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101.
A set of 61 normal modes with periods between 7.8 and 133.1 h has been calculated, using a 1° model of the global ocean, including
the Arctic Ocean. The model explicitly considers frictional forces and ocean self-attraction and loading effects. The latter
effects have generally been taken into account by parameterization, but for some modes the effects have also been considered
fully. Due to friction, the computed eigenfrequencies are complex, exhibiting also the varying dissipative properties of the
modes and their dependence on the distribution of potential and kinetic energies over the oceanic regions. In detail, gravity
modes having periods less then 80 h and dominating the semi-diurnal and the diurnal tides, topographically controlled vorticity
modes with periods longer than diurnal, and two planetary vorticity modes with periods of 96.8 and 119.4 h have been identified.
These planetary vorticity modes have their energies distributed over Pacific, Atlantic, and Indian Oceans, while the other
modes with periods longer than 80 h, as vorticity modes, have their energies concentrated on topographic structures of restricted
extension. The modes are discussed with respect to their wave properties, e.g., concerning quasi-standing-wave resonances
and to the appearance of Kelvin waves of different orders and trapped by different coastlines. In particular, the relevance
of specific modes for the development of the fields of the most important semi-diurnal and diurnal tidal constituents is investigated. 相似文献
102.
103.
104.
Wilfried Brutsaert 《Boundary-Layer Meteorology》1987,39(3):283-300
The budgets of water vapor and sensible heat in the convective atmospheric boundary (mixed) layer are analyzed by means of a simple slab approach adapted to steady large-scale advective conditions with radiation and cloud activity. The entrainment flux for sensible heat is assumed to be a linear function of the surface flux. The flux of water vapor at the top of the mixed layer is parameterized by extending the first-order Betts-Deardorff approach, i.e., by adopting linear changes for both the specific humidity and the flux across the mixed layer and across the inversion layer of finite thickness. In this way the dissimilarity of sensible heat and water vapor transport in the mixed layer can be taken into account. The experimental data were obtained from the Air Mass Transformation Experiment (AMTEX). The entrainment constant for sensible heat at the top of the mixed layer was found to have values similar to those observed in other weakly convective situations, i.e., around 0.4 to 0.6. This appears to indicate that the effect of mechanical turbulence was not negligible; however, the inclusion of this effect in the formulation did not improve the correlation. In contrast to the first-order approach, the zero-order approach, i. e., the jump equation commonly used for the flux of a scalar at the inversion, (ovwc )
h = we c (where w
e is the entrainment velocity and c the concentration jump across the inversion), was found to be invalid and incapable of describing the data. 相似文献
105.
Inversion fluxes of virtual heat were computed for seven clear days over the Pre-Alpine region in Switzerland with profile data from a sequence of radio soundings. Several entrainment models based on the turbulent kinetic energy equation were tested with the data. It was found that the relatively simple equation first proposed by Tennekes (1973) which contains both a convective and a mechanical term for the entrainment does as well as the more complicated parameterizations. In addition, the effect of water vapor on the magnitude of the buoyancy fluxes at the surface and at the inversion was observed to be important since the Bowen ratio normally ranged between 0.1 and 0.2.Now at the Hydrology Laboratory of the Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705, U.S.A. 相似文献
106.
Jeannette Noetzli Christian Huggel Martin Hoelzle Wilfried Haeberli 《Computational Geosciences》2006,10(2):161-178
Changing permafrost conditions caused by present atmospheric warming are expected to affect the stability of steep rock walls
in high mountain areas. The possible increase in periglacial slope instabilities and the especially long potential run-out
distances in glacial environments require more awareness about the kind of events as well as robust models to foresee areas
affected and distances reached. A geographic information system-based flow-routing model is introduced for modelling rock-ice
avalanches on a regional scale. The model application to three major historical events in the European Alps shows the basic
use for simulating such events for first-order assessments. By designating the path of steepest descent while allowing lateral
spreading from the fall track up to 45°, general flow patterns as well as changes in the direction of progression are well
reproduced. The run-out distances are determined using empirically based models and suit well the case studies presented. 相似文献
107.
Local accuracy measures for digital terrain models 总被引:1,自引:0,他引:1
Karl Kraus Wilfried Karel Christian Briese Gottfried Mandlburger 《The Photogrammetric Record》2006,21(116):342-354
108.
Glass-slides were exposed in four different bog lakes located in great forest areas in Northern Germany, about 100 km north of Berlin, in order to examine the protist community of these dystrophic, acid lakes. Species composition and succession of the periphyton were studied during one year. The four investigated bog lakes exhibit similar species compositions, most of the species were present in each of the four lakes. The periphyton was composed of a great variety of protist species. Specimens of all major flagellated protists and of most of the ciliate taxa were found on the slides. Many of these species are ubiquitous. Some species, however, like the flagellates Spongomonas sacculus, Rhipidodendron huxleyi, Cyathobodo sp., and Pseudodendromonas vlkii as well as the ciliates Ophrydium hyalinum, Leptopharynx costatus, Uroleptus caudatus, and Platyophrya sphagni are found more frequently in acid waters. A regular and common occurrence of these species partly characterizes the acid Sphagnum bogs. Besides that, common species like Bodo spp., Cryptomonas spp., Goniomonas truncata, Chilodonella uncinata, Vorticella sp., and Cyrtolophosis mucicola are represented in the periphyton. Examinations of the testate amoebae in the Sphagnum mats show a very different species composition compared to earlier studies.
The investigated bog lakes revealed mesotrophic conditions. In the upper regions of the Sphagnum mats and in the center of the larger bog lakes, oligotrophic conditions still prevail. The lower regions of the Sphagnum mat and the smaller lakes, however, are influenced by the partly degradation of plants and the run-off water from surrounding land. In comparison to earlier studies, the species composition indicates a beginning eutrophication of the bog lakes. A direct anthropogenic impact can be excluded. 相似文献
109.
Morelia Urlaub Mechita C. Schmidt-Aursch Wilfried Jokat Norbert Kaul 《Marine Geophysical Researches》2009,30(4):277-292
The Gakkel Ridge in the Arctic Ocean with its adjacent Nansen and Amundsen Basins is a key region for the study of mantle
melting and crustal generation at ultraslow spreading rates. We use free-air gravity anomalies in combination with seismic
reflection and wide-angle data to compute 2-D crustal models for the Nansen and Amundsen Basins in the Arctic Ocean. Despite
the permanent pack-ice cover two geophysical transects cross both entire basins. This means that the complete basin geometry
of the world’s slowest spreading system can be analysed in detail for the first time. Applying standard densities for the
sediments and oceanic crystalline crust, the gravity models reveal an unexpected heterogeneous mantle with densities of 3.30 × 103, 3.20 × 103 and 3.10 × 103 kg/m3 near the Gakkel Ridge. We interpret that the upper mantle heterogeneity mainly results from serpentinisation and thermal
effects. The thickness of the oceanic crust is highly variable throughout both transects. Crustal thickness of less than 1 km
dominates in the oldest parts of both basins, increasing to a maximum value of 6 km near the Gakkel Ridge. Along-axis heat
flow is highly variable and heat flow amplitudes resemble those observed at fast or intermediate spreading ridges. Unexpectedly,
high heat flow along the Amundsen transect exceeds predicted values from global cooling curves by more than 100%. 相似文献
110.
Rock falls in the Mont Blanc Massif in 2007 and 2008 总被引:1,自引:1,他引:0
Ludovic Ravanel Françoise Allignol Philip Deline Stephan Gruber Mario Ravello 《Landslides》2010,7(4):493-501
Due to a lack of systematic observations, the intensity and volume of rock falls and rock avalanches in high mountain areas are still poorly known. Nevertheless, these phenomena could have burly consequences. To document present rock falls, a network of observers (guides, mountaineers, and hut wardens) was initiated in the Mont Blanc Massif in 2005 and became fully operational in 2007. This article presents data on the 66 rock falls (100 m3?≤?V?≤?50,000 m3) documented in 2007 (n?=?41) and 2008 (n?=?25). Most of the starting zones are located in warm permafrost areas, which are most sensitive to warming, and only four rock falls are clearly out of permafrost area. Different elements support permafrost degradation as one of the main triggering factors of present rock falls in high mountain areas. 相似文献