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101.
Raymond C. Fletcher 《Tectonophysics》1977,39(4):593-606
The folding of a single viscous layer embedded in an uniformly shortening medium is analyzed mathematically by superposing the mean flow corresponding to uniform shortening and a perturbing flow corresponding to folding. The mean flow is coupled to the perturbing flow in the boundary conditions applying at the layer—medium interfaces. These are expanded according to the surface-wave approximation in hydrodynamics, and the solution applies when the amplitude of folding is small. Folding with interfacial adherence and interfacial slip are both treated. The dominant wavelenghts obtained do not agree with those presented in Biot (1959a) and Remberg (1963a, 1970b). 相似文献
102.
Raymond C. Fletcher 《Tectonophysics》1982,83(3-4)
Simple governing equations coupling diffusional transport at a macroscopic scale and deformation in a tight rock are formulated. The deformation alone is described by a linear viscous rheology. Several deformations of geological interest are analyzed, including the folding of an embedded layer. A basic feature is the length-scale dependence of diffusional effects. Interpretation of natural structures permits the estimation of parameters governing the diffusional transport and rate of deformation. 相似文献
103.
Current methods for evaluating Sm-Nd isochron data determine initial ?Nd (?Ndi) values by extrapolation to , resulting in unnecessarily large uncertainties. It is shown that values of ?Ndi can be optimised by determining the present composition of a hypothetical sample having chrondritic . This method of determination requires only a simple data translation for its implementation using standard line-fitting techniques, and is particularly advantageous in providing precise ?Ndi values for sample suites of limited compositional range close to chondritic .A method of constructing error (uncertainty) polygons appropriate to the optimised (?Ndi, T) values is discussed, and optimum?Ndi values are tabulated for all published Precambrian Sm-Nd isochrons. 相似文献
104.
Fletcher G. Driscoll 《Quaternary Research》1980,14(1):31-49
A series of ice-cored Neoglacial moraines at the terminus of the Klutlan Glacier covers an area of 90 km2. Studies were made to determine empirically how long ice persisted in the Klutlan moraines and to develop models that can accurately predict wastage rates under current climatic conditions. A meltout curve based on climatological data reflects the sum of three melting processes: surficial melting, melting by lake water, and melting by geothermal heat. About 950 yr are required to melt 180 m of ice with a debris concentration of 1%, or about 1200 yr for a 1.5% debris load. Another meltout curve, based on seismic data, suggests total meltout in about 875 yr. When all geologic factors are considered, the empirical meltout curve is remarkably similar to that derived by considering the major heat-flux parameters. Meltout rates can be predicted if (1) the fundamental climatic parameters can be ascertained, and (2) the sediment concentration in the ice is known. 相似文献
105.
The biological damage caused by the large oil spill in Bantry Bay and the clean-up measures adopted to deal with it (already reported in the Marine Pollution Bulletin) has been followed up in the months following the oil spill. This report refers to damage to algae and lichens. 相似文献
106.
SHRIMP U–Pb zircon studies on two post-collisional granitic plutons and reassessment of the data previously reported for two anatectic gneissic granites are used to assess the late Neoproterozoic history of the Florianópolis Batholith, southern Brazil. The results, supported by SEM backscattered and cathodoluminescence imagery, identify inherited zircon populations and confirm the long-lived, crustal recycling processes responsible for the accretion of the batholith. The study casts new lights on the timing of the processes involved in the generation and modification of the internal structure of distinct zircon populations, and enables discrimination to be made between inherited cores and melt-precipitated overgrowths. New dating of two post-tectonic plutons (samples 1 and 2) revealed crystals showing magmatic-textured cores sharply bounded by melt-precipitated overgrowths. The U/Pb isotopic results from both samples spread along concordia by ca. 40 m.y. (sample 1) to 100 m.y. (sample 2), clustering in two closely spaced (bimodal), partially overlapping peaks. Melt-precipitated rims and homogeneous new grains, dated at ca. 600 Ma, furnish the crystallisation age of the plutons. The magmatic textured cores and xenocrysts dated at ca. 630–620 Ma are interpreted as inherited restitic material from supposedly short-lived (meta)granitic sources. The reassessment of previous SHRIMP data of two banded anatectic granitoids (samples 3 and 4) revealed more complex morphological patterns, in which the overgrown inherited cores are sharply bounded against large melt-precipitated rims, dated at ca. 600 Ma and 592±2 Ma, respectively. Major populations of magmatic-textured inherited cores dated at 2006±3 Ma and 2175±13 Ma characterise samples 3 and 4, respectively. The latter additionally shows metamorphic and magmatic inherited cores with a large range of ages (ca. 2900–620 Ma), suggesting partial melting of metasedimentary components. The main magmatic Paleoproterozoic core populations are interpreted as inherited restite from partial melting of the adjacent (meta)tonalitic gneiss and amphibolitic country-rock (paleosome). The recognition of the (melt-precipitated) Neoproterozoic overgrowths and new crystals, and the restite provenance of the cores, supplants a previous interpretation of Paleoproterozoic magmatism (cores) and Neoproterozoic (solid-state) metamorphic overprint. As a major consequence of the former interpretation, the unit was mistakenly considered part of major Paleoproterozoic gneissic remnant within the Neoproterozoic Florianópolis Batholith/arc. 相似文献
107.
Large (60 kg, minus 2 mm) sediment samples collected from a 5-km reach of a mature highland stream were used to investigate the effects of bar morphology and channel slope on the downstream dispersion of Au. Results are compared with those for an abundant heavy mineral (magnetite) and are discussed in terms of differential entrapment of light and heavy minerals by gravels and differences in supply of magnetite and Au to the study reach. Gold is selectively trapped in gravels; therefore, highest Au concentrations, a long dispersion train and lowest between-sampling-location variability were obtained with heavy-mineral concentrates of the minus 105+74 μm fraction from sandy gravels. In contrast, sands in bar-tail eddy pools gave the least reliable Au concentrations, due to random (Poisson) sampling errors and local post-depositional winnowing, and show rapid downstream anomaly decay. 相似文献
108.
In an attempt to study the value and utilization of categorical data collected during regional stream-sediment surveys, we have taken data from the Canadian Uranium Reconnaissance Program in S.E. British Columbia. After initial classification of the data into six subsets on the basis of catchment geology, probability plots were constructed for each of 11 elements (Zn, Cu, Pb, Ni, Co, Fe, Mn, Mo, W, Hg and U) and used to select thresholds to reject anomalous samples. The remaining background populations then were successively subdivided into groups according to their classification with respect to four sediment characteristics (abundance of fines, sand, organic matter and sediment colour) and six environmental parameters (physiography, water flow rate, stream class, drainage pattern, bank type and contamination). After calculation of log means for each group and a pooled common standard error, differences between group means were tested for significance using Duncan's Multiple Range Test. The relative degree of confidence in the significance of difference between categorical means for any single field parameter were determined using a ratio method.Results of Duncan's Multiple Range Test, show that, many field observations can be related systematically to metal content of drainage sediments. Some elements are more susceptible than others to environmental factors and some factors and some factors influence few or many elements. For example, in sediments derived from granites there are significant relationships between bank type and concentration of 8 elements (Zn, Cu, Ni, Pb, Co, Fe, Mn and Hg). In contrast, the texture of these sediments, using estimates of fines content as an index, did not significantly affect the concentration of any of the elements studied. In general, results indicate that groups of environmental factors acting collectively are more important than any single factor in determining background metal content of drainage sediments. 相似文献
109.
C.M. Green K.M.U. Fletcher S. Cheyney G.J. Dawson S.J. Campbell 《Geophysical Prospecting》2019,67(6):1611-1619
This paper reviews the impacts of new satellite altimeter data sets and new technology on the production of satellite gravity. It considers the contribution of the increased data volume, the application of new altimeter acquisition technology and the potential for future developments. Satellite altimeter derived gravity has provided gravity maps of the world's seas since the 1980s, but, from 1995 to 2010, virtually all improvements were in the processing as there were no new satellite data with closely spaced tracks. In recent years, new data from CryoSat-2 (launched in 2010) and the geodetic mission of Jason-1 (2012–2013) have provided a wealth of additional coverage and new technology allows further improvements. The synthetic aperture radar mode of CryoSat-2 uses a scanning approach to limit the size of the altimeter sea surface footprint in the along-track direction. Tests indicate that this allows reliable data to be acquired closer to coastlines. The synthetic aperture radar interferometric mode of CryoSat-2 uses two altimeters to locate sea-surface reflection points laterally away from the satellite track. In a study to generate gravity for freshwater lakes, this mode is found to be valuable in extending the available satellite coverage. The AltiKa altimeter uses higher frequency radar to provide less noisy sea-surface signals and its new orbit mode gives potential for further improvements in satellite gravity. Future developments include the potential for swath mapping to provide further gravity improvements. 相似文献
110.
We present recent observations of coronal jets, made by TRACE and Yohkoh/SXT on 28 May and 19 August 1998. The high spatial resolution of TRACE enables us to see in detail the process of material
ejection; in the line of Fe ix (one million degrees) we see both bright emitting material and dark absorbing/scattering material
being ejected, i.e., both hot and cold material, highly collimated and apparently ejected along the direction of the overlying
field lines. Bright ejecta are seen simultaneously in Lyman α for one event and Yohkoh/SXT in the other. The jets on the two days are different in that the 19 August jet displays the morphology typical of a one-sided
anemone jet while the 28 May jet exhibits a two-sided jet morphology. The 19 August jet shows evidence for rotation and an
interesting bifurcation at large distances from the energy release site. We study the physical properties and energetics of
these jetting events, and conclude that existing theoretical models capture the essential physics of the jet phenomena.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005213826793 相似文献