全文获取类型
收费全文 | 383篇 |
免费 | 8篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 17篇 |
地球物理 | 115篇 |
地质学 | 147篇 |
海洋学 | 23篇 |
天文学 | 32篇 |
综合类 | 3篇 |
自然地理 | 44篇 |
出版年
2024年 | 1篇 |
2021年 | 3篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2018年 | 11篇 |
2017年 | 5篇 |
2016年 | 17篇 |
2015年 | 8篇 |
2014年 | 21篇 |
2013年 | 25篇 |
2012年 | 18篇 |
2011年 | 22篇 |
2010年 | 24篇 |
2009年 | 29篇 |
2008年 | 25篇 |
2007年 | 22篇 |
2006年 | 13篇 |
2005年 | 24篇 |
2004年 | 12篇 |
2003年 | 18篇 |
2002年 | 14篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有394条查询结果,搜索用时 31 毫秒
301.
Stefan Bernstein Dirk Frei Roger K. McLimans Christian Knudsen Venkatramaiah N. Vasudev 《Journal of Geochemical Exploration》2008,96(1):25-42
For the characterization of sediments, Computer Controlled Scanning Electron Microscopy (CCSEM) is a powerful method in obtaining chemical data on individual mineral grains and modal analysis of the heavy mineral fraction of sediment samples. Here we show how the CCSEM method can be used to evaluate ilmenite ore grade as well as a tool to investigate the source of heavy mineral deposits.The heavy mineral rich deposits in beach sands around the town of Chavara in SW India are characterized by ilmenite with elevated TiO2 contents, often exceeding 60 wt.%. In order to determine the origin of these high-TiO2 ilmenite deposits, we collected a series of beach sediment samples (22) from a c. 800 km long stretch of coastline from northern Kerala state to well within the Tamil Nadu state. A set (7) of river sediments was also taken, roughly covering the catchment area to the beach samples. The data show that the sediments in the Chavara high-Ti ilmenite deposit are distinguished by minor elements in ilmenite, garnet chemistry and heavy mineral assemblage: Chavara ilmenite has high MgO and low MnO contents; garnets have low grossular components and the heavy mineral assemblage is dominated by sillimanite–kyanite in addition to ilmenite. These features correlate with basement geology in the hinterland, and with sediments from rivers, draining the basement. Based on these observations we conclude that high-Ti ilmenite from Chavara beaches originates in the khondalite belt of high-grade metasediments. Our study demonstrates rapid mineral analyses in sediments by CCSEM to be efficient in the characterization of mineral compositions and assemblages in sediments, in the identification of possible source regions and thus ultimately in exploration for industrial mineral resources. 相似文献
302.
303.
Dirk Küster Rolf L. Romer Dandena Tolessa Desta Zerihun K. Bheemalingeswara Frank Melcher Thomas Oberthür 《Mineralium Deposita》2009,44(7):723-750
The Kenticha rare-element pegmatite, a globally important tantalite source in the Neoproterozoic Adola Belt of southern Ethiopia,
is a highly fractionated, huge (2,000 m long and up to 100 m thick), subhorizontal, sheet-like body, discordantly emplaced
in ultramafic host rock. It corresponds to the spodumene subtype of the rare-element pegmatite class and belongs to the lithium–cesium–tantalum
petrogenetic family. The Kenticha pegmatite is asymmetrically zoned from bottom to top into granitic lower zone, spodumene-free
intermediate zone, and spodumene-bearing upper zone. A monomineralic quartz unit is discontinuously developed within the upper
zone. Whole-rock data indicate an internal geochemical differentiation of the pegmatite sheet proceeding from the lower zone
(K/Rb ~36, K/Cs ~440, Al/Ga ~2,060, Nb/Ta ~2.6) to the upper zone (K/Rb ~19, K/Cs ~96, Al/Ga ~1,600, Nb/Ta ~0.7). The latter
one is strongly enriched in Li2O (up to 3.21%), Rb (up to 4,570 ppm), Cs (up to 730 ppm), Ga (up to 71 ppm), and Ta (up to 554 ppm). Similar trends of increasing
fractionation from lower zone to upper zone were obtained in muscovite (K/Rb 23–14, K/Cs 580–290, K/Tl 6,790–3,730, Fe/Mn
19–10, Nb/Ta 6.5–3.8) and columbite–tantalite (Mn/Mn + Fe 0.4–1, Ta/Ta + Nb 0.1–0.9). The bottom-to-top differentiation of
the Kenticha pegmatite and the Ta mineralization in its upper part are principally attributed to upward in situ fractionation
of a residual leucogranitic to pegmatitic melt, largely under closed system conditions. High MgO contents (up to 5.05%) in
parts of the upper zone are the result of postmagmatic hydrothermal alteration and contamination by hanging wall serpentinite.
U–Pb dating of Mn-tantalite from two zones of the Kenticha pegmatite gave ages of 530.2 ± 1.3 and 530.0 ± 2.3 Ma. Mn-tantalite
from the Bupo pegmatite, situated 9 km north of Kenticha, gave an age of 529.2 ± 4.1 Ma, indicating coeval emplacement of
the two pegmatites. The emplacement of the pegmatites is temporally related to postorogenic granite magmatism, producing slightly
peraluminous, I-type plutons in the area surrounding the Kenticha pegmatite field. Fractionated members of this suite might
be envisaged as potential parental magmas. 相似文献
304.
Post-collisional potassic granitoids from the southern and northwestern parts of the Late Neoproterozoic East African Orogen: a review 总被引:10,自引:0,他引:10
Potassic metaluminous granitoids with enrichments of HFS elements constitute part of widespread post-collisional magmatism related to the Late Neoproterozoic Pan-African orogeny in northeastern Africa (Sudan, Ethiopia, Somalia) and Madagascar. The plutons were emplaced between 580 and 470 Ma and comprise both subsolvus and hypersolvus biotite–granite, biotite–hornblende–granite, quartz–monzonite and quartz–syenite. Pyroxene-bearing granitoids are subordinate. Basic dikes and enclaves of monzodioritic composition are locally associated with the granitoid plutons. Granitoids emplaced in pre-Neoproterozoic crust have Sri-ratios between 0.7060 and 0.7236 and Nd(t) values between −15.8 and −5.6 while those emplaced in, or close to the contact with, juvenile Neoproterozoic crust have lower Sri-ratios (0.7036–0.7075) and positive Nd(t) values (4.6). However, it is unlikely that the potassic granitoids represent products of crustal melting alone. The association with basic magmas derived from subduction-modified enriched mantle sources strongly suggests that the granitoids represent hybrid magmas produced by interaction and mixing of mantle and crust derived melts in the lower crust. The most intense period of this potassic granitoid magmatism occurred between 585 and 540 Ma, largely coeval with HT granulite facies metamorphism in Madagascar and with amphibolite facies retrogression in northeastern Africa (Somalia, Sudan). Granitoid magmatism and high-grade metamorphism are probably both related to post-collisional lithospheric thinning, magmatic underplating and crustal relaxation. However, the emplacement of potassic granites continued until about 470 Ma and implies several magmatic pulses associated with different phases of crustal uplift and cooling. The potassic metaluminous granites are temporally and spatially associated with post-collisional high-K calc-alkaline granites with which they share many petrographical, geochemical and isotopical similarities, except the incompatible element enrichments. The resemblance indicates a strongly related petrogenesis of both granite associations. 相似文献
305.
James M. Dohm Victor R. Baker William V. Boynton Alberto G. Fairén Justin C. Ferris Michael Finch Roberto Furfaro Trent M. Hare Daniel M. Janes Jeffrey S. Kargel Suniti Karunatillake John Keller Kris Kerry Kyeong J. Kim Goro Komatsu William C. Mahaney Dirk Schulze-Makuch Lucia Marinangeli Gian G. Ori Javier Ruiz Shawn J. Wheelock 《Planetary and Space Science》2009,57(5-6):664-684
The Gamma Ray Spectrometer (Mars Odyssey spacecraft) has revealed elemental distributions of potassium (K), thorium (Th), and iron (Fe) on Mars that require fractionation of K (and possibly Th and Fe) consistent with aqueous activity. This includes weathering, evolution of soils, and transport, sorting, and deposition, as well as with the location of first-order geomorphological demarcations identified as possible paleoocean boundaries. The element abundances occur in patterns consistent with weathering in situ and possible presence of relict or exhumed paleosols, deposition of weathered materials (salts and clastic minerals), and weathering/transport under neutral to acidic brines. The abundances are explained by hydrogeology consistent with the possibly overlapping alternatives of paleooceans and/or heterogeneous rock compositions from diverse provenances (e.g., differing igneous compositions). 相似文献
306.
Dirk Frei Axel Liebscher Gerhard Franz Bernd Wunder Stephan Klemme Jon Blundy 《Contributions to Mineralogy and Petrology》2009,157(4):473-490
We determined experimentally the Nernst distribution coefficient between orthopyroxene and anhydrous silicate melt for trace elements i in the system Na2O–CaO–MgO–Al2O3–SiO2 (NCMAS) along the dry model lherzolite solidus from 1.1 GPa/1,230°C up to 3.2 GPa/1,535°C in a piston cylinder apparatus.
Major and trace element composition of melt and orthopyroxene were determined with a combination of electron microprobe and
ion probe analyses. We provide partitioning data for trace elements Li, Be, B, K, Sc, Ti, V, Cr, Co, Ni, Rb, Sr, Y, Zr, Nb,
Cs, Ba, La, Ce, Sm, Nd, Yb, Lu, Hf, Ta, Pb, U, and Th. The melts were chosen to be boninitic at 1.1 and 2.0 GPa, picritic
at 2.3 GPa and komatiitic at 2.7 and 3.2 GPa. Orthopyroxene is Tschermakitic with 8 mol% Mg-Tschermaks MgAl[AlSiO6] at 1.1 GPa while at higher pressure it has 18–20 mol%. The rare earth elements show a continuous, significant increase in
compatibility with decreasing ionic radius from D
Laopx−melt ∼ 0.0008 to D
Luopx−melt ∼ 0.15. For the high-field-strength elements compatibility increases from D
Thopx−melt ∼ 0.001 through D
Nbopx−melt ∼ 0.0015, D
Uopx−melt ∼ 0.002, D
Taopx−melt ∼ 0.005, D
Zropx−melt ∼ 0.02 and D
Hfopx−melt ∼ 0.04 to D
Tiopx−melt ∼ 0.14. From mathematical and graphical fits we determined best-fit values for D
0M1, D
0M2, r
0M1, r
0M2, E
0M1, and E
0M2 for the two different M sites in orthopyroxene according to the lattice strain model and calculated the intracrystalline
distribution between M1 and M2. Our data indicate extreme intracrystalline fractionation for most elements in orthopyroxene;
for the divalent cations D
i
M2−M1 varies by three orders of magnitude between D
CoM2−M1 = 0.00098–0.00919 and D
BaM2−M1 = 2.3–28. Trivalent cations Al and Cr almost exclusively substitute on M1 while the other trivalent cations substitute on
M2; D
LaM2−M1 reaches extreme values between 6.5 × 107 and 1.4 × 1016. Tetravalent cations Ti, Hf, and Zr almost exclusively substitute on M1 while U and Th exclusively substitute on M2. Our
new comprehensive data set can be used for polybaric-polythermal melting models along the Earth’s mantle solidus.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
307.
Contrasting sediment flux in Val Lumnezia (Graubünden, Eastern Swiss Alps), and implications for landscape development 总被引:1,自引:0,他引:1
Marco Schwab Fritz Schlunegger Heinz Schneider Gregor Stöckli Dirk Rieke-Zapp 《Swiss Journal of Geoscience》2009,102(2):211-222
This paper presents qualitative estimates of sediment discharge from opposite valley flanks in the S–N-oriented Val Lumnezia,
eastern Swiss Alps, and relates inferred differences in sediment flux to the litho-tectonic architecture of bedrock. The valley
flank on the western side hosts the deep-seated Lumnezia landslide where an area of ca. 30 km2 has experienced slip rates of several centimetres per year, potentially resulting in high sediment discharge to the trunk
stream (i.e. the Glogn River). High slip rates have resulted in topographic changes that are detectable on aerial photographs
and measurable with geodetic tools. In contrast, a network of tributary channels dissects the valley flank on the eastern
side. There, an area of approximately 18 km2 corresponding to < 30% of the surface has experienced a change in the landscape mainly by rock avalanche and rock fall, and
the magnitudes of changes are below the calibration limit of digital photogrammetry. We thus infer lower magnitudes of sediment
discharge on the eastern tributaries than on the western valley side, where landsliding has been the predominant erosional
process. These differences are interpreted to be controlled by the dip-slope situation of bedrock on the western side that
favours down-slope slip of material.
Morphometric investigations reveal that the western valley side is characterized by a low topographic roughness because this
valley flank has not been dissected by a channel network. It appears that high sediment discharge of the Lumnezia landslide
has inhibited the establishment of a stable channel network and has largely controlled the overall evolution of the landscape.
This contrasts to the general notion that channelized processes exert the first-order control on landscape evolution and formation
of relief and needs to be considered in future studies about landscape architecture, drainage network and sediment discharge. 相似文献
308.
Marek Pękala Jan Dirk Kramers Hans Niklaus Waber Thomas Gimmi Peter Alt-Epping 《Applied Geochemistry》2009
The Opalinus Clay formation in North Switzerland is a potential host rock for a deep underground radioactive waste repository. The distribution of 238U, 234U and 230Th was studied in rock samples of the Opalinus Clay from an exploratory borehole at Benken (Canton of Zurich) using MC-ICP-MS. The aim was to assess the in situ, long-term migration behaviour of 234U in this rock. Very low hydraulic conductivities of the Opalinus Clay, reducing potential of the pore water and its chemical equilibrium with the host rock are expected to render both 238U and 230Th immobile. If U is heterogeneously distributed in the Opalinus Clay, gradients in the supply of 234U from the rock matrix to the pore water by the decay of 238U will be established. Diffusive redistribution separates 234U from its immobile parent 238U resulting in bulk rock 234U/238U activity disequilibria. These may provide a means of estimating the mobility of 234U in the rock if the diffusion rate of 234U is significant compared to its decay rate. Sampling was carried out on two scales. Drilling of cm-spaced samples from the drill-core was done to study mobility over short distances and elucidate possible small-scale lithological control. Homogenized 25-cm-long portions of a 2-m-long drill-core section were prepared to provide information on transport over a longer distance. Variations in U and/or Th content on the cm-scale between clays and carbonate-sandy layers are revealed by β-scanning, which shows that the (dominant) clay is richer in both elements. 相似文献
309.
310.
Petr Dobrovolný Anders Moberg Rudolf Brázdil Christian Pfister Rüdiger Glaser Rob Wilson Aryan van Engelen Danuta Limanówka Andrea Kiss Monika Halíčková Jarmila Macková Dirk Riemann Jürg Luterbacher Reinhard Böhm 《Climatic change》2010,101(1-2):69-107
Monthly temperature series for Central Europe back to AD 1500 are developed from documentary index series from Germany, Switzerland and the Czech Republic (1500–1854) and 11 instrumental temperature records (1760–2007). Documentary evidence from the Low Countries, the Carpathian Basin and Poland are used for cross-checking for earlier centuries. The instrumental station records are corrected for inhomogeneities, including insufficient radiation protection of early thermometers and the urban heat island effect. For overlapping period (1760–1854), the documentary data series correlate with instrumental temperatures, most strongly in winter (86% explained variance in January) and least in autumn (56% in September). For annual average temperatures, 81% of the variance is explained. Verification statistics indicate high reconstruction skill for most months and seasons. The last 20 years (since 1988) stand out as very likely the warmest 20-year period, accounting for the calibration uncertainty and decreases in proxy data quality before the calibration period. The new reconstruction displays a previously unobserved long-term decrease in DJF, MAM and JJA temperature variability over last five centuries. Compiled monthly, seasonal and annual series can be used to improve the robustness of gridded large-scale European temperature reconstructions and possible impact studies. Further improvement of the reconstruction would be achieved if documentary data from other European countries are further developed. 相似文献