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排序方式: 共有321条查询结果,搜索用时 109 毫秒
101.
Keivan Kiani 《Journal of sound and vibration》2011,330(20):4896-4914
The vibration of elastic thin nanoplates traversed by a moving nanoparticle involving Coulomb friction is investigated using the nonlocal continuum theory of Eringen. The eigen function technique and the Laplace transform method are employed to solve the governing equations of the nanoplate. The explicit expressions of the in-plane and transverse displacements are obtained when the moving nanoparticle traverses the nanoplate on an arbitrary straight line. In a special case, the obtained results are also compared with those of other researchers and a reasonably good agreement is achieved. The effects of small-scale parameters and velocity of the moving nanoparticle on the dynamic response as well as the dynamic amplitude factors (DAFs) of the in-plane and transverse displacements are then explored in some detail. The results indicate that the magnitude of DAF of the transverse displacement of the nanoplate (i.e., DAFw) increases with the first small-scale effect parameter, irrespective of the values of the second small-scale effect parameter and the velocity of the moving nanoparticle. As the first small-scale effect parameter grows, the maximum values of DAFw as a function of the moving nanoparticle velocity increase and generally occur in the lower levels of the moving nanoparticle velocity. 相似文献
102.
Paredis K Ono LK Behafarid F Zhang Z Yang JC Frenkel AI Cuenya BR 《Journal of the American Chemical Society》2011,133(34):13455-13464
An in-depth understanding of the fundamental structure of catalysts during operation is indispensable for tailoring future efficient and selective catalysts. We report the evolution of the structure and oxidation state of ZrO(2)-supported Pd nanocatalysts (~5 nm) during the in situ reduction of NO with H(2) using X-ray absorption fine-structure spectroscopy and X-ray photoelectron spectroscopy. Prior to the onset of the reaction (≤120 °C), a NO-induced redispersion of our initial metallic Pd nanoparticles over the ZrO(2) support was observed, and Pd(δ+) species were detected. This process parallels the high production of N(2)O observed at the onset of the reaction (>120 °C), while at higher temperatures (≥150 °C) the selectivity shifts mainly toward N(2) (~80%). Concomitant with the onset of N(2) production, the Pd atoms aggregate again into large (6.5 nm) metallic Pd nanoparticles, which were found to constitute the active phase for the H(2)-reduction of NO. Throughout the entire reaction cycle, the formation and stabilization of PdO(x) was not detected. Our results highlight the importance of in situ reactivity studies to unravel the microscopic processes governing catalytic reactivity. 相似文献
103.
Ahmad Kiani Karanji Maryssa Beasley Daud Sharif Ali Ranjbaran Justin Legleiter Stephen J. Valentine 《Journal of mass spectrometry : JMS》2020,55(1)
The first 17 amino acid residues of Huntingtin protein (Nt17 of htt) are thought to play an important role in the protein's function; Nt17 is one of two membrane binding domains in htt. In this study the binding ability of Nt17 peptide with vesicles comprised of two subclasses of phospholipids is studied using electrospray ionization ‐ mass spectrometry (ESI‐MS) and molecular dynamics (MD) simulations. Overall, the peptide is shown to have a greater propensity to interact with vesicles of phosphatidylcholine (PC) rather than phosphatidylethanolamine (PE) lipids. Mass spectra show an increase in lipid‐bound peptide adducts where the ordering of the number of such specie is 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) > 1‐palmitoyl‐2‐oleoyl‐glycero‐3‐phosphocholine (POPC) > 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3 phosphoethanolamine (POPE). MD simulations suggest that the compactness of the bilayer plays a role in governing peptide interactions. The peptide shows greater disruption of the DOPC bilayer order at the surface and interacts with the hydrophobic tails of lipid molecules via hydrophobic residues. Conversely, the POPE vesicle remains ordered and lipids display transient interactions with the peptide through the formation of hydrogen bonds with hydrophilic residues. The POPC system displays intermediate behavior with regard to the degree of peptide‐membrane interaction. Finally, the simulations suggest a helix stabilizing effect resulting from the interactions between hydrophobic residues and the lipid tails of the DOPC bilayer. 相似文献
104.
Macropolyhedral borane clusters are concave polyhedra constituting fused convex simple polyhedra. They are formally obtained by condensation of simple polyhedral boranes under elimination of between one and four BH(3) or isoelectronic units. The number of eliminated vertexes from simple polyhedra equals the number of shared vertexes in macropolyhedral boranes. For each of the eight classes with general formulae ranging from B(n)H(n-4) to B(n)H(n+10), more than one structure type is possible, differing in the number of shared vertexes and in the types of the two combined cluster fragments. However, only one type of "potential structures" is represented by experimentally known examples and is found to be favored by theoretical calculations. A sophisticated system exists among the favored macropolyhedral borane structures. For each class of macropolyhedral boranes, the number of skeletal electron pairs is directly related to the general formula, the number of shared vertexes and the type of fused cluster fragments. In order to predict the distribution of vertexes among the fused fragments, we propose the concept of preferred fragments. Preferred fragments are those usually present in the thermodynamically most stable structure of a given class of macropolyhedral boranes and are also frequently observed in the experimentally known structures. This allows us to completely predict the cluster framework of the thermodynamically most stable macropolyhedral borane isomers. 相似文献
105.
Esmaeili A Rustaiyan A Nadimi M Larijani K Nadjafi F Tabrizi L Chalabian F Amiri H 《Natural product research》2008,22(6):516-520
The essential oils obtained by hydrodistillation of the leaves, stems and flowers of Salvia reuterana (Lamiaceae) were analysed by GC and GC/MS. Germacrene D and beta-caryophyllene were the major constituents in all the three oils: (28.5, 27.7 and 32.5%) and (15.5, 11.4 and 16.6%), respectively. Bicyclogermacrene (10.2 and 13.2%) was also prodominated in the stem and flower oils. The composition of the oils was mostly quantitativel rather than qualitatively different. All the oils consisted mainly of sesquiterpenes and a small percentage of non-terpenoid compounds. In all the three oils, monoterpenes were in a concentration less than 0.5%. Antibacterial activity was determined by the measurement of growth inhibitory zones. 相似文献
106.
Farzad Kiani 《Journal of Turbulence》2016,17(4):400-419
This study was conducted to investigate the flow structures of turbulent flow passing over a short finite cylinder in which a rigid flag is attached to the rear of the cylinder, in wake region. The length-to-diameter ratio of the cylinder was chosen to be L/D = 2, whereas the rigid flag had a width-to-diameter ratio of W/D = 1.5. Wall-adapted large-eddy simulation (LES-WALE) was used to resolve unsteady turbulent flow structures. The far field Reynolds number based on cylinder diameter was chosen to be 20,000. The results were compared with the regular case wherein no flag was attached to the cylinder. Results revealed that the flow pattern behind the cylinder with flag was totally different in comparison with the regular case one. However, top free end of the cylinder was not influenced by the flag in contrast with the wake region. At far downstream from the cylinder, most of the flow structures in both cases appeared the same. The horseshoe vortices in both cases appeared to be an unsteady phenomenon, with slightly different patterns. Moreover, in the case of flag attachment, the pressure coefficient was smaller than that of with no flag. Finally, it was shown that the main and secondary Strouhal numbers locations were different in both cases. 相似文献
107.
Designing syntheses of cellulose and starch derivatives with basic or cationic N‐functions: part I—cellulose derivatives 下载免费PDF全文
Hamid Salimi Fezzeh Aryanasab Ali Reza Banazadeh Meisam Shabanian Farzad Seidi 《先进技术聚合物》2016,27(1):5-32
The use of cellulose and starch derivatives that bear amino or quaternary ammonium moieties is steadily increasing, and the applications in industry are continuing to grow. These promising products are routinely used in cosmetic and paper‐making industries. This article provides an overview of strategies available to chemists for designing the syntheses of such compounds. The review provides a brief historical perspective on synthesis and describes recent developments that have enabled chemists to enhance their synthesis productivity. However, the graft polymerization techniques are far from the scope of this paper and will be noted in a few words only. In addition to the structural and synthetic aspects, applications of these derivatives are discussed in brief. We have divided this article in two parts mainly because of the vastness of the subject and limited space available. The first part of which reviews the advances in the synthesis of basic and cationic cellulose derivatives having amino or quaternary ammonium moieties and the second part of which considers starch ones. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
108.
Yadollah Yamini Shahram Seidi Farzad Latifeh 《International journal of environmental analytical chemistry》2017,97(13):1223-1236
In the present study, ionic liquid-modified silica-coated magnetic nanoparticles (MNPs) were synthesised and applied as a new anion-exchange sorbent for extraction and determination of Cr(VI) followed by inductively coupled plasma atomic emission spectrometry. The characterisation of MNPs was carried out by scanning electron microscope, Fourier transform infrared and vibrating sample magnetometer. Experimental design and response surface methodology were used for optimisation of different parameters which affect extraction efficiency of Cr(VI). Under the optimised conditions, extraction recoveries within the range of 25–33% with relative standard deviations (RSD%, n = 4) within the range of 3.0–5.0% were obtained. The limit of detection was found to be 0.1 µg L?1. The linearity was studied in the range of 0.5-200 µg L?1 with the determination coefficient of 0.9958. Also, calculated Errors% for determination of Cr(VI) in the range of 5-15 depict that the method offers acceptable accuracy for analysis of Cr(VI). The method was successfully applied for extraction and determination of Cr(VI) selectively in some tannery waste water samples. 相似文献
109.
D. Kiani 《manuscripta mathematica》2007,124(2):269-274
Suppose that D is a division ring with center F and N is a non-central normal subgroup of GL
n
(D). In this paper we generalize some known results about maximal subgroups of GL
n
(D) to maximal subgroups of N. More precisely, we prove that if M is a maximal subgroup of N such that F[M] satisfies a polynomial identity and contains an algebraic element over F or and either n ≥ 2 or n = 1 and M is not abelian, then [D : F] < ∞.
This research was partially supported by a grant from IPM (No. 85160047). 相似文献
110.
Di- and triporphyrin arrays consisting of 5,15-diphenylporphyrinatomagnesium(II) (MgDPP) coordinated to free-base and Ni(II) porphyrinyl mono- and bis-phosphine oxides, as well as the self-coordinating diphenyl[10,20-diphenylporphyrinatomagnesium(II)-5-yl]phosphine oxide [MgDPP(Ph(2)PO)], were synthesised in excellent yields and characterised by various spectroscopic techniques. Phosphine oxides stabilise Mg(II) coordination to porphyrins and the resulting complexes have convenient solubilities, while the Ni(II) complexes exhibit interesting intramolecular fluorescence quenching behaviour. The binding constant of MgDPP to triphenylphosphine oxide (5.3 +/- 0.1 x 10(5) M(-1)) and the very high self-association constant of [MgDPP(Ph(2)PO)] (5.5 +/- 0.5 x 10(8) M(-1)) demonstrate the strong affinity of phosphine oxides towards Mg(II) porphyrins. These complexes are the first strongly bound synthetic Mg(II) multiporphyrin complexes and could potentially mimic the "special pair" in the photosynthetic reaction centre. 相似文献