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61.
62.
位于北喜马拉雅穹隆带东段的然巴构造穹隆外围发育环形韧性剪切带,带内岩石经韧性剪切形成各类糜棱状岩石。石英为带内变形岩中最为常见的造岩矿物,在不同的温度、应变速率下产生不同的显微构造,其中动态重结晶最为常见。重结晶新晶颗粒边界普遍具有锯齿状或港湾状结构,是应变和变形环境的天然记录。新晶粒分维几何统计分析表明:带内动态重结晶石英颗粒边界形态具有自相似性(1≤D≤2),表现出分形特征,分维数值为1.14~1.19,变形温度大约500℃。同构造变质环境属中——高绿片岩相;初步估算古应变速率可能低于10-9.5S-1;根据重结晶粒径估算变形古应力6.2~58.8MPa。 相似文献
63.
Jarkko V. Niemi Heikki Tervahattu Aki Virkkula Risto Hillamo Kimmo Teinil Ismo K. Koponen Markku Kulmala 《Atmospheric Research》2005,75(4):109
Aerosol samples were collected in the Atlantic marine boundary layer between the English Channel and Antarctica during November–December 1999. The composition of coarse (aerodynamic diameter 1–3 μm) individual aerosol particles was studied using the SEM/EDX method. The major particle types observed were fresh sea salt, sea-salt particles reacted partly or totally with sulphuric acid or nitric acid, Mg-sulphate, Ca-sulphate, mixed aluminosilicates and sea salt, aluminosilicates, Ca-rich particles and Fe-rich particles. The relative fractions of sea-salt particles with moderate or strong Cl depletion were high near the coasts of Europe (65–74%) and Northern Africa (44–87%), low far from the coast of Western Africa (10–20%) and very low in remote sea areas between Africa and Antarctica (1%). The Cl depletion was strongest when air masses arrived from the direction of anthropogenic pollution sources. The fractions of Mg-sulphate particles were high (18–25%) in 2 samples near Europe. The Mg-sulphate particles were probably formed as a result of fractional recrystallization of sea-salt particles in which Cl was substituted by sulphate. It remained unclear whether these particles were formed in the atmosphere or during and after sampling. The relative fractions of particles from continental sources were quite low (10–15%) near Europe, very high (25–78%) near the coast of Northwestern Africa and very low in the remote sea areas (0–2%). Most of the continental particles were aluminosilicates and some of them were internally mixed with sea salt. Near the coast of Northwestern Africa, the main source of aluminosilicates was Saharan dust, and near the Gulf of Guinea, emissions from biomass burning were also mixed with aluminosilicates and sea salt. 相似文献
64.
Abstract Observations and microthermometric data on fluid inclusions from a terrane that underwent deformation following peak metamorphic conditions show that grain-boundary migration recrystallization favours the entrapment of carbonic inclusions whereas microfracturing during brittle deformation favours the infiltration and eventual entrapment of aqueous fluids. Our results imply that pure CO2 fluid inclusions in metamorphic rocks are likely to be the residue of deformation-recrystallization process rather than representing a primary metamorphic fluid.
Where the temperature of deformation can be deduced by other means, the densities of fluid inclusions trapped during recrystallization, which we call recrystallization-primary fluid inclusions, can be used to constrain the ambient pressure during deformation. Using these constraints, the data imply that the post-metamorphic Hercynian exhumation in Sardinia brought rocks at 300° C to within 3km of the surface. This conclusion is similar to that described for the rapidly uplifted Southern Alps in New Zealand. 相似文献
Where the temperature of deformation can be deduced by other means, the densities of fluid inclusions trapped during recrystallization, which we call recrystallization-primary fluid inclusions, can be used to constrain the ambient pressure during deformation. Using these constraints, the data imply that the post-metamorphic Hercynian exhumation in Sardinia brought rocks at 300° C to within 3km of the surface. This conclusion is similar to that described for the rapidly uplifted Southern Alps in New Zealand. 相似文献
65.
Metamorphic effect on zircon Lu-Hf and U-Pb isotope systems in ultrahigh-pressure eclogite-facies metagranite and metabasite 总被引:9,自引:0,他引:9
Yong-Fei Zheng Yuan-Bao Wu Shao-Bing Zhang Fu-Yuan Wu 《Earth and Planetary Science Letters》2005,240(2):378-400
The Hf isotope composition of original igneous or detrital zircons in high-grade metamorphic rocks can be used to trace protolith origin, but metamorphic effect on the Hf isotope composition of newly grown domains remains to evaluate. We report a detailed in situ combined study of intragrain U-Pb and Lu-Hf isotopes in zircons from granitic gneiss and eclogite in the Dabie orogen of China that experienced ultrahigh-pressure eclogite-facies metamorphism. The results show correlations in 206Pb / 238U age, initial Hf isotope composition, and Th / U and Lu / Hf ratios between the domains of different origins. The metamorphic domains are characterized by low Th / U and Lu / Hf ratios but high ?Hf(t) values relative to the igneous core and mantle of pre-metamorphic ages. Positive correlations are observed between Th / U and Lu / Hf ratios, pointing to the similar effect of metamorphism on both U-Th-Pb and Lu-Hf isotope systems. Thus the metamorphic domains are distinguished from the igneous core and mantle by their low Lu / Hf ratios that are less than 0.001 for the granitic gneiss and less than 0.0001 for the eclogite. Despite differences in both protolith age and geochemical source between granitic gneiss and eclogite, rim ?Hf(t) values are variably 3.1 to 13.5 greater than core ?Hf(t) values when calculated at timing of protolith formation. This indicates that the zircon overgrowth was associated with a metamorphic medium that has high 176Hf / 177Hf but low 176Lu / 177Hf ratios. While the metamorphic domains contain more radiogenic Hf isotopes than the original igneous core and mantle, their Lu / Hf ratios are significantly lower than those of core and mantle. Therefore, the metamorphic zircons acquired their initial Hf isotope ratios from metamorphic fluids that have high 176Hf / 177Hf ratios but low Lu / Hf ratios with sound variability depending on the Lu-Hf isotope compositions of pre-existing and co-precipitating phases. 相似文献
66.
变质锆石拉曼光谱研究--以大别造山带为例 总被引:5,自引:0,他引:5
对大别山的道士冲辉石岩、双河榴辉岩和碧溪岭石榴橄缆岩的锆石进行了激光拉曼探针,阴极发光(CL)观察和U、Th等微量元素的微区分析及U-Pb同位素测定,发现锆石拉曼光谱波数和半高宽都能指示其蜕晶化程度,但对于高度蜕晶化锆石,波数已经不再完全适用,而只能通过其特征谱峰半高宽来确定。碧溪岭石榴橄榄岩锆石微区微量元素和拉曼探针分析发现,半高宽和Th/U比正相关,这是由岩浆锆石在变质过程中不同程度的固态重结晶作用造成的,其可能曾经遭受过约220Ma的热事件扰动。双河榴辉岩锆石则可能遭受了流体参与下的变质重结晶作用的影响。锆石重结晶作用是变质岩中锆石年龄和化学组成变化的主要原因。 相似文献
67.
68.
69.
砂金的汞齐化增生假说 总被引:1,自引:0,他引:1
根据黑龙江省砂金及与之有关的岩金的详细研究结果,认为该区砂金主要是碎屑成因,但亦可能存在另一种生长机制,即汞齐化增生。列举了金与汞共生的地球化学、矿物学、地质学证据,论述了汞齐化增生的主要内容,即焊接、熔解及重结晶机制。 相似文献
70.
In the Lesser Garhwal Himalaya, the North Almora Thrust separates the overlying medium-grade Dudatoli-Almora crystallines
of Precambrian age from the unmetamorphosed to partly metamorphosed rocks of the Garhwal Group of Late Precambrian age. The
crystalline nappe sheet consists of flaggy to schistose quartzites, granite gneisses and garnetiferous mica schist members
in an ascending order. In different localities. different members of the Dudatoli-Almora crystallines are exposed along the
thrust plane. Southwest of Adbadri fine-grained mylonitized schistose quartzites of Dudatoli-AImora crystallines are in contact
with the underlying metabasites of the Garhwal Group. The mylonitized schistose quartzites consist of alternating thick (1
to 2m) quartzite and thin (10 to 20cm) micaceous quartzite bands. The micaceous quartzites can be further differentiated into
alternating quartz-rich (0-5 to 2.0 cm thick) and mica-rich (0.2 to 1.0 cm thick) layers. In the quartzites the C-surfaces
are parallel to the S-surfaces defined by the alternating quartz-rich and mica-rich layers. Further, the S-surfaces exhibit
almost similar folds with multiple wavelengths where the axial planes are nearly parallel and enveloping surfaces are oblique
to the lithological layering. The evolution of these folds has been envisaged in three phases of deformation on the basis
of field evidence, fold geometry and microstructures.
During the first phase buckle folds (F
1) developed in thin micaceous quartzite layers. whereas thick quartzite bands underwent only layer parallel shortening. During
the second phase the stress orientation changed and the limbs ofF
1 folds were folded (F
2). During the third phase of deformation which coincided with thrusting, the rocks were sheared, mylonitized and developed
microstructures exhibiting dynamic recrystallization by the processes of subgrain rotation, and continual and discontinuai
grain boundary migration. This phase was also responsible for the development of C-surfaces parallel to the lithological layering.
Further, in the folded micaceous quartzite layers shearing resulted in the development of C-surfaces parallel to the axial
planes ofF
2 folds. 相似文献