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71.
Julio Cezar Mendes Silvia Regina de Medeiros Ian McReath Cristina Maria Pinheiro de Campos 《Gondwana Research》2005,8(3):337-345
In the central-southern region of Espírito Santo State, southeastern Brazil, several granitoids with a variable composition intruded high-grade metamorphic rocks, in the northern segment of the Ribeira fold belt. A close relationship between hydrous and anhydrous facies is present in some of the plutons, including the Varzea Alegre Igneous Complex, which has an inner domain formed by gabbro, diorite and granite, and an irregular outer ring of charnockitic rocks. These green megaporphyritic charnockites have primary anhydrous mineral assemblage, I-type and metaluminous character, and high-K calc-alkaline signature. U-Pb zircon single crystal ages obtained by TIMS indicate crystallization at about 500 Ma, similar to other late tectonic plutons of this part of the Ribeira belt. Sr and Nd isotopic ratios ranging from 0.7078 to 0.7096 and 0.5114 to 0.5116 respectively, are interpreted to be indicative of a hybrid origin from crustal and mantle-derived magmas. A binary diagram using Sr isotope ratios also demonstrates that the genesis of the charnockites probably included both magma mixing and fractional crystallization processes. 相似文献
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74.
Seasonal variation of polychlorinated biphenyl concentrations in the southern part of the Baltic Sea 总被引:3,自引:0,他引:3
The impact of seasonal fluctuations in forcing factors such as atmospheric concentration, temperature, and biological productivity on the concentration of polychlorinated biphenyls (PCBs) in the surface water of the southern part of the Baltic Sea was investigated. Water samples were collected on eight cruises over 2 years. A clear seasonal variability in dissolved PCB concentrations was observed with higher levels in summer than in winter and spring. This was attributed to changes in atmospheric concentrations and water temperature, based on measurements showing the PCB levels in the atmosphere and surface water to be close to a partitioning equilibrium. Concentrations in the suspended particulate material (SPM) fraction were also variable, and when the quotient of the organic carbon normalised concentration in SPM and the dissolved concentration was calculated (i.e., the bioaccumulation factor (BAF)), a seasonal pattern was observed which was consistent with kinetic limitations on partitioning into particles caused by plankton growth. However, seasonal variability in the partitioning properties of the SPM may also contribute to this variability. 相似文献
75.
Sergio Grauso Andrea Pagano Grazia Fattoruso Piero De Bonis Filippo Onori Pasquale Regina Carlo Tebano 《Environmental Geology》2008,54(2):219-234
In the present work on-going research is discussed whose primary goal is to test some statistical methods to estimate the
average yearly area-specific sediment yield (SSY). Using geomorphological and climatic parameters various multiple regression
formulae have been set up based on SSY observed data from 16 catchments of Sicily. Three distinct techniques were adopted
to select the parameters to be used in the equations: simple correlation, stepwise regression analysis and a supervised geomorphological–statistical
correlation. The comparison of the results showed the effectiveness of the stepwise analysis, which led to a regression equation
with a coefficient of determination (r
2) of 0.87. Nevertheless, even this methodology showed some elements of uncertainty that have caused, in some cases, appreciable
differences between observed and predicted values (mean percentage error equal to 26%). These differences are likely either
due to the hydraulic regime of most of Sicilian watercourses (typical of semi-arid regions) or to hidden factors (e.g., topography,
human impact and concentrated erosion), which can greatly affect the processes of sediment production and transport. The study
has pointed out the need to take into account a larger number of observations and to perform the analysis of relations between
suitable variables and SSY at a more detailed time resolution. 相似文献
76.
S. Grauso F. Onori M. Esposito M. Neri G. Armiento P. Bartolomei C. Crovato F. Felici M. Marcinnò P. Regina C. Tebano 《Environmental Geology》2008,54(2):235-247
Soil loss evaluation by means of radioisotopic content measurements represents a promising technique, half-way between field
surveys and theoretical models, which still suffers from its practical limits when applied at basin scale. A main limit is
represented by the costs of field investigations and laboratory investigations on the high number of soil samples required
by a traditional sampling scheme, such as regular grid or transects. A non-conventional soil sampling scheme was tested with
the aim to consider a relative scanty number of soil samples and to verify the feasibility of this technique on large areas.
This scheme was based on the hypothesis that land analysis and classification could point out areas characterised by homogeneous
behaviour with respect to the 137Cs deposition and transmission model. A Geographic Information System (GIS)-aided procedure allowed to classify the selected
basin area in pedo-morphological units, representative of the different pedologic, morphologic and land-use conditions, to
locate few sampling points for each unit. Outcomes pointed out a low correlation between 137Cs contents and soil physical and compositional characteristics. Nevertheless, the isotopic methodology allowed to estimate
a total soil loss value at basin scale almost consistent with both observed data, given by reservoir sedimentation measurements
and estimates from the application of the RUSLE model. Thus, the results can be considered encouraging and they allow to deem
that the isotopic methodology can be refined in order to account for erosion and deposition processes even at river basin
scale and with a limited number of soil samples. 相似文献
77.
The thicknesses of slag piles at a smelling site in Midvale. Utah, were determined using geophysical methods; this information was needed to estimate the cost of removing or isolating slag that has the potential to contaminate ground water. From a small-scale preliminary investigation that, included terrain-conductivity profiling, low-frequency resistivity measurements, and induction logging, the electrical resistivities of the slag and the underlying sediment were determined to be approximately 100 Ω-m and 15 Ω-m, respectively. Because electromagnetic measurements are affected by such significant contrasts, terrain-conductivity profiling and time-domain electromagnetic soundings were used to determine the thicknesses of the slag piles. Generally, the estimated thicknesses from both methods were consistent and geologically plausible. In some instances, reliable estimates of the thicknesses could not be obtained because, for example, the measurements were affected by buried metal objects.
In this case study, we emphasize three principles that might help investigators at other smelter sites. First, a small-scale preliminary investigation saves time and money because those geophysical methods that have the greatest likelihood of success can be determined. Second, when the results from several geophysical methods are consistent, the confidence in the interpretation increases. Third, geophysical characterization is not always successful. Nonetheless, because of its outstanding advantages, it should be used before other more expensive characterization methods arc tried. 相似文献
In this case study, we emphasize three principles that might help investigators at other smelter sites. First, a small-scale preliminary investigation saves time and money because those geophysical methods that have the greatest likelihood of success can be determined. Second, when the results from several geophysical methods are consistent, the confidence in the interpretation increases. Third, geophysical characterization is not always successful. Nonetheless, because of its outstanding advantages, it should be used before other more expensive characterization methods arc tried. 相似文献
78.
79.
The availability of fluids and drill cuttings from the active hydrothermal system at Roosevelt Hot Springs allows a quantitative comparison between the observed and predicted alteration mineralogy, calculated from fluid-mineral equilibria relationships. Comparison of all wells and springs in the thermal area indicates a common reservoir source, and geothermometer calculations predict its temperature to be higher () than the maximum measured temperature of 268°C.The composition of the deep reservoir fluid was estimated from surface well samples, allowing for steam loss, gas release, mineral precipitation and ground-water mixing in the well bore. This deep fluid is sodium chloride in character, with approximately 9700 ppm dissolved solids, a pH of 6.0, and gas partial pressures of O2 ranging from 10?32 to 10?35 atm, CO2 of 11 atm, H2S of 0.020 atm and CH4 of 0.001 atm.Comparison of the alteration mineralogy from producing and nonproducing wells allowed delineation of an alteration pattern characteristic of the reservoir rock. Theoretical alteration mineral assemblages in equilibrium with the deep reservoir fluid, between 150° and 300°C, in the system Na2O-K2O-CaO-MgO-FeO-Fe2O3-Al2O3-H4SiO4-H2O-H2S-CO2-HCl, were calculated. Minerals theoretically in equilibrium with the calculated reservoir fluid at include sericite, K-feldspar, quartz, chalcedony, hematite, magnetite and pyrite. This assemblage corresponds with observed higher-temperature () alteration assemblage in the deeper parts of the producing wells. The presence of montmorillonite and mixed-layer clays with the above assemblage observed at temperatures <210°C corresponds with minerals predicted to be in equilibrium with the fluid below 240°C.Alteration minerals present in the reservoir rock that do not exhibit equilibrium with respect to the reservoir fluid include epidote, anhydrite, calcite and chlorite. These may be products of an earlier hydrothermal event, or processes such as boiling and mixing, or a result of errors in the equilibrium calculations as a result of inadequate thermochemical data. 相似文献
80.
Laboratory investigations of CN radical formation by photodissociation of parent molecules have suggested the possibility of observing emission lines in cometary spectra from newly formed CN radicals. These laboratory studies have shown that high initial internal excitation of CN is the rule with excitation of rotational levels N up to 70. In the collisionless environment of the cometary atmosphere this initial excitation would yield a corresponding distribution for the lowest vibrational level of the ground X2Σ+ state. Our calculations show that it is feasible with present observational techniques to detect photochemically excited lines with N ~ 30 in the 0-0 band of the violet system. 相似文献