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171.
P. M. Carreira J. M. Marques M. R. Carvalho D. Nunes M. Antunes da Silva 《Environmental Earth Sciences》2014,71(6):2941-2953
This paper summarizes a new outlook on the conceptual model of Melgaço–Messegães CO2-rich cold (≈18 °C) mineral water systems, issuing in N of Portugal, based on their isotopic (2H, 3H, 13C, 14C and 18O) and geochemical features. Stable isotopes indicate the meteoric origin of these CO2-rich mineral waters. Based on the isotopic fractionation with the altitude, a recharge altitude between 513 up to 740 m a.s.l. was estimated, corroborating the tritium results. The lowest 3H content (0 TU) is found in the groundwater samples with the highest mineralization. The mineral waters circulation are mainly related to a granitic and granodioritic environment inducing two different groundwater types (Ca/Na–HCO3 and Na/Ca–HCO3), indicating different underground flow paths. Calcium dissolution is controlled by hydrolysis of rock-matrix silicate minerals (e.g. Ca-plagioclases) and not associated to anthropogenic sources. The shallow dilute groundwaters exhibit signatures of anthropogenic origins (e.g. NO3) and higher Na/Ca ratios. The stable isotopes together with the geochemistry provided no indication of mixing between the regional shallow cold dilute groundwater and mineral water systems. The heavy isotopic signatures identified in the δ13C data (δ13C = 4.7 ‰, performed on the total dissolved inorganic carbon (TDIC) of CO2-rich mineral waters) could be derived from a deep-seated (upper mantle) source or associated to methanogenesis (CH4 source). The negligible 14C content (≈2 pmC) determined in the TDIC of the mineral waters, corroborates the hypothesis of a mantle-derived carbon source to the mineral groundwater systems or dissolution of carbonate layers at depth. 相似文献
172.
Martins I Lopes RJ Lillebø AI Neto JM Pardal MA Ferreira JG Marques JC 《Marine pollution bulletin》2007,54(6):678-690
A spatially dynamic model for the productivity of spores and adults of green macroalgae (Enteromorpha sp.) was developed for a mesotidal estuary (Mondego estuary, Portugal). Many of the algal processes and parameters included in the model were experimentally obtained. Model predictions were compared to a real time series (1993-1997) of macroalgal biomass variation and the two sets show a good agreement (ANOVA, P<0.001). Results suggest that algal growth is highly sensitive to small changes in depth and exhibits different patterns of variation in different seasons. On a yearly basis, global calculations for the south channel of the estuary (137 ha) suggest that during bloom years, macroalgal biomass may reach about 21,205 ton DW compared to 240 ton DW in regular years. On a seasonal basis, the difference may be even more significant. The consequences of such variations on the nitrogen and phosphorus loading of the system and the adjacent coastal area are discussed. 相似文献
173.
Rudolph Scherreiks Dan Bosence Marcelle BouDagher-Fadel Guillermo Meléndez Peter O. Baumgartner 《International Journal of Earth Sciences》2010,99(6):1317-1334
The Late Triassic and Jurassic platform and the oceanic complexes in Evvoia, Greece, share a complementary plate-tectonic
evolution. Shallow marine carbonate deposition responded to changing rates of subsidence and uplift, whilst the adjacent ocean
underwent spreading, and then convergence, collision and finally obduction over the platform complex. Late Triassic ocean
spreading correlated with platform subsidence and the formation of a long-persisting peritidal passive-margin platform. Incipient
drowning occurred from the Sinemurian to the late Middle Jurassic. This subsidence correlated with intra-oceanic subduction
and plate convergence that led to supra-subduction calc-alkaline magmatism and the formation of a primitive volcanic arc.
During the Middle Jurassic, plate collision caused arc uplift above the carbonate compensation depth (CCD) in the oceanic
realm, and related thrust-faulting, on the platform, led to sub-aerial exposures. Patch-reefs developed there during the Late
Oxfordian to Kimmeridgian. Advanced oceanic nappe-loading caused platform drowning below the CCD during the Tithonian, which
is documented by intercalations of reefal turbidites with non-carbonate radiolarites. Radiolarites and bypass-turbidites,
consisting of siliciclastic greywacke, terminate the platform succession beneath the emplaced oceanic nappe during late Tithonian
to Valanginian time. 相似文献