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71.
Tarpan MA De Cooman H Hole EO Waroquier M Callens F 《The journal of physical chemistry. A》2012,116(13):3377-3387
The radicals obtained in trehalose dihydrate single crystals after 77 K X-irradiation have been investigated at the same temperature using X-band electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and ENDOR-induced EPR (EIE) techniques. Five proton hyperfine coupling tensors were unambiguously determined from the ENDOR measurements and assigned to three carbon-centered radical species (T1, T1*, and T2) based on the EIE spectra. EPR angular variations revealed the presence of four additional alkoxy radical species (T3 to T6) and allowed determination of their g tensors. Using periodic density functional theory (DFT) calculations, T1/T1*, T2, and T3 were identified as H-loss species centered at C4, C1', and O2', respectively. The T4 radical is proposed to have the unpaired electron at O4, but considerable discrepancies between experimental and calculated HFC values indicate it is not simply the (net) H-loss species. No suitable models were found for T5 and T6. These exhibit a markedly larger g anisotropy than T3 and T4, which were not reproduced by any of our DFT calculations. 相似文献
72.
We analyze the effects of the on-site Coulomb repulsion U on a band insulator using dynamical mean field theory (DMFT). We find the surprising result that the gap is suppressed to zero at a critical Uc1 and remains zero within a metallic phase. At a larger Uc2 there is a second transition from the metal to a Mott insulator, in which the gap increases with increasing U. These results are qualitatively different from Hartree-Fock theory which gives a monotonically decreasing but nonzero insulating gap for all finite U. 相似文献
73.
The impact of pH and washing procedure on calcium and magnesium distribution between pulp and filtrate in pulp processing
was investigated. Depending on media pH, the elements are present in the form of ions (Ca2+, Mg2+) and hydrated oxides (Ca(OH)2, Mg(OH)2). Distribution was monitored using binary systems of CaCl2 and MgCl2 dissolved in deionized water or Ca2+ and Mg2+ ions present in filtrates from an industrial pulp mill. Complying with the relevant standards in force, Ca and Mg contents
are expressed as CaO and MgO. The study was aimed at obtaining mathematic relations between pH and calcium and magnesium,
as two important non-process elements, sorption on pulp. Distribution of the elements between pulp and liquid (filtrate or
water) was determined with analytical procedures and simulation of pulp washing. It was found that both pH and filtrate composition
influenced sorption/desorption of the elements on/from pulp. Filtrate from a pulp mill, mainly content of organic substances
in liquid phase, affects their sorption on pulp and desorption to liquid. The higher the pH value the more efficient the sorption
of the elements, magnesium being sorbed on pulp in higher amounts than calcium. Prevalence of the sorbed magnesium is preserved
even at lower concentrations of both elements. Distribution of the elements between pulp and solution is expressed through
mathematic relations which, in turn, can be employed to purposefully modify or optimize the distribution between the solid
(pulp) and liquid (filtrate) media. Moreover, rationalized exploitation of mathematical relations enables balancing the elements
within a cellulose manufacture, regulating media recycling, and predicting an eventual impact on technological processes. 相似文献
74.
Andrii Ozerianskyi Petr Švec Hana Vaňkátová Marcela Vejsová Lenka Česlová Zdeňka Padělková Aleš Růžička Jaroslav Holeček 《应用有机金属化学》2011,25(10):725-734
A series of tri‐ and diorganotin(IV) compounds containing potentially chelating S,N‐ligand(s) (LSN, where LSN is 6‐phenylpyridazine‐3‐thiolate) were prepared and structurally characterized by multinuclear NMR spectroscopy. X‐ray diffraction techniques were used for determination of the structure of compounds containing one [(LSN)Ph2SnCl], two [(n‐Bu)2Sn(LSN)2] and the combination of two LSN and one LCN [(LCN)(n‐Bu)Sn(LSN)2] (where LCN is {2‐[(CH3)2NCH2]C6H4}‐) ligands. The coordination number of the tin atom varies from five to seven and is dependent on the number of chelating ligands present. The formation of the five‐membered azastanna heterocycle is favored over the formation of four‐membered azastannathia heterocycle in compounds containing both types of ligands. The di‐n‐butyl‐substituted compounds are the most efficient ones in inhibition of growth of yeasts, molds and G+ bacteria strains. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
75.
76.
The efficient modeling of execution price path of an asset to be traded is an important aspect of the optimal trading problem. In this paper an execution price path based on the second order autoregressive process is proposed. The proposed price path is a generalization of the existing first order autoregressive price path in literature. Using dynamic programming method the analytical closed form solution of unconstrained optimal trading problem under the second order autoregressive process is derived. However in order to incorporate non-negativity constraints in the problem formulation, the optimal static trading problems under second order autoregressive price process are formulated. For a risk neutral investor, the optimal static trading problem of minimizing expected execution cost subject to non-negativity constraints is formulated as a quadratic programming problem. Whereas, for a risk averse investor the variance of execution cost is considered as a measure for the timing risk, and the mean–variance problem is formulated. Moreover, the optimal static trading problem subject to stochastic dominance constraints with mean–variance static trading strategy as the reference strategy is studied. Using Static approximation method the algorithm to solve proposed optimal static trading problems is presented. With numerical illustrations conducted on simulated data and the real market data, the significance of second order autoregressive price path, and the optimal static trading problems is presented. 相似文献
77.
Arti Maheshwari Manisha Sharma Deepak Sharma 《Journal of inclusion phenomena and macrocyclic chemistry》2013,77(1-4):337-342
Sodium Picosulphate (SPL) is a synthetic drug, widely used for thorough evacuation of the bowel, usually for patients who are preparing to undergo a colonoscopy. Cyclodextrins (CDs) are chiral, truncated cone shaped, cyclic oligosaccharides that can encapsulate a variety of drug molecules into inclusion complexes, thereby increasing their stability and solubility. 1H NMR spectroscopic studies showed the inclusion complexation between β-CD and SPL, based on the upfield shift changes in the β-CD cavity protons (H-3′ and H-5′) and downfield shift changes in the guest (SPL) protons. The structure of inclusion complexes was determined by 2D ROESY spectral data. The 1:1 stoichiometry and overall association constant (Ka) were determined by using Scott’s plot method to be 450 M?1. 相似文献
78.
Dostál L Jambor R Růžička A Jirásko R Holeček J De Proft F 《Dalton transactions (Cambridge, England : 2003)》2011,40(35):8922-8934
A set of four pincer ligands, either the OCO type ligands L(1-3) [2,6-(ROCH(2))(2)C(6)H(3)](-), where R = Me (L(1)), mesityl (L(2)), t-Bu (L(3)) or novel NCO ligand [2-(Me(2)NCH(2))-6-(t-BuOCH(2))C(6)H(3)](-) was studied. The reaction of L(4)Li with PCl(3) resulted in isolation of [2-(OCH(2))-6-(Me(2)NCH(2))C(6)H(3)]PCl (1) as a result of intramolecular ether bond cleavage and elimination of t-BuCl. The conversion between the organolithium compounds L(1,2,4)Li and AsCl(3) led to the desired chlorides, i.e. (L(1))(2)AsCl (2), L(2)AsCl(2) (3), L(4)AsCl(2) (5), but an analogous reaction using the L(3)Li compound gave [2-(OCH(2))-6-(t-BuOCH(2))C(6)H(3)]AsCl (4) as a result of intramolecular cyclization. The organoantimony chloride L(3)SbCl(2) was shown to undergo very slow cyclization in CDCl(3) again via elimination of t-BuCl giving [2-(OCH(2))-6-(t-BuOCH(2))C(6)H(3)]SbCl (6) and it was demonstrated that this reaction may be accelerated by preparation of L(3)Sb(Cl)(OTf) (7) with more Lewis acidic central atom. On the contrary, both antimony derivatives of the NCO ligand L(4), not only the chloride L(4)SbCl(2) (8) but also the ionic pair containing highly Lewis acidic cation [L(4)SbCl](+)[CB(11)H(12)](-) (9), are stable without any indication for etheral bond cleavage. The situation is rather similar in the case of organobismuth derivatives of L(4), which allowed isolation of compounds L(4)BiCl(2) (10), L(4)Bi(Cl)(OTf) (11) and [L(4)BiCl](+)[CB(11)H(12)](-) (12). All studied compounds were characterized by the help of (1)H and (13)C NMR spectroscopy, ESI mass spectrometry, elemental analysis and (except 1) by single-crystal X-ray diffraction. 相似文献
79.
Ravi Mosurkal Lynne A. Samuelson Arti Tewari Arthur C. Watterson Virinder S. Parmar Jayant Kumar 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(12):1228-1232
Aromatic dianhydrides have been identified as potential candidates for crosslinking with biocatalytically synthesized siloxane copolymers containing a functional amino group on the isophthalate moieties. We present the synthesis, characterization, thermal and flame retardant properties of this novel class of crosslinked organo-siloxane copolymers. We also discuss the effect of the concentration of one of the crosslinkers, 1,2,4,5-benzenetetracarboxylic dianhydride (DAH), on thermal decomposition and flame retardant properties using thermogravimetric analysis (TGA) and pyrolysis combustion flow calorimetry (PCFC) studies. The char yields were improved in all the polymers crosslinked with the various aromatic dianhydrides. The heat release capacity of a polymer crosslinked with 20% DAH, compared to the pure polymer, was tremendously reduced from 190 J/gK to 100 J/gK. The decomposition kinetics from TGA showed that the crosslinked polymer is thermally more stable than the non-crosslinked polymer. 相似文献
80.
Recent fluorescence spectroscopy measurements of single-enzyme kinetics have shown that enzymatic turnovers form a renewal stochastic process in which the inverse of the mean waiting time between turnovers follows the Michaelis-Menten equation. We study enzyme kinetics at physiologically relevant mesoscopic concentrations using a master equation. From the exact solution of the master equation we find that the waiting times are neither independent nor identically distributed, implying that enzymatic turnovers form a nonrenewal stochastic process. The inverse of the mean waiting time shows strong departure from the Michaelis-Menten equation. The waiting times between consecutive turnovers are anticorrelated, where short intervals are more likely to be followed by long intervals and vice versa. Correlations persist beyond consecutive turnovers indicating that multiscale fluctuations govern enzyme kinetics. 相似文献