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201.
Bastien Caplain Dominique Astruc Vincent Regard Frédéric Y. Moulin 《Comptes Rendus Geoscience》2011,343(7):471-477
Wave flume experiments have been performed to investigate a sandy cliff recession under monochromatic wave forcing. We varied the wave climate through the wave energy flux F and the surf similarity parameter ξ. The various processes of the cliff erosion cycle are depicted. The sea bed evolution mostly depends on the surf similarity parameter ξ. Steep planar (ξ > 0.7), gentle planar (0.5 < ξ < 0.7) and bared (ξ < 0.5) profiles are observed. We observed different bar dynamics, including steady and unsteady self-sustained oscillating states. Then we analyze the role of the eroded material on the cliff recession rate. We show that the cliff recession rate increases with the wave energy flux. Moreover, for a given wave energy flux, it is larger for a gentle planar profile than for a bared profile. However it is similar for both a bared profile and a steep planar profile. The cliff recession rate is not a monotonic function of the cliff height as the type of bottom profile influences the wave energy at the cliff. 相似文献
202.
Shavkat Rakhmatullaev Antoine Marache Frédéric Huneau Philippe Le Coustumer Masharif Bakiev Mikael Motelica-Heino 《Environmental Earth Sciences》2011,63(3):447-460
The paper presents the results of a new geostatistical approach to generate bathymetric surface models from point measurement
converted into continuous contour surfaces of reservoir bottoms in Uzbekistan. Sedimentation of reservoirs raises engineering,
environmental and economical issues for the communities around the world in areas affected by a strong water deficit. Because
of Uzbekistan’s arid climatic conditions, and uneven spatial and temporal water resources distribution, responsive and innovative
water availability assessment surveys of all major water reservoirs are required. Bathymetric surveying is a traditional method
that is carried out for the estimation of reservoir volumes and surface areas of the corresponding reservoir stages in order
to assess the water availability. Volume and surface area differences derived from multiple surveys of a reservoir provide
storage loss estimates over time due to sedimentation. However, two main factors, such as intensive field data measurement
and post data-processing, often limit the frequency of these surveys. Alternatively, innovative depth measurement technologies
coupled with contouring and surface mapping programs provide automated reservoir volume and surface area calculations. This
significantly reduces time, workload and financial burdens for reservoir sedimentation projects. This research proposes the
use of geostatistical approach to assess the reservoir sedimentation in the Akdarya reservoir of Uzbekistan. The geostatistical
approach includes (semi-) variogram analysis and interpolation (kriging and simulations—turning bands) techniques predicting
values at unsampled locations for generating digital bathymetric surface models of reservoir bottom conditions in order to
calculate the volume and surface area at a given water elevation. The simulation enables to have range of reservoir volumes
and surface areas with the same probability, in comparison to the kriging and traditional methods. This gives a real estimation
of the resource availability for water operators to manage natural resources and hydraulic infrastructure in a sustainable
manner. 相似文献
203.
Frédéric Zagury 《Journal of Astrophysics and Astronomy》2005,26(4):395-420
This paper presents an analysis of a series of spectra in the Red Rectangle nebula. Only the reddest part of the spectra can
safely be attributed to light from the nebula, and indicates Rayleigh scattering by the gas, in conformity with the large
angles of scattering involved and the proximity of the star. In the blue, light from HD 44179, refracted or scattered in the
atmosphere, dominates the spectra. This paper questions the reliability of ground-based broad-band spectra of extended objects
in the blue. 相似文献
204.
205.
Clément Fontana Christian Grenz Christel Pinazo Patrick Marsaleix Frédéric Diaz 《Continental Shelf Research》2009,29(11-12):1397-1409
In order to predict eutrophication events in coastal areas we tested an assimilation scheme based on sequential data assimilation of SeaWiFS chlorophyll data into a coupled 3D physical–biogeochemical model. The area investigated is a semi-enclosed estuarine system (Gulf of Fos–North-western Mediterranean Sea) closely linked to the Rhone River delta. This system is subjected to episodic eutrophication caused by certain hydrodynamic conditions and intermittent nutrient inputs. The 3D hydrodynamic model Symphonie was coupled to the biogeochemical modelling platform Eco3M. Surface chlorophyll concentrations were derived from SeaWiFS data using the OC5 algorithm and were sequentially assimilated using a singular evolutive extended Kalman filter. Assimilation efficiency was evaluated through an independent in situ data set collected during a field survey that took place in May 2001 (ModelFos cruise). An original approach was used in constructing the state vector and the observation vector. By assimilating pseudo-salinity extracted from the model biogeochemical dynamics in both open sea and plume region were respected. We proved that substantial improvements were made in short-term forecasts by integrating such satellite-estimated chlorophyll maps. We showed that missing freshwater inputs could be corrected to a certain extent by the assimilation process. Simulated concentrations of surface chlorophyll and other basic components of the pelagic ecosystem such as nitrates were improved by assimilating surface chlorophyll maps. Finally we showed the coherent spatial behaviour of the filter over the whole modelled domain. 相似文献
206.
Comet Hale-Bopp was observed with the 80 cm reflector + CCD at the Haute-Provence observatory (OHP) and with the 62 cm reflector
+ CCD at the Saint-Véran observatory (Queyras, France). The morphology of the shells was followed from their first appearence
on 1997 Jan. 30, until their disappearance on May 9. These shells spread from the nucleus region with a velocity in agreement
with a nuclear rotation period of about 11.33 hours. We report also a short and bright dust ejection on May 8. CN images show
a long spiral jet in the tailward side invisible on continuum images. The circumnuclear structures have been followed at Saint-Véran
from Apr. 5 to Apr. 11, 1997 with a high spatial resolution (200 km/pixel). We have followed the emergence of a recurrent
linear polar jet. Measurements of its expansion show a constant acceleration of material with typical expansion velocity of
1 km/s. The CCD frames show the interconnection between spiral jets and the successive shells.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
207.
208.
We present preserved‐amplitude downward continuation migration formulas in the aperture angle domain. Our approach is based on shot‐receiver wavefield continuation. Since source and receiver points are close to the image point, a local homogeneous reference velocity can be approximated after redatuming. We analyse this approach in the framework of linearized inversion of Kirchhoff and Born approximations. From our analysis, preserved‐amplitude Kirchhoff and Born inverse formulas can be derived for the 2D case. They involve slant stacks of filtered subsurface offset domain common image gathers followed by the application of the appropriate weighting factors. For the numerical implementation of these formulas, we develop an algorithm based on the true amplitude version of the one‐way paraxial approximation. Finally, we demonstrate the relevance of our approach with a set of applications on synthetic datasets and compare our results with those obtained on the Marmousi model by multi‐arrival ray‐based preserved‐amplitude migration. While results are similar, we observe that our results are less affected by artefacts. 相似文献
209.
Over the last three decades, many regional studies in mountain ranges under temperate climate revealed that it is possible to discriminate debris-flow and fluvial fans from morphometric indicators measured at the scale of the catchment and the fan itself. The most commonly used indicators are the Melton index (R), a normalized index of the gravitational energy of the catchment, and the fan slope (S). A wide range of thresholds have been proposed for discriminating purpose, but these are generally based on a small population of catchments and may be highly influenced by ambiguous fans included in the data set. A database of 620 upland catchments from several mountain ranges under temperate climate was compiled from the literature to propose robust discriminant morphometric thresholds for debris-flow versus fluvial responses. Linear discriminant analysis (LDA) and logistic regression (LR) were performed using the whole data set, and a leave-one-out cross-validation was used to evaluate performances of the models. Sensitivity and specificity scores obtained for LDA and LR were 0.96 and 0.73, and 0.95 and 0.75, respectively. It is also shown that the channel slope above which debris-flow is observed decreases with the gravitational energy of the catchment. Limitations of the morphometric discrimination are discussed. 相似文献
210.