全文获取类型
收费全文 | 252篇 |
免费 | 29篇 |
国内免费 | 87篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 41篇 |
地球物理 | 47篇 |
地质学 | 212篇 |
海洋学 | 27篇 |
天文学 | 4篇 |
综合类 | 7篇 |
自然地理 | 27篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 21篇 |
2015年 | 14篇 |
2014年 | 13篇 |
2013年 | 15篇 |
2012年 | 15篇 |
2011年 | 8篇 |
2010年 | 13篇 |
2009年 | 21篇 |
2008年 | 20篇 |
2007年 | 21篇 |
2006年 | 19篇 |
2005年 | 13篇 |
2004年 | 17篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 11篇 |
2000年 | 10篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有368条查询结果,搜索用时 203 毫秒
1.
Detrital zircon provides a powerful archive of continental growth and recycling processes. We have tested this by a combined laser ablation ICP-MS U–Pb and Lu–Hf analysis of homogeneous growth domains in detrital zircon from late Paleozoic coastal accretionary systems in central Chile and the collisional Guarguaráz Complex in W Argentina. Because detritus from a large part of W Gondwana is present here, the data delineate the crustal evolution of southern South America at its Paleopacific margin, consistent with known data in the source regions.Zircon in the Guarguaráz Complex mainly displays an U–Pb age cluster at 0.93–1.46 Ga, similar to zircon in sediments of the adjacent allochthonous Cuyania Terrane. By contrast, zircon from the coastal accretionary systems shows a mixed provenance: Age clusters at 363–722 Ma are typical for zircon grown during the Braziliano, Pampean, Famatinian and post-Famatinian orogenic episodes east of Cuyania. An age spectrum at 1.00–1.39 Ga is interpreted as a mixture of zircon from Cuyania and several sources further east. Minor age clusters between 1.46 and 3.20 Ga suggest recycling of material from cratons within W Gondwana.The youngest age cluster (294–346 Ma) in the coastal accretionary prisms reflects a so far unknown local magmatic event, also represented by rhyolite and leucogranite pebbles. It sets time marks for the accretion history: Maximum depositional ages of most accreted metasediments are Middle to Upper Carboniferous. A change of the accretion mode occurred before 308 Ma, when also a concomitant retrowedge basin formed.Initial Hf-isotope compositions reveal at least three juvenile crust-forming periods in southern South America characterised by three major periods of juvenile magma production at 2.7–3.4 Ga, 1.9–2.3 Ga and 0.8–1.5 Ga. The 176Hf/177Hf of Mesoproterozoic zircon from the coastal accretionary systems is consistent with extensive crustal recycling and addition of some juvenile, mantle-derived magma, while that of zircon from the Guarguaráz Complex has a largely juvenile crustal signature. Zircon with Pampean, Famatinian and Braziliano ages (< 660 Ma) originated from recycled crust of variable age, which is, however, mainly Mesoproterozoic. By contrast, the Carboniferous magmatic event shows less variable and more radiogenic 176Hf/177Hf, pointing to a mean early Neoproterozoic crustal residence. This zircon is unlikely to have crystallized from melts of metasediments of the accretionary systems, but probably derived from a more juvenile crust in their backstop system. 相似文献
2.
Paul R. Craddock Olivier J. Rouxel Lary A. Ball Wolfgang Bach 《Chemical Geology》2008,253(3-4):102-113
We have developed a technique for the accurate and precise determination of 34S/32S isotope ratios (δ34S) in sulfur-bearing minerals using solution and laser ablation multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). We have examined and determined rigorous corrections for analytical difficulties such as instrumental mass bias, unresolved isobaric interferences, blanks, and laser ablation- and matrix-induced isotopic fractionation. Use of high resolution sector-field mass spectrometry removes major isobaric interferences from O2+. Standard-sample bracketing is used to correct for the instrumental mass bias of unknown samples. Background on sulfur masses arising from memory effects and residual oxygen-tailing are typically minor (< 0.2‰, within analytical error), and are mathematically removed by on-peak zero subtraction and by bracketing of samples with standards determined at the same signal intensity (within 20%). Matrix effects are significant (up to 0.7‰) for matrix compositions relevant to many natural sulfur-bearing minerals. For solution analysis, sulfur isotope compositions are best determined using purified (matrix-clean) sulfur standards and sample solutions using the chemical purification protocol we present. For in situ analysis, where the complex matrix cannot be removed prior to analysis, appropriately matrix-matching standards and samples removes matrix artifacts and yields sulfur isotope ratios consistent with conventional techniques using matrix-clean analytes. Our method enables solid samples to be calibrated against aqueous standards; a consideration that is important when certified, isotopically-homogeneous and appropriately matrix-matched solid standards do not exist. Further, bulk and in situ analyses can be performed interchangeably in a single analytical session because the instrumental setup is identical for both. We validated the robustness of our analytical method through multiple isotope analyses of a range of reference materials and have compared these with isotope ratios determined using independent techniques. Long-term reproducibility of S isotope compositions is typically 0.20‰ and 0.45‰ (2σ) for solution and laser analysis, respectively. Our method affords the opportunity to make accurate and relatively precise S isotope measurement for a wide range of sulfur-bearing materials, and is particularly appropriate for geologic samples with complex matrix and for which high-resolution in situ analysis is critical. 相似文献
3.
A detailed characterization of the site is crucial to designing an efficient method of managing the risks associated with
tailings from abandoned mines. Therefore, samples collected from various depths within tailings in Guryong mine, Korea, were
analyzed for their chemical, physical and mineralogical characteristics. All samples of the Guryong tailings had acid-generating
potential. However, in the oxidation zone, the net acid generation (NAG) was low (30 kg H2SO4 t−1) although the acid neutralization potential (ANP) was less than zero. The ANP values in the unoxidation zone were higher
(> −56.0 kg CaCO3 t−1) than in the other zones. As a result, the amount of alkali ions that are needed to neutralize the acid needs to be considered.
In this experiment G3, G4 and G6 drill cores containing fine tailings particles near the unoxidation zone were observed to
contain calcite (CaCO3) with acid-neutralizing capacity. A low pH (2−4) in the oxidation zone of the tailings changed to a neutral pH in the unoxidation
zone of the tailings. These results suggest that the acid-neutralizing capacity of the tailings was controlled by particle
and mineral composition of tailings. 相似文献
4.
Eric A. Betterton 《Journal of Atmospheric Chemistry》1993,17(4):307-324
An experimental study is described of Fe(III)-S(IV) formation constants measured as a function of pH (1–3), ionic strength (0.2–0.5 M) and [Fe(III)]
T
(2.5–5.0×10–4 M) using a continuous-flow spectrophotometric technique to make observations 160 ms after mixing. Preliminary experiments using pulse-accelerated-flow (PAF) spectrophotometry to measure rate constants on a microsecond timescale are also described. The conditional formation constant at 25 °C can be modeled with the following equation: {ie307-1} where {ie307-2}K
7 andK
8 can be interpreted as intrinsic constants for the coordination of HSO
3
–
by FeOH2+ and Fe3+, respectively, but until further evidence is obtained they should be regarded as fitting constants. PAF spectrophotometry showed that the initial reaction of Fe(III) with S(IV) (pH 2.0) is characterized by a second-order rate constant of 4×106 M–1 s–1 which is comparable to rate of reaction of FeOH2+ with SO
4
2–
. However, the PAF results should be regarded as preliminary since unexpected features in the initial data indicate that the reaction may be more complex than expected. 相似文献
5.
J. P. Putaud N. Mihalopoulos B. C. Nguyen J. M. Campin S. Belviso 《Journal of Atmospheric Chemistry》1992,15(2):117-131
Daily measurements of atmospheric sulfur dioxide (SO2) concentrations were performed from March 1989 to January 1991 at Amsterdam Island (37°50 S–77°30 E), a remote site located in the southern Indian Ocean. Long-range transport of continental air masses was studied using Radon (222Rn) as continental tracer. Average monthly SO2 concentrations range from less than 0.2 to 3.9 nmol m-3 (annual average = 0.7 nmol m-3) and present a seasonal cycle with a minimum in winter and a maximum in summer, similar to that described for atmospheric DMS concentrations measured during the same period. Clear diel correlation between atmospheric DMS and SO2 concentrations is also observed during summer. A photochemical box model using measured atmospheric DMS concentrations as input data reproduces the seasonal variations in the measured atmospheric SO2 concentrations within ±30%. Comparing between computed and measured SO2 concentrations allowed us to estimate a yield of SO2 from DMS oxidation of about 70%. 相似文献
6.
A model for the carbon and sulfur cycles across the Permian–Triassic boundary has been constructed from carbon and sulfur isotopic data. Results indicate a drop in global organic matter burial, the formation of an anoxic deep ocean, and a large drop in atmospheric oxygen over the time span 270 to 240 Ma. Much of these changes were probably due to a drop in terrestrial productivity and preservation and an increase in global aridity. 相似文献
7.
The Zambian Copperbelt forms the southeastern part of the 900-km-long Neoproterozoic Lufilian Arc and contains one of the world’s largest accumulations of sediment-hosted stratiform copper mineralization. The Nchanga deposit is one of the most significant ore systems in the Zambian Copperbelt and contains two major economic concentrations of copper and cobalt, hosted within the Lower Roan Group of the Katangan Supergroup. A Lower Orebody (copper only) and Upper Orebody (copper and cobalt) occur towards the top of arkosic units and within the base of overlying shales. The sulfide mineralogy includes pyrite, bornite, chalcopyrite, and chalcocite, although in the Lower Orebody, sulfide phases are partially or completely replaced by malachite and copper oxides. Carrollite is the major cobalt-bearing phase and is restricted to fault-propagation fold zones within a feldspathic arenite. Hydrothermal alteration minerals include dolomite, phlogophite, sericite, rutile, quartz, tourmaline, and chlorite. Quartz veins from the mine sequence show halite-saturated fluid inclusions, ranging from ~31 to 38 wt% equivalent NaCl, with homogenisation temperatures (ThTOT) ranging between 140 and 180°C. Diagenetic pyrites in the lower orebody show distinct, relatively low δ
34S, ranging from −1 to −17‰ whereas arenite- and shale-hosted copper and cobalt sulfides reveal distinctly different δ
34S from −1 to +12‰ for the Lower Orebody and +5 to +18‰ for the Upper Orebody. There is also a clear distinction between the δ
34S mean of +12.1±3.3‰ (n=65) for the Upper Orebody compared with +5.2±3.6‰ (n=23) for the Lower Orebody. The δ
13C of dolomites from units above the Upper Orebody give δ
13C values of +1.4 to +2.5‰ consistent with marine carbon. However, dolomite from the shear-zones and the alteration assemblages within the Upper Orebody show more negative δ
13C values: −2.9 to −4.0‰ and −5.6 to −8.3‰, respectively. Similarly, shear zone and Upper Orebody dolomites give a δ
18O of +11.7 to +16.9‰ compared to Lower Roan Dolomites, which show δ
18O of +22.4 to +23.0‰. Two distinct structural regimes are recognized in the Nchanga area: a weakly deformed zone consisting of basement and overlying footwall siliciclastics, and a moderate to tightly folded zone of meta-sediments of the Katangan succession. The fold geometry of the Lower Roan package is controlled by internal thrust fault-propagation folds, which detach at the top of the lowermost arkose or within the base of the overlying stratigraphy and show vergence towards the NE. Faulting and folding are considered to be synchronous, as folding predominantly occurred at the tips of propagating thrust faults, with local thrust breakthrough. The data from Nchanga suggests a strong link between ore formation and the development of structures during basin inversion as part of the Lufilian Orogeny. Sulfides tend to be concentrated within arenites or coarser-grained layers within shale units, suggesting that host-rock porosity and possibly permeability played a role in ore formation. However, sulfides are also commonly orientated along, but not deformed by, a tectonic fabric or hosted within small fractures that suggest a significant role for deformation in the development of the mineralization. The ore mineralogy, hydrothermal alteration, and stable isotope data lend support to models consistent with the thermochemical reduction of a sulfate- (and metal) enriched hydrothermal fluid, at the site of mineralization. There is no evidence at Nchanga for a contribution of bacteriogenic sulfide, produced during sedimentation or early diagenesis, to the ores.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.Editorial handling: H. Frimmel 相似文献
8.
Abstract The initial volcanic phase of Cretaceous island arc strata in central Puerto Rico, at the eastern end of the extinct Greater Antilles Arc, comprises a 6‐km thick pile of lava and volcanic breccia (Río Majada Group). Preserved within the sequence is a conspicuous shift in absolute abundances of the more incompatible elements, including Th, Nb, and the light rare earth elements (LREE: La, Ce, Pr and Nd). The compositional shift is marked by a decrease in La/Sm from averages of 2.11 in the lowest third of the pile (Formation A) to 1.48 at the top (Formation C), and by a distinctive flattening of LREE segments of chondrite‐normalized REE patterns. i87Sr/86Sr and ?Nd average about 0.7035 and 8.2, respectively, in early Formation A basalts. These ranges normally overlap samples from later Formations B and C. Isotope compositions of the latter group are more variable, however, and several samples are considerably more radiogenic than Formation A basalts, such that i87Sr/86Sr averages almost 0.7042 while ?Nd‐values decrease to 7.5 in Formation B and C basalts. Theoretical models of non‐modal melting processes in both amphibole peridotite and spinel lherzolite sources provide insight into the origin of depleted Th, Nb, and LREE abundances in Puerto Rican basalts. Low Nb concentrations less than normal mid‐oceanic ridge basalts in Formation A basalts indicate the wedge was slightly depleted by low‐volume decompression fusion due to induced convection in the back‐arc region prior to entry of the source into the arc melting zone. However, depleted patterns in Formation C basalts cannot be generated by relatively greater degrees of decompression fusion in the back‐arc, because addition of the La‐enriched slab‐derived component to more depleted source material invariably produces elevated rather than decreased La/Sm. Refluxing of Formation A harzburgitic residua is similarly precluded. In contrast, the observed patterns are readily reproduced by multistage melting models involving hybridized sources containing normal Formation A lherzolite source material blended with recycled, unrefluxed harzburgite residua. Successful models require hybrid sources containing large volumes of recycled harzburgite (up to 50%) during generation of Formation C basalts. Slightly elevated radiometric Sr and Nd isotopes in a few flows from Formation C are attributed to partial refluxing of the hybrid sources within the wedge. 相似文献
9.
10.