全文获取类型
收费全文 | 444篇 |
免费 | 31篇 |
国内免费 | 5篇 |
专业分类
化学 | 358篇 |
力学 | 14篇 |
数学 | 42篇 |
物理学 | 66篇 |
出版年
2023年 | 6篇 |
2022年 | 20篇 |
2021年 | 16篇 |
2020年 | 31篇 |
2019年 | 34篇 |
2018年 | 31篇 |
2017年 | 32篇 |
2016年 | 41篇 |
2015年 | 26篇 |
2014年 | 33篇 |
2013年 | 48篇 |
2012年 | 25篇 |
2011年 | 24篇 |
2010年 | 15篇 |
2009年 | 13篇 |
2008年 | 27篇 |
2007年 | 18篇 |
2006年 | 10篇 |
2005年 | 3篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 2篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有480条查询结果,搜索用时 15 毫秒
71.
Malihe Samadi Kazemi Elham Ataeei Malihe Nasrabadi 《Russian Journal of Electrochemistry》2016,52(10):975-982
The complexation reaction between Tl+, Ag+ and Pb2+ cations with 2,6-di(furyl-2yl)-4-(4-methoxy phenyl)pyridine as a new synthesis ligand in acetonitrile (ACN)–H2O and methanol (MeOH)–H2O binary solutions has been studied at different temperatures using conductometric method. The conductometric data show that the stoichiometry of the complexes is 1: 1 [M: L] and the stability constant of complexes changes with the binary solutions identity. Also, the structure of the resulting 1: 1 complexes was optimized using the LanL2dz basis set at the B3LYP level of theory using GAUSSIAN03 software. The results show that the change of logKf for (DFMP.Pb)2+ and (DFMP.Ag)+ complexes with the mole ratio of acetonitrile and for (DFMP.Ag)+ and (DFMP.Tl)+ complexes with the mole ratio of methanol have a linear behavior, while the change of logKf of (DFMP.Tl)+complex in ACN–H2O binary solutions (with a minimum in XACN = 0.5) and (DFMP.Ag)+ complex in MeOH–H2O binary solutions (with a minimum in XMeOH = 0.75) show a non-linear behavior. The selectivity order of DFMP ligand for these cations in mol % CAN = 25 and 75 obtain Tl+ > Pb2+ > Ag+ but in mol % CAN = 50, the selectivity order observe Pb2+ > Tl+ > Ag+. Also, this selectivity sequence of DFMP in MeOH–H2O (mol % MeOH = 75 and 100) and (mol % MeOH = 50) is obtained Pb2+ > Ag+ and Tl+ > Ag+ > Pb2+ respectively. The values of thermodynamic parameters show that these values are influenced by the nature and the composition of binary solution. In all cases, the resulting complexes are enthalpy stabilized and entropy destabilized. The TΔSC° versus ΔHC° plot of all obtained thermodynamic data shows a fairly good linear correlation which indicates the existence of enthalpy-entropy compensation in the complexation reactions. 相似文献
72.
Elham Vatandost Fereshteh Chekin Seyed Ahmad Shahidi Yasaghi 《Russian Journal of Electrochemistry》2016,52(10):960-965
Stable silver nanoparticles were synthesized with the aid of a novel, non-toxic, eco-friendly biological material namely, green pepper extract. The aqueous pepper extract was used for reducing silver nitrate. The synthesized silver nanoparticles were analyzed with transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). TEM image shows the formation of silver nanoparticles with average particle size of 20 nm which agrees well with the XRD data. The main advantage of using pepper extract as a stabilizing agent is that it provides long-term stability for nanoparticles by preventing particles agglomeration. To investigate the electrocatalytic efficiency of silver nanoparticles, silver nanoparticles modified carbon-paste electrode (AgNPs–CPE) displayed excellent electrochemical catalytic activities towards hydrogen peroxide (H2O2) and hydrogen evolution reaction (HER). The reduction overpotential of H2O2 was decreased significantly compared with those obtained at the bare CPE. An abrupt increase of the cathodic current for HER was observed at modified electrode. Also, the antibacterial activity of silver nanoparticle was performed using Escherichia coli and Salmonellae. The approach of plant-mediated synthesis appears to be cost efficient, eco-friendly and easy methods. 相似文献
73.
Three reliable, rapid and selective methods have been developed and validated for the determination of lamotrigine in the presence of its impurity, 2,3-dichlorobenzoic acid. The first method is spectrophotometric method using p-chloranilic acid forming a colored product with lambda(max) 519+/-2 nm. All variables affecting the reaction have been investigated and the conditions were optimized. Beer's law was obeyed over a concentration range of 10-200 microg ml(-1) with mean accuracy 100.13+/-0.44%. The molar ratio of the formed ion-association complex is found to be 1 : 1 as deduced by Job's method. The conditional stability constant (K(f)), standard free energy (DeltaG), molar absorptivity(epsilon), and sensitivity index were evaluated. The second method is based on TLC separation of the cited drug (Rf=0.75+/-0.01) from its impurity (Rf=0.23+/-0.01) followed by densitometric measurement of the intact drug spots at 275 nm. The separation was carried on silica gel plates using ethyl acetate : methanol : ammonia 35% (17 : 2 : 1 v/v/v) as a mobile phase. The linearity range was 0.5-10 microg/spot with mean accuracy 99.99+/-1.33%. The third method is accurate and sensitive stability-indicating HPLC method based on separation of lamotrigine from its impurity on a reversed phase C(18) column, using a mobile phase of acetonitrile : methanol : 0.01 M potassium orthophosphate (pH 6.7+/-0.1) (30 : 20 : 50 v/v/v) at ambient temperature 25+/-5 degrees C and UV detection at 275 nm in an overall analysis time of about 6 min., based on peak area. The injection repeatability, intraday and interday repeatability were calculated. The procedure provided a linear response over the concentration range 1-12 microg ml(-1) with mean accuracy of 99.50+/-1.30%. The proposed methods were successfully applied for the determination of lamotrigine in bulk powder, in dosage form and in presence of its impurity. The results obtained were analyzed by ANOVA to assess that no significant difference between each of the three methods and the reported one. The validation was performed according to USP guidelines. 相似文献
74.
75.
Mahmoud Mirzaei Kun Harismah Elham Jafari Oğuz Gülseren Ali Shokuhi Rad 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(1):14
Density functional theory (DFT) calculations were performed to investigate stabilities and properties for uracil (U)-functionalized carbon nanotubes (CNTs). To this aim, the optimized molecular properties were evaluated for (n, 0) models of CNTs (n = 3–16) in the original and U-functionalized forms. The results indicated that the dipole moments and energy gaps were independent of tubular diameters whereas the binding energies showed that the U-functionalization could be better achieved for n = 8–11 curvatures of (n, 0) CNTs. Further studies based on the evaluated atomic-scale properties, including quadrupole coupling constants (C Q ), indicated that the electronic properties of atoms could detect the effects of diameters variations of (n, 0) CNTs, in which the effects were very much significant for the atoms around the U-functionalization regions. Finally, the achieved results of singular U, original CNTs, and CNT-U hybrids were compared to each other to demonstrate the stabilities and properties for the U-functionalized (n, 0) CNTs. 相似文献
76.
Elham Moharrami Nima Jafari Navimipour 《International Journal of Theoretical Physics》2018,57(4):1060-1081
Some new technologies such as Quantum-dot Cellular Automata (QCA) is suggested to solve the physical limits of the Complementary Metal-Oxide Semiconductor (CMOS) technology. The QCA as one of the novel technologies at nanoscale has potential applications in future computers. This technology has some advantages such as minimal size, high speed, low latency, and low power consumption. As a result, it is used for creating all varieties of memory. Counter circuits as one of the important circuits in the digital systems are composed of some latches, which are connected to each other in series and actually they count input pulses in the circuit. On the other hand, the reversible computations are very important because of their ability in reducing energy in nanometer circuits. Improving the energy efficiency, increasing the speed of nanometer circuits, increasing the portability of system, making smaller components of the circuit in a nuclear size and reducing the power consumption are considered as the usage of reversible logic. Therefore, this paper aims to design a two-bit reversible counter that is optimized on the basis of QCA using an improved reversible gate. The proposed reversible structure of 2-bit counter can be increased to 3-bit, 4-bit and more. The advantages of the proposed design have been shown using QCADesigner in terms of the delay in comparison with previous circuits. 相似文献
77.
Elham Y Hashem Magda S Saleh 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(2):239-247
The electronic absorption spectra of some substituted pyridinols in organic solvents of different polarities are studied. Also, the solvent effects on the intramolecular charge transfer bands are discussed using various solvent parameters. The acid-base equilibria of the compounds used are studied spectrophotometrically in various mixed aqueous solvents at 25 degrees C and 0.1 M ionic strength (NaClO4). Furthermore, the influence of the solvents on the dissociation constants and tautomeric equilibria of a pyridinol derivatives are discussed. The effect of molecular structure of the pyridinols on the pK's is also examined. 相似文献
78.
Barbora Laskova Marketa Zukalova Ladislav Kavan Alison Chou Paul Liska Zhang Wei Liu Bin Pavel Kubat Elham Ghadiri Jacques E. Moser Michael Gr?tzel 《Journal of Solid State Electrochemistry》2012,16(9):2993-3001
A nanocrystalline TiO2 (anatase) nanosheet exposing mainly the (001) crystal faces was tested as photoanode material in dye-sensitized solar cells. The nanosheets were prepared by hydrothermal growth in HF medium. Good-quality thin films were deposited on F-doped SnO2 support from the TiO2 suspension in ethanolic or aqueous media. The anatase (001) face adsorbs a smaller amount of the used dye sensitizer (C101) per unit area than the (101) face which was tested as a reference. The corresponding solar cell with sensitized (001)-nanosheet photoanode exhibits a larger open-circuit voltage than the reference cell with (101)-terminated anatase nanocrystals. The voltage enhancement is attributed to the negative shift of flatband potential for the (001) face. This conclusion rationalizes earlier works on similar systems, and it indicates that careful control of experimental conditions is needed to extract the effect of band energetic on the current/voltage characteristics of dye-sensitized solar cell. 相似文献
79.
An efficient, fast, and straightforward procedure for the synthesis of aromatic azides and in situ preparation of 1,2,3-triazoles under mild conditions is described. Aniline derivatives have been treated with task-specific [bmim]NO(2) and [bmim]N(3) ionic liquids to give the related phenyl azides which, on further in situ reaction with 1,3-diketones and ethylacetoacetate, afforded 1,2,3-triazoles in very good to excellent yields in very short reaction time. This procedure, which generates azides followed by azide in situ cycloaddition with diketone, has become an attractive option. In this protocol, [bmim]N(3) is used instead of the highly toxic reagent NaN(3). 相似文献
80.
Let ${(R, \mathfrak{m})}$ be a commutative Noetherian local ring of Krull dimension d, and let C be a semidualizing R-module. In this paper, it is shown that if R is complete, then C is a dualizing module if and only if the top local cohomology module of ${R, H _{\mathfrak{m}} ^{d} (R)}$ , has finite G C -injective dimension. This generalizes a recent result due to Yoshizawa, where the ring is assumed to be complete Cohen-Macaulay. 相似文献