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41.
The structural, electronic and elastic properties of Rb–As systems (RbAs in NaP, LiAs and AuCu structures, RbAs2 in the MgCu2 structure, Rb3 As in Na3As, Cu3 P and Li3Bi structures, and Rb5 As4 in the A5B4 structure) are investigated with the generalized gradient approximation in the frame of density functional theory. The lattice parameters, cohesive energies, formation energies, bulk moduli and the first derivatives of the bulk moduli (to fit Murnaghan’s equation of state) of the considered structures are calculated and reasonable agreement is obtained. In addition, the phase transition pressures are also predicted. The electronic band structures, the partial densities of states corresponding to the band structures and the charge density distributions are presented and analysed. The second-order elastic constants based on the stress-strain method and other related quantities such as Young’s modulus, the shear modulus, Poisson’s ratio, sound velocities, the Debye temperature and shear anisotropy factors are also estimated. 相似文献
42.
Necati Özdemir Om Prakash Agrawal Beyza Billur İskender Derya Karadeniz 《Nonlinear dynamics》2009,55(3):251-260
This paper presents an eigenfunctions expansion based scheme for Fractional Optimal Control (FOC) of a 2-dimensional distributed
system. The fractional derivative is defined in the Riemann–Liouville sense. The performance index of a FOC problem is considered
as a function of both state and control variables, and the dynamic constraints are expressed by a Partial Fractional Differential
Equation (PFDE) containing two space parameters and one time parameter. Eigenfunctions are used to eliminate the terms containing
space parameters and to define the problem in terms of a set of generalized state and control variables. For numerical computation
Grünwald–Letnikov approximation is used. A direct numerical technique is proposed to obtain the state and the control variables.
For a linear case, the numerical technique results into a set of algebraic equations which can be solved using a direct or
an iterative scheme. The problem is solved for different number of eigenfunctions and time discretization. Numerical results
show that only a few eigenfunctions are sufficient to obtain good results, and the solutions converge as the size of the time
step is reduced. 相似文献
43.
ÜMIT ÇAKIR Y. Kemal Yildiz Mahir Alkan 《Journal of inclusion phenomena and macrocyclic chemistry》1999,34(2):155-167
Liquid-liquid extractive-spectrophotometric studies of sodium ion complexes of 18-crown-6(18C6), dibenzo-18-crown-6(DB18C6), 15-crown-5(15C5), and 12-crown-4(12C4) and anionic dyes [4-(2-pyridylazo)-resorcinol monosodium salt monohydrate (PAR), Eriochrom Black T (EBT), and methyl orange (MOR)] and sodium picrate (PICRAT) as the counter ion are described. The overall extraction equilibrium constants for the 1 : 1 complexes of the above crown ethers with sodium dyes between different organic solvents and water have been determined at 25deg;C. They were conducted in various solvent-water systems maintaining an identical initial cation concentration in water, [M0+]w, and macrocyclic ligand concentration in the organic phase, [L0]org}, so that in all extractions [M0+]w : [L0]org ratios were 1 : 1, 1 : 10, 1 : 20, 1 : 50, and 1 : 62.5. An ion association complex formed between the sodium-crown ether complex ion and a dye anion was extracted into the organic solvent, and then the dye concentration of the separated aqueous phase was measured with an ultraviolet-visible spectrophotometer. PAR was the best associated dye with all crown ethers sodium-dyes and the extracted dye occurs as the ion-pair complex. Methylene chloride was found to be better than other extractive solvents used in this study. 相似文献
44.
The most sensitive atomic spectrometric technique has been ETA-AAS for many years. Recently, ICP-MS has emerged as an approach which provides even lower detection limits, but at considerably higher instrument and running costs. Flame AAS, on the other hand, is still being used widely in many laboratories in world. Therefore, alternative approaches for better sensitivity using flame AAS should be relevant and important. 相似文献
45.
Kerli Süleyman Alver Ümit Eskalen Hasan Uruş Serhan Soğuksu Ali Kemal 《Russian Journal of Applied Chemistry》2019,92(2):304-309
Russian Journal of Applied Chemistry - Boron doped vanadium thin films were fabricated on the micro-slide glass substrates by spray pyrolysis technique at substrate temperature of 400°C.... 相似文献
46.
Given a series-parallel queueing network topology with exponential servers of finite capacity, a systematic design methodology is presented that approximately solves the optimal routing and buffer space allocation problems within the network. The multi-objective stochastic nonlinear programming problem in integer variables is described and a two-stage iterative optimization procedure is presented which interconnects the routing and buffer space allocation problems. The algorithmic procedure couples the Expansion method, a decomposition method for computing performance measures in queueing networks with finite capacity, along with Powell's unconstrained optimization procedure which allocates the buffers and a multi-variable search procedure for determining the routing probabilities. The effectiveness and efficiency of the resulting two-stage design methodology is tested and evaluated in a series of experimental designs along with simulations of the network topologies. 相似文献
47.
Yasemin Ö. Çiftci Kemal Çolakoğlu Sefa Kazanç SonerÖzgen 《Central European Journal of Physics》2006,4(4):472-480
This paper describes the effect of pressure on some the mechanical properties of transition metals Cu, Ag, and Au, such as
elastic constants and bulk modulus. Using molecular dynamics (MD) simulation, the present study was carried out using the
modified many-body Morse potential function expression in the framework of the Embedded Atom Method (EAM). The effect of pressure
on equilibrium volume, elastic constants, and bulk modulus were determined, and found to be in agreement with other theoretical
calculations and experimental data. 相似文献
48.
Osman Yilmaz Ali Usanmaz Kemal Alyürük 《Journal of polymer science. Part A, Polymer chemistry》1993,31(13):3205-3211
n-Butyl isocyanate (nBIC) was polymerized in bulk by the Pruitt–Baggett adduct (PBA) at ?23, 0.0, and 25.0°C. Polymerization was accompanied by trimerization to the cyclicisocyanurates at all temperatures. Spectroscopic evidences supported the nylon-1 structure for both trimer and polymer. The polymer/trimer ratio and the molecular weight of produced polymers were found to increase with decreasing temperature. The Pruitt–Baggett catalyst (PBC), which is the reaction product of (PBA + H2O) system, also polymerized nBIC, but with a relatively slower rate. In aromatic and etheric solutions, nBIC was only trimerized by PBA. Copolymerization of nBIC with propylene oxide by PBA and PBC failed. Some selected monoisocyanates were also polymerized by PBA. © 1993 John Wiley & Sons, Inc. 相似文献
49.
3-Aminoquinazolinone–phosphine proligands (5a–e) and their Ru(II) complexes (6a–e) were prepared and characterized by NMR (1H, 13C, 31P{1H}), FTIR and microanalysis. The 3-aminoquinazolinone–phosphine ligands were found to coordinate with the Ru(II) center via their phosphorus and nitrogen atoms. The Ru(II) complexes were applied as catalysts for the hydrogenation and transfer hydrogenation of prochiral ketones. The results showed that these complexes are efficient transfer hydrogenation catalysts. 相似文献
50.
Rainer Kahner Benedikt Waerder Hasan Kemal Arslan Heinz Rehage 《Colloid and polymer science》2010,288(4):461-468
In this publication we describe a new self-association process, which leads to the formation of ultra-thin alginate layers
at the interface between oil and water. The water phase contains a highly dilute solution of sodium alginate. These macromolecules
are negatively charged and they are not surface active. The oil phase contains a small concentration of positively charged
surfactants. At the interface between oil and water, the cationic surfactants tend to form complexes with the negatively charged
alginate polyelectrolytes in the aqueous solutions. This leads to striking adsorption processes of the solved polysaccharide
molecules at the oil-water interface. Upon the addition of calcium ions, a cross-linking process sets in and one obtains the
thin viscoelastic membranes, which are anchored at the interface between oil and water. The thickness of these membranes is
of the order of 0.2 mm. Similar structures can also be formed by solving positively charged Gemini surfactants in the oil
phase. In this case, the cationic surfactant molecules induce the adsorption processes of alginate macromolecules, and they
also act as cross-linking compounds. In a series of experiments, we measured the surface rheological properties of these ultra-thin
alginate membranes. The results of these investigations point to the presence of electrostatically stabilized membranes. Special
interest was given to the influence of the guluronate content of the alginates, which is important for the cross-linking mechanism
according to the egg-box model. Finally, this article finishes with the discussion of the proposed building mechanisms of
these membranes. 相似文献