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101.
Hg and As Minerals in Fluid Inclusions from the Williams Mine,Hemlo,and Their Genetic Implications 总被引:1,自引:0,他引:1
卢焕章 《中国地球化学学报》2002,21(1):1-18
The Hemlo mineralization is enigmatic compared to general Archean lode gold deposits based on the fact that is characterized by an exotic mineralogy containing elements such as As,Hg,Sb,Ba,V and Mo.The genetic concepts range from syngenetc to epigenetic types of mineralization.This reconnaissance study was designed to examine the relationshp of Hg-As minerals with respect of fluid inclusions in the Williams mine(formerly known as the Page Williams mine)covering the A and C ore zones. 相似文献
102.
103.
Don Aldiss Helen Burke Barrie Chacksfield Richard Bingley Norman Teferle Simon Williams David Blackman Richard Burren Nigel Press 《Proceedings of the Geologists' Association. Geologists' Association》2014
Long term planning for flood risk management in coastal areas requires timely and reliable information on changes in land and sea levels. A high resolution map of current changes in land levels in the London and Thames estuary area has been generated by satellite-based persistent scatterer interferometry (PSI), aligned to absolute gravity (AG) and global positioning system (GPS) measurements. This map has been qualitatively validated by geological interpretation, which demonstrates a variety of controlling influences on the rates of land level change, ranging from near-surface to deep-seated mechanisms and from less than a decade to more than 100,000 years’ duration. 相似文献
104.
Anne Charland Don Francis John Ludden 《Contributions to Mineralogy and Petrology》1995,121(3):289-302
Volumetrically subordinate alkaline mafic lava flows form a late capping stage over the earlier felsic lavas that form the
shield of the Itcha Volcanic Complex (IVC), of the Anahim Volcanic Belt (AVB) in central British Columbia (B.C.). The mafic
capping stage of the IVC is dominated by hawaiites which are the earliest of the mafic lavas, and are succeeded by alkali
olivine basalts (AOB) and then by basanites. The alkali olivine basalts can be subdivided into high-, intermediate- and low-MgO
AOB groups, all of which share similar HFSE ratios (e.g. Nb/Zr) with the hawaiites. High Al contents and Sr/Zr ratios indicate
that hawaiites and Fe-rich evolved AOB were derived from primitive AOB parental magmas by crystal fractionation of a wehrlitic
assemblage at pressures on the order of 8 to 10 kbar. High Si and low Fe contents indicate that the majority of the evolved
AOB lavas, however, do not represent an intermediate stage in the liquid line of descent to hawaiites, but were most likely
produced by gabbroic fractionation from primitive AOB magmas at relatively low pressures. The parental magmas of the majority
of these lavas were distinct from those of the observed high-MgO basalts, having higher HFSE contents and being more Si-under-saturated.
The high Al, high Sr/Zr signature of high-pressure fractionation of a clinopyroxene-dominated assemblage in the IVC is shared
by hawaiites of other alkaline volcanic suites of the Canadian Cordillera, such as the Edziza Volcanic Complex in northern
B.C. and appears to be a feature of hawaiites in many localities, including Hawaii and Iceland. Viscosities calculated for
both high- and low-pressure crystal fractionation models suggest that aphyric hawaiites are residual liquids escaped from
a wehrlitic crystalline network, at elevated pressures, possibly at the base of the crust.
Editorial responsibility: T.L. Grove 相似文献
105.
Thermodynamic analysis of the system Na2O-K2O-CaO-Al2O3-SiO2-H2O-F2O–1 provides phase equilibria and solidus compatibilities of rock-forming silicates and fluorides in evolved granitic systems and associated hydrothermal processes. The interaction of fluorine with aluminosilicate melts and solids corresponds to progressive fluorination of their constituent oxides by the thermodynamic component F2O–1. The chemical potential (F2O–1) buffered by reaction of the type: MOn/2 (s)+n/2 [F2O–1]=MFn (s, g) where M=K, Na, Ca, Al, Si, explains the sequential formation of fluorides: carobbiite, villiaumite, fluorite, AlF3, SiF4 as well as the common coexistence of alkali- and alkali-earth fluorides with rock-forming aluminosilicates. Formation of fluorine-bearing minerals first starts in peralkaline silica-undersaturated, proceeds in peraluminous silica-oversaturated compositions and causes progressive destabilization of nepheline, albite and quartz, in favour of villiaumite, cryolite, topaz, chiolite. Additionally, it implies the increase of buffered fluorine solubilities in silicate melts or aqueous fluids from peralkaline silica-undersaturated to peraluminous silica-oversaturated environments. Subsolidus equilibria reveal several incompatibilities: (i) topaz is unstable with nepheline or villiaumite; (ii) chiolite is not compatible with albite because it only occurs only at very high F2O–1 levels. The stability of topaz, fluorite, cryolite and villiaumite in natural felsic systems is related to their peralkalinity (peraluminosity), calcia and silica activity, and linked by corresponding chemical potentials to rock-forming mineral buffers. Villiaumite is stable in strongly peralkaline and Ca-poor compositions (An<0.001). Similarly, cryolite stability requires coexistence with nearly-pure albite (An<2). Granitic rocks with Ca-bearing plagioclase (An>5) saturate with topaz or fluorite. Crystallization of topaz is restricted to peraluminous conditions, consistent with the presence of Li-micas or anhydrous aluminosilicates (cordierite, garnet, andalusite). Fluorite is predicted to be stable in peraluminous biotite granites, amphibole-, clinopyroxene- or titanite-bearing calc-alkaline suites as well as in peralkaline granitic and syenitic rocks. Fluorine concentrations in felsic melts buffered by the coexistence of F-bearing minerals and feldspars increase from peralkaline through metaluminous to mildly peraluminous compositions. At low-temperature conditions, the hydrothermal evolution of peraluminous granitic and greisen systems is controlled by white mica-feldspar-fluoride equilibria. With decreasing temperature, topaz gradually breaks down via: (i) (OH)F–1 substitution and fluorine transfer to fluorite by decalcification of plagioclase below 600 °C, (ii) formation of muscovite and additional fluorite at 475–315 °C, and (iii) formation of paragonite and cryolite, consuming F-rich topaz and albite below 315 °C. These equilibria explain the absence of magmatic fluorite in Ca-bearing topaz granitic rocks; its abundance in hydrothermal rocks is due to: (i) closed-system defluorination of topaz, (ii) open-system decalcification of plagioclase or (iii) hydrolytic alteration. These results provide a complete framework for the investigation of fluorine-bearing mineral stabilities in felsic igneous suites.Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material.Editorial responsibility: T.L. Grove 相似文献
106.
107.
西藏拉萨地块西部扎布耶茶卡火山岩的成因与意义 总被引:2,自引:0,他引:2
近年来在青藏高原南部拉萨地块不断发现的碰撞后钾质和超钾质岩石,对于揭示印度与亚洲大陆碰撞以来高原岩石圈的深部作用与过程发挥了重要作用。分布在拉萨地块西部扎布耶茶卡东岸的钾质和超钾质火山岩主体喷发时代为中新世(约16Ma),出露面积约为400km2,火山岩持续喷发0.45Ma,估算的喷发速率约为0.26×10-3km3/a。岩石包括3种类型,第一类(约16Ma)为超钾质的粗面安山岩,SiO2低(55%~58 %),高Fe2O3、MgO、TiO2;第二类(约27Ma)为钾玄质的响岩和粗面岩;第三类是高SiO2的钾玄质—超钾质粗面岩(SiO2=59%~64%)和流纹岩(SiO2=69%)。岩石显示轻稀土元素、大离子亲石元素高度富集和部分高场强元素亏损的特征,部分中酸性岩石显示高Sr低Y的埃达克岩的属性。岩石的Sr-Nd-Pb-O同位素组成与拉萨地块典型的超钾质岩石明显不同,显示亲青藏高原北部地球化学省的地球化学特征。扎布耶茶卡不同类型的岩浆代表了碰撞后高原南部岩石圈减薄作用导致的岩石圈不同层次的岩石部分熔融的产物。 相似文献
108.
This article explores the potential impact of training and employment with wildfire management agencies on the retention of Indigenous fire knowledge. It focuses on the comparative knowledge and experiences of Indigenous Elders, cultural practitioners, and land stewards in connection with “modern” political constructs of fire in New South Wales and Queensland, Australia, and California in the United States of America. This article emphasises the close link between cross-cultural acceptance, integration of Indigenous and agency fire cultures, and the ways in which knowledge types are shared or withheld. While agency fire fighting provides an opportunity for Indigenous people to connect and care for country, it simultaneously allows for the breaking of traditional rules surrounding what knowledge is shared with whom in the context of Indigenous cultural burning. By highlighting how privilege intersects with ethnicity, class, gender and age, this article demonstrates how greater cross-cultural acceptance could aid ongoing debates on how to coexist with wildfire today. 相似文献
109.
对位于北极Svalbard群岛新奥尔松(Ny-lesund)的Austre Lovénbreen和Pedersenbreen冰川首个物质平衡年(2005/06年度)的冰川表面物质平衡及其运动特征进行研究,并阐述了Austre Lovénbreen冰川末端位置的变化状况。结果表明:(1)Austre Lovénbreen和Pedersenbreen冰川净物质平衡分别为-0.44和-0.20m w.e.,年消融量分别为0.99和0.94m w.e.,对应冰川零平衡线高度分别为478.10和494.87m。(2)两条冰川符合Svalbard地区跃动冰川运动的特征模式。运动速度矢量的水平分量表现为:向主流线辐合或平行于主流线。下游运动速度较慢,而在中上游运动相对较快。Austre Lovénbreen冰川表面各观测点的运动速度平均值为2.28m·a-1,运动速度最大值和最小值分别为3.91和0.81m·a-1;Pedersenbreen冰川表面观测点运动速度平均值为6.74m·a-1,运动速度最大值和最小值分别为8.13和5.49m·a-1。运动速度矢量的垂直分量表现为:消融区冰川消融量随海拔升高而减弱,Austr... 相似文献
110.
We study a set of very high-quality records of first-order overtone Rayleigh waves from the deep-focus earthquake of September 29, 1973, in the Japan Sea. Standard surface wave techniques are used with these overtones, treated as individual seismic phases, to retrieve radiation pattern, Q, moment and phase velocity. A figure of M0 = (6.7 ± 1.4) × 1027dyn-cm is obtained, in total agreement with published values computed from either P waves, or fundamental Rayleigh waves. We also demonstrate the feasibility of using overtones as individual seismic phases in order to investigate their dispersion and attenuation properties. 相似文献