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排序方式: 共有324条查询结果,搜索用时 31 毫秒
321.
Simon T. Belt Guillaume Mass Lindsay L. Vare Steven J. Rowland Michel Poulin Marie-Alexandrine Sicre Makoto Sampei Louis Fortier 《Marine Chemistry》2008,112(3-4):158-167
A C25 highly branched isoprenoid (HBI) monoene hydrocarbon, designated IP25, has been proposed previously to originate from diatoms living in Arctic sea ice, while the presence of IP25 in sediments has been suggested to be a proxy for the occurrence of former Arctic sea ice. Here, we show that the 13C isotopic composition of IP25 in sea ice, in sediment trap material collected under sea ice, and in high latitude northern sediments, is distinctive (isotopically ‘heavy’) and distinguishable from that of organic matter of planktonic or terrigenous origin. Mean δ13C values for IP25 were − 22.3 ± 0.4‰ (sea ice), − 19.6 ± 1.1‰ (sediment traps) and − 19.3 ± 2.3‰ (sediments). These measurements, therefore, support further the proposed use of IP25 as an Arctic sea ice proxy. 相似文献
322.
Jean-Pierre Rivet Farrokh Vakili Olivier Lai David Vernet Mathilde Fouché William Guerin Guillaume Labeyrie Robin Kaiser 《Experimental Astronomy》2018,46(3):531-542
More than sixty years after the first intensity correlation experiments by Hanbury Brown and Twiss, there is renewed interest for intensity interferometry techniques for high angular resolution studies of celestial sources. We report on a successful attempt to measure the bunching peak in the intensity correlation function for bright stellar sources with 1 meter telescopes (I2C project). We propose further improvements of our preliminary experiments of spatial interferometry between two 1 m telescopes, and discuss the possibility to export our method to existing large arrays of telescopes. 相似文献
323.
David V. Bekaert Guillaume Avice Bernard Marty 《Meteoritics & planetary science》2018,53(6):1238-1251
Lunar basalt 15016 (~3.3 Ga) is among the most vesicular (50% by volume) basalts recovered by the Apollo missions. We investigated the possible occurrence of indigenous lunar nitrogen and noble gases trapped in vesicles within basalt 15016, by crushing several cm-sized chips. Matrix/mineral gases were also extracted from crush residues by fusion with a CO2 laser. No magmatic/primordial component could be identified; all isotope compositions, including those of vesicles, pointed to a cosmogenic origin. We found that vesicles contained ~0.2%, ~0.02%, ~0.002%, and ~0.02% of the total amount of cosmogenic 21Ne, 38Ar, 83Kr, and 126Xe, respectively, produced over the basalt's 300 Myr of exposure. Diffusion/recoil of cosmogenic isotopes from the basaltic matrix/minerals to intergrain joints and vesicles is discussed. The enhanced proportion of cosmogenic Xe isotopes relative to Kr detected in vesicles could be the result of kinetic fractionation, through which preferential retention of Xe isotopes over Kr within vesicles might have occurred during diffusion from the vesicle volume to the outer space through microleaks. This study suggests that cosmogenic loss, known to be significant for 3He and 21Ne, and to a lesser extent for 36Ar (Signer et al. 1977 ), also occurs to a negligible extent for the heaviest noble gases Kr and Xe. 相似文献
324.
Hubert Gagné Patrick Lajeunesse Guillaume St-Onge Andrée Bolduc 《Geo-Marine Letters》2009,29(3):191-200
Multibeam sonar data, acoustic sub-bottom profiles and box cores were used to study the activity of submarine canyons and
fans near the city of Les Escoumins, on the North Shore of the Lower St. Lawrence Estuary (Eastern Canada). The multibeam
data were used to generate a high-resolution digital terrain model that reveals the presence of a large number of canyons
and fans along the northern slopes of the Laurentian Channel. This paper focuses on two of the larger canyons, and their associated
submarine fans. The sub-bottom profiles on the fans reveal high-amplitude reflections at the sediment/water interface and
near the seafloor surface, indicating the occurrence of layers of coarse material. A turbidite was observed in a box core
sampled in one of the fans, confirming the nature of the coarse layer. Geophysical and sedimentological data indicate that
the canyons and fans play an important role in transferring coastal sandy sediments to the deeper marine environments by longshore
drift-initiated turbidity flows, and thereby contribute to the negative sediment budget along the coast. The morphology of
the canyons indicates that they were produced by a combination of erosive turbidity flows and retrogressive failures. The
two box cores sampled on the fans reveal a recent (~last 60 years) quasi-exponential increase in sand content near the surface
of the cores, possibly reflecting recent deforestation and/or increased coastal erosion. 相似文献