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61.
Roser Cervellera Xavier Ramis Josep Maria Salla Ana Mantecn Angels Serra 《Journal of polymer science. Part A, Polymer chemistry》2005,43(23):5799-5813
Ytterbium and lanthanum triflates were used as catalysts to cure diglycidylether of bisphenol A with different proportions of 1,3‐dioxan‐2‐one. The curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in the attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and to quantify the evolution of the groups involved in the curing process. We observed the formation of a five‐membered cyclic carbonate that remains unreacted at the chain ends, because of an equilibrium process between the spiroorthocarbonates that had formed as intermediate species. The kinetics were studied by DSC experiments and analyzed with isoconversional procedures. The system catalyzed by ytterbium triflate had a higher curing rate. Thermogravimetric analysis and dynamic mechanical thermal analysis experiments were used to evaluate the properties of the materials obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5799–5813, 2005 相似文献
62.
Xavier Fernández‐Francos Josep M. Salla Ana Cadenato Josep M. Morancho Ana Mantecón Angels Serra Xavier Ramis 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5446-5458
The photocuring process of the diglycidyl ether of bisphenol A (DGEBA) with the bislactone 1,6‐dioxaspiro[4,4]nonane‐2,7‐dione (s(γ‐BL)) was studied. Triarylsulfonium hexafluoroantimonate was employed as photoinitiator. FTIR/ATR was used to study the evolution of epoxy, lactone, and intermediate spiroorthoester groups to identify the different reactions that take place during the photocuring process. Photo‐DSC and DSC were used to study the thermal evolution of the photocuring process and to assess the Tg of the fully cured material. Thermogravimetric analysis (TGA) was used to determine the thermal stability of the fully cured material. The thermomechanical properties of the materials were investigated using dynamic mechanical‐thermal analysis. Shrinkage undergone during photocuring and gelation was studied with TMA. A strong influence of the photocuring temperature on the photocuring process of the DGEBA‐ s(γ‐BL) system was observed. Differences in the reactivity of the different species were observed with respect to the thermally cured system using ytterbium triflate as cationic thermal initiator. As a consequence, photocured materials exhibited a superior thermal stability and lower flexibility. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5446–5458, 2007 相似文献
63.
Cross‐Linked Proteins with Gold Nanoclusters: A Dual‐Purpose pH‐Responsive Material for Controllable Cell Imaging and Antibiotic Delivery 下载免费PDF全文
Pengchang Liu Hui Wang J. Kalervo Hiltunen Zhijun Chen Jiacong Shen 《Particle & Particle Systems Characterization》2015,32(7):749-755
This report describes the development of a facile method for the synthesis of cross‐linked proteins with gold nanoclusters (CP‐GNC). The synthesis reaction is completed within 15 min at 97 °C. The synthesized CP‐GNC are characterized by using UV–vis absorption, fluorescence, X‐ray photoelectron spectroscopy, and transmission electron microscopy. CP‐GNC are approximately 100 nm in diameter and 700 nm in length, whereas AuNCs within the nanorods are approximately 6 nm in size. These materials are highly fluorescent with quantum yield of 7.2% and can be absorbed onto and release from bacterial cells in a pH‐dependent and reversible manner. The recent data show that CP‐GNC can be a useful, new tool with potential applications in fluorescent cell imaging and antibiotic targeting. 相似文献
64.
The thermal degradation of thermosetting materials prepared by cationic copolymerization of mixtures of different proportions of diglycidylether of bisphenol A (DGEBA) with 6,6-dimethyl (4,8-dioxaspiro[2.5]octane-5,7-dione) (MCP) initiated by ytterbium or lanthanum triflate or using a conventional initiator, BF3·MEA was investigated. To study the thermal degradation, several techniques were used such as thermogravimetry (TGA), infrared spectroscopy (FTIR) and calorimetry (DSC) and the volatiles evolved during degradation were identified by mass spectrometry. The materials prepared possess the characteristics of thermally degradable thermosets, due to the presence of ester groups in the polymer chain, which are broken at the beginning of degradation. The degradability increased when lanthanide triflates were used in the curing, especially the ytterbium salt and when the proportion of MCP in the material increased. 相似文献
65.
Servando González Xavier Fernández‐Francos Josep Maria Salla Angels Serra Ana Mantecón Xavier Ramis 《Journal of polymer science. Part A, Polymer chemistry》2007,45(10):1968-1979
Diglycidyl ether of bisphenol A was cured with different proportions of γ‐caprolactone with ytterbium triflate as an initiator. The curing was studied by means of differential scanning calorimetry and Fourier transform infrared in the attenuated total reflection mode. The latter was used to monitor the competitive reactive processes and to quantify the conversions of the epoxide, lactone, and intermediate spiroorthoester groups. A partial depolymerization process from the cured material to free γ‐caprolactone was also identified. The formation of a stable carbocation and the coordinative capability of ytterbium triflate were the reasons for this unexpected process. The thermal and dynamic mechanical properties of the cured materials were determined with differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical thermal analysis. An increase in the proportion of γ‐caprolactone resulted in an increased curing rate, a decrease in the shrinkage after gelation, and a significant decrease in the glass transition temperature. The introduction of ester linkages into the three‐dimensional structure led to more thermally degradable thermosets. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1968–1979, 2007 相似文献
66.
Salla I Montanari T Salagre P Cesteros Y Busca G 《The journal of physical chemistry. B》2005,109(2):915-922
The low temperature adsorption of CO and the room temperature adsorption of acetonitrile, propionitrile, isobutyronitrile, pivalonitrile, benzonitrile, and o-toluonitrile on Na-mordenite (NaMOR) have been investigated by Fourier transform infrared (FT-IR) spectroscopy. The results have been compared with analogous experiments performed on H-mordenite, Na-X zeolite, and Na-silica-alumina. The Na distribution in NaMOR has also been investigated by X-ray diffraction and far-IR spectroscopy. The conclusions are that Na+ ion distribution is essentially random and that, together with the well-known interaction of the probes with Na+ ions in the side pockets and the main channels, a stronger additional interaction occurs in all cases. This new interaction is likely multiple, involving either more Na+ ions or Na and oxygen species. This interaction is more pronounced with the hindered nitriles, whose access at the main channels is likely forbidden. This suggests that this interaction, which is also observed on Na-X zeolites but not with Na-silica-alumina, occurs at the external mouths of the mordenite channels. 相似文献
67.
B. Ponsard J. Hiltunen P. Penttilla H. Vera Ruiz A. L. Beets S. Mirzadeh F. F. Knapp Jr. 《Journal of Radioanalytical and Nuclear Chemistry》2003,257(1):169-174
The rapidly increasing therapeutic applications of 188Re in nuclear medicine, oncology and interventional cardiology require routine production of large, multi-Curie levels of the 188W parent. The capability and effective coordination of back-up production sites is important to insure that high level 188W/188Re generators are continually available. We have coordinated 188W production at the High Flux Isotope Reactor (HFIR - Oak Ridge, US) with production at the BR2 Reactor (Mol, Belgium) characterized by peak thermal neutron fluxes of 2.51·015 (HFIR) and 1·1015 (BR2) neutrons/cm2·sec, respectively. The long 69-day physical half-life permits receipt of 188W from BR2 within 0.25 T
1/2's, even after the 12-day post irradiation cooling required for 187W decay (T
1/2 = 24 hours). Since 188W production by double neutron capture of enriched 186W is a function of the square of the thermal neutron flux, HFIR production (4-5 Ci 188W/g 186W/cycle) is higher than at the BR2 (1.0-1.1 Ci/g 186W/cycle). However, the specific activity (SA) of BR2-produced 188W is still about 0.8-0.9 Ci/g after processing at ORNL following shipment from Belgium. This SA is sufficiently high to permit fabrication of 1 Ci generators suitable for clinical use, since simple post elution concentration of the saline bolus (30-50 ml) obtained from the generator can provide samples with high specific volume (1 ml volume). The time periods from reactor push in Mol and completion of processing, fabrication and shipment of generators from Oak Ridge have been 19-21 days. Six campaigns have been successfully completed since 1998, with processed levels of 188W in Oak Ridge from 8-26 Curies/campaign. 188W has been provided to MAP Medical technologies Oy (Tikkakoski, Finland) for fabrication and distribution of generators for use at IAEA-supported research projects in developing countries. We have thus established and demonstrated an effective collaboration between the Studiecentrum voor Kernenergie-Centre d'Etude de l'Energie Nucléaire (SCK·CEN) and ORNL for back-up production of 188W. This collaboration continues to be especially helpful during periods when interruption of HFIR operation is necessary for maintenance and upgrades. 相似文献
68.
Pia Vuorela Eeva-Liisa Rahko Raimo Hiltunen Heikki Vuorela 《Journal of chromatography. A》1994,670(1-2):191-198
The retention behaviour of fifteen closely related coumarins in normal-phase overpressured layer chromatography (OPLC) was studied with the aim of comparing the retentions with those in normal-phase thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) when optimization of the mobile phase was carried out according to the PRISMA system. The mobile phase optimization was carried out on TLC plates in unsaturated chambers. The resulting mobile phases were transposed to off-line, non-equilibrated OPLC and further to HPLC. The retention in TLC was measured at 37 selectivity points and in OPLC and HPLC at 13 points. Capacity factors (k′) and separation factors () were calculated in order to study the retention behaviour in the different systems. Two- and three-dimensional evaluations of k′ against selectivity points showed similar retention behaviours for the coumarins in TLC, OPLC and HPLC. The values for TLC, OPLC and HPLC showed similar patterns in the three-dimensional evaluations. The retention behaviour at different solvent strengths was also examined. According to quadratic regression, k′ showed a dependence on the change in solvent strength. OPLC, which can be considered as a “planar column” technique, and TLC are closely related methods, whereas HPLC shows a different behaviour in the elution process with regard to solvent strength. 相似文献
69.
Ramis X. Salla J. M. Cadenato A. Morancho J. M. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):707-718
The curing of a thermosetting powder coating was studied by means of differential scanning calorimetry (DSC). The isothermal
cure was simulated by non-isothermal experiments. The results of the simulation were compared with experimental isothermal
data. From non-isothermal isoconversional procedures (free model), it was concluded that these permit simulation of the isothermal
cure but do not enable us to determine the complete kinetic triplet (A preexponential factor, E activation energy, f(a) and/or g(a) function of conversion). Non-isothermal procedures based on a single heating rate or on master curves present difficulties
for determination of all the kinetic parameters, due to the compensation effect between preexponential factor and activation
energy. The kinetic triplet can be determined by a combination of various non-isothermal methods or by using experimental
isothermal data in addition to non-isothermal data.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
70.
We report an analysis of the pH-dependent dissociation of a multimeric metalloprotein, xylose isomerase from Streptomyces rubiginosus (XI), by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Xylose isomerases are industrially significant enzymes that catalyze interconversion of aldose and ketose sugars. XI is biologically active as a approximately 173-kDa tetrameric complex, comprised of four identical approximately 43-kDa subunits and eight metal cations, unequivocally identified as the Mg(2+) cations in this work. ESI FT-ICR mass spectra of XI measured in the pH range of 3.0-6.9 indicated that the dissociation of the intact holo-tetramer is initiated by the loss of all eight Mg(2+) cations at pH 相似文献