首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   118篇
  免费   2篇
  国内免费   4篇
化学   70篇
力学   6篇
数学   14篇
物理学   34篇
  2023年   1篇
  2022年   1篇
  2021年   3篇
  2020年   4篇
  2019年   2篇
  2018年   6篇
  2017年   7篇
  2016年   9篇
  2015年   7篇
  2014年   8篇
  2013年   9篇
  2012年   12篇
  2011年   13篇
  2010年   13篇
  2009年   7篇
  2008年   7篇
  2007年   4篇
  2006年   5篇
  2005年   2篇
  2004年   1篇
  1993年   1篇
  1980年   1篇
  1978年   1篇
排序方式: 共有124条查询结果,搜索用时 15 毫秒
91.
Batch adsorption experiments were carried out for the removal of malachite green (MG) cationic dye from aqueous solution using novel hydrogel nanocomposite that was prepared by graft copolymerization of acrylic acid (AA) onto kappa-carrageenan (κC) biopolymer in the presence of a crosslinking agent, a free radical initiator and aminosilica-functionalized TiO2 nanoparticles (κC-g-PAA/TiO2–NH2). The factors influencing adsorption capacity of the adsorbents such as initial pH value (pH0) of the dye solutions, TiO2–NH2 content (wt%), initial concentration of the dye, amount of adsorbents, and temperature were investigated. The adsorption capacity of hydrogel nanocomposite for MG was compared with hydrogel. The adsorption behaviors of both adsorbents showed that the adsorption kinetics and isotherms were in good agreement with a pseudo-second-order equation and the Langmuir equation. The high adsorption capacity (q m= 666–833 (mg/g)) and the favorable heterogeneity factor (n = 1.2–1.5) calculated from isotherm equations show the efficiency of the novel adsorbents.  相似文献   
92.
Khalili  Malihe  Abedi  Mohammad  Amoli  Hossein Salar 《Ionics》2017,23(3):779-787
Ionics - This study reports the effect of saffron carotenoids and mulberry anthocyanins as natural sensitizers on electron transfer process and performance of dye-sensitized solar cells (DSSCs). A...  相似文献   
93.
In this paper, a multi-buyer multi-vendor supply chain problem is considered in which there are several products, each buyer has limited capacity to purchase products, and each vendor has warehouse limitation to store products. In this chain, the demand of each product is stochastic and follows a uniform distribution. The lead-time of receiving products from a vendor to a buyer is assumed to vary linearly with respect to the order quantity of the buyer and the production rate of the vendor. For each product, a fraction of the shortage is backordered and the rest are lost. The ordered product quantities are placed in multiple of pre-defined packets and there are service rate constraints for the buyers. The goal is to determine the reorder points, the safety stocks, and the numbers of shipments and packets in each shipment of the products such that the total cost of the supply chain is minimized. We show that the model of this problem is of an integer nonlinear programming type and in order to solve it a harmony search algorithm is employed. To validate the solution and to compare the performance of the proposed algorithm, a genetic algorithm is utilized as well. A numerical illustration and sensitivity analysis are given at the end to show the applicability of the proposed methodology in real-world supply chain problems.  相似文献   
94.
Multiwalled carbon nanotubes grafted with vinyl immidazolium‐based ionic liquid (MWCNT‐IL) were synthesized and utilized as a crosslinking agent for the preparation and evaluation of a polymeric gel as a new class of organic solvent absorbent. Based on our earlier organic solvent‐absorbents, the present polymeric gel exhibited high organic solvent absorbency, fast organic solvent absorption rate, and good reusability. To prepare such polymeric gel, radical polymerization was carried out with dodecyl methacrylate and butyl acrylate as comonomers, MWCNT‐ILs as crosslinking agent, and azoisobutyronitrile as initiator, providing polymeric gel in a quantitative yield. The polymeric gel synthesized under the optimized polymerization conditions absorbed 79 times the dry weight in CCl4, 57 times in toluene, 96 in CHCl3, and 100 times in CH2Cl2. The reusability of the prepared‐polymeric gel was also checked which established that the gels could be recycled and reused for at least 10 times. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3166–3172  相似文献   
95.
In this work, we compared formation and properties of heat‐treated Ag nanoparticles in silica matrix synthesized by RF‐reactive magnetron cosputtering and sol–gel methods separately. The sol–gel and sputtered films were annealed at different temperatures in air and in a reduced environment, respectively. The optical UV‐visible spectrophotometry have shown that the absorption peak appears at 456 and 400 nm wavelength indicating formation of silver nanoparticles in SiO2 matrix for both the sol–gel and sputtering methods at 100 and 800 °C, respectively. XPS measurements showed that the metallic Ag0 nanoparticles can be obtained from both the techniques at these temperatures. According to XPS and AFM analysis, by increasing annealing temperature, the concentration of the Ag nanoparticles on the surface decreased and the nanoparticles diffused into the substrate for the sol–gel films, while for the films deposited by cosputtering method, the Ag surface concentration increased by increasing the temperature. Based on AFM observations, the size of nanoparticles on the surface were obtained at about 25 and 55 nm for sputtered and sol–gel films, respectively, supporting our optical data analysis. In comparison, the sputtering technique can produce Ag metallic nanoparticles with a narrower particle size distribution relative to the sol–gel method. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
96.
We report the results of the electronic structure calculation of a newly discovered member of the YBCO high-Tc family, i.e., Y3Ba5Cu8O18 (Y358) with Tc>100, based on the full-potential linearized augmented plane waves method (FP-LAPW) of density functional theory in the generalized gradient approximation (GGA). The evolution of the number of hole carriers in different sites of the CuO2 planes and CuO chains has been investigated in comparison with the other YBCO family members, i.e., Y123, Pr123, Y124, and Y247. The results suggest that pumping hole carriers out of the chains toward the planes enhances the transition temperature. The band structure calculations have been performed for Y358, and the results show similar features with the other family members. Most notably, a van Hove singularity forms near the X point of the Brillouin zone below the Fermi level and within the energy of the buckling phonon mode, for which the interplay is discussed.  相似文献   
97.
We have investigated the Hall measurement of Gd(Ba2−xNdx)Cu3O7+δ with x=0, 0.05, 0.1, 0.15, and 0.2 in a magnetic field of 0–1 T. The nominal samples has been prepared by the conventional solid-state reaction technique. The iodometric titration experiment was carried out for samples. The Rietveld analysis of the X-ray diffraction patterns indicates that samples are mainly single phase. The normal state Hall coefficient behaves as 1/T in all samples. All samples with nominal compositions show single sign reversal with variation of magnetic field and temperature. The Hall resistivity of the samples with x=0 and 0.1 close to the superconducting transition temperature changes its sign with decreasing temperature and tends to a minimum −Δmax, and then monotonically goes to zero. The absolute value of −Δmax decreases with the increase of magnetic field. This can be qualitatively explained by a model calculation based on the time-dependent Ginsburg–Landau theory.  相似文献   
98.
Magnetic anisotropies in FeCo fine particles   总被引:1,自引:0,他引:1  
 The single-domain particles, especially FeCo fine particles have many applications in magnetic information technology. We have prepared Fe1−xCox fine particles for different x by borohydride method and measured the magnetic and structural properties of the samples. We have then determined the variations of coercivity and anisotropy energy versus x in Fe1−xCox fine particles. The obtained results have been analyzed on the basis of various magnetic anisotropies. Magnetic anisotropies affect the coercivity of the medium for each x   as follows: shape and crystal anisotropies for x=0x=0, surface and crystal anisotropies for x=1x=1, shape, induced and crystal anisotropies for x=0.3x=0.3 and 0.5, and shape and induced anisotropies for x=0.45x=0.45.  相似文献   
99.
We have studied the structural, electrical, and magnetic properties of the normal and superconducting states Gd(Ba2-xLax)Cu3O7+ [Gd(BaLa)123] samples with 0.0 x 0.8 prepared by the standard solid-state reaction. XRD characterization shows an orthorhombic-tetragonal structural transition at x=0.2. Iodometric titration analysis shows the oxygen content of the samples increase with the increase of La doping. The resistivity curves show that for x0.15, there is metallic behavior, and for x0.2, there is a gradual insulating transition behavior in the normal state. The metal-insulator and superconductor-insulator transitions occur between x=0.35 and x=0.4. The superconducting transition temperature decreases with the increase of La content as two-step curve. The normal-state resistivity is fitted for two and three dimensional variable range hopping (2D&3D-VRH) and Coulomb gap (CG) regimes, separately. The results show that the dominant mechanism is CG for x0.35, and VRH for x0.4. The pinning energy U, derived from the thermally activated flux creep (TAFC) model and Ambegaokar-Halperin (AH) theory, shows a power-law relation as UH -. The critical current density decreases with the increase of La doping and magnetic field. The E-J curves show that the induced electric field increases with the increase of magnetic field and La concentration. The magnetization measurements indicate that the critical penetration fields and magnetic current density decrease with La doping.  相似文献   
100.
In this research, the effect of Ni, Pd and Ni-Pd catalysts have studied on morphology and structure of synthesized multi-wall carbon nanotubes (MWCNTs). Initially, thin films of Ni (with two thicknesses of 10 and 20 nm), Pd/Ni (5/10 nm) and Pd (10 nm) were deposited as catalysts on SiO2 (60 nm)/Si(1 0 0) substrates, using dc magnetron sputtering technique. The deposited films were annealed at 900 °C in ammonia environment for 45 min, in order to obtain nano-structured catalyst on the surface. Using scanning electron microscopy (SEM), the average size of Ni nano-islands (synthesized by the 10 and 20 nm Ni films), Pd and Ni-Pd nano-islands were measured about 55, 110, 45 and 50 nm, respectively. According to X-ray photoelectron spectroscopy analysis (XPS), the ratio of Ni/Pd on the surface was about 3 for the bilayer sample. The CNTs were synthesized on the nano-island catalysts at 940 °C in CH4 ambient using a thermal chemical vapor deposition method. The results revealed that average diameter of the CNTs were about 70, 110, 120 nm for Ni, Ni-Pd and Pd catalysts, respectively. Raman spectra of the MWCNTs showed that intensity ratio of two main peaks located in the range of 1550-1600 and 1250-1450 cm−1 (as a quality factor for the CNTs) for Ni, Pd and Ni-Pd catalysts were 1.42, 0.91 and 0.85, respectively. Therefore, based on our data analysis, although addition of Pd to Ni catalyst caused a considerable reduction in the quality of the grown MWCNTs as compared to the pure Ni catalyst, but it resulted in an enhancement in the methane decomposition rate. For the pure Pd catalyst samples, both a slow methane decomposition rate as compared with Ni-Pd catalyst samples and a poor quality of CNTs were observed as compared with the Ni catalyst, under similar experimental conditions.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号