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61.
Garnet-sillimanite gneisses, locally known as khondalites, occur abundantly in the Chilka Lake granulite terrane belonging
to the Eastern Ghats Proterozoic belt of India. Though their chemistry has been modified by partial melting, it is evident
that the majority of these rocks are metapelitic, with some tending to be metapsammitic. Five petrographically distinct groups
are present within the khondalites of which the most abundant group is characteristically low in Mg:Fe ratios — the main chemical
discriminant separating the five groups. The variations in Mg:Fe ratios of the garnets, biotites, cordierites, orthopyroxenes
and spinels from the metapelites are compatible with those in the bulk rocks.
A suite of granitoids containing garnet, K-feldspar, plagioclase and quartz, commonly referred to as leptynites in Indian
granulite terranes, are interlayered with khondalites on the scale of exposures; in a few spots, the intercalated layers are
thin. The peraluminous character of the leptynites and presence of sillimanite trails within garnets in some of them suggest
derivation of leptynites by partial melting of khondalites. Here we examine this connection in the light of results derived
from dehydration melting experiments of micas in pelitic and psammitic rocks.
The plots of leptynites of different chemical compositions in a (MgO + FeO)-Na2O-K2O projection match the composition of liquids derived by biotite and muscovite dehydration melting, when corrected for co-products
of melting reactions constrained by mass balance and modal considerations. The melt components of the leptynites describe
four clusters in the M-N-K diagram. One of them matches melts produced dominantly by muscovite dehydration melting, while
three clusters correspond to melting of biotite. The relative disposition of the clusters suggests two trends, which can be
correlated with different paths that pelitic and psammitic protoliths are expected to generate during dehydration melting.
Thus the leptynites evidently represent granitoids which were produced by dehydration melting in metapelites of different
compositions.
The contents of Ti, Y, Nb, Zr and Th in several leptynites indicate departures from equilibrium melt compositions, and entrainment
of restites is considered to be the main causative factor. Disequilibrium in terms of major elements is illustrated by leucosomes
within migmatites developed in a group of metapelites. But the discrete leptynites that have been compared with experimental
melts approach equilibrium melt compositions closely. 相似文献
63.
新疆北部的改造系列花岗岩演化由斜长花岗岩阶段、钾长花岗岩阶段至碱长花岗岩阶段,其稀土配分组成递降曲线簇.新疆北部的同熔型花岗岩类稀土配分基本为轻稀土富集型,具Eu负异常,有递增曲线簇和递降曲线簇两种情况.深源碱性系列轻重稀土比值大、Eu负异常一般不显著.文中还叙述了新疆北部的幔分异系列花岗岩类及一些古老花岗岩的稀土特征. 相似文献
64.
Nadezhda KANYGINA Andrey TRETYAKOV Dmitriy ALEXEIEV Kirill DEGTYAREV Anfisa SKOBLENKO Natalia SOLOSHENKO Boris ERMOLAEV 《《地质学报》英文版》2024,98(1):67-82
The combined petrographic, petrological, geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian tectonic evolution of the Aktau–Yili terrane. It is one of the largest Precambrian crustal blocks in the western Central Asian orogenic belt. The U-Pb single-grain zircon ages indicate that granite-gneisses formed from the same source and crystallised in the early Neoproterozoic ca. 930–920 Ma. The chemical composition of gneisses corresponds to A2-type granites. The whole-rock Nd isotopic characteristics (εNd(t) = ?4.9 to ?1.0 and TNd(DM-2st) = 1.9 to 1.7 Ga) indicate the involvement of Paleoproterozoic crustal rocks in magma generation. Early Neoproterozoic ca. 930–920 Ma A-type granitoids in the Aktau–Yili terrane of South and Central Kazakhstan might reflect within-plate magmatism adjacent to the collisional belt or a local extension setting in back-arc areas of the continental arc. 相似文献
65.
1995年第二季度,全球地震活动恢复到1994年的高水平态势:浅源地震频数猛增,并出现两次Ms7.7以上巨大地震。大洋岛弧带成为本季度地震活动中心。所罗门群岛有两次中强震。菲律宾萨马岛附近发生大震群。千岛群岛大震的余震未息。秘鲁北部和缅印边界各有一次中深源地震。希腊发生中强地震两次。萨哈林岛地震显示全球地震信息。 相似文献
66.
67.
以鄂东铁山、大王寨岩体为例,讨论了花岗岩类岩体中包体拟采取的应变测量方法,其中包括主应变值的测定、包体的原始轴比的确定以及包体与寄主岩存在明显粘性差条件下的应变测量方法。 相似文献
68.
东天山小石头泉铜多金属矿区火山岩-次火山岩地球化学与成矿构造背景 总被引:1,自引:0,他引:1
小石头泉铜多金属矿位于新疆哈密市东北200km,在区域地质构造上处于东天山哈尔里克岛弧东段。本文主要对矿区火山岩的主量、微量元素及同位素组成进行测试和研究。含矿岩石以流纹斑岩、英安岩、英安斑岩为主,SiO_2含量为51.96%~72.58%,Na_2O K_2O 为3.1%~7.73%,计算里特曼指数σ<3.3,显示具有钙碱性岩的特征;稀土元素配分形式为轻稀土相对富集,其中英安岩 Eu 负异常比安山岩更为明显,说明源区有斜长石的残留或岩浆演化经历了结晶分异作用;微量元素具有典型的岛弧火山岩的地球化学特征,如 Ta、Nb、Ti 等元素较板内火山岩的明显亏损;岩石初始锶(~(87)Sr/~(86)Sr)_i 平均值为0.7043,εNd(t)为4.7,反映火山岩形成源区以幔源为主,混有部分壳源物质。以上岩石地球化学研究结果表明,该区火山岩形成于火山岛弧环境。通过与东天山大南湖岛弧火山岩对比,发现两地区的同时代火山岩地球化学属性存在一定差异,大南湖岛弧火山岩区以发育 Adakite 岩为特征,而哈尔里克岛弧缺少Adakite 岩,可能反映该区火山岩的形成与部分熔融的洋壳交代地幔楔有关。本文认为小石头泉地区为典型火山岛弧环境,有利于火山热液型多金属矿床的形成。 相似文献
69.
Proterozoic granitoid rocks in Zhejiang Province were formed in the Shengongian period (1.8–1.9 Ga) and the Late Jinningian
period (0.6–0.9 Ga), respectively. Petrogenetic problems are discussed based on chemical (major, trace elements and REEs)
and Nd-Sr isotopic compositions. The Shengongian granites resulted from partial melting of the Badu Group and the Late Jinningian
granites are of mantle derivation with or without contamination of crustal material. The crust in Zhejiang had undergone three
major periods of growth during 2.6–2.7 Ga, 0.8–1.1 Ga and 0.10–0.12 Ga after it was generated in Archean time. Compositional
fractionation in the process of crust evolution is not evident. The presence of Late Jinningian granites of mantle and mantle-crust-derivation
along the Jiangshan-Shaoxing Fault is indicative of crust subduction at that time.
This project was finantially supported by both the National Natural Science Foundation of China (No. 9490011) and the Zhongguancun
Test Center. 相似文献
70.
胶东招掖地区与金矿化有关花岗岩类继承锆石年龄及其意义 总被引:5,自引:0,他引:5
花岗岩类锆石SHRIMP研究表明,胶东招掖地区与金矿化有关花岗岩类含有大量不同时代的继承锆石,发现3446±2-3114±4Ma的继承锆石表明胶东地区存在古太古代硅铝核。大量印支期继承锆石(平均年龄219Ma)的年龄与南、北克拉通碰撞时代一致,推测这些锆石极可能来自其源岩,即华南、华北克拉通碰撞造山花岗岩。否定了玲珑花岗岩主要是胶东岩群交代-重熔形成的传统认识。郭家岭型花岗岩中含有较多新太古代和古元古代继承锆石,表明其源岩有较多的胶东岩群和荆山群变镁铁质岩石。 相似文献