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排序方式: 共有128条查询结果,搜索用时 718 毫秒
61.
Antony G. Brown Stephen Tooth Richard C. Chiverrell James Rose David S. G. Thomas John Wainwright Joanna E. Bullard Varyl R. Thorndycraft Rolf Aalto Peter Downs 《地球表面变化过程与地形》2013,38(4):431-434
The ‘Anthropocene’, as used to describe the interval of recent Earth history during which humans have had an ‘overwhelming’ effect on the Earth system, is now being formally considered as a possible new geological Epoch. Such a new geological time interval (possibly equivalent to the Pleistocene Epoch) requires both theoretical justification as well as empirical evidence preserved within the geological record. Since the geological record is driven by geomorphological processes that produce terrestrial and near‐shore stratigraphy, geomorphology has to be an integral part of this consideration. For this reason, the British Society for Geomorphology (BSG) has inaugurated a Fixed Term Working Group to consider this issue and advise the Society on how geomorphologists can engage with debates over the Anthropocene. This ESEX Commentary sets out the initial case for the formalisation of the Anthropocene and a priori considerations in the hope that it will stimulate debate amongst, and involvement by, the geomorphological community in what is a crucial issue for the discipline. The Working Group is now considering the practical aspects of such a formalization including the relative magnitude problem, the boundary problem and the spatial diachrony of ‘anthropogenic geomorphology’. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
62.
Venugopal Chandu E. Savithri Devi R. Jayapal George Samuel S. Antony G. Renuka 《Astrophysics and Space Science》2012,339(1):157-164
Kinetic Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory plasmas. In cometary
environments, waves in the hydromagnetic range of frequencies are excited predominantly by heavy ions. We, therefore, study
the stability of the kinetic Alfven wave in a plasma of hydrogen ions, positively and negatively charged oxygen ions and electrons.
Each species was modeled by drifting ring distributions in the direction parallel to the magnetic field; in the perpendicular
direction the distribution was simulated with a loss cone type distribution obtained through the subtraction of two Maxwellian
distributions with different temperatures. We find that for frequencies w* < wcH +\omega^{*} < \omega_{c\mathrm{H}^{ +}} (ω
∗ and wcH +\omega_{c\mathrm{H}^{ +}} being respectively the Doppler shifted and hydrogen ion gyro-frequencies), the growth rate increases with increasing negatively
charged oxygen ion densities while decreasing with increasing propagation angles, negative ion temperatures and negative ion
mass. 相似文献
63.
Aerosol light absorption, black carbon, and elemental carbon at the Fresno Supersite, California 总被引:2,自引:0,他引:2
Judith C. Chow John G. Watson Prakash Doraiswamy Lung-Wen Antony Chen David A. Sodeman Douglas H. Lowenthal Kihong Park W. Patrick Arnott Nehzat Motallebi 《Atmospheric Research》2009,93(4):874-887
Particle light absorption (bap), black carbon (BC), and elemental carbon (EC) measurements at the Fresno Supersite during the summer of 2005 were compared to examine the equivalency of current techniques, evaluate filter-based bap correction methods, and determine the EC mass absorption efficiency (σap) and the spectral dependence of bap. The photoacoustic analyzer (PA) was used as a benchmark for in-situ bap. Most bap measurement techniques were well correlated (r ≥ 0.95). Unadjusted Aethalometer (AE) and Particle Soot Absorption Photometer (PSAP) bap were up to seven times higher than PA bap at similar wavelengths because of absorption enhancement by backscattering and multiple scattering. Applying published algorithms to correct for these effects reduced the differences to 24 and 17% for the AE and PSAP, respectively, at 532 nm. The Multi-Angle Absorption Photometer (MAAP), which accounts for backscattering effects, overestimated bap relative to the PA by 51%. BC concentrations determined by the AE, MAAP, and Sunset Laboratory semi-continuous carbon analyzer were also highly correlated (r ≥ 0.93) but differed by up to 57%. EC measured with the IMPROVE/STN thermal/optical protocols, and the French two-step thermal protocol agreed to within 29%. Absorption efficiencies determined from PA bap and EC measured with different analytical protocols averaged 7.9 ± 1.5, 5.4 ± 1.1, and 2.8 ± 0.6 m2/g at 532, 670, and 1047 nm, respectively. The Angström exponent (α) determined from adjusted AE and PA bap ranged from 1.19 to 1.46. The largest values of α occurred during the afternoon hours when the organic fraction of total carbon was highest. Significant biases associated with filter-based measurements of bap, BC, and EC are method-specific. Correcting for these biases must take into account differences in aerosol concentration, composition, and sources. 相似文献
64.
Spatial and temporal knowledge representation 总被引:1,自引:1,他引:0
Antony Galton 《Earth Science Informatics》2009,2(3):169-187
Knowledge Representation (KR) originated as a discipline within Artificial Intelligence, and is concerned with the representation
of knowledge in symbolic form so that it can be stored and manipulated on a computer. This article surveys that part of KR
that is concerned with the representation of space and time, with particular reference to the use of such representations
in geographical information science.
相似文献
Antony GaltonEmail: |
65.
Quartile-deviation (QDa) and median-diameter (Md) values have been calculated from the grain-size distributions of a variety of Pleistocene and modern glacial and para-glacial sediments. The QDa—Md pairs are plotted on double-log graph paper to determine whether their graphic distributions are distinctive, and to examine their sedimentological implications. Three distributions emerge. The first has a shallow gradient and represents coarse bi-modal tills consisting largely of rock fragments — distribution (a). The second, with an intermediate gradient, represents fine uni- or non-modal tills consisting mainly of monomineralic grains — distribution (b). The third (c) has a steep gradient and consists of bi-modal tills with a dominant proportion of monomineralic grains. Each of these distributions is explained by using the grain-size characteristics of physically weathered rock debris as a starting point for discussion. By a process dominated by the continual addition of weathered-grain populations (population addition), tills with (a) characteristics are formed. By a process dominated by comminution and the selective removal of grains by ablation (population subtraction), tills with (b) characteristics are formed. Any of these tills, when subjected to flowing water, rapidly lose their glacial characteristics and assume QDa—Md characteristics of fluvial deposits (although they are fluvioglacial). 相似文献
66.
This paper uses a numerical ice sheet model to investigate the role of topography in influencing ice sheet growth. The model is applied to the maritime, mid-latitude uplands of Scotland and relies on a series of assumptions about mass balance, topography, and ice flow. It is driven by an imposed pattern of temperature change. The model is able to predict effectively the extent and thickness of the Loch Lomond ice sheet, using a palaeotemperature curve based on Coleoptera assemblages. A series of experiments with a stepped, constant July air temperature depression suggests that in Scotland a change in excess of ?3·0°C is necessary to initiate ice sheet growth; that steady state ice caps build up at changes of ?3 to ? 6·5°C; and that large ice sheets build up at changes of more than ? 6·625°C. The bifurcation revealed by the last two types of behaviour is the result of topography. Both the vertical amplitude and the spatial distribution of bedrock basins and ridges are important in determining the pattern, rate, and extent of ice sheet growth. The implication is that topography plays an important role in determining the dynamics of ice sheet growth. 相似文献
67.
Antony D. Clarke 《Journal of Atmospheric Chemistry》1989,9(1-3):255-266
Thermal and optical techniques were used at Barrow, Alaska during AGASP II (3/20/86–4/7/86) to measure in-situ variability of major aerosol components present in Arctic Haze. The experiment provided continuous data on the concentration, size distribution and relative proportions of sulfate species and refractory aerosol for particle diameters of 0.15 to 5 m. Filter samples were also taken for determination of aerosol optical absorption due to soot (EC-elemental carbon). Although pronounced haze events were absence during this period the haze aerosol present varied in concentration between 2 and 6 g/m3 but showed little change in relative constituents. Apart from local influences, the optical data indicated a persistent fine-mode sulfate aerosol with a NH4
+/SO4
– molar ratio of about 0.4 and a refractory component of somewhat less than 10% by mass. A preliminary comparison of soot estimates determined from the light absorption data with the size distributions of refractory aerosol observed independently by the optical particle counter showed good agreement during the sample period. In the absence of local pollution, values of single scatter albedo derived from light scattering and light absorption showed similar variation about the average value of 0.86 found by us during flights north of Barrow three years earlier during AGASP I. 相似文献
68.
J. Antony Vinoth Kumar S. K. Pathan R. J. Bhanderi 《Journal of the Indian Society of Remote Sensing》2007,35(1):11-20
Urban sprawl is characterized by haphazard patchwork of development, which leads to an improper development in any city. To
prevent this kind of sprawl in future, it is necessary to monitor the growth of the city. Hence, an attempt has been made
in the present study to monitor the urban growth over a period of time by employing Remote Sensing and Geographic Information
System techniques in conjunction with Shannon entropy. Shannon entropy is a measure to determine the compactness or dispersion
of built-up land growth in the urban areas. The growth patterns of urban built-up land have been studied initially by dividing
the area into four zones. The observations have been made with respect to each zone. Then, the study area has been divided
into concentric circles of 1 km buffers and the growth patterns have been studied based on urban built-up density with respect
to each circular buffer in all four zones. These observations have been integrated with road network to check the influence
of infrastructure on haphazard urban growth. It has been found from the study that Shannon entropy is a good measure to determine
the spatial concentration or dispersion of built-up land in the city. The study also proved the potential of RS and GIS techniques
in the spatio-temporal analysis of urban growth trends and their consequences in the lands adjoining to urban areas. 相似文献
69.
Antony Charls Langodan Sabique Dasari Hari Prasad Knio Omar Hoteit Ibrahim 《Natural Hazards》2021,105(2):1797-1814
Natural Hazards - Knowledge about extreme water levels is essential for efficient planning and design of coastal infrastructure. This study uses a high-resolution (~?60 m) coupled... 相似文献
70.
Asten Michael W. Yong Alan Foti Sebastiano Hayashi Koichi Martin Antony J. Stephenson William J. Cassidy John F. Coleman Jacie Nigbor Robert Castellaro Silvia Chimoto Kosuke Cornou Cécile Cho Ikuo Hayashida Takumi Hobiger Manuel Kuo Chun-Hsiang Macau Albert Mercerat E. Diego Molnar Sheri Pananont Passakorn Pilz Marco Poovarodom Nakhorn Sáez Esteban Wathelet Marc Yamanaka Hiroaki Yokoi Toshiaki Zhao Don 《Journal of Seismology》2022,26(4):757-780
Journal of Seismology - Site response is a critical consideration when assessing earthquake hazards. Site characterization is key to understanding site effects as influenced by seismic site... 相似文献