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11.
Lutz Nasdala Wolfgang Hofmeister Nicholas Norberg James M. Martinson Fernando Corfu Wolfgang Dörr Sandra L. Kamo Allen K. Kennedy Andreas Kronz Peter W. Reiners Dirk Frei Jan Kosler Yusheng Wan Jens Götze Tobias Häger Alfred Kröner John W. Valley 《Geostandards and Geoanalytical Research》2008,32(3):247-265
We introduce and propose zircon M257 as a future reference material for the determination of zircon U‐Pb ages by means of secondary ion mass spectrometry. This light brownish, flawless, cut gemstone specimen from Sri Lanka weighed 5.14 g (25.7 carats). Zircon M257 has TIMS‐determined, mean isotopic ratios (2s uncertainties) of 0.09100 ± 0.00003 for 206pb/238U and 0.7392 ± 0.0003 for 207pb/235U. Its 206pb/238U age is 561.3 ± 0.3 Ma (unweighted mean, uncertainty quoted at the 95% confidence level); the U‐Pb system is concordant within uncertainty of decay constants. Zircon M257 contains ~ 840 μg g?1 U (Th/U ~ 0.27). The material exhibits remarkably low heterogeneity, with a virtual absence of any internal textures even in cathodoluminescence images. The uniform, moderate degree of radiation damage (estimated from the expansion of unit‐cell parameters, broadening of Raman spectral parameters and density) corresponds well, within the “Sri Lankan trends”, with actinide concentrations, U‐Pb age, and the calculated alpha fluence of 1.66 × 1018 g?1. This, and a (U+Th)/He age of 419 ± 9 Ma (2s), enables us to exclude any unusual thermal history or heat treatment, which could potentially have affected the retention of radiogenic Pb. The oxygen isotope ratio of this zircon is 13.9%o VSMOW suggesting a metamorphic genesis in a marble or calc‐silicate skarn. 相似文献
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传统认为中国南方的离子吸附型稀土矿床可划分为以“足洞式”为代表的重稀土型和以“河岭式”(或“花山式”)为代表的轻稀土型两种矿化类型。然而,近年来发现的许多矿床(如清溪、寨背和馒头山等)的赋矿风化壳中出现了轻稀土矿与重稀土矿并存现象,表现出特殊的“上轻下重”双层矿体结构。这指示了除重稀土型和轻稀土型之外,还存在着轻重稀土共生型的过渡类型。本研究通过对三种不同成矿类型的若干典型矿床系统对比,指出成矿类型的多样性与母岩性质密切相关,尤其是母岩的稀土元素地球化学和稀土载体矿物属性是制约成矿类型变化的关键因素。统计数据表明,从重稀土型→轻重稀土共生型→轻稀土型,成矿母岩的全岩稀土总量变化不大(ΣREY: 200×10-6~450×10-6→200×10-6~500×10-6→200×10-6~800×10-6),但轻重稀土配分值出现较显著的区间性差异(ΣLREE/ΣHREY: 02~1→1~5→2~10)。与之同时,母岩中能为离子相稀土提供物源且具有重稀土配分属性的稀土副矿物类型和数量明显减少,这与全岩稀土元素地球化学特征中重稀土分量占比的降低趋势也互相匹配。该结果指示,以往认为重稀土配分母岩形成重稀土矿床、轻稀土配分母岩形成轻稀土矿床的传统观点需要外延,即一部分具有低度轻稀土配分属性(1<ΣLREE/ΣHREY<5)且含有丰富易风化稀土副矿物的母岩还可能形成轻重稀土共生型矿床,该认识可为今后离子吸附型稀土矿床勘查工作提供新的找矿依据。 相似文献
13.
L.J. Hou M. Liu J.J. Lu S.Y. Xu D.N. Ou Y. Yang D.G. Zheng 《Environmental Geology》2006,49(7):937-945
The influences of exposure to the atmosphere on ammonium cycle in the intertidal surface sediments were in situ studied with
a geochemical approach at a typical station in the Yangtze Estuary during three tidal cycles in September 2003. During an
about 8-h emersion period of each diurnal tide, six high-resolution vertical profiles of adsorbed and dissolved ammonium were
measured. It was observed that both adsorbed and dissolved ammonium generally had an increasing trend in sediment cores during
the exposure. The rate of ammonium regeneration in sediments was estimated using the accumulation amount of ammonium including
adsorbed and soluble fractions during the daytime emersion. The calculation result showed that there was relatively high ammonification
rate (˜500 nmol N cm−3 day−1), which reflected that organic nitrogen in sediments was quickly decomposed with a residence time of ˜52.7 days. Due to the
dramatic temperature difference observed in sediment profiles, free convection was considered an important mechanism of regulating
the efflux of produced ammonium into overlying waters. The total estimated amount of regenerated ammonium was ˜1.35×105 t N year−1 in the intertidal flat of the Yangtze Estuary, which occupied 7.6% of the total inorganic nitrogen annually transported to
the estuarine ecosystem. 相似文献
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Larissa F. Dobrzhinetskaya Harry W. Green Matthew Weschler Mark Darus Young-Chung Wang Hans-Joachim Massonne Bernhard St ckhert 《Earth and Planetary Science Letters》2003,210(3-4):399-410
A focused ion beam of Ga ions is a relatively new technique that has been developed for microelectronic industries. Now researchers of the Earth sciences find it to be a promising tool for studying various geological materials. Using the FIB technique and an FEI Strata DB 235 dual beam system, we have successfully prepared several electron-transparent foils, which crossed μm-sized diamonds included in host minerals such as zircon and garnet from quartzofeldspathic rocks of the Saxonian Erzgebirge, Germany. Scanning and transmission electron microscopy applied to these foils revealed that the diamonds contain crystalline nanometric inclusions. These inclusions consist of minerals of known stoichiometries such as SiO2 and Al2SiO5, whereas others are characterized by different combinations of Si, K, P, Ti, and Fe in the presence of oxygen (stoichiometries are not clear at this stage of research). One suite of inclusions is assumed to be represented by archerite, KH2PO4, which is known to be stable at pressures of 4–22 GPa, and one nanocrystal containing Pb, oxygen and carbon is interpreted to be PbxOy or PbCO3. Along with solid crystalline inclusions, the diamonds contain cavities filled by liquid/gas that escaped during sample preparation. These are associated with dislocations of diamond growth. Our data are consistent with the concept of diamond crystallization from a COH-rich multicomponent supercritical fluid and suggest that the composition of such a fluid is more consistent with a local crustal source rather than that of a mantle origin. 相似文献
17.
Determination of Halogens (F, Cl, Br, I), Sulfur and Water in Seventeen Geological Reference Materials 总被引:5,自引:0,他引:5
Fluorine, chlorine, bromine, iodine and sulfur were determined in seventeen geological reference materials after extraction by pyrohydrolysis. Fluorine, Cl and S (as sulfate ions) were determined in the extraction solution by ion chromatography with detection limits of around 0.2 mg l−1 . Bromine and I were measured by ICP-MS with detection limits of 1 μg l−1 for Br and 0.1 μg l−1 for I. For rock samples, using normal extraction conditions (500 mg of sample and 100 ml of final solution) detection limits were 40 mg kg−1 for F and Cl, 15 mg kg−1 for S, 0.2 mg kg−1 for Br and 0.02 mg kg−1 for I. These detection limits may be improved by increasing the amount of sample and hence the concentration of the final solution. Water was also determined using an extraction technique based on H2 O degassing, reduction on zinc at 1000 °C and H2 manometry. Our results for fluorine, chlorine, sulfur and water are in good agreement with literature data. Very few reference materials have recommended values for bromine and especially for iodine. Among the analysed samples, three are new reference materials: BHVO-2, BCR-2 and AGV-2. 相似文献
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