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81.
Assessment of the geochemical reactivity of Fe-DOM complexes in wetland sediment pore waters using a nitroaromatic probe compound 总被引:1,自引:0,他引:1
J. Alexandra Hakala Yu-Ping Chin Sheela G. Agrawal 《Geochimica et cosmochimica acta》2009,73(5):1382-6822
The reductive capacity of Fe(II) present in anoxic sediment pore waters affects biogeochemically significant processes that occur in these environments, such as metal speciation, mineral solubility, nutrient bioavailability, and the transformation of anthropogenic organic compounds. We studied the reduction of pentachloronitrobenzene (PCNB) in natural pore waters to elucidate the reductive capacity of Fe(II) complexes, and monitored the redox-active species responsible for the observed kinetics. Differential pulse polarography (DPP) scans of sediment pore waters from a coastal Lake Erie wetland (Old Woman Creek National Estuarine Research Reserve, Huron, OH) revealed an increase in both Fe(III)-organic and Fe(II) species to a depth of ∼30 cm below the sediment-water interface. Concentrations of dissolved organic matter (DOM) in pore waters increased while pH decreased with depth. We found that Fe(II) was necessary for rapid PCNB reduction (<24 h), and observed faster reduction with increased pH. PCNB reduction in preserved pore waters (acidified to pH 2.5 after pore water extraction and raised to the native pH (6.7-7.6) prior to reaction) was similar to that observed in a model system containing Fe(II) and fulvic acid isolated from this site. Conversely, PCNB reduction in unaltered pore water was significantly slower than that observed in preserved pore water, indicating that the Fe(II) speciation and its reductive capacity differed. DPP scans of pore waters used for kinetic studies confirmed that pH-adjustment affected FeT speciation in the pore waters, as the Fe(III)-DOM peak current was lowered or disappeared completely in the preserved pore water samples. These data show that pH-adjustment of pore waters presumably alters both their complexation chemistry and reactivity towards PCNB, and shows how small changes in Fe complexation can potentially affect redox chemistry in anoxic environments. Our results also show that reactive organic Fe(II) complexes are naturally present in wetland sediment pore waters, and that these species are potentially important mediators of Fe(II)/Fe(III) redox biogeochemistry in anoxic sedimentary environments. 相似文献
82.
Lav Kumar Nishtha Agrawal Abhishek K. Rai Shailendra K. Mishra Vinay S. Pandey 《Marine Geodesy》2013,36(6):558-574
AbstractIn the present study, mean rainfall for the months of June-July-August-September (JJAS) during summer monsoon is simulated over India and its adjoining regions for a period between 1982 and 2006. The study was carried out using Regional Climate Model (RegCM) version 4.6 at a resolution of 25?km. The simulated mean JJAS monsoon rainfall was validated against the observational IMD data. Comparison of JJAS seasonal mean summer rainfall for the first decade 1982–1991, with the later decade 1997–2006 indicate that the intensity of rainfall increases over Indian land-mass during the later decade under the forced conditions of Era-Interim. The observed JJAS mean rainfall indicates two maximum rainfall areas i.e. the Western Ghats and the Himalayan region. A significant bias is observed in the central and Jammu and Kashmir (J&K) region. The JJAS mean seasonal surface air temperature distribution at 0.25?×?0.25-degree grids resolution shows a decreasing trend of temperature over the Indian landmass. 相似文献
83.
Enhancing the sustainability of commodity supply chains in tropical forest and agricultural landscapes 总被引:1,自引:0,他引:1
The rapid expansion of the production of agricultural commodities such as beef, cocoa, palm oil, rubber and soybean is associated with high rates of deforestation in tropical forest landscapes. Many state, civil society and market sector actors are engaged in developing and implementing innovative interventions that aim to enhance the sustainability of commodity supply chains by affecting where and how agricultural production occurs, particularly in relation to forests. These interventions – in the form of novel or moderated institutions and policies, incentives, or information and technology – can influence producers directly or achieve their impacts indirectly by influencing consumer, retailer and processor decisions. However, the evidence base for assessing the impacts of these interventions in reducing the negative impacts of commodity agriculture production in tropical forest landscapes remains limited, and there has been little comparative analysis across commodities, cases, and countries. Further, there is little consensus of the governance mechanisms and institutional arrangements that best support such interventions. We develop a framework for analyzing commodity supply chain interventions by different actors across multiple contexts. The framework can be used to comparatively analyze interventions and their impacts on commodity production with respect to the spatial and temporal scales over which they operate, the groups of supply chain actors they affect, and the combinations of mechanisms upon which they depend. We find that the roles of actors in influencing agricultural production depends on their position and influence within the supply chain; that complementary institutions, incentives and information are often combined; and that multi-stakeholder collaborations between different groups of actors are common. We discuss how the framework can be used to characterize different interventions using a common language and structure, to aid planning and analysis of interventions, and to facilitate the evaluation of interventions with respect to their structure and outcomes. Studying the collective experience of multiple interventions across commodities and spatial contexts is necessary to generate more systematic understandings of the impacts of commodity supply chain interventions in forest-agriculture landscapes. 相似文献
84.
85.
R. C. Agrawal 《Geophysical Journal International》1978,54(2):461-473
Summary. One hundred and eight deep-focus earthquakes occurring in the Indian region (6–37° N, 70–100° E) were originally selected for the study of P residuals (Paper I). Of these, 61 earthquakes were found suitable for analysing S residuals.
S times for this region are generally greater than J—B S times. Analysis of residuals reveals that anomalous regions are present both in the upper mantle as well as the lower mantle. 相似文献
S times for this region are generally greater than J—B S times. Analysis of residuals reveals that anomalous regions are present both in the upper mantle as well as the lower mantle. 相似文献
86.
87.
In this paper we use the mineral magnetic data (χ and χfd) to stratigraphically correlate different loess-palaeosol profiles in Kashmir Valley. The two available thermoluminescence (TL) chronologies on the Kashmir loess profiles have been reinterpreted to identify the soil of the Last Interglacial (ca. 125 000 yr BP). We show that the mineral magnetic data correlates well with the global marine δ18O record. This correlation has revealed the well-known Milankovich periodicities of 40 ka and 20 ka in the loess-palaeosol record. On the basis of this study, we conclude that loess deposition in the Kashmir Valley started around 200 ka and not 350 ka ago as suggested by earlier workers, and that magnetic susceptibility variations provide a tool to decipher climatic changes from loess-palaeosol sequences. 相似文献
88.
Estimating the uncertainty of land-cover extrapolations while constructing a raster map from tabular data 总被引:2,自引:0,他引:2
Robert Gilmore?Pontius Jr.Email author Aditya?Agrawal Diana?Huffaker 《Journal of Geographical Systems》2003,5(3):253-273
This paper presents novel techniques to estimate the uncertainty in extrapolations of spatially-explicit land-change simulation models. We illustrate the concept by mapping a historic landscape based on: 1) tabular data concerning the quantity in each land cover category at a distant point in time at the stratum level, 2) empirical maps from more recent points in time at the grid cell level, and 3) a simulation model that extrapolates land-cover change at the grid cell level. This paper focuses on the method to show uncertainty explicitly in the map of the simulated landscape at the distant point in time. The method requires that validation of the land-cover change model be quantified at the grid-cell level by Kappa for location (Klocation). The validation statistic is used to estimate the certainty in the extrapolation to a point in time where an empirical map does not exist. As an example, we reconstruct the 1951 landscape of the Ipswich River Watershed in Massachusetts, USA. The technique creates a map of 1951 simulated forest with an overall estimated accuracy of 0.91, with an estimated users accuracy ranging from 0.95 to 0.84. We anticipate that this method will become popular, because tabular information concerning land cover at coarse stratum-level scales is abundant, while digital maps of the specific location of land cover are needed at a finer spatial resolution. The method is a key to link non-spatial models with spatially-explicit models. 相似文献
89.
We present five new discriminant function diagrams based on an extensive database representative of basic and ultrabasic rocks
from four tectonic settings of island arc, continental rift, ocean-island, and mid-ocean ridge. These diagrams were obtained
after loge-transformation of concentration ratios of major-elements — a technique recommended for a correct statistical treatment of
compositional data. Higher % success rates (overall values from ∼ 83 to 97%) were obtained for proposing these new diagrams
as compared to those (∼82 to 94%) obtained from the discriminant analysis of the raw major-element concentration data (i.e.,
without the loge-transformation and without taking ratios of the compositional data, but using exactly the same database to provide an unbiased
comparison), suggesting that such a data transformation constitutes a statistically correct and recommended technique. The
new diagrams also resulted in less mis-classification of basic and ultrabasic rocks from known tectonic settings than the
diagrams obtained from the raw data. The use of these highly successful new discriminant function diagrams is illustrated
using Miocene to Recent basic and ultrabasic rocks from three areas of Mexico with complex or controversial tectonic settings
(Mexican Volcanic Belt, Los Tuxtlas volcanic field, and Eastern Alkaline Province), as well as older rocks from three areas
(Deccan, Malani, and Bastar) of India. Additionally, the major-element data from two ‘known’ continental arc settings are
used to show that they are similar to those from the island arc setting. Continental rift setting is inferred for all Mexican
cases and for one cratonic area of India (Malani) and an IAB setting for the Bastar craton. The Deccan flood basalt province
of India is used to warn against an indiscriminate use of those discrimination diagrams that do not explicitly include the
likely setting of the area under evaluation. An Excel template is also provided for an easy application of these new diagrams
for discriminating the four settings considered in this work. 相似文献
90.
The Himalayan mountain system has many depressions of regional dimensions, which are found oriented mostly E–W to NE–SW, mainly to the north of the main boundary fault (MBF). The Karewa Basin in the Kashmir Himalaya has sediments belonging to late Neogene to Quaternary formations, which represent an almost 1,300-m-thick succession of sand, mud and gravels exposed in the river valleys and the plateau margins of the entire Kashmir Valley. Sandbox analogue experiments show a great variety of wedge shapes showing significant changes in the taper angles due to the change in basal friction. Between two pop-ups or depressions (pop-down) of significant dimensions develop along the strike of the growing wedge. In order to maintain the critical angle, these depressions initially receive material from the hinterland, and later on, from the foreland end of the wedge. The depressions have developed due to the change in the surface slope of the wedge, and receive the eroded material only from the adjacent upheaved portions of the wedge. On continuation of the experiments (in cases where the wedge is highly unstable), these depressions are coupled with the wedge along with their sand-fills. The depositional history of the Karewa sediments indicates a sequential evolutionary pattern of the basin and thus represents a natural analogue of the sandbox experiments. 相似文献