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排序方式: 共有106条查询结果,搜索用时 15 毫秒
1.
Pirjo Sainio Irma Mäkinen Jaap-Willem Hutter Theo den Ouden Mikael Krysell 《Accreditation and quality assurance》2006,11(3):116-121
The international joint project HYCREF (Contract No. G6RD-CT-2002-00854), funded by the European Commission in the 5th Framework programme, aimed to develop methods to prepare homogeneous and stable reference materials of water, soil, and waste contaminated with mineral oil hydrocarbons and to certify the mineral oil content by gas chromatographic methods. The results of a feasibility study for the preparation of three soil reference materials are discussed in this paper, and for the preparation of three waste reference materials in the second part (Koch et al., Accred Qual Assur submitted for publication). The soil materials were selected to represent different soil types and contamination levels. The project plan set three requirements for these reference materials: uncertainty in the mineral oil content resulting from the certification exercise <5%, a sample inhomogeneity of <3% and a minimum long-term stability of 5 years. For the most part, these requirements were met within this project. 相似文献
2.
Marja Himottu Kalevi Pihlaja Gza Stjer Gbor Bernth Pirjo Vainiotalo 《Journal of mass spectrometry : JMS》1991,26(5):493-497
The mass spectra of four cycloalkane/ene cis- and trans-condensed 2-thioxo-2,3,5,6-tetrahydropyrimidin-4(1H)-ones and the corresponding cycloalkane/ene cis- and trans-condensed [l,3]thiazino[3,2-a]pyrimidinones were measured. Fragmentation pathways were confirmed by metastable ion analyses and exact mass measurements. The bicyclic isomers were easy to distinguish from each other, whereas the corresponding tricyclic isomeric adducts gave fairly similar mass spectra, owing to their favoured reiro-Diels- Alder fragmentations accompanied by the migration of one or two hydrogen atoms. 相似文献
3.
Tuula Partanen Pirjo Vainiotalo Gza Stjer Kalevi Pihlaja 《Journal of heterocyclic chemistry》1994,31(4):893-897
The 70 eV electron ionization (EI) mass spectra were recorded for eight norbornane/ene-fused 2-N-phenyl-iminoperhydro-1,3-oxazines, and the fragmentation patterns were studied by metastable ion analysis and exact mass measurement. Whereas the stereoisomeric unsaturated compounds could not be distinguished on the basis of their EI mass spectra, the stereoisomeric saturated compounds gave rise to clearly different spectra. The ionized unsaturated compounds decomposed mainly by two consecutive retro-Diels-Alder (RDA) reactions. A methyl substituent on the ring nitrogen strongly influenced the charge distribution on the RDA fragments. The ionized saturated compounds fragmented through several pathways. Loss of cyclopentadiene from the molecular ion was the energetically favoured fragmentation reaction for the saturated di-endo-fused compounds but was unimportant for the di-exo-fused compounds. 相似文献
4.
Pirjo Vainiotalo Pentti J. Mlknen Anto Vainiotalo 《Journal of mass spectrometry : JMS》1989,24(6):415-420
The electron impact induced fragmentations of 24 tetrahydropyrane ethers of different types of alcohols were studied by exact mass measurement and metastable ion analysis. The most characteristic features of the spectra were associated with the tetrahydropyrane ring, As the size of the molecule increased, the fragmentations with respect to exocyclic oxygen became more important allowing differentiation among the isomeric aliphatic alcohols. Under isobutane chemical ionization, loss of neutral alcohol from [M + H]+ leading to the formation of a tetrahydropyranium ion was dominant for aliphatic alcohol derivatives, whereas loss of 2-hydroxy tetrahydropyrane giving rise to an alkyl ion was dominant for bicyclic alcohol derivatives. Under ammonia chemical ionization, nucleophilic substitution reactions were always most important. 相似文献
5.
Ammonia, isobutane and methane chemical ionization mass spectra have been measured for some substituted cis-1,3-cyclopentane dicarboxylic acids and their derivatives. The relative proton affinities of the different functional groups determine the protonation site in the molecule and thereby greatly affect the fragmentation. Intramolecular catalysis clearly facilitates the elimination of water in cases where functional groups can interact with each other. 相似文献
6.
Ferenc Fülp Enik Forr Gbor Bernth Istvn Miskolczi Pirjo Vainiotalo Aarne Martinsen 《Journal of heterocyclic chemistry》1997,34(1):289-293
The Hammett-Brown electrophilic substituent constants σ+ for five heteroaryl-substituted phenyl groups were estimated via the ring-chain tautomeric equilibria of three sets of oxazolidines and 1,3-oxazines in deuteriochloroform solution. For oxazolidines derived from norephedrine and norpseudoephedrine, the σ+ values were also determined via the gas-phase ring-chain equilibria, by means of mass spectrometry. The results show that the heteroaromatic substituents studied have a slight electron-withdrawing character, with σ+ in the range -0.03 to 0.59. The gas-phase σ+ values are significantly higher than the solution values. 相似文献
7.
Fast gas chromatography/negative-ion chemical ionization mass spectrometric (GC/NICI-MS) assay combined with rapid and nonlaborious sample preparation is presented for the simultaneous determination of benzodiazepines and alpha-hydroxy metabolites, zaleplon and zopiclone in whole blood. The compounds were extracted from 100 microl of whole blood by simultaneous multitube, microscale liquid-liquid extraction (LLE) and derivatized by N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide (MTBSTFA), without the need for the time-consuming concentration stage. In the analytical separation, various parameters of fast GC/NICI-MS were applied, e.g. the use of hydrogen as a GC carrier gas, a high carrier gas velocity, a small film thickness of the analytical column, fast MS data acquisition, fast temperature ramping, and high initial and final temperatures of GC column. Sensitive identification, screening and quantitation of 18 compounds of interest were achieved in chromatographic separation in only 4.40 min. Accurate and reproducible results were obtained by using five different and carefully selected deuterated analogues on the basis of the chemical properties of the target analytes. Nevertheless, for alpha-OH-midazolam, and for bromazepam and flunitrazepam at low concentrations, the results can be considered only semiquantitative on the basis of the validation data. The extraction efficiencies ranged from 74.3 to 105.7% and the limits of quantitation (LOQ) from 1 to 100 ng ml(-1). Rapid sample preparation and fast chromatographic separation allowed cost-efficient, reliable and high sample-throughput analyses with a low amount of manual work. The method was fully validated and accredited according to EN ISO/IEC 17025 standards and is applicable for sensitive, reliable and quantitative determination of benzodiazepines, zaleplon and zopiclone, e.g. in clinical and forensic toxicology. 相似文献
8.
The influence of nucleus density on optical properties in nucleated isotactic polypropylene 总被引:1,自引:0,他引:1
Alfrd Menyhrd Markus Gahleitner Jzsef Varga Klaus Bernreitner Pirjo Jskelinen Harry
ysd Bla Puknszky 《European Polymer Journal》2009,45(11):3138-3148
The effect and efficiency of three nucleating agents, a sorbitol based clarifier, a traditional heterogeneous nucleating agent and poly(vinylcyclohexane) (PVCH) was studied in polypropylene (iPP) homopolymer. The nucleating agents were added to iPP in different amounts; PVCH in 0–200 ppm, while the other two in 0–2000 ppm. Optical and mechanical properties were determined on injection molded plates or bars, respectively. Nucleation efficiency was studied by thermal analysis, while structure was characterized by polarized light (PLM), scanning electron (SEM) and atomic force microscopy (AFM). Nucleus density was calculated using the method of Lamberti, which is based on the kinetic theory of the crystallization developed by Lauritzen and Hoffmann. The results proved that the nucleating agents modify properties in different ways and extent. PVCH is very efficient already at small concentrations and increases the stiffness of iPP considerably more than the other two compounds. On the other hand, the clarifier and the traditional nucleating agent induce better optical properties even at smaller efficiency. The structure developing in the presence of the three nucleating agents is also different. The clarifier forms a network in iPP and induces the formation of a microcrystalline structure according to the former literature data. Microspherulitic structure develops in the presence of the heterogeneous nucleating agent studied, while relatively large supermolecular units form in iPP nucleated by PVCH even under the conditions of injection molding. The calculation of nucleus density by existing models and the comparison of the results to optical properties proved that haze is determined by the size of the supermolecular units of the polymer and this latter depends on nucleus density. 相似文献
9.
Róbert Berkecz Anna R. M. Hyyryläinen Ferenc Fülöp Antal Péter Tamás Janáky Pirjo Vainiotalo Jaana M. H. Pakarinen 《Journal of mass spectrometry : JMS》2010,45(11):1312-1319
Chiral discrimination of seven enantiomeric pairs of β‐3‐homo‐amino acids was studied by using the kinetic method and trimeric metal‐bound complexes, with natural and unnatural α‐amino acids as chiral reference compounds and divalent metal ions (Cu2+ and Ni2+) as the center ions. The β‐3‐homo‐amino acids were selected for this study because, first of all, chiral discrimination of β‐amino acids has not been extensively studied by mass spectrometry. Moreover, these β‐3‐homo‐amino acids studied have different aromatic side chains. Thus, the emphasis was to study the effect of the side chain (electron density of the phenyl ring, as well as the difference between phenyl and benzyl side chains) for the chiral discrimination. The results showed that by the proper choice of a metal ion and a chiral reference compound, all seven enantiomeric pairs of β‐3‐homo‐amino acids could be differentiated. Moreover, it was noted that the β‐3‐homo‐amino acids with benzyl side chains provided higher enantioselectivity than the corresponding phenyl ones. However, increasing or decreasing the electron density of the aromatic ring by different substituents in both the phenyl and benzyl side chains had practically no role for chiral discrimination of β‐3‐homo‐amino acids studied. When copper was used as the central metal, the phenyl side chain containing reference molecules (S)‐2‐amino‐2‐phenylacetic acid (L ‐Phg) and (S)‐2‐amino‐2‐(4‐hydroxyphenyl)‐acetic acid (L ‐4′‐OHPhg) gave rise to an additional copper‐reduced dimeric fragment ion, [CuI(ref)(A)]+. The inclusion of this ion improved noticeably the enantioselectivity values obtained. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.
The electron impact induced fragmentations of nine 2,2-disubstituted 1,3-oxathiolanes have been studied by means of exact mass measurement and metastable ion analysis. The ring cleavage almost always takes place so that the C(2)? S and C(5)? O bonds are broken, leading to the most stable products. The nature of the substituents determines the primary fragmentations of molecular ions. Ring cleavage is important only if both substituents are alkyl groups or if the carbon attaching to the ring has an alkyl character. The loss of the substituent becomes the most favourable process if it is attached to the ring through the electron-deficient carbon atom. 相似文献