全文获取类型
收费全文 | 175篇 |
免费 | 9篇 |
国内免费 | 5篇 |
专业分类
化学 | 112篇 |
晶体学 | 2篇 |
力学 | 15篇 |
数学 | 21篇 |
物理学 | 39篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 13篇 |
2017年 | 6篇 |
2016年 | 21篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 10篇 |
2012年 | 9篇 |
2011年 | 17篇 |
2010年 | 13篇 |
2009年 | 8篇 |
2008年 | 14篇 |
2007年 | 6篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2003年 | 1篇 |
2002年 | 4篇 |
1999年 | 3篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有189条查询结果,搜索用时 15 毫秒
121.
ABSTRACTThis article investigates wave propagation behavior of a multi-phase nanocrystalline nanobeam subjected to a longitudinal magnetic field in the framework of nonlocal couple stress and surface elasticity theories. In this model, the essential measures to describe the real material structure of nanocrystalline nanobeams and the size effects were incorporated. This non-classical nanobeam model contains couple stress effect to capture grains micro-rotations. Moreover, the nonlocal elasticity theory is employed to study the nonlocal and long-range interactions between the particles. The present model can degenerate into the classical model if the nonlocal parameter, couple stress and surface effects are omitted. Hamilton’s principle is employed to derive the governing equations which are solved by applying an analytical method. The frequencies are compared with those of nonlocal and couple stress-based beams. It is showed that wave frequencies and phase velocities of a nanocrystalline nanobeam depend on the grain size, grain rotations, porosities, interface, magnetic field, surface effect and nonlocality. 相似文献
122.
Daryoush Afzali Ali Mostafavi Farzad Etemadi Ali Ghazizadeh 《Arabian Journal of Chemistry》2012,5(2):187-191
In this work, the potential of modified multiwalled carbon nanotubes for separation and preconcentration of trace amounts of manganese ion is studied. Multiwalled carbon nanotubes were oxidized with concentrated HNO3 and then modified with loading 1-(2-pyridylazo)-2-naphtol. Mn(II) ions could be quantitatively retained by modified multiwalled carbon nanotubes in the pH range of 8–9.5. Elution of the adsorbed manganese was carried out with 5.0 mL of 0.1 mol L?1 HNO3. Detection limit is 0.058 ng mL?1 and analytical curve is linear in the range of 0.1 ng mL?1–5.0 μg mL?1 in the initial solution with a correlation coefficient 0.9977 and the preconcentration factor is 100. Relative standard deviation for eight replicate determination of 0.5 μg mL?1 of manganese in the final solution is 0.41%. The effects of the experimental parameters, including the sample pH, flow rates of sample and eluent solution, eluent type, breakthrough volume and interference ions, were studied for preconcentration of Mn(II) ions in detail to optimize the conditions. The method was successfully applied for separation, preconcentration and determination of manganese in different samples. 相似文献
123.
Farzad Alavi 《Molecular physics》2013,111(1):161-174
A dipolar–quadrupolar contribution to the residual Helmholtz energy for a polar square well (a square well plus either a point dipole or a point quadrupole) fluid is developed based on the Padé approximation. Taking the square well system as reference, the contribution is formulated using an expansion for radial distribution function of the reference system. In addition to square well potential parameters the contribution depends only on dipole and quadrupole moments. This term is added as perturbation to a generalized equation of state for square well fluids. The results are then compared with the available simulation data in the literature. With the new equation obtained, it was possible to predict liquid–vapour equilibrium properties and critical properties of polar square well fluids more accurately than with available perturbation theories for multipolar square well systems. Application of the equation of state to a real dipolar (water) and a real quadrupolar (carbon dioxide) fluid indicated that the polar contribution greatly improved the predictions of saturation properties. Accurate prediction of critical properties for polar square well fluids remains as a challenge. This work can be useful in the development of better equations of state. 相似文献
124.
Mohebbi S Falcón-Pérez JM González E Millet O Mato JM Kobarfard F 《Chemical & pharmaceutical bulletin》2012,60(1):70-78
A series of 2-substituted-4,6-diaminipyrimidine derivatives were synthesized and evaluated for their dihydrofolate reductase (DHFR) inhibitory activity. Saturation transfer difference (STD) (1)H-NMR experiments were used to probe the binding characteristics of the compounds with human DHFR enzyme. The most potent molecules, 12 and 15, in enzyme assay study showed the best results in STD experiments indicating their intimate interaction with the receptor. The docking studies were followed to explain the structural basis for the observed interaction between the ligands and DHFR. All the compounds were also assayed in vitro for their growth inhibitory activity on MCF-7, HepG2, SKHep1, and Hela tumor cell lines. Compounds 16, 17, and 22 demonstrated the most potent in vitro anti-proliferative activity among the others. 相似文献
125.
H. Raissi Abraham F. Jalbout B. Abbasi F. Fazli F. Farzad E. Nadim Aned de Leon 《International journal of quantum chemistry》2010,110(4):893-901
The molecular structure and intramolecular hydrogen bond energy of 18 conformers of 3‐imino‐propenyl‐amine were investigated at MP2 and B3LYP levels of theory using the standard 6‐311++G** basis set. The atom in molecules or AIM theory of Bader, which is based on the topological properties of the electron density (ρ), was used additionally and the natural bond orbital (NBO) analysis was also carried out. Furthermore calculations for all possible conformations of 3‐imino‐propenyl‐amin in water solution were also carried out at B3LYP/6‐311++G** and MP2/6‐311++G** levels of theory. The calculated geometrical parameters and conformational analyses in gas phase and water solution show that the imine–amine conformers of this compound are more stable than the other conformers. B3LYP method predicts the IMA‐1 as global minimum. This stability is mainly due to the formation of a strong N? H···N intramolecular hydrogen bond, which is assisted by π‐electrons resonance, and this π‐electrons are established by NH2 functional group. Hydrogen bond energies for all conformers of 3‐imino‐propenyl‐amine were obtained from the related rotamers methods. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
126.
Despite its success for modeling electrolyte thermodynamics in aqueous media, the use of the Pitzer approach for the investigation
of electrolytes in nonaqueous or in mixed solvent media is still very limited. Further, a review of the literature reveals
that there are no more than a few research groups who have used the exact form of the Pitzer–Simonson–Clegg (PSC) ion-interaction
approach for the investigation of electrolytes in mixed solvent systems. As a continuation of our previous studies, the present
investigation reports modeling of HCl in the 2-propanol + water mixed solvent system with the Pitzer, PSC and an extended
form of the PSC ion-interaction approaches using the experimental potentiometric data from a cell containing pH glass membrane
and Ag/AgCl electrodes. The electrochemical measurements were performed over the HCl molality range from 0.01 to 4.5 mol⋅kg−1 in mixed 2-propanol (x%)+water (100−x%) solvents, with different solvent percent mass fractions (x%=10,20,30,40 and 50%) at 298.15±0.05 K. 相似文献
127.
The principle of a general potentiometric method based on Emerson-Trinder reaction for the assay of various hydrogen peroxide generating systems is reported. Emerson-Trinder reaction, habitually employed as a spectrophotometric indicator reaction, is exploited in this method as a potentiometric indicator reaction. This method is based on the detection of F− ions, liberated from the oxidation of a fluorophenol compound used as hydrogen-donor in Emerson-Trinder reaction, by a fluoride ion-selective electrode. The ability and usefulness of this method are illustrated by an initial-rate potentiometric determination of uric acid in aqueous and human serum samples, for which, initial-rate reaction progress curves, linear calibration curve, within-day precisions, upper and lower detection limits, and also its analytical recovery were reported. 相似文献
128.
聚乙烯基胺包裹Fe3O4@SiO2磁性微球用于Knoevenagel缩合(英文)简 总被引:1,自引:0,他引:1
Polyvinyl amine coated Fe3O4@SiO2 composite microspheres with a core-shell structure were prepared and employed as a magnetic catalyst for Knoevenagel condensation under mild conditions. The catalyst can be readily recovered using a magnet and reused several times without loss in activity or selectivity. The performance of the magnetic base catalyst was compared with that of polyvinyl amine functionalized mesoporous SBA-15, which showed that the magnetic nanoparticles gave improved reaction rate and yield. 相似文献
129.
130.
Farzad Nasirpouri 《Ionics》2011,17(4):331-337
Electrodeposition mechanism of lead on polycrystalline copper from a perchlorate solution in the presence of chloride ions
was investigated. Electrochemical quartz crystal microbalance data including frequency and resistance were simultaneously
recorded with cyclic voltammograms and current transients. The change of frequency and resistance shows that a rigid bulk
film forms at the potentials more negative than −0.52 V saturated calomel electrode (SCE), exhibiting the overpotential deposits
of Pb (OPD). However, at the potentials ranging from −0.38 to −0.43 V SCE, a monolayer of lead as the underpotential deposit
of Pb (UPD) is formed. The measured real mass of the OPD of Pb compared to the charge passed through the cell elucidates the
formation of Pb (II). The magnitude of the applied overpotential has considerable effect on the growth of the OPD of lead.
The Pb OPDs formed at the lower overpotentials (or applied potentials in a range of −0.54 to −0.58 V SCE) show slight positive
deviation of the electrochemical equivalent (M/n) of Pb (II). We ascribe this evidence to the possible incorporation of adsorbed/alloyed elements like chlorine in the film
composition. At the higher overpotentials (or applied potentials of negative than −0.58 V SCE), the ratio starts to decrease,
mainly due to the hydrogen evolution associated with the possible morphology change of deposit. Our results also show that
the nucleation and growth of Pb OPD can be described with the instantaneous mechanism based on Scharifker–Hills prediction
with nondimensional plots. 相似文献