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141.
Water balance,nutrient and carbon export from a heath forest catchment in central Amazonia,Brazil 下载免费PDF全文
Fabrício B. Zanchi Maarten J. Waterloo Andrés Peralta Tapia Maria S. Alvarado Barrientos Marcos A. Bolson Flávio J. Luizão Antônio O. Manzi Albertus J. Dolman 《水文研究》2015,29(17):3633-3648
Carbon storage values in the Amazon basin have been studied through different approaches in the last decades in order to clarify whether the rainforest ecosystem is likely to act as a sink or source for carbon in the near future. This water balance, dissolved organic carbon (DOC) and nutrient export study were carried out in a micro‐scale heath forest (Campina) catchment in central Amazonia, Brazil. For a 1‐year study period (18 March 2007 until 19 March 2008), rainfall amounted to 3054 mm; of which, 1532 mm was evaporated by the forest (4.1 mm day?1). Rainfall interception loss amounted to 15.6% of gross rainfall. Surface runoff amounted to 485 mm, whereas another 1071 mm was discharged as regional groundwater outflow. Accumulated DOC exports in surface runoff amounted to 15.3 g m?2 year?1, whereas the total carbon exported was 55.9 g m?2. This is much higher than that observed for a nearby tall rainforest catchment in central Amazonia (DOC export < 20 g m?2). As Campina heath forest areas cover a significant proportion of the Amazon Basin, these differences in ecosystem hydrological carbon exports should be taken into account in future studies assessing the carbon budget for the Amazon Basin. Macro‐nutrient exports were low, but those of calcium and potassium were higher than those observed for tall rainforest in the Amazon, which may be caused by a lower retention capacity of the heath forest ecosystem. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
142.
Marilia Mitidieri F. de Oliveira Nelson Francisco F. Ebecken Jorge Luiz F. de Oliveira Eric Gilleland 《Theoretical and Applied Climatology》2011,104(3-4):377-385
Statistical analysis of extreme values is applied to wind data from National Centers for Environmental Prediction and National Center for Atmospheric Research reanalysis grid points over the ocean region bounded at 23°S and 40°W and 42°W towards the south and southeastern Brazilian coast. The period of analysis goes from 1975 to 2006. The generalized extreme value and generalized Pareto distributions are employed for annual and daily maxima, respectively. The Pareto?CPoisson point process characterization is also used to analyze peaks over threshold. Return levels for 10, 25, 50, and 100?years are calculated at each grid point. However, most of the reanalysis data fall within 1?C10-year return periods, suggesting that hazardous wind speed with low probability (return periods of 50?C100) have rarely measured in this period. Wide confidence intervals on these levels show that there is not enough information to make predictions with any degree of certainty to return periods over 100?years. Low extremal index (??) values are found for excess wind speeds over a high threshold, indicating the occurrence of consecutively high peaks. In order to obtain realistic uncertainty information concerning inferences associated with threshold excesses, a declustering method is performed, which separates the excesses into clusters, thereby rendering the extreme values more independent. 相似文献
143.
This work analyzes some physical and microphysical properties of Mesoscale Convective Systems (MCSs) and cloud-to-ground lightning. Satellite data from the GOES-10 infrared and NOAA-18 and TRMM microwave channels and lightning information from the Brazilian lightning detection network (BrasilDAT) were utilized for the period from 2007 to 2009. Based on an automatic MCSs detection method, 720 MCSs life cycles were identified during the period and in the region of study, with a lightning detection efficiency of over 90%. During the diurnal cycle, maximum electrical activity occurred close to the time of maximum convective cloud fraction (18 UTC), and 3 h after the maximum normalized area expansion rate. Diurnal cycles of both properties were modulated by diurnal heating, and thus could be used to monitor diurnal variability of lightning occurrence. The electrical activity was more intense for the widest (Pearson’s correlation of 0.96) and deeper (Pearson’s correlation of 0.84) clouds, which reached 390 km size and 17 km maximum cloud top height. Area growth during the initial phase of MCSs exerted a strong influence on their size and duration, and thus also showed a potential for defining the possibility of electrical activity during their life cycle. The average lightning life cycle exhibited a maximum close to MCSs maturation, while the maximum average lightning density occurred in the MCSs initial life cycle stage. The growth rate of electrical activity during the early stages can indicate the strength of convection and the possible duration of systems with lightning occurrence. Strong condensation processes and mass flux during the growth phase of the systems can provide favorable conditions for cloud electrification and lightning occurrence. A comparison of high microwave frequencies with lightning data showed a strong relationship of vertically integrated ice content and particle size with lightning occurrence, with Pearson's correlation of 0.86 and 0.96, respectively. The polarization difference in the 85 GHz channel showed that electrical activity increases linearly with polarization reduction, associated with a high value of Pearson's correlation coefficient (above 0.90). This suggests that regions with more intense electrical activity are predominantly located in areas with a high concentration of larger ice particles that are vertically oriented, due to the existence of intense updrafts and the electric field. These results demonstrate the potential use of thermodynamic, dynamic and microphysical characteristics for analyzing thunderstorms severity, and as additional information for nowcasting and monitoring electrical activity over large regions that lack ground-based lightning sensors. 相似文献
144.
Silke Triebold George Luiz Luvizotto Raimon Tolosana-Delgado Thomas Zack Hilmar von Eynatten 《Contributions to Mineralogy and Petrology》2011,161(4):581-596
Investigation by Raman spectroscopy of samples from different geological settings shows that the occurrence of TiO2 polymorphs other than rutile can hardly be predicted, and furthermore, the occurrence of anatase is more widespread than
previously thought. Metamorphic pressure and temperature, together with whole rock chemistry, control the occurrence of anatase,
whereas variation of mineral assemblage characteristics and/or fluid occurrence or composition takes influence on anatase
trace element characteristics and re-equilibration of relict rutiles. Evaluation of trace element contents obtained by electron
microprobe in anatase, brookite, and rutile shows that these vary significantly between the three TiO2 phases. Therefore, on the one hand, an appropriation to source rock type according to Nb and Cr contents, but as well application
of thermometry on the basis of Zr contents, would lead to erroneous results if no phase specification is done beforehand.
For the elements Cr, V, Fe, and Nb, variation between the polymorphs is systematic and can be used for discrimination on the
basis of a linear discriminant analysis. Using phase group means and coefficients of linear discriminants obtained from a
compilation of analyses from samples with well-defined phase information together with prior probabilities of groupings from
a natural sample compilation, one is able to calculate phase grouping probabilities of any TiO2 analysis containing at least the critical elements Cr, V, Fe, and Nb. An application of this calculation shows that for the
appropriation to the phase rutile, a correct-classification rate of 99.5% is obtained. Hence, phase specification by trace
elements proves to be a valuable tool besides Raman spectroscopy. 相似文献
145.
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
146.
Lauren C. Duarte Leo A. Hartmann Luiz H. Ronchi Zsolt Berner Thomas Theye Hans J. Massonne 《Mineralium Deposita》2011,46(3):239-255
Stable isotopes (C, O, S) and mineralogical studies of the world-class amethyst-geode deposits of the Los Catalanes gemological
district, Uruguay, constrain processes operative during mineral deposition. The mineralized basaltic andesites from the Cretaceous
Paraná volcanic province are intensely altered to zeolites (clinoptilolite) and clay minerals. Variations in the δ18O values of silica minerals in geodes (chalcedony, quartz, and amethyst) are much larger and the values generally somewhat
lower (21.2–31.5‰) in the Uruguayan deposits than in the Ametista do Sul area of southern Brazil. The range of δ34S values (−15.0 to −0.3‰) of altered basaltic rocks requires (in addition to sulfur of magmatic origin) the involvement of
34S-depleted sedimentary sulfur from bacterial sulfate reduction. The results delimit the mineralizing processes to a post-eruption
environment characterized by low temperature and strong interaction of the lava flows with meteoric water. 相似文献
147.
Jo?o Luiz Luft Jr Farid Chemale Jr Richard Armstrong 《International Journal of Earth Sciences》2011,100(2-3):305-321
Detailed structural and isotopic analyses in the Hoanib and Ugab River Valleys indicate the existence of an exotic 1.7- to 1.8-Ga terrane in the Pan-African Kaoko Belt. This crustal block, called as Mudorib Complex, is imbricated between autochthonous and para-autochthonous rocks of Congo Craton, Kaoko Basin, and Western Kaoko Batholith units during the main tectono-thermal phase of Kaoko Belt collision around 580?Ma, involving the Rio de La Plata, Congo and Kahalari paleoplates. This terrain is positioned between the 1.9-Ga Pruwes Complex units of SW edge of the Congo Craton and the 0.58- to 0.55-Ga Amspoort Suite granitoids of the Western Kaoko Batholith. It is coincident with a regional positive aeromagnetic anomaly trending from NNW in the Ugab region to the Namibia-Angola border. Internally, Mudorib Complex consists in 1.73- to 1.81-Ga tonalitic?Ctrondhjemitic?Cdioritic?Cgranodioritic sequence of gneisses associated with cogenetic gabbroic and anothositic-gneisses in the core zone of this Pan-African structure. Field relationship and U?CPb zircon and Sm?CNd whole-rock isotope data combined with geochemical information suggest the existence of two rock associations in the Mudorib Complex, namely late Paleoproterozoic tonalitic?Ctrondhjemitic?Cdioritic-gneisses with island-arc affinity and tholeiitic metabasites of juvenile origin, showing Nd model age of 1.73?C2.17?Ga and ??Nd(t) of ?2.05?C+4.3. This 1.8- to 1.7-Ga complex is also intruded by granitic dykes formed at 1.49?C1.50?Ga with Nd model age of 1.75?C2.34?Ga during stable tectonic conditions. In addition to widespread Pan-African tectono-metamorphic events, a secondary metamorphic event of ~1.3?Ga is also recognized in the Mudorib rocks, which may be associated with accretion process of the complex to the Paleoproterozoic to Archean nucleus of the Kaoko Belt in the Hoanib River Valley. 相似文献
148.
Some of the characteristics of predicted climate changes for South America are analysed for the years 2010 and 2050. These predictions are based on the results of three-dimensional Global Circulation Models (GCMs). The results differ between models (GISS, NCAR-CCMs and GFDL), particularly when applied to regional and sub-regional scales and to time scales of less than one-year intervals. It is concluded that these differences are due to the particular structure of each model as well as to the lack of sufficient basic data from the South American sub-continent. The dynamics of vegetation cover play an important role in future water balance changes. The changes in surface temperatures predicted by the GISS model are discussed in relation to changes in the climatic-dynamic base stemming from anthropogenic changes in the vegetation cover. 相似文献
149.
150.
Viviane S. Guerra Otávio C. Acevedo Luiz E. Medeiros Pablo E. S. Oliveira Daniel M. Santos 《Boundary-Layer Meteorology》2018,166(3):395-422
The study of the boundary layer can be most difficult when it is in transition and forced by a complex surface, such as an urban area. Here, a novel combination of ground-based remote sensing and in situ instrumentation in central London, UK, is deployed, aiming to capture the full evolution of the urban boundary layer (UBL) from night-time until the fully-developed convective phase. In contrast with the night-time stable boundary layer observed over rural areas, the night-time UBL is weakly convective. Therefore, a new approach for the detection of the morning-transition and rapid-growth phases is introduced, based on the sharp, quasi-linear increase of the mixing height. The urban morning-transition phase varied in duration between 0.5 and 4 h and the growth rate of the mixing layer during the rapid-growth phase had a strong positive relationship with the convective velocity scale, and a weaker, negative relationship with wind speed. Wind shear was found to be higher during the night-time and morning-transition phases than the rapid-growth phase and the shear production of turbulent kinetic energy near the mixing-layer top was around six times larger than surface shear production in summer, and around 1.5 times larger in winter. In summer under low winds, low-level jets dominated the UBL, and shear production was greater than buoyant production during the night-time and the morning-transition phase near the mixing-layer top. Within the rapid-growth phase, buoyant production dominated at the surface, but shear production dominated in the upper half of the UBL. These results imply that regional flows such as low-level jets play an important role alongside surface forcing in determining UBL structure and growth. 相似文献