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51.
Apples and other fruits are frequently cultivated in gardens and are part of our daily diet. Uptake of pollutants into apples may therefore contribute to the human daily intake of toxic substances. In current risk assessment of polluted soils, regressions or models are in use, which were not intended to be used for tree fruits. A simple model for uptake of neutral organic contaminants into fruits is developed. It considers xylem and phloem transport to fruits through the stem. The mass balance is solved for the steady-state, and an example calculation is given. The Fruit Tree Model is compared to the empirical equation of Travis and Arms (T&A), and to results from fruits, collected in contaminated areas. For polar compounds, both T&A and the Fruit Tree Model predict bioconcentration factors fruit to soil (BCF, wet weight based) of >1. No empirical data are available to support this prediction. For very lipophilic compounds (log K OW >5), T&A overestimates the uptake. The conclusion from the Fruit Tree Model is that the transfer of lipophilic compounds into fruits is not relevant. This was also found by an empirical study with PCDD/F. According to the Fruit Tree Model, polar chemicals are transferred efficiently into fruits, but empirical data to verify these predictions are lacking. 相似文献
52.
Changing attitudes to irradiation throughout the food chain 总被引:1,自引:0,他引:1
C. Hunter 《Radiation Physics and Chemistry》2000,57(3-6):239-243
Recent studies of consumer attitudes in the United States indicate an increased willingness to purchase irradiated food in order to have a safer product. The reasons for the change in attitude are discussed. Basic consumer buying habits are considered and how these fit in with marketing irradiated food. Food retailers, restaurants and producers have attitudes of their own, and these can sometimes be the most difficult to change. The key to this puzzle can be found in their basic motivations, including the fear of activists. Recommendations are made as to how this information can be used to promote the development of food irradiation. 相似文献
53.
《Analytical letters》2012,45(13):2321-2333
The determination of ultra-trace levels of chromium and nickel in biological samples had previously been very difficult due to serious contamination problems in conventional laboratories. Contamination control in a conventional laboratory was studied and contamination due to various sources was minimized systematically. In addition to chromium and nickel, zinc was also determined as an indicator element prone to contamination. Measurements were carried out using electrothermal atomic absorption spectrometry (ETAAS). Contamination from the sample handling steps, digestion vessels, atmospheric fallout, and the effect of the liquid contact area were studied. In the sample handling steps, even simple procedures, such as transferring the sample solution from the volumetric flask by pouring, led to significant contamination due to the large area of liquid contact. This contamination source was eliminated by transferring the sample solution using an automatic pipette. The most suitable method for decontamination of the digestion vessels was steaming with boiling nitric acid as opposed to leaching with nitric acid at room temperature. Quartz was found to be a more suitable digestion vessel material than Teflon-PFA when Cr and Ni were determined. For Zn determination, Teflon-PFA was more suitable. Contamination from atmospheric fallout was highest in the fume hood and was reduced by simply closing the labware into Minigrip® bags before use. The surface area of the labware in contact with the handled liquid volume should be kept at a minimum because even a simple procedure, such as preparing standard solutions in volumetric flasks, can lead to significant contamination if the vessel surface area is too large. Finally, low enough contamination was achieved so that the total procedure blanks were below the instrumental detection limits for Cr and Ni. 相似文献
54.
Solutions of portfolio optimization problems are often influenced by a model misspecification or by errors due to approximation, estimation and incomplete information. The obtained results, recommendations for the risk and portfolio manager, should be then carefully analyzed. We shall deal with output analysis and stress testing with respect to uncertainty or perturbations of input data for static risk constrained portfolio optimization problems by means of the contamination technique. Dependence of the set of feasible solutions on the probability distribution rules out the straightforward construction of convexity-based global contamination bounds. Results obtained in our paper [Dupa?ová, J., & Kopa, M. (2012). Robustness in stochastic programs with risk constraints. Annals of Operations Research, 200, 55–74.] were derived for the risk and second order stochastic dominance constraints under suitable smoothness and/or convexity assumptions that are fulfilled, e.g. for the Markowitz mean–variance model. In this paper we relax these assumptions having in mind the first order stochastic dominance and probabilistic risk constraints. Local bounds for problems of a special structure are obtained. Under suitable conditions on the structure of the problem and for discrete distributions we shall exploit the contamination technique to derive a new robust first order stochastic dominance portfolio efficiency test. 相似文献
55.
56.
ICP-MS测定自来水中的金属元素 总被引:1,自引:0,他引:1
利用电感耦合等离子体质谱仪的高灵敏度、高准确性和多元素同时分析的特点,可以快速精确地测定自来水中的微量金属元素含量。由于自来水样品中的有害金属元素含量比较低,需要高灵敏度的分析方法,所以与其他元素分析技术相比ICP-MS优势明显,在自来水样品分析中已经得到了广泛的应用。本文用电感耦合等离子体质谱法(ICP-MS)和原子吸收分光光度法(AAS)测定自来水中的金属元素,并对中国与日本自来水进行了取样分析和比较。 相似文献
57.
58.
A comparative experimental study is presented of the electronic properties of MnSi films grown on Si(1 1 1) and of MnSi single crystals, using X-ray absorption spectroscopy (XAS), and core level and valence band photoemission spectroscopy (PES). No significant differences in the electronic structure of the two systems can be found.Absorption measurements on the Mn 2p threshold show a mixed valence ground state, where the multiplet structure is washed out by the hybridisation of the Mn 3d states with the Si sp states. These results are also confirmed by photoemission (PE) spectra from the valence band and the Mn 3s, 3p and 2p core levels.Strong attention has been paid to the effect of contamination. The occurrence of multiplet effects in the absorption spectra indicates unambiguously the localisation of the Mn 3d electrons in Mn-O bonds, which strongly influences the electronic properties of these systems. 相似文献
59.
This paper presents a discussion involving practical aspects of applying contamination indices and ecological risk factors derived from chemical elements in the environmental assessment of soils and sediments. The single and integrated indices: Geoaccumulation index (Igeo), Enrichment factor (EF), Contamination factor (CF), Pollution Index (PI), Ecological risk factor (Eir), Pollution Load Index (PLI), Degree of contamination (Cdeg), Modified Contamination Factor (mCdeg), and potential ecological risk index (PERI) were discussed, and some applications were presented didactically. The analytical care needed to obtain reliable indices with the studied ecosystem is also evidenced. In addition, the advantages and limitations of the use of these indices are presented. 相似文献
60.
Phase behaviour measurement of binary mixtures of perfluoro-1,3-dimethylcyclohexane with methane and propane, and ternary mixtures of perfluoro-1,3-dimethylcyclohexane with methane + n-hexane and methane + n-decane at 373.15 K and over a wide range of concentration are presented. Measurements are made at the liquid bubble point and retrograde dew point pressures of the mixtures. A constant composition expansion test was carried out on perfluoro-1, 3-dimethylcyclohexane + methane mixture at 373.15 K. 相似文献