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The magnetosphere, ionosphere and solar–terrestrial physics community gathered at the Department of Chemistry, University of York from 9–11 April 2001. Neil Arnold and Ian Mann report. 相似文献
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The dynamics of thin shells with variable viscosity and the origin of toroidal flow in the mantle 总被引:4,自引:0,他引:4
Neil M. Ribe 《Geophysical Journal International》1992,110(3):537-552
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Neil Trentham 《Monthly notices of the Royal Astronomical Society》1998,293(1):71-88
We present the luminosity function and measurements of the scalelengths, colours and radial distribution of dwarf galaxies in the Coma cluster down to R =24. Our survey area is 674 arcmin2 ; this is the deepest and most detailed survey covering such a large area.
Our measurements agree with those of most previous authors at bright and intermediate magnitudes. The new results are as follows.
(1) Galaxies in the Coma cluster have a luminosity function φ( L )∝ Lα that is steep (α∼−1.7) for −15< MR <−11, and is shallower brighter than this. The curvature in the luminosity function at MR ∼−15 is statistically significant.
(2) The galaxies that contribute most strongly to the luminosity function at −14< MR <−12 have colours and scalelengths that are consistent with those of local dwarf spheroidal galaxies placed at the distance of Coma.
(3) These galaxies with −14< MR <−12 have a colour distribution that is very strongly peaked at B − R =1.3. This is suggestive of a substantial degree of homogeneity in their star formation histories and metallicities.
(4) These galaxies with −14< MR <−12 also appear to be more confined to the cluster core ( r ∼200 kpc) than the brighter galaxies. Alternatively, this observation may be explained in part or whole by the presence of an anomalously high number of background galaxies behind the cluster core. Velocity measurements of these galaxies would distinguish between these two possibilities. 相似文献
Our measurements agree with those of most previous authors at bright and intermediate magnitudes. The new results are as follows.
(1) Galaxies in the Coma cluster have a luminosity function φ( L )∝ L
(2) The galaxies that contribute most strongly to the luminosity function at −14< M
(3) These galaxies with −14< M
(4) These galaxies with −14< M
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The fractionation of 13C between calcite and graphite, Δ(Cc-Gr). is consistently small (2.6–4.8 permil) in 34 assemblages from upper amphibolite- and granulite-facies marbles of the Grenville Province. In 25 samples from the Adirondack Mountains, New York, it decreases regularly with increasing metamorphic temperature. The fractionations are independent of absolute δ13C values of calcite (?2.9 to +5.0). For T = 600–800°C, the Adirondack data are described by Δ(Cc-Gr) = ?0.00748T (°C) + 8.68. This good correlation between Δ and T suggests that carbon isotope equilibrium was attained in these high-grade marbles and that the theoretical calculations of this fractionation by Bottinga are approximately 2 permil too large in this temperature range. Because of the relatively high temperature sensitivity suggested by these results and by Bottinga's calculations, and the pressure independence of isotope fractionation, Δ(Cc-Gr) may provide a very good thermometer for high-grade marbles.Comparison of this field calibration for Δ(Cc-Gr) vs temperature with results from other terranes supports the utility of Δ(Cc-Gr) for geothermometry and suggests that graphite is much more sluggish to exchange than calcite, that exchange between calcite and graphite occurs at temperatures as low as 300°C, and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500–600°C.Because 13C exchange is an unavoidable metamorphic process at temperatures above 300°C, high values of δ13C(Gr) in moderate- to high-grade carbonate-bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite. 相似文献
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Allan R. Chivas James R. ONeil George Katchan 《Earth and Planetary Science Letters》1984,68(2):326-334
Hydrogen and oxygen isotope analyses of sericites and kaolinites from four young porphyry copper deposits (Ok Tedi (1.2 Ma) and Yandera (6.5 Ma), Papua New Guinea; Koloula (1.5 Ma), Solomon Islands; and Waisoi (<5 Ma), Fiji) indicate that the fluids from which these minerals precipitated were of mixed magmatic and non-magmatic sources. The non-magmatic component of the fluid from the island arc deposits (Koloula, Waisoi) was ocean water.For Ok Tedi, the non-magmatic component was a meteoric water with an isotopic composition different from that of the present meteoric water in the region. The isotopic signature of the former meteoric water is consistent with a surface elevation of 200 m a.s.l. or less at the time of mineralization. The deposit was later exposed and supergene kaolinitization commenced at approximately 1200 m a.s.l. Uplift and erosion has continued to the present at which time the elevation of the exposed deposit is 1800 m a.s.l. This rate of uplift is consistent with that known from other geological evidence. If the rate of uplift were approximately constant during the last 1.2 Ma, the age of supergene enrichment can be dated at approximately 0.4 Ma B.P.Similarly, influx of meteoric water at Yandera occurred when the ground surface above the deposit was at an elevation of approximately 600 m a.s.l. The deposit's present elevation is 1600 m a.s.l. In this case a total uplift of approximately 2.2 km is indicated, with removal of 1.2 km of overburden by erosion. 相似文献