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61.
M. Houmad Z. Zarhri Y. Ziat Y. Benhouria A. Benyoussef A. El Kenz 《Chinese Journal of Physics (Taipei)》2018,56(1):404-410
Using first principles calculations based on KKR Korringa Kohn Rostoker method related to the Coherent Potential Approximation (CPA), we have investigated the magnetic properties of silicon-carbide doped by transition metals (TM). In addition, for some concentrations of the TM elements (Mn, Cr), we have found that the ferromagnetic states appear in the 3C–Si1?x?yMnxCryC system. Moreover, the total magnetic moment of 3C–Si1?xTMxC increases with increasing TM (TM?=?Mn or Cr) concentrations. As well, our results indicate that the Curie temperature of 3C–Si1?xTMxC and 3C–Si1?x?yMnxCryC increases with increasing transition metal concentration. Finally, we have found that the double exchange interaction between Cr and Mn is the mechanism responsible for the ferromagnetism in 3C–Si1?xTMxC and 3C–Si1?x?yMnxCryC systems. 相似文献
62.
Hasibeh Parsazadeh Younes Valadbeigi Morteza Rouhani 《International journal of quantum chemistry》2020,120(8):e26144
New classes of organic Brønsted acids were designed with pyrrole and cyclopentadiene scaffolds, and their acidity was assessed theoretically by the B3LYP/6-311++G(d,p) method. The hydrogen atom of NH group in pyrrole was substituted by an –BX2 (X = H, F, Cl, CN, CF3). The boron atom stabilizes the conjugated bases by interaction with the center of negative charge after deprotonation. The acidity of the compounds was promoted by substitution of the hydrogen atoms of the rings with CN moiety as a strong electron withdrawing group. Also, after deprotonation, delocalization of the negative charge in both pyrrole and cyclopentadiene rings causes stability of the conjugated bases and consequently enhances the acidity. The charge delocalization in the neutral acids and their conjugated bases was compared using nucleus-independent chemical shift index. Enthalpies and Gibbs free energies of deprotonation in gas phase, ∆Hacid and ∆Gacid, were used as a measure of acidity. Both compounds with isolated and fused pyrrole and cyclopentadiene rings were investigated and it was found that the formers are more acidic. Using these strategies, several acids and superacids with wide range of acidity with ∆Gacid values of 244 to 328 kcal mol−1 were obtained. 相似文献
63.
Younes Valadbeigi 《Molecular physics》2013,111(6):577-583
Reactions between CH3NHNH2 and OOH radical were studied using computational methods. The activation energies (Ea) and Gibbs free energies of activation (ΔG#) were calculated at the MP2 and B3LYP levels of theory. The calculated activation energies of the hydrogen abstraction reactions were less than 100 kJ/mol and those for the substitution reactions were about 150–250 kJ/mol. The calculated activation energies for the intra-molecular hydrogen transfer reactions in CH3NHNH, CH2NNH2 and CH3NN molecules were 210–250 kJ/mol. Catalytic effect of the water molecule on the intra-molecular hydrogen transfer reactions was studied. It was found that the water molecule decreases the activation energies by about 70–100 kJ/mol. Rate constants of the reactions were calculated using transition state theory in the temperature range of 298–2000 K. Consecutive hydrogen abstraction reactions from CH3NHNH2 led to the formation of CH2NN, which was a very stable molecule. 相似文献
64.
Laurent Younes 《Foundations of Computational Mathematics》2012,12(3):295-325
We design optimal control strategies in spaces of diffeomorphisms and shape spaces in which the Eulerian velocities of the
evolving deformations are constrained to belong to a suitably chosen finite-dimensional space, which is also following the
motion. This results in a setting that provides a great flexibility in the definition of Riemannian metrics, extending previous
approaches in which shape spaces are built as homogeneous spaces under the action of the diffeomorphism group equipped with
a right-invariant metric. We provide specific instances of this general setting, and describe in detail the resulting numerical
algorithms, with experimental illustrations in the case of plane curves. 相似文献
65.
Abdolali Alemi Younes Hanifehpour Sang Woo Joo Aliakbar KhandarAli Morsali Bong-Ki Min 《Physica B: Condensed Matter》2012,407(1):38-43
New LnxSb2−xSe3 (Ln: Yb3+, Er3) based nanomaterials were synthesized by a co-reduction method. Powder XRD patterns indicate that the LnxSb2−xSe3crystals (Ln=Yb3+, Er3+, x=0.00-0.12) are isostructural with Sb2Se3. The cell parameters b and c decrease for Ln=Er3+ and Yb3+ upon increasing the dopant content (x), while a increases. SEM images show that doping of the lanthanide ions in the lattice of Sb2Se3 generally results in nanoflowers. UV-vis absorption and emission spectroscopy reveals mainly electronic transitions of the Ln3+ ions in case of Yb3+ doped nanomaterials. Emission spectra of doped materials, in addition to the characteristic red emission peaks of Sb2Se3, show additional emission bands centered at 955 nm, originating from the 2F7/2→2F5/2 transition (f-f transitions) of the Yb3+ ions. DSC curves indicate that Sb2Se3 has the highest thermal stability. The temperature dependence of the electrical resistivity of doped-Sb2Se3 with Yb3+ and Er3+ was studied. 相似文献
66.
Two fluorescent heteroditopic ligands (2a and 2b) for zinc ion were synthesized and studied. The efficiencies of two photophysical processes, intramolecular charge transfer (ICT) and photoinduced electron transfer (PET), determine the magnitudes of emission bathochromic shift and enhancement, respectively, when a heteroditopic ligand forms mono- or dizinc complexes. The electron-rich 2b is characterized by a high degree of ICT in the excited state with little propensity for PET, which is manifested in a large bathochromic shift of emission upon Zn(2+) coordination without enhancement in fluorescence quantum yield. The electron-poor 2a displays the opposite photophysical consequence where Zn(2+) binding results in greatly enhanced emission without significant spectral shift. The electronic structural effects on the relative efficiencies of ICT and PET in 2a and 2b as well as the impact of Zn(2+)-coordination are probed using experimental and computational approaches. This study reveals that the delicate balance between various photophysical pathways (e.g. ICT and PET) engineered in a heteroditopic ligand is sensitively dependent on the electronic structure of the ligand, i.e. whether the fluorophore is electron-rich or poor, whether it possesses a donor-acceptor type of structure, and where the metal binding occurs. 相似文献
67.
Samir Chakhari Mohamed Kadri Younes Alain Rives Abdelhamid Ghorbel 《Journal of Sol-Gel Science and Technology》2014,69(2):378-385
Zirconia doped by heteropolytungstic acid HPW have been synthesized by sol–gel method using two drying techniques of the solvent evacuation. Samples were analyzed with adsorption–desorption of N2 at 77 K, and the aerogel catalyst was found to exhibit a higher surface area and a higher average pore diameter compared to xerogel. XRD results show that aerogel develops ZrO2 tetragonal phase, whereas xerogel is amorphous. The thermal analysis studies show that the aerogel’s thermal stability is better than the xerogel one. The catalytic behavior of the aerogel and xerogel toward the nature of the isomerization products probably depends on the acidity and the presence of carbide species. This has been explained by XPS and isopropanol dehydration reaction. In fact, the deconvolution aerogel’s Cls bands reveals the presence of four carbon species assigned to C–C, C=O, C–O and carbide species. 相似文献
68.
Absorption and Emission Sensitivity of 2‐(2′‐Hydroxyphenyl)benzoxazole to Solvents and Impurities 下载免费PDF全文
Zhao Yuan Qing Tang Kesavapillai Sreenath J. Tyler Simmons Ali H. Younes De‐en Jiang Lei Zhu 《Photochemistry and photobiology》2015,91(3):586-598
2‐(2′‐Hydroxyphenyl)benzoxazole (HBO) is known for undergoing intramolecular proton transfer in the excited state to result in the emission of its tautomer. A minor long‐wavelength absorption band in the range 370–420 nm has been reported in highly polar solvents such as dimethylsulfoxide (DMSO). However, the nature of this species has not been entirely clarified. In this work, we provide evidence that this long‐wavelength absorption band might have been caused by base or metal salt impurities that are introduced into the spectral sample during solvent transport using glass Pasteur pipettes. The contamination by base or metal salt could be avoided by using borosilicate glass syringes or nonglass pipettes in sample handling. Quantum chemical calculations conclude that solvent‐mediated deprotonation is too energetically costly to occur without the aid of a base of an adequate strength. In the presence of such a base, the deprotonation of HBO and its effect on emission are investigated in dichloromethane and DMSO, the latter of which facilitates deprotonation much more readily than the former. Finally, the absorption and emission spectra of HBO in 13 solvents are reported, from which it is concluded that ESIPT is hindered in polar solvents that are also strong hydrogen bond acceptors. 相似文献
69.
Application of ion mobility spectrometry in study of surfactants adsorbed on different dish surfaces
Younes Valadbeigi Mahmoud Tabrizchi 《International Journal for Ion Mobility Spectrometry》2014,17(1):35-41
Sodium lauryl sulfate (SLS) and sodium lauryl ether sulfate (SLES) are commonly used in many dishwashing liquids. These chemicals are adsorbed on the dish surface during the washing process and then transferred to food or drink in the cooking process. In this work, the adsorption of SLS and SLES on different dish surfaces in aqueous solution was studied. Stainless steel, copper, aluminum, Pyrex, Teflon and arcopal china ware were used in this study. The adsorbed chemical remained on the surface after rinsing was measured by thermal desorption using an ion mobility spectrometer as the detector. Although arcopal china ware showed the maximum amount of adsorption, and Pyrex and stainless steel dishes showed the minimum amount of residual chemical, the results showed that the amount of adsorbed chemicals on dish surfaces is less than 428 ng.cm?2, which is well below the health risk dosage. The released SLS and SLES from dish surfaces into cold or hot water were also measured and compared for different dishes. 相似文献
70.
Ghorbel-Bellaaj O Jellouli K Younes I Manni L Ouled Salem M Nasri M 《Applied biochemistry and biotechnology》2011,164(4):410-425
A solvent-stable protease-producing bacterium was isolated and identified as Pseudomonas aeruginosa A2. The strain was found to produce high level of protease activity when grown in media containing only fresh shrimp waste
(FSW) or shrimp waste powder (SWP), indicating that it can obtain its carbon, nitrogen, and salts requirements directly from
shrimp waste. Maximum protease activities 17,000 and 12,000 U/mL were obtained with 80 g/L SWP and 135 g/L FSW, respectively.
The optimum temperature and pH for protease activity were 60 °C and 8.0, respectively. The crude protease, at different enzyme/substrate
(E/S) ratio, was tested for the deproteinization of shrimp waste to produce chitin. The crude enzyme of P. aeruginosa A2 was found to be effective in the deproteinization of shrimp waste. The protein removals after 3 h hydrolysis at 40 °C
with an E/S ratio of 0.5 and 5 U/mg protein were about 56% and 85%, respectively. 13C CP/MAS-NMR spectral analysis of the chitin prepared by treatment with the crude protease was carried out and was found to
be similar to that of the commercial α-chitin. These results suggest that enzymatic deproteinization of shrimp waste by A2
protease could be applicable to the chitin production process. 相似文献