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71.
Sandrine Roy Riccardo Vassallo Joseph Martinod Matías C. Ghiglione Christian Sue Pascal Allemand 《地学学报》2020,32(1):1-10
Across the extreme south of Patagonia, the Magallanes‐Fagnano Fault (MFF) accommodates the left‐lateral relative motion between South America and Scotia plates. In this paper, we present an updated view of the geometry of the eastern portion of the MFF outcropping in Tierra del Fuego. We subdivide the MFF in eight segments on the basis of their deformation styles, using field mapping and interpretation of high‐resolution imagery. We quantify coseismic ruptures of the strongest recorded 1949, Mw7.5 earthquake, and determine its eastern termination. We recognize several co‐seismic offsets in man‐made features showing a sinistral shift up to 6.5 m, greater than previously estimated. Using 10Be cosmogenic nuclides depth profiles, we date a cumulated offset in post‐glacial morphologies and estimate the long‐term slip rate of the eastern MFF. We quantify a 6.4 ± 0.9 mm/a left‐lateral fault slip rate, which overlaps geodetic velocity and suggests stable fault behaviour since Pleistocene. 相似文献
72.
Robert Thomas Bachmann Sharifah Adawiyah Thilagam Krishnan Benson Khoo Tan Sue Sian Trevor Richards 《Arabian Journal of Geosciences》2018,11(15):426
The extensive use of peat moss as potting medium in nurseries worldwide is not sustainable causing peatland depletion and greenhouse gas emissions. This research seeks to explore whether wood biochar produced by the environment-friendly flame curtain method can partially substitute peat moss in plant nurseries without affecting plant growth and health. Biochar was produced from durian wood logs in a top-quenched Kon-Tiki earth kiln, crushed, and mixed with peat moss at dosages of 0, 1, 2.5 and 5% (w/w). Durian seedlings were grown in 2.5 L polybags arranged in randomised complete block design with 4 replicates per treatment. Plant height, collar diameter, pH, moisture content, number of branches and leaves, and plant health were monitored weekly for 94 days. Liquid fish fertiliser was used as organic fertiliser. Our results demonstrated that biochar can substitute at least 5% (w/w) peat moss without negatively affecting plant height, collar diameter, number of leaves and branches, and plant health. In addition, organic fertiliser is not required during the first 3 months of cultivation resulting in cost savings to the nursery operator. Plant height was found to be the most accurate yet simple monitoring parameter studied. A better understanding of the effect of higher biochar application rates as well as the number of times the potting medium can be reused without loss of potting medium properties and health can help to further cut nursery cost and reduce reliance on peat moss. 相似文献
73.
Identifying granite sources by SHRIMP U-Pb zircon geochronology: an application to the Lachlan foldbelt 总被引:23,自引:1,他引:23
Sue Keay David Steele William Compston 《Contributions to Mineralogy and Petrology》1999,137(4):323-341
The potential genetic link between granites and their host sediments can be assessed using zircon age inheritance patterns.
In the Lachlan fold belt, southeastern Australia, granites and associated high-grade metasedimentary rocks intrude low-grade
Ordovician country rock. This relationship is well-exposed in the Tallangatta region, northeast Victoria (part of the Wagga-Omeo
Metamorphic Complex). In this region granites (two I-types and two S-types) have intruded during the mid-late Silurian between
approximately 410–430 Ma based on the ages of magmatic zircons. The age spectra for inherited zircons from the granites have
been compared with those of detrital zircons from the enclosing low- and high-grade metasediments. In broad terms, both for
detrital zircons in all four sediments and for inherited zircons in three of the four granites, the dominant ages are early
Paleozoic and Late Precambrian, with sporadic older Precambrian ages extending up to 3.5 Ga. The ages of the youngest detrital
zircons from the low-grade Lockhart and Talgarno terranes limit the time of sedimentation to ca. 466 Ma or younger. The youngest
detrital zircons from two samples of the high-grade Gundowring terrane are 473 Ma, making these sediments Ordovician or younger,
not Cambrian as originally suggested. However, the individual age spectra for the four selected metasediments are not well
matched when closely examined. The age spectra of the inherited zircons in the granites also do not adequately match those
in any of the metasediments. Thus, the metasediments might not be representative of the actual source rocks of the granites.
While the exact source of the granites cannot be identified from the analysed samples, the existence of a large population
of ca. 495 Ma inherited zircon grains in the S-type granites requires that the granite source contains a significant proportion
of Cambrian or younger material. This does not preclude the existence of a Precambrian basement to the Lachlan fold belt but
indicates that at the level of S-type magma generation, a Cambrian and/or younger protolith is required.
Received: 28 August 1998 / Accepted: 7 July 1999 相似文献
74.
Assessment of agricultural drought using a simple water balance model in the Free State Province of South Africa 总被引:1,自引:1,他引:0
Water Requirement Satisfaction Index (WRSI) at three different probability levels (20%, 50%, and 80%) was used to quantify drought affecting rain-fed maize production in the Free State Province of South Africa based on climate data from 227 weather stations. Results showed high spatial variability in the suitability of different areas: the southern and southwestern localities are unsuitable due to high drought incidences; the northern, central, and western regions are marginally suitable; the eastern, northerneastern areas and a few patches in the northwest are highly suitable with relatively low drought severity. Proper choice of maize varieties to suit conditions at different localities is crucial. The Mann–Kendall test and coefficient of variation were further used to determine trends and temporal variability, respectively, in the WRSI, seasonal rainfall, and seasonal maize water requirements. Results of this analysis revealed no significant positive trends in the WRSI, no significant negative trends in seasonal rainfall, and no significant positive trends in maize water requirements, contradicting previous findings of increased drought severity. Seasonal rainfall and the WRSI showed high interseasonal variability, while seasonal maize water requirements showed low variability. In view of these observations, it is apparent that realignment of management practices is an overdue prerequisite for sustainable maize production. 相似文献
75.
Sustaining agricultural production and food security in Southern Africa: an improved role for climate prediction? 总被引:1,自引:0,他引:1
Emma Archer Elijah Mukhala Sue Walker Maxx Dilley Kennedy Masamvu 《Climatic change》2007,83(3):287-300
Livelihoods and household food security in the Southern African region can be extremely vulnerable to the negative effects
of climate stress as shown by the 2002–2004 ‘complex emergency.’ Climate prediction may prove a valuable resource in mitigating
these effects. If climate prediction is applied successfully, it may be able to help guide responses in populations at risk
to reduce vulnerability to climate stress. The study presented here seeks to understand what would constitute an improved
role for climate prediction in contributing to sustaining agricultural production and food security in Southern Africa. Investigation
undertaken during the 2002/2003 rainy season under regional conditions of elevated disaster risk shows, however, that a number
of weaknesses and gaps persistently characterize climate information systems in the Southern African region, and constrain
such systems’ ability to benefit key sectors, particularly agriculture. The stakeholder identification of such gaps forms
the basis for distilling concrete recommendations to improve process and organizational efficiency. Such recommendations,
while developmental, should better enable institutions and stakeholders involved in climate prediction to fulfill their potential
in supporting development of successful adaptation strategies in populations and sectors at risk. 相似文献
76.
77.
Lateglacial and Holocene relative sea‐level changes and first evidence for the Storegga tsunami in Sutherland,Scotland 下载免费PDF全文
Antony J. Long Natasha L. M. Barlow Sue Dawson Jon Hill James B. Innes Catherine Kelham Fraser D. Milne Alastair Dawson 《第四纪科学杂志》2016,31(3):239-255
78.
Scott A. SANDFORD Saša BAJT Simon J. CLEMETT George D. CODY George COOPER Bradley T. DEGREGORIO Vanessa
De VERA Jason P. DWORKIN Jamie E. ELSILA George J. FLYNN Daniel P. GLAVIN Antonio LANZIROTTI Thomas LIMERO Mildred P. MARTIN Christopher J. SNEAD Maegan K. SPENCER Thomas STEPHAN Andrew WESTPHAL Sue WIRICK Richard N. ZARE Michael E. ZOLENSKY 《Meteoritics & planetary science》2010,45(3):406-433
Abstract– Numerous potential sources of organic contaminants could have greatly complicated the interpretation of the organic portions of the samples returned from comet 81P/Wild 2 by the Stardust spacecraft. Measures were taken to control and assess potential organic (and other) contaminants during the design, construction, and flight of the spacecraft, and during and after recovery of the sample return capsule. Studies of controls and the returned samples suggest that many of these potential sources did not contribute any significant material to the collectors. In particular, contamination from soils at the recovery site and materials associated with the ablation of the heatshield do not appear to be significant problems. The largest source of concern is associated with the C present in the original aerogel. The relative abundance of this carbon can vary between aerogel tiles and even within individual tiles. This C was fortunately not distributed among a complex mixture of organics, but was instead largely present in a few simple forms (mostly as Si‐CH3 groups). In most cases, the signature of returned cometary organics can be readily distinguished from contaminants through their different compositions, nonterrestrial isotopic ratios, and/or association with other cometary materials. However, some conversion of the carbon indigenous to the flight aerogel appears to have happened during particle impact, and some open issues remain regarding how this C may be processed into new forms during the hypervelocity impact collection of the comet dust. 相似文献
79.
Mary Sue Bell 《Meteoritics & planetary science》2016,51(4):619-646
A study of pure, single crystal calcite shocked to pressures from 9.0 to 60.8 GPa was conducted to address contradictory data for carbonate shock behavior. The recovered materials were analyzed optically and by transmission electron microscopy (TEM), as well as by thermogravimetry (TGA), X‐ray diffraction (XRD), and Raman‐spectroscopy. In thin section, progressive comminution of calcite is observed although grains remain birefringent to at least 60.8 GPa. TGA analysis reveals a positive correlation between percent of mass loss due to shock and increasing shock pressure (R = 0.77) and suggests that shock loading leads to the modest removal of structural volatiles in this pressure range. XRD patterns of shocked Iceland spar samples produce peaks that are qualitatively and quantitatively less intense, more diffuse, and shift to lower o2θ. However, the regularity observed in these shocked powder patterns suggests that structures with very uniform unit cell separations persist to shock pressures as high as 60.8 GPa. Raman spectral analyses indicate no band asymmetry and no systematic peak shifting or broadening. TEM micrographs display progressively diminishing crystallite domain sizes. Selected area electron diffraction (SAED) patterns reveal no signatures of amorphous material. These data show that essentially intact calcite is recovered at shock pressures up to 60.8 GPa with only slight mass loss (~7%). This work suggests that the amount of CO2 gas derived from shock devolatilization of carbonate by large meteorite impacts into carbonate targets has been (substantially) overestimated. 相似文献
80.
Mark D. Bateman Andrew S. Carr Adam C. Dunajko Peter J. Holmes David L. Roberts Sue J. McLaren Robert G. Bryant Margaret E. Marker Colin V. Murray-Wallace 《Quaternary Science Reviews》2011,30(1-2):63-81
Barrier systems contain lengthy, but complex, records of long-term environmental fluctuations. The Wilderness embayment, South Africa, contains a system of shore-parallel barriers reaching up to 200 m above modern sea level. This study reports the results of chronological, topographical (both on- and off-shore), sedimentological and micromorphological analyses within the Wilderness embayment. Sixty-one new luminescence ages from sixteen sites in unconsolidated dunes and three separate barriers are presented which, when combined with previously published luminescence ages from the area, provide a high-resolution chronological framework for the emplacement and evolution of the barrier system. The preserved barriers have been constructed within at least the last two glacial–interglacial cycles with notable phases between 241–221 ka, 159–143 ka, 130–120 ka, 92–87 ka and post 6 ka. Multiple phases of barrier construction occurred during sea-level highstands, with sediment deposition on each individual barrier occurring over at least two interglacials. Holocene evolution of the system sheds light on earlier events, with dune preservation occurring only during early regression from the Mid-Holocene highstand. Tectonic stability at Wilderness allowed glacio-eustatically formed shorelines to occupy similar positions on multiple occasions. This, in conjunction with a relatively humid climate and a well-vegetated landscape, enabled deflated sediment from beaches to form dunes which stacked upon each other to form an extensive and complex vertical accretionary sequence. Repeated erosion and recycling of pre-existing barriers as well as barrier construction on what is currently the off-shore platform during still-stands in sea-level regressional cycles, when sea levels dropped below ca ?50 m from the present day, has added to the complexity of the preserved terrestrial barrier record. The Wilderness barrier system contrasts with barriers developed elsewhere in the world where higher rates of crustal uplift have allowed preservation of a more complete and more widely spaced palaeorecord. This research also shows the utility of integrating off-shore topography as revealed by bathymetry, with terrestrial topographic data for the better understanding of the evolution of palaeo-coastlines and the preserved dune record found on present-day coastal plains. Local variation in the topography of the continental shelf at Wilderness has generated spatial and temporal complexity within the sedimentary records of individual barriers as well as having a significant influence on preservation. 相似文献