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491.
Theoretical studies of the dynamics of the reactions O(3p)+H2/HD(ν=0, j=0)→OH+H have been performed with quasi-classical trajectory method (QCT) on an ab initio potential surface for the lowest triplet electronic state of H2O(aA"). The QCT-calculated integral cross sections are in good agreement with the earlier time-dependent quantum mechanics results. The state-resolved rotational distributions reveal that the product OH rotational distributions for O+HD have a preference for populating highly internally excited states compared with the O+H2 reaction. Distributions of differential cross sections show that directions of scattering are strongly dependent on the choice of quantum state. The polarization dependent generalized differential cross-sections and the distributions were calculated and a pronounced isotopic effect is revealed. The calculated results indicate that the product polarization is very sensitive to the mass factor. 相似文献
492.
M. Dehghany 《Journal of Molecular Spectroscopy》2008,247(2):123-127
The rotationally resolved spectra of 15N15N16O dimer for the polar and nonpolar isomers are studied in the region of the N-N stretching fundamental of the monomer (∼2150 cm−1) using a rapid-scan tunable diode laser spectrometer to probe a pulsed supersonic jet expansion. These spectra are very similar to the corresponding spectra of the normal species, (14N14N16O)2. Structural parameters and vibrational shifts obtained here are compared with those of the normal species and ab initio values. These results confirm that the nonpolar isomer has a centrosymmetric slipped-antiparallel structure while the polar isomer consists of two slipped and (approximately) parallel monomer units. 相似文献
493.
P. Saraswathy K. Sunanda 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(7):1252-1259
The B0u+-X0g+ and B1u-X1g transitions of 80Se2 and 78Se2 are reinvestigated. Several new bands are reported, especially for the B1u-X1g system, their vibrational numbering being confirmed by isotope shift studies. The Franck-Condon factors and r-centroid values are evaluated. By correlating the theoretically computed intensities with observed values, the internuclear distance dependence of the electronic transition moments of these two systems is determined for the first time. 相似文献
494.
495.
Stürup S 《Analytical and bioanalytical chemistry》2004,378(2):273-282
The use of stable isotope tracers in human studies is a rapidly growing research field that benefits from the many new developments in inorganic mass spectrometric instrumentation and from the better availability of mass spectrometric techniques to nutritional scientists during the last three decades. Traditionally, thermal ionization mass spectrometry (TIMS) has been the preferred technique for these studies, but the development of new inductively coupled plasma mass spectrometric (ICPMS) techniques with better isotope-ratio measurement and interference-removal capabilities (e.g. single and multi-detector ICPMS and reaction/collision cell ICPMS) has enabled broader use of ICPMS for determination of stable isotope tracers in nutritional research. This review discusses the current and future use of ICPMS in stable isotope tracer studies in humans. 相似文献
496.
Resonance Ionization Mass Spectrometry (RIMS) is a sensitive and selective method for ultratrace analysis of long-lived radioisotopes and isotope ratio measurements. It provides extremely high isobaric suppression and good overall efficiency. The experimental limits of detection are as low as 106 atoms per sample and isotopic selectivities of 5×1012 have been obtained. The widespread potential of RIMS, using different experimental arrangements, is demonstrated for the determination of the radiotoxic isotopes Pu-238 to Pu-244 and Sr-89/Sr-90 in various environmental samples as well as for Ca-41 in nuclear reactor components and biomedical samples. 相似文献
497.
V.?N.?PanteleevEmail author A.?E.?Barzakh D.?V.?Fedorov M.?Menna F.?V.?Moroz Yu.?M.?Volkov 《The European Physical Journal A - Hadrons and Nuclei》2005,26(1):147-150
A new version of integrated target-ion source unit (ionising target) has been developed for the on-line production of radioactive
single-charged ions. The target is able to withstand temperatures up to 2500 °C and acts also as an ion source of the surface and laser ionisation. Off-line and on-line experiments with the ionising target,
housing tantalum foils as a target material, have been carried out at the IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron)
facility. The off-line surface ionisation efficiency measured for stable atoms of Li, Rb and Cs was correspondingly 6% , 40%
and 55% at the target temperature of 2000 °C and 3-10% for atoms of rare-earth elements Sm, Eu, Tm and Yb at a temperature of 2200 °C. The off-line measured values of the ionisation efficiency for stable Gd and Eu atoms by the laser beam ionisation inside
the target were 1% and 7%, respectively. The radioactive beam intensities of neutron-deficient rare-earth nuclides from Eu
to Lu produced by the integrated target-ion source unit have been measured at a temperature of 2500 °C. The results of the integrated target-ion source unit use for on-line laser resonance ionisation spectroscopy study of neutron-deficient
Gd isotopes have been also presented. 相似文献
498.
A system is presented which combines multidimensional GC with isotope ratio mass spectrometry. The performance of the system is demonstrated with an application from the field of flavor analysis. Potentials and limitations of the technique are also discussed. 相似文献
499.
The oxygen isotope effect in high-TC superconductors has been investigated on the basis of a two-band model where superconducting phase transition is induced by interband (mainly Coulombic) interaction. The isotope shift of TC appears due to the dependence of averaged interband electronphonon coupling constant on oxygen mass. This coupling has a repulsive nature and gives a relatively small contribution to the total interaction inducing superconductivity. The calculated isotope effect exponent depending on the carrier concentration has been compared with the experimental one as a function of x for La2-xSrxCuO4. 相似文献
500.
Methyl-branched fatty acids (MBFAs) are the dominant form of fatty acid found in many bacteria. They are also found at low
levels in a range of foodstuffs, where their presence has been linked to bacterial sources. In this study we evaluated the
potential of compound-specific isotope analysis to obtain insights into the stable carbon isotope ratios (δ13C values in ‰) of individual MBFAs and to compare them to the stable carbon isotope ratios of straight-chain fatty acids in
food. Due to their low abundance in foodstuffs, the MBFAs were enriched prior to gas chromatography coupled to isotope ratio
mass spectrometric (GC–IRMS) analysis. After transesterification, urea complexation was used to suppress the 16:0 and 18:0
methyl esters that were dominant in the samples. Following that, silver-ion high performance liquid chromatography was used
to separate the saturated from the unsaturated fatty acids. The resulting solutions of saturated fatty acids obtained from
suet, goat’s milk, butter, and human milk were studied by GC–IRMS. The δ13C values of fatty acids with 12–17 carbons ranged from −25.4‰ to −37.6‰. In all samples, MBFAs were most depleted in carbon-13,
followed by the odd-chain fatty acids 15:0 and 17:0. 14:0 and 16:0 contained the highest proportions of carbon-13. The results
from this study illustrate that MBFAs have distinctive δ13C values and must originate from other sources and/or from very different substrates. These measurements support the initial
hypothesis that δ13C values can be used to attribute MBFAs to particular sources. 相似文献