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231.
Andrej Oriňák Ivan Talian Evtim V. Efremov Freek Ariese Renata Oriáaková 《Chromatographia》2008,67(3-4):315-319
Hyphenation of thin layer chromatography (TLC) with surface-based spectral methods requires a homogeneous surface for direct
and quantitative analysis on the chromatographic plate after separation. Since most chromatographic materials do not produce
strong background signals in Raman spectroscopy (RS) or surface-enhanced RS (SERS), we tested the suitability of two different
chromatographic substrates and one interface for coupling SERS with TLC. This was carried out by using a chromatographic thin
layer, specially produced for RS measurements, and a monolithic silica thin layer. A typical TLC plate with a modified aluminium
backplate foil on one side was used as an interface. Three biologically active diterpenes, namely gibberellic acid (GA), abietic
acid (AA) and kaurenoic acid (KA), were used as test analytes. Stock solutions were applied directly onto the surface, followed
by the addition of silver colloid and measurements were taken by SERS. The strongest signal (excitation at 514.5 nm) was obtained
for GA using a Raman treated thin layer where the enhancement factor value was determined to be 102. Several fundamental Raman bands for GA were found at 1622, 1593, 1570, 1542, 1366 and 1236 cm−1. When the monolithic silica layer was used, no useful SERS signals were observed. The SERS spectra on modified aluminium
backplate for AA and GA were quite similar and no SERS spectrum was obtained for KA. Future research will be concerned towards
the use of nanostructured surfaces for SERS analysis.
An erratum to this article can be found at 相似文献
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The interactions of water, carbon dioxide, and Xe with octadecanethiol (C(18)H(37)SH, ODT) self-assembled monolayers (SAMs) were studied under ultrahigh vacuum conditions employing temperature-programmed desorption and optical diffraction measurements. The ODT layer was grown on a 1 nm thick gold film deposited over a Ru(001) single-crystal substrate. The gases used in this report differ in their lateral interactions while adsorbed on ODT-SAM being either repulsive (Xe) or attractive (H(2)O, CO(2)). The activation energies for desorption of the first layer from ODT are E(a) = 3.6 +/- 0.9, 4.1 +/- 0.5, and 8.5 +/- 0.9 kcal/mol for Xe, CO(2), and H(2)O, respectively. Sticking probabilities of the three gases on the soft ODT surface are S(0) = 0.7 +/- 0.1, 0.8 +/- 0.1, and 0.95 +/- 0.05 for xenon, CO(2), and water, respectively, derived from the respective adsorption curves. Optical diffraction studies from multilayer coverage grating of Xe on ODT-SAM have demonstrated that sublimation is a thermodynamically more favorable process over diffusion and wetting. The significantly lower binding energy of the first layers of H(2)O and CO(2) adsorbed on the soft surface of ODT compared to that on clean metals and oxides, reflects generally weak (CO(2)) and hydrophobic (H(2)O) interactions that are important for understanding the behavior of these molecules on interfaces that are found in biological systems. 相似文献
234.
Quadrupole excitation of ions in linear quadrupole ion traps with added octopole fields 总被引:1,自引:1,他引:0
Zhao X Granot O Douglas DJ 《Journal of the American Society for Mass Spectrometry》2008,19(4):510-519
Modeling and experimental studies of quadrupole excitation of ions in linear quadrupole traps with added octopole fields are described. An approximate solution to the equations of motion of ions trapped in a quadrupole with added octopole and dodecapole fields, with quadrupole excitation and damping is given. The solutions give the steady-state or stationary amplitudes of oscillation with different excitation frequencies. Trajectory calculations of the oscillation amplitudes are also presented. The calculations show that there can be large changes in the amplitude of ion oscillation with small changes in excitation frequency, on both the low and high-frequency sides of a resonance. Results of experiments with quadrupole excitation of reserpine ions in linear quadrupole traps with 2.0%, 2.6%, and 4.0% added octopole fields are given. It is found that as the excitation frequency is changed, two resonances are generally observed, which are attributed to the motion in the x and y directions. The two resonances can have quite different intensities. Sudden jumps or sharp sided resonances are not observed, although in some cases asymmetric resonances are seen. The calculated frequency differences between the two resonances are in approximate agreement with the experiments. 相似文献
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