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81.
Photodissociation lifetime of 32s2in comets is calculated by absorption of solar photons into the B3– state and velocity distributions of sulphur atoms are determined. Absorption of solar photons of wavelength ~ 280 nm leads to a photodissociation lifetime of about 250 s for 32S2 molecule in comets when sun-comet distance is 1 AU. Forbidden lines corresponding to 1D-3P transitions of neutral sulphur atom may be detectable at about 11 306 and 10 821 Å in comets. The production rate of 32S2 dimer in comet IRAS-Araki-Alcock 1983d compares well with the production rate of CS, observed in comet Bradfield, when compared at the same heliocentric distance. The chemistry of 32S2 dimer formation in the inner coma of a comet is discussed in the framework of some gas phase reactions.Work partially supported by the CNPq, Brasilia, Brasil under contract No. 30.4076/77. 相似文献
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83.
Quantifying the effects of Eucalyptus plantations and management on water resources at plot and catchment scales
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Auro C. Almeida Philip J. Smethurst Anders Siggins Rosane B. L. Cavalcante Norton Borges Jr 《水文研究》2016,30(25):4687-4703
Our aim was to quantify the effects of forest plantation and management (clear cut or 30% partial harvest) in relation to pasture, on catchment discharge in southeast Rio Grande do Sul state, Brazil. A paired‐catchment approach was implemented in two regions (Eldorado do Sul and São Gabriel municipalities) where discharge was measured for 4 years at three catchments in each region, two of which were predominantly eucalypt plantation (mainly Eucalyptus saligna, rotation of approximately 7–9 years) with native forest and grass in streamside zones. The third catchment was covered with grazed pasture. Weather, soils, canopy interception, groundwater level, tree growth, and leaf area index were also measured. The 3‐PG process‐based forest productivity model was adapted to predict spatial daily plantation and pasture water balance including precipitation interception, soil evaporation, transpiration, soil moisture, drainage, discharge, and monthly plantation growth. The TOPMODEL framework was used to simulate water pools and fluxes in the catchments. Discharge was higher under pasture than pre‐harvesting plantation and increased for 1–2 years after complete plantation harvest; this change was less pronounced in the catchments under partial harvest. The ratio of discharge to precipitation before harvesting varied from 7% to 13% in the eucalypt catchments and 28% to 29% under pasture. The ratio increases to 23–24% after total harvest, and to 17% after partial harvesting. The ratio under pasture also increases during this period (to 32–44%) owing to increased precipitation. The baseflow, in relation to total discharge, varied from 28% to 62% under Eucalyptus and from 38% to 43% in the pasture catchments. Hence, eucalypt plantations in these regions can be expected to influence discharge regimes when compared with pasture land use, and modelling suggests that partial harvesting would moderate the magnitude of discharge variation compared with a full catchment plantation harvesting. The model efficiency coefficient (Nash–Sutcliffe model efficiency coefficient) varied from 0.665 to 0.799 for the total period of the study. Simulation of alternative harvesting scenarios suggested that at least 20% of the catchment planted area must be harvested to increase discharge. This model could be a useful practical tool in various plantation forestry contexts around the world. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
84.
P. Bécognée M. Moyano C. Almeida J.M. Rodríguez E. Fraile-Nuez A. Hernández-Guerra S. Hernández-León 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(3):330-343
The distribution of fish larvae in relation to a filament shed from the Northwest African coastal upwelling was studied in February 2001. During the cruise, the filament was located between 27°N and 28°N, extending from the African coastal upwelling zone to the south of Fuerteventura Island (Canary Islands). This filament was trapped and remained over the quasi-permanent cyclonic eddy observed in previous studies. Almost all Sardina pilchardus, Engraulis encrasicolus and Sardinella aurita larvae caught during the cruise were associated with upwelled waters and filament structures. The sampled larval fish assemblage was composed by 12.6% of clupeoid larvae. These were distributed as follows: 73.9% were S. pilchardus, 20.7% were E. encrasicolus and 5.4% were S. aurita. Their distribution suggested that the coastal upwelling filament is a mechanism of transport from the upwelling area to oceanic waters, but its junction with the generated cyclonic eddy may not always work as a retention structure for those transported larvae, as described in previous studies. Physiological studies based on gut fluorescence and ETS activity of clupeoid larvae, as proxies for grazing and respiration, respectively, denoted a switch from pigmented food near the upwelling zone to unpigmented food toward the ocean. This pattern agrees with observed mesozooplankton feeding along an upwelling filament in previous studies. Therefore, this work confirms the close relationship between clupeoids distribution and mesoscale circulation, as well as constitutes the first assessment of the metabolic activity of those larvae in the region. 相似文献
85.
Liliane Janikian Renato Paes de Almeida Antonio Romalino Santos Fragoso-Cesar Veridiana Teixeira de Souza Martins Elton Luiz Dantas Eric Tohver Ian McReath Manoel Souza D'Agrella-Filho 《Gondwana Research》2012,21(2-3):466-482
During the Ediacaran, southern Brazil was the site of multiple episodes of volcanism and sedimentation, which are best preserved in the 3000 km2 Camaquã Basin. The interlayered sedimentary and volcanic rocks record tectonic events and paleoenvironmental changes in a more than 10 km-thick succession. In this contribution, we report new U–Pb and Sm–Nd geochronological constraints for the 605 to 580 Ma Bom Jardim Group, the 570 Ma Acampamento Velho Formation, and a newly-recognized 544 Ma volcanism. Depositional patterns of these units reveal the transition from a restricted, fault-bounded basin into a wide, shallow basin. The expansion of the basin and diminished subsidence rates are demonstrated by increasing areal distribution and compressed isopachs and increasing onlap of sediments onto the basement to the west. The Sm–Nd isotopic composition of the volcanic rocks indicates mixed sources, including crustal rocks from the adjacent basement. Both Neoproterozoic and Paleoproterozoic sources are indicated for the western part of the basin, whereas only the older Paleoproterozoic signature can be discerned in the eastern part of the basin. 相似文献
86.
Paula Chainho Gilda Silva Michael F. Lane José L. Costa Tadeu Pereira Carla Azeda Pedro R. Almeida Inês Metelo Maria J. Costa 《Estuaries and Coasts》2010,33(6):1314-1326
Long-term monitoring studies are needed to understand changes in ecosystem status when restoration measures are implemented.
A long-term data series (1996–2007) of the Tagus estuary (Portugal) intertidal and subtidal benthic communities was collected
in a degraded area where mitigation measures were implemented. Multivariate analysis was used to analyze spatial and temporal
patterns in benthic community composition and trends in five benthic community metrics (i.e., taxonomic richness, density,
biomass, Shannon–Wiener diversity and the AMBI index) were also examined. The results revealed a clear separation between
intertidal and subtidal assemblages, although they had 50% of taxa in common, including the most abundant. Significant positive
trends were found for all metrics showing that both intertidal and subtidal communities responded to the restoration measures
implemented. Nevertheless, biotic indices need some adaptation before being universally applied to intertidal and subtidal
habitats. 相似文献
87.
88.
Andrews José de Lucena Otto Corrêa Rotunno Filho José Ricardo de Almeida França Leonardo de Faria Peres Luciano Nóbrega Rodrigues Xavier 《Theoretical and Applied Climatology》2013,111(3-4):497-511
This paper aims to map the thermal field in the metropolitan region of Rio de Janeiro (MARJ) considering the atmospheric characteristics and the land use that contribute to understanding the urban heat island. Three thermal maps are defined through the use of Landsat5-TM satellite images for three winter events chosen for the decades of 1980, 1990, and 2000, respectively. The results reveal a concentration of warmer cores in urban central areas as well as some local warmer areas in suburban region. Sites with lower temperatures correspond to vegetated areas which are away from the central part of the MARJ, including points of suburban areas. This work emphasizes the importance of the combined analysis of surface temperature with land use and atmospheric conditions, depicting a distinct pattern of heat islands for tropical climate. 相似文献
89.
P. J. Polglase A. Reeson C. S. Hawkins K. I. Paul A. W. Siggins J. Turner D. F. Crawford T. Jovanovic T. J. Hobbs K. Opie J. Carwardine A. Almeida 《Climatic change》2013,121(2):161-175
The theoretical potential for carbon forests to off-set greenhouse gas emissions may be high but the achievable rate is influenced by a range of economic and social factors. Economic returns (net present value, NPV) were calculated spatially across the cleared land area in Australia for ‘environmental carbon plantings’. A total of 105 scenarios were run by varying discount rate, carbon price, rate of carbon sequestration and costs for plantation establishment licenses for water interception. The area for which NPV was positive ranged from zero ha for tightly constrained scenarios to almost the whole of the cleared land (104 M ha) for lower discount rate and highest carbon price. For the most plausible assumptions for cost of establishment and commercial discount rate, no areas were identified as profitable until a carbon price of AUD$40 t CO2 ?1 was reached. The many practical constraints to plantation establishment mean that it will likely take decades to have significant impact on emission reductions. Every 1 M ha of carbon forests established would offset about 1.4 % of Australia’s year 2000 emissions (or 7.4 Mt CO2 year?1) when an average rate of sequestration per ha was reached. All studies that predict large areas of potentially profitable land for carbon forestry need to be tempered by the realities that constrain land use change. In Australia and globally, carbon plantings can be a useful activity to help mitigate emissions and restore landscapes but it should be viewed as a long-term project in which co-benefits such as biodiversity enhancement can be realised. 相似文献
90.
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