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21.
22.
The kinetics of the gas phase reactions of NO2 with a series of organics have been studied at 295 ± 2 K. It was observed that only 2,3-dimethyl-2-butene and the conjugated dialkenes studied reacted at observable rates, with rate constants which ranged from 1.5 × 10?20 cm3 molecule?1 s?1 for 2,3-dimethyl-2-butene to 1.3 × 10?17 cm3 molecule?1 s?1 for α-phellandrene. These rate constants are compared with the available literature data and the mechanisms of these reactions are discussed. 相似文献
23.
A rapid and accurate method for the determination of bismuth in rock samples is described. Automated equipment is used to generate bismuth hydride from solutions of rock samples prepared by digestion with a mixture of hydrofluoric and perchloric acids. The evolved hydride is carried to a heated quartz tube by a stream of argon, and the atomic absorption of bismuth recorded. Thiosemicarbazide and 1,10-phenanthroline are used as masking agents to minimize interferences from copper and nickel. As little as 20 ng Bi g-1 can be determined; the average r.s.d. is 5.4%. Results obtained for six USGS standard rocks are in close agreement with the recommended values obtained by an isotope dilution technique. 相似文献
24.
The homogeneous gas-phase reaction of N2H4 with O3 in air atmospheric pressure has been used to generate OH radicals in the dark, allowing the determination of relative OH radical rate constants for compounds which photolyze rapidly. This technique was first validated by determining the OH radical rate constant ratios for n-butane/cyclohexane and methanol/dimethyl ether, both of which are in excellent agreement with the literature values. The rate constant for the reaction of OH radicals with methyl nitrite at 300 ± 3 K was then determined relative to those for the reaction of OH radicals with n-hexane and dimethyl ether. The resulting rate constant of 1.8 × 10?13 cm3/molecule·s is about seven times lower than those of previous measurements which employed a different nonphotolytic relative rate method. 相似文献
25.
James N. Pitts Eugenio Sanhueza Roger Atkinson William P. L. Carter Arthur M. Winer Geoffrey W. Harris Christopher N. Plum 《国际化学动力学杂志》1984,16(7):919-939
The formation of nitrous acid (HONO) in the dark from initial concentrations of NO2 of 0.1–20 ppm in air, and the concurrent disappearance of NO2, were monitored quantitatively by UV differential optical absorption spectroscopy in two different environmental chambers of ca.4300- and 5800-L volume (both with surface/volume ratios of 3.4 m?1). In these environmental chambers the initial HONO formation rate was first order in the NO2 concentration and increased with the water vapor concentration. However, the HONO formation rate was independent of the NO concentration and relatively insensitive to temperature. The initial pseudo-first-order consumption rate of NO2 was (2.8 ± 1.2) × 10?4 min?1 in the 5800-L Teflon-coated evacuable chamber and (1.6 ± 0.5) × 10?4 min?1 in a 4300-L all-Teflon reaction chamber at ca.300 K and ca.50% RH. The initial HONO yields were ca.40–50% of the NO2 reacted in the evacuable chamber and ca.10–30% in the all-Teflon chamber. Nitric oxide formation was observed during the later stages of the reaction in the evacuable chamber, but ca.50% of the nitrogen could not be accounted for, and gas phase HNO3 was not detected. The implications of these data concerning radical sources in environmental chamber irradiations of NOx? organic-air mixtures, and of HONO formation in polluted atmospheres, are discussed. 相似文献
26.
Evaluation of a simple plasma catecholamine extraction procedure prior to high-performance liquid chromatography and electrochemical detection 总被引:7,自引:0,他引:7
The modified extraction method for catecholamines described in this study is reproducible, simple, rapid, economical and relatively hazard-free. This method is based on the principle that plasma catecholamines are selectively adsorbed on acid-washed alumina at pH 8.6 and then eluted at a pH between 1.0 and 2.0. No statistically significant differences were obtained by using either 0.5 or 1.0 ml of plasma with 0.5 or 1.0 ml of Tris buffer. A 15-min mixing time during the adsorption and desorption steps was found to be practical, but any standardized time up to 1 h can be used. If the washing step was omitted, the catecholamines could not be eluted from the acid-washed alumina. To prevent dilution, the alumina had to be centrifuged and not aspirated to dryness after the washing step. An amount of 50 mg of WA-4 alumina was found to be the most practical in this study. Extracted or unextracted plasma as well as catecholamine standards were stable for four months at -20 degrees C. 相似文献
27.
28.
Chemiluminescence spectra (300–800 nm) from the reactions of ozone with acetylene and allene have been obtained. These spectra show the production of electronically excited CHO, OH(2Πi, υ ? 9) and possibly C2(B3Πg, υ′ = 0 → X3Πu, υ″ = 6) from the O3 + C2H2 reaction. CH(2Δ), OH(2Σ+) and OH(2Πj, υ ? 9) emissions were identified from the O3 + C3H4 reaction in addition to the CH2O(1A″) emission previously reported. 相似文献
29.
William P.L. Carter Karen R. Darnall Alan C. Lloyd Arthur M. Winer James N. Pitts 《Chemical physics letters》1976,42(1):22-27
We have calculated approximate room temperature rate constants for intramolecular hydrogen shift isomerizations of alkyl, alkoxy and alkylperoxy radical intermediates in photochemical smog and found that alkoxy radicals with δ hydrogens appear to undergo 1,5 hydrogen shifts at ambient conditions. Product distributions observed during irradiations of alkane (n-butane, n-pentane and n-hexane)NOxair systems in two quite-different ≈6000-liter environmental chambers were found to be consistent with this prediction. For example, in the n-pentaneNO xair system the observed large yields of 3-pentanone relative to 2-pentanone were consistent with room temperature rate constants which we have estimated for the corresponding hydrogen shift isomerizations. While such isomerizations have been well recognized in studies of free radicals and high temperature hydrocarbon oxidations, they are not taken into account in current kinetic mechanisms for alkane oxidation under ambient atmospheric conditions. This has implications for the construction of computer models of photo-chemical smog formation. 相似文献
30.
R.G. Smith J.C. Van Loon J.R. Knechtel J.L. Fraser A.E. Pitts A.E. Hodges 《Analytica chimica acta》1977
An inexpensive 50-ml disposable (hypodermic) syringe is used as the arsine generation vessel. The arsine is passed into a 10-cm long. 10-mm i.d. electrically heated silica tube atomizer with nitrogen carrier gas. Excess of hydrogen is burned off in a hydrogen diffusion flame at the ends of the tube. Samples containing appreciable silica are fused with KOH—MgOXXX while organic samples are digested with H2SO4—H2O2. Parameters affecting the determination of arsenic as arsine have been investigated. Collaborative results on a variety of standard reference materials agree well with literature values. The advantages of the proposed method are that it is sensitive, selective, fast, simple, inexpensive, precise and accurate. 相似文献