全文获取类型
收费全文 | 406篇 |
免费 | 12篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 24篇 |
地球物理 | 91篇 |
地质学 | 210篇 |
海洋学 | 24篇 |
天文学 | 25篇 |
综合类 | 4篇 |
自然地理 | 34篇 |
出版年
2022年 | 3篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 14篇 |
2013年 | 20篇 |
2012年 | 17篇 |
2011年 | 18篇 |
2010年 | 19篇 |
2009年 | 36篇 |
2008年 | 18篇 |
2007年 | 15篇 |
2006年 | 16篇 |
2005年 | 17篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1989年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 4篇 |
1979年 | 3篇 |
1975年 | 3篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1967年 | 3篇 |
1966年 | 3篇 |
1962年 | 3篇 |
1959年 | 3篇 |
1954年 | 3篇 |
1953年 | 2篇 |
1952年 | 2篇 |
1939年 | 2篇 |
1938年 | 3篇 |
1937年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有423条查询结果,搜索用时 31 毫秒
331.
Hydrogeology Journal - Coefficients B and C of the Jacob (1947) equation, usually derived from step-drawdown tests, are commonly attributed to “aquifer losses” and “well... 相似文献
332.
Georg Schwamborn Lutz Schirrmeister Ali Mohammadi Hanno Meyer Andrei Kartoziia Flavio Maggioni Jens Strauss 《Sedimentology》2023,70(1):235-258
Arctic warming and permafrost thaw visibly expose changes in the landscape of the Lena River delta, the largest Arctic delta. Determining the past and modern river regime of thick deltaic deposits shaping the Lena River mouth in north-eastern Siberia is critical for understanding the history of delta formation and carbon sequestration. Using a 65 m long sediment core from the delta apex a set of sedimentological techniques is applied to aid in reconstructing the Lena River history. The analysis includes: (i) grain-size measurements and the determination of the bedload composition; (ii) X-ray fluorescence, X-ray diffractometry, and magnetic susceptibility measurements and heavy mineral analysis for tracking mineral change; (iii) pH, electrical conductivity, ionic concentrations, and the δ18O and δD stable isotope composition from ground ice for reconstructing permafrost formation. In addition; (iv) total and dissolved organic carbon is assessed. Chronology is based on; (vi) radiocarbon dating of organic material (accelerator mass spectrometry and conventional) and is complemented by two infrared – optically stimulated luminescence dates. The record stretches back approximately to Marine Isotope Stage 7. It holds periods from traction, over saltation, to suspension load sedimentation. Minerogenic signals do not indicate provenance change over time. They rather reflect the change from high energy to a lower energy regime after Last Glacial Maximum time parallel to the fining-up grain-size trend. A prominent minimum in the ground ice stable isotope record at early Holocene highlights that a river arm migration and an associated refreeze of the underlying river talik has altered the isotopic composition at that time. Fluvial re-routing might be explained by internal dynamics in the Lena River lowland or due to a tectonic movement, since the study area is placed in a zone of seismic activity. At the southern Laptev Sea margin, onshore continental compressional patterns are bordering offshore extensional normal faults. 相似文献
333.
The sedimentation record of Lago Grande di Monticchio (LGM) is one of the most prominent paleoclimatic archives in the non-glaciated
areas of Europe. However, the modern lake system has never been the subject of intense limnological studies. On the basis
of hydrochemical water profiles, detailed investigations of sediment short cores and in situ pore water profiles from the
littoral to the profundal zone, we elucidate spatial variations of sediment genesis within the lake basin and the importance
of various depth sections for the lake’s internal nutrient cycling. Sediments from the smaller meromictic Lago Piccolo di
Montichio are discussed as a reference. Our study demonstrates: (i) distinctly higher sediment accumulation for the centre
of the lake basin by focussing of the settling particle flux; (ii) decline of carbonate from the littoral to the profundal
zones; (iii) non-synchronous change of calcite net-accumulation for various water depths; (iv) exceptionally high cation release
from sediments covering the steeply inclining sector of the lake basin; (v) relatively constant dissolved silica concentrations
in the pore waters (SiO2 ∼42 mg/l) independent of water depth and sediment composition; (vi) influx of oxygen-bearing groundwater into the anoxic
hypolimnion after heavy rainfall and the associated precipitation of Fe-oxihydroxides; (vii) higher release of NH4 by anaerobic degradation of organic matter at a water depth of 23 m than for sediments at a maximum water depth of 32 m,
whereby the latter reflects the importance of seasonal sediment re-oxidation for anaerobic degradation of organic debris;
(viii) although seasonal re-oxidation of sediments from various water depths is quite different, Oxygen Index values of LGM
sediments fall in a small range, which reflects rapid microbial consumption of seasonally re-generated easily bio-degradable
organic molecules. 相似文献
334.
Georg F. Zellmer Stephen Blake Derek Vance Chris Hawkesworth Simon Turner 《Contributions to Mineralogy and Petrology》1999,136(4):345-357
The diffusive relaxation of trace element profiles in plagioclase phenocrysts may provide important constraints on magma
residence times in crustal magma chambers. Initial trace element profiles in plagioclase phenocrysts are governed by variations
in the concentration of a trace element in the melt and by the plagioclase-melt partition coefficient. Trace element diffusion
will subsequently act to modify this initial profile and – given enough time – produce a profile that is in equilibrium with
the anorthite variations within the crystal. We argue that the trace element partition coefficient Da/b between two parts a and b of a plagioclase crystal of variable anorthite content is equal to the ratio of their crystal-liquid
partition coefficients, and that the equilibrium profile of the crystal can be calculated. The time required to establish
diffusive equilibrium is dependent on the wavelength and amplitude of the initial trace element concentration range and on
the diffusivity of the trace element in plagioclase. Strontium plagioclase-melt partition coefficients and diffusivities are
calculated for a range of magmatic temperatures and plagioclase compositions. A one-dimensional diffusion model is developed
that describes the diffusive destruction of oscillatory trace element zoning with time and allows the calculation of upper
limits for plagioclase crystal residence times in a magma reservoir. The model is tested using major and trace element concentrations
measured along crystal traverses of plagioclase phenocrysts from the Kameni Island dacites, Santorini, and from the 1979 Soufriere
andesite, St. Vincent. Three out of eight plagioclase phenocrysts have Sr concentration profiles that are not in diffusive
equilibrium. For these, the diffusion model is employed to calculate maximum crystal residence times from incomplete diffusive
equilibration of trace element zoning in plagioclase. Maximum crystal residence times range from 100 to 450 years. This is
in good agreement with estimates from crystal size distribution and from Ra-Th disequilibrium studies for the Kameni Islands.
For Soufriere, however, such short residence times are incompatible with U-Th mineral errorchron data that suggest residence
times of >40 ka in a thermally buffered magma reservoir. To reconcile these apparently different ages, we invoke a more complicated
magmatic history for Soufriere where an initially buffered magma reservoir is disturbed by magma mixing and suffers limited
additional crystal fractionation prior to eruption.
Received: 20 October 1998 / Accepted: 22 March 1999 相似文献
335.
336.
Sergei Stanchits Jerome Fortin Yves Gueguen Georg Dresen 《Pure and Applied Geophysics》2009,166(5-7):843-868
We investigated initiation and propagation of compaction bands (CB) in six wet and four dry Bentheim sandstone samples deformed in axial compression tests with strain rates ranging from 3.2 × 10?8 s?1 to 3.2 × 10?4 s?1. Circumferential notches with 0.8-mm width and 5-mm depth served to initiate CB at mid-sample length. Wet samples were saturated with distilled water and deformed at 195 MPa confining pressure and 10 MPa pore pressure. Dry samples were deformed at 185 MPa confining pressure. Twelve P-wave sensors, eight S-wave sensors and two pairs of orthogonally oriented strain-gages were glued to the sample surface to monitor acoustic emission (AE), velocities and local strain during the loading process. Nucleation of compaction bands is indicated by AE clusters close to the notch tips. With progressive loading, AE activity increased and AE hypocenters indicated propagation of a single CB normal to the sample axis. CB propagation from the sample periphery towards the centre was monitored. Microstructural analysis of deformed samples shows excellent agreement between location of AE clusters and CBs. In both dry and wet samples the lateral propagation of CBs was about 100 times faster than axial shortening rates. At the slowest displacement rate, AE activity during band propagation was reduced and CB nucleation in wet samples occurred at 20% lower stresses. This may indicate an increasing contribution of stress corrosion processes to the formation of the compaction bands. In dry and wet samples inelastic compaction energy per area ranged between 16 and 80 kJ m?2. This is in good agreement with previous estimates from laboratory and field studies. 相似文献
337.
Georg F. Zellmer Tobias P. Fischer Chang-Hwa Chen 《Journal of Volcanology and Geothermal Research》2008
In this introduction, recent progress in the study of the evolution, transfer and release of magmas and volcanic gases is briefly reviewed, based on discussions at the MAG2007 international conference held in Taipei, Taiwan, in April 2007. The meeting pooled the diverse expertise of igneous and volcanic gas geochemists. This special issue, which presents six case studies covering a range of topics from variations in mantle source compositions to the nature of volcanic degassing, reflects that diversity. 相似文献
338.
Steffen Popp Innokenty Belolyubsky Frank Lehmkuhl Andrei Prokopiev Christine Siegert Valentin Spektor Georg Stauch Bernhard Diekmann 《Geological Journal》2007,42(5):477-497
A provenance analysis of late Quaternary deposits from tributaries of the Aldan and Lena rivers in Central Yakutia (eastern Siberia) was carried out using analysis of heavy minerals and clay mineralogy. Cluster analysis revealed one assemblage that is characterized by relatively high proportions of amphibole, orthopyroxene and garnet as well as pedogenic clay minerals, reflecting a sediment provenance from the wide catchment area of the Lena and Aldan rivers. In contrast, the three other clusters are dominated by stable heavy minerals with varying amounts of clinopyroxene, apatite and garnet, as well as high percentages of illite and chlorite that are indicative of source rocks of the Verkhoyansk Mountains. Glacial moraines reveal the local mountain source signal that is overprinted by the Lena‐Aldan signal in the oldest moraines by reworking processes. Alluvial sediments in the Verkhoyansk Foreland show a clear Lena source signal through intervals of the middle and late Pleistocene, related to a stream course closer to the mountains at that time. Loess‐like cover sediments are characterized by the dominant Lena provenance with increasing proportions of local mountain sources towards the mountain valleys. Aeolian sands in an alluvial terrace section at the mountain margin covering the time between 30 ka and 10 ka BP reflect temporarily dominant inputs of aeolian materials from the Lena Plains. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
339.
Reservoirs have become an important component in the worldwide river sediment flux. Reservoirs prevent downstream sediment transport and have become a major sediment sink. In this study, sediment deposition during the last 115 years in the Urft Reservoir in western Germany is reconstructed. The Urft Reservoir is the oldest reservoir in the Eifel Mountains and was almost completely drained in 2020. This enabled a detailed mapping of the lake bottom using an unmanned aerial system and the computation of a high-resolution digital surface model. Topographic maps with a nominal resolution of 1:1000 from the time prior to the construction of the dam (around 1900) were used to construct a pre-reservoir elevation model. A digital elevation model of difference (DoD) was calculated from these two datasets for the reservoir floor (0.72 km2). Based on the DoD, a net sediment accumulation of 1.16 × 106 m3 was calculated alongside a propagated volume error of 6.91 × 105 m3, resulting in a mean accumulation of 1.54 m. Conservative vertical error propagation results in an average level of detection (LoD) of 1.8 m. In contrast, the comparison of the DoD with 47 cores in the upper part of the reservoir showed a mean difference of −0.11 m, indicating a high, independently assessed accuracy of the DoD. Three depositional hotspots were identified in the reservoir. One is close to the Urft dam where very fine sediments are draped across the pre-reservoir topography. Two areas are related to reservoir management. Sediment deposition in the Urft Reservoir has been comparably low in comparison to other regions globally, resulting in a 3.25% ± 1.93% loss of reservoir volume between 1905 and 2020. To analyse the effect of strong flooding events, a subset of the reservoir was analysed after an extreme event in July 2021, but accumulation did almost entirely not exceed the LoD. 相似文献
340.