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1.
An investigation has been carried out on the influence of the velocity of voltage change, of the radius of the capillary and of the size of the electrodes on the decrease of the peak current caused by back-diffusion in anodic amalgam voltammetry. 相似文献
2.
Lothar Metzger Günter G. Willems und Rolf Neeb 《Fresenius' Journal of Analytical Chemistry》1978,292(1):20-22
Zusammenfassung Die starke Temperaturabhängigkeit des polarographischen Zinn(II/0)-Signals in Lösungen des vierwertigen Zinns ermöglicht bei –32° C in methanolischer salzsaurer Grundlösung die Bestimmung des Bleis neben hohem Zinnüberschuß. Eine Anwendung des Verfahrens zur wechselstrompolarographischen Bestimmung des Bleis in Rohzinn wird beschrieben.
Investigations on the simultaneous electrochemical determination of lead and tinII. Polarographic determination of lead in the presence of tin at lower temperatures
Summary The strong temperature dependence of the polarographic tin(II/0) signal in solutions containing tin(IV) renders possible the determination of lead in the presence of a high excess of tin at working temperatures of –32° C in hydrochloric methanol as supporting electrolyte solution. An application of the procedure to the ac-polarographic determination of lead in crude tin is described.
Die vorliegende Arbeit wurde in dankenswerter Weise durch Mittel der Deutschen Forschungsgemeinschaft und des Verbandes der Chemischen Industrie ermöglicht. 相似文献
3.
The turnover of a small continuously stirred tank reactor with variable volume is measured by two independent methods simultaneously: conventional flow-through fluorimetry is used for integral measurement of the total turnover and flow-through impulse fluorimetry for measurement of the dispersed turnover of the particles themselves. The hydrolysis of resorufin-β-d-galactopyranoside by β-galactosidase immobilized on Sepharose 4B and on Eupergit C serves as fluorogenic reaction. All parameters (flow rates, stirrer speed, concentrations, gel particle density and growth functions) are controlled by a computer. The allometric turnover kinetics of the growing bioreactor are compared with those of growing organisms. 相似文献
4.
The universal voltammetric instrument, described in part I of this series, is used for comparative studies on the most important polarographic methods, direct current, derivative pulse, simple and phase-sensitive alternating current, double-tone, and harmonic-wave polarography. In general the peak-heights of these methods are influenced in the same measure by the composition of base electrolyte. In single cases characteristic differences are observed. 相似文献
5.
H. Willems A.G.C. Kobussen I.C. Vinke J.H.W. De Wit G.H.J. Broers 《Journal of Electroanalytical Chemistry》1985,194(2):287-303
Open-circuit overpotential decays on an aged cobalt electrode in the oxygen evolution range in 6 M KOH show different slopes for two overpotential regions. These slopes are lower than the Tafel slope in the same region: Tafel slopes of ~100 and ~40 mV/dec, at high and low overpotentials, respectively. compared to decay slopes of ~?60 and ~?20 to ?30 mV/dec. For a fresh cobalt electrode a decay slope of ~?40 mV/dec is found at high overpotentials. From impedance measurements during a decay it is concluded that the electrode capacitance cannot account for the decay curves obsered. By means of steady-state potentiostatic impedance measurements (with stabilization times > 24 h) it is found that the differential Tafel slope remains constant at ~40–50 mV/dec and differs considerably from the Tafel slope at high overpotentials, ~100 mV/dec. Galvanostatic pulse experiments give evidence of the presence of CoO2 in the oxide layer.Two models which may explain the observed experimental results are analysed. Both include a potential-dependent (extra) process which is fixed by the amount of CoO2 at the surface. In one model, CoO2 is responsible for partial surface blockage (parallel process); in the other model, CoO2 controls the conductivity of the top layer of the oxide layer on the electrode. 相似文献
6.
A capillary zone electrophoresis-negative electrospray ionization-quadrupole time of flight-mass spectrometric method was developed for the characterization of oligonucleotides after synthesis, using model compounds. The major difficulty is the adduction of metal cations to the polyanionic backbone of the oligonucleotide sample, resulting in complex spectra and decreased sensitivity. Several approaches were investigated to circumvent this problem. Separation was performed in an ammonium carbonate buffer. During separation, the interfering metal ions were exchanged for ammonium ions, which are less tightly bound to the oligonucleotide when ionized. The influence of the addition of piperidine and imidazole or trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) to the running buffer for further reduction of cation adduction was investigated. Addition of CDTA to the buffer system resulted in a deconvoluted spectrum with very little adducts. On-line sample stacking proved vital to preconcentrate the samples. The pH and the concentration of the ammonium carbonate buffer as well as the electrophoresis voltage were optimized to achieve the best signal response for the oligonucleotides and a maximum reduction of the cation adducts as well as a short analysis time. Finally, the sheath liquid composition was examined for further improvement of the signal. The developed method was used to analyze different oligonucleotides (5000-9200 Da) in light of its use as a final quality control method for oligonucleotides in terms of purity and sequence homogeneity of the synthesized products. In all cases, very little adducts were observed in the deconvoluted spectra, and the relative errors of the measured molecular masses ranged from 3 to 35 ppm. 相似文献
7.
8.
The turnover of bioreactors is commonly determined from the total consumption or production rates of substrates and products. However, conventional techniques provide no information about the dispersion of catalytic particles such as cells or enzyme carrier beads. Flow-through microfluorometry enables the dispersive measurement on-line of static parameters (e.g. distribution of size and enzyme load), and of dynamic parameters of particle suspensions (e.g. distribution of individual turnover rates in bioreactors). This allows the influence of heterogeneity of the carrier matrix or cells on the kinetics of the system to be estimated. 相似文献
9.
H. Willems M. Moers G.H.J. Broers J.H.W. De Wit 《Journal of Electroanalytical Chemistry》1985,194(2):305-315
It was found that the oxygen evolution reaction on La0.5Sr0.5CoO3 in strong alkaline solutions has a Tafel slope of ~ 60 mV/dec and a reaction order at constant overpotential with respect to the KOH activity of 0.6–0.8. From impedance measurements differential Tafel slopes were calculated and were found to be ~ 60 mV/dec at overpontentials > 250 mV. Effective capacitances having a broad maximum at an overpotential of about 200 mV in all alkaline solutions were calculated. The effective capacitance increased with increasing KOH concentration. Furthermore, the material decomposed at the surface when exposed to strong oxygen evolution. From the results a modified Krasil'shchikov reaction path is analysed. 相似文献
10.
A Dembowski semi-plane is a semi-plane obtained from a projective plane by Dembowski's method [1]. A semi Laguerre plane is an incidence structure J = (P, B1 ∪ B2, I) for which: (a) every element of P is incident with one element of B1, (b) an element of B1 and an element of B2 are incident with at most one common element of P, (c) each residual space of J (with respect to B1) is a Dembowski semi-plane, (d) B2 ≠ ? and each element of B2 is incident with at least 4 elements of P. We prove that all semi Laguerre planes are substructures of Laguerre planes or special Laguerre planes (in the sense of Thas, Willems [3], [4]). Therefore, these incidence structures are related to optimal codes ([5], [6]). 相似文献