全文获取类型
收费全文 | 138篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 11篇 |
地球物理 | 32篇 |
地质学 | 57篇 |
海洋学 | 12篇 |
天文学 | 17篇 |
综合类 | 1篇 |
自然地理 | 14篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 10篇 |
2012年 | 10篇 |
2011年 | 8篇 |
2010年 | 9篇 |
2009年 | 20篇 |
2008年 | 4篇 |
2007年 | 7篇 |
2006年 | 6篇 |
2005年 | 3篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1995年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有147条查询结果,搜索用时 234 毫秒
81.
Anja Zander Detlev Degering Frank Preusser Haino Uwe Kasper Helmut Brückner 《Quaternary Geochronology》2007,2(1-4):123-128
Shallow marine and intertidal shell rich sediments from the low coastal plain of Dubai were dated by optically stimulated luminescence. Combined high-resolution gamma spectrometry and ICP–MS analyses revealed significant disequilibria in the 238U decay series. Time dependent dose rates were modelled for two scenarios including a closed system and an open system with linear U and Ra uptake. OSL ages that were calculated using the linear uptake model are in good agreement with archaeological evidence and radiocarbon datings on shells and wood. The presented results illustrate that luminescence-dating techniques are suitable to set up a chronostratigraphic frame for calcareous coastal environments if an appropriate model is applied to consider the influence of radioactive disequilibria and time dependent dose rates. A comprehensive radionuclide analysis of the sediments is thought necessary to perform geochemically supported dose rate simulations. 相似文献
82.
Traces of historical tropical cyclones and tsunamis in the Ashburton Delta (north‐west Australia)
下载免费PDF全文
![点击此处可从《Sedimentology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Simon Matthias May Dominik Brill Max Engel Anja Scheffers Anna Pint Stephan Opitz Volker Wennrich Peter Squire Dieter Kelletat Helmut Brückner 《Sedimentology》2015,62(6):1546-1572
Although the north‐western coast of Western Australia is highly vulnerable to tropical cyclones and tsunamis, little is known about the geological imprint of historic and prehistoric extreme wave events in this particular area. Despite a number of site‐specific difficulties such as post‐depositional changes and the preservation potential of event deposits, both tropical cyclones and tsunamis may be inferred from the geomorphology and the stratigraphy of beach ridge sequences, washover fans and coastal lagoons or marshes. A further challenge is the differentiation between tsunami and storm deposits in the geological record, particularly where modern deposits and/or historical reports on the event are not available. This study presents a high‐resolution sedimentary record of washover events from the Ashburton River delta (Western Australia) spanning approximately the last 150 years. A detailed characterization of event deposits is provided, and a robust chronostratigraphy for the investigated washover sequence is established based on multi‐proxy sediment analyses and optically stimulated luminescence dating. Combining sedimentological, geochemical and high‐resolution optically stimulated luminescence data, event layers are assigned to known historical events and tropical cyclone deposits are separated from tsunami deposits. For the first time, the 1883 Krakatoa and 1977 Sumba tsunamis are inferred from sedimentary records of the north‐western part of Western Australia. It is demonstrated that optically stimulated luminescence applied in coastal sedimentary archives with favourable luminescence characteristics can provide accurate chronostratigraphies even on a decadal timescale. The results contribute to the data pool of tropical cyclone and tsunami deposits in Holocene stratigraphies; however, they also demonstrate how short‐lived sediment archives may be in dynamic sedimentary environments. 相似文献
83.
Determination of volatile concentrations in fluorapatite of Martian shergottite NWA 2975 by combining synchrotron FTIR,Raman spectroscopy,EMPA, and TEM,and inferences on the volatile budget of the apatite host‐magma
下载免费PDF全文
![点击此处可从《Meteoritics & planetary science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ewa Słaby Monika Koch‐Müller Hans‐Jürgen Förster Richard Wirth Dieter Rhede Anja Schreiber Ulrich Schade 《Meteoritics & planetary science》2016,51(2):390-406
We combined the focused ion beam sample preparation technique with polarized synchrotron‐based FTIR (Fourier transform infrared) spectroscopy, laser‐Raman spectroscopy, electron microprobe analysis (EMPA), and transmission electron microscope (TEM) analysis to identify and quantify structurally bound OH, F, Cl, and CO3 groups in fluorapatite from the Northwest Africa 2975 (NWA 2975) shergottite. In this study, the first FTIR spectra of the OH‐stretching region from a Martian apatite are presented that show characteristic OH‐bands of a F‐rich, hydroxyl‐bearing apatite. Depending on the method of apatite‐formula calculation and whether charge balance is assumed or not, the FTIR‐based quantification of the incorporated OH, expressed as wt% H2O, is in variably good agreement with the H2O concentration calculated from electron microprobe data. EMP analyses yielded between 0.35 and 0.54 wt% H2O, and IR data yielded an average H2O content of 0.31 ± 0.03 wt%, consistent with the lower range determined from EMP analyses. The TEM observations implied that the volatiles budget of fluorapatite is magmatic. The water content and the relative volatile ratios calculated for the NWA 2975 magma are similar to those established for other enriched or intermediate shergottites. It is difficult to define the source of enrichment: either Martian wet mantle or crustal assimilation. Comparing the environment of parental magma generation for NWA 2975 with the terrestrial mantle in terms of water content, it displays a composition intermediate between enriched and depleted MORB. 相似文献
84.
85.
Nicole Kowalski Olaf Dellwig Melanie Beck Maik Grunwald Sibylle Fischer Maike Piepho Thomas Riedel Holger Freund Hans-Jürgen Brumsack Michael E. Böttcher 《Ocean Dynamics》2009,59(2):333-350
Tidal and seasonal behaviour of the redox-sensitive trace metals Mn, Fe, Mo, U, and V have been investigated in the open-water
column and shallow pore waters of the backbarrier tidal flats of the island of Spiekeroog (Southern North Sea) in 2002 and
2007. The purpose was to study the response of trace metal cycles on algae blooms, which are assumed to cause significant
changes in the redox state of the entire ecosystem. Trace metal data were complemented by measurements of nutrients and enumeration
of algae cells in 2007. Generally, Mn and V show a tidal cyclicity in the water column with maximum values during low tide
which is most pronounced in summer due to elevated microbial activity in the sediments. Mo and U behave almost conservatively
throughout the year with slightly increasing levels towards high tide. Exceptions are observed for both metals after summer
algae blooms. Thus, the seasonal behaviour of the trace metals appear to be significantly influenced by productivity in the
water column as the occurrence of algae blooms is associated with an intense release of organic matter (e.g. transparent exopolymer
particles, TEP) thereby forming larger organic-rich aggregates. Along with elevated temperatures in summer, the deposition
of such aggregates favours microbial activity within the surface sediments and release of DOC, nutrients and trace metals
(Mn, Mo and V) during the degradation of the aggregates. Additionally, pronounced reducing conditions lead to the reduction
of Mn(IV)-oxides and Fe(III)-(oxihydr)oxides, thereby releasing formerly scavenged compounds as V and phosphate. Therefore,
pore-water profiles show significant enrichments in trace metals especially from July to September. Finally, the trace metals
are released to the open water column via draining pore waters (esp. Mo, Mn, and V) and/or fixed in the sediment as sulphides
(Fe, Mo) and bound to organic matter (U). Non-conservative behaviour of Mo in oxygenated seawater, first observed in the investigation
area by Dellwig et al. (Geochim Cosmochim Acta 71:2745–2761, 2007a), was shown to be a recurrent phenomenon which is closely coupled to bacterial activity after the breakdown of algae blooms.
In addition to the postulated fixation of Mo in oxygen-depleted micro-zones of the aggregates or by freshly formed organic
matter, a direct removal of Mo from the water column by reduced sediment surfaces may also play an important role. 相似文献
86.
Friedemann T. Freund Ipek G. Kulahci Gary Cyr Julia Ling Matthew Winnick Jeremy Tregloan-Reed Minoru M. Freund 《Journal of Atmospheric and Solar》2009,71(17-18):1824-1834
Pre-earthquake signals have been widely reported, including perturbations in the ionosphere. These precursory signals, though highly diverse, may be caused by just one underlying physical process: activation of highly mobile electronic charge carriers in rocks that are subjected to ever increasing levels of stress. The charge carriers are defect electrons associated with O? in a matrix of O2?. Known as positive holes or pholes h, they flow out of the stressed rock into the unstressed rock volume, traveling meters in the laboratory, probably kilometers in the field. At the rock–air interface they cause: (i) positive surface potential, (ii) field-ionization of air molecules, (iii) corona discharges. The rate of formation of airborne ions can exceed 109 cm?2 s?1. Massive air ionization prior to major earthquakes increases the electrical conductivity in the air column and may cause ionospheric perturbations, earthquake lights, and unusual animal behavior as well as infrared emission. 相似文献
87.
In 1969, prior to the discovery of the subglacial Lake Vostok, an Askania Gs-11 gravimeter was operated at Vostok Station (78.466°S, 106.832°E; 3478 m asl) to observe tidal gravity variations. To gain a better understanding of the lake's tidal dynamics, we reanalyzed these data using a Bayesian Tidal Analysis Program Grouping method (BAYTAP-G and -L programs). The obtained phase leads for the semidiurnal waves M2 (6.6 ± 2.1°) and S2 (10.1 ± 4.2°) are more pronounced than those of the diurnal waves, among which the largest phase lead (for K1) was 5.0 ± 0.5°. The obtained δ factor for M2 was 0.890 ± 0.032, significantly less than the theoretical value of 1.16. For three global ocean tide models (NAO99b, FES2004, and TPXO6.2), the estimated load tides on waves Q1, O1, P1, K1, M2, and S2 range from 0.1–0.2 μGal (Q1 and S2) to 0.6–0.7 μGal (K1). The difference in amplitude among the three models is less than 0.14 μGal (M2), and the difference in phase is generally less than 10°. In calculating the residual tide vectors using the ocean models, the TPXO6.2 model generally gave the smallest residual amplitudes. Our result for the K1 wave was anomalously large (1.36 ± 0.25 μGal), while that for the M2 wave was sufficiently small (0.37 ± 0.17 μGal). The associated uncertainty is half that reported in previous studies. It is interesting that the residual K1 tide is approximately 90° phase-leaded, while the M2 tide is approximately 180° phase-leaded (delayed). Importantly, a similar reanalysis of data collected at Asuka Station (71.5°S, 24.1°E) gave residual tides within 0.2–0.3 μGal for all major diurnal and semidiurnal waves, including the K1 wave. Therefore, the anomalous K1 residual tide observed at Vostok Station must be linked to the existence of the subglacial lake and the nature of solid–ice–water dynamics in the region. 相似文献
88.
Anja DUFRESNE Michael H. POELCHAU Thomas KENKMANN Alex DEUTSCH Tobias HOERTH Frank SCHÄFER Klaus THOMA 《Meteoritics & planetary science》2013,48(1):50-70
Abstract– Hypervelocity (2.5–7.8 km s?1) impact experiments into sandstone were carried out to investigate the influence of projectile velocity and mass, target pore space saturation, target‐projectile density contrast, and target layer orientation on crater size and shape. Crater size increases with increasing projectile velocity and mass as well as with increasing target pore space saturation. Craters in water‐saturated porous targets are generally shallower and larger in volume and in diameter than craters from equivalent impacts into dry porous sandstone. Morphometric analyses of the resultant craters, 5–40 cm in diameter, reveal features that are characteristic of all of our experimental craters regardless of impact conditions (I) a large central depression within a fragile, light‐colored central part, and (II) an outer spallation zone with areas of incipient spallation. Two different mechanical processes, grain fragmentation and intergranular tensile fracturing, are recorded within these crater morphologies. Zone (I) approximates the shape of the transient crater formed by material compression, displacement, comminution, and excavation flow, whereas (II) is the result of intergranular tensile fracturing and spallation. The transient crater dimensions are reconstructed by fitting quadric parabolas to crater profiles from digital elevation models. The dimensions of this transient and of the final crater show the same trends: both increase in volume with increasing impact energy, and with increasing water saturation of the target pore space. The relative size of the transient crater (in percent of the final crater volume) decreases with increasing projectile mass and velocity, signifying a greater contribution of spallation on the final crater size when projectile mass and velocity are increased. 相似文献
89.
The quality of real-time GPS positions based on the method of precise point positioning (PPP) heavily depends on the availability and accuracy of GPS satellite orbits and satellite clock corrections. Satellite-based augmentation systems (SBAS) provide such corrections but they are actually intended to be used for wide area differential GPS with positioning results on the 1-m accuracy level. Nevertheless, carrier phase-based PPP is able to achieve much more accurate results with the same correction values. We applied SBAS corrections for dual-frequency PPP and compared the results with PPP obtained using other real-time correction data streams, for example, the GPS broadcast message and precise corrections from the French Centre National d’Etudes Spatiales and the German Deutsches Zentrum für Luft- und Raumfahrt. Among the three existing SBAS, the best results were achieved for the North American wide area augmentation system (WAAS): horizontal and vertical position accuracies were considerably smaller than 10 cm for static 24-h observation data sets and smaller than 30 cm for epoch-by-epoch solutions with 2 h of continuous observations. The European geostationary navigation overlay service and the Japanese multi-functional satellite augmentation system yield positioning results with biases of several tens of centimeters and variations larger by factors of 2–4 as compared to WAAS. 相似文献
90.
Jing Wang Roderik Overzier Guinevere Kauffmann Anja von der Linden Xu Kong 《Monthly notices of the Royal Astronomical Society》2010,401(1):433-444
Many brightest cluster galaxies (BCGs) at the centres of X-ray selected clusters exhibit clear evidence for recent star formation. However, studies of BCGs in optically selected clusters show that star formation is not enhanced when compared to control samples of non-BCGs of similar stellar mass. Here, we analyse a sample of 113 BCGs in low-redshift ( z < 0.1) , optically selected clusters, a matched control sample of non-BCGs, and a smaller sample of BCGs in X-ray selected clusters. We convolve the Sloan Digital Sky Survey images of the BCGs to match the resolution of the Galaxy Evolution Explorer ( GALEX ) data and we measure UV-optical colours in their inner and outer regions. We find that optically selected BCGs exhibit smaller scatter in optical colours and redder inner NUV − r colours than the control galaxies, indicating that they are a homogenous population with very little ongoing star formation. The BCGs in the X-ray selected cluster sample span a similar range in optical colours, but have bluer NUV − r colours. Among X-ray selected BCGs, those located in clusters with central cooling times of less than 1 Gyr are significantly bluer than those located in clusters where the central gas cooling times are long. Our main conclusion is that the location of a galaxy at the centre of its halo is not sufficient to determine whether or not it is currently forming stars. One must also have information about the thermodynamic state of the gas in the core of the halo. 相似文献