; they, instead, contain abundant inclusions that consist of fine grains (<1 μm) of homogeneous Fe-rich olivine, thus resembling the fine-grained variety of dark inclusions in CV3 chondrites. The external shapes of inclusions in the clasts bear a close resemblance to those of chondrules and chondrule fragments; some of the inclusions are surrounded by dark rims similar to chondrule rims. Our SEM observations reveal the following unusual characteristics: 1) the inclusions are not mere random aggregates of olivine grains but have peculiar internal textures, that is, assemblages of round or oval shaped outlines, which are suggestive of pseudomorphs after porphyritic olivine chondrules; 2) one of thick inclusion rims contains a network of vein-like strings of elongated olivine grains; 3) an Fe-Ni metal aggregate in one of the clasts has an Fe-, Ni-, S-rich halo suggesting a reaction between its precursor and the surrounding matrix; and 4) olivine in the clasts commonly shows a swirly, fibrous texture similar to that of phyllosilicate. These characteristics suggest that the dark clasts in Vigarano are not primary aggregates of dust in the solar nebula but were affected by aqueous alteration and subsequent dehydration by heating after accretion to the meteorite parent body. The fine olivine grains in these clasts were presumably produced by thermal transformation of phyllosilicate, as is the case with those in the two thermally metamorphosed Antarctic CM chondrites, Belgica-7904 and Yamato-86720. From textural and mineralogical similarities, some of the dark inclusions and clasts previously reported from CV3 chondrites and other types of meteorites may have origins common with these clasts in Vigarano. 相似文献
72.
Fine-grained Ca-Al-rich inclusions (FGIs) in Yamato-81020 (CO3.0) and Kainsaz (CO3.1-CO3.2) chondrites have been studied by secondary ion mass spectrometry. The FGIs from Yamato-81020 consist of aggregates of hibonite, spinel, melilite, anorthite, diopside and olivine grains with no petrographic evidence of alteration. In contrast, the FGIs from Kainsaz commonly contain alteration products such as nepheline. From replacement textures and chemical compositions of altered and unaltered FGIs, we conclude that the alteration products formed by decomposition of melilite and anorthite. All phases in the Yamato-81020 FGIs are enriched in 16O, with δ17, 18O = ∼−40‰ except for one FGI that experienced melting. Oxygen isotopic compositions of melilite, anorthite, some spinel and diopside in Kainsaz FGIs changed from δ17, 18O = ∼−40‰ toward 0‰ by aqueous alteration. Alteration products in FGIs are depleted in 16O relative to primary phases, with δ17, 18O = ∼0‰. These results show that FGIs in CO chondrites commonly had 16O-rich compositions in the solar nebula. The original 16O-rich FGIs were modified to 16O-poor compositions during aqueous alteration in the parent body. 相似文献
73.
Homogenization temperature and salinity were determined for fluid inclusions in mostly quartz and partly sphalerite, cassiterite, and barite from the 28 tin-polymetallic ore deposits in Bolivia. Generally, the homogenization temperatures and salinities of these fluid inclusions are comparatively high for ore deposits formed by cassiterite mineralization, such as Morococala and Avicaya in the Oruro district, frequently indicating a temperature higher than 300°C and salinity higher than 20 equiv. wt% NaCl. Particularly, it is quite possible that tin deposits associated with the W-Bi and tourmaline mineralizations such as Viloco and Caracoles have been produced by such high-temperature hypersaline fluid ranging up to 500°C and 56 equiv. wt% NaCl, similar to the porphyry copper type. This feature reveals that the hydrothermal fluid related to the Sn-W-Bi mineralization may be of magmatic origin. Homogenization temperatures for the Pb-Zn deposits with no tin minerals are low, mostly ranging 170°–300°C. At the Avicaya-Bolivar mining area in the Oruro district as well as at the Tasna and Chocaya-Animas mining areas in the Quechisla district temperature gradients consistent with the zonal distributions of ore minerals were confirmed. 相似文献
74.
The synoptic map of the solar wind speed (SWS) estimated by the computer-assisted tomography (CAT) method with interplanetary scintillation observations is constructed for the 1909 Carrington rotation. A similar synoptic map of expansion rate (RBR) of the coronal magnetic field calculated by the so-called 'potential model' with the photospheric magnetic field is also constructed under the radial field assumption (RF model). These maps consist of 64800 (180×360) data points of equal area. We examine for the first time relations between the SWS estimated by the CAT technique and the RBR calculated by the RF model. A highly significant correlation is found between the SWS and the RBR. A simple correlation coefficient is about –0.72; that is, high-velocity winds emanate from photospheric areas corresponding to a low expansion rate of the coronal magnetic field, and low-velocity winds emanate from photospheric areas of high expansion rate. This result suggests that there is some acceleration mechanism relating to the coronal field expansion. 相似文献
75.
Discovery of local topics by using latent spatio-temporal relationships in geo-social media 总被引:1,自引:0,他引:1
Kyoung-Sook Kim Isao Kojima Hirotaka Ogawa 《International journal of geographical information science》2016,30(9):1899-1922
ABSTRACTSocial networks have played a crucial role as information channels for people to understanding their daily lives beyond merely being communication tools. In particular, coupling social networks with geographic location has boosted the worth of social media to not only enable comprehension of the effects of natural phenomena such as global warming and disasters, but also the social patterns of human societies. However, the high rate of social data generation and the large amounts of noisy data makes it difficult to directly apply social media to decision-making processes. This article proposes a new system of analyzing the spatio-temporal patterns of social phenomena in real time and the discovery of local topics based on their latent spatio-temporal relationships. We will first describe a model that represents the local patterns of populations of geo-tagged social media. We will then define a local topic whose keywords share a region in space and time and present a system implementation based on existing open source technologies. We evaluated the model of local topics with several ways of visualization in experiments and demonstrated a certain social pattern from a dataset of daily Twitter streams. The results obtained from experiments revealed certain keywords had a strong spatio-temporal proximity even though they did not occur in the same message. 相似文献
76.
Yasufumi Kojima 《Monthly notices of the Royal Astronomical Society》1998,293(1):49-52
Quasi-toroidal oscillations in slowly rotating stars are examined within the framework of general relativity. Unlike the Newtonian case, the oscillation frequency to first order of the rotation rate is not a single value, even for uniform rotation. All the oscillation frequencies of the r -modes are purely neutral and form a continuous spectrum limited to a certain range. The allowed frequencies are determined by the resonance condition between the perturbation and the background mean flow. The resonant frequency varies with the radius according to the general relativistic dragging effect. 相似文献
77.
Shigeaki Kojima 《Journal of Oceanography》2002,58(2):343-363
I review chemoautosynthesis-based faunal communities which have been discovered in the deep-sea areas in the Northwestern
Pacific. Fauna of each community and further biological studies are summarized. Zoogeographical and evolutionary status of
communities in the Northwestern Pacific is discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
78.
Utsumi Motoo Kojima Shigeaki Nojiri Yukihiro Ohta Suguru Seki Humitake 《Journal of Oceanography》1994,50(6):635-642
Mesoscale distribution of the density and productivity of bacterioplankton at representative geological locations in the rift ecosystem of the North Fiji Basin were clarified by sampling using a mannedShinkai 6500 submersible. The bacterioplankton density inside the hot and warm fluids of hydrothermal vents was one order magnitude greater than that in the deep water outside the vent plume. The bacterial production was highest inside the hot and warm vent fluids, and was higher just outside the hot and warm vent fluids than further outside in the deep water surrounding the vent plume, respectively. Productivity from outside to inside the vent fluid varied from 0.01 to 0.71 gC m–3 day–1. 相似文献
79.
Shin’ichiro Kako Atsuhiko Isobe Satoquo Seino Azusa Kojima 《Journal of Oceanography》2010,66(2):291-297
The present study attempts to establish a scientifically reliable method capable of computing the drifting-object sources
and their outflows. First, the temporal variability of the drifting-object amount is investigated every two months on a beach
west of Japan, where various source regions are anticipated because of spatiotemporally variable northeastward ocean currents
over the East China Sea. Next, in order to specify drifting-object sources, two-way particle tracking model (PTM) experiments
are carried out using simulated ocean currents and leeway drift estimated from QuikSCAT/Seawinds wind data. Finally, an inverse
method with a Lagrange multiplier is applied to estimate drifting-object outflows at each source on the basis of the two-way
PTM results and beach surveys. Accuracy of object-source identification using the two-way PTM is validated by comparing disposable-lighter
sources suggested by phone numbers printed on the lighter surface with those computed by the model. In order to examine the
reliability of the inverse estimation, the number of plastic-bottle caps found in actual beach surveys is compared with that
computed using a forward in-time PTM during the same period of actual beach surveys, over which the outflows obtained using
the inverse method are given at each source in the model. 相似文献
80.
Uemoto Jyunpei Moriyama Toshifumi Nadai Akitsugu Kojima Shoichiro Umehara Toshihiko 《Natural Hazards》2019,95(3):485-503
Natural Hazards - The recognition of landslides and making their inventory map are considered to be urgent tasks not only for damage estimation but also for planning rescue and restoration... 相似文献