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151.
152.
Robin Robertson 《Ocean Dynamics》2011,61(1):69-88
Interactions of tidal constituents and the transfer of energy from the tidal frequencies to other frequencies are investigated
using 3-D tidal simulations for the Indonesian seas, focusing on an area of active internal tides. Semidiurnal tides strongly
affect diurnal tides; however, semidiurnal tides are essentially unaffected by diurnal tides. The semidiurnal and diurnal
constituents interact with each other through non-linear interference, both destructive and constructive. Semidiurnal tides
generate harmonics at nearly the diurnal frequency and higher vertical wavenumbers. In Ombai Strait, these harmonics are out
of phase with the diurnal tides and interact destructively with the diurnal tides, effectively negating the diurnal response
in some locations. However, this is not a general response, and interactions differ between locations. Energy is also transferred
from both semidiurnal and diurnal tides to other frequencies across the spectrum, with more energy originating from semidiurnal
tides. These energy transfers are not homogeneous, and the spectral responses differ between the Makassar and Ombai Straits,
with the region east of Ombai showing a more active surface response compared to a more intense benthic response in Makassar.
In deep water away from topography, velocity spectra generally follow the Garrett–Munk (GM) relation. However, in areas of
internal tide generation, spectral density levels exceed GM levels, particularly between 4 and 8 cycles per day (cpd), indicating
increased non-linear interactions and energy transfer through resonant interactions. The model indicates strong surface trapping
of internal tides, with surface velocity spectra having significantly higher energy between 4 and 8 cpd even 100 km away from
the prominent sill generating the internal tides. 相似文献
153.
Field measurements were conducted in Mont-Saint-Michel Bay, a megatidal embayment (spring tidal range of 15 m), in order to monitor, over the course of a tidal cycle, sediment transport variability due to waves and tides on the upper part of a tidal flat characterised by shallow water depths. Sensors used to measure currents, water depth and turbidity were installed just above the bed (0.04 m). Two experiments were conducted under contrasting hydrodynamic conditions. The results highlight wave activity over the tidal flat even though observed wind waves were largely dissipated due to the very shallow water depths. Very high suspended sediment concentrations (up to 6 kg/m3) were recorded in the presence of wave activity at the beginning of the local flood, when significant sediment transport occurred, up to 7 times as much as under conditions of no wave activity. This influence may be attributed to the direct action of waves on bed sediments, to wave-induced liquefaction, and to the erosive action of waves on tidal channel banks. The sediment composition, comprising a clay fraction of 2-5%, may also enhance sediment transport by reducing critical shear stress through the sand lubrication effect. The results also show that antecedent meteorological conditions play an important role in suspended sediment transport on the tidal flat. Total sediment flux directions show a net transport towards the inner part of the bay that contributes to deposition over the adjacent salt marshes, and this tendency also prevails during strong wave conditions. Such sediment transport is characterised by significant variability over the course of the tidal cycle. During fair and moderate weather conditions, 83% and 71% of the total flux was observed, respectively, over only 11% and 28% of the duration of the local tidal cycle and with water depths between 0.04 and 0.3 m. These results suggest that in order to improve our understanding of sediment budgets in this type of coastal environment, it is essential to record data just at the beginning and at the end of tidal submergence close to the bed. 相似文献
154.
Future projections of temperature-related climate change impacts on the railway network of Great Britain 总被引:1,自引:0,他引:1
Erika J. Palin Hazel E. Thornton Camilla T. Mathison Rachel E. McCarthy Robin T. Clark John Dora 《Climatic change》2013,120(1-2):71-93
Great Britain’s main line railway network is known to experience various temperature-related impacts, e.g. track buckling and overhead power line sag at high ambient temperatures. Climate change could alter the frequency of occurrence of these impacts. We have therefore investigated the climate change impact on various temperature-related issues, identified during workshops with rail industry specialists, using a perturbed physics ensemble (PPE) of the Met Office’s regional climate model (RCM), HadRM3. We have developed novel approaches to combine RCM data with railway industry knowledge, typically by identifying key meteorological thresholds of interest and analysing exceedance of these out to the 2040s. We performed a statistical analysis of the projected changes for each issue, via bootstrapping of the unperturbed PPE member. Although neither the PPE nor the bootstrapping analysis samples the full range of uncertainty in the projections, they nonetheless provide complementary perspectives on the suitability of the projections for use in decision-making. Our main findings include projected increases in the summertime occurrence of temperature conditions associated with (i) track buckling, (ii) overhead power line sag, (iii) exposure of outdoor workers to heat stress, and (iv) heat-related delays to track maintenance; and (v) projected decreases in the wintertime occurrence of temperatures conditions associated with freight train failure owing to brake problems. For (i), the statistical significance varied with track condition and location; for (ii) and (iii), with location; and for (iv) and (v), projected changes were significant across Great Britain. As well as assessing the changes in climate-related hazard, information about the vulnerability of the network to past temperature-related incidents has been summarised. Combining the hazard and vulnerability elements will eventually support a climate risk assessment for the industry. 相似文献
155.
R.?Bernhart?OwenEmail author Robin?W.?Renaut Michael?G.?Stamatakis 《Journal of Paleolimnology》2011,46(1):151-166
The Mytilinii Basin, eastern Samos Island, Greece, is one of many basins that developed in southeastern Europe during the
Upper Neogene. The oldest lacustrine portion is of Late Miocene age, and besides tuffs, includes bituminous limestones, marlstones,
dolostones and porcelanites of the Pythagorion Formation, and the limestones and diatomites of the overlying Hora Beds. Younger
sedimentary rocks of Turolian through Pliocene age partially covered the Pythagorion Formation and Hora Beds (PFHB). Diatom
floras range from well preserved to highly corroded and from sparse to abundant. The main taxa include Cyclotella aegaea, C. aegaea var. pythagoria, an unidentified Cyclotella and Nitzschia frustulum, and less common Epithemia turgida, E. reichelti, Synedra ulna, Tryblionella granulata, Encyonema silesiaca, Diploneis ovalis and Cocconeis placentula. Chrysophyte cysts, Hydrobia molluscs and trace fossils occur sporadically. The environmental evolution of the PFHB can be divided into three major stages.
Fluctuating shallow to deeper waters in a saline lake characterized Stage A. Saline lake and playa environments with evidence
for frequent earthquake events in the form of convolute bedding, drape folds and brecciated sediments characterized Stage
B. During Stage C, the lake may have partially or completely split into two separate lakes. In the southeast, a saline playa
passed laterally into a deeper-water lake. Locally, fresher-water ponds occurred. Subsequently, a deeper, possibly oligotrophic
lake developed. In contrast, a saline lake with abundant diatoms formed in the northwest of the basin, in which diatom blooms
led to whiting events and deposition of carbonate laminae. Cyclotella dominated the early floras in this water body, with later assemblages being co-dominated by Cyclotella and Nitzschia frustulum, possibly reflecting seasonal changes. Sedimentation was terminated by uplift and (or) increasing aridity associated with
the Messinian Salinity Crisis. 相似文献
156.
Annie C. Robin 《Astrophysics and Space Science》1994,217(1-2):163-168
Models of population synthesis for the Galaxy have been developed in order to understand galactic structure and evolution. They allow to test scenarii of evolution by comparisons between model predictions and observed distributions. Forthcoming near-infrared surveys will enormously increase the amount of information about the distributions of late type stars in the Galaxy. We show here how population synthesis models will help to analyse these surveys and to interprete them in terms of mass function, star formation history and stellar evolution. 相似文献
157.
Robin Pilcher 《Geology Today》1996,12(1):31-34
Collecting geological data in the desert of east-central Oman is very different from working in temperate countries. The fieldwork depends largely on traditional methods, combined with the advantage of modern aids such as the Global Positioning System and radio communication. The information gained on the ground, followed up by modern laboratory and computing techniques in the UK, is being used to shed light on the sedimentological and structural evolution of this fascinating area. 相似文献
158.
In this paper we describe a set of models to predict the colours of galaxies over a wide range of redshifts. We present examples of output from the simulations, and discuss their application to the selection of galaxies at high redshifts, particularly through identification of the Lyman break. Additionally we consider the optimal choices of filters for selection at a range of redshifts.
An interface to a subset of the simulations has been made available on the World Wide Web for the benefit of the community at the location http://www-astro.physics.ox.ac.uk/~rejs/research/galcols.html/ 相似文献
An interface to a subset of the simulations has been made available on the World Wide Web for the benefit of the community at the location http://www-astro.physics.ox.ac.uk/~rejs/research/galcols.html/ 相似文献
159.
Time-sequences of line profile data have been subjected to a unique analysis which produces an amplitude and phase of the velocity and intensity at several line depths for each time sample and spatial point on the Sun. The data have been filtered to pass only the frequencies and spatial wavenumbers of the 5-min band. Yet, a secondary oscillation emerges, the phase of which propagates downward. Empirical eigenfunctions for velocity and intensity are given, and the kinetic energy flux is computed.Operated by the Association of Universities for Research in Astronomy under contract with the National Science Foundation. 相似文献
160.
The 1356 Basel earthquake was the strongest event to have shaken NW Europe in the last thousand years. The peculiar location of this historical event makes it possible to relate it to normal faulting along the edges of the Rhine Graben, as well as to reverse faulting along the Jura frontal thrust or to fault reactivation within the Hercynian basement. Alternate hypotheses are discussed and their implications compared taking into account available structural data and results of the morphotectonic study performed in the epicentral area. This study combines field observations with the analysis of SPOT satellite imagery, aerial photographs, and detailed topography. It is concluded that the Basel earthquake most probably reactivated a basement fault (reverse or wrench fault) beneath the shallow-depth aseismic detachment that underlies the Jura Mountains. 相似文献