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31.
A high resolution multi-proxy record of pronounced recent environmental change at Baker Lake,Nunavut
A. S. Medeiros C. E. Friel S. A. Finkelstein R. Quinlan 《Journal of Paleolimnology》2012,47(4):661-676
Arctic aquatic systems are considered to be especially sensitive to anthropogenic disturbance, which can have cascading effects
on biological communities as aquatic food-web structure is altered. Bio-indicators that respond to major limnological changes
can be used to detect and infer major environmental change, such as climate warming, with the use of paleolimnological techniques.
A multi-proxy approach was used to quantify recent environmental changes at Baker Lake, Nunavut, Arctic Canada. Analyses of
fossilized remains of chironomids and diatoms were conducted on a sediment core of 20 cm in length sampled at 0.5-cm intervals.
A new surface sediment training set of subfossil chironomid assemblages from 65 lakes across the eastern Canadian Arctic generated
a robust (r
jack2 = 0.79) surface water paleotemperature transfer function. The transfer function was applied to stratigraphic intervals from
the Baker Lake sediment core to generate a paleotemperature reconstruction of sub-decadal resolution. The surface water temperature
reconstruction inferred a 2°C increase in mid-summer surface water temperature for Baker Lake over the last 60 years, which
was corroborated by the local instrumental record spanning the period of 1950–2007 AD. The chironomid record shows a recent
decline of several cold-water taxa and appearance of warm-water indicators. This shift in community structure began circa
1906 AD, and intensified after 1940 AD. The corresponding fossil diatom record showed an increase in small planktonic Cyclotella taxa over the past 60 years, intensifying in the last 5 years, which also suggests a warmer climate and longer ice-free periods.
The shifts in the diatom assemblages began later than the shifts in the chironomid assemblages, and were of lower magnitude,
reflecting differences in the mechanisms in which these two indicators respond to environmental change. 相似文献
32.
José Bandeira Brasil Eunice Maia de Andrade Helba Araújo de Queiroz Palácio Julio Cesar Neves dos Santos Pedro Henrique Augusto Medeiros 《水文科学杂志》2020,65(10):1640-1651
ABSTRACT The interception process impacts rainfall magnitude and intensity under the canopy. In this study, the effect of plant interception on throughfall characteristics was assessed in the deciduous Caatinga vegetation, at different canopy development stages and for temporal scales ranging from seasonal to the intra-event scale. Throughfall and stemflow percentages were slightly higher at the onset of the rainy season, when leaf area density is low, with resulting lower interception losses. However, there was no statistical difference among the variables at the seasonal scale. At the intra-event scale, average and maximum throughfall intensity at different time intervals showed statistical difference between the stages of canopy development. Regardless of leaf area density and rainfall depth, vegetation is able to retain all the water up to 2 min in the beginning of each rainfall event with accumulated rainfall smaller than 0.6 mm. Furthermore, the Caatinga vegetation attenuates the rainfall intensity by 30–40%. 相似文献
33.
34.
Atmospheric gravity wave propagation direction observed by airglow imaging in the South American sector 总被引:1,自引:0,他引:1
A.F. Medeiros H. Takahashi R.A. Buriti K.M. Pinheiro D. Gobbi 《Journal of Atmospheric and Solar》2005,67(17-18):1767
Airglow all sky imaging observation has been carried out in three different locations in south America, at Cachoeira Paulista (22.7°S, 45.0°W) in 1999, São João do Cariri (7.5°S, 36.5°W) in 2001 and Boa Vista (2.8°N, 60.7°W) in 2002. Comparing the atmospheric gravity wave characteristics retrieved from the image data for the three different sites and including a previous work at Alcântara (2.3°S, 44.5°W) carried out by Taylor et al. [1997. Journal of Geophysical Research 102 (D22) 26,283–26,299], we found that there is a preferential propagation direction, from the Continent to the Atlantic Ocean. The observed wave propagation directions reveal that a major part of the waves have their direction from Continent toward Ocean. The possible source of the wave generation is discussed. 相似文献
35.
A generic gravity source moment is an integral, over the source volume, of the product of the density distribution by a polynomia
in the Cartesian coordinates of a point belonging to this volume. We obtained a formal expression for a generic moment in
terms of integrals involving the gravity anomaly and the gravity potential. By analyzing the conditions under which this expression
is valid, we conclude that, without usinga priori information regarding the sources, it is possible to determine, from the gravity anomaly, any moment or linear combination
of moments whose associated polynomial has null Laplacian and depends only on the coordinates defining the measurement plane.
Additionally, no moment whose associated polynomial has a nonnull laplacian can be determined without usinga priori information of the source. 相似文献
36.
Naira Chaouch Marouane Temimi Scott Hagen John Weishampel Stephen Medeiros Reza Khanbilvardi 《水文研究》2012,26(11):1617-1628
This work proposes a method for detecting inundation between semi‐diurnal low and high water conditions in the northern Gulf of Mexico using high‐resolution satellite imagery. Radarsat 1, Landsat imagery and aerial photography from the Apalachicola region in Florida were used to demonstrate and validate the algorithm. A change detection approach was implemented through the analysis of red, green and blue (RGB) false colour composites image to emphasise differences in high and low tide inundation patterns. To alleviate the effect of inherent speckle in the SAR images, we also applied ancillary optical data. The flood‐prone area for the site was delineated a priori through the determination of lower and higher water contour lines with Landsat images combined with a high‐resolution digital elevation model. This masking technique improved the performance of the proposed algorithm with respect to detection techniques using the entire Radarsat scene. The resulting inundation maps agreed well with historical aerial photography as the probability of detection reached 83%. The combination of SAR data and optical images, when coupled with a high‐resolution digital elevation model, was shown to be useful for inundation mapping and have a great potential for evaluating wetting/drying algorithms of inland and coastal hydrodynamic models. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
37.
Jiabin Zhou Tieguan Wang Yanping Zhang Ningning Zhong Patricia M. Medeiros Bernd R.T. Simoneit 《Atmospheric Research》2009,93(4):849-861
The solvent-extractable organic compounds of atmospheric PM10 samples, collected over two years beginning in 2003 at urban and suburban sites of Beijing, were characterized using gas chromatography–mass spectrometry (GC–MS). The elemental carbon (EC) contents were determined and ranged from 4.3 to 42 μg m− 3. Organic compounds in total extracts were identified and included unresolved complex mixture (UCM) and series of n-alkanes, n-alkanols, n-alkanoic acids, polycyclic aromatic hydrocarbons (PAHs); saccharides, alkanedioic acids, steroids, and other biomarkers and source tracers. The seasonal variations of their relative abundances are discussed. The abundance order for the major molecular classes in the particulate organic matter (POM) was the following: UCM > saccharides > n-alkanoic acids >n-alkanes > n-alkanols > PAHs > hydroxy-PAHs > other biomarker tracers. Based on the genetic significance of the molecular tracers, the dominant sources of POM are proposed for the two sampling sites. The emissions from fossil fuel use (both coal and petroleum products), biomass combustion, other pyrolysis sources, higher plant wax, and secondary products contribute > 98.0% of the POM mass. The fossil fuel use (average = 65% of POM) is the largest contributor and derives mainly from vehicular traffic. 相似文献
38.
Luiz Carlos Ruiz Pessenda Paulo Eduardo De Oliveira Milene Mofatto Vanda Brito de Medeiros Ricardo Jos Francischetti Garcia Ramon Aravena Jos Albertino Bendassoli Accio Zuniga Leite Antonio Roberto Saad Mario Lincoln Etchebehere 《Quaternary Research》2009,71(3):437-452
The lack of paleoecological records from the montane Atlantic Rainforest of coastal Brazil, a hotspot of biological diversity, has been a major obstacle to our understanding of the vegetational changes since the last glacial cycle. We present carbon isotope and pollen records to assess the impact of the glaciation on the native vegetation of the Serra do Mar rainforest in São Paulo, Brazil. From ca. 28,000 to 22,000 14C yr BP, a subtropical forest with conifer trees is indicative of cool and humid conditions. In agreement carbon isotopic data on soil organic matter suggest the presence of C3 plants and perhaps C4 plants from 28,000 to 19,000 14C yr BP. The significant increase in the sedimentation rate and algal spores from 19,450 to 19,000 14C yr BP indicates increasing humidity, associated to an erosion process between 19,000 and 15,600 14C yr BP. From 15,600 14C yr BP to present there is a substantial increase in arboreal elements and herbs, indicating more humid and warmer climate. From 19,000 to 1000 14C yr BP, δ13C values indicated the predominance of C3 plants. These results are in agreement with studies in speleothems of caves, which suggest humid conditions during the last glacial maximum. 相似文献
39.
I. Paulino H. Takahashi A.F. Medeiros C.M. Wrasse R.A. Buriti J.H.A. Sobral D. Gobbi 《Journal of Atmospheric and Solar》2011,73(11-12):1575-1580
During the Conjugate Point Experiment (COPEX) campaign performed at Boa Vista (, dip angle ) from October to December 2002, 15 medium-scale gravity waves in the OHNIR airglow images were observed. Using a Keogram image analysis, we estimate their parameters. Most of the waves propagate to Northwest, indicating that their main sources are Southeast of Boa Vista. Quasi-simultaneous plasma bubble activities in the OI 630 nm images were observed in seven cases. The distances between the bubble depletions have a linear relationship with the wavelengths of the gravity waves observed in the mesosphere, which suggests a direct contribution of the mesospheric medium-scale gravity waves in seeding the equatorial plasma bubbles. 相似文献
40.
João Medeiros Carlo R. Contaldi 《Monthly notices of the Royal Astronomical Society》2006,367(1):39-45
We investigate the effect of foreground residuals in the WMAP ( Wilkinson Microwave Anisotropy Probe ) data by adding foreground contamination to Gaussian ensembles of cosmic microwave background (CMB) signal and noise maps. We evaluate a set of non-Gaussian estimators on the contaminated ensembles to determine with what accuracy any residual in the data can be constrained using higher-order statistics. We apply the estimators to the raw and cleaned Q -, V - and W -band first-year maps. The foreground subtraction method applied to clean the data in Bennett et al. appears to have induced a correlation between the power spectra and normalized bispectra of the maps which is absent in Gaussian simulations. It also appears to increase the correlation between the Δℓ= 1 inter-ℓ bispectrum of the cleaned maps and the foreground templates. In a number of cases the significance of the effect is above the 98 per cent confidence level. 相似文献