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81.
The acoustic signature of fluid flow in complex porous media 总被引:2,自引:0,他引:2
Effective medium approximations for the frequency-dependent and complex-valued effective stiffness tensors of cracked/porous rocks with multiple solid constituents are developed on the basis of the T-matrix approach (based on integral equation methods for quasi-static composites), the elastic–viscoelastic correspondence principle, and a unified treatment of the local and global flow mechanisms, which is consistent with the principle of fluid mass conservation. The main advantage of using the T-matrix approach, rather than the first-order approach of Eshelby or the second-order approach of Hudson, is that it produces physically plausible results even when the volume concentrations of inclusions or cavities are no longer small. The new formulae, which operates with an arbitrary homogeneous (anisotropic) reference medium and contains terms of all order in the volume concentrations of solid particles and communicating cavities, take explicitly account of inclusion shape and spatial distribution independently. We show analytically that an expansion of the T-matrix formulae to first order in the volume concentration of cavities (in agreement with the dilute estimate of Eshelby) has the correct dependence on the properties of the saturating fluid, in the sense that it is consistent with the Brown–Korringa relation, when the frequency is sufficiently low. We present numerical results for the (anisotropic) effective viscoelastic properties of a cracked permeable medium with finite storage porosity, indicating that the complete T-matrix formulae (including the higher-order terms) are generally consistent with the Brown–Korringa relation, at least if we assume the spatial distribution of cavities to be the same for all cavity pairs. We have found an efficient way to treat statistical correlations in the shapes and orientations of the communicating cavities, and also obtained a reasonable match between theoretical predictions (based on a dual porosity model for quartz–clay mixtures, involving relatively flat clay-related pores and more rounded quartz-related pores) and laboratory results for the ultrasonic velocity and attenuation spectra of a suite of typical reservoir rocks. 相似文献
82.
Three-Dimensional Geopositioning Accuracy of Ikonos Imagery 总被引:3,自引:0,他引:3
An investigation of the accuracy potential of Ikonos 1m satellite imagery is reported. Three sensor orientation/triangulation models are applied to stereo- and three-image configurations of "Geo" imagery with the aim of achieving 3D geopositioning to sub-metre accuracy. The models considered comprise rational functions with bias compensation, affine projection and the direct linear transformation. Test results from the Melbourne Ikonos Testfield are reported and these show that with modest provision of good quality ground control, Ikonos "Geo" imagery can yield 3D object-point determination to an accuracy of 0.5m in planimetry and 0.7m in height. The accuracy achieved is not only consistent with expectations for rigorous sensor orientation models, but is also readily attainable in practice with only a small number of ground control points being required 相似文献
83.
ABSTRACT A genetic annealing (GAN) algorithm is used to derive an empirical model which predicts compressional-wave velocity values for overpressured siliciclastic rocks. The algorithm involves non-linear random searching and mutation techniques and its annealing component imposes a very strict control over the rate of convergence of the search. This technique provides an alternative to the standard calculations involving the effective stress coefficient ( n ). The pore pressure is introduced into the model as an explicit variable and as part of an overpressure coefficient, ( P p / P c ) − the ratio of pore to confining pressure. Empirical model-derived data and known laboratory data are compared and their differences are shown to be within statistically acceptable error limits. The empirical equation fits all under- and overpressured data simultaneously, irrespective of pore fluid pressure level, with the same parameters. It is used to predict seismic velocities very accurately for extreme levels of overpressure, starting from normally pressured experimental data. The model highlights the effect of pore pressure on the compressional-wave velocity of fully saturated samples with different clay contents. It can be used when the experimental data available are sparse and particularly when a prediction of material behaviour is necessary at specific pore fluid pressure and depth conditions. 相似文献
84.
Greg Brown Jonathan Rhodes Daniel Lunney Ross Goldingay Kelly Fielding Nicole Garofano Scott Hetherington Marama Hopkins Jo Green Skye McNamara Angie Brace Lorraine Vass Linda Swankie Clive McAlpine 《Transactions in GIS》2019,23(6):1184-1203
Geographic citizen science has much potential to assist in wildlife research and conservation, but the quality of observation data is a key concern. We examined the effects of sampling design on the quality of spatial data collected for a koala citizen science project in Australia. Data were collected from three samples—volunteers (n = 454), an Internet panel (n = 103), and landowners (n = 35)—to assess spatial data quality, a dimension of citizen science projects rarely considered. The locational accuracy of koala observations among the samples was similar when benchmarked against authoritative data (i.e., an expert‐derived koala distribution model), but there were differences in the quantity of data generated. Fewer koala location data were generated per participant by the Internet panel sample than the volunteer or landowner samples. Spatial preferences for land uses affecting koala conservation were also mapped, with landowners more likely to map locations for residential and tourism development and volunteers less likely. These spatial preferences have the potential to influence the social acceptability of future koala conservation proposals. With careful sampling design, both citizen observations and land use preferences can be included within the same project to augment scientific assessments and identify conservation opportunities and constraints. 相似文献
85.
Clive E. Willman 《Mineralium Deposita》2007,42(5):449-463
The Bendigo and Castlemaine goldfields are classic examples of structurally controlled orogenic gold deposits in the Bendigo
Zone of central Victoria, SE Australia. Detailed mapping and biostratigraphic interpretation has led to a better understanding
of the regional structural controls of this type of gold-quartz mineralisation. Mineralised quartz veins are hosted by the
Castlemaine Group, an Early-to-Middle Ordovician turbidite succession at least 3,000 m thick. Gold deposits are controlled
by low-displacement faults that are clustered into several belts (the goldfields) indicating a regional structural control.
The timing of mineralisation overlapped with that of the major period of deformation including folding, cleavage development
and regional faulting. The Bendigo and Castlemaine goldfields are located in an area termed the Whitelaw thrust sheet bounded
by two unmineralised, high-displacement, regional-scale faults. Mapping has revealed an interrelationship between the regional-scale
faults, regional structural style and goldfield location. The goldfields lie immediately west of the boundary between the
upper and lower portions of the thrust sheet and are characterised by symmetric folds with sub-horizontal to synclinal enveloping
surfaces, relatively low co-axial strains and moderate cleavage development. The non-gold-bearing areas immediately east of
each goldfield correspond with the lower part of the Whitelaw thrust sheet and are characterised by higher non-coaxial strains,
stronger cleavage and folds with wide west-dipping limbs giving rise to easterly vergent sections and steeply west-dipping
enveloping surfaces. That mineralisation was an integral part of the thin-skinned style of deformation in the central Bendigo
Zone is indicated by timing relationships and the interrelationship between local-scale mineralised structures and regional-scale
features such as large-displacement unmineralised faults, regional variations in fold style and overall thrust sheet geometry.
The work supports previous models that suggest mineralised fluids were focussed along a linked system of deep-seated faults.
The primary conduits may have been major regional-scale ‘intrazone’ faults, which are inferred to sole into detachments near
the base of the Castlemaine Group. It is proposed that these structures linked with minor intrazone faults and then with networks
of low-displacement mineralised faults that were strongly controlled by folds. The location of minor intrazone faults was
probably controlled by internal thrust sheet geometry. The distribution of gold deposits and of gold production suggests that
maximum fluid flow was concentrated along the eastern margins of networks of low-displacement faults. 相似文献
86.
87.
Arsenic concentrations were determined in the several stages of a short food chain culminating in school whiting (Sillago bassensis) from Waterman, Western Australia. Arsenic was shown to be present in school whiting as arsenobetaine. Analyses of plant material from Waterman suggest that the primary concentrator of arsenic from seawater is the brown kelp Ecklonia radiata. Analyses of trumpeter whiting (Sillago maculata) from Cockburn Sound, a semi-enclosed marine basin receiving arsenic-containing industrial effluents, reveal significantly lower levels of arsenic than school whiting from Waterman, an unpolluted environment. 相似文献
88.
Clive A. Foss 《Geophysical Journal International》1981,65(1):217-221
Summary. Working graphs are presented which, when used in conjunction with a stereographic projection, enable (a) magnitude and direction of the difference between two vectors to be estimated, and (b) a vector to be resolved into two or three components of prescribed directions. Applications of the methods to multicomponent natural remanent magnetizations are illustrated. 相似文献
89.
90.
SHAO Juliang Clive Fraser 《地球空间信息科学学报》2000,3(2):13-18,40
1 IntroductionThreedimensional(3_D)linearobjecttrackingisakeyoperationforanumberofstereovisionappli cations,forexample ,autonomouson_roadvehiclenavigation[2 ,5 ,9] andmobilemapping[3,1 1 ,1 8] .Suchsystemstypicallyexploittwostereoimagesonlyforlinearobjecttracking .Bi… 相似文献