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61.
62.
Use of Systematic, Palaeoflood and Historical Data for the Improvement of Flood Risk Estimation. Review of Scientific Methods 总被引:2,自引:0,他引:2
Gerardo Benito Michel Lang Mariano Barriendos M. Carmen Llasat Felix Francés Taha Ouarda Varyl Thorndycraft Yehouda Enzel Andras Bardossy Denis Coeur Bernard Bobée 《Natural Hazards》2004,31(3):623-643
The catastrophic floods recently occurring in Europe warn of the critical need forhydrologic data on floods over long-time scales. Palaeoflood techniques provideinformation on hydrologic variability and extreme floods over long-time intervals(100 to 10,000 yr) and may be used in combination with historical flood data (last1,000 yr) and the gauge record (last 30–50 yr). In this paper, advantages anduncertainties related to the reconstruction of palaeofloods in different geomorphologicalsettings and historical floods using different documentary sources are described.Systematic and non-systematic data can be combined in the flood frequency analysisusing different methods for the adjustment of distribution functions. Technical toolsintegrating multidisciplinary approaches (geologic, historical, hydraulic and statistical)on extreme flood risk assessment are discussed. A discussion on the potential theoreticalbases for solving the problem of dealing with non-systematic and non-stationary data ispresented. This methodology is being developed using new methodological approachesapplied to European countries as a part of a European Commission funded project (SPHERE). 相似文献
63.
Guillermo R. Angeles Gerardo M. E. Perillo M. Cintia Piccolo Jorge O. Pierini 《Geomorphology》2004,57(3-4):263-274
The fractal dimension (D) was estimated for nine tidal channels depicted in thematic mapper (TM) Landsat-5 imagery to derive information about the degree of geomorphological control on a tidal channel network characteristic of the Bahía Blanca Estuary (Argentina). Two methods, box counting and contiguity, were used to estimate fractal dimensions for each tidal channel. All channels produced D values close to 1, meaning that they are self-affine fractal features. However, these fractal dimensions do not represent the meandering pattern complexity characteristic of the tidal channels analysed. Although both methods allowed for estimation of D, the contiguity method showed that three of the channels actually are not fractal but have sinusoidal characteristics, a condition that was not detected by the former method. 相似文献
64.
Microdeformation of lacustrine laminite sequences from Late Miocene formations of SE Spain: an interpretation of loop bedding 总被引:2,自引:0,他引:2
Jose P. Calvo Miguel Rodriguez-Pascua Silvia Martin-Velazquez Sergio Jimenez & Gerardo De Vicente 《Sedimentology》1998,45(2):279-292
Lacustrine laminated sediments (laminites) present in Late Miocene formations of the Híjar Basin, SE Spain, display well developed loop bedding, a structure consisting of bundles of laminae that are sharply constricted at intervals, giving a morphology of loops or links of a chain. The laminite sequences, which are interbedded with turbidite marlstones, were accumulated on the bottom of a permanently stratified lake developed in a rapidly subsiding basin limited by 010° and 105° normal faults. As deduced from both macro- and microdeformational analyses, the basin evolved under an extensional stress field throughout the Late Miocene. Four main types of loops, simple and complex loops with subcategories, have been recognized within the laminite sequence. Simple loops of type 1 show the best definite pattern, quite similar to ' pinch and swell structures ', a type of boudinage typical of stretching of alternating beds where the competence contrast is not strongly marked. The remaining loop types display contortion and occasional breakage of laminae (microfaulted edges) indicative of microdeformation near the boundary between the ductile-brittle deformational fields. The distribution of the various loop types across the laminite sequence reflects an interplay between progressive lithification of the laminites as sedimentation progressed and tectonic stresses which affected the sediment sequence. Accordingly, a mechanism of deformation under an extensional stress field, ultimately related to the creep movement of the main basin faults which resulted in successive seismic shocks of low magnitude, is proposed to explain the formation of loop bedding in the laminites. 相似文献
65.
66.
The relevant potential theory is given for a current point source in the presence of a conductive slab embedded in a homogeneous host region of infinite extent. The thin sheet representation is obtained from the exact integral formulation by a simple mathematical limit process. The same result is also deduced directly at the outset by applying a thin sheet boundary condition. The apparent resistivity for a two electrode array is then computed for the case where the bore hole intersects the thin sheet at right angles. The corresponding results for the dilution factor, relevant to the induced polarization response, are also obtained. It is shown that the apparent resistivity and the dilution factor are constant when the potential and the current electrode straddle the sheet but there is a characteristic decrease as the electrodes move away from the sheet. 相似文献
67.
Pedro A. BASILE Gerardo A. RICCARDI Center for Hydroenvironmental Research National University of Rosario Riobamba bis 《国际泥沙研究》2002,(1)
1 INTRODUCTION Mathematical models to analyze the one-dimensional morphological evolution of alluvial rivers, induced either by natural events or anthropic actions, have been commonly applied since the original work of de Vries (1957, 1965, 1969). In the last decades much effort was made in developing suitable 2D horizontal and 3D time-depending mathematical models to study riverbed changes. In fact, full 2D-H hydro-morphological models (Olesen, 1987; Spasojevic and Holly, 1988) as w… 相似文献
68.
One hundred and three samples of granitic rock taken systematically from the Andean part of Colombia reveal that the observed variation in phosphorus content reflects the variation observed for the wholerock chemical composition. This relationship was established using a form of trend analysis termed COMTRENA and information-theory statistics. 相似文献
69.
Ignacio S. Torres-Alvarado Surendra P. Verma Gerardo Carrasco-Núñez 《Journal of Earth System Science》2000,109(1):67-78
Seven hundred and twenty-five Sr, two hundred and forty-three Nd and one hundred and fifty-one Pb isotopic ratios from seven
different Mexican magmatic provinces were compiled in an extensive geochemical database. Data were arranged according to the
Mexican geological provinces, indicating for each province total number of analyses, range and mean of values and two times
standard deviation (2σ). Data from seven provinces were included in the database: Mexican Volcanic Belt (MVB), Sierra Madre
Occidental (SMO), Baja California (BC), Pacific Ocean (PacOc), Altiplano (AP), Sierra Madre del Sur (SMS), and Sierra Madre
Oriental (SMOr). Isotopic values from upper mantle and lower crustal xenoliths, basement outcrops and sediments from the Cocos
Plate were also compiled. In the MVB the isotopic ratios range as follows:87Sr/86Sr 0.703003-0.70841;143Nd/144Nd 0.512496-0.513098;206Pb/204Pb 18.567-19.580;207Pb/204Pb 15.466-15.647;208Pb/204Pb 38.065-38.632. The SMO shows a large variation in87Sr/86Sr ranging from ∼0.7033 to 0.71387.143Nd/144Nd ratios are relatively less variable with values from 0.51191 to 0.51286. Pb isotope ratios in the SMO are as follows:206Pb/204Pb 18.060-18.860;207Pb/204Pb 15.558-15.636;208Pb/204Pb 37.945-38.625. PacOc rocks show the most depleted Sr and Nd isotopic ratios (0.70232-0.70567 for Sr and 0.512631-0.513261
for Nd). Pb isotopes for PacOc show the following range:206Pb/204Pb 18.049-19.910;207Pb/2047Pb 15.425-15.734;208Pb/204Pb 37.449-39.404. The isotopic ratios of the AP rocks seem to be within the range of those from the PacOc.
Most samples with reported Sr and Nd isotopic data are spread within and around the “mantle array”. The SMO seems to have
been formed by a mixing process between mantle derived magmas and continental crust. The MVB appears to have a larger mantle
component, with AFC as the dominant petrogenetic process for the evolved rocks. There is still a need for Pb isotopic data
in all Mexican magmatic provinces and of Nd isotopes in BC, AP, SMS, and SMOr. 相似文献
70.
Natural Hazards - The ranking of events is a powerful tool to evaluate risks of catastrophic events. Here we analyze the rank-statistical profile of the North Atlantic annual accumulated cyclone... 相似文献