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排序方式: 共有120条查询结果,搜索用时 192 毫秒
51.
The detailed reconstruction of the directional spectrum of wind waves from measurements of the wave field is an essential requirement for several applications, including the numerical modeling of wave evolution. Three reconstruction techniques that provide estimates of the directional distribution function D(f,θ), given the one-dimensional frequency spectrum, are compared using data from a coastal locality at the southern Brazilian coast. The techniques are the maximum entropy method (MEM), the Fourier Expansion Method using a cos2 type function (FEMcos) and the Fourier Expansion Method using a sech type function (FEMsech). The main patterns of the wave climate at the study site are qualitatively assessed. Three main sea states, including swell, transition between local sea and swell, and directionally bimodal wind sea, are identified. Time series from three events associated with the main sea states provide test cases for inter comparison of the three reconstruction techniques. Maximum entropy estimates of D(f,θ) provide results that are more consistent than those obtained from the two FEM techniques in all cases considered. 相似文献
52.
Ferreira da Silva Glauciene Justino de Oliveira Nádja Melo Santos Celso Augusto Guimarães da Silva Richarde Marques 《Natural Hazards》2020,102(3):939-964
Natural Hazards - Vegetation indices have been widely used for monitoring the spatiotemporal variables of vegetation and characterizing droughts, primarily in semiarid regions. Drought is a... 相似文献
53.
Judith Sippel Aline Saintot Michel Heeremans Magdalena Scheck-Wenderoth 《Marine and Petroleum Geology》2010
The geodynamic history of a region is archived in its geologic record which, in turn, may reflect deformation patterns that causally can be related to certain configurations of paleostresses. In the Oslo Region, the exposed geological record ranges from Precambrian high-grade metamorphic rocks through Cambro-Silurian sedimentary rocks to Permo-Carboniferous sedimentary and magmatic rocks, the latter being related to the development of the Oslo rift system. We investigate the kinematics of outcrop-scale faults to derive the diversity of paleostress states responsible for the observed strain. For this purpose, we combine different graphical and numerical approaches to separate heterogeneous fault-slip data sets and estimate the associated reduced stress tensors. A reduced stress tensor consists of the directions of the three principal stress axes with σ1 ≥ σ2 ≥ σ3 and the ratio of principal stress differences, R = (σ2 − σ3)/(σ1 − σ3). 相似文献
54.
R. R. Cuzinatto C. A. M. de Melo L. G. Medeiros P. J. Pompeia 《Astrophysics and Space Science》2011,332(1):201-208
We construct a phenomenological theory of gravitation based on a second order gauge formulation for the Lorentz group. The
model presents a long-range modification for the gravitational field leading to a cosmological model provided with an accelerated
expansion at recent times. We estimate the model parameters using observational data and verify that our estimative for the
age of the Universe is of the same magnitude than the one predicted by the standard model. The transition from the decelerated
expansion regime to the accelerated one occurs recently (at ∼9.3 Gyr). 相似文献
55.
Olivier Pourret Gérard Gruau Aline Dia Mélanie Davranche Jérôme Molénat 《Aquatic Geochemistry》2010,16(1):31-59
A 7-year monitoring period of rare earth element (REE) concentrations and REE pattern shapes was carried out in well water samples from a 450 m long transect setup in the Kervidy/Coët-Dan experimental catchment, France. The new dataset confirms systematic, topography-related REE signatures and REE concentrations variability but challenges the validity of a groundwater mixing hypothesis. Most likely, this is due to REE preferential adsorption upon mixing. However, the coupled mixing–adsorption mechanism still fails to explain the strong spatial variation in negative Ce anomaly amplitude. A third mechanism—namely, the input into the aquifer of REE-rich, Ce anomaly free, organic colloids—is required to account for this variation. Ultrafiltration results and speciation calculations made using Model VI agree with this interpretation. Indeed, the data reveal that Ce anomaly amplitude downslope decrease corresponds to REE speciation change, downhill groundwaters REE being mainly bound to organic colloids. Water table depth monitoring shows that the colloid source is located in the uppermost, organic-rich soil horizons, and that the colloid input occurs mainly when water table rises in response to rainfall events. It appears that the colloids amount that reaches groundwater increases downhill as the distance between soil organic-rich horizons and water table decreases. Topography is, therefore, the ultimate key factor that controls Ce anomaly spatial variability in these shallow groundwaters. Finally, the <0.2 μm REE fraction ultimately comes from two solid sources in these groundwaters: one located in the deep basement schist; another located in the upper, organic-rich soil horizon. 相似文献
56.
Masato Kobiyama Aline de Almeida Mota Fernando Grison Joana Nery Giglio 《Natural Hazards》2011,59(2):1077-1086
The rainfall events that occurred in the Cubat?o do Norte River watershed, Santa Catarina State, Brazil, in 2008, were characterized
by both high intensities and amounts and triggered landslides in this watershed. The objective of the present study was to
analyze the influence of landslides on the turbidity and the total solid concentration (TS) in this river using turbidity,
TS, and river discharge data obtained from March 23, 2008, to June 11, 2010. The comparison between turbidity and discharge
patterns implies that the landslide process was not continuous and increased the turbidity intermittently and irregularly.
The sediment yield during the landslide occurrence was approximately five times higher than without the landslide, even though
the discharges were similar. The turbidity/discharge relationship during the landslide occurrence was markedly different from
that before and after the occurrence. The correlation coefficients between turbidity and TS showed that the landslide significantly
changed the sediment yield in this watershed. The result indicates that sediment yield estimations at the watershed level
should be treated more carefully when landslides occur. 相似文献
57.
Rui Company Angela Serafim Richard Cosson Aline Fiala-Médioni David R. Dixon & Maria João Bebianno 《Marine Ecology》2007,28(1):93-99
The vent mussel Bathymodiolus azoricus is the dominant member of the Northern Mid‐Atlantic Ridge (MAR) hydrothermal megafauna, and lives in an environment characterized by temporal and spatial variations in the levels of heavy metals, methane and hydrogen sulphide, substances which are known to increase reactive oxygen species levels in the tissues of exposed organisms. To evaluate the effects of two contrasting hydrothermal environments on the antioxidant defence system of this vent mussel species, a 2‐week transplant experiment was carried out involving mussels collected from the relatively deep (2300 m), and chemical rich, Rainbow vent field. These were transplanted to the shallower (1700 m), and relatively less toxic, Lucky Strike vent field. To achieve this objective, levels of superoxide dismutase, catalase (CAT), total glutathione peroxidase (GPx), selenium‐dependent glutathione peroxidase and lipid peroxidation (LPO) were measured in the gills and mantle tissues of resident and transplant mussels before and after the transplant experiment. With the exception of CAT, the gills of the transplanted mussels had significantly higher antioxidant enzyme activity compared with the basal levels in the donor (Rainbow) and recipient (Lucky Strike) populations; whereas the antioxidant enzyme levels in the mantle tissues of the transplants reflected the baseline levels of activity in the native Lucky Strike mussels after 2 weeks. In contrast, LPO levels were significantly higher in both tissue types in the transplants than in either the source or the recipient populations, which suggested a response to hydrostatic pressure change (note, the transplant animals were brought to the surface for transportation between the two vent fields). The fact that the Rainbow mussels survived the transplant experience indicates that B. azoricus has a very robust constitution, which enables it to cope behaviourally, physiologically and genetically with the extreme conditions found in its naturally contaminated deep‐sea environment. 相似文献
58.
Rémi Marsac Mélanie Davranche Gérard Gruau Martine Bouhnik-Le Coz Aline Dia 《Geochimica et cosmochimica acta》2011,75(19):5625-5637
The Humic Ion Binding Model VI (Model VI) - previously used to model the equilibrium binding of rare earth elements (REE) by humic acid (HA) - was modified to account for differences in the REE constant patterns of the HA carboxylic and phenolic groups, and introduced into PHREEQC to calculate the REE speciation on the HA binding sites. The modifications were shown to greatly improve the modeling. They allow for the first time to both satisfactorily and simultaneously model a large set of multi-REE experimental data with the same set of equations and parameters. The use of PHREEQC shows that the light rare earth elements (LREE) and heavy rare earth elements (HREE) do not bind to HA by the same functional groups. The LREE are preferentially bound to carboxylic groups, whereas the HREE are preferentially bound to carboxy-phenolic and phenolic groups. This binding differentiation might lead to a fractionation of REE-HA patterns when competition between REE and other metals occur during complexation. A survey of the available data shows that competition with Al3+ could lead to the development of HREE-depleted HA patterns. This new model should improve the hydrochemical modeling of the REE since PHREEQC takes into account chemical reactions such as mineral dissolution/precipitation equilibrium and redox reactions, but also models kinetically controlled reactions and one-dimensional transport. 相似文献
59.
Aline Anderson de Castro Luz Adriana Cuartas Michael T. Coe Celso Von Randow Andrea Castanho Alex Ovando 《水文科学杂志》2013,58(13-14):1954-1966
ABSTRACTWe coupled the hydrologic routing and flood dynamics model Terrestrial Hydrology Model with Biogeochemistry (THMB) to the Integrated LAND Surface Model (INLAND) and compared simulations of the discharge and flood extent area against gauge station and satellite-based information in the Amazon Basin. The coupled model represents well the seasonality of the flooding and discharge, but underestimates both of them. This can be related to an already discussed underestimate of the precipitation in the east of the Andes Mountains. A photosynthesis limitation on the flooded area was also included, showing changes in plant productivity and reduction in vegetation carbon stocks. Despite its limitations, the model proves to be a valuable tool for studies of the hydrological cycle and flood dynamics response to climate change projections, allowing it to be used to represent the feedbacks between continental surface water cycle and vegetation. 相似文献
60.
André Gustavo da Silva Melo Honorato Gustavo Barbosa Lima da Silva Celso Augusto Guimarães Santos 《水文科学杂志》2013,58(15-16):2060-2075
ABSTRACTCombinations of low-frequency components (also known as approximations) resulting from the wavelet decomposition are tested as inputs to an artificial neural network (ANN) in a hybrid approach, and compared to classical ANN models for flow forecasting for 1, 3, 6 and 12 months ahead. In addition, the inputs are rewritten in terms of the flow, revealing what type of information was being provided to the network, in order to understand the effect of the approximations on the forecasting performance. The results show that the hybrid approach improved the accuracy of all tested models, especially for 1, 3 and 6 months ahead. The input analyses show that high-frequency components are more important for shorter forecast horizons, while for longer horizons, they may worsen the model accuracy. 相似文献