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81.
David Deibe Margarita Amor Ramón Doallo 《International journal of geographical information science》2019,33(3):593-617
In recent years, the evolution and improvement of LiDAR (Light Detection and Ranging) hardware has increased the quality and quantity of the gathered data, making the storage, processing and management thereof particularly challenging. In this work we present a novel, multi-resolution, out-of-core technique, used for web-based visualization and implemented through a non-redundant, data point organization method, which we call Hierarchically Layered Tiles (HLT), and a tree-like structure called Tile Grid Partitioning Tree (TGPT). The design of these elements is mainly focused on attaining very low levels of memory consumption, disk storage usage and network traffic on both, client and server-side, while delivering high-performance interactive visualization of massive LiDAR point clouds (up to 28 billion points) on multiplatform environments (mobile devices or desktop computers). HLT and TGPT were incorporated and tested in ViLMA (Visualization for LiDAR data using a Multi-resolution Approach), our own web-based visualization software specially designed to work with massive LiDAR point clouds. 相似文献
82.
Beatriz Ortega Gabriel Vázquez Margarita Caballero Isabel Israde Socorro Lozano-García Peter Schaaf Esperanza Torres 《Journal of Paleolimnology》2010,44(3):745-760
Geochemical data obtained from X-ray fluorescence, physical properties, total organic and inorganic carbon content (TOC/TIC),
and diatom analysis from a 6.61-m-long sedimentary sequence near the modern northern shore of Lake Zirahuen (101° 44′ W, 19°
26′ N, 2000 m asl) provide a reconstruction of lacustrine sedimentation during the last approximately 17 cal kyr BP. A time
scale is based on ten AMS 14C dates and by tephra layers from Jorullo (AD 1759-1764) and Paricutin (AD 1943-1952) volcanoes. The multiproxy analyses presented
in this study reveal abrupt changes in environmental and climatic conditions. The results are compared to the paleo-record
from nearby Lake Patzcuaro. Dry conditions and low lake level are inferred in the late Pleistocene until ca. 15 cal kyr BP,
followed by a slight but sustained increase in lake level, as well as a higher productivity, peaking at ca. 12.1 cal kyr BP.
This interpretation is consistent with several regional climatic reconstructions in central Mexico, but it is in opposition
to record from Lake Patzcuaro. A sediment hiatus bracketed between 12.1 and 7.2 cal kyr BP suggests a drop in lake level in
response to a dry early Holocene. A deeper, more eutrophic and turbid lake is recorded after 7.2 cal kyr BP. Lake level at
the coring site during the mid Holocene is considered the highest for the past 17 cal kyr BP. The emplacement of the La Magueyera
lava flows (LMLF), dated by thermoluminiscence at 6560 ± 950 year, may have reduced basin volume and contributed to the relative
deepening of the lake after 7.2 cal kyr BP. The late Holocene (after 3.9 cal kyr BP) climate is characterized by high instability.
Extensive erosion, lower lake levels, dry conditions and pulses of high sediment influx due to high rainfall are inferred
for this time. Further decrease in lake level and increased erosion are recorded after ca. AD 1050, at the peak of Purepechas
occupation (AD 1300–1521), and until the eighteenth century. Few lacustrine records extend back to the late Pleistocene—early
Holocene in central Mexico; this paper contributes to the understanding of late Pleistocene-Holocene paleoclimates in this
region. 相似文献
83.
Mayuresh Sarpotdar Joice Mathew A. G. Sreejith Nirmal K. S. Ambily Ajin Prakash Margarita Safonova Jayant Murthy 《Experimental Astronomy》2017,43(1):99-117
We have developed a low-cost off-the-shelf component star sensor (StarSense) for use in minisatellites and CubeSats to determine the attitude of a satellite in orbit. StarSense is an imaging camera with a limiting magnitude of 6.5, which extracts information from star patterns it records in the images. The star sensor implements a centroiding algorithm to find centroids of the stars in the image, a Geometric Voting algorithm for star pattern identification, and a QUEST algorithm for attitude quaternion calculation. Here, we describe the software package to evaluate the performance of these algorithms as a star sensor single operating system. We simulate the ideal case where sky background and instrument errors are omitted, and a more realistic case where noise and camera parameters are added to the simulated images. We evaluate such performance parameters of the algorithms as attitude accuracy, calculation time, required memory, star catalog size, sky coverage, etc., and estimate the errors introduced by each algorithm. This software package is written for use in MATLAB. The testing is parametrized for different hardware parameters, such as the focal length of the imaging setup, the field of view (FOV) of the camera, angle measurement accuracy, distortion effects, etc., and therefore, can be applied to evaluate the performance of such algorithms in any star sensor. For its hardware implementation on our StarSense, we are currently porting the codes in form of functions written in C. This is done keeping in view its easy implementation on any star sensor electronics hardware. 相似文献
84.
Joice Mathew S. Ambily Ajin Prakash Mayuresh Sarpotdar K. Nirmal A. G. Sreejith Margarita Safonova Jayant Murthy Noah Brosch 《Experimental Astronomy》2018,45(2):201-218
Though the ultraviolet (UV) domain plays a vital role in the studies of astronomical transient events, the UV time-domain sky remains largely unexplored. We have designed a wide-field UV imager that can be flown on a range of available platforms, such as high-altitude balloons, CubeSats, and larger space missions. The major scientific goals are the variability of astronomical sources, detection of transients such as supernovae, novae, tidal disruption events, and characterizing active galactic nuclei variability. The instrument has a 80 mm aperture with a circular field of view of 10.8 degrees, an angular resolution of ~22 arcsec, and a 240 - 390 nm spectral observation window. The detector for the instrument is a Microchannel Plate (MCP)-based image intensifier with both photon counting and integration capabilities. An FPGA-based detector readout mechanism and real time data processing have been implemented. The imager is designed in such a way that its lightweight and compact nature are well fitted for the CubeSat dimensions. Here we present various design and developmental aspects of this UV wide-field transient explorer. 相似文献
85.
Maritza Liliana Arganis-Juárez Margarita Preciado-Jiménez Óscar A. Fuentes-Mariles Alejandro Mendoza-Reséndiz Ramón Domínguez-Mora Faustino De Luna-Cruz 《水文科学杂志》2019,64(8):934-947
To design and review the operation of spillways, it is necessary to estimate design hydrographs, considering their peak flow, shape and volume. A hybrid method is proposed that combines the shape of the design hydrograph obtained with the UNAM Institute of Engineering Method (UNAMIIM) with the peak flow and volume calculated from a bivariate method. This hybrid method is applied to historical data of the Huites Dam, Sinaloa, Mexico. The goal is to estimate return periods for the maximum discharge flows (that account for the damage caused downstream) and the maximum levels reached in the dam (measure of the hydrological dam safety) corresponding to a given spillway and its management policy. Therefore, to validate the method, the results obtained by the flood routing of the 50-year hydrograph are compared with those obtained by the flood routing of the three largest historical floods. Both maximum flow and elevation were in the range of values observed within 37.5–75 years corresponding to the length of the historical record. 相似文献
86.
Daniel Karthe Sergey Chalov Vsevolod Moreido Margarita Pashkina Anna Romanchenko Gunsmaa Batbayar Andrei Kalugin Katja Westphal Marcus Malsy Martina Flörke 《Water Resources》2017,44(3):399-416
The Selenga River is the main artery feeding Lake Baikal. It has a catchment of ~450000 km² in the boundary region between Northern Mongolia and Southern Siberia. Climate, land use and dynamic socioeconomic changes go along with rising water abstractions and contaminant loads originating from mining sites and urban wastewater. In the future, these pressures might have negative impacts on the ecosystems of Lake Baikal and the Selenga River Delta, which is an important wetland region in itself and forms the last geobiochemical barrier before the Selenga drains into Lake Baikal. The following study aims to assess current trends in hydrology and water quality in the Selenga-Baikal basin, identify their drivers and to set up models (WaterGAP3 framework and ECOMAG) for the prediction of future changes. Of particular relevance for hydrological and water quality changes in the recent past were climate and land use trends as well as contaminant influx from mining areas and urban settlements. In the near future, additional hydrological modifications due to the construction of dams and abstractions/water diversions from the Selenga’s Mongolian tributaries could lead to additional alterations. 相似文献
87.
88.
López-Álzate Margarita E. Sayol Juan-Manuel Hernández-Carrasco Ismael Osorio Andrés F. Mason Evan Orfila Alejandro 《Ocean Dynamics》2022,72(9-10):679-693
Ocean Dynamics - The spatial distribution, and the monthly and seasonal variability of mesoscale eddy observations derived from the AVISO eddy atlas are assessed in the Caribbean Sea during... 相似文献
89.
Jose Rosas-Elguera Bertha Aguilar Reyes Avto Goguitchaichvili Macario Rocha Margarita López Martínez Miriam M. Tostado-Plascencia Luis M. Alva Valdivia Cecilia Caballero Miranda 《Studia Geophysica et Geodaetica》2011,55(2):265-278
For long time the western-central Mexico has been affected by oblique subduction caused by Farallon plate beneath North America.
As result, smaller plates (e.g. Cocos Plate), several fault systems outlining crustal blocks (e.g. Michoacán block) and magmatic
arcs (e.g. Paleocene-Early Oligocene magmatism and the Trans-Mexican Volcanic Belt) were developed. Still, no paleomagnetic
data are available for Oligocene and Miocene. The principal aim of this study is to evaluate whether the tectonic rotations
and relative motions of these blocks occurred before the Miocene. Here, we report a detailed rock-magnetic and paleomagnetic
results from Tecalitlan area, located in the Michoacán block. Sixteen sites (about 150 oriented samples) were collected including
one radiometrically dated diabase dike (35.0 ± 1.8 Ma). Rock-magnetic experiments permitted identification of magnetic carriers
and assessment of the paleomagnetic stability. Continuous susceptibility measurements vs temperature in most cases yield reasonably
reversible curves with Curie points close to that of magnetite. Reliable paleomagnetic directions were obtained for 12 sites.
Inclination I and declination D of the mean paleomagnetic direction obtained in this study are I = 33.1°, D = 345.0°, and
Fisherian statistical parameters are k = 25, α95 = 8.9°. The corresponding mean paleomagnetic pole position is Plat = 75.7°, Plong = 166.6°, K = 31, A95 = 8.0°. The mean inclination is in reasonably good agreement with the expected value, as derived from reference poles for
the stable North America. Magnetic declination is not significantly different from that expected which is in disagreement
with a counterclockwise tectonic rotation of about 20° previously reported for the studied area. Based on paleomagnetic results
obtained in this study compiled with those currently available from the Michoacán Block, we propose a simple model suggesting
that sometime in Eocene epoch the convergence vector of the Farallon plate relative to North America plate was normal to the
trench before reaching an actual oblique convergence. 相似文献
90.
Peña-Icart M Villanueva Tagle ME Alonso-Hernández C Rodríguez Hernández J Behar M Pomares Alfonso MS 《Marine environmental research》2011,72(1-2):60-66
Knowing the metal extraction capacity of a digestion method is crucial for a better environmental interpretation of metal concentrations determined in sediments. One of the main problems at the present is the lack of harmonization of information obtained by two of the most popular sediment partial digestion methods: ISO 11466.3 (aqua regia) and EPA 3050B (HNO?--H?O?--HCl). In the present work, the amount of Cu, Ni and Pb leached by using both methods was compared with the total content of those elements in marine sediments collected, as an example, from the Cienfuegos Bay, Cuba. Similar amounts of Cu were extracted by both methods; while leaching of Ni and Pb were different. Generally, the EPA method extracted more Ni than the ISO method. In contrast, Pb was extracted in a larger amount by the ISO method. Some explanations are given for the observed results. X-ray Diffraction, X-ray Fluorescence, Particle Induced X-ray Emission Spectrometry and Energy Dispersive X-ray coupled to Scanning Electron Microscopy were employed for this purpose. On the other hand, none of the methods studied extracted simultaneously the fraction of all the metals, probably provided by human activity (Theoretical Anthropogenic Fraction) in both sediments studied. The use of ISO 11466.3 or EPA 3050B is recommended since the analytical performance parameters of both, in combination with Flame Atomic Absorption Spectrometry, are adequate. For a better environmental interpretation of the analytical results, information on the extraction efficiency of the selected method for specific elements and sediments under study should also be provided, together with the determined concentrations. 相似文献