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41.
Several goethites were obtained through the hydrolysis at 60 °C of Fe(III) solutions containing variable amounts of Mn(II) ions. The obtained samples were thermally treated at temperatures ranging from 180 to 310 °C until the complete phase transformation to hematite was achieved. The effect of Mn in the dehydroxylation process was investigated using X-ray diffraction (XRD) and the Rietveld refinement of XRD data together with scanning electron microscopy (SEM), differential thermogravimetric analysis (DTA) and Fourier transform infrared spectroscopy (FTIR). In all cases, the formed hematites retained the acicular shape of the precursor goethite. The dehydroxylation temperature increased with the increase of the Mn content in the parent goethite. The cell parameters of both phases decreased with the thermal treatment, however the decrease in the goethite b-parameter was more pronounced. This fact could be attributed to the distortion in the goethite structure by the presence of manganese. The band shifts in the FT-IR spectra of the goethites with different Mn substitution were analysed. The intensities of the hydroxyl vibrations were indicative of the degree of dehydroxylation.The chemical reactivity of all the samples, before and after the thermal treatment, was also studied. The kinetic experiments were carried out at 40 °C in 4 mol dm− 3 HCl. The acid dissolution of all Mn-goethites showed a congruent behavior indicative of a homogeneous distribution of Mn in the goethite crystals, this trend was not observed in the formed hematites presenting a high Mn content. The dissolution rate in goethites increased with the increase of Mn content, the opposite effect was observed in the corresponding hematites. The activation energy in both phases was also obtained and indicated that the Mn substitution produces an opposite effect on goethite- and hematite-phases. Different kinetic laws were applied in order to explain the dissolution behavior, but the modified first-order Kabai equation described the dissolution data best. 相似文献
42.
Surface and groundwater pollution by organochlorine compounds in a typical soybean system from the south Pampa,Argentina 总被引:3,自引:0,他引:3
Mariana Gonzalez Karina S. B. Miglioranza Valeria M. Shimabukuro Orlando M. Quiroz Londoño Daniel E. Martinez Julia E. Aizpún Víctor J. Moreno 《Environmental Earth Sciences》2012,65(2):481-491
Organochlorine pesticides (OCPs) use has been restricted or forbidden in Argentina since 1998 and technical endosulfan is
the last currently used OCPs on the soybean-wheat production. As they persist in soil for several years after application,
OCPs constitute a source of environmental pollution. This work aims to assess OCPs contamination of groundwater (Gw) and streamwater
(Sw) in the Quequén Grande River watershed from south Argentinean Pampas in relation to the hydrogeological characteristics.
OCPs were analyzed in Sw, Gw, surface bottom sediments, soils and borehole cutting sediments (Cs) by gas chromatograph-electron
capture detector. Pesticide distribution in Cs was dependent on the characteristic of the non-saturated zone. Leached pesticides
over 3 m in Cs showed the pattern: HCHs = endosulfan > chlordanes > DDTs, and from 3 to 6 m heptachlor was the main group
as a consequence of the past use of this compound in the area, mainly on potato crops. Endosulfan reaches Gw during application
season as well as during flooding events while a retard effect was observed for Sw. Levels of α- and β-isomers were in certain
cases above national (7 ng L−1) and international (3 ng L−1) limits for aquatic biota protection. As the endosulfan sulfate metabolite was present in Gw and Sw and due to its high toxicity,
it should be considered in the establishment of water quality criteria for human and environmental protection. 相似文献
43.
Caroline Aubry-Wake Lauren D. Somers Haley Alcock Aspen M. Anderson Amin Azarkhish Samuel Bansah Nicole M. Bell Kelly Biagi Mariana Castaneda-Gonzalez Olivier Champagne Anna Chesnokova Devin Coone Tasha-Leigh J. Gauthier Uttam Ghimire Nathan Glas Dylan M. Hrach Oi Yin Lai Pierrick Lamontagne-Hallé Nicolas R. Leroux Laura Lyon Sohom Mandal Bouchra R. Nasri Nataša Popović Tracy E. Rankin Kabir Rasouli Alexis Robinson Palash Sanyal Nadine J. Shatilla Brandon Van Huizen Sophie Wilkinson Jessica Williamson Majid Zaremehrjardy 《水文研究》2020,34(8):2001-2006
44.
Impact of ocean model resolution on CCSM climate simulations 总被引:1,自引:1,他引:0
Ben P. Kirtman Cecilia Bitz Frank Bryan William Collins John Dennis Nathan Hearn James L. Kinter III Richard Loft Clement Rousset Leo Siqueira Cristiana Stan Robert Tomas Mariana Vertenstein 《Climate Dynamics》2012,39(6):1303-1328
The current literature provides compelling evidence suggesting that an eddy-resolving (as opposed to eddy-permitting or eddy-parameterized) ocean component model will significantly impact the simulation of the large-scale climate, although this has not been fully tested to date in multi-decadal global coupled climate simulations. The purpose of this paper is to examine how resolved ocean fronts and eddies impact the simulation of large-scale climate. The model used for this study is the NCAR Community Climate System Model version 3.5 (CCSM3.5)—the forerunner to CCSM4. Two experiments are reported here. The control experiment is a 155-year present-day climate simulation using a 0.5° atmosphere component (zonal resolution 0.625 meridional resolution 0.5°; land surface component at the same resolution) coupled to ocean and sea-ice components with zonal resolution of 1.2° and meridional resolution varying from 0.27° at the equator to 0.54° in the mid-latitudes. The second simulation uses the same atmospheric and land-surface models coupled to eddy-resolving 0.1° ocean and sea-ice component models. The simulations are compared in terms of how the representation of smaller scale features in the time mean ocean circulation and ocean eddies impact the mean and variable climate. In terms of the global mean surface temperature, the enhanced ocean resolution leads to a ubiquitous surface warming with a global mean surface temperature increase of about 0.2?°C relative to the control. The warming is largest in the Arctic and regions of strong ocean fronts and ocean eddy activity (i.e., Southern Ocean, western boundary currents). The Arctic warming is associated with significant losses of sea-ice in the high-resolution simulation. The sea surface temperature gradients in the North Atlantic, in particular, are better resolved in the high-resolution model leading to significantly sharper temperature gradients and associated large-scale shifts in the rainfall. In the extra-tropics, the interannual temperature variability is increased with the resolved eddies, and a notable increases in the amplitude of the El Ni?o and the Southern Oscillation is also detected. Changes in global temperature anomaly teleconnections and local air-sea feedbacks are also documented and show large changes in ocean–atmosphere coupling. In particular, local air-sea feedbacks are significantly modified by the increased ocean resolution. In the high-resolution simulation in the extra-tropics there is compelling evidence of stronger forcing of the atmosphere by SST variability arising from ocean dynamics. This coupling is very weak or absent in the low-resolution model. 相似文献
45.
Sebastián E. Sabatini Iara Rocchetta Carlos M. Luquet Mariana I. Guido María del Carmen Ríos de Molina 《Limnologica》2011,41(4):356-362
The effect of chronic exposure to Escherichia coli on morphometrical parameters, different antioxidant defenses, lipid peroxidation and protein oxidation has been studied in digestive gland of the freshwater mussel Diplodon chilensis in the laboratory during 6 weeks. In, a parallel field study, we evaluated morphometrical and oxidative stress parameters in digestive glands of mussels collected from a sewage polluted area (SMA) and from a pristine area (control). Both sites were characterized by analyzing bacteriological and physic-chemical parameters. In the laboratory D. chilensis was able to filter bacteria at high concentrations with a clearing rate of 0.510 ± 0.036 L/h per gram of dry soft tissue mass. The digestive gland mass to shell length ratio (DGM/SL), reduced glutathione (GSH), lipid peroxidation, as concentration of thiobartituric acid reactive substances (TBARS), and glutathione-S-transferase (GST) activity of mussels fed with bacteria were significantly higher than those of control mussels after the fourth week. Fecal bacteria in lake water samples were undetectable in the control, and higher than 24,000 MPN (most probable number)/100 mL in SMA. DGM/SL was higher in SMA. No differences between sites were observed in total lipid and protein content, neither in superoxide dismutase activity. GSH content was higher in SMA, with no difference in the oxidized form. GST activity and MDA were significantly higher in SMA but protein oxidation was not affected. 相似文献
46.
This introductory paper to the special section of Global Environmental Change entitled “Global transformations, social metabolism and the dynamics of socio-environmental conflicts” argues that the emergence of new global economic centers is inducing a major expansion in the global social metabolism—the flows of energy and materials into the world economy —, a transformation in the systems for the extraction and provision of natural resources, as well as setting the conditions for socio-environmental conflicts at the commodity frontiers, particularly in areas with a dense human occupation of the territory. We point out that we are currently experiencing global transformations that constitute the beginning of a new historical phase of modern capitalism. The aim of the paper is to draw an overall picture of such transformations, to discuss some of their implications for resource-rich countries, particularly in Latin America and Africa, and by doing so to provide an analytical framework that allow us to make explicit the linkages between the different papers that compose the special section. 相似文献
47.
1 INTRODUCTION The Parana River in South America ranks as the sixth largest in the world in terms of average discharge (22 x 103 m3/s according to Schumm and Winkley, 1994), and its Argentinean reach stretches from Puerto Iguazu on the north to the Rio de la Plata estuary in the south (Fig. 1). Its estimated average suspended load, bed load, and total load are 23 x 106, 2.2 x 106, and 25.2 x 106 metric tons per year, respectively (Paoli and Schreider, 2001.) The economic developmen… 相似文献
48.
49.
CIVIL SOCIETY PARTICIPATION IN THE DECENTRALISATION OF BRAZIL'S WATER RESOURCES: ASSESSING PARTICIPATION IN THREE STATES 总被引:1,自引:0,他引:1
Christian Brannstrom James Clarke Mariana Newport 《Singapore journal of tropical geography》2004,25(3):304-321
Decentralisation, the transfer of powers to a lower level of government, is thought to encourage more efficient and equitable management of natural resources. Participation of civil society organisations (CSOs) is considered critical to create positive outcomes of decentralisation. Here we examine aspects of civil society participation in decentralised management using the case of Brazil's water resources management. Several Brazilian states have enacted reforms mandating watershed committees in which the participation of civil society is either encouraged or required. However, actual participation of civil society is not yet well understood. To assess participation, we collected qualitative data on watershed districts in three Brazilian states (Bahia, Paraná and São Paulo). Our findings reaffirm the importance of the state in establishing a transparent legal framework to encourage participation and in defining “civil society”. The ability of civil society leaders to obtain and deploy local environmental knowledge, which frames environmental issues in new geographical scales, is useful to achieve the efficiency and efficacy objectives of decentralisation. However, by “upscaling” political activities beyond decentralisation's new territories, CSOs could make decentralisation irrelevant to local environmental issues. 相似文献
50.
Emiliano Donadio Sebastian Di Martino Mariana Aubone Andres J. Novaro 《Journal of Arid Environments》2004,56(4):709
We studied the feeding ecology of the Andean hog-nosed skunk (Conepatus chinga) in three areas with different land use in Patagonia. Two areas were heavily grazed by sheep or horses and wild exotic herbivores and the third area was lightly grazed by cattle. In each area, we assessed skunk diet, prey abundance and carrion availability. Skunks were generalist feeders, with invertebrates composing the bulk of their diet, but also consumed small vertebrates and carrion. Differences in diet composition were found among areas, mainly because skunks consumed more beetle larvae in the sheep area and more cricetines and spiders in the exotic-herbivore area. All prey but rodents were significantly more abundant in spring and summer than in fall and winter, but skunk diets were similar among seasons. In the sheep area, where the soil was most disturbed, we found reduced abundances of invertebrate prey and rodents. High consumption of beetles during autumn and winter when these were least abundant and in the sheep area indicates that skunks had a preference for beetles and their larvae. We conclude that Andean hog-nosed skunks in Patagonia might be negatively affected by reductions of their main prey due to soil and plant alterations by livestock. 相似文献