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51.
Unraveling the Schneeberg garnet puzzle: a numerical model of multiple nucleation and coalescence 总被引:1,自引:0,他引:1
Harvey?T.?Dobbs Luca?PeruzzoEmail author Flavio?Seno Richard?Spiess David?J.?Prior 《Contributions to Mineralogy and Petrology》2003,146(1):1-9
A quantitative kinetic model for the growth of the different garnet porphyroblast microstructures (type 1 and type 2) of the Western Schneeberg Complex (WSC) is presented. These porphyroblasts formed by a multiple nucleation and coalescence mechanism. Our numerical simulation shows that at constant diffusion rates: (1) low interface reaction rates result in a fully amalgamated porphyroblast (type 2); (2) intermediate reaction rates result in a porphyroblast, where coalescence of grains closer to the margin prevented amalgamation of those in the centre (similar to type 1 porphyroblasts); and (3) high interface reaction rates result in a porphyroblast microstructure with an atoll form. All three microstructures are characterised by distinctive cluster size distributions. A 2-D cluster size distribution analysis of type 1 porphyroblasts of WSC shows that these did not form because of intermediate interface reaction rates, but because the diffusion rate of nutrients was too low to keep pace with the interface reaction rate.Editorial responsibility: T.L. Grove 相似文献
52.
Mark A Sephton Lauren E Howard Phil A Bland Rachael H James Sara S Russell Dave J Prior Mark E Zolensky 《Astronomy& Geophysics》2006,47(6):6.37-6.38
What are the strange dark clasts within carbonaceous chondrites? How did they form? And what do they tell us about the early solar system? Mark Sephton, one of a team investigating the Allende meteorite, summarizes their findings. 相似文献
53.
Erosional furrows are recognized on the seafloor off the Mississippi Delta, trending downslope over the shelf edge. They occur
in water depths of 150 to 380 m seaward of presently active mudslides on the delta slope. The furrows cross an area of former
mudslide deposition and part of the outer shelf. Their origin is likely to be related to cross-shelf secondary helical flows,
although delta-front mass movement could cause similar erosional gouging. 相似文献
54.
W. J. Wiseman Jr. Y. -B. Fan B. D. Bornhold G. H. Keller Z. -Q. Su D. B. Prior Z. -X. Yu L. D. Wright F. -Q. Wang Q. -Y. Qian 《Geo-Marine Letters》1986,6(2):107-113
Studies to date indirectly indicate that only a small percentage of the sediment discharged by the Huanghe (Yellow River) is presently transported from the Gulf of Bohai to the Huanghai (Yellow Sea). Direct measurements in early summer 1985 show low concentrations of suspended sediment east of 119°45E but high concentrations in Bohai Bay. Stokes drift associated with an amphidrome of the M2 tide may contribute to a northwestward transport of Huanghe sediment. 相似文献
55.
N. Z. Lu J. N. Suhayda D. B. Prior B. D. Bornhold G. H. Keller Wm. J. Wiseman Jr. L. D. Wright Z. S. Yang 《Geo-Marine Letters》1991,11(1):9-15
Laboratory analysis of clayey silt from the offshore Huanghe Delta reveals thixotropic behavior. Fall cone tests show strength
loss on remolding followed by strength regain at virtually constant water contents. The delta-front sediments experience wave
loading during storms and widespread mass movement has been detected by acoustic surveying. Measurements from sea floor instruments
and repeated sonographic survey during storms indicate repeated episodes of sediment motion consistent with thixotropy. 相似文献
56.
The frequency of turbidity currents in Bute Inlet and Knight Inlet (British Columbia, Canada) was monitored. A prototype instrument (turbidity event detector) was deployed adjacent to prominent incised sea-floor channels. Approximately 25–30 turbidity currents occur annually. They appear closely correlated to periods of higher river discharge into the heads of the fjords. Two peaks in both discharge and turbidity current fequency occur, one in response to snow melt in late June–early July, the other to glacier melt in August. Virtually no turbidity currents were observed in winter. River mouth bars, channel deposits, and other deltaic sediments build up during lower discharge periods and are swept onto the steep delta front and into subaqueous channels, along with bedload, during floods. 相似文献
57.
Scott A. Whattam Roger H. Hewins Bosmat A. Cohen Nicholas C. Seaton David J. Prior 《Earth and Planetary Science Letters》2008,269(1-2):200-211
Granoblastic olivine aggregates (GOA) have been discovered in some Type I magnesian chondrules within carbonaceous chondrites by Libourel and Krot [Libourel, G., Krot, A.N., 2007. Evidence for the presence of planetesimal material among the precursors of magnesian chondrules of nebular origin. Earth Planet. Sci. Lett. 254, 1–8], who proposed an origin from pre-existing planetesimals. Amoeboid olivine aggregates (AOA), generally considered as aggregates of solar nebula condensates and found within similar carbonaceous chondrites, display similar equilibrium texture, though on a finer scale. For these reasons, we conducted experiments to determine if annealing of olivine required time scales appropriate to planetesimal or nebular heating. Pressed < 43 µm and < 63 µm San Carlos olivine powder (Fo88.4) was isothermally heated at temperatures ranging from 1350–1550 °C for 1–100 h. The 100 h runs yield olivine aggregates with well-developed granoblastic texture at all temperatures, manifest as a network of randomly-oriented and sutured olivine grains with 120° triple junctions. Individual olivine grains are 4–6 sided and polygonal by 1450 °C and equigranular texture is developed at high temperature (1500–1550 °C). Melting of olivine commences at 1450–1500 °C and aids in ‘ripening’ and suturing (grain coarsening and grain boundary migration). Textural equilibrium is clearly met at 1550 °C. A planetesimal origin cannot be ruled out; however, the experimental evidence reveals that granoblastic texture can be reproduced in an interval not inconsistent with heating times for nebular objects. GOA may have experienced higher degrees of thermal processing than the finer-grained AOA. If the precursors were the same, grain coarsening would have to be accompanied by modification to bulk and isotopic compositions. However, the precursors could have been olivine condensates formed later than AOA. Annealing may have been a widespread process operating in the primordial solar nebula responsible for thermal processing and formation of GOA prior to their incorporation into chondrules. 相似文献
58.
This article reviews the theoretical foundations for the concept of peak minerals; drawing on similarities and differences
with peak oil as modelled using Hubbert style curves. Whilst several studies have applied peak modelling to selected minerals,
discussion of the appropriateness of using Hubbert style curves in the minerals context remains largely unexplored. Our discussion
focuses on a comparison between oil and minerals, on the key variables: rates of discovery, estimates of ultimately recoverable
resources and demand and production trends. With respect to minerals, there are several obstacles which complicate the application
of Hubbert style curves to the prediction of future mineral production, including the lack of accurate discovery data, the
effect of uncertain reserve estimates, and varying ore quality and quantity. Another notable difference is that while oil
is often combusted during use, minerals are used to make metals which are inherently recyclable. Notwithstanding, by using
a range of estimates of resources and/or reserves, a period of time can be identified which indicates when a peak in minerals
production may occur. This information may then be used to plan for a transition from using a potentially constrained resource,
to using substitutes if available, or to reducing demand for that mineral in society. 相似文献
59.
D. Heath Jones Mike A. Read Will Saunders Matthew Colless Tom Jarrett Quentin A. Parker Anthony P. Fairall † Thomas Mauch Elaine M. Sadler Fred G. Watson Donna Burton Lachlan A. Campbell Paul Cass Scott M. Croom John Dawe † Kristin Fiegert Leela Frankcombe Malcolm Hartley John Huchra Dionne James Emma Kirby Ofer Lahav John Lucey Gary A. Mamon Lesa Moore Bruce A. Peterson Sayuri Prior Dominique Proust Ken Russell Vicky Safouris Ken-ichi Wakamatsu Eduard Westra Mary Williams 《Monthly notices of the Royal Astronomical Society》2009,399(2):683-698
We report the final redshift release of the 6dF Galaxy Survey (6dFGS), a combined redshift and peculiar velocity survey over the southern sky (| b | > 10°) . Its 136 304 spectra have yielded 110 256 new extragalactic redshifts and a new catalogue of 125 071 galaxies making near-complete samples with ( K , H , J , r F , b J ) ≤ (12.65, 12.95, 13.75, 15.60, 16.75) . The median redshift of the survey is 0.053. Survey data, including images, spectra, photometry and redshifts, are available through an online data base. We describe changes to the information in the data base since earlier interim data releases. Future releases will include velocity dispersions, distances and peculiar velocities for the brightest early-type galaxies, comprising about 10 per cent of the sample. Here we provide redshift maps of the southern local Universe with z ≤ 0.1 , showing nearby large-scale structures in hitherto unseen detail. A number of regions known previously to have a paucity of galaxies are confirmed as significantly underdense regions. The URL of the 6dFGS data base is http://www-wfau.roe.ac.uk/6dFGS . 相似文献
60.
Mathematical Geosciences - 相似文献