全文获取类型
收费全文 | 201篇 |
免费 | 6篇 |
专业分类
化学 | 156篇 |
晶体学 | 6篇 |
力学 | 10篇 |
数学 | 6篇 |
物理学 | 29篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 12篇 |
2013年 | 19篇 |
2012年 | 19篇 |
2011年 | 8篇 |
2010年 | 5篇 |
2009年 | 4篇 |
2008年 | 17篇 |
2007年 | 9篇 |
2006年 | 3篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有207条查询结果,搜索用时 15 毫秒
171.
Younes Ali Alliot Cyrille Ali Jafar Sunga Bonraisin Anne-Cécile Mokili Marcel Happel Steffen Bombard Aude Haddad Ferid Montavon Gilles 《Journal of Radioanalytical and Nuclear Chemistry》2020,324(2):823-828
Journal of Radioanalytical and Nuclear Chemistry - A method for the production and purification of polonium from an irradiated bismuth target that minimizes processing time, cost, and generation of... 相似文献
172.
Nanoclusters of lead (Pb n , n = 1–6) were studied theoretically employing MP2 and M062X methods. Structural and thermodynamic properties as well as ionization energies and electron affinities of two isomers of Pb3, six isomers of Pb4, seven isomers of Pb5 and seven isomers of Pb6 were obtained at 298 K. Rhombic, pyramidal and octagonal structures were the most stable forms of the Pb4, Pb5 and Pb6 clusters, respectively. Proton affinities of the Pb n clusters were computed, which were in the range of 200–250 kcal/mol. Adsorption of C2H2, C2H4, CO, CO2, CH2O, HNO, O3, NO, N2O, NO2, N2O4 and N2O5 on the Pb n clusters was studied. O3 showed the strongest interaction with the Pb n clusters with adsorption enthalpies of 80–130 kcal/mol. HNO, O3, N2O, N2O4 and N2O5 were dissociated after adsorption on the Pb n clusters. N2O decomposes to adsorbed O atom and a free N2 molecule, while N2O4 and N2O5 release a NO2 molecule. 相似文献
173.
Sana Kachbouri Najib Mnasri Elimame Elaloui Younes Moussaoui 《Journal of Saudi Chemical Society》2018,22(4):405-415
Spherical and rod mesoporous silica nanoparticles with hexagonal mesostructure were prepared using the modified Stöber method. The morphology, size and internal pore structure can be controlled by simple changing of surfactant concentration and water:ethanol molar ratio. Monodispersed spheroid MCM-41 was obtained at 40 °C under basic conditions using cetyltrimethylammonium bromide (C16TAB) as template. Obtained materials were characterized by X-ray diffraction (XRD), nitrogen physisorption (BET), transmission electron microscopy (TEM) and scanning electronic microscopy (SEM). The results reveal that the pore volume and surface area increase when the amount of C16TAB increases whereas the pore diameter and particle size decrease. However, the use of ethanol as cosolvent led to an increase in the particles’ size. Moreover, the addition of a 3-aminopropyltriethoxysilane greatly influenced the final particle shape. The material was effectively used for the removal of two fluorescent dyes (Hoechst 33342 and rhodamine 6g) from aqueous solution. Adsorption isotherm models, Langmuir, Freundlich and Temkin were used to simulate the equilibrium data. The Langmuir model was found to fit the experimental data better than others models. 相似文献
174.
Gity Mir Mohamad Sadeghi Alireza Namjoo Soleyman Hosseinzadeh Samira Abdolbaghi Younes Saadat 《Polymer Science Series B》2018,60(5):589-597
Golf ball-like poly(methyl methacrylate) particles were produced via seeded dispersion polymerization of 2-ethylhexyl methacrylate with poly(methyl methacrylate) seed beads in the presence of saturated hydrocarbon droplets and evaporation of the hydrocarbon after the polymerization. It was observed that the particles are acquired in the form of a stable dispersion if the reaction is ceased around 42% of monomer conversion. Moreover, the effect of different reaction conditions (e.g. hydrocarbon and stabilizer type, initiator and monomer content, and polarity of the medium) on the shape and stability of the produced particles was investigated. It was revealed that the number and size of the dents on the surface of the golf ball-like particles could be manipulated easily with a simple change in each one of the parameters referred to above. In addition, the experimental results showed that some of the particles become unstable and diffuse into each other during polymerization, resulting in the formation of huge golf ball-like objects. The production of disk-like poly(methyl methacrylate) particles via fully developed seeded dispersion polymerization in the presence of a hydrocarbon which owns lengthy alkyl chain was another interesting finding of this study. 相似文献
175.
I.?R.?Saad A.?M.?Abdel-GaberEmail author G.?O.?Younes B.?Nsouli 《Russian Journal of Applied Chemistry》2018,91(2):245-252
The inhibiting action, thermodynamics, and adsorptive properties of 1, 2, 4-triazolo[1, 5-a]pyrimidine (TP) have been investigated for the corrosion of mild steel in 0.5 M H2SO4 and 0.5 M H3PO4 solutions by means of potentiodynamic, electrochemical impedance spectroscopy techniques and quantum chemical calculations. Results obtained revealed that TP is more effective in 0.5 M H3PO4 than in 0.5 M H2SO4. Theoretical fitting of different adsorption isotherms such as Langmuir, Flory–Huggins, Temkin, and the kinetic-thermodynamic models were tested. The obtained experimental data fitted all the applied adsorption isotherms except Langmuir. The thermodynamic activation parameters were calculated. The potential of zero charge was also determined using AC measurements to clarify the nature of surface charge of the mild steel in both acidic solutions. Quantum chemical parameters were calculated and explained. The data explained that the inhibition of mild steel in both acidic solutions takes place through physicochemical adsorption mechanism. 相似文献
176.
Younes Khalili Ahmad Mahboubi 《Particuology》2014,(4):138-150
In this study, a novel approach to incorporate the pore water pressure in the discrete element method (DEM) to comprehensively model saturated granular media was developed. A numerical model was constructed based on the DEM by implanting additional routines in the basic DEM code; pore water pressure calculations were used with a two-dimensional (2D) model to simulate the undrained behavior of satu- rated granular media. This model coupled the interaction of solid particles and the pore fluid in saturated granular media. Finally, several 2D undrained shear tests were simulated. The test results showed that the model could predict the response of the saturated granular soil to shear loading. The effect of initial compaction was investigated. Biaxial tests on dense and loose specimens were conducted, and the effect of the initial density on the change in shear strength and the volume change of the system was inves- tigated. The overall behavior of loose and dense specimens was phenomenologically similar to the real granular material. Constant volume tests were simulated, and the results were compared to those from the coupled model. Induced anisotropy was micromechanically investigated by studying the contact force orientation. The change in anisotropy depended on the modeling scheme. However, the overall responses of the media obtained usinz the couoled and constant volume methods were similar. 相似文献
177.
Cid B. de Araújo Glauco S. Maciel Leonardo de S. Menezes Nikifor Rakov Edilson L. Falco-Filho Vladimir A. Jerez Younes Messaddeq 《Comptes Rendus Chimie》2002,5(12)
We present recent results on frequency upconversion (UPC) obtained in fluoroindate glasses (FIG) doped with Ho3+, Tm3+ and Nd3+ ions and codoped with Pr3+/Nd3+ and Yb3+/Tb3+ ions. The results for the Ho3+-doped samples show strong evidence of energy transfer (ET) between Ho3+ ions resonantly excited at 640 nm. The origin of the blue-green upconverted fluorescence observed was identified and the dynamics of the signals revealed the pathways involved in the UPC process. In the case of Tm3+-doped FIG, the samples were resonantly excited at 650 nm and the main mechanism that contributes for the red-to-blue upconversion is excited-state absorption (ESA). The FIG samples codoped with Pr3+/Nd3+ were excited at 588 nm in resonance with transitions starting from the ground state of the Nd3+ and the Pr3+ ions. It was observed that the presence of Nd3+ ions enhanced the Pr3+ emission at 480 nm by two orders of magnitude. Multiphonon (MP)-assisted upconversion is also discussed for Nd3+-doped FIG pumped at 866 nm. Emission at 750 nm with a peculiar linear dependence with the laser intensity was observed and explained. A rate-equation model that includes MP absorption via thermally coupled electronic excited states of Nd3+ was developed and describes well the experimental results. The role played by effective phonon modes is clearly demonstrated. MP-assisted UPC process was also studied in Yb3+/Tb3+-codoped FIG samples excited at 1064 nm, which is off-resonance with electronic transitions starting from the ground state. It was determined that the mechanism leading to Tb3+ emission in the blue is due to ET from a pair of excited Yb3+ ions followed by ESA in the Tb3+ ions. 相似文献
178.
Anis Younes 《国际流体数值方法杂志》2004,45(2):157-178
An accurate finite‐volume Eulerian Lagrangian localized adjoint method (ELLAM) is presented for solving the one‐dimensional variable coefficients advection dispersion equation that governs transport of solute in porous medium. The method uses a moving grid to define the solution and test functions. Consequently, the need for spatial interpolation, or equivalently numerical integration, which is a major issue in conventional ELLAM formulations, is avoided. After reviewing the one‐dimensional method of ELLAM, we present our strategy and detailed calculations for both saturated and unsaturated porous medium. Numerical results for a constant‐coefficient problem and a variable‐coefficient problem are very close to analytical and fine‐grid solutions, respectively. The strength of the developed method is shown for a large range of CFL and grid Peclet numbers. Copyright 2004 John Wiley & Sons, Ltd. 相似文献
179.
Younes Valadbeigi 《International journal of quantum chemistry》2017,117(3):190-196
A new class of superacids was designed using enolic derivatives of fulvene. After deprotonation, bond rearrangement leads in a stable conjugate base with an aromatic cyclopentadienyl ring and a carboxyl group. The gas phase enthalpies ( ) of the deprotonation, as an index of acidity, were calculated employing the B3LYP method and 6‐311++G(d,p) and aug‐cc‐PVDZ basis sets. The acidity of these compounds without any electron withdrawing groups was more than H2SO4 in gas phase. The acidity increased by substituting electron withdrawing groups (? F, ? CN, and ?O) into the molecules so that we could achieve a cyano derivative of fulvene with = 250 kcal/mol. 相似文献
180.
Shaaban K. Mohamed Sabry H. H. Younes Eman M. M. Abdel‐Raheem Joel T. Mague Mehmet Akkurt Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(11):959-964
The wide diversity of applications of thiosemicarbazones and bis(thiosemicarbazones) has seen them used as anticancer and antitubercular agents, and as ligands in metal complexes designed to act as site‐specific radiopharmaceuticals. Molecules of 1,1′‐({[(ethane‐1,2‐diyl)dioxy](1,2‐phenylene)}bis(methanylylidene))bis(thiosemicarbazide) {alternative name: 2,2′‐[ethane‐1,2‐diylbis(oxy)]dibenzaldehyde bis(thiosemicarbazide)}, C18H20N6O2S2, (I), lie across twofold rotation axes in the space group C2/c, with an O—C—C—O torsion angle of −59.62 (13)° and a trans‐planar arrangement of the thiosemicarbazide fragments relative to the adjacent aryl rings. The molecules of (I) are linked by N—H...S hydrogen bonds to form sheets containing R24(38) rings and two types of R22(8) ring. In the N,N‐dimethylformamide disolvate, C18H20N6O2S2·2C3H7NO, (II), the independent molecular components all lie in general positions, but one of the solvent molecules is disordered over two sets of atomic sites having occupancies of 0.839 (3) and 0.161 (3). The O—C—C—O torsion angle in the ArOCH2CH2OAr component is −75.91 (14)° and the independent thiosemicarbazide fragments both adopt a cis‐planar arrangement relative to the adjacent aryl rings. The ArOCH2CH2OAr components in (II) are linked by N—H...S hydrogen bonds to form deeply puckered sheets containing R22(8), R24(8) and two types of R22(38) rings, and which contain cavities which accommodate all of the solvent molecules in the interior of the sheets. Comparisons are made with some related compounds. 相似文献