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961.
Ana-Voica Bojar Stanislaw Halas Hans-Peter Bojar Dan Grigorescu Stefan Vasile 《Geochronometria》2011,38(2):182-188
In order to constrain the age of the Upper Cretaceous continental Densuş-Ciula Formation from the Haţeg basin, South Carpathians,
and correlate it with the other continental unit that occurs in the region, the Sanpetru Formation, we separated and dated
by the K-Ar method biotites and amphiboles from volcanoclastic deposits. The mineral phases analysed are from two tuff layers
and volcanic bombs cropping out near Rachitova village. Two tuff layers from the Densuş-Ciula Formation give early Maastrichtian
ages of 69.8±1.3 and 71.3±1.6 Ma, respectively. The ages determined for the tuff layers constrain the age of deposition for
the Densuş-Ciula Formation and enable further correlations with the available palaeomagnetic data from the deposits occurring
along the Sibişel Valley that belong to the Sanpetru Formation. The volcanic bombs collected near to Răchitova village are
andesites and dacites. The age determined by K-Ar method on hornblende separated from a volcanic bomb is 82.7±1.5 Ma, which
is older than the underlying Campanian marine deposits in turbidite facies. This suggests that the volcanic bombs were re-deposited
during the early Maastrichtian. Thus, the volcanics found at Răchitova have at least two origins: one type is related to an
explosive synsedimentary volcanic activity, and the other type is represented by older andesitic/dacitic bombs, which most
probably originate from a volcanic centre situated in the Haţeg region. 相似文献
962.
Piotr Weckwerth Krzysztof Przegiętka Alicja Chruścińska Barbara Woronko Hubert L. Oczkowski 《Geochronometria》2011,38(4):397-412
The deposits of the Toruń Basin are dominated by a few-metre thick sand series which fill up buried valley-like depressions.
In many cases they underlie the Weichselian till which builds up the ice marginal streamway (pradolina) terraces or they are
exposed at the basin slopes. As the results of the geological and sedimentological studies, as well as of the dating of the
deposits at the sites in the Toruń Basin indicate, the deposits include two fluvial series accumulated before the advancement
of the Leszno Phase ice sheet, i.e. in Middle Weichselian and at the beginning of Late Weichselian. The oldest fluvial series
connected with the Saalian Glaciation was found at the mouth section of the Drwęca Valley. The fluvial system of the Toruń
Basin during Middle Weichselian and at the beginning of Late Weichselian developed in two phases of the sand-bed braided river.
During the first one the river channel were dominated by large mid-riverbed sandbars, while during the second phase the water
flow was smaller and, as a result, low transverse sandbars and two-dimensional dunes developed. Other active river channel
also showed low-energy flows, more intensive meandering than in the case of the braided rivers, as well as sandy side-bars.
Analysis of the rounding and frosting of the quartz grains indicate that the studied series of the Weichselian sandy deposits
represent alluvia of a river which were fed from two diverse sources. The first one might have represented the alluvia of
a warm river which transformed its load, while the other one might have mainly carried the underlying Quaternary deposits. 相似文献
963.
964.
P. Morthekai Mayank Jain Pedro P. Cunha José M. Azevedo Ashok K. Singhvi 《Geochronometria》2011,38(3):223-230
The use of feldspar for luminescence dating has been restricted because of anomalous fading. This has made its application
to several important geological problems such as volcanic terrains difficult. Presently, two correction procedures are used
to correct for anomalous fading. The present study tests these correction procedures using volcanic samples of known ages
spanning the time period of 400 ka to 2.2 Ma. These correction procedures provided grossly underestimated ages (up to 60%).
The possible causes for the underestimation are discussed. 相似文献
965.
Reza Sohbati Andrew S. Murray Mayank Jain Jan-Pieter Buylaert Kristina J. Thomsen 《Geochronometria》2011,38(3):249-258
There are many examples of buried rock surfaces whose age is of interest to geologists and archaeologists. Luminescence dating
is a potential method which can be applied to dating such surfaces; as part of a research project which aims to develop such
an approach, the degree of resetting of OSL signals in grains and slices from five different cobbles/boulders collected from
a modern beach is investigated. All the rock surfaces are presumed to have been exposed to daylight for a prolonged period
of time (weeks to years). Feldspar was identified as the preferred dosimeter because quartz extracts were insensitive. Dose
recovery tests using solar simulator and IR diodes on both K-feldspar grains and solid slices taken from the inner parts of
the rocks are discussed. Preheat plateau results using surface grains and slices show that significant thermal transfer in
naturally bleached samples can be avoided by keeping preheat temperatures low. Equivalent doses from surface K-feldspar grains
were highly scattered and much larger than expected (0.02 Gy to >100 Gy), while solid surface slices gave more reproducible
small doses (mean = 0.17±0.02 Gy, n = 32). Neither crushing nor partial bleaching were found to be responsible for the large
scattered doses from grains, nor did the inevitable contribution from Na-feldspar to the signal from solid slices explain
the improved reproducibility in the slices. By modelling the increase of luminescence signal with distance into the rock surface,
attenuation factors were derived for two samples. These indicate that, for instance, bleaching at a depth of 2 mm into these
samples occurs at about ∼28% of the rate at the surface. We conclude that it should be possible to derive meaningful burial
doses of >1 Gy from such cobbles; younger samples would probably require a correction for incomplete bleaching. 相似文献
966.
967.
968.
Vasilios Melfos Bruno Helly Panagiotis Voudouris 《Archaeological and Anthropological Sciences》2011,3(2):165-172
Pliny the Elder (first century A.D.) mentioned that the Thessalian magnetite from Magnesia in ancient Greece was second in
quality after the Ethiopic. This magnetite should be related with the origin of the Homeric Magnetes of the eighth century
B.C. who lived around Ossa mountain in central Greece. A new euhedral magnetite occurrence derived from the Kampitsios area
at the north-western slopes of Mavrovouni mountain in “Amyrikon Pedion”, probably shows that this region should have been
connected with the origin of the Homeric Magnetes. The magnetites under study are found as porphyroblasts in the talc schists.
They are almost pure with rare inclusions, mainly ilmenite, rutile, pseudorutile and a PbO phase. The alteration of magnetite
to hematite is restricted only along the fissures and cracks as well as along the rims, forming very thin films of a few micrometres
in thickness. Microprobe analyses showed that the magnetites are almost pure and they contain only traces of Cr2O3 (1.01–3.41%). The high-quality magnetites of Kampitsios could be probably related with those mentioned by Pliny, and they
should be related with the origin of the Homeric Magnetes of the eighth century B.C. who lived around Ossa mountain in Thessaly. 相似文献
969.
Ivan Briz i Godino José Ignacio Santos José Manuel Galán Jorge Caro Myrian Álvarez Débora Zurro 《Journal of Archaeological Method and Theory》2014,21(2):343-363
This paper presents the theoretical basis and first results of an agent-based model (ABM) computer simulation that is being developed to explore cooperation in hunter–gatherer societies. Specifically, we focus here on Yamana, a hunter-fisher-gatherer society that inhabited the islands of the southernmost part of Tierra del Fuego (Argentina–Chile). Ethnographical and archaeological evidence suggests the existence of sporadic aggregation events, triggered by a public call through smoke signals of an extraordinary confluence of resources under unforeseeable circumstances in time and space (a beached whale or an exceptional accumulation of fish after a low tide, for example). During these aggregation events, the different social units involved used to develop and improve production, distribution and consumption processes in a collective way. This paper attempts to analyse the social dynamics that explain cooperative behaviour and resource-sharing during aggregation events using an agent-based model of indirect reciprocity. In brief, agents make their decisions based on the success of the public strategies of other agents. Fitness depends on the resource captured and the social capital exchanged in aggregation events, modified by the agent’s reputation. Our computational results identify the relative importance of resources with respect to social benefits and the ease in detecting—and hence punishing—a defector as key factors to promote and sustain cooperative behaviour among population. 相似文献
970.
At the end of the Neolithic Era, during the third millennium BCE, there were fewer humid periods, and the sub-Saharan and Sahelian zones from the Atlantic to Lake Chad assumed their current geographical form. Since then, the climate has continued undergoing major variations. The succession of climatic episodes, humid or dry, is pointed out along with the episodes’ complex interactions. These variations are placed in parallel to cultural phases of evolution in archaeology and history. Climate-related events have always had heavy consequences on the peopling of this vast region, often subject to extreme natural conditions. The relative synchronism between the principal cultural trends from west to east across the Sahel seems to have often been subject to swings in the climate and the resulting environmental changes. 相似文献