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1.
Summary In virtually all neutron activation analysis laboratories, researchers are given film badges known as thermoluminescence dosimeters
(TLD's) that are monitored on a monthly basis. Sometimes additional pocket dosimeters are worn to get a daily reading of exposure,
while in other instances ring badges are worn to assess beta doses. However, more than often little consideration is given
to beta-exposure rates that arise from the plethora of radionuclides produced in the many types of samples irradiated. A common
mistake is to assess gamma-exposures of activated samples that rely on the use of a beta-shield on the survey meter. Our experimental
results have shown that there are many high energy beta-particles from neutron activated samples that can easily penetrate
the beta-shield and thus give an underestimation of the total beta-exposure. 相似文献
2.
Bromine can be determined by neutron activation analysis (NNA) through either the activation of79Br (50.69% naturally abundant) or81Br (49.31% naturally abundant). When79Br is activated, both80mBr and80Br are produced.80mBr (4.42 h) decays to80Br (17.66 m) which then beta decays to either80Se or80Kr. If one would like to determine bromine concentrations with short lived NAA, special equations must be used to account for the parent daughter relationship between80mBr after their simultaneous production. The development of the equations needed to calculate bromine concentrations with short-lived NAA is described including variations on irradiation times, decay times, and count times. 相似文献
3.
M. Sanchez S. Landsberger J. Braisted 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(2):487-490
Summary Potassium is an extremely important major element to the human body. Potassium is made up of three isotopes with abundances
of 39K at 93.1%, 40K at 0.0118% and 41K at 6.88%. It is also very well known that 40K with its 1.3 . 109 years half-life is a major naturally occurring isotope in the body and food. The usual way to determine total 40K is to measure the single 1460.8 keV photon from beta-decay. However, this procedure requires a significant amount of sample
and typical counting periods of at least a day in well-shielded germanium counting system. Another approach is to determine
total potassium via neutron activation analysis using the well known 41K(n,g)42K (T1/2 = 12.8 h) reaction and then evaluate 40K using the usual activity equation A = lN. In our laboratory we have effectively used epithermal neutron activation analysis and Compton suppression to determine potassium
in air filters and other geological material. Upwards to 10-15 samples can be analyzed in one day using only gram quantities
of material. In such way one can increase the output of determining 40K by at least one order of magnitude. Results of a detailed investigation optimization of the methodology, quality control
and detection limits will be presented for reference material and various food samples. 相似文献
4.
For every integrable allocation (X
1,X
2, ...,X
n
) of a random endowmentY=
i
=1/n
X
i
amongn agents, there is another allocation (X
1*,X
2*, ...,X
n
*) such that for every 1in,X
i
* is a nondecreasing function ofY (or, (X
1*,X
2*, ...,X
n
*) areco-monotone) andX
i
* dominatesX
i
by Second Degree Dominance.If (X
1*,X
2*, ...,X
n
*) is a co-monotone allocation ofY=
i
=1/n
X
i
*, then for every 1in, Y is more dispersed thanX
i
* in the sense of the Bickel and Lehmann stochastic order.To illustrate the potential use of this concept in economics, consider insurance markets. It follows that unless the uninsured position is Bickel and Lehmann more dispersed than the insured position, the existing contract can be improved so as to raise the expected utility of both parties, regardless of their (concave) utility functions. 相似文献
5.
6.
S. Landsberger 《Journal of Radioanalytical and Nuclear Chemistry》1988,127(5):319-323
Non-destructive neutron activation analysis was employed to determine zinc in ten biological standard reference materials from the National Bureau of Standards and the National Research Council of Canada. The use of a 4 h. irradiation at a medium neutron flux allows excellent accuracies, precision and sensitivities to be attained for all the samples analyzed. It is suggested that neutron activation analysis be one of the benchmark methods for the determination of zinc in biological reference materials for concentrations as low as the one part per million level. 相似文献
7.
S. Landsberger 《Journal of Radioanalytical and Nuclear Chemistry》1994,180(2):295-300
An overview of the nuclear analytical methods oppurtunities at the University of Illinois at Urbana-Champaign is given. Undergraduate and graduate level teaching and research are highlighted. The TRIGA reactor and neutron activation analysis facilities are described in the context of this role within an inter-disciplinary environment. 相似文献
8.
In order to determine the elemental concentrations of three new soil standard reference materials SRMs 2709, 2710 and 2711 from the National Institute of Standards and Technology (NIST), a comparative study of different medium-lived neutron activation analysis methods was carefully performed. Three irradiation conditions (1-hour thermal, 1-hour epithermal and 5-minute epithermal) and two counting modes (normal and Compton suppression) have been evaluated for following ten elements: As, Au, Cd, Ga, K, La, Mo, Sb, Sm, and W. The results show that the method of 5-minute epithermal and a 1-day decay is the optimum way to analyze Ga, while the addition of the Compton suppression is very beneficial for the determination of K. Using the Compton suppression system in conjunction with the 1-hour epithermal and a 1-week decay, is ideal to determine Au, Cd, Mo and W, while routine 1-hour thermal and a 1-week decay, is adequate to determine As, Sb, Sm and La in concentrations found in soil. 相似文献
9.
S. Landsberger W. D. Cizek P. Domagala 《Journal of Radioanalytical and Nuclear Chemistry》1992,160(1):277-287
We have developed a PC based program for neutron activation data analysis using the FORTRAN and C languages. The routines are based on creating files associated with conventional ORTEC hardware and output software. The main features of the program include radionuclide identification, and the use of semi-automatic integration or the peak fitting SAMPO routine. Other developments are hard and soft copy records for detailed sample identification and particular irradiation, decay and counting procedures. Flux variations, high deadtime corrections, counting geometries, spectral and nuclear interferences, as well as uranium fission interferences are also automatically accounted for. The data output includes concentration values in %, ppm, g or ppb units with associated errors, while detection limits for each individual sample are indicated. Further data output can easily be generated which can be imported to most spreadsheet programs for various statistical uses. A future implementation to the program will include batch-file processing and automated self-absorption calculations for geological samples. 相似文献
10.