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41.
The thermal and kinetic aspects of gas phase decomposition reactions can be extremely complex due to a large number of parameters, a variety of possible intermediates, and an overlap in thermal decomposition traces. The experimental determination of the activation energies is particularly difficult when several possible reaction pathways coexist in the thermal decomposition. Ab initio calculations intended to provide an interpretation of the experiment are often of little help if they produce only the activation barriers and ignore the kinetics of the decomposition process. To overcome this ambiguity, a theoretical study of a complete picture of gas phase thermo-decomposition, including reaction energies, activation barriers, and reaction rates, is illustrated with the example of the β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) molecule by means of quantum-chemical calculations. We study three types of major decomposition reactions characteristic of nitramines: the HONO elimination, the NONO rearrangement, and the N-NO(2) homolysis. The reaction rates were determined using the conventional transition state theory for the HONO and NONO decompositions and the variational transition state theory for the N-NO(2) homolysis. Our calculations show that the HMX decomposition process is more complex than it was previously believed to be and is defined by a combination of reactions at any given temperature. At all temperatures, the direct N-NO(2) homolysis prevails with the activation barrier at 38.1 kcal/mol. The nitro-nitrite isomerization and the HONO elimination, with the activation barriers at 46.3 and 39.4 kcal/mol, respectively, are slow reactions at all temperatures. The obtained conclusions provide a consistent interpretation for the reported experimental data. 相似文献
42.
Maija Blomquist Johan Bobacka Ari Ivaska Kalle Levon 《Journal of Solid State Electrochemistry》2012,16(8):2783-2789
Covalent attachment of thiolated probes to conducting polymers such as polyaniline (PANI) is a promising approach towards the development of electrochemical sensors and biosensors. However, thiolation alters the conjugated polymer backbone and influences the electrochemical behavior of the conducting polymer. PANI studied in this work was electropolymerized on glassy carbon (GC) electrodes from a solution of 0.1 M aniline in 0.5 or 1.0 M H2SO4. The GC/PANI electrodes were then functionalized by covalent attachment of 2-mercaptoethanol to the PANI backbone. The progress of thiolation was studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Thiolation of PANI was found to cause an initial decrease in electroactivity at 0–0.25 V and an increase in electroactivity at 0.25–0.6 V. However, prolonged thiolation caused a loss of electroactivity of PANI, which could be seen from EIS measurements as a dramatic decrease in the bulk redox capacitance of PANI. 相似文献
43.
The synthesis and characterization of new tetramethoxy resorcinarene bis-crown ethers BC4 and BC5 are described. The complexation properties of the compounds toward alkali metal cations were studied by 1H NMR spectroscopy and X-ray crystallography, which revealed that BC5 can accommodate two cations simultaneously inside the crown pockets formed by the crown ether bridges and the resorcinarene skeleton. [reaction: see text]. 相似文献
44.
Maija H. Kuokkanen 《Central European Journal of Physics》2010,8(2):178-183
The dielectric properties of microparticles were characterized by quadrupole electrode geometry. Quadruple microelectrode
geometry with hyperbolic active interfaces was designed and fabricated. The dielectrophoretic mobility coefficients of the
polystyrene microparticles were attained from negative dielectrophoresis. With the mobility coefficients and hypothetical
inflection frequencies of the particles, the permittivity and electric conductivity of the particles in suspension were calculated.
This demonstration established that dielectrophoretic mobility attained with a hyperbolic electrode can be used to characterize
microparticle properties in suspension. 相似文献
45.
Małgorzata Pamuła Prof. Maija Nissinen Dr. Kaisa Helttunen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(33):7374-7383
The synthesis of tetramethoxyresorcinarene podands bearing p-toluene arms connected by -SO3- ( 1 ) and -CH2O- ( 2 ) linkers is presented herein. In the solid state, the resorcinarene podand 1 forms an intramolecular self-inclusion complex with the pendant p-toluene group of a podand arm, whereas the resorcinarene podand 2 does not show self-inclusion. The conformations of the flexible resorcinarene podands in solution were investigated by variable-temperature experiments using 1D and 2D NMR spectroscopic techniques as well as by computational methods, including a conformational search and subsequent DFT optimisation of representative structures. The 1H NMR spectra of 1 and 2 at room temperature show a single set of proton signals that are in agreement with C4v symmetry. At low temperatures, the molecules exist as a mixture of boat conformations featuring slow exchange on the NMR timescale. Energy barriers (ΔG≠298) of 55.5 and 52.0 kJ mol−1 were calculated for the boat-to-boat exchange of 1 and 2 , respectively. The results of the ROESY experiments performed at 193 K and computational modelling suggest that in solution the resorcinarene podand 1 adopts a similar conformation to that present in its crystal structure, whereas podand 2 populates a more versatile range of conformations in solution. 相似文献
46.
Kirsi S. Mikkonen Jasna S. Stevanic Catherine Joly Patrice Dole Kari Pirkkalainen Ritva Serimaa Lennart Salmén Maija Tenkanen 《Cellulose (London, England)》2011,18(3):713-726
Two future wood biorefinery products, spruce galactoglucomannans (GGM) and microfibrillated spruce wood cellulose (MFC), were
mixed to form composite films. The films were plasticized with different amounts of glycerol, and the preparation of films
was successful even with low glycerol contents. The film properties were studied using optical microscopy and scanning electron
microscopy, x-ray diffraction, water sorption, dielectric analysis, moisture scanning dynamic mechanical analysis, and tensile
testing. The addition of MFC clearly affected the properties of the films by decreasing the moisture uptake and increasing
the relative humidity of softening of the films and by increasing the glass transition temperature, tensile strength, and
Young’s modulus of the films. The effect of MFC addition on the tensile properties of films was emphasized at low glycerol
contents. The addition of MFC did not affect the degree of crystallinity of GGM in the films, which was between 20 and 25%.
MFC can be efficiently used as reinforcement of GGM films to form wood-based composite materials and to prepare GGM-based
films and coatings with low plasticizer content. 相似文献
47.
Antti J. Koivisto Maija M?kinen Elina M. Rossi Hanna K. Lindberg Mirella Miettinen Ghita C.- M. Falck Hannu Norppa Harri Alenius Anne Korpi Joakim Riikonen Esa Vanhala Minnamari Vippola Pertti Pasanen Vesa-Pekka Lehto Kai Savolainen Jorma Jokiniemi Kaarle H?meri 《Journal of nanoparticle research》2011,13(7):2949-2961
This study presents a novel exposure protocol for synthesized nanoparticles (NPs). NPs were synthesized in gas phase by thermal decomposition of metal alkoxide vapors in a laminar flow reactor. The exposure protocol was used to estimate the deposition fraction of titanium dioxide (TiO2) NPs to mice lung. The experiments were conducted at aerosol mass concentrations of 0.8, 7.2, 10.0, and 28.5 mg m?3. The means of aerosol geometric mobility diameter and aerodynamic diameter were 80 and 124 nm, and the geometric standard deviations were 1.8 and 1.7, respectively. The effective density of the particles was approximately from 1.5 to 1.7 g cm?3. Particle concentration varied from 4 × 105 cm?3 at mass concentrations of 0.8 mg m?3 to 12 × 106 cm?3 at 28.5 mg m?3. Particle phase structures were 74% of anatase and 26% of brookite with respective crystallite sized of 41 and 6 nm. The brookite crystallites were approximately 100 times the size of the anatase crystallites. The TiO2 particles were porous and highly agglomerated, with a mean primary particle size of 21 nm. The specific surface area of TiO2 powder was 61 m2 g?1. We defined mice respiratory minute volume (RMV) value during exposure to TiO2 aerosol. Both TiO2 particulate matter and gaseous by-products affected respiratory parameters. The RMV values were used to quantify the deposition fraction of TiO2 matter by using two different methods. According to individual samples, the deposition fraction was 8% on an average, and when defined from aerosol mass concentration series, it was 7%. These results show that the exposure protocol can be used to study toxicological effects of synthesized NPs. 相似文献
48.
Glucomannan composite films with cellulose nanowhiskers 总被引:1,自引:1,他引:0
Kirsi S. Mikkonen Aji P. Mathew Kari Pirkkalainen Ritva Serimaa Chunlin Xu Stefan Willför Kristiina Oksman Maija Tenkanen 《Cellulose (London, England)》2010,17(1):69-81
Spruce galactoglucomannans (GGM) and konjac glucomannan (KGM) were mixed with cellulose nanowhiskers (CNW) to form composite
films. Remarkable effects of CNW on the appearance of the films were detected when viewed with regular and polarizing optical
microscopes and with a scanning electron microscope. Addition of CNW to KGM-based films induced the formation of fiberlike
structures with lengths of several millimeters. In GGM-based films, rodlike structures with lengths of several tens of micrometers
were formed. The degree of crystallinity of mannan in the plasticized KGM-based films increased slightly when CNW were added,
from 25 to 30%. The tensile strength of the KGM-based films not containing glycerol increased with increasing CNW content
from 57 to 74 MPa, but that of glycerol-plasticized KGM and GGM films was not affected. Interestingly, the notable differences
in the film structure did not appear to be related to the thermal properties of the films. 相似文献
49.
Jorma Kumpulainen Maija Paakki Raija Tahvonen 《Fresenius' Journal of Analytical Chemistry》1988,332(6):685-688
Summary A potato reference material (RM) was prepared for the analytical quality control program to be employed by the Sub-network on Trace Elements in Food of the FAO European Co-operative Network on Trace Elements. Approximately 50 kg of commercially available potato granules prepared from baked, mashed and roller-dried potatoes, containing 2.8% ash and 3 mg/kg added butylhydroxyanisole was purchased. The granules were carefully homogenised in large glass cylinders followed by division into 50 g portions into numbered acid-washed bottles. The bottled material was tested for homogeneity by taking ten bottles throughout the bottling line and determining by validated atomic absorption spectrometric methods 1.0 g samples for seven mineral elements. Homogeneity for Mg, Ca, Zn, Fe, Mo, Ni and Cd was better than 5%. An international network on experienced, high-quality reference laboratories was established to conduct an interlaboratory comparison study on the determination of 14 mineral elements in the RM. A total of seven methods based on independent analytical principles were employed by the reference laboratories. After excluding outlying analytical results, the criteria defined by the IAEA were used for classification of the overall medians obtained through the interlaboratory comparison study. The relative standard deviations for the 95% confidence limits of the medians were as follows: P=4.2%, K=0.7%, Na=4.7%, Ca=5.5%, Mg=2.4%, Fe=9.3%, Mn=4.0%, Zn=3.6%, Cu=4.7%, Mo=23%, Ni=22%, Cr=19%, Pb=11% and Cd=4.6%. With the exception of Cr, all of the recommended concentration values obtained for the above indicated elements fell into category A, i.e. values recommended with a high degree of confidence according to the classification criteria of the IAEA. The present RM is the only certified potato RM currently available for mineral elements.
Charakterisierung eines Kartoffel-Referenzmaterials für Haupt-, Neben- und Spurenelemente相似文献
50.
Mansikkamäki H Nissinen M Rissanen K 《Chemical communications (Cambridge, England)》2002,(17):1902-1903
Crystallisation studies of ethyl resorcinarene with diquats 2b and 3a (1,4-dimethyl-1,4-diazoniabicyclo[2.2.2]octane dibromide and 1,4-diazoniabicyclo[2.2.2]octane dichloride, respectively) resulted in hydrogen bonded molecular capsules in which the cations are encapsulated in between the cavities of two resorcinarene molecules and anions are located in the middle of the lower rim ethyl chains. 相似文献