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51.
Arecoline (methyl-1,2,5,6-tetrahydro-1-methyl nicotinate) is an alkaloid found in the areca catechu nut which is a major component of the 'betel quid' chewed by a large proporation of the population in India, South Asia and the South Pacific islands. It is commonly associated with the development of oral leukoplakia, oral submucous fibrosis and oral cancer. We have developed a new ion-pairing reversed-phase high-performance liquid chromatographic (HPLC) method for the determination of arecoline in saliva, using arecaidine (1,2,5,6-tetrahydro-1-methylnicotinic acid) as an internal standard. The optimal wavelength was established using UV absorbance scans. It was showed that 215 nm is the optimal wavelength to maximise the signal in detecting arecoline in the mobile phase. Arecoline was extracted from saliva with hexane-isoamyl alcohol (1%) and reconstituted with mobile phase for HPLC analysis. The developed method is an easy and reliable method of determining arecoline concentrations in saliva. Sensitivity, specificity, precision, accuracy and reproducibility of the method were demonstrated to be satisfactory for measuring the arecoline level. 相似文献
52.
Haynes A Maitlis PM Morris GE Sunley GJ Adams H Badger PW Bowers CM Cook DB Elliott PI Ghaffar T Green H Griffin TR Payne M Pearson JM Taylor MJ Vickers PW Watt RJ 《Journal of the American Chemical Society》2004,126(9):2847-2861
The iridium/iodide-catalyzed carbonylation of methanol to acetic acid is promoted by carbonyl complexes of W, Re, Ru, and Os and simple iodides of Zn, Cd, Hg, Ga, and In. Iodide salts (LiI and Bu(4)NI) are catalyst poisons. In situ IR spectroscopy shows that the catalyst resting state (at H(2)O levels > or = 5% w/w) is fac,cis-[Ir(CO)(2)I(3)Me](-), 2. The stoichiometric carbonylation of 2 into [Ir(CO)(2)I(3)(COMe)](-), 6, is accelerated by substoichiometric amounts of neutral promoter species (e.g., [Ru(CO)(3)I(2)](2), [Ru(CO)(2)I(2)](n), InI(3), GaI(3), and ZnI(2)). The rate increase is approximately proportional to promoter concentration for promoter:Ir ratios of 0-0.2. By contrast anionic Ru complexes (e.g., [Ru(CO)(3)I(3)](-), [Ru(CO)(2)I(4)](2)(-)) do not promote carbonylation of 2 and Bu(4)NI is an inhibitor. Mechanistic studies indicate that the promoters accelerate carbonylation of 2 by abstracting an iodide ligand from the Ir center, allowing coordination of CO to give [Ir(CO)(3)I(2)Me], 4, identified by high-pressure IR and NMR spectroscopy. Migratory CO insertion is ca. 700 times faster for 4 than for 2 (85 degrees C, PhCl), representing a lowering of Delta G(++) by 20 kJ mol(-1). Ab initio calculations support a more facile methyl migration in 4, the principal factor being decreased pi-back-donation to the carbonyl ligands compared to 2. The fac,cis isomer of [Ir(CO)(2)I(3)(COMe)](-), 6a (as its Ph(4)As(+) salt), was characterized by X-ray crystallography. A catalytic mechanism is proposed in which the promoter [M(CO)(m)I(n)] (M = Ru, In; m = 3, 0; n = 2, 3) binds I(-) to form [M(CO)(m)I(n+1)](-)H(3)O(+) and catalyzes the reaction HI(aq) + MeOAc --> MeI + HOAc. This moderates the concentration of HI(aq) and so facilitates catalytic turnover via neutral 4. 相似文献
53.
Reported is the synthesis of various derivatives of 2-imino-5-chloro-1,3-oxathiolanes, 2-imino-1,3-oxathioles and 1,3-thiazolin-2-ones from N-aryl- and N-alkyl-S-chloroisothiocarbamoyl chlorides and ketones. 相似文献
54.
A procedure is explained to determined the amount of several pairs of diametrical loads applied to the outside boundary of
a ring when stresses at selected points of the inside or outside boundaries are known. Coefficients of influence are used,
following an approach similar to the one presented in a previous paper. Examples of application are given and the possible
increase in precision is shown when the number of points of measurements is larger than the number of loads to be determined. 相似文献
55.
Zhang Q. Vickers M.E. Patel A. Whatmore R.W. 《Journal of Sol-Gel Science and Technology》1998,11(2):141-152
The formation and growth of polymeric particles during the hydrolysis and condensation of PbZr0.3Ti0.7 O3 (PZT 30/70) sol-gel precursor solutions have been investigated by using photon correlation spectroscopy (PCS), small angle X-ray scattering (SAXS) and by measuring their rheological properties. The measurements showed that the growth of the particles in the transition of PZT sol to gel followed a simple polymerisation process. Solution A (containing by-products) and Solution B (by-products removed) displayed a similar plot of logarithmic viscosity against logarithmic time, indicating that the particles in both solutions have similar structures after hydrolysis. The changes in viscosity and particle size with time were described by single logarithmic growth models. However, the increasing rate of logarithmic particle size in Solution B is higher than that in Solution A. A model for the form of the aggregates is discussed which is applicable to PZT organometal-particle aggregation process in systems with acetic acid as a modifier. 相似文献
56.
57.
X Fang KW Ledingham P Graham DJ Smith T McCanny RP Singhal AJ Langley PF Taday 《Rapid communications in mass spectrometry : RCM》1999,13(14):1390-1397
The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
58.
D. Vickers L.A. Archer T. Floyd-Smith 《Colloids and surfaces. A, Physicochemical and engineering aspects》2009,348(1-3):39-44
Narrow size distribution cubic Co3O4 nanoparticles were synthesized and rheological properties of suspensions of the cubes in oligomeric polyethylene glycol (PEG) were explored over a range of particle volume fractions and rotational shear flow conditions. At low and high particle volume fractions, the relative viscosity of the suspensions is described by a Krieger–Dougherty formula with an intrinsic viscosity consistent with expectations for suspensions of ideal cuboids. At intermediate to high particle loadings, the suspensions manifest complex rheological behavior, including shear thinning and shear-thickening features. These observations are discussed in terms of the charge carried by the cubes and the shear rate/volume fraction dependency of the transition from shear thinning to shear thickening. 相似文献
59.
60.