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221.
We define a procedure which allows estimation of the optical thickness of a cometarydust coma and the ambient illumination
of the nucleus for any given comet, if estimatesof the nucleus radius and the dust activity (Afρ) are available. The calculation
isperformed for a singly scattering coma with a cos(ϑ) distribution of dust overits day side. We find that the ambient illumination
is of the same order as the incidentsunlight if the optical thickness is of order one. The optical thickness increases, all
elseequal, linearly with the nucleus radius. Therefore the effect of the presence of the comamay be neglected for small (≈
1 km diameter) comets, but is important forcomets such as 1P/Halley and Hale–Bopp. 相似文献
222.
J. Clem W. Droege P. A. Evenson H. Fischer G. Green D. Huber H. Kunow D. Seckel 《Astroparticle Physics》2002,16(4):1145-395
We present results from the initial flight of our Balloon Air CHerenkov (BACH) payload. BACH detects air Cherenkov radiation from cosmic ray nuclei as coincident flashes in two optical modules. The flight (dubbed PDQ–BACH) took place on April 22, 1998 from Ft. Sumner, New Mexico. During an exposure of 2.75 h, with a typical threshold energy for iron nuclei of 2.2×1013 eV, we observed several events cleanly identifiable as iron group nuclei. Analysis of the data yields a new flux measurement that is fully consistent with that reported by other investigations. 相似文献
223.
Zdenka Misanovic Lawrence Cram Anne Green 《Monthly notices of the Royal Astronomical Society》2002,335(1):114-124
A sample of eight small-diameter radio sources has been selected from the Molonglo Galactic Plane Survey (MGPS) as candidates for young Galactic supernova remnants. The sources have been identified in the IRAS and Midcourse Space Experiment infrared data bases and imaged in the H107α radio recombination line (RRL) using the Australia Telescope Compact Array (ATCA). Seven of the sources display high ratios of infrared-to-radio-continuum flux density and/or detectable RRLs and are almost certainly H ii regions. One source (G282.8−1.2) is identified as a possible new young Galactic supernova remnant, based on its relatively weak infrared emission, steep radio spectrum, and possible X-ray emission. The adopted method for distinguishing thermal and non-thermal Galactic radio sources seems promising and could be fruitfully applied to more than 100 small-diameter sources listed in the MGPS. 相似文献
224.
The 'blurring of boundaries' between 'work' and 'home': perspectives from case studies in the East Midlands 总被引:2,自引:0,他引:2
Summary This article seeks to contribute to the debate surrounding the temporal and spatial 'blurring of boundaries' between 'home' and 'work' by presenting selected results from an empirical study of dual career households in the East Midlands relating to the 'temporal' and 'spatial' strategies adopted by individuals and households for managing the demands of 'paid work careers' and 'household careers'. 相似文献
225.
J. D. Silverman K. A. Eriksen P. J. Green S. H. Saar 《Monthly notices of the Royal Astronomical Society》2001,323(3):577-583
We report the serendipitous discovery of a flare star observed with the ROSAT X-ray observatory. From optical spectra, which show strong and variable emission lines of the hydrogen Balmer series and neutral helium, we classify this object as a M3.0Ve star, and estimate a distance of 52 pc from published photometry. Owing to the close proximity of the star (13.6 arcmin) to the calibration source and RS CVn binary AR Lacertae, long-term X-ray coverage is available in the ROSAT archive (∼50 h spanning 6.5 yr). Two large flare events occurred early in the mission (1990 June–July), and the end of a third flare was detected in 1996 June. One flare, observed with the Position Sensitive Proportional Counter (PSPC), had a peak luminosity L X =1.1×1030 erg s−1 , an e-folding rise time of 2.2 h and a decay time of 7 h. This decay time is one of the longest detected on a dMe star, providing evidence for the possibility of additional heating during the decay phase. A large High Resolution Imager (HRI) flare (peak L X =2.9×1030 erg s−1 ) is also studied. The 'background' X-ray emission is also variable – evidence for low-level flaring or microflaring. We find that 59 per cent of the HRI counts and 68 per cent of the PSPC counts are caused by flares. At least 41 per cent of the HRI exposure time and 47 per cent of the PSPC are affected by detectable flare enhancement. 相似文献
226.
Larissa F. Dobrzhinetskaya Harry W. Green II Alex P. Renfro Krassimir N. Bozhilov Dirk Spengler Herman L. M. van Roermund 《地学学报》2004,16(6):325-330
Our experimental simulations of the exhumation path of mantle peridotites show that high‐temperature (1400 °C) decompression of lherzolite from 14 to 13 and 12 GPa results in exsolution of interstitial blebs of diopside and Mg2SiO4 (wadsleyite) lamellae from majoritic garnet. At lower pressures (from 8 to 5 GPa, at T = 1400 °C) only enstatite exsolves as blebs at garnet boundaries. Continuous high‐temperature decompression from 14 to 7 GPa produces zoned majoritic garnet containing blebs of exsolved pyroxenes inside garnet rims. No intracrystalline precipitation of pyroxene was observed in garnet, although such lamellae are found in some natural garnet peridotites. The explanation appears to be the three orders of magnitude difference in grain size between experimental and natural specimens. Our data suggest that Mg2SiO4 and diopside exsolutions reflect the deepest point of the exhumation path of garnet peridotites, whereas enstatite precipitation may be restricted to garnets with less majoritic component at shallower depths. 相似文献
227.
228.
229.
A.L. Jaques P.L. Lowenstein D.H. Green E. Kiss W.B. Nance S.R. Taylor N.G. Ware 《Meteoritics & planetary science》1975,10(4):289-301
The Ijopega (Papua New Guinea) meteorite is a new H6 group chondrite fall which contains olivine (Fa 19.9 mole %), bronzite (Fs 17.8 mole %), plagioclase (An 12.1 Or 6.3 Ab 81.6 mole %), diopside, kamacite, taenite, troilite, chromite and whitlockite. The meteorite is extensively recrystallized and brecciated, and shows evidence of moderate shock deformation. Examination of Fe2+ and Mg partitioning between ortho- and clinopyroxene indicates a high equilibration temperature (940° or 880 °C). Chemical analysis shows the meteorite to be rich in S, containing about twice the average H-group abundance. Trace elements, including REE, are in accord with established H-group chondrite abundances. 相似文献
230.
O. Groussin J. Licandro J. Helbert J. L. Reynaud P. Levacher M. Reyes García-Talavera V. Alí-Lagoa P. E. Blanc E. Brageot B. Davidsson M. Delbó M. Deleuze A. Delsanti J. J. Diaz Garcia K. Dohlen D. Ferrand S. F. Green L. Jorda E. Joven Álvarez J. Knollenberg E. Kührt P. Lamy E. Lellouch J. Le Merrer B. Marty G. Mas C. Rossin B. Rozitis J. Sunshine P. Vernazza S. Vives 《Experimental Astronomy》2016,41(1-2):95-115
We present THERMAP, a mid-infrared spectro-imager for space missions to small bodies in the inner solar system, developed in the framework of the MarcoPolo-R asteroid sample return mission. THERMAP is very well suited to characterize the surface thermal environment of a NEO and to map its surface composition. The instrument has two channels, one for imaging and one for spectroscopy: it is both a thermal camera with full 2D imaging capabilities and a slit spectrometer. THERMAP takes advantage of the recent technological developments of uncooled microbolometer arrays, sensitive in the mid-infrared spectral range. THERMAP can acquire thermal images (8–18 μm) of the surface and perform absolute temperature measurements with a precision better than 3.5 K above 200 K. THERMAP can acquire mid-infrared spectra (8–16 μm) of the surface with a spectral resolution Δλ of 0.3 μm. For surface temperatures above 350 K, spectra have a signal-to-noise ratio >60 in the spectral range 9–13 μm where most emission features occur. 相似文献