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381.
Nikolay V. Pimenov Marina O. Ulyanova Timur A. Kanapatsky Elena F. Veslopolova Pavel A. Sigalevich Vadim V. Sivkov 《Geo-Marine Letters》2010,30(3-4):439-448
In the Russian sector of the Gdansk Basin (Baltic Sea), high organic matter influx fuels microbial processes resulting in the formation of reduced sediments with elevated methane concentrations. Investigated areas of geoacoustic anomalies (~245 km2) were found to contain three distinct geomorphologic structures (pockmarks), with a total area of ~1 km2. Methane anomalies recorded in the water above one of these pockmarks were traced as high as 10 m above the bottom. In pockmark sediments, sulfate reduction and anaerobic oxidation of methane (AOM) occurred at high rates of 33 and 50 µmol dm?3 day?1, respectively. Integrated over 0–180 cm sediment depths, AOM exceeded methanogenesis almost tenfold. High AOM rates resulted from methane influx from deeper sediment layers. The δ13C signature of methane carbon (?78.1 to ?71.1‰) indicates the biogenic origin of pockmark methane. In pockmark sediments, up to 70% of reduced sulfur compounds was possibly produced via AOM. 相似文献
382.
This study presents the first preliminary U–Pb zircon data on tin-bearing S-type granites from the Gemeric unit of the Western Carpathians (Slovakia). U–Pb single zircon dating controlled by cathodoluminescence suggests crystallization of the Gemeric granites during Permian to Early Triassic (303–241 Ma) time. Post-crystallization, low-temperature metamorphic overprint is reflected by partial Pb loss in zircons. These Gemeric granites are younger than the highly fractionated, S-type, tin- and rare-element-bearing leucogranites in the European Variscides. They may have resulted from partial melting, triggered by increased heat flow from the mantle below the continental crust, and most probably intruded during the post-collisional extension and initial rifting of the Variscan orogenic belt. During Alpine orogeny, the Gemeric granites were affected by a low-temperature deformation and metamorphism. 相似文献
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Pavel Kroupa † Jerome Bouvier 《Monthly notices of the Royal Astronomical Society》2003,346(2):369-380
386.
We present detailed data on 8 bright meteors recorded simultaneously by different observational techniques. All meteors were
recorded by all-sky cameras at the Czech stations of the European Fireball Network and by image intensified TV cameras placed
at Ondrejov and Kunzak observatories. As well as direct photographic and LLLTV recordings, most of meteors were recorded also
by the spectral TV camera and some also by photographic spectral cameras. For 6 cases, lightcurves from radiometers with very
high time resolution (1200 s−1) are also available. From all these detections we found a significant difference between TV and photographic beginning heights.
TV beginnings are in average about 40 km higher than the photographic ones. We found that meteor brightness is up to 2 magnitudes
higher in the photographic system than in the TV system. This difference for high velocity meteors is mainly caused by the
presence of strong Ca+ lines in the blue part of the spectrum, where the image intensifier is only marginally sensitive. At heights above 110 km,
the Na line is usually brighter than the Mg line, while at lower heights both lines have comparable brightness. In one of
two captured spectra of short duration luminous trains, a small initial brightening of the Mg and Na lines caused by recombination
processes was observed. 相似文献
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389.
Jií Bruthans Michal Filippi Milan Gerl Mohammad Zare Jaroslava Melkov Anna Pazdur Pavel Bosk 《第四纪科学杂志》2006,21(8):843-857
Slightly inclined Holocene marine terraces cover parts of two circular salt diapirs (Hormoz and Namakdan) in the Persian Gulf. Their relative altitude above present sea level results from a combination of general marine transgression/regression affecting the whole area, and of local uplift related to salt diapirism. Differential uplift rate of the studied diapirs in centre‐to‐rim profiles was calculated from results based on: (i) radiocarbon ages of skeletal remains of benthic faunas (19 samples), which originally grew close to sea level; (ii) original altitude of samples, estimated from general sea‐level oscillation curves for the last 10 kyr, and (iii) present sample altitude measured in the field. Calculated uplift rates increase from rim to centre on both diapirs in the range from: 2 mm yr?1 at the rim to 5–6 mm yr?1 at the interior of Hormoz, and 1–3 mm yr?1 at the rim to 3–5 mm yr?1 at the interior of Namakdan. Such uplift rate distributions fit into the parabolic profile of Newtonian fluid rather than to profiles typical for pseudoplastic fluids. The increase in uplift rate with distance from rim to centre of diapirs is gradual as demonstrated also by generally smooth surface of marine terraces. No tectonic dissections were found. The depositional history on both salt diapirs is similar although they are situated more than 100 km apart. Marine sedimentation started at about 9.6k cal. yr BP on Hormoz and at 8.6k cal. yr BP on Namakdan. Owing to rapid transgression, the sea partially truncated both salt diapirs and rapidly deepened, and carbonate mud was deposited on the peripheries of both salt diapirs. Between 7 and 5k cal. yr BP beach deposition replaced carbonate mud. Soon after 5k cal. yr BP, the sea retreated from most of the marine terraces on both salt diapirs. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
390.