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131.
A flare rising from behind the solar limb was recorded simultaneously by the UCSD X-ray detector on OSO-III (7.7–200 keV)
and the Caltech photoheliograph on Robinson Laboratory roof (Hα). The de-occultation gives excellent spatial resolution of
the X-ray source. Spectra suggest that the material was already heated to 27 000 000° and that the increase in flux was due
to the de-occultation. The flux rise to maximum was proportional to the apparent area. The uniformity of this rise shows that
there was no special kernel of emission. Comparison of the deduced volume with the bremsstrahlung formula gives a density
of about 1010 for the 27 000 000° component of the flare; this is confirmed by consideration of the maximum possible coulomb braking. The
actual decay is more likely by escape rather than coulomb braking. 相似文献
132.
133.
Harold Zirin 《Solar physics》1969,9(1):77-87
Some parameters of chromospheric structure are drawn from recently published XUV spectroheliograms. The HeII emission above the limb arises from the small amount of He+ still existing at 106°. The larger amounts of He+ in the cooler corona at the poles explain the polar cap absorption in 304. The flat distribution of emission in Oiv and Ov, with a sharp spike at the limb, is caused by the rough structure of the chromosphere and the variable excitation in the emitting spicules. The intensity of the Nevii lines shows that the transition zone between chromosphere and corona is very sharp.This research was supported by the National Aeronautics and Space Administration under Grant NASA NGR 05 002 034. 相似文献
134.
Harold Clénet Patrick Pinet Yves Daydou Frédérick Heuripeau Christine Rosemberg David Baratoux Serge Chevrel 《Icarus》2011,213(1):404-422
An automatic procedure has been implemented on the original MGM approach (Sunshine et al., 1990) in order to deal with an a priori unknown mafic mineralogy observed in the visible-near infrared by reflectance spectroscopy in the case of laboratory or natural rock spectra. We consider all the mixture possibilities involving orthopyroxene, clinopyroxene and olivine, and use accordingly for each configuration different numbers of Gaussians, depending on the potential complexity of the mixture. A key issue is to initialize the MGM procedure with a proper setting for the Gaussians parameters. An automatic analysis of the shape of the spectrum is first performed. The continuum is handled with a second order polynomial adjusted on the local maxima along the spectrum and Gaussians parameters initial settings are made on the basis of laboratory results available in the literature in the case of simple mixtures of mafic minerals. The returned MGM solutions are then assessed on spectroscopic grounds and either validated or discarded, on the basis of a mineralogical sorting.The results presented in this paper are a first quantitative step to characterize both modal and chemical compositions of pyroxenes and olivines. A demonstration of the methodology on specific examples of binary and ternary olivine-pyroxenes mixtures has been made, which shows that the different non-linear effects which affect the Gaussian parameters (center and strength) can be successfully handled. Of note is the fact that the band center positions associated with the different mafic minerals are not set here in the inverse problem, and thus the MGM outputs are truly informative of the chemical composition of pyroxenes and olivines. With the consideration of some limits on the detection thresholds, these results are quite promising for increasing the operational use of the Modified Gaussian Model with large hyperspectral data sets in view of establishing detailed mineralogical mappings of magmatic units. 相似文献
135.
Land cover mapping forms a reference base for resource managers in their decision-making processes to guide rural/urban growth and management of natural resources. The aim of this study was to map land cover dynamics within the Upper Shire River catchment, Malawi. The article promotes innovation of automated land cover mapping based on remote sensing information to generate data products that are both appropriate to, and usable within different scientific applications in developing countries such as Malawi. To determine land cover dynamics, 1989 and 2002 Landsat images were used. Image bands were combined in transformations and indices with physical meaning; together with spatial data, to enhance classification accuracy. A maximum likelihood classification for each image was computed for identification of land cover variables. The results showed that the combination of spatial and digital data enhanced classification accuracy and the ability to categorise land cover features, which are relatively inhomogeneous. 相似文献
136.
AbstractThe potential impacts of future climate change on the evolution of groundwater recharge are examined at a local scale for a 546-km2 watershed in eastern Canada. Recharge is estimated using the infiltration model Hydrologic Evaluation of Landfill Performance (HELP), with inputs derived from five climate runs generated by a regional climate model in combination with the A2 greenhouse gas emissions scenario. The model runs project an increase in annual recharge over the 2041–2070 period. On a seasonal basis, however, a marked decrease in recharge during the summer and a marked increase during the winter are observed. The results suggest that increased evapotranspiration resulting from higher temperatures does not offset the large increase in winter infiltration. In terms of individual water budget components, clear differences are obtained for the different climate change scenarios. Monthly recharge values are also found to be quite variable, even for a given climate scenario. These findings are compared with results from two regional-scale studies.
Editor D. Koutsoyiannis; Associate editor M. Besbes 相似文献
137.
Four recently drilled, closely spaced wells near Kalkaska, Michigan encountered a thick zone of organic-rich sediments at a depth of about 130 m; all are interpreted as part of the same unit. Two radiocarbon dates and botanical data derived from the carbonaceous material along with associated sediments indicate that about 35,000 B.P. the site was ice-free, poorly drained, and supported first an open and later a closed boreal forest. These two and eight additional radiocarbon determinations (four finite and four “infinite”) from wood recovered during other research are compared with all other previously published dates for Middle Wisconsinan material from southern Michigan. This array of ages suggests that at least parts of the state were not glaciated during much if not all of the Middle Wisconsinan, including the Cherrytree Stadial. Botanical evidence also indicates that about 35,000 B.P. the climate in the northwest part of the Southern Peninsula was considerably cooler than at present, possibly being influenced by a glacier with a margin in Ontario. 相似文献
138.
139.
This paper reports experimental measurements performed to test the ability of electrical resistivity tomography (ERT) imaging to provide quantitative information about transport parameters in porous media such as the dispersivity α, the mixing front velocity u, and the retardation factor R(f) associated with the sorption or trapping of the tracers in the pore structure. The flow experiments are performed in a homogeneous porous column placed between two vertical set of electrodes. Ionic and dyed tracers are injected from the bottom of the porous media over its full width. Under such condition, the mixing front is homogeneous in the transverse direction and shows an S-shape variation in the flow direction. The transport parameters are inferred from the variation of the concentration curves and are compared with data obtained from video analysis of the dyed tracer front. The variations of the transport parameters obtained from an inversion performed by the Gauss-Newton method applied on smoothness-constrained least-squares are studied in detail. While u and R(f) show a relatively small dependence on the inversion procedure, α is strongly dependent on the choice of the inversion parameters. Comparison with the video observations allows for the optimization of the parameters; these parameters are found to be robust with respect to changes in the flow condition and conductivity contrast. 相似文献
140.
Harold K. Farr 《Marine Geodesy》2013,36(2):77-93
Abstract In May, 1977, the first non‐military version of a multi‐beam, wide swath, deep ocean, bathymetric sonar was placed in service. Called SEA BEAM, this equipment provides high resolution bathymetric data across a swath width approximately equal to 78% of the depth. Angu ar resolution is 2.7° with a maximum operating depth of 11,000 m. Real time displays include a CRT presentation of the thwartship profile and a continuous strip chart of bottom contours. All sounding data are recorded on digital magnetic tape for final processing and merging with corrected navigation data. More recently, a companion system called HYDRO CHART has gone into operation for continental shelf surveys. 相似文献