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71.
72.
J Arnarp J Bielawski B M Dahlin O Dahlman C R Enzell T Pettersson 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1989,43(1):44-50
A series of alkyl and alkenyl substituted guaiacols, which comprise a group of biologically and organoleptically active compounds, have been synthesized. Mass spectra and GC retention times for these have been recorded and compared with those obtained for constituents of a weakly acidic fraction of smoke condensate derived from American blend type cigarettes. On the basis of these results, 25 guaiacols have been identified, 18 of which have not been detected in tobacco smoke condensate previously. 相似文献
73.
Dan Haupt Curt Pettersson Douglas Westerlund 《Fresenius' Journal of Analytical Chemistry》1995,352(7-8):705-711
A three-factor central composite face design (CCF) has been used for the optimization of the chiral resolution of the enantiomers of alprenolol, oxprenolol, trimipramine and propranolol on CHIRAL-AGP. The variables (factors) investigated were pH and concentrations of the micellar agent Tween® 20 and heptanoic acid. The responses evaluated were resolution (RS), capacity factor (k) of the last eluted enantiomer and a chromatographic response function (CRF) defined as CRF = P5/log tret, where P is the peak-valley ratio according to Kaiser and tret is the retention time. The computed models, one for each substance and one for each response (in total 12 models), showed that the main factor for the regulation of RS as well as k and CRF in the experimental domain is the pH. The optimal pH for the substances could be found between pH 5.5 and 6.5. The optimum was evaluated by generating contour plots for the CRF models. The computed mathematical models were statistically evaluated and the predictive power of the models was tested by experimentation.Dedicated to Professor Dr. Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday 相似文献
74.
75.
Winters MU Pettersson K Mårtensson J Albinsson B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(2):562-573
The temperature- and solvent-dependence of photoinduced electron-transfer reactions in a porphyrin-based donor-bridge-acceptor (DBA) system is studied by fluorescence and transient absorption spectroscopy. Two competing processes occur: sequential and direct superexchange-mediated electron transfer. In a weakly polar solvent (2-methyltetrahydrofuran), only direct electron transfer from the excited donor to the appended acceptor is observed, and this process has weak temperature dependence. In polar solvents (butyronitrile and dimethylformamide), both processes are observed and the sequential electron transfer shows strong temperature dependence. In systems where both electron transfer processes are observed, the long-range superexchange-mediated process is more than two times faster than the sequential process, even though the donor-acceptor distance is significantly larger in the former case. 相似文献
76.
Wernet P Testemale D Hazemann JL Argoud R Glatzel P Pettersson LG Nilsson A Bergmann U 《The Journal of chemical physics》2005,123(15):154503
The local hydrogen-bonding environment in supercritical water (380 degrees C, 300 bars, density 0.54 gcm3) was studied by x-ray Raman scattering at the oxygen K edge. The spectra are compared to those of the gas phase, liquid surface, bulk liquid, and bulk ice, as well as to calculated spectra. The experimental model systems are used to assign spectral features and to quantify specific local hydrogen-bonding situations in supercritical water. The first coordination shell of the molecules is characterized in more detail with the aid of the calculations. Our analysis suggests that approximately 65% of the molecules in supercritical water are hydrogen bonded in configurations that are distinctly different from those in liquid water and ice. In contrast to liquid water the bonded molecules in supercritical water have four intact hydrogen bonds and in contrast to ice large variations of bond angles and distances are observed. The remaining approximately 35% of the molecules exhibit two free O-H bonds and are thus either not involved in hydrogen bonding at all or have one or two hydrogen bonds on the oxygen side. We determine an average O-O distance of 3.1+/-0.1 A in supercritical water for the H bonded molecules at the conditions studied here. This and the corresponding hydrogen bond lengths are shown to agree with neutron- and x-ray-diffraction data at similar conditions. Our results on the local hydrogen-bonding environment with mainly two disparate hydrogen-bonding configurations are consistent with an extended structural model of supercritical water as a heterogeneous system with small patches of bonded molecules in various tetrahedral configurations and surrounding nonbonded gas-phase-like molecules. 相似文献
77.
Qian Xiang Y. Y. Lee Pär O. Pettersson Robert W. Torget 《Applied biochemistry and biotechnology》2003,107(1-3):505-514
Hydrolysis of α-cellulose by H2SO4 is a heterogeneous reaction. As such the reaction is influenced by physical factors. The hydrolysis reaction is therefore
controlled not only by the reaction conditions (acid concentration and temperature) but also by the physical state of the
cellulose. As evidence of this, the reaction rates measured at the high-temperature region (above 200°C) exhibited a sudden
change in apparent activation energy at a certain temperature, deviating from Arrhenius law. Furthermore, α-cellulose, once
it was dissolved into concentrated H2SO4 and reprecipitated, showed a reaction rate two orders of magnitude higher than that of untreated cellulose, about the same
magnitude as cornstarch. The α-cellulose when treated with a varying level of H2SO4 underwent an abrupt change in physical structure (fibrous form to gelatinous form) at about 65% H2SO4. The sudden shift of physical structure and reaction pattern in response to acid concentration and temperature indicates
that the main factor causing the change in cellulose structure is disruption of hydrogen bonding. Finding effective means
of disrupting hydrogen bonding before or during the hydrolysis reaction may lead to a novel biomass saccharification process. 相似文献
78.
Josephs RD Krska R MacDonald S Wilson P Pettersson H 《Analytical and bioanalytical chemistry》2004,378(5):1182-1189
Several previous interlaboratory studies in the field of mycotoxin analysis have revealed considerable problems, apparent as high between-laboratory standard deviations, or rather non-comparable and non-traceable results. A major reason is lack of proper calibrants for external calibration. Public awareness of substances that mimic or interfere with the activity of natural hormones (endocrine disrupters) has led to increased interest in mycotoxins with estrogenic potential, e.g. zearalenone (ZON). During a large-scale standard measurement and testing (SMT) project of the European Commission (EC) dealing with the preparation and certification of reference materials for determination of the mycotoxin ZON in maize, a ZON calibrant in acetonitrile was prepared and intensively checked for purity, homogeneity, and stability. Preparation of the material, study of its homogeneity and stability, and characterisation of the calibrant on the basis of its preparation, with discussion of the results obtained, are described in this paper. The certified value of 9.95 µg mL–1 for ZON in acetonitrile and its corresponding expanded uncertainty of ±0.30 µg mL–1 were calculated in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM). 相似文献
79.
Bhikhabhai R Sjöberg A Hedkvist L Galin M Liljedahl P Frigård T Pettersson N Nilsson M Sigrell-Simon JA Markeland-Johansson C 《Journal of chromatography. A》2005,1080(1):83-92
A new chromatography system, AKTAxpress (GE Healthcare, Amersham Biosciences, Uppsala, Sweden) has been designed to meet the demand for high-throughput purification of proteins in structural genomics and drug discovery. The system offers a number of automated multistep purification protocols for affinity-tagged proteins. All protocols start with affinity chromatography followed by combinations of desalting, ion exchange chromatography and gel filtration. As an option, tag removal can be included in the purification protocols. Up to 16 proteins can be purified per day and the yield can be as high as 50 mg of each protein at > 90% purity. To highlight the versatility of the system, this paper presents several case studies; purifications of hexahistidine- and glutathione S-transferase-tagged proteins using different protocols, automated on-column tag cleavage and optimization studies for a hexahistidine-tagged kinase. 相似文献
80.