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121.
122.
Element transport by dehydration of subducted sediments: Implication for arc and ocean island magmatism 总被引:5,自引:0,他引:5
High-pressure experiments on a natural pelite have been conducted at 2–11-GPa pressures in order to evaluate contributions of subducted sediments to arc and ocean island magmatism. Obtained phase relations suggest that, at least in modern subduction zones, subsolidus dehydration of chlorite and phengitic muscovite in the subducted sediments, rather than partial melting, is a predominant process in overprinting sediment components onto the magma source region. Trace element compositions of sediment-derived fluids are estimated based on dehydration experiments at 5.5 GPa and 900/1300°C. Pb is effectively transported by fluids relative to other elements. This results in the Pb enrichment for arc basalts by fluids, generated by the dehydration of subducted sediments, together with altered mid-ocean ridge basalt (MORB), and complementary depletion of Pb in subducted sediments. Inferred arc magma compositions obtained by model calculations based on the present experimental results agree well with a natural primitive arc basalt composition. A large increase in the U/Pb ratio in the subducted sediments at deeper levels than major dehydration depths results in a high Pb isotopic ratio through radioactive decay after long periods of isolation. Combined with other isotopic ratios such as Sr and Nd, it is possible to produce the EM II source, one of the enriched geochemical reservoirs for ocean island basalt magmas, by mixing of a small amount of subducted sediments with depleted or primitive mantle. 相似文献
123.
Stream temperature ranged from 3 to 4°C at an experimental site during snowmelt on Hokkaido Island, Japan, which provided direct evidence of major contributions of subsurface water to stream water. In contrast, stream temperatures during rainstorms in summer decreased gradually after stream flow peaked, attaining a nearly constant temperature ranging from 9 to 11°C. During storm flow recession, stream temperatures during summer or snowmelt were similar to the soil temperature at 1·8 m below the land surface, suggesting that subsurface water contributions to stream flow are derived from this depth. The hygrographs during two rainstorms, August 1987 and September 1989, were separated using temperature. The stream temperature was assumed to depend on the mixing of surface flow, having a temperature ranging from that of rainfall to that of shallow (50 cm deep) soil water, and subsurface flow, having the temperature of the soil at 1·8 m below the land surface. Subsurface flow was estimated to contribute 85–90% of the total stream flow during each rainstorm. A two‐component hydrograph separation was also evaluated using specific conductance. Runoff contributions from the two sources for the temperature and specific conductance analysis were similar. Analysis of the temperature and conductance–discharge hysteresis loop, and of individual flow components for storm hygrographs, provide a general picture of the runoff process in the experimental basin. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
124.
Ryuichi Shinjo Takele Chekol Daniel Meshesha Tetsumaru Itaya Yoshiyuki Tatsumi 《Contributions to Mineralogy and Petrology》2011,162(1):209-230
Major and trace element and isotopic ratios (Sr, Nd and Pb) are presented for mafic lavas (MgO > 4 wt%) from the southwestern
Yabello region (southern Ethiopia) in the vicinity of the East African Rift System (EARS). New K/Ar dating results confirm
three magmatic periods of activity in the region: (1) Miocene (12.3–10.5 Ma) alkali basalts and hawaiites, (2) Pliocene (4.7–3.6 Ma)
tholeiitic basalts, and (3) Recent (1.9–0.3 Ma) basanite-dominant alkaline lavas. Trace element and isotopic characteristics
of the Miocene and Quaternary lavas bear a close similarity to ocean island basalts that derived from HIMU-type sublithospheric
source. The Pliocene basalts have higher Ba/Nb, La/Nb, Zr/Nb and 87Sr/86Sr (0.70395–0.70417) and less radiogenic Pb isotopic ratios (206Pb/204Pb = 18.12–18.27) relative to the Miocene and Quaternary lavas, indicative of significant contribution from enriched subcontinental
lithospheric mantle in their sources. Intermittent upwelling of hot mantle plume in at least two cycles can explain the magmatic
evolution in the southern Ethiopian region. Although plumes have been originated from a common and deeper superplume extending
from the core–mantle boundary, the diversity of plume components during the Miocene and Quaternary reflects heterogeneity
of secondary plumes at shallower levels connected to the African superplume, which have evolved to more homogeneous source. 相似文献
125.
Michinori Honda Shintaro Ohno Atsushi Iizuka Katsuyuki Kawai Hideki Ohta 《Geotechnical and Geological Engineering》2011,29(2):171-180
An evaluation method for the mechanical behavior of unsaturated soils is studied in this paper. Although the mechanical behavior
of unsaturated soils is complicated, a simple modeling is preferable in practice. This is because the soil properties are
not homogeneous and ground data is limited when structures are being designed. In addition, in order to evaluate the reliability
of the design, the physical meanings of the parameters applied in the prediction model should be clear. Firstly, the authors
study the relationship between compaction curves and compression indexes in the unsaturated state that is used in the proposed
constitutive model. Based on the constitutive model, the stress paths for constant volume shear tests are formulated under
a constant void ratio condition and the stress paths for undrained shear tests are calculated under a constant water content
condition. In the case of unsaturated specimens, the volume of these specimens changes with the shear deformation and the
stress paths depend on the initial degree of saturation. The results of the calculation qualitatively describe the test results
by considering the changes in effective confining pressure in the undrained condition and the water retention curves. 相似文献
126.
127.
In order to understand the kinematics which likely facilitated the speedy rupturing process of the 1999 Mw 7.6 Taiwan Chi-Chi earthquake, we examined exposed rocks in the Taiwan Slate belt, where the pressure and temperature conditions most resembled the hypocentre of the Chi-Chi earthquake, i.e. sub-greenschist facies. Field observations and composition analyses of the silicified vein-rich zones beneath the duplex structure suggest that impermeable slate layers may serve as cap rocks for confining deep-seated fluids. These fluids most likely come from the Taiwan metamorphic complex at deeper depths by the dehydration and decarbonation reactions (or partial melting). In addition, the gouge zone of a link fault above the detachment also indicates the presence of overpressured fluids during faulting. It is probable that episodic leakage of the confined fluid reservoirs may provide essential fluids for fault lubrication during earthquake ruptures. 相似文献
128.
Toshitaka Suzuki Yoshinori Iizuka Teruo Furukawa Kenichi Matsuoka Kokichi Kamiyama Okitsugu Watanabe 《极地研究(英文版)》2003,14(1)
1 IntroductionAntarcticicesheetisaburialgroundforatmosphericdeposition .Sincethereiscon tinuousinteractionbetweentheicesheetandtheatmosphere,variousatmosphericsub stancesareinjectedtotheicesheetsequentiallyintimeandspace.Therefore,verticalanalysesoftheicesheetprovideuswithinformationaboutpastclimaticchange (Delmas1 992 ;LegrandandMayewski 1 997)andhorizontalanalysesoftheicesheetprovideuswithknowledgeregardinglong rangetransportofairbornematerials (Kamiyamaetal.1 989;KreutzandMayewski 1 999)… 相似文献
129.
Yoshinori Iizuka 《极地研究(英文版)》2003,14(1)
1 IntroductionBasaliceofglaciersandicesheetshasbeenwidelystudiedtounderstandtheinacces sibleice bedinterface (e.g.,Lawson 1 979;Gowetal.1 979;Knight 1 994;HubbardandSharp 1 995 ,Souchez1 988) .Useofstableisotopesofbasaliceisasuperiormethodtodeterminewhetherthebasalicewasformedbymelt refreezingornon meltingattheinlandbaseofglaciersandicesheets.Inatheoreticalstudyofstableisotopes,JouzelandSouchez ( 1 982 )showedthatforaclosedsystem ,wherenowaterisinputoroutput,theslopegradientdefinedbyδ18O… 相似文献
130.
Tsuyoshi Iizuka Malcolm T. McCulloch Tsuyoshi Komiya Takazo Shibuya Kenji Ohta Haruka Ozawa Emiko Sugimura Kenneth D. Collerson 《Contributions to Mineralogy and Petrology》2010,160(6):803-823
Mt. Narryer and Jack Hills meta-sedimentary rocks in the Narryer Gneiss Complex of the Yilgarn Craton, Western Australia are
of particular importance because they yield Hadean detrital zircons. To better understand the tectonothermal history and provenance
of these ancient sediments, we have integrated backscattered scanning electron images, in situ U–Pb isotopic and geochemical
data for monazites from the meta-sediments. The data indicate multiple periods of metamorphic monazite growth in the Mt. Narryer
meta-sediments during tectonothermal events, including metamorphism at ~3.3–3.2 and 2.7–2.6 Ga. These results set a new minimum
age of 3.2 Ga for deposition of the Mt. Narryer sediments, previously constrained between 3.28 and ~2.7 Ga. Despite the significant
metamorphic monazite growth, a relatively high proportion of detrital monazite survives in a Fe- and Mn-rich sample. This
is likely because the high Fe and Mn bulk composition resulted in the efficient shielding of early formed monazite by garnet.
In the Jack Hills meta-sediments, metamorphic monazite growth was minor, suggesting the absence of high-grade metamorphism
in the sequence. The detrital monazites provide evidence for the derivation of Mt. Narryer sediments from ca. 3.6 and 3.3 Ga
granites, likely corresponding to Meeberrie and Dugel granitic gneisses in the Narryer Gneiss Complex. No monazites older
than 3.65 Ga have been identified, implying either that the source rocks of >3.65 Ga detrital zircons in the sediments contained
little monazite, or that >3.65 Ga detrital minerals had experienced significant metamorphic events or prolonged sedimentary
recycling, resulting in the complete dissolution or recrystallization of monazite. 相似文献