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101.
Ponzevera E Quétel CR Berglund M Taylor PD Evans P Loss RD Fortunato G 《Journal of the American Society for Mass Spectrometry》2006,17(10):1412-1427
A long known way of anchoring isotope ratio values to the SI system is by means of gravimetrically prepared isotopic mixtures. Thermal ionization mass spectrometry (TIMS) is the traditionally associated measurement technique, but multi-collector double focusing inductively coupled plasma (MC-ICP)-MS now appears to be an attractive alternative. This absolute calibration strategy necessitates that mass discrimination effects remain invariant in time and across the range of isotope ratios measured. It is not the case with MC-ICPMS and the present work illustrates, in the case of Zn isotopic measurements carried out using locally produced synthetic Zn isotope mixtures (IRMM-007 series), how this calibration strategy must be adjusted. First, variation in mass discrimination effects across the measurement sequence is propagated as an uncertainty component. Second, linear proportionality during each individual measurement between normalized mass discrimination and the average mass of the isotope ratios is used to evaluate mass discrimination for the ratios involving low abundance isotopes. Third, linear proportionality between mass discrimination and the logarithm of the isotope ratio values for n(67Zn)/n(64Zn) and n(68Zn)/n(64Zn) in the mixtures is used iteratively to evaluate mass discrimination for the same ratios in the isotopically enriched materials. Fourth, ratios in natural-like materials (including IRMM-3702 and IRMM-651) are calibrated by external bracketing using the isotopic mixtures. The relative expanded uncertainty (k = 2) estimated for n(68Zn)/n(64Zn) and n(67Zn)/n(64Zn) ratio values in the synthetic isotopic mixtures and the natural-like zinc samples was in the range of 0.034 to 0.048%. The uncertainty on the weighing (0.01%, k = 1) was the largest contributor to these budgets. The agreement between these results and those obtained with a single detector TIMS and with another MC-ICPMS further validated this work. The absolute isotope ratio values found for IRMM-3702-material also proposed as "delta 0" for delta-scale isotopic measurements-are n(66Zn)/n(64Zn) = 0.56397 (30), n(67Zn)/n(64Zn) = 0.082166 (35), n(68Zn)/n(64Zn) = 0.37519 (16), and n(70Zn)/n(64Zn) = 0.012418 (23). The derived Zn atomic weight value Ar(Zn) = 65.37777 (22) differs significantly from the current IUPAC value by Chang et al. [1]. Remeasurement, with isotopic mixtures from the IRMM-007 series, of the Zn isotope ratios in the same Chang et al. [1] material have revealed large systematic differences (1.35 (27)% per atomic mass unit) that suggest unrecognized measurement biases in their results. 相似文献
102.
Denk E Hillegonds D Vogel J Synal A Geppert C Wendt K Fattinger K Hennessy C Berglund M Hurrell RF Walczyk T 《Analytical and bioanalytical chemistry》2006,386(6):1587-1602
Bone research is limited by the methods available for detecting changes in bone metabolism. While dual X-ray absorptiometry
is rather insensitive, biochemical markers are subject to significant intra-individual variation. In the study presented here,
we evaluated the isotopic labeling of bone using 41Ca, a long-lived radiotracer, as an alternative approach. After successful labeling of the skeleton, changes in the systematics
of urinary 41Ca excretion are expected to directly reflect changes in bone Ca metabolism. A minute amount of 41Ca (100 nCi) was administered orally to 22 postmenopausal women. Kinetics of tracer excretion were assessed by monitoring
changes in urinary 41Ca/40Ca isotope ratios up to 700 days post-dosing using accelerator mass spectrometry and resonance ionization mass spectrometry.
Isotopic labeling of the skeleton was evaluated by two different approaches: (i) urinary 41Ca data were fitted to an established function consisting of an exponential term and a power law term for each individual;
(ii) 41Ca data were analyzed by population pharmacokinetic (NONMEM) analysis to identify a compartmental model that describes urinary
41Ca tracer kinetics. A linear three-compartment model with a central compartment and two sequential peripheral compartments
was found to best fit the 41Ca data. Fits based on the use of the combined exponential/power law function describing urinary tracer excretion showed substantially
higher deviations between predicted and measured values than fits based on the compartmental modeling approach. By establishing
the urinary 41Ca excretion pattern using data points up to day 500 and extrapolating these curves up to day 700, it was found that the calculated
41Ca/40Ca isotope ratios in urine were significantly lower than the observed 41Ca/40Ca isotope ratios for both techniques. Compartmental analysis can overcome this limitation. By identifying relative changes
in transfer rates between compartments in response to an intervention, inaccuracies in the underlying model cancel out. Changes
in tracer distribution between compartments were modeled based on identified kinetic parameters. While changes in bone formation
and resorption can, in principle, be assessed by monitoring urinary 41Ca excretion over the first few weeks post-dosing, assessment of an intervention effect is more reliable ∼150 days post-dosing
when excreted tracer originates mainly from bone. 相似文献
103.
Geminal difluorination of dithiolane 9 affords bis benzyl ether 4b which is converted to beta-fluoroenals 3Z/3E. Reaction of these enals with the stannylmethyl Wadsworth-Emmons reagent 2 produces dienyl esters 14Z/14E which are converted to highly functionalized dienylic stannanes 1Z and 1E. 相似文献
104.
105.
A new technique for accurate Mg isotope ratio measurements has been developed with MgF2 as sample compound. With the help of a fluorinating agent negatively charged MgF3 molecular ions were formed in the ion source of a thermal ionisation mass spectrometer. An evaporation study has been performed
and the results clearly show that Mg is evaporated from the filament as MgF2 molecules. The MgF2 technique has been applied in the certification of a candidate 26Mg-enriched Spike Isotope Reference Material. The result from this new technique has been compared with results obtained for
the same material using ICP-MS.
Received: 14 December 1998 / Revised: 5 March 1999 / Accepted: 11 March 1999 相似文献
106.
K Oberg A Berglund U Edlund B Eliasson 《Journal of chemical information and computer sciences》2001,41(3):811-814
The nonlinear optical quantities, second and third harmonics (beta and gamma), were predicted using a quantitative structure-property relationship (QSPR) approach. Molecular orbital ab initio calculations were applied to generate easily accessible variables to be used in the partial least-squares analysis. Simplified equations are presented that could be used to predict the experimental beta and gamma responses, prior to further investigations of potentially interesting molecules for use in optical materials. 相似文献
107.
Emil Berglund 《Fresenius' Journal of Analytical Chemistry》1885,24(1):196-199
Ohne Zusammenfassung 相似文献
108.
Correlation curves are reported relating deuteron quadrupole coupling constants (e2qQ/h) to O-H and O-D stretching frequencies (vOH and vOD) for isotopically-dilute HDO molecules. Correlation curves are also given relating these quantities to hydrogen-bond distances.The best correlations are found to be between (e2qQ/h) and vOH andvOD whereas the correlations involving intermolecular geometries show considerably greater scatter.Complications caused by the effects of anharmonicity on the stretching vibrations and of vibrational averaging of the quadrupole coupling and geometrical parameters are discussed in light of the observed correlations. It is concluded that, although these effects are large, their magnitude is also strongly correlated with the stretching frequencies, quadrupole couplings and geometrical parameters. 相似文献
109.
One of the major problems involved in the direct analysis of solid samples by electrothermal atomic absorption spectrometry (ETAAS) lies in the calibration step because non-spectral interference effects are often pronounced. Three standardization techniques have been described and used in solid sampling-ETAAS: (i) standard additions method; (ii) calibration relative to a certified reference material; and (iii) calibration curve technique. However, an adequate statistical evaluation of the uncertainty in the analyte concentration in the solid sample is most frequently neglected, and reported errors may be seriously underestimated. This can be attributed directly to the complexity of the statistical expressions required to accurately account for errors in each of the calibration techniques mentioned above, and the general lack of relevant reference literature. The object of this work has been to develop a computer package which will perform the necessary statistical analyses of solid sampling-ETAAS data; the result is the program “SOLIDS” described here in the form of an electronic publication in Spectrochimica Acta Electronica, the electronic section of Spectrochimica Acta Part B. The program could also be useful in other analytical fields where similar calibration methods are used. The hard copy text, outlining the calibration models and their associated errors, is accompanied by a diskette containing the program, some data files, and a manual. Use of the program is exemplified in the text, with some of the data files discussed included on the diskette which, together with the manual, should enable the reader to become familiarized with the operation of the program, and the results generated. 相似文献
110.
Malin Bergenstr?hle-Wohlert Lars A. Berglund John W. Brady P. Tomas Larsson Per-Olof Westlund Jakob Wohlert 《Cellulose (London, England)》2012,19(1):1-12
A combined solid-state NMR and Molecular Dynamics simulation study of cellulose in urea aqueous solution and in pure water
was conducted. It was found that the local concentration of urea is significantly enhanced at the cellulose/solution interface.
There, urea molecules interact directly with the cellulose through both hydrogen bonds and favorable dispersion interactions,
which seem to be the driving force behind the aggregation. The CP/MAS 13C spectra was affected by the presence of urea at high concentrations, most notably the signal at 83.4 ppm, which has previously
been assigned to C4 atoms in cellulose chains located at surfaces parallel to the (110) crystallographic plane of the cellulose
Iβ crystal. Also dynamic properties of the cellulose surfaces, probed by spin-lattice relaxation time 13CT
1 measurements of C4 atoms, are affected by the addition of urea. Molecular Dynamics simulations reproduce the trends of the
T
1 measurements and lends new support to the assignment of signals from individual surfaces. That urea in solution is interacting
directly with cellulose may have implications on our understanding of the mechanisms behind cellulose dissolution in alkali/urea
aqueous solutions. 相似文献