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91.
Thiophene- and selenophene-based heteroacenes: combined quantum chemical DFT and spectroscopic Raman and UV-Vis-NIR study 总被引:1,自引:0,他引:1
Osuna RM Ponce Ortiz R Okamoto T Suzuki Y Yamaguchi S Hernandez V López Navarrete JT 《The journal of physical chemistry. B》2007,111(26):7488-7496
In this article, we report the characterization of a series of thiophene- and selenophene-based heteroacenes, materials with potential applications in organic electronics. In contrast to the usual alpha-oligothiophenes, these annelated oligomers have a larger band gap than most semiconductors currently used in the fabrication of organic field-effect transistors (OFETs) and therefore they are expected to be more stable in air. The synthesis of these fused-ring molecular materials was motivated by the notion that a more rigid and planar structure should reduce defects (such as torsion about single bonds between alpha-linked units or S-syn defects) and thus improve pi-conjugation for better charge-carrier mobility. The conjugational properties of these heteroacenes have been investigated by means of FT-Raman spectroscopy, revealing that pi-conjugation increases with the increasing number of annelated rings. DFT and TDDFT quantum chemical calculations have been performed, at the B3LYP/6-31G** level, to assess information regarding the minimum-energy molecular structure, topologies, and absolute energies of the frontier molecular orbitals around the gap, vibrational normal modes related to the main Raman features, and vertical one-electron excitations giving rise to the main optical absorptions. 相似文献
92.
Rocío Rincón Margarita Jiménez José Muñoz Manuel Sáez María Dolores Calzada 《Plasma Chemistry and Plasma Processing》2014,34(1):145-157
Molecular hydrogen production from ethanol decomposition by two microwave atmospheric pressure plasma sources (surfatron and Torche a Injection Axiale sur Guide d’Onde (TIAGO) torch) was studied by optical emission spectroscopy and mass spectrometry. In both cases ethanol was almost completely decomposed, thus giving place to molecular hydrogen. However, the atmosphere surrounding the discharge significantly influences the overall decomposition process. When the surfatron is used, C2H2 and CO are obtained as exhaust gases. Likewise, H2O and HCN are also detected at plasma exit when sustained with the TIAGO torch. 相似文献
93.
Ana Martín‐Sómer Dr. Al Mokhtar Lamsabhi Prof. Manuel Yáñez Dr. Juan Z. Dávalos Javier González Rocío Ramos Dr. Jean‐Claude Guillemin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(49):15699-15705
The gas‐phase acidity of a series of amine–borane complexes has been investigated through the use of electrospray mass spectrometry (ESI‐MS), with the application of the extended Cooks kinetic method, and high‐level G4 ab initio calculations. The most significant finding is that typical nitrogen bases, such as aniline, react with BH3 to give amine–borane complexes, which, in the gas phase, have acidities as high as those of either phosphoric, oxalic, or salicylic acid; their acidity is higher than many carboxylic acids, such as formic, acetic, and propanoic acid. Indeed the complexation of different amines with BH3 leads to a substantial increase (from 167 to 195 kJ mol?1) in the intrinsic acidity of the system; in terms of ionization constants, this increase implies an increase as large as fifteen orders of magnitude. Interestingly, this increase in acidity is almost twice as large as that observed for the corresponding phosphine–borane analogues. The agreement between the experimental and the G4‐based calculated values is excellent. The analysis of the electron‐density rearrangements of the amine and the borane moieties indicates that the dative bond is significantly stronger in the N‐deprotonated anion than in the corresponding neutral amine–borane complex, because the deprotonated amine is a much better electron donor than the neutral amine. On the top of that, the newly created lone pair on the nitrogen atom in the deprotonated species, conjugates with the BN bonding pair. The dispersion of the extra electron density into the BH3 group also contributes to the increased stability of the deprotonated species. 相似文献
94.
95.
Using molecular dynamics experiments, we analyze equilibrium and dynamical characteristics related to the solvation of excess protons in water-acetone mixtures. Our approach is based on the implementation of an extended valence-bond Hamiltonian, which incorporates translocation of the excess charge between neighboring water molecules. Different mixtures have been analyzed, starting from the pure water case down to solutions with a water molar fraction x(w) = 0.25. In all cases, we have verified that the structure of the first solvation shell of the H(3)O(+) moiety remains practically unchanged, compared to the one observed in pure water. This shell is composed by three water molecules acting as hydrogen bond acceptors, with no evidence of hydrogen bond donor-like connectivity. Moreover, the increment in the acetone concentration leads to a gradual stabilization of Eigen-like [H(3)O[middle dot](H(2)O)(3)](+) configurations, in detriment of Zundel-like [H[middle dot](H(2)O)(2)](+) ones. Rates of proton transfer and proton diffusion coefficients have been recorded at various water-acetone relative concentrations. In both cases, we have found a transition region, in the vicinity of x(w) ~ 0.8, where the concentration dependences of the two magnitudes change at a quantitative level. A crude estimate shows that, at this tagged concentration, the volumes "occupied" by the two solvents become comparable. The origins of this transition separating water-rich from acetone-rich realms is rationalized in terms of modifications operated in the nearby, second solvation shell, which in the latter solutions, normally includes at least, one acetone molecule. Our results would suggest that one possible mechanism controlling the proton transfer in acetone-rich solutions is the exchange of one of these tagged acetone molecules, by nearby water ones. This exchange would give rise to Zundel-like structures, exhibiting a symmetric, first solvation shell composed exclusively by water molecules, and would facilitate the transfer between neighboring water molecules along the resonant complex. 相似文献
96.
Sánchez-de-Armas R San-Miguel MA Oviedo J Sanz JF 《The Journal of chemical physics》2012,136(19):194702
In this work, new coumarin based dyes for dye sensitized solar cells (DSSC) have been designed by introducing several substituent groups in different positions of the NKX-2311 structure. Two types of substitutions have been considered: the introduction of three electron-donating groups (-OH, -NH(2), and -OCH(3)) and two different substituents with steric effect: -CH(2)-CH(2)-CH(2)- and -CH(2)-HC=CH-. The electronic absorption spectra (position and width of the first band and absorption threshold) and the position of the LUMO level related to the conduction band have been used as theoretical criteria to evaluate the efficiency of the new dyes. The introduction of a -NH(2) group produces a redshift of the absorption maximum position and the absorption threshold, which could improve the cell efficiency. In contrast, the introduction of -CH(2)-CH(2)-CH(2)- does not modify significantly the electronic structure of NKX-2311, but it might prevent aggregation. Finally, -CH(2)-HC=CH- produces important changes both in the electronic spectrum and in the electronic structure of the dye, and it would be expected as an improvement of cell efficiency for these dyes. 相似文献
97.
Comparison of arsenate, chromate and molybdate binding on schwertmannite: Surface adsorption vs anion-exchange 总被引:3,自引:0,他引:3
J Antelo S Fiol D Gondar R López F Arce 《Journal of colloid and interface science》2012,369(1):338-343
We have synthesized a series of nanocatalysts with different sizes (50-200 nm) for polymerization of 1,3-butadiene (Bd) by immobilizing salicylaldimine cobalt complexes on the mesoporous silica nanoparticles (MSNs). The prepared catalysts have been characterized by infrared (IR) spectra, thermal gravimetric analyses (TGAs), chemical composition analysis, nitrogen adsorption-desorption, scanning electron microscope (SEM), and transmission electron microscope (TEM). The nanocatalysts in combination with methylaluminoxane (MAO) show excellent catalytic efficiency in polymerization of 1,3-butadiene. The results reveal that these nanocatalysts also show higher activity than the homogeneous analog of cobalt complex and the same catalyst on bulky mesoporous silica supporting materials. The yield and the molecular weight of the poly-butadiene product depend on the particle size of the catalyst support. This catalysis process is also a facile way to directly synthesize the polymer/silica composite materials. 相似文献
98.
Sánchez-Fernández EM Rísquez-Cuadro R Ortiz Mellet C García Fernández JM Nieto PM Angulo J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(27):8527-8539
The synthesis of mimics of the α(1→6)- and α(1→4)-linked disaccharides isomaltose and maltose featuring a bicyclic sp(2)-iminosugar nonreducing moiety O-, S-, or N-linked to a glucopyranoside residue is reported. The strong generalized anomeric effect operating in sp(2)-iminosugars determines the α-stereochemical outcome of the glycosylation reactions, independent of the presence or not of participating protecting groups and of the nature of the heteroatom. It also imparts chemical stability to the resulting aminoacetal, aminothioacetal, or gem-diamine functionalities. All the three isomaltose mimics behave as potent and very selective inhibitors of isomaltase and maltase, two α-glucosidases that bind the parent disaccharides either as substrate or inhibitor. In contrast, large differences in the inhibitory properties were observed among the maltose mimics, with the O-linked derivative being a more potent inhibitor than the N-linked analogue; the S-linked pseudodisaccharide did not inhibit either of the two target enzymes. A comparative conformational analysis based on NMR and molecular modelling revealed remarkable differences in the flexibility about the glycosidic linkage as a function of the nature of the linking atom in this series. Thus, the N-pseudodisaccharide is more rigid than the O-linked derivative, which exhibits conformational properties very similar to those of the natural maltose. The analogous pseudothiomaltoside is much more flexible than the N- or O-linked derivatives, and can access a broader area of the conformational space, which probably implies a strong entropic penalty upon binding to the enzymes. Together, the present results illustrate the importance of taking conformational aspects into consideration in the design of functional oligosaccharide mimetics. 相似文献
99.
Montoya-Mayor R Fernández-Espinosa AJ Ternero-Rodríguez M 《Analytical and bioanalytical chemistry》2011,399(6):2031-2041
In this study a new method of principal component (PC) analysis, sequential PC analysis (SPCA), is proposed and assessed on
real samples. The aim was to identify the atmospheric emission sources of soluble compounds in rainwater samples, and the
sample collection was performed with an automatic sampler. Anions and cations were separated and quantified by ion chromatography,
whereas trace metals and metalloids were determined by inductively coupled plasma mass spectrometry. SPCA results showed eight
interfering PCs and ten significant PCs. The interfering cases originated from different atmospheric sources, such as resuspended
crustal particles, marine aerosols, urban traffic and a fertilizer factory. The significant PCs explained 84.6% of the total
variance; 28.1% accounted for the main contribution, which was resuspended industrial soil from a fertilizer factory containing
NO2-, NH4+, NO3-, SO42-, F-, Al, K+, Mn, Sb and Ca2+ as indicators of the fertilizer factory. Another important source (15.0%) was found for Na+, Mg2+, K+, Cl- and SO42-, which represents the marine influence from south and southwest directions. Emissions of Ba2+, Pb, Sr2+, Sb and Mo, which represent a traffic source deposited in soils, were identified as another abundant contribution (12.1%)
to the rainwater composition. Other important contributions to the rainwater samples that were identified through SPCA included
the following: different urban emissions (Cu, As, Cd, Zn, Mo and Co, 18.1%), emissions from vegetation (HCOO-, 7.7%) and emissions from industrial combustion processes (Ni, V 15.6%). The application of SPCA proved to be a useful tool
to identify the complete information on rainwater samples as indicators of urban air pollution in a city influenced mainly
by vehicle traffic emissions and resuspended polluted soils. 相似文献
100.