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We report results on the construction of cosmological braneworld models in the context of the Einstein-Gauss-Bonnet gravity,
which include the leading correction to the Einstein-Hilbert action suggested by superstring theory. We obtain and study the
equations governing the dynamics of the standard cosmological models. We find that they can be written in the same form as
in the case of the Randall-Sundrum model but with time-varying four-dimensional gravitational and cosmological constants.
Finally, we discuss the cosmological evolution predicted by these models and their compatibility with observational data.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
65.
C. Serra A. Burgueño M. D. Martínez X. Lana 《Theoretical and Applied Climatology》2006,85(3-4):165-183
Summary A spatiotemporal trend analysis of different magnitudes related to the number and length of the dry spells in Catalonia (NE
Spain) has been conducted based on daily rainfall records taken from 40 rain gauges during the second half of the 20th century. Dry spells have been computed for threshold levels of 0.1, 1, 5 and 10 mm/day at annual and semi-annual scales.
The winter half-year is defined from October to March and the summer half-year from April to September. The magnitudes considered
are the number, the maximum length and the mean length of the dry spells for every year and half-year. The spatial patterns
of the average values of these magnitudes at the annual scale show a greater similarity with those of the summer half-year
than with those of the winter half-year. A S–N or SW–NE gradient of the number of dry spells appears during the summer half-year
for every threshold level. Trends of the analysed magnitudes are derived from linear regression and local statistical significances
at the 95% confidence level are established using the Mann-Kendall test. Field significant trends are investigated by means
of Monte Carlo simulations. The most relevant finding is that the number of dry spells per year depicts significant trends
for the annual and winter-half series, with an overall decreasing trend for 5 and 10 mm/day thresholds. These observed trends
are in agreement with changes in North Atlantic cyclone tracks and in Mediterranean Low dynamics, due to increasing greenhouse
gas concentrations. 相似文献
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Summary
A long series of maximum and minimum daily temperatures recorded at the Fabra Observatory (Barcelona) from 1917 to 1998 has
permitted a detailed study of significant hot and cold events, based on the crossing theory and on the Markovian process.
The former allows us to obtain statistical distributions of the number of hot and cold events per year, the starting date
and the magnitude of an event. The Poisson, the normal and the exponential distributions are the respective models. On the
other hand, the Markovian process estimates probabilities for the duration of several hot and cold events above or below different
temperature threshold levels. It should be stressed that the threshold levels, which define the significant hot and cold events,
are almost coincident with those whose lengths follow a Markovian process. From a more applied point of view, two examples
of hot and cold events of high magnitude are shown and their associated synoptic situations discussed. Some other typical
synoptic situations leading to relevant hot and cold events in Barcelona and the surrounding areas are also summarised.
Received March 1, 2001 Revised July 30, 2001 相似文献
69.
An algorithm of annealing is applied to a joint inversion of travel times and waveforms belonging to a synthetically generated seismic refraction experiment. The medium (crust and upper mantle) is modelled by a set of plane stratified layers and a halfspace. The obtained structure (elastic parameters and depth of layers) shows that, in spite of contaminating seismic noise and poor knowledge of the seismic source, annealing methods are a good tool in these kinds of inversion problems. We think that many characteristics of the annealing process described here could be used with real data and more sophisticated media for the crust and upper mantle of the earth than the present example. 相似文献
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