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41.
42.
Robert L. Nowack Wang-Ping Chen Ulrich Kruse Saptarshi Dasgupta 《Pure and Applied Geophysics》2007,164(10):1921-1936
We carry out a sequence of numerical tests to understand conditions under which rapid changes in crustal thickness can be
reliably imaged by teleseismic body waves. Using the finite-difference method over a 2-D grid, we compute synthetic seismograms
resulting from a planar P-wavefield incident below the grid. We then image the Moho using a migration scheme based on the Gaussian beam representation
of the wavefield. The use of Gaussian beams for the downward propagation of the wavefield is particularly advantageous in
certain geologically critical cases such as overthrusting of continental lithosphere, resulting in the juxtaposition of high-velocity
mantle material over crustal rocks. In contrast to ray-based methods, Gaussian beam migration requires no special treatment
to handle such heterogeneities. Our results suggest that with adequate station spacing and signal-to-noise ratios, offsets
of the Moho, on the order of 10 km in height, can be reliably imaged beneath thickened crust at depths of about 50 km. Furthermore,
even sharp corners and edges are faithfully imaged when precise values of seismic wave speeds are available. Our tests also
demonstrate that flexibility in choices of different types of seismic phases is important, because any single phase has trade-offs
in issues such as spatial resolution, array aperture, and amplitude of signals. 相似文献
43.
Detlef W. Fasshauer Bernd Wunder Niranjan D. Chatterjee Günther W. H. Höhne 《Contributions to Mineralogy and Petrology》1998,131(2-3):210-218
The heat capacity of synthetic, stoichiometric wadeite-type K2Si4O9 has been measured by DSC in the 195≤T(K)≤598 range. Near the upper temperature limit of our data, the heat capacity observed by DSC agrees with that reported by
Geisinger et al. (1987) based on a vibrational model of their infrared and Raman spectroscopic data. However, with decreasing
temperature, the Cp observed by DSC is progressively higher than that predicted from the vibrational model, suggesting that
the standard entropy of K2Si4O9 is likely to be larger than 198.9 ± 4.0 J/K · mol computed from the spectroscopic data. A fit to the DSC data gave: Cp(T) = 499.13 (±1.87) − 4.35014 · 103(±3.489 · 101) · T
−0.5, with T in K and average absolute percent deviation of 0.37%. The room-temperature compressibilities of kalsilite and leucite, hitherto
unknown, have been measured as well. The data, fitted to the Murnaghan equation of state, gave K
o = 58.6 GPa, K
o
′ = 0.1 for kalsilite and K
o = 45 GPa, K
o
′ = 5.7 for α-leucite. Apart from the above mentioned data on the properties of the individual phases, we have also obtained
reaction-reversals on four equilibria in the system K2O-Al2O3-SiO2. The Bayesian method has been used simultaneously to process the properties of 13 phases and 15 reactions between them to
derive an internally consistent thermodynamic dataset for the K2O-Al2O3-SiO2 ternary. The enthalpy of formation of K2Si4O9 wadeite is in perfect agreement with its revised calorimetric value, the standard entropy is 232.1 ± 10.4 J/K · mol, ∼15%
higher than that implied by vibrational modeling. The phase diagram, generated from our internally consistent thermodynamic
dataset, shows that for all probable P-T trajectories in the subduction regime, the stable pressure-induced decomposition of K-feldspar will produce coesite + kalsilite rather than coesite + kyanite + K2Si4O9 (cf. Urakawa et al. 1994).
Received: 11 June 1997 / Accepted: 2 December 1997 相似文献
44.
Variations in the gravity field are introduced by mass or density redistribution in the vicinity of the measuring point as well as far field or global effects but also any crustal process which involves a height variation has a direct implication on the temporal variation of the gravity field.The measuring techniques involved in the WEGENER project include absolute and high precision relative gravity measurements and stationary measurements with superconducting gravity meters. The state of the art for both techniques is discussed and shown that systematic errors or the measurement of their changes can be detected by inter-comparison with other absolute gravimeters and frequently repeated measurements at a reference station monitored by a superconducting gravimeter. In the combination of the available gravity techniques it is possible to achieve a precision at the micro-Gal level for secular trends and a higher accuracy for period events which enable improvements in the modelling of environmental effects induced by ocean, atmospheric and ground water loading effects from the long term processes. 相似文献
45.
46.
47.
Dik van de Meent Stephen C. Brown R.Paul Philp Bernd R.T. Simoneit 《Geochimica et cosmochimica acta》1980,44(7):999-1013
A series of kerogens and kerogen precursors isolated from DSDP samples, oil shales and Recent algal mats have been examined by Curie point pyrolysis-high resolution gas chromatography and gas chromatography-mass spectrometry. This study has shown that the three main types of kerogens (marine, terrestrial and mixtures of both) can be characterized using these techniques. The marine (algal) kerogens yield principally aliphatic products and the terrestrial kerogens yield more aromatic and phenolic products with some n-alkanes and n-alkenes. The yields of n-alkanes and n-alkenes increase and phenols decrease with increasing geologic age, however, pyrolysis-GC cannot be used to characterize the influence of short term diagenesis on the kerogen structure. 相似文献
48.
Bernd Schönwald 《Boundary-Layer Meteorology》1978,15(4):453-464
A useful method for remote sensing of vertical temperature profiles in the atmospheric boundary layer is described. From angular measurements of brightness temperature at 58 GHz, profiles have been inferred up to an altitude of 700 m. Calculations were done with an iterative inversion procedure (Smith et al., 1972) using Twomey-type smoothing (Twomey, 1963). It is shown how an initial-guess profile can be directly derived from the radiation measurements using, a nomogram. 相似文献
49.
Bernd R.T Simoneit 《Geochimica et cosmochimica acta》1977,41(4):463-476
Cyclic diterpenoid compounds have been found by various investigators in the geosphere (e.g. fossil resins, coals, soil, shale and deep-sea sediments). These compounds occur in significant amounts only in higher plants and are therefore potential markers of terrigenous plant lipids.Diterpenoids with the abietane skeleton (mainly dehydroabietic acid) have been identified in the lipids of sediment samples from the northeast Pacific Ocean, Black Sea and North Atlantic Ocean. The presence of these resin-derived compounds correlated with the terrigenous clay components and with the presence of pollen. The presence of polycyclic diterpenoids was also correlated with the distribution patterns and inferred sources of other sediment lipid constituents (e.g. n-alkanes, n-fatty acids, etc.).Potamic transport, followed by turbidite redistribution are the probable input mechanisms of these resin-derived compounds to the deep-sea sediments. These diterpenoids appear to be excellent biological markers of resinous higher plants. 相似文献
50.
Paolo Nimis Paolo Omenetto Bernd Buschmann Peter Jonas Vladimir A. Simonov 《Mineralogy and Petrology》2010,100(3-4):201-214
Ultramafic–mafic- and ultramafic-hosted Cu (Co, Ni, Au) volcanogenic massive sulfide (VMS) deposits from ophiolite complexes of the Main Uralian Fault, Southern Urals, are associated with island arc-type igneous rocks. Trace element analyses show that these rocks are geochemically analogous to Early Devonian boninitic and island arc tholeiitic rocks found at the base of the adjacent Magnitogorsk volcanic arc system, while they are distinguished both from earlier, pre-subduction volcanic rocks and from later volcanic products that were erupted in progressively more internal arc settings. The correlation between the sulfide host-rocks and the earliest volcanic units of the Magnitogorsk arc suggests a connection between VMS formation and infant subduction-driven intraoceanic magmatism. 相似文献