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71.
Far-UV echelle spectroscopy of the radio-quiet QSO H1821+643 (zem=0.297), obtained with the Space Telescope Imaging Spectrograph (STIS) at approximately 7 km s-1 resolution, reveals four definite O vi absorption-line systems and one probable O vi absorber at 0.15相似文献
72.
Hornblende geothermometry of amphibolite layers of the Popple Hill gneiss, north-west Adirondack Lowlands, New York, USA 总被引:1,自引:0,他引:1
The exchange reaction tschermakite+2 diopside+2 quartz=tremolite+2 anorthite (HPCQ), in combination with the thermodynamic database TWQ (version 1.02, Berman, 1991), has been evaluated for its usefulness as a geothermometer. This reaction, which is both water conserving (independent of water fugacity) and which does not require the presence of garnet, is well suited for studying pyroxene‐bearing amphibolites. As an application of this geothermometer, we have re‐examined the amphibolites occurring in the Popple Hill gneiss of the Adirondack Lowlands of New York, USA, to better understand the magnitude of temperature variation preserved in the amphibolites themselves in this classic locality. At an assumed constant pressure of 7 kbar, the temperatures range from 619 to 682 °C from Edwards to Pierrepont and are uncorrelated with either distance along the strike of the region or with modal mineralogical variations. Hornblende exhibits a narrow compositional range suggesting that there has been little or no thermal gradient along the strike of the Lowlands. Temperatures recorded just north of Colton are, however, distinctly higher (694–758 °C). Although it is likely that the Popple Hill gneiss amphibolites experienced some effects of progressive metamorphism, particularly in the vicinity of Colton, the variations in modal mineralogy are most likely the result of such factors as local variations in the bulk chemistry of the protolith and in the fugacity of H2O due to infiltration of diluting species (e.g. CO2, CH4), rather than a regional temperature variation. Temperatures recorded by the HPCQ geothermometer reported here are similar in magnitude and geographic trend to those reported for graphite–calcite carbon‐isotope thermometry by Kitchen & Valley (1995), suggesting that peak metamorphism in the Adirondack Lowlands involved laterally extensive and fairly uniform isotherms. 相似文献
73.
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75.
Katie Jenkins Jim Hall Vassilis Glenis Chris Kilsby Mark McCarthy Clare Goodess Duncan Smith Nick Malleson Mark Birkin 《Climatic change》2014,124(1-2):105-117
High temperatures and heatwaves can cause large societal impacts by increasing health risks, mortality rates, and personal discomfort. These impacts are exacerbated in cities because of the Urban Heat Island (UHI) effect, and the high and increasing concentrations of people, assets and economic activities. Risks from high temperatures are now widely recognised but motivation and implementation of proportionate policy responses is inhibited by inadequate quantification of the benefits of adaptation options, and associated uncertainties. This study utilises high spatial resolution probabilistic projections of urban temperatures along with projections of demographic change, to provide a probabilistic risk assessment of heat impacts on urban society. The study focuses on Greater London and the surrounding region, assessing mortality risk, thermal discomfort in residential buildings, and adaptation options within an integrated framework. Climate change is projected to increase future heat-related mortality and residential discomfort. However, adjusting the temperature response function by 1–2 °C, to simulate adaptation and acclimatisation, reduced annual heat related mortality by 32–69 % across the scenarios tested, relative to a no adaptation scenario. Similar benefits of adaptation were seen for residential discomfort. The study also highlights additional benefits in terms of reduced mortality and residential discomfort that mitigating the urban heat island, by reducing albedo and anthropogenic heat emissions, could have. 相似文献
76.
David M. Jenkins 《Contributions to Mineralogy and Petrology》2011,162(4):725-738
The reaction glaucophane + 2 diopside + 2 quartz = tremolite + 2 albite is proposed to model the transition from the blueschist
to greenschist facies. This reaction was investigated experimentally over the range of 1.0–2.1 GPa and 500–800°C using synthetic
phases in the chemical system Na2O–CaO–MgO–Al2O3–SiO2–H2O. Reversals of this reaction were possible at 500 and 550°C and growth of the low-pressure assemblage at 600°C; however,
at temperatures of 600°C and higher and at pressures above 1.6 GPa omphacite nucleation (at the expense of diopside and albite)
became quite strong and prevented attaining clear reversals of this reaction. Compositional changes in the amphiboles were
determined by both electron microprobe analyses and correlations between unit-cell dimensions and composition. Glaucophane
and particularly tremolite showed clear signs of compositional re-equilibration and merged to a single amphibole of winchite
composition by about 754°C. These data were used to model the miscibility gap between glaucophane and tremolite using either
the asymmetric multicomponent formulism parameters of W
TR,GL
of 68 kJ with αTR of 1.0 and αGL of 0.75 or a simple two-site asymmetric thermodynamic mixing expression with Margules parameters W
NaCa
of 13.4 kJ and W
CaNa
of 19.3 kJ. Combination of these thermodynamic models of the miscibility gap with extant thermodynamic data for the other
phases yields a calculated location of the above reaction, involving pure diopside and albite, that is in good agreement with
the observed experimental reversals and amphibole compositions over the range of 0.94–1.93 GPa and 400–754°C. The calculated
effect of jadeite solid solution into diopside is to reduce the dP/dT slope from 0.0028 to 0.0021 GPa/°C and decrease the
pressure by 0.28 GPa at 754°C. The dP/dT slope of this reaction boundary lies close to a linear geotherm of 13°C/km and is
consistent with the slopes of other solid–solid reactions that have been used to model the blueschist-to-greenschist facies
transition. 相似文献
77.
78.
A model of the ionosphere and plasmasphere is used to study some of the signatures of an idealized SAID (subauroral ion drift) event in the nightside ionosphere. A closed subauroral tube of plasma is considered under solar maximum atmospheric conditions and the westward velocity of 3 km s−1 persists for 30 min. By pursuing, in turn, calculations in which plasma diffusion is suppressed and in which chemical loss of O+ is suppressed, the signatures of O+ chemistry alone and of field-aligned diffusion alone during the SAID event can be elucidated. Both chemical loss and transport contribute to the decay of the F-layer. Results from full calculations (including both chemistry and transport) demonstrate strong chemical-transport interaction. 相似文献
79.
80.
P. A. Thomas Orrarujee Muanwong F. R. Pearce H. M. P. Couchman A. C. Edge A. Jenkins L. Onuora 《Monthly notices of the Royal Astronomical Society》2001,324(2):450-462
We have extracted over 400 clusters, covering more than two decades in mass, from three simulations of the τ CDM cosmology. This represents the largest uniform catalogue of simulated clusters ever produced. The clusters exhibit a wide variety of density profiles. Only a minority are well-fitted in their outer regions by the widely used density profile of Navarro, Frenk & White (NFW), which is applicable to relaxed haloes. Others have steeper outer density profiles, show sharp breaks in their density profiles, or have significant substructure. If we force a fit to the NFW profile, then the best-fitting concentrations decline with increasing mass, but this is driven primarily by an increase in substructure as one moves to higher masses. The temperature–mass relations for properties measured within a sphere enclosing a fixed overdensity all follow the self-similar form, T ∝ M 2/3 ; however, the normalization is lower than the value inferred for observed clusters. The temperature–mass relations for properties measured within a fixed physical radius are significantly steeper then this. Both can be accurately predicted using the NFW model. 相似文献