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531.
Daniel Smrzka Jennifer Zwicker David Misch Christoph Walkner Susanne Gier Patrick Monien Gerhard Bohrmann Jrn Peckmann 《Sedimentology》2019,66(6):2318-2353
Oil seeps from the southern Gulf of Mexico can be regarded as natural laboratories where the effect of crude oil seepage on chemosynthesis‐based communities and carbonate precipitation can be studied. During R/V Meteor cruise 114 the seep sites UNAM (Universidad Nacional Autónoma de México) Ridge, Mictlan Knoll and Tsanyao Yang Knoll (Bay of Campeche, southern Gulf of Mexico) were investigated and sampled for authigenic carbonate deposits containing large amounts of liquid oil and solid asphalt. The δ13C values of individual carbonate phases including: (i) microcrystalline matrix aragonite and calcite; (ii) grey, cryptocrystalline to microcrystalline aragonite; and (iii) clear, fibrous aragonite cement, are between ?30‰ and ?20‰, agreeing with oil as the primary carbon source. Raman spectra reveal that residual heavy oils from all sites are immature and most likely originate from the same reservoir. Geochemical batch modelling using the software code PHREEQC demonstrates how sulphate‐driven oxidation of oil‐derived low‐molecular to high‐molecular weight hydrocarbons affects carbonate saturation state, and shows that the oxidation state of carbon in hydrocarbon compounds and oxidation rates of hydrocarbons control carbonate saturation and precipitation at oil seeps. Phase‐specific trace and rare earth element contents of microcrystalline aragonite and calcite, grey cryptocrystalline aragonite and clear aragonite were determined, revealing enrichment in light rare earth elements for grey aragonite. By comparing trace element patterns of carbonates with those of associated oils, it becomes apparent that liquid hydrocarbons constitute an additional source of trace metals to sedimentary pore waters. This work not only demonstrates that the microbial degradation of oil at seeps may result in the precipitation of carbonate minerals, it also elucidates that trace metal inventories of seep carbonates archive diagnostic elemental patterns, which can be assigned to the presence of heavy hydrocarbons in interstitial pore waters. 相似文献
532.
533.
Zamyatin Dmitry A. Shchapova Yuliya V. Votyakov Sergey L. Nasdala Lutz Lenz Christoph 《Mineralogy and Petrology》2017,111(4):475-497
Mineralogy and Petrology - The U-Th-Pb isotope system in the accessory mineral zircon may be disturbed, as for instance by the secondary loss of radiogenic lead. The recognition of such alteration... 相似文献
534.
Compositional data analysis was performed on chemical compositions of martian surface materials in order to unravel scenarios of past and present weathering and to evaluate the role of meteoritic accumulation. The observed chemical variability is analyzed by means of principal component analysis. Potential reservoirs that may have contributed primary material to soil formation are assessed. Chemical alteration in the course of in situ weathering is described in terms of alteration vectors that link the compositions of fresh rocks and their weathering crusts. The interplay of localized chemical alteration and global scale re-distribution and mixing of fines material is documented through the identification of different soil forming branches. These branches emanate from distinct compositional domains, which comprise basaltic and basalt-andesitic primary materials, and they converge to a global dust composition, which represents the product of chemical and physical disintegration and subsequent global mixing. Mass balance considerations applied to localized weathering phenomena are in line with findings from experimental acid-sulfate weathering on olivine-bearing basalts and the persistence of secondary silica in evaporitic rocks. In addition the composition and oxidation state of involved volcanic gases is deduced. Our findings corroborate the past activity of volcanic exhalation products in combination with liquid water. We conclude that average martian crust is dominated by basaltic materials at its topmost level and that the amount of meteoritic accumulation may contribute about 6 wt% to the martian fines. From the meteoritic contribution minimum soil formation rates of 60±20 cm/Gyr are derived. Sequestration of atmospheric oxygen during weathering of primary materials may account for the oxygen deficiency of the martian atmosphere. A 4-14-m-thick layer of oxidized martian fines may account for the estimated deficit of 1.7×1018 mol O2 in the martian atmosphere depending on the primary oxidation state of volatile volcanic emanations. 相似文献
535.
An elementary integral equation technique is used to construct strong and weak stationary shock solutions from the one-dimensional Vlasov equation. It is shown that the plasma is Penrose stable in all points in space under certain conditions.This work was supported in part by the Atomic Energy Commission Grant No. AT(11-1)-2059, and NSF Grant GA-31676.supported by a CSIR bursary. 相似文献
536.
Carbon,sulfur, oxygen and strontium isotope records,organic geochemistry and biostratigraphy across the Permian/Triassic boundary in Abadeh,Iran 总被引:6,自引:0,他引:6
Christoph?KorteEmail author Heinz?W.?Kozur Michael?M.?Joachimski Harald?Strauss Ján?Veizer Lorenz?Schwark 《International Journal of Earth Sciences》2004,93(4):565-581
Pelagic deposits at Abadeh represent a complete biostratigraphic record across the Permian/Triassic boundary (PTB). The presumed water depth during deposition of these sediments was between 60 and 90 m. Similar to other Permian/Triassic boundary sections, the succession at Abadeh is characterised by a negative carbon isotope shift of approximately 4. The values start to decrease in the lower C. changxingensis - C. deflecta s.l. Zone, reach –0.12 (V-PDB) in the uppermost Permian just below the PTB, remain low to the early I. isarcica Zone (–0.32) and increase subsequently in the upper I. isarcica Zone. For the time interval of the PTB negative carbon isotope excursion, between the C. iranica and the I. isarcica Zones, no correlation exists between the 13Ccarb and the 18Ocarb. The above observations argue against the conclusion of Heydari et al. (2001) that the carbon isotope event at the P/T transition is an alteration artefact and not a global signal. The decrease in 13Ccarb is accompanied by a ~5 (and potentially up to 10) increase in 34SSSS. Together, these features are thought to reflect a complex global event, notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves. For the carbon isotope drop, other factors, such as the collapse of ocean primary productivity may also have played a role. The 87Sr/86Sr ratios of Dzhulfian seawater show only a minor increase from 0.70705 to 0.70710, reaching 0.70720 in the Dorashamian. The increase becomes steeper in the Early Triassic reaching 0.70754 in the N. dieneri Zone. The rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost Permian (C. meishanensis - H. praeparvus Zone) and the lack of a dense land vegetation in the Early Triassic, prior to the Spathian (Upper Olenekian). 相似文献
537.
Landslide risk management in Switzerland 总被引:1,自引:2,他引:1
538.
In the deep subsurface of the northeast German basin products of extensive volcanism are present that formed during the waning
phase of the Variscan orogeny (Permian–Carboniferous boundary). Large volumes (≥48,000 km3) of dominantly felsic magma were emplaced in the northern foreland of the Variscan mountains in a terrestrial semi-arid environment.
Most of these units were inferred by previous authors to represent the products of explosive volcanic eruptions such as ignimbrites.
However, a detailed analysis of the volcanic texture and lithofacies association shows that most units are best interpreted
as coherent lavas emplaced either as extrusive units or as shallow intrusions, with important implications for the reconstruction
of the paleo-environment. This study shows that detailed textural examination of drill cores provide important observations,
which can be applied as criteria for the interpretation of the mode of volcanic eruptions. Furthermore, phenocryst logging
and geochemical fingerprinting based on immobile element ratios can be employed for the classification and discrimination
of individual emplacement units. 相似文献
539.
Wen-chao Su Christoph A. Heinrich Thomas Pettke Xing-chun Zhang Rui-zhong Hu Bin Xia 《矿物岩石地球化学通报》2006,25(Z1):192
The Shuiyindong and Yata Carlin-type gold deposits, located in Southwestern Guizhou, China, are hosted by Permianbioclastic limestone in the form of stratabound mineralization and Middle Triassic calcareous clastic rocks as fault-controlled mineralization, respectively. In these deposits, quartz crystals in the veins or veinlets associated with mineralization have contained several populations of fluid inclusions with relatively quite big size and clear paragenetic relationship of entrapment. Petrography, microthermometry, Raman and LA-ICPMS of fluid inclusions analyses are used to characterize fluids chemistry and their evolution of Carlin-type system in Guizhou. 相似文献
540.