全文获取类型
收费全文 | 174篇 |
免费 | 3篇 |
国内免费 | 4篇 |
专业分类
化学 | 111篇 |
力学 | 11篇 |
数学 | 34篇 |
物理学 | 25篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2018年 | 2篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2014年 | 2篇 |
2013年 | 11篇 |
2012年 | 10篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 19篇 |
2008年 | 18篇 |
2007年 | 9篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1985年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有181条查询结果,搜索用时 15 毫秒
51.
Starting from a free hemiacetalic hydroxyl group, the glycosylation is performed by means of the DMF-COCl2 Vilsmeier-Haack reagent and silver tosylate. The nature of the reactive species is discussed. 相似文献
52.
Dimitris Kostopoulos François Beniere K.V. Reddy 《Journal of Physics and Chemistry of Solids》1979,40(5):357-367
Validity of the Arrhenius law has been investigated by measuring the influence of temperature on the transport processes in very pure single crystals of sodium iodide. For the first time, due to the high experimental accuracy and the precision of the temperature control, diffusion coefficients could be measured in a solid in steps of a few degrees up to a few tenths of a degree of the temperature of fusion. We have studied: (a) ionic conductivity, (b) self-diffusion of the cation Na+ and (c) self-diffusion of the anion I?. The three transport processes follow the same temperature dependence: (a) strict verification of the Arrhenius law over several orders of magnitude up to about thirty degrees below the melting point and (b) in the last thirty degrees a positive departure from the simple exponential law is observed which increases rapidly to reach 50% at fusion. The different possible reasons of this departure are discussed. The phenomenon seems to be connected with the lattice dynamics before melting. 相似文献
53.
The applicability of simplified models for the determination of ion exchange diffusion coefficients in zeolites is examined. The simplified models examined are Vermeulen's, Paterson's, and Nernst-Plank's approximations for isotopic and ion exchange processes, used in ion exchange systems analysis. Parameter analysis indicates the limits for fractional attainment of equilibrium U(t), the ratio of exchangeable ions in liquid to solid phase (w), and the ratio of surface diffusion coefficients of exchangeable ions (a), all clearly inter-related, within which the above-mentioned simplified models can be successfully used. Studies of the applicability of the isotopic exchange simplified models to experimental data for batch-type Na(+)-Pb(2+) exchange on clinoptilolite confirm the parameter analysis conducted. Copyright 2001 Academic Press. 相似文献
54.
Katsanos NA Iliopoulou E Plagianakos V Mangou H 《Journal of colloid and interface science》2001,239(1):10-19
Physicochemical parameters for adsorption of gases at the submonolayer regions of heterogeneous solid surfaces are measured experimentally as a function of time, and then interrelated as local isotherms θ against adsorption energy varepsilon, fractional changes of adsorption sites f(varepsilon)/c*(max) against varepsilon, θ against f(varepsilon)/c*(max), and distribution functions θ f(varepsilon)/c*(max) over adsorption energy values varepsilon, without using at all the well-known integral equation Theta(p, T)=integral(infinity)(0)θ(p, T, varepsilon)f(varepsilon)dvarepsilon and assumptions concerning the pair f(varepsilon) and θ(p, T, varepsilon). The method uses only chromatographic experimental data obtained by the inverse gas chromatography technique known as reversed-flow gas chromatography. It has been applied to the adsorption of cis-2-butene and trans-2-butene onto particles of Penteli marble at temperatures of 302, 314, 323, and 333 K. The results obtained are comparable with those calculated on the basis of the well-known integral equation. Copyright 2001 Academic Press. 相似文献
55.
Panagiotis Loginos Anastasios Patsidis Katerina Vrettos George Sotiriadis Georgios C. Psarras Vassilis Kostopoulos Vasilios Georgakilas 《Molecules (Basel, Switzerland)》2022,27(20)
In this work, UV-curable resin poly (ethylene glycol) diacrylate (PEGDA) was reinforced with three different types of nanofillers: pristine graphene (G), multiwalled carbon nanotubes (MWNTs), and a hybrid of MWNTs and graphene 70/30 in mass ratio (Hyb). PEGDA was mixed homogenously with the nanofiller oligomer by shear mixing and then photopolymerized, affording thin, stable films. The thermomechanical properties of the afforded nanocomposites indicated the superior reinforcing ability of pristine graphene compared with MWNTs and an intermediate behavior of the hybrid. 相似文献
56.
Figuerola A Diaz C Ribas J Tangoulis V Sangregorio C Gatteschi D Maestro M Mahía J 《Inorganic chemistry》2003,42(17):5274-5281
The reaction of Ln(NO(3))(3).aq with K(3)[Fe(CN)(6)] or K(3)[Co(CN)(6)] and 2,2'-bipyridine in water led to five one-dimensional complexes: trans-[M(CN)(4)(mu-CN)(2)Ln(H(2)O)(4) (bpy)](n)().XnH(2)O.1.5nbpy (M = Fe(3+) or Co(3+); Ln = Sm(3+), Gd(3+), or Yb(3+); X = 4 or 5). The structures for [Fe(3)(+)-Sm(3+)] (1), [Fe(3)(+)-Gd(3+)] (2), [Fe(3)(+)-Yb(3+)] (3), [Co(3)(+)-Gd(3+)] (4), and [Co(3)(+)-Yb(3+)] (5) have been solved; they crystallize in the triclinic space P1 and are isomorphous. The [Fe(3+)-Sm(3+)] complex is a ferrimagnet, its magnetic studies suggesting the onset of weak ferromagnetic 3-D ordering at 3.5 K. The [Fe(3+)-Gd(3+)] interaction is weakly antiferromagnetic. The isotropic nature of Gd(3+) allowed us to evaluate the exchange interaction (J = 0.77 cm(-)(1)). 相似文献
57.
Dimitrakopoulou A Psycharis V Raptopoulou CP Terzis A Tangoulis V Kessissoglou DP 《Inorganic chemistry》2008,47(17):7608-7614
The reaction between Mn(ClO 4) 2 and di-(2-pyridyl)-ketone in the presence of the sodium salt of propanediol as a base in MeOH leads to the formation of a hexanuclear manganese cluster. This cluster has been characterized by the formula [Mn(II) 3Mn(III) 3O(OH)(CH 3pdol) 3(Hpdol) 3(pdol)](ClO 4) 4 ( 1). Molecular conductance measurements of a 10 (-3) M solution of compound 1 in CH 3CN, DMSO, or DMF give Lambda m = 529, 135, or 245 muS/cm, respectively, which suggests a 1:4 cation/anion electrolyte. The crystal structure of hexanuclear manganese cluster 1 consists of two distinct trinuclear units with a pseudocubane-like arrangement. The trinuclear units show two different valence distributions, Mn(II)/Mn(III)/Mn(II) and Mn(III)/Mn(II)/Mn(III). Additional features of interest for the compound include the fact that (a) two of the Mn(III) ions show a Jahn-Teller elongation, whereas the third ion shows a Jahn-Teller compression; (b) one bridge between Mn(III) atoms is an oxo (O (2-)) ion, whereas the bridge between Mn(II) and Mn(III) is a hydroxyl (OH (-)) group; and (c) the di-(2-pyridyl)-ketone ligand that is methanolyzed to methyl-Hpdol and R 2pdol (R = CH 3, H) acts in three different modes: methyl-pdol(-1), Hpdol(-1), and pdol(-2). For magnetic behavior, the general Hamiltonian formalism considers that (a) all of the interactions inside the two "cubanes" between Mn(II) and Mn(III) ions are equal to the J 1 constant, those between Mn(II) ions are equal to the J 2 constant, and those between the Mn(III) ions are equal to the J 3 constant and (b) the interaction between the two cubanes is equal to the J 4 constant. The fitting results are J 1 = J 2 = 0.7 cm (-1), J 3 approximately 0.0, J 4 = -6.2 cm (-1), and g = 2.0 (fixed). According to these results, the ground state is S = 1/2, and the next excited states are S = 3/2 and 5/2 at 0.7 and 1.8 cm (-1), respectively. The EPR spectra prove that the spin ground state at a low temperature is not purely S = 1/2 but is populated with the S = 3/2 state, which is in accordance with the susceptibility and magnetization measurements. 相似文献
58.
We show that every virtually torsion-free subgroup of the outer automorphism group of a conjugacy separable hyperbolic group
is residually finite. As a result, we are able to prove that the group of outer automorphisms of every finitely generated
Fuchsian group and of every free-by-finite group is residually finite. 相似文献
59.
Vassilis G. Papanicolaou Effie G. Papageorgiou Dimitris C. Lepipas 《Methodology and Computing in Applied Probability》2012,14(2):285-297
Consider a stochastic process that lives on n-semiaxes joined at the origin. On each ray it behaves as one dimensional Brownian Motion and at the origin it chooses a ray
uniformly at random (Kirchhoff condition). The principal results are the computation of the exit probabilities and certain
other probabilistic quantities regarding exit and occupation times. 相似文献
60.
Vassilis G. Papanicolaou 《Complex Analysis and Operator Theory》2016,10(6):1227-1265
For a general ordinary differential operator \(\mathcal {L}\) with periodic coefficients we prove that the characteristic polynomial of the Floquet matrix is irreducible over the field of meromorphic functions. We also consider a multipoint eigenvalue problem and show that its eigenspaces are spanned by pure or generalized Floquet solutions. Finally, at the end of the paper we mention some relevant conjectures and open questions. 相似文献