全文获取类型
收费全文 | 282篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 195篇 |
力学 | 18篇 |
数学 | 45篇 |
物理学 | 34篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 22篇 |
2019年 | 21篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 21篇 |
2015年 | 11篇 |
2014年 | 23篇 |
2013年 | 28篇 |
2012年 | 18篇 |
2011年 | 20篇 |
2010年 | 13篇 |
2009年 | 12篇 |
2008年 | 7篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 10篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 2篇 |
1997年 | 1篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1970年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有292条查询结果,搜索用时 15 毫秒
31.
McLachlan N Nigjeh BK Hasell A 《The Journal of the Acoustical Society of America》2003,114(1):505-511
Musical bells have had limited application due to the presence of inharmonic partials in the lower part of their acoustic spectra. A series of bells has been designed that contains up to seven partial frequencies in the harmonic series beginning at the fundamental frequency. This was achieved by choosing geometries for finite-element analysis models in which as many purely circumferential bending modes as possible occurred at frequencies below any mode with an axial ring node. The bell models were then fine tuned using gradient projection method shape optimization and the resulting profiles were cast in silicon bronze. A range of bell geometries and timbres is analyzed using psycho-acoustic models and is discussed in relation to European carillon bells. 相似文献
32.
Behzad Khorshidi 《Journal of Geometry》2009,96(1-2):81-91
A direct and easy general method is described for finding the center of gravity of all types of convex and concave polygons such as quadrilaterals, pentagons, hexagons and n-sided polygons. 相似文献
33.
Mostafa Kiamehr Batoul Alipour Leyla Mohammadkhani Behzad Jafari Peter Langer 《Tetrahedron》2017,73(21):3040-3047
Various novel polycyclic thiopyranoindol annulated [3,4-c]quinolone derivatives were synthesized via domino Knoevenagel-hetero-Diels–Alder reactions of indoline-2-thions and novel N-acrylated anthranilaldehydes in refluxing ethanol as a solvent in the presence of 20 mol% ZnBr2 as a Lewis acid catalyst. All reactions proceed with high yields with excellent regio- and stereoselectivity. 相似文献
34.
Hamid Beyzaei Mohammadreza Moghaddam-Manesh Reza Aryan Behzad Ghasemi Alireza Samzadeh-Kermani 《Chemical Papers》2017,71(9):1685-1691
Pyrazolo[3,4-d]pyrimidines are one of the most important classes of fused heterocyclic compounds which exhibit a broad range of biological and medicinal properties. They are known as anticancer, antifungal, antibacterial, antiviral and anti-inflammatory agents. In this study, some new 6-substituted 4-amino-pyrazolo[3,4-d]pyrimidine derivatives were prepared via reaction of 5-amino-3-methyl-1-phenyl-1H-pyrazole-4-carbonitrile with various nitriles in the presence of sodium ethoxide as catalyst. The inhibitory properties of synthesized compounds were studied according to CLSI guidelines against some pathogenic bacteria including four gram-positive strains (Streptococcus pyogenes, Staphylococcus aureus, Bacillus cereus and Bacillus subtilis subsp. spizizenii) and three gram-negative strains (Pseudomonas aeruginosa, Shigella flexneri and Salmonella enterica subsp. enterica). The antibacterial effects of all derivatives were compared with those of antibiotics belonging to different classes. The values were reported as inhibition zone diameter (IZD), minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The effect of substituents on the biological activity of derivatives was discussed as well. The inhibitory effect of compound 6a, was shown to be the most, with MIC values in the range of 32–4096 μg/mL. Since most of the synthesized compounds were effective against Streptococcus pyogenes and Pseudomonas aeruginosa, they can be considered as inhibitors of these two bacteria. 相似文献
35.
Mehdi Dehghan Behzad Nemati Saray Mehrdad Lakestani 《Mathematical Methods in the Applied Sciences》2014,37(6):894-912
The current paper proposes a technique for the numerical solution of Burgers equations. The method is based on finite difference formula combined with the Galerkin method, which uses the interpolating scaling functions. Several test problems are given, and the numerical results are reported to show the accuracy and efficiency of the new algorithm. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
36.
Moayad Hossaini Sadr Behzad Soltani Alireza Jalili Faeghe Nejadghafar Reza Kia James T. Engle Christopher J. Ziegler 《Transition Metal Chemistry》2012,37(7):611-617
The novel bidentate N,S-donor anionic ligands [PhNCSIndz]?, [PhNCSImz]?, [PhNCSPzMe3]?, and [EtNCSPz]?, where Indz?=?indazole, Imz?=?imidazole, PzMe3?=?3,4,5-trimethylpyrazole, and Pz?=?pyrazole, were synthesized and used to prepare Cu(II) complexes of general formula [Cu(N^S)2]. The ligands were synthesized via direct addition of phenylisothiocyanate or ethylisothiocyanate into THF suspensions of the corresponding sodium-pyrazolate salts. All of the synthesized compounds, including the ligands and the complexes, were characterized by physico-chemical and spectroscopic methods, and crystal structures of [Cu(EtNCSPz)2] and [Cu(PhNCSPzMe2)2] were determined by X-ray diffraction analysis, showing a trans-square planar geometry for [Cu(EtNCSPz)2] and a distorted tetrahedral geometry for [Cu(PhNCSPzMe2)2]. 相似文献
37.
Behzad Koozegar Kaleji Navid Hosseinabadi Akira Fujishima 《Journal of Sol-Gel Science and Technology》2013,65(2):195-203
In this study, preparation of Sn and Nb co-doped TiO2 dip-coated thin films on glazed porcelain substrates via sol–gel process have been investigated. The effects of co-doping content on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD), field emission SEM (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and UV–Vis absorption spectroscopy. Surface chemical state of thin films was examined by atomic X-ray photoelectron spectroscopy (XPS). XRD results suggest that adding impurities has a great effect on the crystallinity and particle size of TiO2. Titania Rutile phase formation in thin film was promoted by Sn4+ addition but was inhibited by Nb5+ doping. The prepared co-doped TiO2 photo-catalyst films showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of methylene blue (MB) solution under solar irradiation. Comparison with undoped and Sn or Nb-doped TiO2, codoped TiO2 shows an obviously higher catalytic activity under solar irradiation. 相似文献
38.
Mohammad Fallahian Behzad Pourabbas Mehdi Sharif Kamran Froutani Mehrnoosh Mahmoodian Mahdi Mohammadizadeh 《Polymer Science Series B》2017,59(3):308-319
In this study polypyrrole (PPy) nanoparticles were deposited as a thin film on the modified surface of polyethyleneterephthalate (PET) by in situ chemical polymerization in the presence of sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (DBSNa) and mixture of them as the surfactant. The surface of PET was modified by KOH before deposition and was investigated for conductivity and adhesion of PPy nanoparticles to PET. Resulting conductive flexible films were characterized by UV–Vis spectroscopy, fieldemission scanning electron microscopy, contact angle measurements and four-point-probe technique for conductivity. Direct morphological observation (FESEM) and electrical measurements indicated that the morphology, conductivity and the nature of deposited PPy films depend on surfactant, surface modification of PET and monomer concentration. In optimized process condition, uniform conductive films of PPy were obtained with good adhesion to PET. 相似文献
39.
We introduce the notion of almost expansive sequences and curves and study their ergodic and asymptotic properties in a Hilbert
space H. We apply our results to study the asymptotic behavior of solutions to the quasi-autonomous expansive type evolution system
(du/dt)(t) + f(t) ∈ Au(t) on [0, ∞). 相似文献
40.
Nunes SP Karunakaran M Pradeep N Behzad AR Hooghan B Sougrat R He H Peinemann KV 《Langmuir : the ACS journal of surfaces and colloids》2011,27(16):10184-10190
The supramolecular assembly of PS-b-P4VP copolymer micelles induced by selective solvent mixtures was used to manufacture isoporous membranes. Micelle order in solution was confirmed by cryo-scanning electron microscopy in casting solutions, leading to ordered pore morphology. When dioxane, a solvent that interacts poorly with the micelle corona, was added to the solution, polymer-polymer segment contact was preferential, increasing the intermicelle contact. Immersion in water gave rise to asymmetric porous membranes with exceptional pore uniformity and high porosity. The introduction of a small number of carbon nanotubes to the casting solution improved the membrane stability and the reversibility of the gate response in the presence of different pH values. 相似文献