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71.
A simple and robust time-based on-line sequential injection system for trace mercury determination via cold vapour atomic absorption spectrometry (CVAAS), employing a new integrated gas-liquid separator (GLS), which in parallel operates as reactor, was developed. Sample and reductant are sequentially loaded into the GLS while an argon flow delivers the released mercury vapour through the atomic absorption cell. The proposed method is characterized by the ability of successfully managing variable sample volume up to 30 ml in order to achieve high sensitivity. For 20 ml sample volume, the sampling frequency is 25 h−1. The calibration curve is linear over the concentration range 0.05-5.0 μg l−1 of Hg(II), the detection limit is cL = 0.02 μg l−1, and the relative standard deviation is sr = 2.6% at 1.0 μg l−1 Hg(II) level. The performance of the proposed method was evaluated by analyzing certified reference material and applied to the analysis of natural waters and biological samples. 相似文献
72.
Summary Part I of this review paper discusses applications of superselective liquid phases containing transition metal salts or complexes in gas chromatography. 相似文献
73.
Summary Different types of diatomaceous supports, (pink and white) were deactivated in different ways: HCl gas treatment at high temperature, silanization and polymer coating with Carbowax 20 M. The adsorption effects of those supports when not coated with stationary phase were tested with samples of different polarity. The Carbowax modification of supports gives a surface of very low activity, irrespective of whether the pink or the cleaner white diatomite type was the initial material. The polymer coating behaves like a thin-layer of stationary phase, of considerably less polarity than the original Carbowax, and gives rise to a partition-like retention. The silanized supports are of moderate activity, the white type being less active than the pink one. This is explained by the higher content of aprotonic active sites in the latter, which cannot be blocked by silanization. 相似文献
74.
S. Mora J. Daillant 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):417-428
We calculate height-height correlation functions, near-surface density-density correlation functions and the corresponding
frequency integrated spectra for a heat conducting viscous fluid. We calculate scattering cross-sections for the static and
dynamic X-ray scattering experiments recently developed to investigate the nanometer-scale structure and fluctuations of liquid
interfaces. We show that the density-density correlations make an important contribution to the scattering, even using evanescent
waves, and that they are strongly affected by the surface. We also discuss the implications for X-ray photon correlation spectroscopy
and X-ray inelastic scattering.
Received 12 October 2001 Published online 6 June 2002 相似文献
75.
Summary A sensitive, specific and rapid GLC assay for khellin in serum and urine has been developed using flame ionization The method involves the addition of hyoscine as an internal standard, extraction with chloroform and the use of a 3% OV-17 on Gas Chromosorb column. The suitability of this procedure for serum sample analysis from rats after oral administration of the drug is reported. 相似文献
76.
J. Hegseth A. Oprisan Y. Garrabos C. Lecoutre-Chabot V. S. Nikolayev D. Beysens 《The European physical journal. E, Soft matter》2008,26(4):345-353
The heating of coexisting gas and liquid phases of pure fluid through its critical point makes the fluid extremely compressible,
expandable, slows the diffusive transport, and decreases the contact angle to zero (perfect wetting by the liquid phase).
We have performed experiments on near-critical fluids in a variable volume cell in the weightlessness of an orbiting space
vehicle, to suppress buoyancy-driven flows and gravitational constraints on the liquid-gas interface. The high compressibility,
high thermal expansion, and low thermal diffusivity lead to a pronounced adiabatic heating called the piston effect. We have
directly visualized the near-critical fluid’s boundary layer response to a volume quench when the external temperature is
held constant. We have found that when the system’s temperature T is increased at a constant rate past the critical temperature T
c
, the interior of the fluid gains a higher temperature than the hot wall (overheating). This extends previous results in temperature
quenching experiments in a similarly prepared system when the gas is clearly isolated from the wall. Large elliptical wetting
film distortions are also seen during these ramps. By ray tracing through the elliptically shaped wetting film, we find very
thick wetting film on the walls. This wetting film is at least one order of magnitude thicker than films that form in the
Earth’s gravity. The thick wetting film isolates the gas bubble from the wall allowing gas overheating to occur due to the
difference in the piston effect response between gas and liquid. Remarkably, this overheating continues and actually increases
when the fluid is ramped into the single-phase supercritical phase. 相似文献
77.
78.
79.
Summary A classical plate-type model developed to simulate the separation of binary mixtures by sequential semicontinuous chromatography is modified by the inclusion of a separate expression to account for the effects of solute concentration on the feed plate. The improved model is tested on three systems of different separation difficulty, for which experimental data are available. Comparison of experimental and simulated separations is achieved by consideration of the solute concentration profiles. In determining the success of the simulation, particular note is made of profile shape, feed point location and concentration levels. Best agreement between experimental and simulated profiles is shown to exist for high separation factor systems at low flowrates and low temperatures. Relatively poor agreement for difficult systems at higher flowrates is attributed to phase changes, column temperature effects and the influence of the anti-Langmuir shape of the absorption isotherm. 相似文献
80.
Changjin Wei 《Talanta》2007,73(3):540-545
A novel procedure was developed for the determination of arsenite (As(III)), arsenate (As(V)), monomethylarsonic (MMA) and dimethylarsinic acid (DMA) with ion chromatography-hydride generation-atomic fluorescence spectrometry (IC-HG-AFS) by employing a new gas-liquid separator (GLS). The effective separation of the four arsenic species was achieved in about 12 min. With a sample loading volume of 20 μl, the measurable minimum for As(III), DMA, MMA and As(V) were 0.02, 0.045, 0.043 and 0.166 ng, respectively, along with relative standard deviations of 1.1, 1.1, 1.7 and 2.2% at the 100 μg l−1 level (n = 6) for As(III), DMA, MMA and As(V), respectively. The present procedure was applied for the speciation of arsenic in underground water and in urine samples, and the sum of the four arsenic species by IC-HG-AFS was in good agreement with the total value by HG-AFS. 相似文献