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91.
92.
Jonas Mota e Silva Cesar Fonseca Ferreira Filho Bernhard Bühn Elton Luiz Dantas 《Mineralium Deposita》2011,46(1):57-90
The “Americano do Brasil” Complex (ABC) is part of a cluster of coeval synorogenic mafic–ultramafic intrusions emplaced during
the Brasiliano/Pan-African Orogenic Cycle in Brazil. The medium-sized ABC consists of interlayered dunite, peridotite, websterite,
and gabbronorite. High Fo values of olivine (up to Fo88) and the crystallization sequence of the ABC (Ol + Chr ≥ Ol + Opx + Chr ≥ Cpx + Opx ≥ Opx + Pl + Cpx ≥ Opx + Pl + Cpx + Ilm + Mag)
suggest crystallization from tholeiitic high-MgO parental magmas. Light rare earth element (REE)-enriched mantle-normalized
REE profiles and εNd(T) values of +2.4 for cumulate rocks from the ABC suggest a depleted mantle source for the parental magma.
The ABC Ni–Cu sulfide deposit (3.1 Mt at 1.12 wt.% Ni and 1.02 wt.% Cu) consists of three distinctively different orebodies
(S1, S2, and G2). The S2 orebody, an unusual occurrence of stratiform massive sulfide hosted by dunite and peridotite in the
interior of a layered intrusion, results from sulfides accumulated at the transient base of the magma chamber following a
new influx of parental magma. The G2 orebody has an irregular and roughly cylindrical shape, consisting mainly of net-textured
sulfides. The G2 orebody is hosted by peridotite and pyroxenite and located stratigraphically below the S1 orebody. S2 and
G2 orebodies are characterized by low Cu/Cu + Ni ratios (mainly below 0.4). The S1 orebody, hosted by websterite and gabbronorite
in the more fractionated sequence of the ABC, is a cluster of several irregular discontinuous orebodies of Ni–Cu disseminated
sulfides. The sulfides of the S1 orebody have high Cu/Cu + Ni ratios (mainly between 0.5 and 0.8) and are highly depleted
in PGE. The S1 orebody is interpreted to result from a later event of sulfide segregation in the magma chamber, possibly following
the event that originated the G2 orebody. The bulk of δ34S values for sulfides of the ABC orebodies and their host rocks fall in the range of 0 ± 2‰. Higher δ34S values (between 3‰ and 5‰) are restricted to pyrite from xenoliths of gneiss located close to the S1 orebody and sulfides
from the S1 orebody. Crustal xenoliths and chemical data (lithogeochemistry and sulfur isotope composition) provide evidence
of crustal contamination of the igneous rocks hosting the S1 orebody, suggesting that sulfur saturation was induced by contamination
with sulfide-bearing crustal rocks. The ABC deposit is an example of Ni–Cu sulfide mineralization hosted by synorogenic mafic–ultramafic
intrusions. The S2 orebody is the first documented example of an economic stratiform massive sulfide orebody located within
layered intrusions, expanding the opportunities for exploration of Ni–Cu sulfides in orogenic regions worldwide. 相似文献
93.
Induced polarization,resistivity, and self-potential: a case history of contamination evaluation due to landfill leakage 总被引:2,自引:1,他引:1
José Domingos Faraco Gallas Fabio Taioli Walter Malagutti Filho 《Environmental Earth Sciences》2011,63(2):251-261
This article compares the efficiency of induced polarization (IP) and resistivity in characterizing a contamination plume
due to landfill leakage in a typical tropical environment. The resistivity survey revealed denser electrical current flow
that induced lower resistivity values due to the high ionic content. The increased ionic concentration diminished the distance
of the ionic charges close to the membrane, causing a decrease in the IP phenomena. In addition, the self-potential (SP) method
was used to characterize the preferential flow direction of the area. The SP method proved to be effective at determining
the flow direction; it is also fast and economical. In this study, the resistivity results were better correlated with the
presence of contamination (lower resistivity) than the IP (lower chargeability) data. 相似文献
94.
Ecological consideration of trace element contamination in sediment cores from Sundarban wetland,India 总被引:2,自引:1,他引:1
E. V. Silva Filho M. P. Jonathan M. Chatterjee S. K. Sarkar S. M. Sella A. Bhattacharya K. K. Satpathy 《Environmental Earth Sciences》2011,63(6):1213-1225
This article reports on the concentration of selected trace elements (Mn, Zn, Cr, Cu, Ba, As, B, V, and Hg) and major elements
(Fe and Al) from the intertidal sediment cores from Sundarban wetland, India. This is a typical meso-macrotidal estuarine
area affected by domestic and industrial activities located upstream. The overall concentrations range is low to moderate,
indicating the environmental conditions in the outfall zone (grain size, hydrodynamic regime, and confinement), which favors
the in situ accumulation of pollutants. The extent of contamination from trace elements in Sundarban core sediments is evaluated
through a two-pronged approach: (i) by determining the metal enrichment in the sediments through the calculation of Pollution
Load Index (PLI), Enrichment Factor (EF) and Index of Geoaccumulation (I
geo), and (ii) by defining a potential level of biological risk by the use of quality criteria such as Threshold Effect Level
(TEL) and Effects Range-Low (ERL) benchmarks. On the basis of the calculated indices, sediments are particularly enriched
with Cr, Cu, B, V, and As. Those enrichments seem to be due to the fine granulometry of the regions with Fe and Mn oxi-hydroxides
being the main metal carriers. Trace Elements input to the Sundarban wetland need to be kept under strict control in future
specially with reference to As since, according to TEL and ERL benchmarks, it already appears to be associated with a potential
biological risk. 相似文献
95.
Robson Willians da Costa Silva Walter Malagutti Filho 《Environmental Earth Sciences》2012,66(5):1371-1383
This paper presents the results of electrical resistivity methods in the area delineation that was potentially contaminated by liquefaction products, which are also called putrefactive liquids in Vila Rezende municipal cemetery, Piracicaba, São Paulo, Brazil. The results indicate a depth of water table between 3.1 and 5.1 m, with two groundwater direction flows, one to the SW and another to the SE. Due to the contamination plumes, which have the same groundwater direction flow, as well the conductive anomalies observed in the geoelectric sections, the contamination suspicions in the area were confirmed. The probable plume to the SE extends beyond the limits of the cemetery. The location of the conductive anomalies and the probable contamination plumes showed that the contamination is linked with the depth of the water table and the burial time. Mapping using the geostatistical method of ordinary kriging applied to the work drew structural characteristics of the regional phenomenon and spatial behavior of the electrical resistivity data, resulting in continued surfaces. Thus, this method has proved to be an important tool for mapping contamination plumes in cemeteries. 相似文献
96.
This study focuses on the spectral characterization of superficial effects caused by natural gaseous hydrocarbon (HC) escapes (microseepages) on onshore basins and means to detect the phenomena using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery. The Northern Tucano basin (NTB) (Brazil) displays archetypal onshore microseepages, and it is used here as a case study area. Regional HC geochemical data yielded from NTB soil samples helped to outline the strategies for imagery processing and assessment of results. We firstly devised a generic detection model for onshore basins in which microseepages indicated by HC geochemistry should spatially match a number of surface expressions with key remote sensing signatures, such as bleached soil and rocks (i.e., reduction in Fe3+ to Fe2+), concentration of specific clays (kaolinite), and carbonates (siderite) and geobotanical markers. These evidences guided the use of remote sensing data and information extraction techniques to find more sites favorable to host HC microseepages in the NTB. ASTER data processed through spectral mixing analysis and supervised and unsupervised neural network systems highlighted sites where features predicted in the detection model concurred seamlessly with geochemical anomalies. The approach also revealed other sites with similar characteristics, but for which no geochemical data exist. These sites are taken as new potential targets for the presence of microseepages and possibly HC reservoirs. The research demonstrated the potential of remote sensing data and spectral–spatial methodologies for economical, onshore detection of HCs for exploration purposes. Potential ramifications of the study include indirect detection of gaseous HC reservoirs in terrestrial planets (fostering the search for signs of life) and depiction of non-negligible, replenishable continental sources of HC emissions on Earth that may contribute to global warming. 相似文献
97.
Daniel T. C. Yao Waldyr Lopes de Oliveira‐Filho Xiao‐Chuan Cai Dobroslav Znidarcic 《国际地质力学数值与分析法杂志》2002,26(2):139-161
The consolidation and desiccation behaviour of soft soils can be described by two time‐dependent non‐linear partial differential equations using the finite strain theory. Analytical solutions do not exist for these governing equations. In this paper, we develop efficient numerical methods and software for finding the numerical solutions. We introduce a semi‐implicit time integration scheme, and show numerically that our method converges. In addition, the numerical solution matches well with the experimental result. A boundary refinement method is also developed to improve the convergence and stability for the case of Neumann type boundary conditions. Interface governing equations are derived to maintain the continuity of consolidation and desiccation processes. This is useful because the soil column can undergo desiccation on top and consolidation on the bottom simultaneously. The numerical algorithms has been implemented into a computer program and the results have been verified with centrifuge test results conducted in our laboratory. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
98.
99.
Mangrove habitat use by fishes in Southeastern Brazil: are there temporal changes in the structure of the community?
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Márcia C. C. de Azevedo Antonio G. da Cruz‐Filho Francisco G. Araújo 《Marine Ecology》2016,37(6):1223-1238
We compared fish community structure in Guaratiba Mangrove, SE Brazil, among three seasons of the hydrological cycle [(i) spring, increasing temperature and rainfall, decreasing salinity; (ii) summer/early fall, high temperature and rainfall, intermediate salinity; (iii) late fall/winter, low temperature and rainfall, high salinity] and between the years 2002–2003 and 2008–2009. The aim was to test the hypothesis that the fish community structure changes seasonally, associated with seasonal changes in environmental conditions, and that changes occurred between the two yearly periods because of increased anthropogenic activities. The sampling protocol for the two surveys was identical. A total of 63 species was recorded, with 38 species occurring in 2002–2003, and 53 species in 2008–2009. The main changes in the mangrove's fish assemblage between 2002–2003 and 2008–2009 were (i) an increase in species richness, fish density and total biomass; and (ii) an increase in the zoobenthivorous species of gerreids Eucinostomus argenteus, Diapterus rhombeus and Ulaema lefroyi, and a decrease in the planktivorous clupeid Harengula clupeola. Other abundant species, such as the opportunistic atherinopsid. Atherinella brasiliensis, the detritivorous mullet Mugil liza and the zoobenthivorous pufferfish Sphoeroides testudineus did not differ in abundance between the two yearly periods. Ten species occurred only in 2002–2003, and 23 species only in 2008–2009, indicating significant changes in community structure over the 6‐year period. Seasonal changes in community structure were more conspicuous in 2008–2009, when species abundance and richness were greatest. The highest fish abundance was recorded in spring and in summer/early fall, and the lowest in late fall/winter. The increased abundance and richness over time may be at least partially attributable to protection policies because of the effective implementation of a biological reserve in the area. 相似文献
100.