全文获取类型
收费全文 | 122篇 |
免费 | 1篇 |
国内免费 | 3篇 |
专业分类
化学 | 33篇 |
力学 | 4篇 |
综合类 | 2篇 |
物理学 | 87篇 |
出版年
2023年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 2篇 |
2013年 | 27篇 |
2012年 | 6篇 |
2011年 | 4篇 |
2010年 | 2篇 |
2009年 | 1篇 |
2008年 | 7篇 |
2007年 | 3篇 |
2006年 | 4篇 |
2005年 | 9篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 1篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1994年 | 3篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有126条查询结果,搜索用时 15 毫秒
1.
The identification of incomplete signal re-setting of optically stimulated luminescence signals in sedimentary quartz is a vitally important step in the continued improvement of optical dating. It is shown that narrow spectrum (blue-green) laboratory partial bleaching of aliquots of natural sedimentary quartz has a significant effect on equivalent dose (measured using a single aliquot procedure) calculated as a function of measurement time (De(t)). The blue-green stimulation spectrum mimics that found underwater and the results suggest that incomplete re-setting of waterlain sediments may be possible using the De(t) method. 相似文献
2.
TIMING OF COLLISION BETWEEN THE NORTH AND SOUTH CHINA BLOCKS——THE Sm-Nd ISOTOPIC AGE EVIDENCE 总被引:8,自引:0,他引:8
Sm-Nd isotopic ages for C-type eclogite (243.9±5.6 Ma) and mafic and ultramafic rocks(230.6±30.7 Ma and 402.6±17.4 Ma) from the Qinling-Dabieshan orogenic belt are reported.These ages suggest that at the early Triassic, the North and South China Blocks have beenunited along the Qinling-Dabieshan collision zone, and before the final collision, a se-ries of ophiolite obductions took place successively away from the continental marginduring the Paleozoic. 相似文献
3.
Simplified method for the Re-Os dating of molybdenite using acid digestion and isotope dilution ICP-MS 总被引:1,自引:0,他引:1
An analytical method was developed for Os-Re dating of molybdenite. The method is based on determination of Os and Re concentrations in molybdenite by isotope dilution inductively-coupled plasma mass spectrometry (ID-ICP-MS). Sample digestion and sample/spike equilibration were achieved by a two-stage autoclave-based procedure using a mixture of nitric and sulphuric acids. Os was separated from the sample digest by modified single-stage distillation of osmium tetraoxide (OsO4) using elevated temperature and on-line addition of hydrogen peroxide. OsO4(g) was trapped in a mixture of 0.05% thiourea in 0.05 M sodium hydroxide. An anion-exchange column was used to separate Re from excess Mo in the solution remaining after distillation. Os and Re isotope ratio measurements were performed by single-collector, double focusing inductively-coupled plasma mass spectrometry (ICP-MS) with on-line mass-bias correction. Typical instrumental precision was in the range 0.02-0.2% relative standard deviation (R.S.D.) depending on the analyte concentrations. Notorious Os memory effects in the ICP-MS introduction system were eliminated using 5% ammonia solution, both as matrix for final dilution of the trap mixture as well as for washing between the samples. The reproducibility of the entire analytical procedure was accessed by replicate dating of two molybdenite standards and three molybdenite separates, and was found to be in the range 0.87-1.52% R.S.D. Though accuracy of the method is limited by difficulties in evaluating exact concentration of Os in spike solution, ages obtained in the course of these work agrees well with previously published data. 相似文献
4.
We have developed a new statically operated oxygen plasma method that allows direct14C dates to be obtained from ancient rock paintings. The method is applicable even to paintings on limestone (CaCO3) walls. A sample of a pictograph which had naturally spalled offa shelter wall in the Lower Pecos region of Texas was subjected to a low temperature ( 150°C) oxygen plasma to selectively remove the organic carbon-containing material used in the paint as CO2, without contamination from the limestone substrate. The Zürich EHT accelerator mass spectrometer was then used to determine the radiocarbon age of this prehistoric rock painting. It was successfully dated at 3865 ± 100 years BP, in good accord with the archaeological context which has set the onset of this Pecos River style of pictograph between 4100 and 3200 years BP. The method appears feasible and is applicable to rock art in which organic materials were used in the paint. 相似文献
5.
6.
Leonard I. Wassenaar Liang-Feng Han Thomas Schiefer Gustav Kainz Luis Araguas-Araguas Pradeep K. Aggarwal 《Isotopes in environmental and health studies》2018,54(3):274-287
Tritium (3H) is an essential tracer of the Earth's water cycle; yet widespread adoption of tritium in hydrologic studies remains a challenge because of analytical barriers to quantification and detection of 3H by electrolytic pre-concentration. Here, we propose a simple tritium electrolytic enrichment system based on the use of solid polymer electrolyte membranes (PEMs) that can be used to enrich 3H in 250–3000?mL environmental water samples to a 10-mL final volume. The IAEA PEM-3H system reported here can produce high enrichment factors (>70-fold) and, importantly, removes some of the deterrents to conventional 3H enrichments methods, including the use of toxic electrolysis and neutralization chemicals, spike standards, a complex electrolysis apparatus that requires extensive cooling and temperature controls, and improves precision by eliminating the need for tracking recovery gravimetrics. Preliminary results with varying operating conditions show 3H enrichments to 70-fold and higher are feasible, spanning a wide range of tritium activities from 5 to 150 TU with a precision of ~4.5?%. Further work is needed to quantify inter-sample memory and to establish lower 3H detection limits. The IAEA PEM-3H system is open source, with 3-D CAD and design files made freely available for adoption and improvement by others. 相似文献
7.
《Analytical letters》2012,45(3):215-221
Abstract An enzymatic method for estimating the age of biological specimens is described. The method is based on the slow racemization of L-aspartic acid to the D isomer. Conditions for protein extraction, enzymatic hydrolysis, pretreatment with stereospecific enzymes and assaying are discussed. The results obtained by this method are compared with the more conventional radiocarbon technique and its application to Holocene climatology is discussed. 相似文献
8.
9.
H. Jordan D. Hebert K. Fröhlich R.-P. Scholz R. Gellermann 《Isotopes in environmental and health studies》2013,49(3):79-82
The migration of radionuclides and other tracers in porous layers is determined by substance transport. The physical and hydraulic basis of retardation is investigated. A definition of a factor of retardation is given, describing the ratio between the pore velocity of the water and the velocity of tracer migration. Consequences to the groundwater protection are discussed. 相似文献
10.
In ESR dating of Early Pleistocene fossil tooth enamel samples, the fitting function used for the evaluation of the DE value is undoubtedly among the major sources of uncertainty. Dose recovery tests performed on fossil tooth enamel showing DE values >1,000 Gy demonstrate: (i) that high precision ESR measurements (<0.5%) and high DE reproducibility (<5%) may be achieved; (ii) the appropriateness of the Double Saturating Exponential (DSE) fitting function for ESR dose reconstruction. In contrast, the SSE function, which has been almost exclusively used so far, does simply not correctly describe the behavior of the radiation induced ESR signal of tooth enamel with the dose.Several fitting functions and data weighting options were tested and the combination of a DSE with data weighted by the inverse of the squared intensities is the procedure providing the most accurate DE results. However, the SSE may nevertheless sometimes produce consistent results if Dmax does not exceed 6*DE. Further work is required in that direction in order to determine more precisely in which conditions the SSE could be used as a fair approximation of the DSE function for these samples. 相似文献