全文获取类型
收费全文 | 124篇 |
免费 | 0篇 |
专业分类
化学 | 43篇 |
力学 | 6篇 |
数学 | 28篇 |
物理学 | 47篇 |
出版年
2023年 | 1篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 6篇 |
2013年 | 10篇 |
2012年 | 13篇 |
2011年 | 3篇 |
2010年 | 5篇 |
2008年 | 6篇 |
2007年 | 6篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 10篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有124条查询结果,搜索用时 15 毫秒
71.
Christian Bellacanzone Mario Prosa Michele Muccini Giampiero Ruani Mirko Seri Margherita Bolognesi 《Particle & Particle Systems Characterization》2021,38(2):2000219
Aqueous suspensions of composite nanoparticles of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) are fabricated by miniemulsion method using three different ionic surfactants. The aim is to study how the length and conformation of the surfactants alkyl chains affect the properties of the nanoparticles. While the morphology and dimensions of the nanoparticles are similar, UV–vis spectroscopy evidences that the internal aggregation and ordering of the P3HT chains varies within the three nanoparticle formulations. The surfactant with branched alkyl chains promote the highest degree of ordering of P3HT chains in the nanoparticles (leading to increased conjugation length). In contrast, the lowest ordering is found for the nanoparticles with the surfactant having the shortest linear alkyl chain. The optical/structural properties of nanoparticles are partially retained in the films. Besides, the surfactant with branched alkyl chains favors the strongest coalescence of nanoparticles in the thin film, promoting a further ordering of the polymeric chains in the most external shell of the nanoparticles as evidenced by steady-state and time-resolved UV–vis spectroscopy and confocal fluorescence microscopy. These findings might guide the engineering of new surfactants for composite nanoparticles for optoelectronic applications. 相似文献
72.
Caira MR Bettinetti G Sorrenti M Catenacci L Cruickshank D Davies K 《Chemical communications (Cambridge, England)》2007,(12):1221-1223
The well-known, fourfold symmetry of the gamma-CD molecule in its solid inclusion complexes is lost on peracetylation, which yields a highly distorted host molecule in which self-inclusion of acetyl residues divides the macrocyclic cavity into two distinct sub-cavities that accommodate solvent molecules. 相似文献
73.
Continuous fine tuning of both chemistry and architecture of heterogeneous, isospecific MgCl2/TiCl4 catalyst systems for propene polymerization has led to a significant improvement in their performances in terms of activity, stereoselectivity, and capability to control both molecular parameters and morphology of the resulting polymers. As a result, a number of improved/innovative propene‐based products has recently been developed that clearly outperform the previously available materials. In particular, a family of reactor‐grade polymers has been synthesized including homopolymers and heterophasic copolymers offering, respectively, an unprecedented relationship between fluidity and stiffness and between stiffness and impact strenght, and supersoft polypropene alloys that could not have been achieved even via mechanical blending. 相似文献
74.
Luigi Cavallo Rosalisa Fedele Giampiero Morini Jean-Marie Ducéré Andrea Melchior Andrea Correa Fabrizio Piemontesi Marilena Tolazzi 《Macromolecular Symposia》2007,260(1):122-126
Calorimetric and computational investigation on the interaction of TiCl4 with some Lewis bases (esters and ethers) is presented. The bases were chosen for their relevance in heterogeneous Ziegler-Natta polymerization of propene. Comparison of the theoretical data with the calorimetric data indicates that calculations consistently underestimate the experimental binding energies. In light of this consistency, we propose that an empirical correction term added to the theoretical binding energies could represent an empirical solution for the prediction of the TiCl4/donor binding energies with reasonable accuracy. 相似文献
75.
Donato Bini Giampiero Esposito Andrea Geralico 《General Relativity and Gravitation》2012,44(2):467-490
Gravitational perturbations of the de Sitter spacetime are investigated using the Regge–Wheeler formalism. The set of perturbation
equations is reduced to a single second order differential equation of the Heun-type for both electric and magnetic multipoles.
The solution so obtained is used to study the deviation from an initially radial geodesic due to the perturbation. The spectral
properties of the perturbed metric are also analyzed. Finally, gauge- and tetrad-invariant first-order massless perturbations
of any spin are explored following the approach of Teukolsky. The existence of closed-form, i.e. Liouvillian, solutions to
the radial part of the Teukolsky master equation is discussed. 相似文献
76.
Ester Piedipalumbo Paolo Scudellaro Giampiero Esposito Claudio Rubano 《General Relativity and Gravitation》2012,44(10):2611-2643
We first study dark energy models with a minimally-coupled scalar field and generalized exponential potentials, admitting exact solutions for the cosmological equations: actually, it turns out that for this class of potentials the Einstein field equations exhibit alternative Lagrangians, and are completely integrable and separable. We analyze their analytical solutions, especially discussing when they are compatible with a late time quintessential expansion of the universe. As a further issue, we discuss how quintessential scalar fields with exponential potentials can be connected to the inflationary phase, building up a quintessential inflationary scenario: actually, it turns out that the transition from inflation toward late-time exponential quintessential tail admits a kination period, which is an indispensable ingredient of this kind of theoretical models. All such considerations have been made by including also radiation into the model. 相似文献
77.
Starting from the Boltzmann kinetic equations for a mixture of gas molecules whose internal structure is described by a discrete set of internal energy levels, hydrodynamic equations at Euler level are deduced by a consistent hydrodynamic limit in the presence of a two-scale collision process. The fast process driving evolution is constituted by mechanical encounters between particles of the same species, whereas inter-species scattering proceeds at the macroscopic scale. The resulting multi-temperature and multi-velocity fluid-dynamic equations are briefly commented on, and some results in closed analytical form are given for special simplified situations like Maxwellian collision kernels, or mono-atomic hard sphere gases. 相似文献
78.
Previous work in the literature had built a formalism for spatially averaged equations for the scale factor, giving rise to
an averaged Raychaudhuri equation and averaged Hamiltonian constraint, which involve a backreaction source term. The present
paper extends these equations to include models with variable Newton parameter and variable cosmological term, motivated by
the nonperturbative renormalization program for quantum gravity based upon the Einstein–Hilbert action. We focus on the Brans–Dicke
form of the renormalization-group improved action functional. The coupling between backreaction and spatially averaged three-dimensional
scalar curvature is found to survive, and a variable-G cosmic quintet is found to emerge. Interestingly, under suitable assumptions, an approximate solution can be found where
the early universe tends to a Friedmann–Lemaitre–Robertson–Walker model, while keeping track of the original inhomogeneities
through three effective fluids. The resulting qualitative picture is that of a universe consisting of baryons only, while
inhomogeneities average out to give rise to the full dark-side phenomenology. 相似文献
79.
Michele La Rocca Claudia Adduce Valentina Lombardi Giampiero Sciortino Reinhard Hinkelmann 《国际流体数值方法杂志》2012,70(8):1048-1072
In this paper the dynamics of a two‐layered liquid, made of two immiscible shallow‐layers of different density, has been investigated within the framework of the lattice Boltzmann method (LBM). The LBM developed in this paper for the two‐layered, shallow‐water flow has been obtained considering two separate sets of LBM equations, one for each layer. The coupling terms between the two sets have been defined as external forces, acted on one layer by the other. Results obtained from the LBM developed in this paper are compared with numerical results obtained solving the two‐layered, shallow‐water equations, with experimental and other numerical results published in literature. The results are interesting. First, the numerical results obtained by the LBM and by the shallow‐water model can be considered as equivalent. Second, the LBM developed in this paper is able to simulate motion conditions on nonflat topography. Third, the agreement between the LBM (and also shallow‐water model) numerical results and the experimental results is good when the evolution of the flow does not depend on the viscosity, that is, during the initial phase of the flow, dominated by gravity and inertia forces. When the viscous forces dominate the evolution of the flow the agreement between numerical and experimental results depends strongly on the viscosity; it is good if the numerical LBM viscosity has the same order of magnitude of the liquid's kinematic viscosity. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
80.
Thin deposits and patterning of room-temperature-switchable one-dimensional spin-crossover compounds
Cavallini M Bergenti I Milita S Kengne JC Gentili D Ruani G Salitros I Meded V Ruben M 《Langmuir : the ACS journal of surfaces and colloids》2011,27(7):4076-4081
We present a study on thin deposits and patterning of 1-D spin-crossover compounds Fe(II)-(L)(2)H](ClO(4))(3)·MeOH [L = 4'-(4'-pyridyl)-1,2':6'1'-bis- (pyrazolyl) pyridine] (1) that exhibit a reversible, thermally driven spin transition at room temperature. Micrometric rodlike crystals of 1 on silicon surfaces are achieved by drop casting and solvent annealing. We observed that the crystallinity of thin deposits and spin-transition properties critically depends on the deposition procedure. Furthermore, we proved processability and patterning using unconventional wet lithography that reduces the crystallite formation time by 1 order of magnitude. Thin deposits of 1 were characterized by atomic force microscopy, polarized optical microscopy and X-rays, and the switching properties were characterized by Raman spectroscopy. 相似文献