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121.
The distribution of polygenetic and monogenetic volcanoes of the Neogene-Quaternary Cappadocian Volcanic Province (CVP) is analyzed to investigate the relationship between vent location and regional tectonic lineaments. Two fault systems exist in the province. One system (Miocene-Quaternary Tuzgölü–Ecemiş system) is oblique, whereas the other system (late Miocene–Pliocene CVP system) is parallel to the long axis of the CVP. The polygenetic volcanoes are aligned parallel to the second system but concentrate around the major faults of the first system. Regional offsets are proposed along the first fault system based on the distribution of the polygenetic volcanoes. The monogenetic volcanoes group into five geographically distinct clusters. In the western part of the CVP, the monogenetic cones are aligned parallel to the CVP system, whereas in the central part the cones are fed by dikes injected along the recent fractures of the Tuzgölü–Ecemiş system. In the eastern part, the monogenetic cones form along the radial fractures of the Erciyes composite volcano. 相似文献
122.
黑龙江尚志一面坡固安屯组火山碎屑岩LA-ICP-MS锆石U-Pb定年和岩石化学特征 总被引:1,自引:0,他引:1
对黑龙江尚志一面坡地区固安屯组砂、板岩中火山碎屑岩的夹层晶屑凝灰岩进行LA-ICP-MS锆石U-Pb同位素定年和地球化学分析。结果表明,岩石Si O2含量为63.43%~75.01%,相对较高,主要为英安质和流纹质晶屑凝灰岩,属于钙碱性系列和高钾钙碱性系列;具有富集大离子亲石元素Rb、K等,而亏损Sr元素;轻稀土富集,重稀土亏损,有较明显的负铕异常,具有火山弧岩浆成分特点。主要获得晶屑凝灰岩,加权平均年龄为258.0±1.6 Ma(MSWD=0.113),代表固安屯组上部火山碎屑岩夹层的形成年龄。此结果表明,在黑龙江尚志一面坡地区发育的固安屯组的形成时代为晚二叠世。 相似文献
123.
铁铝榴石在凝灰岩中有两种产状:一种呈晶屑状稀疏地分布于凝灰岩中;另一种为四角三八面体和菱形十二面体的聚形铁铝榴石晶体,生于凝灰岩的孔洞中和柱状节理面上。 铁铝榴石为褐红色,少数为血红色,玻璃光泽,断口油脂光泽,透明。摩式硬度6—7.5,无解理,比重:D_1(晶屑)=4.15、D_2(晶体)=4.10。薄片下为浅褐色,均质体,折射率:N_1(晶屑)=1.822、N_2(晶体)=1.823。铁铝榴石结晶化学式: 晶屑:(Fe_(1.779)~(2 )Mn_(0.750)Mg_(0.022)Ca_(0.057))_(2.608)(Al_(1.890)Fe_(0.178)~(3 )Ti_(0.009))_(2.077)Si_(3.133)O_(12) 晶体:(Fe_(2.045)~(2 )Mn_(0.614)Mg_(0.025)Ca_(0.065))_(2.749)(Al_(1.759)Fe_(0.062)~(3 )Ti_(0.006))_(1.327)Si_(3.254)O_(12) 本文还作出了铁铝榴石晶屑和晶体的红外光谱吸收曲线。 流纹英安凝灰岩中的铁铝榴石晶屑是从岩浆中原始结晶的。而生于凝灰岩孔洞中和柱状节理面上的铁铝榴石晶体,则是凝灰岩在冷却成岩过程中火山气水热液作用的产物。 流纹英安凝灰岩中铁铝榴石的发现,为研究石榴石的产状提供了新资料。 相似文献
124.
Jeju Island, the largest Quaternary volcanic island in Korea, has formed mostly since the early Pleistocene, but its latest chronology of volcanism and sedimentation is still poorly constrained. Here we report optically stimulated luminescence (OSL) ages for two hydromagmatic volcanoes on the southwestern coast of Jeju Island, i.e., the Songaksan and Suwolbong tuff rings. The basaltic tuffs of these volcanoes contain abundant quartz sands from underlying marine sedimentary sequences. Two samples collected from the middle part of the Songaksan Tuff yielded highly reproducible quartz single-aliquot regenerative-dose (SAR) OSL ages of 7.0±0.3 ka, providing the first direct age estimate of Holocene volcanism in Jeju Island. The quartz OSL age estimate of 5.1±0.3 ka for the younger reworked basaltic tuff (the Hamori Formation) is comparable with previous radiocarbon and U-series disequilibrium dating of fossil mollusk shells. Two samples from the Suwolbong Tuff show quartz OSL age estimates of 18.3±0.7 and 18.6±0.9 ka, which are identical within error ranges and younger than the quartz OSL age estimate of 23.2±1.0 ka for the underlying Gosan Formation. This study confirms that volcanism and attendant sedimentation were active in Jeju Island until very recently. 相似文献
125.
Hydrogeologic characteristics of the alluvial tuff aquifer of northern Sahand Mountain slopes, Tabriz, Iran 总被引:3,自引:0,他引:3
The Tabriz area is a densely populated area of northwestern Iran (more than 1.5 million in population) with a large proportion of its drinking, domestic, industrial and agricultural water supplied from groundwater resources. The average rate of drinking and industrial water use in the city of Tabriz is about 3.45 m3 s–1. The Plio-Pleistocene unconfined alluvial tuff aquifer (about 1,275 km2), the most important aquifer in the area, has been known for many years as a reliable resource. The greatest estimated thickness of the alluvial tuff lies in the Saidabad area, with 350 m thickness. There are 994 deep and 284 shallow active pumping wells and 83 qanats operate in the alluvial tuff aquifer. The total water withdrawal from all these artificial discharge points has been measured at 72, 3.8 and 17 million m3/year, respectively. Analytical and numerical methods have been applied to the constant rate pumping test data from the Saidabad wellfield (eight pumping and three observation wells). The values of electrical conductivity in the groundwater of alluvial tuff aquifer range from 203 to 960 μS cm–1 and bicarbonate type water dominates. 相似文献
126.
127.
The 12·710·5 Ma Cougar Point Tuff in southernIdaho, USA, consists of 10 large-volume (>102103 km3each), high-temperature (8001000°C), rhyolitic ash-flowtuffs erupted from the BruneauJarbidge volcanic centerof the Yellowstone hotspot. These tuffs provide evidence forcompositional and thermal zonation in pre-eruptive rhyolitemagma, and suggest the presence of a long-lived reservoir thatwas tapped by numerous large explosive eruptions. Pyroxene compositionsexhibit discrete compositional modes with respect to Fe andMg that define a linear spectrum punctuated by conspicuous gaps.Airfall glass compositions also cluster into modes, and thepresence of multiple modes indicates tapping of different magmavolumes during early phases of eruption. Equilibrium assemblagesof pigeonite and augite are used to reconstruct compositionaland thermal gradients in the pre-eruptive reservoir. The recurrenceof identical compositional modes and of mineral pairs equilibratedat high temperatures in successive eruptive units is consistentwith the persistence of their respective liquids in the magmareservoir. Recurrence intervals of identical modes range from0·3 to 0·9 Myr and suggest possible magma residencetimes of similar duration. Eruption ages, magma temperatures,Nd isotopes, and pyroxene and glass compositions are consistentwith a long-lived, dynamically evolving magma reservoir thatwas chemically and thermally zoned and composed of multiplediscrete magma volumes. KEY WORDS: ash-flow tuff; BruneauJarbidge; rhyolite; Yellowstone hotspot; residence time 相似文献
128.
I. P. Skilling 《Bulletin of Volcanology》1994,56(6-7):573-591
Marine shallow-water to emergent volcanoes have been described in detail, but comparable englacial centres are not well documented. Brown Bluff is a Pleistocene, shallow water, alkali basaltic volcano whose deposits were ponded within an englacial lake, enclosed by ice >400 m thick. Its evolution is divided chronologically into pillow volcano, hyalotuff cone, slope failure and hyaloclastite delta/subaerial stages. Seventeen lithofacies and five structural units (A-E) are recognised and described. The pillow volcano stage (Unit A) is similar to those of many submarine seamount volcanoes. It comprises extrusive and intrusive pillow lavas draped by slumped hyaloclastite. Units B and D define the hyalotuff cone stage, which was centred on a summit vent(s), and comprises slumped, poorly sorted hyalotuffs redeposited downslope by sediment gravity flows and ponded against an ice barrier. This stage also includes water-cooled subaerial lavas and massive hyalotuffs ponded within a crater. Cone construction was interrupted by drainage of the lake and slope failure of the northeast flank, represented by debris avalanche-type deposits (Unit C). Unit E represents the youngest stage and consists of a Gilbert-type hyaloclastite delta(s), which prograded away from a summit vent(s), and compound subaerial lavas. A second drainage episode allowed subaerial lavas to accumulate in the surrounding trough. 相似文献
129.
临澧县白土坡玻屑凝灰岩(或半固结火山灰)赋存在第四系下更新统,层状或似层状,岩石松散,镜下具典型的玻屑凝灰结构。主要由流纹质火山玻屑,少量斜长石、石英及黑云母晶屑以及粘上矿物等组成。流纹质火山玻璃的电子探针分析平均值(%):SiO_274.97、Al_2O_314.046、CaO0.326、KzO6.933、Na_2O2.536、FeO0.51,总量99.52。 相似文献
130.
印支运动深刻地改变了华南大陆和东亚的古地理格局,导致了大规模的海陆变迁。在扬子北缘发育有以紫红色碎屑岩为主的巴东组及相关地层,代表了从碳酸盐岩为主的海相沉积到碎屑岩为主的陆相沉积的转变。巴东组可划分为三段,即一、三段的紫红色粉砂岩、泥岩夹二段灰岩泥灰岩。由于巴东组三段的化石稀少,其年代归属一直存有争议。本文运用LA-ICP-MS定年方法,对新发现于鄂西秭归地区巴东组二段的凝灰岩夹层进行了锆石U-Pb定年。结果表明,来自于巴东组二段中部和顶部的两件凝灰岩样品分别形成于241.7±1.7Ma和237.5±2Ma。结合凝灰岩层的就位年龄和生物化石记录,巴东组地层时代被限定为中三叠世安尼期至晚三叠世卡尼期。凝灰岩中锆石颗粒多呈长柱状,无磨圆,发育明显的振荡环带,且具有与造山型岩浆锆石一致的微量元素化学特征。以巴东组灰岩为代表的"最高海相层"穿时地分布于鄂东南至川西一线,反映了上、中扬子区由中三叠世安尼期晚期至晚三叠世卡尼期海水大规模向西退去的海陆变迁特征。 相似文献