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71.
Jamesina J. Simpson 《Surveys in Geophysics》2009,30(2):105-130
Advances in computing technologies in recent decades have provided a means of generating and performing highly sophisticated
computational simulations of electromagnetic phenomena. In particular, just after the turn of the twenty-first century, improvements
to computing infrastructures provided for the first time the opportunity to conduct advanced, high-resolution three-dimensional
full-vector Maxwell’s equations investigations of electromagnetic propagation throughout the global Earth-ionosphere spherical
volume. These models, based on the finite-difference time-domain (FDTD) method, are capable of including such details as
the Earth’s topography and bathymetry, as well as arbitrary horizontal/vertical geometrical and electrical inhomogeneities
and anisotropies of the ionosphere, lithosphere, and oceans. Studies at this level of detail simply are not achievable using
analytical methods. The goal of this paper is to provide an historical overview and future prospectus of global FDTD computational
research for both natural and man-made electromagnetic phenomena around the world. Current and future applications of global
FDTD models relating to lightning sources and radiation, Schumann resonances, hypothesized earthquake precursors, remote sensing,
and space weather are discussed.
相似文献
Jamesina J. SimpsonEmail: |
72.
On 3 December 1987, the supply ship Nella Dan ran aground at Macquarie Island (54°29′S, 158°58′E) releasing about 270 000 I of oil, mostly light marine diesel, into the sea. At the time of the incident, many marine invertebrates were washed up dead along 2 km of shoreline. Twelve months later, the shore community was investigated using 1. algal and invertebrate populations of the littoral and sublittoral rocky shore, and 2. the invertebrate communities living in the holdfasts of the giant kelp Durvillaea antarctica, which were collected for later examination. Investigations were undertaken at both affected and control locations. Analyses of differences in community structure involved nested ANOVA and multidimensional scaling techniques. On the rocky substrate, the effect of the spill was restricted to some biota of the lower littoral and sublittoral zones—particularly echinoderms and the patellid limpet Nacella macquariensis. There were differences in cover for some algal species between locations. Within the kelp holdfasts, communities were dominated by peracarid crustaceans at control locations and by polychaetes (particularly the opportunistic groups—capitellids, cirratulids and spionids) at oil-affected locations.
The communities have recently been re-surveyed (in the summer of 1994–1995) to assist in the interpretation of the results and to gauge the extent of recovery of the affected biota. 相似文献
73.
74.
Barbara G. Simpson Ph.D. 《地震工程与结构动力学》2020,49(14):1406-1427
Strongback-braced frames employ an essentially elastic steel truss, or strongback, that distributes demands more uniformly to delay or prevent story mechanisms. Because inertial forces are no longer limited by the formation of a story mechanism, strongback-braced frames can exhibit large elastic force demands, particularly in the higher modes. This paper characterizes the higher-mode force response of strongback-braced frames. Four-story archetypes were designed using nonlinear dynamic analyses to incorporate higher-mode force demands into the design process. The response of the archetypes was compared with that of reference buckling-restrained braced frames that were allowed to form story mechanisms. The force demands in the strongback were then described using equivalent-static forces to represent the inertial forces induced by the higher modes. Force demands in the strongback arise from a yielding first-mode ‘pivoting’ and elastic higher-mode ‘bending’ response. These higher-mode force demands are elastic, ill-constrained by the strength of the yield mechanism, and depend significantly on the choice of ground motion record used for the analysis. In remaining elastic in the higher modes, the strongback distributes demands more uniformly and mitigates the formation of story mechanisms. Consequently, design and analysis methods for strongback-braced frames need to include estimates for these near-elastic higher-mode force demands. 相似文献
75.
The coastal plain of the Río de la Plata constitutes a large wetland which develops on the right margin of the river estuary. Anthropic activities such as intensive exploitation of groundwater carried out in the vicinity of the wetland can modify the natural hydrological regime. The aim of this work is to asses the effects of intensive aquifer exploitation in coastal wetlands using hydrogeological models. Such models allow to evaluate changes in the environmental conditions of wetland at regional level. The hydrogeological model exposed in this work shows how the intensive groundwater exploitation affects the wetland area, generating important variations both in the groundwater flows and in the salinity of the groundwater. Identification of these modifications to the environment is important to generate guidelines leading to minimize these affectations. 相似文献
76.
ADCP and temperature chain measurements have been used to estimate the rate of energy input by wind stress to the water surface in the south basin of Windermere. The energy input from the atmosphere was found to increase markedly as the lake stratified in spring. The efficiency of energy transfer (Eff), defined as the ratio of the rate of working in near-surface waters (RW) to that above the lake surface (P 10), increased from ~0.0013 in vertically homogenous conditions to ~0.0064 in the first 40 days of the stratified regime. A maximum value of Eff~0.01 was observed when, with increasing stratification, the first mode internal seiche period decreased to match the diurnal wind period of 24 h. The increase in energy input, following the onset of stratification was reflected in enhancement of the mean depth-varying kinetic energy without a corresponding increase in wind forcing. Parallel estimates of energy dissipation in the bottom boundary layer, based on determination of the structure function show that it accounts for ~15% of RW in stratified conditions. The evolution of stratification in the lake conforms to a heating stirring model which indicates that mixing accounts for ~21% of RW. Taken together, these estimates of key energetic parameters point the way to the development of full energy budgets for lakes and shallow seas. 相似文献
77.
87Sr/86Sr ratios of ground waters in the Bighorn and Laramie basins' carbonate and carbonate-cemented aquifer systems, Wyoming, United States, reflect the distinctive strontium isotope signatures of the minerals in their respective aquifers. Well water samples from the Madison Aquifer (Bighorn Basin) have strontium isotopic ratios that match their carbonate host rocks. Casper Aquifer ground waters (Laramie Basin) have strontium isotopic ratios that differ from the bulk host rock; however, stepwise leaching of Casper Sandstone indicates that most of the strontium in Casper Aquifer ground waters is acquired from preferential dissolution of carbonate cement. Strontium isotope data from both Bighorn and Laramie basins, along with dye tracing experiments in the Bighorn Basin and tritium data from the Laramie Basin, suggest that waters in carbonate or carbonate-cemented aquifers acquire their strontium isotope composition very quickly--on the order of decades. Strontium isotopes were also used successfully to verify previously identified mixed Redbeds-Casper ground waters in the Laramie Basin. The strontium isotopic compositions of ground waters near Precambrian outcrops also suggest previously unrecognized mixing between Casper and Precambrian aquifers. These results demonstrate the utility of strontium isotopic ratio data in identifying ground water sources and aquifer interactions. 相似文献
78.
Abstract The Samborombón Bay area (Argentina) is a coastal plain environment that contains groundwater resources with high salinity. In addition, there are local freshwater lenses associated with shell ridges and sand sheets in the region. In this work, the groundwater travel time in these freshwater lenses is estimated based on their geological conditions, which include hydraulic conductivity, recharge, morphology and discharge to surface freshwater or to saline groundwater. Groundwater travel times in the freshwater lenses were calculated from the equations developed by Chesnaux and Allen. The travel times estimated for the different scenarios were relatively short. The results indicate that the groundwater flow tends to be strongly dependent on the recharge conditions, with an excess of water in the water balance. The results can be applied to help design sustainable management methods to exploit this water resource system and also to assess the impact of contaminant plumes on this groundwater resource. Citation Carol, E., Kruse, E. & Roig, A. (2010) Groundwater travel time in the freshwater lenses of Samborombón Bay, Argentina. Hydrol. Sci. J. 55(5), 754–762. 相似文献
79.
Lance A. Waller Li Zhu Carol A. Gotway Dennis M. Gorman Paul J. Gruenewald 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):573-588
Past studies consistently indicate measurable local associations between alcohol distribution and the incidence of violence.
These results, coupled with measurements of spatial correlation, reveal the importance of spatial analysis in the study of
the interaction of alcohol and violence. While studies increasingly incorporate spatial correlation among model residuals
to improve precision and reduce bias, to date, most analyses assume associations that are constant and independent of location,
an assumption coming under increasing scrutiny in the quantitative geography literature. In this paper, we review and contrast
two approaches for the estimation of and inference for spatially heterogeneous effects (i.e., associative factors whose impacts on the outcome of interest vary throughout geographic space). Specifically,
we provide an in-depth comparison of “geographically weighted regression” models (allowing covariate effects to vary in space
but only allowing relatively ad hoc inference) with “variable coefficient” models (allowing varying effects via spatial random
fields and providing model-based estimation and inference, but requiring more advanced computational techniques). We compare
the approaches with respect to underlying conceptual structures, computational implementation, and inferential output. We
apply both approaches to violent crime, illegal drug arrest, and alcohol distribution data from Houston, Texas and compare
results in light of the differing methodological structures of the two approaches. 相似文献
80.
Richard Hope Simpson 《Geoarchaeology》2007,22(1):111-120
The survey of Messenia by the University of Minnesota Messenia Expedition (UMME) was recently followed by the Pylos Regional Archaeological Project (PRAP). Despite improvements in survey methodology, problems remain, particularly with the interpretation of field data and with extrapolation, especially when this is made based on survey results alone, without excavation. In addition, the work of the archaeologists has not yet been fully integrated with that of the earth scientists. Some examples are given of the difficulties encountered in this survey, especially concerning retrodictions (predictions about the past) of ancient settlement patterns and numbers. Suggestions are made here for further survey and selective excavation, especially in eastern Messenia, where fieldwork has been far less extensive than in western Messenia. More fieldwork is needed to determine the pattern of geomorphic changes in the region, especially in relation to the varying degrees of visibility and/or preservation of the ancient sites. Meanwhile, increased recent human activity is rapidly destroying or endangering those remains that have hitherto survived, so that survey is often de facto of a rescue nature. © 2007 Wiley Periodicals, Inc. 相似文献