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991.
In this paper we present a model for the growth of a maar-diatreme complex in a shallow marine environment. The Miocene-age
Costa Giardini diatreme near Sortino, in the region of the Iblei Mountains of southern Sicily, has an outer tuff ring formed
by the accumulation of debris flows and surge deposits during hydromagmatic eruptions. Vesicular lava clasts, accretionary
lapilli and bombs in the older ejecta indicate that initial eruptions were of gas-rich magma. Abundant xenoliths in the upper,
late-deposited beds of the ring suggest rapid magma ascent, and deepening of the eruptive vent is shown by the change in slope
of the country rock. The interior of the diatreme contains nonbedded breccia composed of both volcanic and country rock clasts
of variable size and amount. The occurrence of bedded hyaloclastite breccia in an isolated outcrop in the middle-lower part
of the diatreme suggests subaqueous effusion at a low rate following the end of explosive activity. Intrusions of nonvesicular
magma, forming plugs and dikes, occur on the western side of the diatreme, and at the margins, close to the contact between
breccia deposits and country rock; they indicate involvement of volatile-poor magma, possibly during late stages of activity.
We propose that initial hydromagmatic explosive activity occurred in a shallow marine environment and the ejecta created a
rampart that isolated for a short time the inner crater from the surrounding marine environment. This allowed explosive activity
to draw down the water table in the vicinity of the vent and caused deepening of the explosive center. A subsequent decrease
in the effusion rate and cessation of explosive eruptions allowed the crater to refill with water, at which time the hyaloclastite
was deposited. Emplacement of dikes and plugs occurred nonexplosively while the breccia sediment was mostly still soft and
unconsolidated, locally forming peperites. The sheltered, low-energy lagoon filled with marine limestones mixed with volcaniclastic
material eroded from the surrounding ramparts. Ultimately, lagoonal sediments accumulated in the crater until subsidence or
erosion of the tuff ring caused a return to normal shallow marine conditions. 相似文献
992.
A knowledge of seismic wave velocities in the sedimentary cover is of great importance for interpreting reflection and refraction
seismic data, deep seismic soundings and regional and global seismic tomography. This is particularly true for regions characterized
by significant thicknesses and a complex sedimentary cover structure. This paper presents the results of an analysis of seismic
P-wave velocities in the sedimentary cover of Poland, a complex area of juxtaposition of major tectonic units: the Precambrian
East European Craton, the Palaeozoic Platform of Central and Western Europe, and the Alpine orogen represented by the Carpathian
Mountains. Based on vertical seismic profiling data from 1188 boreholes, the dependence of velocity versus depth was determined for regional geological units and for successions from the Tertiary and Quaternary to the Cambrian.
The data have been approximated by polynomials, and velocity-depth formulas are given down to 6000 m depth. The velocities
in the sedimentary cover have been compared with those from other areas in Europe. 相似文献
993.
Leszek Czechowski 《Acta Geophysica》2012,60(4):1192-1212
Thermal history of Rhea from the beginning of accretion is investigated. We developed a numerical model of convection combined with the parameterized theory. Large scale melting of the satellite’s matter and gravitational differentiation of silicates from ices are included. The results are confronted with observational data from Cassini spacecraft that indicate minor differentiation of the satellite’s interior. We suggest that partial differentiation of the satellite’s interior is accompanied (or followed) by the process of light fraction uprising to the surface. The calculation indicates that the partial differentiation of the matter of the satellite’s interior is possible only for narrow range of parameters. In particular, we found that the time from the formation of CAI (calciumaluminum rich inclusions in chondrites) to the end of accretion of Rhea is in the range of 3–4 My. 相似文献
994.
Sebastian Sobek Roland Zurbrügg Ilia Ostrovsky 《Aquatic Sciences - Research Across Boundaries》2011,73(3):355-364
Even though lake sediments constitute a significant long-term carbon sink, studies on the regulation of carbon burial in lakes
sediments have, to date, been surprisingly few. We investigated to what degree the organic carbon (OC) being deposited onto
the bottom of Lake Kinneret (Israel) is buried in the sediment at four different sites with varying degrees of oxygenation
and varying supply of allochthonous particles from the River Jordan. For estimation of the OC burial efficiency (OC BE), i.e.,
the ratio between buried and deposited OC, we calculated OC burial from dated sediment cores, and calculated OC deposition
using three different approaches. Calculation of OC deposition from sediment trap-derived mass deposition rates multiplied
with the OC content of surface sediment yielded OC BE values that were at odds with published values for sediments dominated
by autochthonous OC sources. Calculation via sediment trap data on organic matter flux collected within the Lake Kinneret
monitoring program, as well as calculation of OC deposition as the sum of OC burial plus OC mineralization, returned fairly
congruent estimates of OC BE (range 10–41%), but only if the sediment trap data were corrected for the proportion of resuspended
particles in the traps. Differences in OC BE between sites were small, indicating that OC source (common to all sites) was
a more important regulator of OC BE in Lake Kinneret than oxygen exposure or mineral particles characteristics. 相似文献
995.
996.
Anna Zacharioudaki Shunqi Pan Dave Simmonds Vanesa Magar Dominic E. Reeve 《Ocean Dynamics》2011,61(6):807-827
In this paper, we investigate changes in the wave climate of the west-European shelf seas under global warming scenarios.
In particular, climate change wind fields corresponding to the present (control) time-slice 1961–2000 and the future (scenario)
time-slice 2061–2100 are used to drive a wave generation model to produce equivalent control and scenario wave climate. Yearly
and seasonal statistics of the scenario wave climates are compared individually to the corresponding control wave climate
to identify relative changes of statistical significance between present and future extreme and prevailing wave heights. Using
global, regional and linked global–regional wind forcing over a set of nested computational domains, this paper further demonstrates
the sensitivity of the results to the resolution and coverage of the forcing. It suggests that the use of combined forcing
from linked global and regional climate models of typical resolution and coverage is a good option for the investigation of
relative wave changes in the region of interest of this study. Coarse resolution global forcing alone leads to very similar
results over regions that are highly exposed to the Atlantic Ocean. In contrast, fine resolution regional forcing alone is
shown to be insufficient for exploring wave climate changes over the western European waters because of its limited coverage.
Results obtained with the combined global–regional wind forcing showed some consistency between scenarios. In general, it
was shown that mean and extreme wave heights will increase in the future only in winter and only in the southwest of UK and
west of France, north of about 44–45° N. Otherwise, wave heights are projected to decrease, especially in summer. Nevertheless,
this decrease is dominated by local wind waves whilst swell is found to increase. Only in spring do both swell and local wind
waves decrease in average height. 相似文献
997.
Devendraa Siingh R. P. Singh Ashok K. Singh M. N. Kulkarni A. S. Gautam Abhay K. Singh 《Surveys in Geophysics》2011,32(6):659-703
The physics of solar forcing of the climate and long term climate change is summarized, and the role of energetic charged
particles (including cosmic rays) on cloud formation and their effect on climate is examined. It is considered that the cosmic
ray-cloud cover hypothesis is not supported by presently available data and further investigations (during Forbush decreases
and at other times) should be analyzed to further examine the hypothesis. Another player in climate is lightning through the
production of NOx; this greenhouse gas, water vapour in the troposphere (and stratosphere) and carbon dioxide influence the global temperature
through different processes. The enhancement of aerosol concentrations and their distribution in the troposphere also affect
the climate and may result in enhanced lightning activity. Finally, the roles of atmospheric conductivity on the electrical
activity of thunderstorms and lightning discharges in relation to climate are discussed. 相似文献
998.
Despite vigorous tidal and wind mixing, observations in an estuarine tidal inlet in the Wadden Sea show that during part of
the tidal cycle, vertical stratification and internal waves may still develop. Acoustic Doppler current profiler (ADCP) and
conductivity, temperature, depth observations, collected over the past 6 years at 13 h anchor stations (ASs), reveal that
these occur especially during slack tide, when there is little wind and large freshwater discharge from nearby Lake IJssel.
Measurements with a moored ADCP show that in the same tidal phase, strong cross-channel circulation develops, which may suddenly
reverse circulation sense due to passing density fronts. In the vertically stratified phase that follows after the front passage,
propagating mode-one solitary internal waves are observed. These are resonantly generated during decelerating tidal ebb currents
when the (shear) flow passes a transcritical regime (Froude number equal to 1). A combination of photographs (including one
from the International Space Station), bathymetric data, and ASs data leads to the discovery of yet another source of internal
waves in this area, produced during slackening tide by propagating lee waves that develop over a deep trench. We suggest that
both the cross-channel circulation as well as the (solitary) internal waves may locally be of importance for the (re)distribution
and transport of sediments and nutrients and may influence tidally averaged transports. 相似文献
999.
Numerical study of the barotropic responses to a rapidly moving typhoon in the East China Sea 总被引:1,自引:1,他引:1
Yang Ding Huaming Yu Xianwen Bao Liang Kuang Caixia Wang Wenjuan Wang 《Ocean Dynamics》2011,61(9):1237-1259
Barotropic responses of the East China Sea to typhoon KOMPASU are investigated using a high-resolution, three-dimensional,
primitive equation, and finite volume coastal ocean model. Even the fact that the typhoon KOMPASU only brushed across the
brink of China mainland without landing, it still imposed great influence across China's east coastal area, where storm surges
ranging from 35 to 70 cm were intrigued during this event and a large wake of water setdown due to the outward radial transport
driven by the cyclonic wind stress was generated after the KOMPASU traveled across the Yellow Sea. Analysis of the numerical
results reveals that the barotropic waves propagating along the coast after the typhoon's landing can be identified as Kelvin
wave and the currents associated with the storm are geostrophic currents. A series of model runs are initiated to diagnose
the effects of wind stress, atmospheric pressure, and storm track variation on the surge's spatial distribution in the East
China Sea. The barotropic waves affected by the atmospheric disturbance due to the typhoon in deep Pacific Ocean travel far
more rapidly, arriving at the coastal regions at least 60 h ahead of the typhoon. The wave amplitudes are merely 0.2–0.4 cm
and damp gradually due to friction. The model experiments also confirm that the surge levels in nearshore regions are highly
dominated by winds, whereas the water level variations in deeper areas are controlled by the atmospheric pressure forcing
during typhoon events in the East China Sea. 相似文献
1000.
Tidal circulation in Cobscook Bay, a macro tidal basin, is simulated using the three-dimensional, nonlinear, finite element
ocean model, QUODDY_dry. Numerical particles are released from various transects in the bay at different tidal phases and tracked for several tidal
cycles. Initially, nearby particles in the main tidal channel experience a great deal of spreading and straining, and after
a few tidal cycles, they are separated in different parts of the bay. The fundamental mechanism for particle dispersion is
the chaotic advection that arises from long tidal excursions passing through many residual eddies. A loosely correlated, inverse
relationship between the two dimensionless parameters, ν (the ratio of the residual current to the tidal current) and λ (the ratio of the tidal excursion to the main topographic scale), can be constructed for large values of ν. Several Lagrangian statistical measures are used to quantify and distinguish dispersion regimes in different parts of Cobscook
Bay. It is found that the effective Lagrangian dispersion coefficient can be estimated using the product of the magnitude
of residual currents and the tidal excursion. 相似文献