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排序方式: 共有297条查询结果,搜索用时 15 毫秒
1.
M. I. Vitorino P. L. da Silva Dias N. J. Ferreira 《Meteorology and Atmospheric Physics》2006,93(1-2):17-35
Summary Atmospheric variability in outgoing long-wave radiation (OLR) and tropospheric relative vorticity (VOR) over the South American
region was studied from 1979 to 1996 using the complex Morlet wavelet function. The analyses focus on spatial variation in
intraseasonal and submonthly scales. Scalograms were used to measure submonthly intraseasonal oscillations in convection,
which were found to be predominant in the tropical regions. However, 7-day and 15-day oscillations were observed at tropical
and extratropical latitudes in spring and winter, indicating that transient disturbances play a more prominent role. Regarding
VOR, tropical energy intensities were highest in the spring and summer, whereas subtropical and extratropical energy intensities
were highest in the autumn and winter. The dynamics of the 25-day and 45-day VOR oscillations indicates a possible correlation
with Rossby waves over the eastern tropical Pacific Ocean, mainly during the summer. During winter, the 7-day and 15-day VOR
oscillations are more frequent at higher latitudes and are enhanced along storm tracks. It was also observed that convection
amplitudes in the regions of maximum intensity change appreciably from year to year and from season to season, showing that
the behavior of the submonthly and intraseasonal oscillations is nonperiodic and correlates strongly with El Ni?o/Southern
Oscillation years. These results confirm the efficiency of wavelet analysis for time-scale studies of atmospheric variability. 相似文献
2.
M. Nunes
. Ferreira M. Schaefer J. Clifton B. Baily D. Moura C. Loureiro 《Ocean & Coastal Management》2009,52(10):506-515
Coastal hazards are in the interface of human activities with natural coastal processes. The conflicts arising from this relationship require new approaches suitable for coastal management that consider the dynamic of coastal areas. A method to assess hazard in rock cliffs is presented, combining cliff evolution forcing mechanisms along with protection factors, according to a weighted factors system. This method provides a rapid evaluation of vulnerability for cliffed areas, supporting coastal management and hazard mitigation. The method was applied to the rocky cliffs of the densely populated coastal zone between Galé and Olhos de Água (Southern Portugal), where high and very high hazard values were found to be dominant. A method validation was made using the vulnerability areas and the recorded mass movements over a 45 year period in the same area. 相似文献
3.
The paper suggests modelling the long-term distribution of significant wave height with the Gamma, Beta of the first and second kind models. The three models are interrelated, flexible and cover the three different tail types of Extreme Value Theory. They can be used simultaneously as a means of assessing the uncertainty effects that result from choosing equally plausible models with different tail types. This procedure is intended for those applications that require the long-term distribution of significant wave height as input rather than the prediction of extreme values. The models are fitted to some significant wave data as an illustration. Details about maximum likelihood estimation are given in A. 相似文献
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Filipa Simes Brito Ferreira Oliveira 《Ocean Engineering》2007,34(2):337-342
Two numerical formulations of the breaking phenomenon were implemented in a numerical model for random wave propagation based on the elliptic formulation of the mild-slope equation. The randomness of the wave field was simulated based on a spectral component method, in which the 3-D spectrum is discretised in components of equal energy. One of the breaking process formulations is based on the concept of breaking each independent spectral component. The other is based on the distribution of the local amount of energy dissipated through the independent spectral components. The model based on the concept of breaking each independent spectral component produces the best estimates of the wave field, when the numerical results are compared with laboratory data. 相似文献
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9.
Reconnection X-winds: spin-down of low-mass protostars 总被引:1,自引:0,他引:1
Jonathan Ferreira Guy Pelletier Stefan Appl 《Monthly notices of the Royal Astronomical Society》2000,312(2):387-397
We investigate the interaction of a protostellar magnetosphere with a large-scale magnetic field threading the surrounding accretion disc. It is assumed that a stellar dynamo generates a dipolar-type field with its magnetic moment aligned with the disc magnetic field. This leads to a magnetic neutral line at the disc mid-plane and gives rise to magnetic reconnection, converting closed protostellar magnetic flux into open field lines. These are simultaneously loaded with disc material, which is then ejected in a powerful wind. This process efficiently brakes down the protostar to 10–20 per cent of the break-up velocity during the embedded phase. 相似文献
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