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排序方式: 共有470条查询结果,搜索用时 15 毫秒
131.
Numerical comparison of different convergent plate contacts: subduction channel and subduction fault 总被引:2,自引:0,他引:2
At convergent plate boundaries, the properties of the actual plate contact are important for the overall dynamics. Convergent plate boundaries both mechanically decouple and link tectonic plates and accommodate large amounts of strain. We investigate two fundamental physical states of the subduction contact: one based on a fault and the other based on a subduction channel. Using a finite element method, we determine the specific signatures of both states of the subduction contact. We pay particular attention to the overriding plate. In a tectonic setting of converging plates, where the subducting plate is freely moving, the subduction channel reduces compression relative to the fault model. In a land-locked basin setting, where the relative motion between the far field of the plates is zero, the subduction channel model produces tensile stress regime in the overriding plate, even though the amount of slab roll-back is small. The fault model shows a stronger development of slab roll-back and a compressive stress regime in the upper plate. Based on a consistent comparison of fault and channel numerical models, we find that the nature of the plate contact is one of the controlling factors in developing or not of backarc extension. We conclude that, the type of plate contact plays a decisive role in controlling the backarc state of stress. To obtain backarc extension, roll-back is required as an underling geodynamic process, but it is not always a sufficient condition. 相似文献
132.
V. González-Quiñones A. de la Torre M. P. García A. Polo R. Jiménez-Ballesta 《Environmental Geology》2007,53(3):527-531
In the region of Castilla-La Mancha (Spain), over half of the soils are under cropping. This vast agricultural activity, combined
with other anthropological uses, has led to a deterioration of the soil quality and virtual degradation. Therefore, it was
deemed to assess the quality of these soils, which was achieved by applying two different methods. Three soils, representative
of typical conditions in this community, were sampled and diverse properties were analysed in order to apply two different
approaches. The first soil evaluation was carried out by a traditional method developed by FAO using a productivity index,
whereas the second method consisted of the application of a new method called SINDI, developed in New Zealand. Both approaches
make an evaluation based on a number of indicators that differs in each case. These differences explain why each method ranked
the soils studied in different order reaching diverse conclusions on their quality. 相似文献
133.
J. Aroba J. A. Grande J. M. Andújar M. L. de la Torre J. C. Riquelme 《Environmental Geology》2007,53(1):135-145
In this article, a set of clustering algorithms based on Fuzzy Logic and Data Mining are applied, allowing to obtain data
in the form of linguistic rules and charts about the behaviour of the Tinto and Odiel river estuary (SW Spain) affected by
Acid Mine Drainage (AMD). In order to provide researchers with no skills on data mining techniques an easy and intuitive interpretation,
we have developed a computer tool based on fuzzy logic that allows immediate qualitative analysis of the data contained in
a data from the estuary water chemical analyses, and serves as a contrast to functioning models previously proposed with classical
statistics. 相似文献
134.
Angelo Minissale Mohamed A. Mattash Orlando Vaselli Franco Tassi Ismail N. Al-Ganad Enrico Selmo Nasr M. Shawki Dario Tedesco Robert Poreda Abdassalam M. Ad-Dukhain Mohammad K. Hazzae 《Applied Geochemistry》2007
Most thermal springs of continental Yemen (about 65 emergences at 48 sampling sites) and a couple of fumaroles and boiling water pools have been sampled and analyzed for chemical and isotopic composition in the liquid phase and the associated free-gas phase. Whatever the emergence, all the water discharges have an isotopic signature of meteoric origin. Springs seeping out from high altitudes in the central volcanic plateau show a prevalent Na–HCO3-composition, clearly affected by an anomalous flux of deep CO2 deriving from active hydrothermal systems located in the Jurassic Amran Group limestone sequence and/or the Cretaceous Tawilah Group, likely underlying the 2000–3000 m thick volcanic suite. At lower elevations, CO2 also affects the composition of some springs emerging at the borders of the central volcanic plateau. 相似文献
135.
An earthquake scenario for the microzonation of Sofia and the vulnerability of structures designed by use of the Eurocodes 总被引:3,自引:0,他引:3
Paskaleva Ivanka Dimova Silvia G.F. Panza Giuliano Vaccari Franco 《Soil Dynamics and Earthquake Engineering》2007,27(11):1028-1041
The study of the site effects and the microzonation of a part of the metropolitan Sofia, based on the modelling of seismic ground motion along three cross-sections are performed. Realistic synthetic strong motion waveforms are computed for scenario earthquakes (M=7) applying a hybrid modelling method, based on the modal summation technique and finite differences scheme. The synthesized ground motion time histories are source and site specific. The site amplification is determined in terms of response spectra ratio (RSR). A suite of time histories and quantities of earthquake engineering interest are provided. The results of this study constitute a “database” that describes the ground shaking of the urban area. A case study of experiment-based assessment of vulnerability of a cast-in-situ single storey, industrial, reinforced concrete frame, designed according to Eurocodes 2 and 8 is presented. The main characteristics of damage index and storey drift are discussed for the purposes of microzonation. 相似文献
136.
K. Frhlich T. Schmidt M. Ern P. Preusse A. de la Torre J. Wickert Ch. Jacobi 《Journal of Atmospheric and Solar》2007,69(17-18):2238
Five years of global temperatures retrieved from radio occultations measured by Champ (Challenging Minisatellite Payload) and SAC-C (Satelite de Aplicaciones Cientificas-C) are analyzed for gravity waves (GWs). In order to separate GWs from other atmospheric variations, a high-pass filter was applied on the vertical profile. Resulting temperature fluctuations correspond to vertical wavelengths between 400 m (instrumental resolution) and 10 km (limit of the high-pass filter). The temperature fluctuations can be converted into GW potential energy, but for comparison with parameterization schemes GW momentum flux is required. We therefore used representative values for the vertical and horizontal wavelength to infer GW momentum flux from the GPS measurements. The vertical wavelength value is determined by high-pass filtering, the horizontal wavelength is adopted from a latitude-dependent climatology. The obtained momentum flux distributions agree well, both in global distribution and in absolute values, with simulations using the Warner and McIntyre parameterization (WM) scheme. However, discrepancies are found in the annual cycle. Online simulations, implementing the WM scheme in the mechanistic COMMA-LIM (Cologne Model of the Middle Atmosphere—Leipzig Institute for Meteorology) general circulation model (GCM), do not converge, demonstrating that a good representation of GWs in a GCM requires both a realistic launch distribution and an adequate representation of GW breaking and momentum transfer. 相似文献
137.
A.Bressan M.Della Valle P.Marziani 《Monthly notices of the Royal Astronomical Society》2002,331(3):L25-L29
This paper estimates the relative frequency of different types of core-collapse supernovae, in terms of the ratio between the number of Type Ib–Ic and of Type II supernovae. We estimate independently for all normal and Seyfert galaxies whose radial velocity is ≤14 000 km s−1 , and which had at least one supernova event recorded in the Asiago catalogue from 1986 January to 2000 August. We find that the ratio is ≈0.23±0.05 in normal galaxies. This value is consistent with constant star formation rate and with a Salpeter initial mass function and an average binary rate ≈50 per cent. On the contrary, Seyfert galaxies exceed the ratio in normal galaxies by a factor ≈4 at a confidence level ≳2 σ . A caveat is that the numbers for Seyferts are still small (six of Type Ib–Ic and six of Type II supernovae discovered as yet). Assumed to be real, this excess of Type Ib/c supernovae may indicate a burst of low-age star formation ( τ ≲20 Myr) , a high incidence of binary systems in the inner regions ( r ≲0.4 R 25 ) of Seyfert galaxies, or a top-loaded mass function. 相似文献
138.
Giancarlo Della Ventura Günther J. Redhammer Gianluca Iezzi Frank C. Hawthorne Arnaud Papin Jean-Louis Robert 《Physics and Chemistry of Minerals》2005,32(2):103-113
A series of amphiboles along the magnesioriebeckite—Na2Mg3Fe3+ 2Si8O22(OH)2– ferri-clinoholmquistite—Li2Mg3Fe3+ 2Si8O22(OH)2 - join, defined by the BLiB Na–1 exchange vector, were hydrothermally synthesized at 700°C, 0.4 GPa, NNO + 1 redox conditions. Powder XRD and SEM-EDAX showed a very high (> 90%) amphibole yield for all samples. X-ray patterns were indexed in the C2/m space group; refined cell-parameters show a linear decrease of a and as a function of chemistry. IR spectra in the OH-stretching region show four main and rather sharp bands; these are assigned to Mg and Fe2+ at M(1,3), and indicate that the obtained amphiboles depart from the nominal octahedral composition (M1,3Mg3). The IR spectra also show that there is an increasing filling-up of the A-site for increasing Na in the system (increasing solid-solution toward, arfvedsonite). Mössbauer spectra show four well-defined quadrupole doublets which are assigned to Fe3+ at M2 and to Fe2+ at M1, M3 and M4, respectively. The Fe3+/Fe2+ content derived from fitted peak areas show variable Fe3+ concentration along the series. Mössbauer spectra also show a distinct alteration of 57Fe hyperfine parameters with changing Na–Li at M4. The most evident variation is observed for the quadrupole splitting of Fe3+ at M2, which increases by 50% from ferri-clinoholmquistite to magnesio-riebeckite; this suggest that the M2 octahedron in ferri-clinoholmquistite is much closer to the ideal geometry than the M2 octahedron in magnesio-riebeckite. Mössbauer spectra show also a well-defined increase in the Fe2+ quadrupole splitting of the M1 and M3 octahedra, which is attributed to the Na–Li distribution at the B-sites. 相似文献
139.
C. Torre 《Mineralogy and Petrology》1954,4(1-4):288-300
Ohne ZusammenfassungMit 3 Textabbildungen. 相似文献
140.