全文获取类型
收费全文 | 156篇 |
免费 | 14篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 7篇 |
地球物理 | 48篇 |
地质学 | 63篇 |
海洋学 | 20篇 |
天文学 | 13篇 |
综合类 | 3篇 |
自然地理 | 15篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 15篇 |
2015年 | 4篇 |
2014年 | 9篇 |
2013年 | 9篇 |
2012年 | 6篇 |
2011年 | 17篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 6篇 |
2007年 | 10篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
排序方式: 共有172条查询结果,搜索用时 15 毫秒
71.
Paulo Pinheiro da Silva Leonardo Salayandía Aída Gándara Ann Q. Gates 《Earth Science Informatics》2009,2(4):249-269
The realization of an international cyberinfrastructure of shared resources to overcome time and space limitations is challenging
scientists to rethink how to document their processes. Many known scientific process requirements that would normally be considered
impossible to implement a few years ago are close to becoming a reality for scientists, such as large scale integration and
data reuse, data sharing across distinct scientific domains, comprehensive support for explaining process results, and full
search capability for scientific products across domains. This article introduces the CI-Miner approach that can be used to
aggregate knowledge about scientific processes and their products through the use of semantic annotations. The article shows
how this aggregated knowledge is used to benefit scientists during the development of their research activities. The discussion
is grounded on lessons learned through the use of CI-Miner to semantically annotate scientific processes in the areas of geo-sciences,
environmental sciences and solar physics: A use case in the field of geo-science illustrates the CI-Miner approach in action. 相似文献
72.
Antonio Donato Nobre Luz Adriana Cuartas Marcos Rodrigo Momo Dirceu Luís Severo Adilson Pinheiro Carlos Afonso Nobre 《水文研究》2016,30(2):320-333
Tools for accurately predicting environmental risks, such as the location and spatial extent of potential inundation, are not widely available. A dependence on calibration and a lack of available flood data have prevented the widespread application of existing hydrodynamic methods for predicting the extent of inundation. We use the height above the nearest drainage (HAND) terrain model to develop a simple static approach for mapping the potential extent of inundation that does not depend on flood observations and extends beyond methods for mapping low‐lying areas. While relying on the contour concept, the method utilizes drainage‐normalized topography and flowpaths to delineate the relative vertical distances (drop) to the nearest river. The HAND‐delineated relative drop is an effective distributed predictor of flood potential, which is directly related to the river stage height. We validated the new HAND contour approach using a flood event in Southern Brazil for which high‐resolution maps were available. The results indicated that the flood hazard‐mapping method accurately predicted the inundation extent of the channel carrying the flood wave and the channels influenced by flooding. For channels positioned outside of the flood‐wave area, the method overestimated the actual flood extent. As an original static assessment of floodwaters across the landscape, the HAND contour method could be used to map flood hazards in areas with poor information and could promote the development of new methods for predicting hydrological hazards. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
73.
A New Ionosphere Monitoring Technology Based on GPS 总被引:1,自引:0,他引:1
Claudio Brunini Amalia Meza Francisco Azpilicueta María Andrea Van Zele Mauricio Gende Alejandro Díaz 《Astrophysics and Space Science》2004,290(3-4):415-429
Although global positioning system (GPS) was originally planned as a satellite-based radio-navigation system for military purposes, civilian users have significantly increased their access to the system for both, commercial and scientific applications. Almost 400 permanent GPS tracking stations have been stablished around the globe with the main purpose of supporting scientific research. In addition, several GPS receivers on board of low Earth orbit satellites fitted with special antennas that focus on Earth's horizon, are tracking the radio signals broadcasted by the high-orbiting GPS satellites, as they rise and set on Earth horizon. The data of these ground and space-born GPS receivers, readily accessible through Internet in a ‘virtual observatory’ managed by the International GPS Service, are extensively used for many researches and might possibly ignite a revolution in Earth remote sensing. By measuring the changes in the time it takes for the GPS signals to arrive at the receiver as they travel through Earth's atmosphere, scientists can derive a surprising amount of information about the Earth's ionosphere, a turbulent shroud of charged particles that, when stimulated by solar flares, can disrupt communications around the world. This contribution presents a methodology to obtain high temporal resolution images of the ionospheric electron content that lead to two-dimensional vertical total electron content maps and three-dimensional electron density distribution. Some exemplifying results are shown at the end of the paper. 相似文献
74.
Rhythmic movements in response to tidal cycles are characteristic of infaunal inhabitant of intertidal soft-bottoms, allowing
them to remain in the area with best living conditions. The effect of bioturbators as modifier of local environmental conditions
and thus of gradients in intertidal habitats, has not been investigated yet. The Atlantic estuarine intertidal areas are dominated
by the burrowing crabChasmagnathus granulatus that generates strong environmental heterogeneity by affecting the physical-chemical characteristics of the sediment. The
comparison between intertidal areas with and without crab shows that sediments in the crab beds remain more humid, softer,
and homogeneous across the intertidal and along the tidal cycle than areas without crabs. The densities of infauna were higher
at high intertidal zones in crab beds than in similar areas without crabs. Infaunal organisms performed vertical movements
into the sediment following the tidal cycle that were always of higher magnitude in habitats without crabs. Infaunal species
tend to spend most of the time buried into the sediment in the crab bed. Migratory shorebirds use the Atlantic estuarine environments
as stopover or wintering sites. They feed (mainly on polychaetes) in the low intertidal zones of both habitats (with and without
crabs), but they also feed in the upper intertidal of the crab bed; polychaete per capita mortality rate is higher in the
upper part of the crab bed. Environmental heterogeneity produced by crab disturbance has an effect on the infaunal behavior,
risk of mortality, and the zonation pattern. This is another example of the ecosystem engineering ability of a burrowing intertidal
species. 相似文献
75.
Salvador E. Lluch-Cota Eugenio A. Aragón-Noriega David Aurioles-Gamboa Richard C. Brusca Roberto Cortés-Altamirano Alfonso Esquivel-Herrera Michel E. Hendrickx Hugo Herrera-Cervantes Miguel Lavín Daniel B. Lluch-Cota Silvio G. Marinone Sofia Ortega-García Alejandro Parés-Sierra Mauricio Ramírez-Rodríguez Richard A. Schwartzlose Arturo P. Sierra-Beltrán 《Progress in Oceanography》2007,73(1):1-26
The Gulf of California is unique because of its geographical location and conformation. It hosts diverse ecosystems and important fisheries that support industry and provide livelihood to coastal settlements. It is also the site of interests and problems, and an intense interaction among managers, producers, and conservationists. In this report, we scrutinize the abiotic (hydrography, climate, ocean circulation, and chemistry) and biotic (phyto- and zooplankton, fish, invertebrates, marine mammals, birds, and turtles) components of the marine ecosystem, and some particular aspects of climate variability, endemisms, harmful algal blooms, oxygen minimum layer, and pollution. We also review the current conditions and conflicts around the main fisheries (shrimp, small and large pelagic fishes, squid, artisanal and sportfishing), the most important human activity in the Gulf of California. We cover some aspects of management and conservation of fisheries, especially the claimed overexploitation of fish resources and the ecosystems, and review proposals for creating networks of marine protected areas. We conclude by identifying main needs for information and research, particularly the integration of data bases, the implementation of models and paleoreconstructions, establishment of monitoring programs, and the evaluation of fishing impacts and management actions. 相似文献
76.
Fernandez MA de Luca Rebello Wagener A Limaverde AM Scofield AL Pinheiro FM Rodrigues E 《Marine environmental research》2005,59(5):435-452
An integrated biological-chemical survey of organotin compounds was carried out in Guanabara Bay, the second most important Brazilian harbor complex. The biological survey revealed high levels of imposex in Stramonita haemastoma populations. Inside the bay values of relative penis length index from 42.7 to 107.6 and vas deferens sequence index from III to VI were found, while organisms collected outside the bay had values ranging from <0.1 to 35.2 and from 0 to II. None of the females sampled inside the bay were normal and imposex was found in all stations. Surface sediments in the bay are contaminated by tributyltin (10-522 ng/g d.w.) and triphenyltin (<3.9-39.4 ng/g d.w.) with greater concentrations close to shipyards and marinas. The observed predominance of parent compounds (TBT and TPT) is commonly found when recent inputs occur, but may also indicate slow degradation processes in the anoxic conditions of these sediments. To our knowledge, this is the first report of a combined imposex-sediment approach to evaluate organotin contamination in marine environments of South America, and also the first report of TPT detection in environmental matrices in this region. 相似文献
77.
78.
Natural specimens of green gemological euclase (chemical formula BeAlSiO4(OH)) from Brazil were investigated by electron paramagnetic resonance (EPR) and optical absorption. In addition to iron-related
EPR spectra, analyzed recently in blue and colorless euclase, chromium and vanadium-related EPR spectra were also detected
in green euclase. Their role as color causing centers is discussed. The results indicate that Cr3+ ions substitute for Al3+ ions in the euclase structure. The EPR rotation patterns of Cr3+ with electron spin S = 3/2 were analyzed with monoclinic spin Hamiltonian leading to the parameters of g
xx
, g
yy
and g
zz
equal to 2.018, 2.001 and 1.956 and electronic fine structure parameters of D = −8.27 GHz and E = 1.11 GHz, respectively, with high asymmetry ratio E/D = 0.13. For the vanadium-related EPR spectra the situation is different. It is concluded that vanadium is incorporated as
the vanadyl radical VO2+ with electron spin S = 1/2 with nearly axial spin Hamiltonian parameters gzz = 1.9447, g
xx
= 1.9740 g
yy
= 1.9669 and axial hyperfine interactions due to the nuclear spin I = 7/2 of the 51V isotope leading to A
zz
= 502 MHz, A
xx
= 150 MHz and A
yy
= 163 MHz. The green color of euclase is caused by two strong broad absorption bands centered at 17,185 and 24,345 cm−1 which are attributed to the 4A2g → 4T2g, 4T1g transitions of Cr3+, respectively. Vanadyl radicals may introduce some absorption bands centered in the near infrared with tail extending into
the visible spectral range. 相似文献
79.
Surface water quality in a sulfide mineral‐rich arid zone in North‐Central Chile: Learning from a complex past,addressing an uncertain future 下载免费PDF全文
Mauricio Flores Jorge Núñez Jorge Oyarzún Gustavo Freixas Hugo Maturana Ricardo Oyarzún 《水文研究》2017,31(3):498-513
This study presents an analysis of up to 30 years of hydrological variables and selected water quality parameters (pH, SO4, Fe, Cu, and As) in the upper area of the Elqui River basin in North‐Central Chile. A correlation analysis determined statistically significant positive relationship for SO4‐Cu, Fe‐As, and Fe‐Cu. In terms of historical behaviour, no statistically significant trends were detected for precipitation or temperature. In contrast, for flow, there is an overall decreasing pattern for the entire area of study, although only in one case this trend was statistically significant. Along with the aforementioned analysis, a characterization of the flow‐water quality relationships is considered for the time period analyzed. Although erratic behaviours were confirmed, a negative (i.e., inverse) flow‐concentration relationship was identified for SO4, a positive (i.e., direct) relationship for Fe, and undefined relationships for As and Cu were obtained. From these analyses and based on previous studies on projections regarding climate change for the Andean region, and in particular for the upper Elqui zone, an estimation of the possible effects of the change in water regimes on water quality in the area of study is developed. It is likely that a decrease in surface flow, as a consequence of climate change could translate into improvements in water quality in terms of Fe and eventually As and Cu, but into an impairment in the case of SO4. In any case, this is a complex situation that demands special attention in the face of industrial activities that could be developed in tributaries like the Claro River, which currently play an important role in depurating or diluting contaminants in the waters of the Elqui River. Finally, it should be noted that this study addresses an issue that goes beyond the local interest and could be used as a reference to compare other transitional environments containing sulphide ores or areas of hydrothermal alterations, which are considered to be highly vulnerable to climate change and variability. 相似文献
80.
Mariano A. Larrovere Camilo R. de los Hoyos Alejandro J. Toselli Juana N. Rossi Miguel A.S. Basei Mauricio E. Belmar 《Journal of South American Earth Sciences》2011,31(2-3):279-297
New petrologic, thermobarometric and U-Pb monazite geochronologic information allowed to resolve the metamorphic evolution of a high temperature mid-crustal segment of an ancient subduction-related orogen. The El Portezuelo Metamorphic-Igneous Complex, in the northern Sierras Pampeanas, is mainly composed of migmatites that evolved from amphibolite to granulite metamorphic facies, reaching thermal peak conditions of 670–820 °C and 4.5–5.3 kbar. The petrographic study combined with conventional and pseudosection thermobarometry led to deducing a short prograde metamorphic evolution within migmatite blocks. The garnet-absent migmatites represent amphibolite-facies rocks, whereas the cordierite-garnet-K-feldspar-sillimanite migmatites represent higher metamorphic grade rocks. U-Pb geochronology on monazite grains within leucosome record the time of migmatization between ≈477 and 470 Ma. Thus, the El Portezuelo Metamorphic-Igneous Complex is an example of exhumed Early Ordovician anatectic middle crust of the Famatinian mobile belt. Homogeneous exposure of similar paleo-depths throughout the Famatinian back-arc and isobaric cooling paths suggest slow exhumation and consequent longstanding crustal residence at high temperatures. High thermal gradients uniformly distributed in the Famatinian back-arc can be explained by shallow convection of a low-viscosity asthenosphere promoted by subducting-slab dehydration. 相似文献