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61.
Hervey Bay, a large coastal embayment situated off the central eastern coast of Australia, is a shallow tidal area (average
depth = 15 m), close to the continental shelf. It shows features of an inverse estuary, due to the high evaporation rate (approx.
2 m/year), low precipitation (less than 1 m/year) and on average almost no freshwater input from rivers that drain into the
bay. The hydro- and thermodynamical structures of Hervey Bay and their variability are presented here for the first time,
using a combination of four-dimensional modelling and observations from field studies. The numerical studies are performed
with the Coupled Hydrodynamical Ecological Model for Regional Shelf Seas (COHERENS). Due to the high tidal range (>3.5 m),
the bay is considered as a vertically well-mixed system, and therefore, only horizontal fronts are likely. Recent field measurements,
but also the numerical simulations, indicate characteristic features of an inverse/hypersaline estuary with low salinity (35.5 psu)
in the open ocean and peak values (>39.0 psu) in the head water of the bay. The model further predicts a nearly persistent
mean salinity gradient of 0.5 psu across the bay (with higher salinities close to the shore). The investigation further shows
that air temperature, wind direction and tidal regime are mainly responsible for the stability of the inverse circulation
and the strength of the salinity gradient across the bay. Due to an ongoing drying trend, the occurrence of severe droughts
at the central east coast of Australia and, therefore, a reduction in freshwater supply, the salinity flux out of the bay
has increased, and the inverse circulation has also strengthened. 相似文献
62.
The equatorial Atlantic oscillation and its response to ENSO 总被引:6,自引:3,他引:3
An internal equatorial Atlantic oscillation has been identified by analyzing sea surface temperature (SST) observations. The equatorial Atlantic oscillation can be viewed as the Atlantic analogue of the El Niño/Southern Oscillation (ENSO) phenomenon in the equatorial Pacific, but it is much less vigorous. The equatorial Atlantic oscillation is strongly influenced by the Pacific ENSO with the equatorial Atlantic sea surface temperature lagging by about six months. This lag can be explained by the dynamical adjustment time of the equatorial Atlantic to low-frequency wind stress variations and the seasonally varying background state, which favours strongest growth of perturbations in summer. Results of an extended-range simulation with a coupled ocean-atmosphere GCM support this picture. 相似文献
63.
The El Niño-Southern Oscillation (ENSO) is investigated in a multicentury integration conducted with the coupled general circulation model (CGCM) ECHAM3/LSG. The quasiperiodic interannual oscillations of the simulated equatorial Pacific climate system are due to subsurface temperature anomaly propagation and a positive atmosphere-ocean feedback. The gravest internal wave modes contribute to the generation of these anomalies. The simulated ENSO has a characteristic period of 5–8 years. Due to the coarse resolution of the ocean model the ENSO amplitude is underestimated by a factor of three as compared to observations. The model ENSO is associated with the typical atmospheric teleconnection patterns. Using wavelet statistics two characteristic interdecadal modulations of the ENSO variance are identified. The origins of a 22 and 35?y ENSO modulation as well as the characteristic ENSO response to greenhouse warming simulated by our model are discussed. 相似文献
64.
65.
Fabio?OrianiEmail authorView authors OrcID profile Raj?Mehrotra Grégoire?Mariethoz Julien?Straubhaar Ashish?Sharma Philippe?Renard 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(2):321-340
Daily rainfall is a complex signal exhibiting alternation of dry and wet states, seasonal fluctuations and an irregular behavior at multiple scales that cannot be preserved by stationary stochastic simulation models. In this paper, we try to investigate some of the strategies devoted to preserve these features by comparing two recent algorithms for stochastic rainfall simulation: the first one is the modified Markov model, belonging to the family of Markov-chain based techniques, which introduces non-stationarity in the chain parameters to preserve the long-term behavior of rainfall. The second technique is direct sampling, based on multiple-point statistics, which aims at simulating a complex statistical structure by reproducing the same data patterns found in a training data set. The two techniques are compared by first simulating a synthetic daily rainfall time-series showing a highly irregular alternation of two regimes and then a real rainfall data set. This comparison allows analyzing the efficiency of different elements characterizing the two techniques, such as the application of a variable time dependence, the adaptive kernel smoothing or the use of low-frequency rainfall covariates. The results suggest, under different data availability scenarios, which of these elements are more appropriate to represent the rainfall amount probability distribution at different scales, the annual seasonality, the dry-wet temporal pattern, and the persistence of the rainfall events. 相似文献
66.
Gottfried Grünthal Dietrich Stromeyer Christian Bosse Fabrice Cotton Dino Bindi 《Bulletin of Earthquake Engineering》2018,16(10):4339-4395
The basic seismic load parameters for the upcoming national design regulation for DIN EN 1998-1/NA result from the reassessment of the seismic hazard supported by the German Institution for Civil Engineering (DIBt). This 2016 version of the national seismic hazard assessment for Germany is based on a comprehensive involvement of all accessible uncertainties in models and parameters and includes the provision of a rational framework for integrating ranges of epistemic uncertainties and aleatory variabilities in a comprehensive and transparent way. The developed seismic hazard model incorporates significant improvements over previous versions. It is based on updated and extended databases, it includes robust methods to evolve sets of models representing epistemic uncertainties, and a selection of the latest generation of ground motion prediction equations. The new earthquake model is presented here, which consists of a logic tree with 4040 end branches and essential innovations employed for a realistic approach. The output specifications were designed according to the user oriented needs as suggested by two review teams supervising the entire project. Seismic load parameters, for rock conditions of \(v_{S30}\) = 800 m/s, are calculated for three hazard levels (10, 5 and 2% probability of occurrence or exceedance within 50 years) and delivered in the form of uniform hazard spectra, within the spectral period range 0.02–3 s, and seismic hazard maps for peak ground acceleration, spectral response accelerations and for macroseismic intensities. Results are supplied as the mean, the median and the 84th percentile. A broad analysis of resulting uncertainties of calculated seismic load parameters is included. The stability of the hazard maps with respect to previous versions and the cross-border comparison is emphasized. 相似文献
67.
Johannes Becherer Jacobus Hofstede Ulf Gräwe Kaveh Purkiani Elisabeth Schulz Hans Burchard 《Ocean Dynamics》2018,68(1):131-151
The impact of sea level rise (SLR) on the future morphological development of the Wadden Sea (North Sea) is investigated by means of extensive process-resolving numerical simulations. A new sediment and morphodynamic module was implemented in the well-established 3D circulation model GETM. A number of different validations are presented, ranging from an idealized 1D channel over a semi-idealized 2D Wadden Sea basin to a fully coupled realistic 40-year hindcast without morphological amplification of the Sylt-Rømøbight, a semi-enclosed subsystem of the Wadden Sea. Based on the results of the hindcast, four distinct future scenarios covering the period 2010–2100 are simulated. While these scenarios differ in the strength of SLR and wind forcing, they also account for an expected increase of tidal range over the coming century. The results of the future projections indicate a transition from a tidal-flat-dominated system toward a lagoon-like system, in which large fractions of the Sylt-Rømøbight will remain permanently covered by water. This has potentially dramatic implications for the unique ecosystem of the Wadden Sea. Although the simulations also predict an increased accumulation of sediment in the back-barrier basin, this accumulation is far too weak to compensate for the rise in mean sea level. 相似文献
68.
Analysis of a dust sample (e.g. collected during a cometary rendezvous mission) by SIMS (Secondary Ion Mass Spectroscopy) can provide information on elemental abundances (? 100 amu), the molecular composition of grain surfaces, and isotopic ratios of selected elements. This can be accomplished with dust covering as little as 10?4 of the collector surface area. In order to demonstrate these capabilities a special experimental set-up for substrate preparation, dust collection and SIMS analysis of dust under ultrahigh vacuum conditions was developed. The comparison of elemental abundance ratios for different olivines and pyroxenes measured with the special SIMS equipment with that measured by an electron microprobe indicated an accuracy for SIMS of the elemental abundance measurements of ? 30%. By varying the energy threshold of secondary ions to be mass-analysed from 0 to 50 eV it is possible to identify molecular ions in the spectra and to estimate their abundance with respect to elemental ions on the same mass line. The ratios of molecular to elemental ions vary by a factor of 1–25. The concept for a future cometary rendezvous experiment as well as first results of chemical investigation on mineral dust samples obtained are reported. 相似文献
69.
Light variations of a representative sample of 26 more or less periodically variable carbon stars were analyzed on the basis
of 2220 individual observations made by the Hipparcos satellite and 33 544 visual observations listed in AFOEV and VSOLJ databases
within the interval JD = 2 448 000 (1988) ±6 cycles. We found the osculating linear ephemerides of all stars and their mean
light curves, as well. We found that the light curves of the carbon Miras in our set can be satisfactorily expressed as a
linear combination of only two basic light curves. The analysis was done by an own method combining robust regression and
principal component analysis. 相似文献
70.
Ø. Grøn 《Astrophysics and Space Science》1988,140(2):429-430
The gravitational field equations in Dunn's scalar-tensor theory of gravitation are generalized by including a cosmological constant. The resulting equations are solved for a Robertson-Walker line-element with flat three-space. The solution represents a cosmological model that develops into an inflationary era. 相似文献