全文获取类型
收费全文 | 452篇 |
免费 | 24篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 35篇 |
大气科学 | 43篇 |
地球物理 | 80篇 |
地质学 | 176篇 |
海洋学 | 43篇 |
天文学 | 71篇 |
综合类 | 1篇 |
自然地理 | 35篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 25篇 |
2015年 | 16篇 |
2014年 | 14篇 |
2013年 | 24篇 |
2012年 | 26篇 |
2011年 | 32篇 |
2010年 | 30篇 |
2009年 | 37篇 |
2008年 | 17篇 |
2007年 | 20篇 |
2006年 | 18篇 |
2005年 | 21篇 |
2004年 | 15篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 12篇 |
2000年 | 4篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有484条查询结果,搜索用时 62 毫秒
441.
442.
Mercury in lake sediments of the Precambrian Shield near Huntsville, Ontario, Canada 总被引:10,自引:0,他引:10
P. E. Rasmussen D. J. Villard H. D. Gardner J. A. C. Fortescue S. L. Schiff W. W. Shilts 《Environmental Geology》1998,33(2-3):170-182
Long sediment cores (>1 m) were collected from eight Precambrian Shield lakes in southern Ontario, Canada and analyzed for
mercury (Hg), loss-on-ignition (LOI), and a suite of 36 other elements. Results indicated at least 100-fold variation in sediment
Hg concentrations between lakes in close proximity (from 450 ppb), comparable to the variation reported for lakes across the
whole of Canada. Strong areal correlations between Hg concentrations and LOI (r
2
=0.77), between Hg and other trace element concentrations (Pb, Zn, Cd, Sb, As, Br), and similarities in the vertical concentration
profiles of Hg and LOI, all point to the importance of organic matter in the release, transport and redistribution of metals
in watershed systems. The spatial pattern of Hg concentrations in deep, precolonial sediments (>20 cm) was found to mirror
the pattern of Hg concentrations in modern surface sediments, an observation that was confirmed in a follow-up survey (r
2
=0.85;n=25 lakes), indicating that natural processes govern the unequal distribution of Hg among these lakes. Between-lake differences
in surface sediment Hg concentrations normalized to organic carbon (Hg/C) were also reflected by Hg concentrations in smallmouth
bass normalized to 35 cm length (R
2
=0.63;n=15 lakes). The latter relationship suggests that smallmouth bass and lake sediment indicators provide mutually supportive
information regarding Hg loading to the lacustrine environment from geological sources in the watershed system.
Received: 31 October 1996 · Accepted: 27 May 1997 相似文献
443.
Diopside (CaMgSi2O6) and pseudowollastonite (CaSiO3) have been studied by X-ray powder diffraction and Raman spectroscopy up to their respective melting points. In agreement
with previous unit-cell parameters determinations below 1100 K, thermal expansion of diopside along the a and c axis is much smaller than along the b axis. For pseudowollastonite, the axis expansivity increases slightly in the order b>a>c. For both minerals, the change in unit-cell angles is very small and there are no anomalous variations of the other unit-cell
parameters near the melting point. With increasing temperatures, the main changes observed in the Raman spectra are strong
increases of the linewidths for those bands which mainly represent Si−O−Si bending (near 600 cm−1) or involve Ca−O or Mg−O stretching, in the range 270–500 cm−1 for diopside, and 240–450 cm−1 for pseudowollastonite. At temperatures near the onset of calorimetric premelting effects, this extensive band widening results
in a broad Raman feature that can no longer be deconvoluted into its individual components. No significant changes affect
the Si−O streching modes. For both diopside and pseudowollastonite, premelting appears to be associated with enhanced dynamics
of the alkaline-earth elements. This conclusion contrasts markedly with that drawn for sodium metasilicate in which weaker
bonding of sodium allows the silicate framework to distort and deform in such a way as to prefigure the silicate entities
present in the melt.
Received 16 July 1997 / Revised, accepted: 6 March 1998 相似文献
444.
Pascal Willis Bruce Haines Jean-Paul Berthias Pierre Sengenes Jean-Louis Le Mouël 《Comptes Rendus Geoscience》2004,336(9):839-846
We point out an acceleration of the DORIS clock on-board the Jason satellite during passes over the South Atlantic Anomaly (SAA). When this effect is ignored in the current geodetic positioning of the DORIS stations, derived coordinates show almost linear trends in time, corresponding to anomalous horizontal and vertical velocities of the order of 1 m yr?1. We propose a simple scientific explanation of this physical phenomenon that is corroborated by direct Jason/TOPEX clock comparisons with respect to the DORIS master beacons in Kourou and Toulouse. To cite this article: P. Willis et al., C. R. Geoscience 336 (2004). 相似文献
445.
Prof. Dr. Villard S. Griffin Jr. 《International Journal of Earth Sciences》1978,67(1):180-201
Recent mapping has provided a close look at detail relationships contrasting a major infrastructural zone with an adjacent suprastructural area in the southern U.S. Piedmont. The Inner Piedmont belt infrastructural flow folds terminate against a northeast trending polydeformational cataclastic zone as one traverses toward the southeast along the South Carolina — Georgia border. The broad axial part of the infrastructural Inner Piedmont is represented by a complex of sillimanite-bearing mica gneiss and schist. Interlayered amphibolite permits recognition of major nappe-like antiforms and synforms. The southeastern edge of the Inner Piedmont is devided from the axial core by a tectonic slide, and is a separate and distinct nappe. Granitoid gneiss and amphibolite dominate in it.Suprastructural rock terrane lies southeast of the cataclastic Lowndesville (Kings Mountain) belt, which is considered to have behaved as a detachment zone between the plastic infrastructure in the northwest and the stiffer suprastructure in the south-east. Mafic metamorphosed rocks dominate the lower stratigraphic section in the suprastructural area. These Charlotte belt rocks are overlain by low grade metavolcanic rocks of the Carolina Slate belt. Tight upright folds characterize the suprastructure.Granitoid bodies of large to small size intrude the Piedmont of this area. Extensive migmatite is associated with this granitoid material in the infrastructural Inner Piedmont belt. Much of the granitoid material formed during the stockwork tectonic phase in an early Paleozoic orogenesis.
Zusammenfassung Neue geologische Kartierungen im südlichen Appalachen-Vorgebirge ergaben einen engen Zusammenhang zwischen Oberbau und Unterbau. In der inneren Piedmont-Zone endet der Fließfaltenbau gegen eine mehrfach deformierte, kataklastische Zone, die sich nach SE entlang der South Carolina/Georgia-Grenze erstreckt. Die breite Achsialzone des Unterbaues im Bereich des inneren Piedmont wird aus Sillimanitführenden Glimmer-Gneisen und Schiefern aufgebaut. Zwischengelagerte Amphibolite erlauben in Synklinen und Antiklinen größere deckenartige Strukturen zu erkennen. Der SE-Teil des inneren Piedmont ist vom achsialen Kern durch eine tektonische Bewegungsfläche getrennt und stellt eine eigene Decke dar. Hier dominieren Granit-Gneise und Amphibolite.Der Oberbau folgt SE der kataklastischen Lowndesville (Kings Mountain) Zone als vom plastischeren Unterbau abgescherter starrer Komplex. Mafische Metamorphite bilden den stratigraphisch liegenden Teil des Oberbaues. Diese Charlotte Belt-Gesteine werden von niedrig metamorphen metavulkanischen Gesteinen des Carolina Slate Belt überlagert. Aufrechte Falten charakterisieren den Oberbau.Granitkörper von verschiedenen Dimensionen intrudieren in das Piedmont. Migmatisierung ist vor allem im inneren Piedmont zu beobachten. Das granitische Material wurde während der Ausbildung der Stockwerkstektonik in einer frühpaläozoischen Gebirgsbildung geformt.
Résumé Une étude géologique récente fournit une première connaissance des contrastes qui existent entre une zone majeure infrastructurale dans le Piedmont des Appalaches du Sud et une région adjacente, superstructurale. Des plis infrastructuraux d'écoulement se terminent contre une zone cataclastique qui s'étend vers le sud-est le long de la frontière entre la Géorgie et la Caroline du Sud. Cette zone, comme toutes les zones, court vers le nord-est. La large zone axiale de l'infrastructure, est représentée par uncomplexe de gneiss et de schistes à mica et à sillimanite. Des intercalations d'amphibolite permettent de reconnaître dans les antiformes et synformes de grandes structures en nappes. Le bord sud-est de l'Inner Piedmont, qui est une nappe distincte, est séparé de la partie centrale par une faille. Le gneiss granitique et l'amphibolite y prédominent.Le domaine superstructural se trouve au sud-est de la zone cataclastique du Lowndesville (Kings Mountain), qui est considérée comme la zone de détachement entre l'infrastructure plastique du nord-ouest et la superstructure plus rigide du sud-est. Des roches métamorphiques et basiques prédominent dans les couches stratigraphiques inférieurs dans la partie rigide. Ces roches de la bande Charlotte sont recouvertes par les roches volcaniques, moins métamorphiques, de la zone Caroline du Slate. Des plissements serrés et verticaux caractérisent la zone megastructurales.Des plutons granitiques de dimensions variées pénètrent le Piedmont, avec migmatitisation surtout dans la zone d'infrastructure. Le materiau granitique s'est formé, au cours de la formation d'une tectonique en Stockwerk lors d'une orogénie dans le Paleozoique ancien.
. Piedmont , SE : /. Piedmont , . . SE Piedmont . - . Lowndesville SE — King Mountain — . . Charlotte Carolina Slate, . . Piedmont . Piedmont . .相似文献
446.
447.
448.
449.
Melting and premelting of silicates: Raman spectroscopy and X-ray diffraction of Li2SiO3 and Na2SiO3
The isostructural lithium (Li2SiO3) and sodium (Na2SiO3) metasilicates have been investigated from room temperature up to the melting point by single-crystal Raman spectroscopy and energy-dispersive X-ray powder diffraction. The unit-cell parameters and Raman frequencies of Li2SiO3 vary regularly with temperature up to the melting point, which is consistent with the lack of premelting effects in calorimetric measurements. In contrast, Na2SiO3 undergoes a transition at about 850 K from orthorhombic Cmc 21 symmetry, to a lower symmetry (possibly Pmc 21), and shows near 1200 K changes in the Raman spectra that correlate well with the premelting effects as determined from calorimetry observations. In both compounds, a high alkali mobility likely sets in several hundreds of degrees below the melting point. Premelting in Na2SiO3 is associated with extensive deformation of the silicate chains as evidenced near the melting point by similarities in the Raman spectra of the crystalline and liquid phases. 相似文献
450.