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81.
Hydrofracturing stress measurements have been carried out to about 0.4 km in two boreholes in Quaternary volcanic rocks in Reykjavik, Iceland, on the flank of the Reykjanes-Langjökull continuation of the Mid-Atlantic Ridge. The measurements indicate a dominant orientation of H max approximately perpendicular to the axial rift zone, in contrast to earthquake focal mechanism solutions from within the axial rift zone of the Reykjanes Peninsula. In one hole (H32) a depth-dependent change in stress orientation is indicated, with 1 horizontal above a depth of about 0.25 km, and vertical below it; however the orientation of H max remains unchanged. The data thus suggest reconciliation of an apparent conflict between the dominantly compressive indications of shallow overcoring stress measurements and dominant extension as required by focal mechanism solutions. The measured stresses are supported by the more reliable of overcoring measurements from southeast Iceland, and by recent focal mechanism solutions for the intraplate Borgarfjördur area. A fundamental change in crustal stresses appears therefore to occur as a function of distance from the axis of the axial rift zone. The data seem reasonably explicable in terms of a combination of thermoelastic mechanisms associated with accretion and cooling of spreading lithosphere plates. Stresses directly associated with the driving mechanisms of plate tectonics apparently do not dominate the observed stress pattern. 相似文献
82.
Guanajuato State, located in central Mexico, with less than 2% of the countrys area, has almost 17,000 deep water wells, from which nearly 4,000 cubic hectometers (hm3) per year are being extracted, more than 1,000 hm3 over the estimated renewable yield. Since, in Mexico, water is administered under federal jurisdiction by the National Water Commission (CNA, for its Spanish acronym), the state government faces the challenge of ensuring its populations economic development without formal means of intervention. Being thus limited to apply mandatory policies and measures, the state water program has focused on the implementation of a two-sided strategy. First, basic hydrogeological studies and mathematical groundwater hydrodynamic models were developed upon a comprehensive survey of existing wells and a general revision of the states geological framework. Second, a structure for water users participation in water management actions was promoted (from the dissemination of information to the implementation of pilot efficient water use projects) with financial, technical and political support from the state. Simultaneously, a coordinated effort towards the completion of the water users registry was performed with the federal authority along with other supporting measures such as training and monitoring programs. In this paper, a general overview of the projects achievements and challenges is presented.To make direct contact with the water-user associations mentioned in this paper, please write to Eng. Aurelio Navarrete of the State Water Council at: cehgto@prodigy.net.mx. 相似文献
83.
Numerical, experimental and theoretical models of fluvial architecture and palaeosol development are tested with outcrops of Upper Pliocene-Lower Pleistocene sediment in the southern Rio Grande rift, New Mexico. The sediment was deposited and subsequently exhumed in the Jornada del Muerto basin, a westward-tilted half graben whose footwall corresponds to the Rincon Hills and San Diego Mountain fault blocks. The axial river, the ancestral Rio Grande, shared time between the Jornada del Muerto basin and the adjacent Corralitos basin. The ancestral Rio Grande entered the Jornada del Muerto basin via a gap between the footwall blocks, periodically flowing southward towards San Diego Mountain, or making a broad northward sweep into the northern fluvial salient towards the Rincon Hills fault block and unfaulted northern edge of the basin. Ten logged sections up to 35 m thick are correlated using the top of the formation (La Mesa surface), a 1·59 Ma pumice conglomerate, and a ground-water carbonate/opal bed. Additionally, one of the sections is dated by reversal magnetostratigraphy. Consistent with the model of Bridge & Leeder (1979 ) and Bridge & Mackey (1993a ), differential tilting of the Jornada del Muerto half graben resulted in sections directly adjacent to the faults that consist almost exclusively of multistorey channel sands/sandstones, whereas more distal sections contain a greater proportion of crevasse-splay fine sand and overbank mudstone and calcic palaeosols. Along the axis of the northern fluvial salient, a northward decrease in channel/floodplain ratio, a decrease in channel recurrence interval from 171 kyr to 685 kyr, and an increase in the maturity of calcic palaeosols are consistent with southward tilt of the unfaulted northern edge of the basin. An upsection decrease in sediment accumulation rate in the northern fluvial salient from 0·036 mm/ yr to 0·017 mm/ yr corresponds to an increase in the ratio of channel/floodplain facies and in the number of multistorey channel sands/sandstones, and is consistent with the model of Bridge & Leeder (1979 ) in which avulsion frequency is independent of sediment accumulation rate. Stage II and III calcic palaeosols indicate 103−105 year of landscape stability and soil formation between periods of floodplain deposition in response not only to basin tilting but also because the ancestral Rio Grande had multiple paths within the Jornada del Muerto basin and shared time between the Corralitos and Jornada del Muerto basins. 相似文献
84.
WOLFF J. A.; ROWE M. C.; TEASDALE R.; GARDNER J. N.; RAMOS F. C.; HEIKOOP C. E. 《Journal of Petrology》2005,46(2):407-439
The MioceneQuaternary Jemez Mountains volcanic field(JMVF), the site of the Valles caldera, lies at the intersectionof the Jemez lineament, a Proterozoic suture, and the CenozoicRio Grande rift. Parental magmas are of two types: K-depletedsilica-undersaturated, derived from the partial melting of lithosphericmantle with residual amphibole, and tholeiitic, derived fromeither asthenospheric or lithospheric mantle. Variability insilica-undersaturated basalts reflects contributions of meltsderived from lherzolitic and pyroxenitic mantle, representingheterogeneous lithosphere associated with the suture. The Kdepletion is inherited by fractionated, crustally contaminatedderivatives (hawaiites and mugearites), leading to distinctiveincompatible trace element signatures, with Th/(Nb,Ta) and La/(Nb,Ta)greater than, but K/(Nb,Ta) similar to, Bulk Silicate Earth.These compositions dominate the mafic and intermediate lavas,and the JMVF is therefore derived largely, and perhaps entirely,from melting of fertile continental Jemez lineament lithosphereduring rift-related extension. Significant variations in Pband Nd isotope ratios (206Pb/204Pb = 17·2018·93;143Nd/144Nd = 0·512440·51272) result fromcrustal contamination, whereas 87Sr/86Sr is low and relativelyuniform (0·70400·7048). We compare theeffects of contamination by low-87Sr/86Sr crust with assimilationof high-87Sr/86Sr granitoid by partial melting, with Sr retainedin a feldspathic residue. Both models satisfactorily reproducethe isotopic features of the rocks, but the lack of a measurableEu anomaly in most JMVF mafic lavas is difficult to reconcilewith a major role for residual plagioclase during petrogenesis. KEY WORDS: Jemez Mountains volcanic field; Rio Grande rift; lithospheric mantle; crustal contamination; trace elements; radiogenic isotopes 相似文献
85.
A procedural paleosurface mapping tool, using hypsometric curves and digital elevation models, was developed and applied to
three hydrographic basins that erode common areas in the coastal ranges of Brazil, in southeastern South America. The method
consists of identifying areas favorable for the occurrence of paleosurfaces and their corresponding surficial formations as
correlated to specific erosion events. Attributes from hypsometric curves, and logarithmic functions fitted to proper curve
segments, are combined with common morphometric properties of paleosurfaces given a set of criteria. Zones satisfying the
criteria are mapped as pertaining to specific paleosurfaces. Field survey confirms the agreement between predicted and observed
occurrence and absence of paleosurfaces. 相似文献
86.
87.
对磁通门磁变仪状态函数的测定方法进行了研究,提出了磁通门磁变仪标度值——状态函数的测定和磁通门磁变仪记录的校正计算方法。 相似文献
88.
Dynamic Method of Seismic Casualty Assessment 总被引:1,自引:0,他引:1
The concept of Initial Casualty Matrix is introduced. Using some probability distribution functions, the initial casualty matrix of masonry is determined. The dynamic method of seismic casualty assessment is established and then applied to the Tangshan earthquake data, with some conclusions drawn. 相似文献
89.
超长灌注桩检测结果分析 总被引:1,自引:0,他引:1
本文通过四根超长大直径灌注桩单桩竖向承载力静载荷试验以及其它方法检测结果可知 ,超长桩承载力与使用反循环工艺、缩短成孔成桩时间、合理的泥浆性能、桩身混凝土完整性以及清渣彻底性有着密切相关。 相似文献
90.