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81.
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
82.
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
83.
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
84.
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
85.
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
86.
Angela Ullrich Wilfried Schranz Ronald Miletich 《Physics and Chemistry of Minerals》2009,36(10):545-555
The high-pressure behavior of the lattice elasticity of spodumene, LiAlSi2O6, was studied by static compression in a diamond-anvil cell up to 9.3 GPa. Investigations by means of single-crystal XRD and
Raman spectroscopy within the hydrostatic limits of the pressure medium focus on the pressure ranges around ~3.2 and ~7.7 GPa,
which have been reported previously to comprise two independent structural phase transitions. While our measurements confirm
the well-established first-order C2/c–P21/c transformation at 3.19 GPa (with 1.2% volume discontinuity and a hysteresis between 0.02 and 0.06 GPa), both unit-cell dimensions
and the spectral changes observed in high-pressure Raman spectra give no evidence for structural changes related to a second
phase transition. Monoclinic lattice parameters and unit-cell volumes at in total 59 different pressure points have been used
to re-calculate the lattice-related properties of spontaneous strain, volume strain, and the bulk moduli as a function of
pressure across the transition. A modified Landau free energy expansion in terms of a one component order parameter has been
developed and tested against these experimentally determined data. The Landau solution provides a much better reproduction
of the observed anomalies than any equation-of-state fit to data sets truncated below and above P
tr, thus giving Landau parameters of K
0 = 138.3(2) GPa, K′ = 7.46(5), λ
V
= 33.6(2) GPa, a = 0.486(3), b = −29.4(6) GPa and c = 551(11) GPa. 相似文献
87.
88.
89.
Cristian Vallejo Richard A. Spikings Leonard Luzieux Wilfried Winkler David Chew Laurence Page 《地学学报》2006,18(4):264-269
The determination of accurate and precise ages for the timing of collision between oceanic plateaus and continental crust requires an understanding of how the indenting and buttressing plates respond to the collision. We present geochronological, thermochronological, geochemical and isotopic analyses of magmatic rocks from the Ecuadorian Andes, which relate to the collision of the Late Cretaceous Caribbean Plateau and Great Arc sequence with NW South America. The cessation of subduction magmatism during 65–64 Ma beneath the eastern edge of Caribbean Plateau was synchronous with accelerated surface uplift and exhumation within the buttressing continental margin during 75–65 Ma. We interpret this as the collision of the leading edge of the Caribbean Plateau and arc sequence with the South American Plate at 75–65 Ma. A U/Pb (zircon) SHRIMP age of 87.10 ± 1.66 (2σ) Ma, yielded by an accreted fragment of the plateau, precludes previous estimates of collision at 85–80 Ma if the plateau erupted above the Galápagos hotspot. Terra Nova, 18, 264–269, 2006 相似文献
90.