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991.
Hermann D. Bermúdez Jenny García Wolfgang Stinnesbeck Gerta Keller José Vicente Rodríguez Michael Hanel Jens Hopp Winfried H. Schwarz Mario Trieloff Liliana Bolívar Francisco J. Vega 《地学学报》2016,28(1):83-90
The discovery of a new Cretaceous/Palaeogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub impact spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well‐preserved glass spherules up to 1.1 mm in diameter. About 70–90% of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size‐grading, delicate spherule textures, welded melt components and an absence of bioturbation or traction transport suggest that the Gorgonilla spherule layer represents an almost undisturbed settling deposit. 相似文献
992.
Paula M. Carreira José M. Marques M. Rosário Carvalho Giorgio Capasso Fausto Grassa 《Journal of Volcanology and Geothermal Research》2010,189(1-2):49-56
Na–HCO3–CO2-rich thermomineral waters issue in the N of Portugal, within the Galicia-Trás-os-Montes region, linked to a major NNE-trending fault, the so-called Penacova-Régua-Verin megalineament. Along this tectonic structure different occurrences of CO2-rich thermomineral waters are found: Chaves hot waters (67 °C) and also several cold (16.1 °C) CO2-rich waters. The δ2H and δ18O values of the thermomineral waters are similar to those of the local meteoric waters. The chemical composition of both hot and cold mineral waters suggests that water–rock reactions are mainly controlled by the amount of dissolved CO2 (g) rather than by the water temperature. Stable carbon isotope data indicate an external CO2 inorganic origin for the gas. δ13CCO2 values ranging between ? 7.2‰ and ? 5.1‰ are consistent with a two-component mixture between crustal and mantle-derived CO2. Such an assumption is supported by the 3He/4He ratios measured in the gas phase, are between 0.89 and 2.68 times the atmospheric ratio (Ra). These ratios which are higher than that those expected for a pure crustal origin (≈ 0.02 Ra), indicating that 10 to 30% of the He has originated from the upper mantle. Release of deep-seated fluids having a mantle-derived component in a region without recent volcanic activity indicates that extensive neo-tectonic structures originating during the Alpine Orogeny are still active (i.e., the Chaves Depression). 相似文献
993.
Telmo M. Bento dos Santos José M. Munhá Colombo C.G. Tassinari Paulo E. Fonseca 《Journal of South American Earth Sciences》2011,31(2-3):262-278
Elemental and Sr–Nd isotopic data on metatexites, diatexites, orthogneisses and charnockites from the central Ribeira Fold Belt indicate that they are LILE-enriched weakly peraluminous granodiorites. Harker and Th–Hf–La correlation trends suggest that these rocks represent a co-genetic sequence, whereas variations on CaO, MnO, Y and HREE for charnockites can be explained by garnet consumption during granulitic metamorphism.Similar REE patterns and isotopic results of ?Nd565 = ?5.4 to ?7.3 and 87Sr/86Sr565 = 0.706–0.711 for metatexites, diatexites, orthogneisses and charnockites, as well as similar TDM ages between 2.0 and 1.5 Ga are consistent with evolution from a relatively homogeneous and enriched common crustal (metasedimentary) protolith.Results suggest a genetic link between metatexites, diatexites, orthogneisses and charnockites and a two-step process for charnockite development: (a) generation of the hydrated igneous protoliths by anatexis of metasedimentary rocks; (b) continuous high-grade metamorphism that transformed the “S-type granitoids” (leucosomes and diatexites) into orthogneisses and, as metamorphism and dehydration progressed, into charnockites. 相似文献
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996.
River water temperature is a very important variable in ecological studies, especially for the management of fisheries and aquatic resources. Temperature can impact on fish distribution, growth, mortality and community dynamics. River evaporation has been identified as an important heat loss and a key process in the thermal regime of rivers. However, its quantification remains a challenge, mainly because of the difficulty of making direct measurements. The objectives of this study were to characterize the evaporative heat flux at different scales (brook vs river) and to improve the estimation of the evaporative heat flux in a stream temperature model at the hourly timescale. Using a mass balance approach with floating minipans, we measured river evaporation at an hourly timescale in a medium‐sized river (Little Southwest Miramichi) and a small brook (Catamaran Brook) in New Brunswick, Canada. With these direct measurements of evaporation, we developed mass transfer equations to estimate hourly evaporation rates from microclimate conditions measured 2 m above the stream. During the summer 2012, river evaporation was more important for the medium‐sized river with a mean daily evaporation rate of 3.0 mm day?1 in the Little Southwest Miramichi River compared with that of 1.0 mm day?1 in Catamaran Brook. Evaporation was the main heat loss mechanism in the two studied streams and was responsible for 42% of heat losses in the Little Southwest Miramichi River and 34% of heat losses in Catamaran Brook during the summer. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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998.
Gómez-Navarro Juan José Werner Johannes Wagner Sebastian Luterbacher Jürg Zorita Eduardo 《Climate Dynamics》2015,45(5-6):1395-1413
Climate Dynamics - This study aims at assessing the skill of several climate field reconstruction techniques (CFR) to reconstruct past precipitation over continental Europe and the Mediterranean at... 相似文献
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An Evaluation of the Effects of Primary and Cross‐Contamination during the Preparation of Rock Powders for Chemical Determinations
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José P. Sertek Sandra Andrade Horstpeter H. Ulbrich 《Geostandards and Geoanalytical Research》2015,39(3):381-397
Quartz crystals from the Batatal site, Minas Gerais, southern Brazil, were used to determine quantitatively primary contamination when submitting the samples to milling processes. Crushing devices used were a primary steel jaw crusher (br1), a secondary tungsten carbide (WC) crusher (br2) and a hydraulic press with stainless steel plates (pr). Fragments with suitable sizes were then ground in different Fritsch planetary mills, equipped with agate, WC and chromium‐steel rings for 7, 4 and 3 min, respectively. Solutions of the powders were analysed initially with the TotalQuant? method in a quadrupole ICP‐MS instrument, providing semi‐quantitative results for seventy‐five elements. Contamination from crushers and mills was visible in major and minor elements such as Fe, Mn and Ti, and noticeable in trace elements such as Cr, Co, Ni, Cu and also V, Zr, Sc; significant contamination was observed from W, Mo, Co, Ta and Nb (mainly by use of the WC devices). Little or no contamination was observed for Pb, REE, Sr and Rb, elements that are important in routine isotopic determinations. Cross‐contamination was tested by grinding either a granite or a basalt sample, followed by conventional cleaning with mica‐free quartz sand, before the working quartz powder was prepared. 相似文献