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151.
The synthesis of three key intermediates of the hydrogenation pathway in the hydrodesulfurization of 4,6‐dimethyldibenzothiophene (4,6‐DM‐DBT; 1 ) is described. The hydrogenated derivatives 1,2,3,4‐tetrahydro‐4,6‐dimethyldibenzothiophene (= 4,6‐dimethyl‐1,2,3,4‐tetrahydrodibenzothiophene; 4,6‐DM‐TH‐DBT; 2 ), 1,2,3,4,4a,9b‐hexahydro‐4,6‐dimethyldibenzothiophene (= 4,6‐dimethyl‐1,2,3,4,4a,9b‐hexahydrodibenzothiophene; 4,6‐DM‐HH‐DBT; 3 ), and dodecahydro‐4,6‐dimethyldibenzothiophene (= 4,6‐dimethylperhydrodibenzothiophene; 4,6‐DM‐PH‐DBT; 4 ) were prepared by direct hydrogenation of 1 . The reactions were carried out in continuous and batch reactors by using metal sulfide as well as noble‐metal catalysts. The influence of the reaction conditions on the formation of the products and the distribution of their stereoisomers was studied in detail. The isomers of the main products were isolated and characterized by NMR, GC/MS/MS, and X‐ray crystal‐structure diffractometry. 相似文献
152.
A combined chemical ionisation and tandem mass spectrometry (MS/MS) approach has been used for investigation of the gas-phase ion chemistry of systems containing the amino acids Glu and Met, and the dipeptides gamma-Glu-Met and Met-Glu. The metastable fragmentation of the protonated dimer, (Glu)2H(+), reveals an intracluster reaction leading to the elimination of the Glu residue. The main features of the ion-molecule reactions observed in the systems containing Glu and Glu + Met can be described in terms of sequential adduct formation. The results obtained for the thermal dehydration of Glu were used to rationalise the formation of the proton-bound structures (Glu-H2O...H(+)...(Glu-H2O) and (Glu-H2O)3-H(+). The adduct ions, [(Glu-H2O) + H + Glu](+) and [(Glu-H2O) + H + Met](+), and further association products were also observed. The results lead to a reconsideration of the structural aspects proposed earlier for these species in the sense that they suggest that the systems correspond to a mixture of isomeric covalent and proton-bound structures. The thermal effects on the decomposition of the neutral (gamma-Glu-Met) and its protonated form, (gamma-Glu-Met)H(+), at m/z 279 were investigated, and dramatic changes in the MI spectra of the m/z 279 ion with temperature were found. A mechanistic explanation for the observed evolution of higher mass ion peaks in the mass spectra is developed. 相似文献
153.
Fatty acid profiling of raw human plasma and whole blood using direct thermal desorption combined with gas chromatography-mass spectrometry 总被引:2,自引:0,他引:2
Gas chromatography (GC) has in recent times become an important tool for the fatty acid profiling of human blood and plasma. An at-line procedure used in the fatty acid profiling of whole/intact aquatic micro-organisms without any sample preparation was adapted for this work. A direct thermal desorption (DTD) interface was used to profile the fatty acid composition of human plasma and whole human blood of eight volunteers in a procedure omitting the usual lipid extraction steps that precede sample methylation in the traditional (off-line) protocols. Trimethylsulfonium hydroxide (TMSH) was used as reagent for thermally assisted methylation. In a fully automated manner, the liner of the GC injector is used as a sample-and-reaction container with the aid of the DTD interface. The fatty acid methyl ester (FAME) profiles obtained using this novel approach, were very identical to those obtained when the traditional off-line protocol was applied. FAME yields obtained in the at-line DTD method were found to be very similar for saturated fatty acids, but significantly higher for polyunsaturated fatty acids compared to off-line yields. As a result of the contribution of circulating cell membranes in blood, substantial differences were observed when the amount of FAMEs obtained in whole human blood and human plasma samples were compared after their analysis. Thanks to the fully automated operation of this novel procedure, large series of analyses can easily be performed. 相似文献
154.
De Mondt R Van Vaeck L Heile A Arlinghaus HF Nieuwjaer N Delcorte A Bertrand P Lenaerts J Vangaever F 《Rapid communications in mass spectrometry : RCM》2008,22(10):1481-1496
Static secondary ion mass spectrometry (S-SIMS) is one of the potentially most powerful and versatile tools for the analysis of surface components at the monolayer level. Current improvements in detection limit (LOD) and molecular specificity rely on the optimisation of the desorption-ionisation (DI) process. As an alternative to monoatomic projectiles, polyatomic primary ion (P.I.) bombardment increases ion yields non-linearly. Common P.I. sources are Ga+ (liquid metal ion gun (LMIG), SF5+ (electron ionisation) and the newer Au(n)+, Bi(n)q+ (both LMIG) and C60+ (electron ionisation) sources. In this study the ion yield improvement obtained by using the newly developed ion sources is assessed. Two dyes (zwitterionic and/or thermolabile polar functionalities on a largely conjugated backbone) were analysed as a thin layer using Ga+, SF5+, C60+, Bi+, Bi3(2+) and Bi5(2+) projectiles under static conditions. The study aims at evaluating the improvement in LOD, useful and characteristic yield and molecular specificity. The corrected total ion count values for the different P.I. sources are compared for different instruments to obtain a rough estimate of the improvements. Furthermore, tentative ionisation and fragmentation schemes are provided to describe the generation of radical and adduct ions. Characteristic ion yields are discussed for the different P.I. sources. An overview of the general appearances of the mass spectra obtained with the different P.I. sources is given to stress the major improvement provided by polyatomic P.I.s in yielding information at higher m/z values. 相似文献
155.
In this work, the flow of different kinds of liquids (differences in polarity, aromaticity, molecular size) through a layer
of Friedland clay and the interaction of these liquids with the clay particles are investigated by means of electrical impedance
measurements. The instationary flow can be described by data obtained from complex impedance plots. The gradient of the ohmic
part of the impedance gives information about the strength of the driving force and the speed of flow/diffusion of the liquid
through the clay. Different kinds of liquids lead to completely different impedance spectra. From time-dependent impedance
measurements on a layer of defined thickness, information can be gained about the contents of the liquid flowing or diffusing
through the clay. The impedance spectroscopy could be a powerful method for the development of an in situ monitoring system
in waste disposal sites having clay barriers.
Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000. 相似文献
156.
Oxidative potential of silver nanoparticles measured by electron paramagnetic resonance spectroscopy
Bryan?HellackEmail authorView authors OrcID profile Carmen?Nickel Roel?P.?F.?Schins 《Journal of nanoparticle research》2017,19(12):404
The oxidative potential (OP) of engineered nanomaterials (NM) is considered as promising metric for nanosafety research and risk assessment. Here, we present findings on the analysis of the oxidative potential of three different silver NM by means of a complementary electron paramagnetic resonance (EPR) spectroscopy-based approach, i.e., using the spin trap DMPO (5,5-dimethyl-1-pyrroline-N-oxide) and the spin probe CPH (l-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine hydrochloride). The results revealed that both methods are principally applicable for OP analysis of nanosilver. However, one of the Ag NM (i.e., NM300) did not cause notable OH? generation in the presence of hydrogen peroxide, while a clear OP was detected using the CPH method for all three Ag NPs tested. For the NM300, also a strong OH? scavenging potency could be demonstrated, which was due to its surfactant-containing dispersant. This finding may explain for the reported differences in effects of this widely applied reference nanosilver versus other types of Ag NM in toxicological studies. Our findings also demonstrate the relevance of using more than one assay to determine the OP of NM in general. 相似文献
157.
158.
The Green's function for wave propagation can be extracted by cross-correlating field fluctuations excited on a closed surface that surrounds the employed receivers. This study treats an acoustic multiple scattering medium with discrete scatterers and shows that for a given source the cross-correlation of waves propagating along most combinations of scattering paths gives unphysical arrivals. Because theory predicts that the true Green's function is retrieved, such unphysical arrivals must cancel after integration over all sources. This cancellation occurs because the scattering amplitude of each scatterer satisfies the generalized optical theorem. The cross-correlation of scattered waves with themselves does not lead to the correct retrieval of scattered waves, because the cross-terms between the direct and scattered waves is essential. 相似文献
159.
Anuji Abraham Roel Prins Jeroen A. van Bokhoven Ernst R.H. van Eck Arno P.M. Kentgens 《Solid state nuclear magnetic resonance》2009,35(2):61-66
A combination of 27Al magic-angle spinning (MAS)/multiple-quantum (MQ) MAS, and 27Al–{14N} TRAnsfer of Population in DOuble-Resonance (TRAPDOR) nuclear magnetic resonance (NMR) was used to study aluminium environments in zeolite ZSM-5. 27Al–{14N} TRAPDOR experiments, in combination with 14N NMR were employed to show that the two tetrahedral peaks observed in the 27Al MAS/3Q-MAS spectra of as-synthesized ZSM-5 are due to aluminium atoms occupying crystallographically inequivalent T-sites. A 13C–{27Al} TRAPDOR experiment was used to study the template, tetrapropyl ammonium bromide (TPABr), in the three-dimensional pore system of ZSM-5. The inequivalency of the methyl groups of TPA was observed in the 13C–{27Al} TRAPDOR spectra of as-synthesized ZSM-5 and the motion of the methyl end of the propyl chain appeared to be more restricted in the sinusoidal channel than in the straight channel. 相似文献
160.