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91.
A stationary storage process with Brownian input and constant service rate is studied. Explicit formulae for quantities related to busy periods (excursions) are derived. In particular, we compute the distributions of the occupation times the process spends above and below, respectively, the present level during the on-going busy period, and make the surprising observation that these occupation times are identically distributed. 相似文献
92.
93.
The normalized amplitude quotient (NAQ), defined as the ratio between the peak-to-peak amplitude of the flow pulse and the negative peak amplitude of the differentiated flow glottogram and normalized with respect to period time, has been shown to be related to glottal adduction. Glottal adduction, in turn, affects mode of phonation and hence perceived phonatory pressedness. The relationship between NAQ and perceived phonatory pressedness was analyzed in a material collected from a professional female singer and singing teacher who sang a triad pattern in breathy, flow, neutral, and pressed phonation in three different loudness conditions (soft, middle, loud). In addition, she also sang the same triad pattern in four different styles of singing, classical, pop, jazz, and blues, in the same three loudness conditions. A panel of experts rated the degree of perceived phonatory press along visual analogue scales. Comparing the obtained mean rated pressedness ratings with the mean NAQ values for the various triads showed that about 73% of the variation in perceived pressedness could be accounted for by variations of NAQ. 相似文献
94.
Neuvonen H Neuvonen K Koch A Kleinpeter E Pasanen P 《The Journal of organic chemistry》2002,67(20):6995-7003
(13)C NMR chemical shifts and nu(C[double bond]O) frequencies have been measured for several series of phenyl- or acyl-substituted phenyl acetates and for acyl-substituted methyl acetates to investigate the substituent-induced changes in the electrophilic character of the carbonyl carbon. Charge density, bond order, and energy calculations have also been performed. The spectroscopic and charge density results indicate that opposite to the conventional thinking, electron-withdrawing substituents do not increase the electrophilicity of the carbonyl carbon but instead decrease it. On the other hand, reaction energies of the isodesmic reactions designed show that electron-withdrawing substituents destabilize the carbonyl derivatives investigated. So, a significant ground-state destabilization of carboxylic acid esters, and carbonyl compounds in general, due to the decreased resonance stabilization, is proposed as a novel concept to explain both the increase in their reactivity and the changes in the chemical shifts and carbonyl frequencies induced by electron-withdrawing substituents. 相似文献
95.
The enolate anions of chlorophylls (Chl) are ambident nucleophiles that are of considerable organic chemical interest in relation to the theory of electron delocalization (aromaticity) and charge-transfer in large conjugated π-systems, as well as for their chemical reactivity. Under deaerated conditions, the (−)- and (+)-enantiomers of (10-camphorsulfonyl)oxaziridine (CSOAI) are effective oxidants for the enolate anions of Chl a and Chl b, when 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) serves as a base. In this study, the use of these sterically hindered reagents to hydroxylate Chl a and Chl b is described for the first time. The total yield of 132(S/R)-HO-Chl a was 71 and 90% for the oxidations of Chl a with (−)-CSOAI and (+)-CSOAI, respectively. Chl b, however, behaved clearly differently from Chl a. The total yield of 132(S/R)-HO-Chl b was 40% in the oxidation with (−)-CSOAI and 60% in the reaction with (+)-CSOAI. A competing side-reaction, which resulted in the 152-methyl, 173-phytyl ester of Mg-151(S/R)-unstable rhodin, was found to lower the yields of the desired main products. The formation of the side-products was largely avoided and the yield of 132(S/R)-HO-Chl b was improved by increasing the volume of hexane and using phosphate buffer in the first step of the work-up. With (−)-CSOAI, a 94% diastereomeric excess (de) was achieved for 132(R)-HO-Chl a, whereas the de for 132(R)-HO-Chl b was 66%. With (+)-CSOAI, the de was 10% for 132(R)-HO-Chl a and 8% for 132(R)-HO-Chl b. The results were interpreted in terms of a nucleophilic reaction mechanism, kinetically controlled by steric hindrance, originating on the one hand in the 17-propionate phytyl ester side-chain, protruding over the isocyclic ring E of the Chl enolate ion, and on the other hand in the bulky camphorsulfonyl unit of CSOAI. Possible reasons for the different results from the Chl b oxidations as compared with those of the Chl a oxidations are discussed. Comparison of the differences in the NMR δC-values between 132(S)- and 132(R)-HO-Chl a as well as those between 132(S)- and 132(R)-HO-Chl b, indicated that the change of stereochemical configuration at C-132 induces only slight differences in the δC-values. Of special interest are the δC-values of C-132, which are at ca. 91 ppm for the a- and b-series diastereomers. This carbon is deshielded by ca. 25 ppm relative to the C-132 of 132(R)-Chl a (δC=65.5). Owing to this, 13C NMR spectroscopy is a good method to distinguish the 132-hydroxylated chlorophylls from the intact, naturally occurring chlorophylls. 相似文献
96.
Matti Niemelä Harri Kola Paavo Perämäki Juha Piispanen Jarmo Poikolainen 《Mikrochimica acta》2005,150(3-4):211-217
Different temperature-pressure controlled microwave-assisted digestion methods were compared for the digestion of dust samples prior to the determination of rhodium and platinum by inductively coupled plasma mass spectrometry (ICP-MS). The results obtained for platinum and rhodium in the digested reference material (BCR-723, road dust) were generally in good agreement with the certified values. However, the determination of matrix elements (Zn, Rb, Sr, Y, Hf and Pb) showed clear differences between the digestion methods. In addition, different internal standards were compared in the determination rhodium, palladium and platinum by ICP-MS. According to the results, even serious non-spectral interferences can be corrected by choosing a suitable internal standard or combination of internal standards. 相似文献
97.
Langmuir-Blodgett assemblies of 1-palmitoyl-2-pyrenedecanoylphosphatidylcholine and dipalmitoylphosphatidylcholine were transferred from an air/water interface onto germanium or silicon attenuated total reflection (ATR) crystals and were investigated by Fourier transform infrared spectroscopy. A detailed attention has been paid to optimize the deposition conditions and to study the organization of transferred mono- and multimolecular layers. 相似文献
98.
Comparison of Two Inverse Filtering Methods in Parameterization of the Glottal Closing Phase Characteristics in Different Phonation Types 总被引:1,自引:0,他引:1
SUMMARY: Inverse filtering (IF) is a common method used to estimate the source of voiced speech, the glottal flow. This investigation aims to compare two IF methods: one manual and the other semiautomatic. Glottal flows were estimated from speech pressure waveforms of six female and seven male subjects producing sustained vole /a/ in breathy, normal, and pressed phonation. The closing phase characteristics of the glottal pulse were parameterized using two time-based parameters: the closing quotient (C1Q) and the normalized amplitude quotient (NAQ). The information given by these two parameters indicates a strong correlation between the two IF methods. The results are encouraging in showing that the parameterization of the voice source in different speech sounds can be performed independently of the technique used for inverse filtering. 相似文献
99.
A novel method for the quantitative assessment of the membrane partitioning of a ligand from the aqueous phase is described,
demonstrated here with the thoroughly studied antipsychotic chlorpromazine (CPZ). More specifically, collisional quenching
of the fluorescence of a pyrene labeled fluorescent lipid analog 1-palmitoyl-2[10-(pyren-1-yl)]decanoyl-sn-glycero-3-phosphocholine (PPDPC) by CPZ was utilized, using 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine and -serine (POPC and POPS) liposomes as model membranes. The molar partition coefficient is obtained
from two series of titrations, one with constant [phospholipid] and increasing [drug] and the other with constant [drug] and
varying total [phospholipid], the latter further comprising of large unilamellar vesicles (LUVs) of POPC/POPS/PPDPC at a constant
concentration of 10 μM and indicated concentrations of POPC/POPS LUVs. Notably, the approach described is generic and can
be employed in screening for the membrane partitioning of compounds, providing that a suitable fluorescence parameter can
be incorporated into one population of liposomes utilized as model membranes. 相似文献
100.
Harri Kola Toivo Kuokkanen Ilkka Välimäki Paavo Perämäki Risto Lauhanen 《International journal of environmental analytical chemistry》2013,93(2):157-165
Different chain oils (tall, rape seed and mineral oils) have been used as model compounds to evaluate and optimize the applicability of UV-persulphate TOC-analyzer for quantitative determination of forestry oils and to follow the progress of their biodegradability. It was shown, that K 2 S 2 O 8 -UV-oxidation method is not sufficient to oxidize chain oils completely. There were differences in oxidation efficiency between different oils, changing from about 46% measured for tall oil to about 25% observed for rape seed chain oil. The addition of Triton X-100 surfactant up to 2% (w/w) was observed to increase the oxidation efficiency, e.g. to 75% for tall oil. The observations can be explained by assuming that in the presence of surfactant the emulsions are more homogeneous and stable. Optimization using two-level full factorial design (temperature of the oxidation chamber and the amount of persulphate) was studied. The results show that the UV-persulphate-oxidation TOC-analyzer is not suitable method to monitor biodegradability of chain oils. 相似文献