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211.
ACHIM BRAUER THOMAS LITT JÖRG F. W. NEGENDANK BERND ZOLITSCHKA 《Boreas: An International Journal of Quaternary Research》2001,30(1):83-88
In this paper we briefly compare previously published data on four lateglacial sediment profiles from lakes Holzmaar and Meerfelder Maar in the Eifel region. Two of these profiles (one from each lake) are varvedated, whereas the other two pollen profiles are on depth scales. In general, the palynological signal in all profiles compares well, proving the regional validity of the individual data sets. There are some discrepancies between Holzmaar and Meerfelder Maar, however, mainly concerning varve dating of major lateglacial features, and these are explained after detailed correlation using a combination of varve dating and palynological signals. The result is a consistent varve-dated biostratigraphy for the Lateglacial in the Eifel region. Moreover, it is demonstrated that a combination of varve chronology and high resolution palynostratigraphy in several lake profiles enables even gaps of a few decades up to a few centuries to be detected, thus providing a valuable tool for precise regional palaeoenvironmental study. This multi-core study on two lakes from the same region demonstrates the likelihood of undetected errors in single-core studies on non-varved sediments. 相似文献
212.
JOHN ALEXANDER STRøMME THOMAS WANJOHI NGARI KARL ERIK ZACHARIASSEN 《Polar research》1986,4(2):199-204
Metabolic rates and Q10 values were determined for three species of Spitsbergen Coleoptera, Amara quenseli, Simplocaria metallica and Rhynchaenus flagellum . The beetles had metabolic rates which were elevated compared to values of Coleoptera from other regions. This is interpreted as an adaptation to the prevailing low temperatures and short activity period on Spitsbergen.
A. quenseli had rates of water loss comparable to values of beetles in temperate and tropical xeric habitats, indicating that the habitat of the beetles on Spitsbergen at least occasionally is xeric.
Determination of cold-hardiness parameters such as supercooling point and haemolymph melting point of A. quenseli beetles revealed that the beetles had values corresponding to those of active insects in the temperate and tropical region. They had no thermal hysteresis factors. Thus, during summer they show no physiological adaptations to cold. 相似文献
A. quenseli had rates of water loss comparable to values of beetles in temperate and tropical xeric habitats, indicating that the habitat of the beetles on Spitsbergen at least occasionally is xeric.
Determination of cold-hardiness parameters such as supercooling point and haemolymph melting point of A. quenseli beetles revealed that the beetles had values corresponding to those of active insects in the temperate and tropical region. They had no thermal hysteresis factors. Thus, during summer they show no physiological adaptations to cold. 相似文献
213.
Optically Stimulated Luminescence (OSL) dating of glacial sediments from Arctic Russia - depositional bleaching and methodological aspects 总被引:1,自引:0,他引:1
PUTHUSSERRY J. THOMAS REW S. MURRAY KURT H. KJæR SVEND FUNDER EILIV LARSEN 《Boreas: An International Journal of Quaternary Research》2006,35(3):587-599
Optical dating has been extensively used for stratigraphical correlation in the reconstruction of Eurasian ice-sheet dynamics and palaeoenvironmental changes during the last glaciation. In recent terrestrial studies in Arctic Russia, Optically Stimulated Luminescence (OSL) is the main chronological tool, and has been used across the whole of the Eurasian north. We report new OSL ages obtained on glaciofluvial and glaciolacustrine sediments from the Arkhangelsk and Taymyr regions of Arctic Russia and discuss the characteristics of the quartz OSL signal in terms of its saturation limit, variability among samples from the same location, and initial signal resetting in different depositional environments. It is shown that effect of partial bleaching in our mainly Weichselian samples is trivial because: modern analogues are well zeroed; there is good agreement between OSL and 14C ages in young samples; and skewness in the dose distribution of relatively older samples is mainly due to varying shapes of the growth curves. The overall reliability of the OSL ages from Arctic Russia, when compared with the limited independent age controls available, appears to be good. 相似文献
214.
ANDREAS D. MUELLER FLAVIO S. ANSELMETTI DANIEL ARIZTEGUI MARK BRENNER DAVID A. HODELL JASON H. CURTIS JAIME ESCOBAR ADRIAN GILLI DUSTIN A. GRZESIK THOMAS P. GUILDERSON STEFFEN KUTTEROLF MICHAEL PLÖTZE 《Sedimentology》2010,57(5):1220-1245
Long sediment cores were collected in spring 2006 from Lake Petén Itzá, northern Guatemala, in water depths ranging from 30 to 150 m, as part of an International Continental Scientific Drilling Program project. The sediment records from deep water consist mainly of alternating clay, gypsum and carbonate units and, in at least two drill sites, extend back >200 kyr. Most of the lithostratigraphic units are traceable throughout the basin along seismic reflections that serve as seismic stratigraphic boundaries and suggest that the lithostratigraphy can be used to infer regional palaeoenvironmental changes. A revised seismic stratigraphy was established on the basis of integrated lithological and seismic reflection data from the basin. From ca 200 to ca 85 ka, sediments are dominated by carbonate‐clay silt, often interbedded with sandy turbidites, indicating a sediment regime dominated by detrital sedimentation in a relatively humid climate. At ca 85 ka, an exposure horizon consisting of gravels, coarse sand and terrestrial gastropods marks a lake lowstand or partial basin desiccation, indicating dry climate conditions. From ca 85 to ca 48 ka, transgressive carbonate‐clay sediments, overlain by deep‐water clays, suggest a lake level rise and subsequent stabilization at high stage. From ca 48 ka to present, the lithology is characterized by alternating clay and gypsum units. Gypsum deposition correlates with Heinrich Events (i.e. dry climate), whereas clay units coincide with more humid interstadials. 相似文献