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91.
Colin Frank Wilson Eric Chassefière Emmanuel Hinglais Kevin H. Baines Tibor S. Balint Jean-Jacques Berthelier Jacques Blamont Georges Durry Csaba S. Ferencz Robert E. Grimm Takeshi Imamura Jean-Luc Josset Fran?ois Leblanc Sebastien Lebonnois Johannes J. Leitner Sanjay S. Limaye Bernard Marty Ernesto Palomba Sergei V. Pogrebenko Scot C. R. Rafkin Dean L. Talboys Rainer Wieler Liudmila V. Zasova Cyrill Szopa 《Experimental Astronomy》2012,33(2-3):305-335
The European Venus Explorer (EVE) mission described in this paper was proposed in December 2010 to ESA as an ‘M-class’ mission under the Cosmic Vision programme. It consists of a single balloon platform floating in the middle of the main convective cloud layer of Venus at an altitude of 55?km, where temperatures and pressures are benign (~25°C and ~0.5 bar). The balloon float lifetime would be at least 10 Earth days, long enough to guarantee at least one full circumnavigation of the planet. This offers an ideal platform for the two main science goals of the mission: study of the current climate through detailed characterization of cloud-level atmosphere, and investigation of the formation and evolution of Venus, through careful measurement of noble gas isotopic abundances. These investigations would provide key data for comparative planetology of terrestrial planets in our solar system and beyond. 相似文献
92.
Benoît Laignel Florence Quesnel Robert Meyer Jean-Jacques Macaire 《Geodinamica Acta》2013,26(4):171-181
RésuméDepuis plus d’un siècle, l’origine autochtone ou allochtone des formations résiduelles à silex (en abrégé RS : résidus à silex) par rapport aux craies a fait l’objet de multiples discussions. Pour répondre à ce problème, un bilan d’altération entre ces deux formations a été effectué. Il repose sur une connaissance précise des âges des craies-mères des RS et sur des comparaisons granulométrique et chimique entre craie et RS. Ces comparaisons s’appuient sur les quantités de silex contenues dans les craies et les RS, sachant que les silex sont reconnus comme autochtones et que leur degré de dissolution est calculé. Les résultats apportent des informations sur l’évolution crétacée du Bassin anglo-parisien, avec la mise en évidence de la craie du Maastrichtien dans le bassin de Paris et la reconstitution des épaisseurs de craie dissoutes. De plus, ils indiquent que la stratigraphie des craies est conservée dans les profils de RS. Ils montrent également que les silex, éléments autochtones des RS, sont faiblement altérés. Les matrices des RS sont, quant à elles, en grande partie allochtones, notamment dans les dix mètres supérieurs de la formation. L’allochtonie diminue avec la profondeur, avec des RS pouvant être considérés comme des résidus d’altération de la craie au sens strict à partir de 20 mètres de profondeur. © Elsevier, Paris 相似文献
93.
Michael M. McGlue Kiram E. Lezzar Andrew S. Cohen James M. Russell Jean-Jacques Tiercelin Anna A. Felton Evelyne Mbede Hudson H. Nkotagu 《Journal of Paleolimnology》2008,40(2):635-653
New intermediate-resolution, normal-incidence seismic reflection profiles from Lake Tanganyika’s central basin capture dramatic
evidence of base-level change during two intervals of the late Pleistocene. Four seismically-defined stratigraphic sequences
(A–D) tied to radiocarbon-dated sediment cores provide a chronology for fluctuating environmental conditions along the Kalya
Platform. Stacked, oblique clinoforms in Sequence C are interpreted as prograding siliciclastic deltas deposited during a
major regression that shifted the paleo-lake shore ∼21 km towards the west prior to ∼106 ka. The topset-to-foreset transitions
in these deltas suggest lake level was reduced by ∼435 m during the period of deposition. Mounded reflections in the overlying
sequence are interpreted as the backstepping remnants of the delta system, deposited during the termination of the lowstand
and the onset of transgressive conditions in the basin. The youngest depositional sequence reflects the onset of profundal
sedimentation during the lake level highstand. High amplitude reflections and deeply incised channels suggest a short-lived
desiccation event that reduced lake level by ∼260 m, interpreted as a product of Last Glacial Maximum (32–14 ka) aridity.
Paleobathymetric maps constructed for the two interpreted regressions reveal that despite the positive lake-floor topography
created by the Kavala Island Ridge Accommodation Zone, Lake Tanganyika remained a large, mostly connected water body throughout
the late Pleistocene. The results of this analysis further imply that Lake Tanganyika is the most drought resistant water
body in the East African tropics, and may have acted as a refuge for local and migrating fauna during periods of prolonged
aridity. 相似文献
94.
Jim Braun Jon Dumm Francesco De Palma Chad Finley Albrecht Karle Teresa Montaruli 《Astroparticle Physics》2008,29(4):299-305
Neutrino telescopes are moving steadily toward the goal of detecting astrophysical neutrinos from the most powerful galactic and extragalactic sources. Here we describe analysis methods to search for high energy point-like neutrino sources using detectors deep in the ice or sea. We simulate an ideal cubic kilometer detector based on real world performance of existing detectors such as AMANDA, IceCube, and ANTARES. An unbinned likelihood ratio method is applied, making use of the point spread function and energy distribution of simulated neutrino signal events to separate them from the background of atmospheric neutrinos produced by cosmic ray showers. The unbinned point source analyses are shown to perform better than binned searches and, depending on the source spectral index, the use of energy information is shown to improve discovery potential by almost a factor of two. 相似文献
95.
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98.
Denudation rates on cratonic landscapes: comparison between suspended and dissolved fluxes,and 10Be analysis in the Nyong and Sanaga River basins,south Cameroon
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Vincent Regard Sébastien Carretier Jean‐Loup Boeglin Jules‐Rémy Ndam Ngoupayou Jean‐Guy Dzana Jean‐Pierre Bedimo Bedimo Jean Riotte Jean‐Jacques Braun 《地球表面变化过程与地形》2016,41(12):1671-1683
South Cameroon is located in a tropical and tectonically quiescent region, with landscapes characterized by thick highly weathered regolith, indicative of the long‐term predominance of chemical weathering over erosion. Currently this region undergoes huge changes due to accelerated mutations related to a growing population and economical developments with associated needs and increasing pressures on land and natural resources. We analysed two of the main south Cameroon rivers: the Nyong River and Sanaga River. The Sanaga catchment undergoes a contrasted tropical climate from sub‐humid mountainous and humid climate and is impacted by deforestation, agriculture, damming, mining and urbanization, especially in the Mbam sub‐basin, draining the highly populated volcanic highlands. By contrast, the Nyong catchment, only under humid tropical climate, is preserved from anthropogenic disturbance with low population except in the region of Yaoundé (Méfou sub‐basin). Moreover the Nyong basin is dam‐free and less impacted by agriculture and logging. We explore both denudation temporal variability and the ratio between chemical and physical denudation through two catchment‐averaged erosion and denudation datasets. The first one consists of an 11‐year long gauging dataset, while the second one comes from cosmogenic radionuclides [CRNs, here beryllium‐10 (10Be)] from sand sampled in the river mainstreams (timescale of tens to hundreds of thousands of years). Modern fluxes estimated from gauging data range from 5 to 100 m/Ma (10 to 200 t/km2/yr); our calculations indicate that the usual relative contribution of chemical versus physical denudation is 60% and 40%, respectively, of the total denudation. Beryllium‐10 denudation rates and sediment fluxes range from 4.8 to 40.3 m/Ma or 13 to 109 t/km2/yr, respectively, after correction for quartz enrichment. These fluxes are slightly less than the modern fluxes observed in Cameroon and other stable tropical areas. The highest 10Be‐derived fluxes and the highest physical versus chemical denudation ratios are attributed to anthropogenic impact. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
99.
Philippe Rentzel Frank Preusser Christine Pümpin Jean-Jacques Wolf 《Swiss Journal of Geoscience》2009,102(3):387-401
Pedological investigations in combination with luminescence dating have been used to reconstruct the genesis and chronology
of a sediment succession at Sierentz, France. The sequence comprises loess and palaeosols on top of gravel attributed to the
High Terrace of River Rhine. According to the dating results, three phases of soil development occurred during different warm
phases of Marine Isotope Stage (MIS) 7 (245–190 ka). Soil development on top of the gravel occurred either during early MIS
7 or during an earlier warm phase, possibly MIS 9. The results imply a minimum age of 250 ka for the formation of the High
Terrace in this part of the Upper Rhine Graben, contrary to previous assumptions that correlated gravel sheet deposition with
MIS 6 (ca. 150 ka). These results and recent findings at other sites suggest that the chronological setting of terrace formation
north of the Alps is much more complex than previously assumed. 相似文献
100.
Christophe Falgures Jean-Jacques Bahain Carlo Tozzi Giovanni Boschian Jean-Michel Dolo Norbert Mercier Hlne Valladas Yuji Yokoyama 《Quaternary Geochronology》2008,3(4):390-398
The Visogliano shelter, in north-eastern Italy, is an important Middle Pleistocene occupation site where human remains were found together with an archaic lithic industry, including choppers, chopping tools and a few protobifaces. It is of utmost importance to try to document this period, when a second wave of settlement colonised Western Europe, carrying new flaking techniques and tools.Combined ESR/U-series analyses, integrated with biostratigraphical and environmental data, define a chronological frame for the layers from which the artefacts were unearthed. The lower levels, including human remains, can be dated to the 350–500 kyr time span, in agreement with micromammal and stratigraphical studies.These data make Visogliano one of the oldest palaeoanthropological sites in Italy, where human remains are directly associated with protobifaces, choppers and chopping tools. In Western Europe, Visogliano is contemporaneous to the G soil of the Arago Cave, France, with which it shares several similarities in faunal assemblages and radiometric data, and which contains human remains also. These data make Visogliano as one of the oldest sites in Europe where the Acheulian culture is observed. 相似文献