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排序方式: 共有185条查询结果,搜索用时 31 毫秒
161.
M. A. Zwaan M. J. Meyer R. L. Webster L. Staveley-Smith M. J. Drinkwater D. G. Barnes R. Bhathal W. J. G. de Blok M. J. Disney R. D. Ekers K. C. Freeman D. A. Garcia B. K. Gibson J. Harnett P. A. Henning M. Howlett H. Jerjen M. J. Kesteven V. A. Kilborn P. M. Knezek B. S. Koribalski S. Mader M. Marquarding R. F. Minchin J. O'Brien T. Oosterloo M. J. Pierce R. M. Price M. E. Putman E. Ryan-Weber S. D. Ryder E. M. Sadler J. Stevens I. M. Stewart F. Stootman M. Waugh A. E. Wright 《Monthly notices of the Royal Astronomical Society》2004,350(4):1210-1219
162.
163.
Mass-to-light ratio gradients in early-type galaxy haloes 总被引:1,自引:0,他引:1
N. R. Napolitano M. Capaccioli A. J. Romanowsky N. G. Douglas M. R. Merrifield K. Kuijken M. Arnaboldi O. Gerhard K. C. Freeman 《Monthly notices of the Royal Astronomical Society》2005,357(2):691-706
Owing to the fact that the near future should see a rapidly expanding set of probes of the halo masses of individual early-type galaxies, we introduce a convenient parameter for characterizing the halo masses from both observational and theoretical results: ∇ℓ ϒ , the logarithmic radial gradient of the mass-to-light ratio. Using halo density profiles from Λ-cold dark matter (CDM) simulations, we derive predictions for this gradient for various galaxy luminosities and star formation efficiencies εSF . As a pilot study, we assemble the available ∇ℓ ϒ data from kinematics in early-type galaxies – representing the first unbiased study of halo masses in a wide range of early-type galaxy luminosities – and find a correlation between luminosity and ∇ℓ ϒ , such that the brightest galaxies appear the most dark-matter dominated. We find that the gradients in most of the brightest galaxies may fit in well with the ΛCDM predictions, but that there is also a population of fainter galaxies whose gradients are so low as to imply an unreasonably high star formation efficiency εSF > 1 . This difficulty is eased if dark haloes are not assumed to have the standard ΛCDM profiles, but lower central concentrations. 相似文献
164.
165.
D.E. Freeman K. Yoshino J.R. Esmond W.H. Parkinson 《Planetary and Space Science》1984,32(9):1125-1134
Laboratory measurements at high resolution of the absorption cross section of SO2 at the temperature 213 K have been performed in the wavelength region 172–240 nm with a 6.65 m scanning spectrometer/spectrograph operated at an instrumental width of 0.002 nm. The measured cross sections are presented graphically in representative wavelength regions and are available throughout the region 172–240 nm at wavenumber intervals of 0.4–0.1 cm?1 as a numerical tabulation stored on magnetic tape from the National Space Science Data Center, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, U.S.A. The measured cross sections, which are relevant to the photochemistry of planetary atmospheres, possess significantly more spectroscopic structure, and are more accurate, than previous measurements made at lower resolution. 相似文献
166.
167.
J.E.T. Channell R. Freeman F. Heller W. Lowrie 《Earth and Planetary Science Letters》1982,58(2):189-201
Magnetite, haematite, and to a minor extent maghaemite are recognised in the Cretaceous and Paleocene red pelagic limestones at Gubbio. The magnetite is detrital (or biological), whereas the haematite grew during diagenesis from a goethitic precursor. Thermal and AF demagnetization of samples collected from close to reversal boundaries indicate that the various magnetization components do not record the polarity reversal at exactly the same stratigraphic level. In the few tens of centimetersbelow a recorded geomagnetic reversal, defined by the magnetite magnetization, some of the haematite grains are magnetized in the post-reversal field. The blocking temperature spectra of this haematite fraction (with post-reversal magnetization) are found to shift toward higher temperatures as the reversal boundary is approached. The blocking temperature spectra reflect the grain size spectra of the haematite, which we interpret as arising by the continual nucleation of grains down to a certain burial depth where the conditions are no longer conducive to further haematite growth. The depth below reversal boundaries to which haematite with post-reversal magnetization can occur, is estimated to be about 60 cm (after compaction), and is equivalent to a time of about 105 years for these particular sediments. A detailed study of the magnetization components at reversal boundaries indicates that the first diagenetic growth of haematite through the single-domain critical volume occurs prior to the mechanical fixation of the detrital (or biological) magnetite. Subsequently the diagenetic haematite grains do not rotate in response to the ambient geomagnetic field polarity as easily as the magnetite, because of their occurrence as pigmentary coatings on larger non-magnetic grains. 相似文献
168.
169.
Bidigare RR Fluegge A Freeman KH Hanson KL Hayes JM Hollander D Jasper JP King LL Laws EA Milder J Millero FJ Pancost R Popp BN Steinberg PA Wakeham SG 《Global biogeochemical cycles》1997,11(2):279-292
The carbon isotopic fractionation accompanying formation of biomass by alkenone-producing algae in natural marine environments varies systematically with the concentration of dissolved phosphate. Specifically, if the fractionation is expressed by epsilon p approximately delta e - delta p, where delta e and delta p are the delta 13C values for dissolved CO2 and for algal biomass (determined by isotopic analysis of C37 alkadienones), respectively, and if Ce is the concentration of dissolved CO2, micromole kg-1, then b = 38 + 160*[PO4], where [PO4] is the concentration of dissolved phosphate, microM, and b = (25 - epsilon p)Ce. The correlation found between b and [PO4] is due to effects linking nutrient levels to growth rates and cellular carbon budgets for alkenone-containing algae, most likely by trace-metal limitations on algal growth. The relationship reported here is characteristic of 39 samples (r2 = 0.95) from the Santa Monica Basin (six different times during the annual cycle), the equatorial Pacific (boreal spring and fall cruises as well as during an iron-enrichment experiment), and the Peru upwelling zone. Points representative of samples from the Sargasso Sea ([PO4] < or = 0.1 microM) fall above the b = f[PO4] line. Analysis of correlations expected between mu (growth rate), epsilon p, and Ce shows that, for our entire data set, most variations in epsilon p result from variations in mu rather than Ce. Accordingly, before concentrations of dissolved CO2 can be estimated from isotopic fractionations, some means of accounting for variations in growth rate must be found, perhaps by drawing on relationships between [PO4] and Cd/Ca ratios in shells of planktonic foraminifera. 相似文献
170.
Simple calculations indicate that the spatial density in the galaxy of extinct civilizations, and of planets inhabited by intelligent creatures who do not have technical civilizations, may be quite large. 相似文献