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101.
Behavior of Siderophile and Chalcophile Elements in the Subcontinental Lithospheric Mantle beneath the Changbaishan Volcano,NE China 总被引:1,自引:0,他引:1
The mantle xenoliths in the Quaternary ChangbaishanVolcano in southern Jilin Province contain spinel-facies lherzolites. The equilibration temperatures for these samples range from 902oC to 1064oC based on the two-pyroxene thermometer of Brey and K?hler (1990), and using the oxybarometry of Nell and Wood (1991), the oxidation state was estimated from FMQ-1.32 to -0.38 with an average value of FMQ-0.81 (n?=?8), which is comparable to that of abyssal peridotites and the asthenospheric mantle. The fO2 values of peridotites, together with their bulk rock compositions (e.g., Mg#, Al2O3, CaO, Ni, Co, Cr) and mineral compositions (e.g., Mg# of olivine and pyroxene, Cr# [=Cr/[Cr+Al]] and Mg# [=Mg/[Mg+Fe2+] of spinel), suggest that the present-day subcontinental lithospheric mantle (SCLM) beneath the Changbaishan Volcano most likely formed from an upwelling asthenosphere at some time after the late Mesozoic and has undergone a low degree of partial melting. The studied lherzolite xenoliths show low concentrations of S, Cu, and platinum group elements (PGE), which plot a flat pattern on primitive-mantle normalized diagram. Very low concentrations in our samples suggest that PGEs occur as alloys or hosted by silicate and oxide minerals. The compositions of the studied samples are similar to those of peridotite xenoliths in the Longgang volcanic field (LVF) in their mineralogy and bulk rock compositions including the abundance of chalcophile and siderophile elements. However, they are distinctly different from those of peridotite xenoliths in other areas of the North China Craton (NCC) in terms of Cu, S and PGE. Our data suggest that the SCLM underlying the northeastern part of the NCC may represent a distinct unit of the newly formed lithospheric mantle. 相似文献
102.
长白山天池火山区上地壳Q值结构 总被引:4,自引:0,他引:4
同天然地震资料相比,人工地震剖面观测资料具有震源球对称且位置已知,观测点位密集、震源和观测点呈直线排列、速度结构已知等突出优点。本文提出了一种利用人工地震振幅资料反演分层介质中Q值的新方法。在利用该方法得到Q值深度函数的基础上,综合各炮点的结果,可研究Q值沿剖面的横向变化。利用上述方法计算了长白山L1剖面上地壳的Q值值结构。发现长白山天池火山区下方Q值明显低于邻近地区,该区域位于天池地区壳内低速异常体的上部,对应于已往的火山喷发通道。 相似文献
103.
长白山天池火山双岩浆房岩浆作用与互动式喷发 总被引:6,自引:0,他引:6
广义的长白山火山在我国境内包括天池火山、望天鹅火山、图们江火山和龙岗火山,是我国最大的第四纪火山岩分布区。长白山各个火山区的火山活动具有此起彼伏的穿时性特征,天池火山之下地壳和地幔两个岩浆房具有上下呼应、互动式喷发之特点。一方面来自地幔的钾质粗面玄武岩浆直接喷出地表,在天池火山锥体内外形成诸多小火山渣锥;另一方面钾质粗面玄武岩浆持续补给地壳岩浆房,发生岩浆分离结晶作用和混合作用,形成双峰式火山岩特征并触发千年大喷发。西太平洋板块俯冲-东北亚大陆弧后引张是长白山天池火山喷发的动力学机制。 相似文献
104.
中国大陆火山活动对气候与环境影响的研究进展 总被引:1,自引:0,他引:1
本文简要回顾了我国中、新生代典型中酸性火山活动的气候环境效应的研究进展,重点讨论了新生代长白山天池火山喷发和中生代辽西火山活动对气候环境造成的影响。天池火山气体含量呈现两个相同趋势的旋回式变化,从早到晚,卤化物和H2O呈降低趋势,而硫化物气体呈增加趋势。火山旋回早期富含HF气体导致动物窒息、甚至大批集群死亡;晚期喷出的大量硫化物气体可以形成大规模酸雨和剧毒火山灰云幕,对周围的动植物生长有严重影响。辽西火山气体可分为三种组合,形成酸雨,导致地表温度下降,加速臭氧浓度降低,甚至破坏臭氧层,从而对生物的生存环境造成严重危害。 相似文献
105.
长白山火山地幔不均一性——微量元素及同位素地球化学研究 总被引:2,自引:3,他引:2
大陆火山的复杂性是一个普遍关注的全球性问题,也是一个长期以来悬而未解决的地质问题。长白山火山位于亚洲板块东部的活动边缘,受到西太平洋俯冲的影响,新生代构造和火山活动活跃,为探讨大陆火山成因及其地幔源区特点提供了极佳的天然实验室。天池火山和龙岗火山是长白山地区两个重要的新生代火山区,其火山岩分布具有空间相邻、火山活动时代相似的特点,本文通过对基性火山岩的岩石学和地球化学对比研究,指出天池火山和龙岗火山具有明显的地球化学不均一性,包括微量元素不均一性和 Sr、Nd、Pb 同位素不均一性,来自于不同的地幔源区,天池火山和龙岗火山火山岩分布相邻,覆盖范围东西最大不过100多公里,因此这是典型的小尺度地幔地球化学不均一的特点。Sr、Nd 同位素特征显示龙岗火山来自于原始地幔,而天池火山来自于原始地幔和富集地幔混合源区。不相容元素 Nb、Ta 显示,天池火山 Ta 元素含量很低(主要落在0.17~2.15 ppm 的范围),具有明显的负 Ta 异常和明显的 Nb/Ta 分异(Nb/Ta=10~50,个别达到100以上),可能是板片部分熔融产物与金红石等副矿物反应的结果,暗示了西太平洋板块俯冲机制的影响;而龙岗火山没有明显 Nb、Ta 亏损或者分异。 相似文献
106.
Attenuation of Coda Waves at the Changbaishan Tianchi Volcanic Area in Northeast China 总被引:2,自引:0,他引:2
21 earthquakes recorded by a temporary seismic network in the Changbaishan Tianchi volcanic area in Northeast China operated
during the summer of 2002 and 2003 were analyzed to estimate the S coda attenuation. The attenuation quality factor Qc was estimated using the single scattering attenuation model of Sato (1977) in the frequency band from 4 to 24 Hz. All the
events studied in this paper occurred at depths from 2 to 6 km with ML of 1.4–2.8. The epicentral distances are less than
25 km. For all events which occurred near the Tianchi Lake (caldera), the Qc patterns obtained at the stations near the lake are similar, and the Qc values are relatively small. At the stations located about 15 km east of the Tianchi Lake, however, the average Qc is significantly higher. For an event which occurred 25km from the lake to the west, Qc patterns derived at the stations near the lake are quite similar to the above mentioned Qc for stations located in the east. Further study shows that Qc value in the north and central areas of the volcano is relatively lower than that in the surrounding area. Compared to other
volcanic areas in the world, the average Qc of the Changbaishan Tianchi volcanic area is obviously lower. The deep seismic sounding and teleseismic receiver function
studies indicated more than one lower velocity layer in the crust. The MT studies suggested the presence of high conductive
bodies beneath the area. We interpret the strong attenuation of coda waves near the Changbaishan Tianchi volcano as being
possibly related to high temperature medium caused by shallow magma chambers. 相似文献
107.
A Preliminary Study of the Types of Volcanic Earthquakes and Volcanic Activity at the Changbaishan Tianchi Volcano 总被引:1,自引:0,他引:1
Ming Yuehong 《中国地震研究》2006,20(3):286-294
INTRODUCTIONThe Changbaishan volcano is located in Jilin Province , along the border of China and NorthKorea .It isthelargest nature reservein China .Changbaishan belongstothe northeastern Asian activebelt in the eastern margin of the Euro-Asia plate . The Changbaishan volcano is a gigantic ,polygenetic ,central volcano,and has been active since Holocene .The early eruption started in thePliocene andformedthe basaltic shield. Duringthe middle and late Pleistocene ,the volcanic cone … 相似文献
108.
109.
110.
高频S波随着传播距离的增大其均方根(RMS)包络逐渐变宽,我们把这种现象称为S波包络展宽现象.S波传播路径上随机分布的非均匀体对S波的多次前向散射和绕射作用是导致S波包络展宽现象的主要原因,因此可用S波包络展宽现象来研究介质非均匀性.本文采用S波包络峰值延时来对S波包络展宽现象进行量化.S波包络峰值延时定义为S波初至与其均方根包络峰值最大值之间的时间差.本文选用长白山天池火山区的小震记录,运用S波包络峰值延时对长白山天池火山口地区的介质非均匀性进行了评价.结果发现长白山天池火山区呈现强烈的介质非均匀性,在0~2 km深度范围内介质非均匀性表现出南部强北部弱的空间分布特征;在2~5 km深度范围内介质非均匀性的空间分布特征与频率具有相关性;天池火山区介质非均匀性具有明显的多尺度特性;强弱非均匀性接触带,往往是地震频发地带.根据地震与非均匀体在空间分布的相对位置,我们认为火山区介质非均匀性可能反映了火山早期喷发堆积物介质结构的差异. 相似文献