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61.
Abstract Fusulinoidean faunal succession from Paleo–Tethyan seamount-type carbonates of the Yutangzhai section in the Central zone of the Changning–Menglian Belt of West Yunnan, Southwest China, is presented for the first time. The Changning–Menglian Belt is one of the orogenic belts that represent the closed main Paleo–Tethys in East Asia. The Yutangzhai section is represented by basalts and overlying carbonates, about 1100 m thick. It exhibits a continuous faunal succession composed of 17 fusulinoidean assemblages ranging from the Serpukhovian (late Mississippian/late Early Carboniferous) to Midian/Capitanian (late Middle Permian/late Guadalupian). No significant faunal break can be recognized in this section. The generic and some specific composition of the Yutangzhai assemblages indicates that the faunal succession is similar to those observed in Tethyan and Panthalassan areas and is of tropical Tethyan type although their generic diversity is definitely lower than those of Paleo–Tethyan shelves, such as South China, Indochina, and Central Asia. Throughout the Yutangzhai section, the carbonate rocks are essentially massive, very pure in composition, and devoid of terrigenous siliciclastic inputs. These lithologic characters are identical to those observed in accreted shallow-marine carbonate successions of seamount origin in Permian and Jurassic accretionary complexes of Japan, for example the Akiyoshi Limestone. This evidence further demonstrates the seamount origin of the basalt–limestone succession in the Central zone of the Changning–Menglian Belt from the viewpoint of lithofacies. In middle Mississippian (middle Early Carboniferous) time, oceanic submarine volcanism that was probably related to hot spot activities formed a number of seamounts and oceanic plateaus. It was active not only in the Panthalassa, but also in the Paleo–Tethys. 相似文献
62.
Abstract: Microorganisms found at terrestrial and seafloor hydrothermal systems are classified based on their optimum growth temperatures. Prokaryotes exhibiting optimum growth temperatures above 45C are defined as thermophiles, while those with optimum growth temperatures above 80C are called hyperthermophiles. Hyperthermophiles have chemically and thermodynamically stable cytoplasmic‐membrane consisting of ether–lipids. Hyperthermophiles observed at temperature up to 113C in seafloor hydrothermal areas should have thermostable proteins. Presumably, the thermostable proteins are replacing certain amino acid residue by proline instead of alanine in order to increase hydrogen bonds and salt bridges. Microorganisms inhabiting terrestrial and seafloor hydrothermal areas obtain energy mainly by use of chemical disequilibrium, so that their habitat may be restricted to the redox boundary between ambient water and reduced hydrothermal fluids. Among more than 200 species of cultivable thermophiles and hyperthermophiles, hyperthermophiles mainly obtain energy by sulfur reduction, because this reaction can produce energy efficiently at > 80C. Some hyperthermophilic sulfur reducers can reduce Cr(VI), Mn(IV), Fe(III), Co(III), As(V), Se(VI), Tc(VII), Au(III) and U(VI) through hydrogen or organic compounds that act as reducing agents for yielding energy. Some hyperther‐mophiles use W instead of Mo for activating their enzymes. Bacteria can pump out toxic metal ions from their cells, however toxic metal resistance systems of archaea, including hyperthermophiles, have not yet been studied. Methane producing hyperthermophiles can yield energy by the autotrophic reaction, when sufficient carbon dioxide and molecular hydrogen can be supplied and methane can be removed from hydrothermal systems. If nitrogen can be supplied into a hydrothermal system, hydrogen oxidization by nitrogen species (e.g. NO3‐, NO2‐, NO and N2O) may be expected through the metabolism of some hyperthermophiles. 相似文献
63.
Ken-ichiro Hisada Masaaki Sugiyama Katsumi Ueno Punya Charusiri Shoji Arai 《Island Arc》2004,13(1):119-127
Abstract Thailand comprises two continental blocks: Sibumasu and Indochina. The clastic rocks of the Triassic Mae Sariang Group are distributed in the Mae Hong Son–Mae Sariang area, north‐west Thailand, which corresponds to the central part of Sibumasu. The clastic rocks yield abundant detrital chromian spinels, indicating a source of ultramafic/mafic rocks. The chemistry of the detrital chromian spinels suggests that they were derived from three different rock types: ocean‐floor peridotite, chromitite and intraplate basalt, and that ophiolitic rocks were exposed in the area, where there are no outcrops of them at present. Exposition of an ophiolitic complex denotes a suture zone or other tectonic boundary. The discovery of chromian spinels suggests that the Gondwana–Tethys divide is located along the Mae Yuam Fault zone. Both paleontological and tectonic aspects support this conclusion. 相似文献
64.
Jun-Ichi Matsuda Kenji Notsu Jun Okano Katsumi Yaskawa Leonard Chungue 《Tectonophysics》1984,104(1-2)
Sr isotopes and K-Ar ages were determined for volcanic rocks from three islands, Samoa, Rarotonga and Rurutu in the Austral-Gilbert-Marshall chain. We have established that Rurutu originated from the same “hot spot” as Tubuai and Raivavae in the Cook-Austral chain as indicated by its 11 m.y. K-Ar age and (
) ratios. The (
) ratios for Rurutu, Tubuai and Raivavae lie in the restricted range 0.7026–0.7035. K-Ar ages of all volcanic rocks from Samoa and Rarotonga are all less than 4 m.y. and their (
) ratios are much higher than those in Rurutu, Tubuai and Raivavae. These findings suggest that Samoa and Rarotonga did not originate in a single hot spot for the Cook-Austral islands. 相似文献
65.
Recent high-resolution observations of crustal movements have revealed silent slip events (SSEs) with propagation velocities of around 10–15 km d−1 and with intervals of 3–14 months along the deeper parts of the Cascadia and Nankai subduction zones. This study develops 2-D and 3-D models of these short-interval SSEs considering the frictional behaviour that was confirmed experimentally by Shimamoto for the unstable–stable transition regime. To represent this frictional behaviour, a small cut-off velocity to an evolution effect is introduced in a rate- and state-dependent friction law. When the cut-off velocity to the evolution effect is significantly smaller than that to a direct effect, steady-state friction exhibits velocity weakening at low slip velocities and velocity strengthening at high slip velocities. At the deeper Cascadia and Nankai subduction interfaces, the pore pressure is inferred to be high because of the dehydration of materials in the descending plate. Under conditions where the pore-fluid pressure is nearly equal to the lithostatic pressure and the critical weakening displacement is very small, short-interval SSEs with propagation velocities and slip velocities of 4–8 km d−1 and 2 − 4 × 10−7 m s−1 , respectively, can be reproduced. The propagation velocity of short-interval SSEs is in proportion to the slip velocity. The results also show that during the nucleation process of large earthquakes, the occurrence of short-interval SSEs becomes irregular because of the accelerated slips that occur at the bottom of the seismogenic zone. Our results suggest that monitoring of short-interval SSEs might be useful for forecasting the main earthquakes. 相似文献
66.
67.
Integrated primary production (IPP) datasets from the eastern East China Sea (ECS) were used to validate the depth dependent
and time integrated model (TIM), the empirical model (EM), and the vertically generalized production model (VGPM). Employing
constant maximum chlorophyll-a (Chl-a) specific carbon fixation rate (P
opt
B
), the original TIM could not explain measured IPP variance, while the low P
opt
B
estimated using P
opt
B
models originally embedded in the EM were responsible for original EM low estimations. The disparity between P
opt
B
expressions originally embedded in the VGPM and that observed in this study was responsible for the low accuracy of the original
VGPM. After locally tuning on the P
opt
B
model, TIM and VGPM could predict well, whereas EM still gave low estimates. This was probably due to the fact that, unlike
TIM and VGPM, EM employs a constant factor instead of a light dependent function in describing the depth of light-saturation
primary production. The high accuracy of TIM was limited by the complexity of estimating many variable inputs. EM, as a simplest
model, should be used with caution in the eastern ECS. Global VGPM with locally adjusted P
opt
B
seemed to be an effective model for estimating IPP in the eastern ECS. 相似文献
68.
69.
The responses of atmospheric pCO2 and sediment calcite content to changes in the export rain ratio of calcium carbonate to organic carbon are examined using
a diffusion-advection ocean biogeochemical model coupled to a one-dimensional sediment geochemistry model. Our model shows
that a 25% reduction in rain ratio decreases atmospheric pCO2 by 59 ppm. This is caused by alkalinity redistribution by a weakened carbonate pump and an alkalinity increase in the whole
ocean via carbonate compensation with decreasing calcite burial. The steady state responses of sedimentary calcite content
and calcite preservation efficiency are rather insensitive to the deepening of the saturation horizon of 1.9 km. This insensitivity
is a result of the reduced deposition flux that decreases calcite burial, counteracting the saturation horizon deepening that
increases calcite burial. However, in the first 10,000 years the effect of reduced calcite deposition on the burial change
is more prominent; while after 10,000 years, the effect of saturation horizon deepening is more dominant. The lowering of
sediment calcite content for the first 10,000 years is effectively decoupled from the 1.9 km downward shift of the saturation
horizon. Our results are in part a consequence of the more dominant role that respiration CO2 plays in sediment calcite dissolution over bottom water chemistry in our control run and support the decoupling of calcite
lysocline depth and saturation horizon shifts, as suggested originally by Archer and Maier-Reimer (1994) and Archer et al. (2000). 相似文献
70.
Hidetoshi HARA Miyuki KUNII Ken-ichiro HISADA Katsumi UENO Yoshihito KAMATA Punya CHARUSIRI Thasinee CHAROENTITIRAT 《地球学报》2012,33(S1):15-15
The accretionary complex related to the Pa-leo-Tethys subduction was developed along western margin of the Indochina Block in northern Thailand. The provenance, source rock compositions, and sedi-ment supply system of the accretionary complex were reconstructed based on the petrography and geochem-istry of clastic rocks, U-Pb dating of detrital zircons. 相似文献