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排序方式: 共有114条查询结果,搜索用时 15 毫秒
61.
A case study of airborne and satellite remote sensing of a spring bloom event in the Gulf of Finland
Sampsa Koponen Jenni Attila Jouni Pulliainen Kari Kallio Timo Pyhälahti Antti Lindfors Kai Rasmus Martti Hallikainen 《Continental Shelf Research》2007
The concentrations of chlorophyll-a (chl-a), total suspended solids (TSS) and the absorption coefficient of colored dissolved organic matter (aCDOM(400)) are estimated in Case II waters using medium resolution imaging spectrometer (MERIS) satellite (full resolution [FR] level 1b, 300 m resolution) and AISA airborne spectrometer data acquired during a spring bloom in the Gulf of Finland, Baltic Sea on April 27, 2004. The accuracy of the estimation is analyzed using empirical band-ratio algorithms together with in situ observations that include water samples analyzed in a laboratory (variation ranges: 22–130 μg/l, 2.9–20 mg/l, and 1.29–2.61 m−1 for chl-a, TSS and aCDOM(400), respectively). Additional in situ estimates (transects) on these characteristics are available through absorption and scattering coefficients measured with an ac-9 absorption and attenuation meter installed in a flow-through system. The retrieval accuracy (R2) of all three water quality characteristics with MERIS data is close to or above 0.9, while the RMSE is 7.8 μg/l (22%), 0.74 mg/l (16%) and 0.08 m−1 (5%), for chl-a, TSS and aCDOM(400), respectively. The validity of the chl-a algorithm is tested using nine additional data points. The BIAS-error for these points is 5.2 μg/l and the RMSE is 10.6 μg/l. The effects of changes in the atmospheric characteristics on band-ratio algorithms in cases where no concurrent in situ reference data are available are analyzed using the MODerate spectral resolution atmospheric TRANSmittance algorithm and computer model (MODTRAN). The additional error due to these changes is estimated to be below 20% for the applied ratio algorithms. The water quality data available in the level 2 MERIS-product distributed by the European Space Agency did not include valid results for the date investigated here. 相似文献
62.
63.
This paper presents a numerical study of thermal shock weakening of granite rock under dynamic loading. A fully 3D numerical scheme based on a combined continuum viscodamage-embedded discontinuity model and an explicit scheme to solve the underlying thermomechanical problem was developed and validated through numerical examples. First, the dynamic Brazilian disc test is simulated on intact numerical rock. Then, thermal shock-induced cracking due to a moving external heat flux boundary condition, mimicking experiments based on plasma jet treatment, is numerically predicted. Finally, numerical Brazilian disc test is conducted on the thermal shocked numerical samples. The predicted and experimental weakening effects are in good agreement demonstrating that the present modeling approach has good predictive capabilities. The practical significance of the results is that heat shock pretreatment can substantially enhance rock gravel and rubble crushing. 相似文献
64.
Lea Obrocki Andreas Vött Dennis Wilken Peter Fischer Timo Willershäuser Benjamin Koster Franziska Lang Ioannis Papanikolaou Wolfgang Rabbel Klaus Reicherter 《Sedimentology》2020,67(3):1274-1308
The western Peloponnese was repeatedly hit by major tsunami impacts during historical times as reported by historical accounts and recorded in earthquake and tsunami catalogues. Geological signatures of past tsunami impacts have also been found in many coastal geological archives. During the past years, abundant geomorphological and sedimentary evidence of repeated Holocene tsunami landfall was found between Cape Katakolo and the city of Kyparissia. Moreover, neotectonic studies revealed strong crust uplift along regional faults with amounts of uplift between 13 m and 30 m since the mid-Holocene. This study focuses on the potential of direct push in situ sensing techniques to detect tsunami sediments along the Gulf of Kyparissia. Direct push measurements were conducted on the landward shores of the Kaiafa Lagoon and the former Mouria Lagoon from which sedimentary and microfaunal evidence for tsunami landfall are already known. Direct push methods helped to decipher in situ high-resolution stratigraphic records of allochthonous sand sheets that are used to document different kinds of sedimentological and geomorphological characteristics of high-energy inundation, such as abrupt increases in grain size, integration of muddy rip-up clasts and fining upward sequences which are representative of different tsunami inundation pulses. These investigations were completed by sediment coring as a base for local calibration of geophysical direct push parameters. Surface-based electrical resistivity tomography and seismic data with highly resolved vertical direct push datasets and sediment core data were all coupled in order to improve the quality of the geophysical models. Details of this methodological approach, new in palaeotsunami research, are presented and discussed, especially with respect to the question of how the obtained results may help to facilitate tracing tsunami signatures in the sedimentary record and deciphering geomorphological characteristics of past tsunami inundation. Using direct push techniques and based on sedimentary data, sedimentary signatures of two young tsunami impacts that hit the Kaiafa Lagoon were detected. Radiocarbon age control allowed the identification of these tsunami layers as candidates for the ad 551 and ad 1303 earthquake and tsunami events. For these events, there is reliable historical data on major damage on infrastructure in western Greece and on the Peloponnese. At the former Mouria Lagoon, corroborating tsunami traces were found; however, in this case it is difficult to decide whether these signatures were caused by the ad 551 or the ad 1303 event. 相似文献
65.
Günter Leydecker Timo Schmitt Holger Busche Thomas Schaefer 《Soil Dynamics and Earthquake Engineering》2008,28(9):754-762
Within the scope of the licensing procedure for 12 interim storage facilities for spent nuclear fuel at nuclear power plants (NPP) and one for the dismantling of a NPP in Germany, site-specific expert reports were carried out to determine seismo-engineering design parameters. Our work was based on the German nuclear safety standard KTA 2201 part 1 “Design of Nuclear Power Plants against Seismic Events” which requires the derivation of the design earthquake in terms of (macroseismic) intensity. The intensity of the particular design earthquake was evaluated by the deterministic method stipulated in KTA 2201 part 1. According to the current state-of-the-art of science and technology supplementary to the deterministic approach, probabilistic evaluations were done setting a probability of exceedance for the occurrence of the design earthquake of 10−5 year−1. Geological development and neotectonic conditions of the site surrounding areas were included in the evaluations. For 13 interim storage facility sites, soil-dependent design spectra and corresponding strong-motion duration values were determined.For sites with low seismic hazard site-specific design spectra from the literature were used. In the case of sites with higher seismic hazard (design earthquakeVII 1/2 MSK) strong-motion registrations representative for the site were selected from world wide data and subsequently evaluated to derive site-specific design spectra. 相似文献
66.
Geomagnetism and Aeronomy - This study investigates the impacts of geomagnetic storms on the performance of the International Reference Ionosphere 2016 (IRI-2016) foF2 predictions at different... 相似文献
67.
68.
Eeva Mäkiranta Timo Vihma Anna Sjöblom Esa-Matti Tastula 《Boundary-Layer Meteorology》2011,140(1):105-123
Sonic anemometer and profile mast measurements made in Wahlenbergfjorden, Svalbard Arctic archipelago, in May 2006 and April
2007 were employed to study the atmospheric boundary layer over sea-ice. The turbulent surface fluxes of momentum and sensible
heat were calculated using eddy correlation and gradient methods. The results showed that the literature-based universal functions
underestimated turbulent mixing in strongly stable conditions. The validity of the Monin-Obukhov similarity theory was questionable
for cross-fjord flow directions and in the presence of mesoscale variability or topographic effects. The aerodynamic roughness
length showed a dependence on the wind direction. The mean roughness length for along-fjord wind directions was (2.4 ± 2.6)
× 10−4 m, whereas that for cross-fjord directions was (5.4 ± 2.8) × 10−3 m. The thermal stratification and turbulent fluxes were affected by the synoptic situation with large differences between
the 2 years. Channelling effects and drainage flows occurred especially during a weak large-scale flow. The study periods
were simulated applying the Weather Research and Forecasting (WRF) model with 1-km horizontal resolution in the finest domain.
The results for the 2-m air temperature and friction velocity were good, but the model failed to reproduce the spatial variability
in wind direction between measurement sites 3 km apart. The model suggested that wind shear above the stable boundary layer
provided a non-local source for the turbulence observed. 相似文献
69.
Timo?M.?Kirchner Kathryn?M.?GillisEmail author 《Contributions to Mineralogy and Petrology》2012,164(1):123-141
Tectonic exposures of upper plutonics (>800 m) that are part of a contiguous section of young East Pacific Rise (EPR) crust
at the Hess Deep Rift provide the first regional-scale constraints on hydrothermal processes in the upper plutonic crust formed
at a fast-spreading ridge. Submersible-collected samples recovered over a 4-km-wide region show that the sheeted dike complex
is largely underlain by a 150- to 200-m-thick gabbro unit, followed by a more primitive gabbronorite unit. Gabbroic samples
are variably altered by pervasive fluid flow along fracture networks to amphibole-dominated assemblages. The gabbroic rocks
are significantly less altered (average 11% hydrous phases) than the overlying sheeted dike complex (average 24%), and the
percentage of hydrous alteration diminishes with depth. Incipient, pervasive fluid flow occurred at amphibolite facies conditions
(average 720°C), with slightly higher temperatures in the lower 500 m of the section. The extent of subsequent lower-temperature
alteration is generally low and regionally variable. The gabbroic samples are slightly elevated in 87Sr/86Sr relative to fresh rock values (0.7024) and less enriched than the overlying sheeted dike complex. 87Sr/86Sr for the pervasively altered gabbroic samples ranges from 0.70244 to 0.70273 (mean 0.70257), tonalites is 0.7038, and pyroxene
hornfels ranges from 0.70259 to 0.70271. 87Sr/86Sr does not vary with depth, and there is a strong positive correlation with the percentage of hydrous phases. Strontium contents
of igneous and hydrothermal minerals, combined with bulk rock 87Sr/86Sr, indicate that Sr-isotopic exchange is largely controlled by the uptake of fluid 87Sr/86Sr in hydrous minerals and does not require Sr gain or loss. The minimum, time-integrated fluid–rock ratio for the sheeted
dike complex and upper plutonics is 0.55–0.66, and the fluid flux calculated by mass balance is ~2.1 to 2.5 × 106 kg m−2, 30–60% higher than fluid fluxes calculated in the same manner for sheeted dike complexes on their own at Hess and Pito Deeps,
and Ocean Drilling Program Hole 504B. Alteration patterns within the upper plutonics evolved in response to axial magma chamber
(AMC) dynamics at the EPR, such that magma replenishment led to assimilation and thermal metamorphism of the country rock,
and the position of the hydrothermal root-zone tracked the vertical migration of the AMC. The freshness of the lowermost gabbroic
rocks suggests that pervasive fluid flow does not lead to significant fluid and heat fluxes at and near fast-spreading ridges. 相似文献
70.
Polygonal finite elements are gaining an increasing attention in the computational mechanics literature, but their application in rock mechanics is very rare. This paper deals with numerical modeling of rock failure under dynamic loading based on polygonal finite elements. For this end, a damage-viscoplastic constitutive model for rock based on the Mohr-Coulomb criterion with the Rankine criterion as a tensile cutoff is employed and implemented with the polygonal finite element method. Moreover, the mineral mesostructure or rock is described by randomly mapping groups of polygonal elements representing the constituent minerals into a global mesh and assigning these groups with the corresponding mineral material properties. The performance of the polygonal elements is compared with that of the linear and quadratic triangular and bilinear quadrilateral elements in numerical simulations of controlled shear band formation under uniaxial compression and lateral splitting failure in the dogbone tension test. Numerical simulations of uniaxial tension and compression tests as well as dynamic Brazilian disc test under increasing loading rates demonstrate that the present approach predicts the correct failure modes as well as the dynamic increase in strength of rock. 相似文献