全文获取类型
收费全文 | 1262篇 |
免费 | 142篇 |
国内免费 | 348篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 7篇 |
地球物理 | 102篇 |
地质学 | 1555篇 |
海洋学 | 16篇 |
天文学 | 4篇 |
综合类 | 42篇 |
自然地理 | 24篇 |
出版年
2024年 | 4篇 |
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 21篇 |
2020年 | 28篇 |
2019年 | 42篇 |
2018年 | 38篇 |
2017年 | 32篇 |
2016年 | 36篇 |
2015年 | 38篇 |
2014年 | 36篇 |
2013年 | 85篇 |
2012年 | 64篇 |
2011年 | 49篇 |
2010年 | 38篇 |
2009年 | 67篇 |
2008年 | 55篇 |
2007年 | 83篇 |
2006年 | 82篇 |
2005年 | 62篇 |
2004年 | 70篇 |
2003年 | 65篇 |
2002年 | 56篇 |
2001年 | 59篇 |
2000年 | 59篇 |
1999年 | 66篇 |
1998年 | 53篇 |
1997年 | 51篇 |
1996年 | 58篇 |
1995年 | 62篇 |
1994年 | 54篇 |
1993年 | 55篇 |
1992年 | 33篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 27篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1981年 | 1篇 |
排序方式: 共有1752条查询结果,搜索用时 901 毫秒
441.
一种刚玉夕线钾长片麻岩的岩石学矿物学特征及形成环境 总被引:3,自引:0,他引:3
刚玉夕线钾长片麻岩是产于新太古代迭布斯格岩群中的一种低Si、高Al、高K的特殊岩石,主要包括刚玉钾长金红石片麻岩、黑云夕线钾长金红石片麻岩2种岩石组合,呈互层状产出。刚玉、夕线石和钾长石是通过白云母的变质分解和白云母 SiO2的变质反应而生成的。形成温度约为720—760℃,压力约为0.6-0.8GPa。由于温度和压力稍高,岩石中已开始出现重熔钾长石细脉。环带状次生白云母的出现属退变质反应。变质程度为区域中高温变质作用,达高角闪岩相,与围岩的变质程度一致。其原岩是在较短的稳定条件下由富K、富Al的花岗质岩石经强烈风化搬运进入大陆边缘沉积盆地,再经化学分解和沉积作用而形成的不同的原岩组合。 相似文献
442.
Barbara Seth Richard A. Armstrong Annett Büttner Igor M. Villa 《Earth and Planetary Science Letters》2005,230(3-4):355-378
This study presents the chronological evolution of the upper amphibolite facies Orue Unit in NW Namibia. Metasedimentary and meta-igneous rocks of the Orue Unit were investigated using the Pb–Pb stepwise leaching technique on garnet and rutile, U–Pb multi-grain analysis on rutile, Sm–Nd–Lu–Hf leaching technique on garnet, SHRIMP analysis on zircon and Ar–Ar dating on amphibole. Each of these techniques pertains to different processes that occurred before, during, or after the metamorphic peak. Our age data can be integrated with petrological constraints to provide a more complete understanding of the metamorphic cycle. Our pre-peak metamorphic zircon ages, peak metamorphic garnet ages and peak to late peak metamorphic amphibole 39Ar–40Ar ages bracket the upper amphibolite facies metamorphic event including hydration or dehydration processes into a time span of only ca. 20 Ma. The age data obtained by peak metamorphic mineral analyses cluster around 1340–1320 Ma. Based on age data and field observation, we interpret the upper amphibolite facies metamorphism as a large-scale regional mid-crustal event. Spot analyses of inherited zircon cores obtained by SHRIMP reflect the sedimentary origin of the respective rocks of the Orue Unit and derivation from Palaeoproterozoic protoliths. The metamorphic rocks south of the anorthositic Kunene Intrusive Complex (KIC) have previously been ascribed to the Palaeoproterozoic Epupa Complex at the SW margin of the Congo craton and were thus thought to be older than the Mesoproterozoic KIC. Our data show that the high-grade metamorphic overprint took place 30–50 Ma after emplacement of the KIC. Rutile growth ages of 1248 Ma in one sample reflect fluid activity which seems to be a local phenomenon since there is no other evidence of geological activity throughout the Orue Unit at that time. The rutile ages predate the emplacement of satellite intrusions in that area by 30 Ma and there is no causal relation between these two events. 相似文献
443.
Ultrahigh pressure (>7 GPa) gneissic K-feldspar (-bearing) garnet clinopyroxenite in the Altyn Tagh, NW China: Evi- dence from clinopyroxene exsolution in garnet 总被引:13,自引:0,他引:13
LIU Liang CHEN Danling ZHANG Anda SUN Yong WANG Yan YANG Jiaxi & LUO Jinhai . Key Laboratory of Continental Dynamics of the Ministry of Education of China Northwest University Xi’an China . College of Earth Science Land Resources Chang’an University Xi’an China . The Laboratory of Orogen Basin of the Ministry of Education Peking University Beijing China 《中国科学D辑(英文版)》2005,48(7)
Since the ultra-high pressure metamorphic rocks with coesite and diamond indicators,which are formed under the condition of deep-subduction of continental crust,have been recognized[1―4],exsolution structures of the ultra-high pressure minerals such as pyroxene,olivine,garnet and sphene in the various kinds of rocks have attracted the great interests and attention of many researchers[5―18].Some exsolution structures,such as clinopyroxene+rutile+apatite[13]or quartz+rutile+apatite[15]exsolutio… 相似文献
444.
Vapor-Absent Melting of Tonalite at 15-32 kbar 总被引:13,自引:0,他引:13
The behavior of igneous continental crust during subductionis modeled by means of vapor-absent partial melting experimentson a tonalite, containing equal amounts of biotite and hornblende,at pressures of 1532 kbar. The experiments produce leucograniticmelts coexisting with garnet + omphacitic clinopyroxene + K-feldspar+ kyanite + quartz/coesite ± phengite ± zoisite.Experimental constraints and geometrical analysis of phase equilibriashow that the hydrous phases that control dehydration-meltingof tonalites in deep thickened continental crust and in theupper mantle are phengite and zoisite. The negatively slopingamphibole + quartz vapor-absent solidus characteristic of amphibolitesis largely suppressed in tonalites, because amphibole is eliminatedby water-conserving reactions that also consume K-feldspar andkyanite and produce phengite and zoisite. The temperature atwhich melt first appears in the experiments varies from <900°Cat 15 kbar, to 1000°C at 27 kbar, to <925°C at 32kbar. Moderate degrees of partial melting (2030%) yieldresidual assemblages with mantle-like densities but which canstill contain minor amounts of hydrous phases. Partial meltingof tonalitic crust during continental subduction can thus generateincompatible element-rich residues that would be able to remainin the mantle indefinitely, acting as long-term sources of metasomaticfluids. KEY WORDS: mantle; melting; metasomatism; tonalite; UHP metamorphism 相似文献
445.
In the Sandıklı-Afyon area, the very low-grade metamorphic Sandıklı Basement Complex with clastic sediments and Late Neoproterozoic felsic igneous rocks are unconformably overlain by a cover succession with red continental clastic rocks, tholeiitic basalts and siliciclastic rocks with Early Cambrian trace fossils. Illite crystallinity studies reveal that both the basement and cover units were metamorphosed at high anchizonal to epizonal conditions ( 300 °C). Textural data together with the detailed evaluation of the P–T–b0 grid, however, indicate that this thermal event has multiple phases. The first tectonothermal event was realized at pressures of 4.2 kb on the basis of b0-data and resulted in development of blastomylonites. This is supported by the presence of dynamo-metamorphosed pebbles within the basal conglomerates of the Lower Paleozoic cover series. The second event is post-Ordovician–pre-Jurassic in age, occurred at lower pressures 3.2 kb and produced a weakly developed cleavage in the siliciclastic rocks of the cover. The mineralogical/textural data across the basement-cover boundary therefore indicate the removal of an entire metamorphic zone and thus a metamorphic hiatus.
These data suggest that the Taurides were affected by a Late Neoproterozoic event as part of the peri-Gondwana during the Cadomian orogeny. 相似文献
446.
Yong-Jiang Liu Franz Neubauer Johann Genser Akira Takasu Xiao-Hong Ge Robert Handler 《Island Arc》2006,15(1):187-198
Abstract Pelitic schists from Qingshuigou in the Northern Qilian Mountains of China contain mainly glaucophane, garnet, white mica, clinozoisite, chlorite and piemontite. Isotopic age dating of these schists provides new constraints on the formation of the high-grade blueschists at Qingshuigou. White mica 40 Ar/39 Ar ages range from 442.1 to 447.5 Ma (total fusion age of single grain) and from 445.7 to 453.9 Ma (integrated age of white mica concentrates). These ages (442.1–453.9 Ma) represent the peak metamorphic ages or cooling ages of the blueschists during exhumation shortly after peak metamorphism. The 40 Ar/39 Ar dates in the present study are similar to ages previously reported for eclogites and blueschists in the area; this suggests that both the eclogites and pelitic sediments underwent high-grade metamorphism during the same subduction event. From this chronological evidence and the presence of well-developed Silurian remnant-sea flysch and Devonian molasse, it is concluded that the Northern Qilian Ocean had closed by the end of the Ordovician, and rapid orogenic uplift followed in the Devonian. 相似文献
447.
从天气系统背景、FY-2C卫星产品、水汽通量分布特征和大气稳定度特征等方面,分析了受台风低压倒槽与东移锋面云系的共同影响,于2005年7月21日夜间到23日邯郸市出现的大范围的暴雨天气,结果发现:500hPa槽前中尺度切变线是直接影响产生暴雨的重要系统;地形作用使迎风坡降水增强;中尺度对流云团和雨团关系密切,暴雨中心位于OLR和TBB低值区下面;西部山区的暴雨区水汽主要来源于南海、东海,东部平原大暴雨水汽主要来源于南海;暴雨区上空低层为对流不稳定,高层为对称不稳定。 相似文献
448.
449.
Conodont colour alteration index (CAI) data in Upper Ordovician rocks from several areas of the Variscan domain in the Iberian Peninsula indicate conditions ranging from diagenesis to low-grade metamorphism. In most of the areas, where studies using other indicators, such as illite crystallinity (IC) or where vitrinite reflectance are lacking, the CAI method has permitted a preliminary estimation of the metamorphic grade. In the Almadén syncline (Central-Iberian Zone), where IC studies are available, the thermal conditions inferred from CAI data agree with those obtained by the IC method. In the Puertollano–Almuradiel syncline, the thermal interval obtained primarily from fluid inclusions (270–370°C) overlaps considerably with that obtained from CAI data (180–340°C). In general, cleavage in rocks is present in anchizonal or epizonal conditions, whereas in diagenetic conditions with CAI 2.5, cleavage is scarce. The conodont texture changes with increasing metamorphism, and apatite recrystallisation appears in general with CAI 5. Variation of CAI values within a single sample and/or within short stratigraphic distances observed at several localities is due to hydrothermal activity. 相似文献
450.
A moderate pressure / high temperature zonal metamorphic complex in the Tongulack Mountain Ridge, Altai, Russia, is described, and the applicability of the models of magmatic intrusion and fluid flow to explanation of its origin discussed. The Precambrian complex was formed at 500-700℃ and 3.0-5.5 kbars; it is a linear, 25-30 km wide, thermal anticline with a curved axis showing symmetric metamorphic zoning. The metamorphism was isochemical by its nature, as is corroborated by the chemical compositions of the rocks. Four zones can be recognized within the metamorphic complex: chloritic (on the peripheries), cordieritic, sillimanitic and staurolite-out (in the centre). The zones are separated by successive isograds: cordierite, staurolite-in or sillimanite and staurolite-out. It is argued that the origin of the metamorphic zoning can be explained best by a combined fluid-magmatic model; conductive heat flow from the intrusion predominated considerably over the fluid flux in heat transfer: the fluid flow 相似文献