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941.
Andrzej Z. Rakowski 《Geochronometria》2011,38(4):314-324
The traditional radiocarbon method widely used in archaeology and geology for chronological purposes can also be used in environmental
studies. Combustion of fossil fuels like coal, natural gas, petroleum, etc., in industrial and/or heavily urbanized areas,
has increased the concentration of carbon dioxide in the atmosphere. The addition of fossil carbon caused changes of carbon
isotopic composition, in particular, a definite decrease of 14C concentration in atmospheric CO2 and other carbon reservoirs (ocean and terrestrial biosphere), known as the Suess effect. Tree rings, leaves, as well as
other annual growing plants reflected the changes of radiocarbon concentration in the atmosphere due to processes of photosynthesis
and assimilation of carbon from the air. By measuring radiocarbon concentration directly in atmospheric CO2 samples and/or biospheric material growing in industrial and/or highly urbanized areas where high emission of dead carbon
is expected, it is possible to estimate the total emission of dead CO2. Based on equations of mass balance for CO2 concentration, stable isotopic composition of carbon and radiocarbon concentration it is possible to calculate CO2 con-centration associated with fossil fuel emission into the atmosphere. The procedure use differences between the radiocarbon
concentration and stable isotope composition of carbon observed in clean areas and industrial or/and highly urbanized areas. 相似文献
942.
Victor N. Karmanov Natalia E. Zaretskaya Andrey V. Panin Alexey V. Chernov 《Geochronometria》2011,38(2):128-137
In river valleys, both human occupation and subsequent preservation of archaeological sites are affected by active landscape
transformation caused by river lateral migration, incision/aggradation cycles and changes of river hydrological regime. In
the middle Vychegda River valley (Northern Russia), there are numerous traces of human presence since the Mesolithic. We exploit
multi-disciplinary archaeological, geomorphological and geochronological approach to elucidate the environmental preferences
of settlements positioning during different epochs of the Holocene. High resolution space image supplemented with data on
alluvial stratigraphy derived from bank exposures and hand cores, as well as 51 radiocarbon dates were used to make the geomorphic
map showing ages of floodplain/terrace segments and palaeochannels. Using this map together with sediment facial interpretation,
position of archaeological sites was analysed in the context of local geomorphic and hydrologic situation. The majority of
archaeological sites and modern settlements are found on terraces at river banks or at oxbow lakes which were well connected
to the river. Few exceptions from this rule may be explained by seasonal character of dwelling functioning, ritual burial
practice or specialization of settlements. Geomorphic situation was used as a background for planning further prospection
of different-age archaeological objects. 相似文献
943.
A new measurement protocol has been tested on K-feldspars from Whanganui Inlet and Parengarenga Harbour, New Zealand. A Single
Aliquot Regenerative (SAR) dose protocol, using two successive infrared (IR) stimulations (post-IR IR SAR protocol) is setup
for these young (<1000 years) coastal sediments. Significant anomalous fading (g
2days
=7 %/decade) is observed using the conventional IR signal measured at 50°C. In contrast, the fading rate of the IR signal
measured at elevated temperature (150°C) after the IR stimulation at 50°C (a post-IR IR signal) is not significant (g
2days
≤ 1 %/decade). Surprisingly low residual infrared stimulated luminescence (IRSL) signals were observed for a surface sample,
suggesting that accurate ages as young as ∼50 years can be obtained for these recent deposits. IRSL ages ranging between 48±6
years and 1050±50 years are obtained from six samples, indicating that sediment accumulation has occurred at the two sites
during the last millennia, despite a falling trend in relative sea-level in Whanganui Inlet and a stable relative sea-level
at Parengarenga Harbour. 相似文献
944.
In luminescence dating of sediments, Mayya et al. (2006) pointed out that at single grain level, the beta dose for quartz grains is heterogeneous. This heterogeneity arises
due the fact that the total potassium in sediment is contributed by few feldspar grains with up to 11–14% stoichiometric potassium
(Huntley and Baril, 1997). Beta particles have a range of ∼2 mm, which is comparable to grain sizes and inter-grain distances.
This fact implies that the spatial fluctuation of beta emitters (K-feldspars) around individual quartz grains results in heterogeneous
dose deposition. These fluctuations therefore, lead to an inherent spread in palaeodoses received by individual quartz grains. 相似文献
945.
Jan-Pieter Buylaert Christine Thiel Andrew S. Murray Dimitri A.G. Vandenberghe Shuangwen Yi Huayu Lu 《Geochronometria》2011,38(4):432-440
Using a set of modern/young (0 to about 200 years old) dust samples collected from the Chinese Loess Plateau the bleachability
of IRSL measured at 50°C (IR50) and post-IR50 elevated temperature IRSL (measured at 225°C and at 290°C) is investigated by measuring the apparent (residual) doses recorded
by these signals. Doses recorded by quartz OSL are used as a reference. Allowing for differences in dose rates it seems that
both IRSL and post-IR IRSL signals yield residual doses that are significantly larger than the doses measured in quartz. These
residual doses can be largely explained by thermal transfer caused by preheating. Nevertheless, we advise against the use
of a low temperature preheat (<200°C) with IR50 to date loess samples because, as has been reported before, the signal appears to be thermally unstable. In general, we conclude
that it may not be advisable to apply post-IR IRSL dating to Chinese loess samples where residuals of up to ∼20 Gy are a significant
fraction of the total dose. However, these residuals quickly become unimportant when dating older samples, and this is the
age range in which post-IR IRSL dating is likely to be most useful. 相似文献
946.
Shin Toyoda 《Geochronometria》2011,38(3):242-248
Quartz is one of the minerals useful for electron spin resonance (ESR) dating. The E1′ center is one of well-known paramagnetic defects in crystalline quartz. This center has a unique feature; its intensity
increases on heating. An electronic process to explain this increase was found to be controlled not only by the number of
oxygen vacancies, which are the precursors, but also by the number of Al hole centers, which depend on the previous radiation
dose and on the Al concentration. 相似文献
947.
The estimation of firing temperature of ceramics using methods based on pre-dose sensitization of the 110°C TL peak of quartz
have yielded incoherent results. Recently the fast component of the CW-OSL of quartz has been observed to have pre-dose characteristics
similar to that of the 110°C TL peak. The motivation for this study has been to look into the feasibility of this signal,
the OSL counter part of pre-dosed TL emission, for the firing temperature identification. The variation in the sensitization
ratio of the TL and OSL emissions with different heating temperatures was also utilized to unveil the firing temperature mark
of the specimen. 相似文献
948.
An assessment of the luminescence sensitivity of Australian quartz with respect to sediment history 总被引:2,自引:0,他引:2
Kathryn E. Fitzsimmons 《Geochronometria》2011,38(3):199-208
This study provides a preliminary systematic characterisation of OSL sensitivity, with respect to sediment history, of single
grains of Australian quartz from a variety of source rocks and depositional contexts. Samples from two distinct lithologies
and with relatively short modern sedimentary histories were compared in an examination of the influence of rock type on OSL
sensitivity. Sediments derived from weathered sandstone were found to be brighter than those from metamorphosed schists, suggesting
that sensitivity may be inherited from the source rock and its earlier sedimentary history. Secondly, quartz from the same
source, but different modes of deposition, was compared to assess the effect on sensitivity of nature of exposure to light
during the most recent bleaching event. Quartz grain sensitivity appears not to vary depending on the mode of sediment deposition,
suggesting that the nature of exposure to light during deposition is less important in the sensitisation process. This study
highlights the complexity and variety of natural sedimentary quartz, demonstrating the limitations of an investigation based
solely on OSL sensitivity. Further systematic investigation into the physical, geological and geomorphological characteristics
of sediments is proposed to better understand the mechanisms of luminescence sensitisation in quartz. 相似文献
949.
950.