全文获取类型
收费全文 | 356篇 |
免费 | 13篇 |
国内免费 | 1篇 |
专业分类
化学 | 277篇 |
力学 | 5篇 |
数学 | 59篇 |
物理学 | 29篇 |
出版年
2022年 | 3篇 |
2021年 | 19篇 |
2020年 | 8篇 |
2019年 | 12篇 |
2018年 | 4篇 |
2017年 | 11篇 |
2016年 | 20篇 |
2015年 | 3篇 |
2014年 | 15篇 |
2013年 | 42篇 |
2012年 | 23篇 |
2011年 | 17篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 22篇 |
2007年 | 15篇 |
2006年 | 20篇 |
2005年 | 17篇 |
2004年 | 16篇 |
2003年 | 16篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1972年 | 1篇 |
1968年 | 1篇 |
1958年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有370条查询结果,搜索用时 218 毫秒
51.
Riassunto In questo lavoro ci occupiamo di problemi al contorno per una classe di operatori lineari quasi ellittici del tipoA+σ, dove σ è una perturbazione assegnata; proviamo che l'operatore associato al problema è di Fredholm con indice zero e studiamo
le proprietà spettrali dell'operatore associato al problema con condizioni al contorno omogenee.
Lavoro eseguito nell'Istituto di Scienze dell'Informazione dell'Università di Salerno, nell'ambito del Gruppo Nazionale per l'Analisi Funzionale e le sue Applicazioni del C.N.R. 相似文献
Summary In this paper we study boundary value problems for linear quasi elliptic (A+σ)-type operators, where σ is an assigned perturbation; we prove that the related operator is a Fredholm operator whose index is zero. Then we study spectral properties of the operator related to the problem with homogeneous boundary conditions.
Lavoro eseguito nell'Istituto di Scienze dell'Informazione dell'Università di Salerno, nell'ambito del Gruppo Nazionale per l'Analisi Funzionale e le sue Applicazioni del C.N.R. 相似文献
52.
J. Solla-Gullón Elvira Gómez Elisa Vallés Antonio Aldaz Juan M. Feliu 《Journal of nanoparticle research》2010,12(4):1149-1159
PtCo nanoparticles with homogeneous size (around 3–4 nm) have been synthesized in a water-in-oil microemulsion of water/polyethylenglycol–dodecylether (BRIJ®30)/n-heptane. X-ray diffraction study revealed the formation of a cubic phase with a gradual decrease of the cell parameter with increasing cobalt incorporation in the crystalline lattice of platinum. In relation to their magnetic properties, the PtCo nanoparticles present a superparamagnetic behaviour even after annealing, although higher permeability was induced by the thermal treatment. Finally, the electrocatalytic activity of the particles towards oxalic acid oxidation in H2SO4 was evaluated. The Pt74Co26 nanoparticles showed the highest reactivity for this reaction. 相似文献
53.
Khomich E Kashapov M Vatsouro I Shokova E Kovalev V 《Organic & biomolecular chemistry》2006,4(8):1555-1560
Herein we report on the synthesis and ionophore properties of the first asymmetric p-tert-butylcalix[4]-p-R-thiacalix[4]tubes 7a-c (R = t-Bu, H, 1-adamantyl). The target compounds were obtained by the condensation of tosyloxyethoxy-p-tert-butylcalix[4]arene with the corresponding p-R-thiacalix[4]arenes in the presence of K2CO3 in acetonitrile. The complexation with sodium, potassium and rubidium iodides was studied in CDCl3-CD3OD (4:1) medium by means of 1H NMR measurements. It was found that the ionophore properties of calixtubes 7a-c are controlled by the character of the substituents at the upper rim of the thiacalix[4]arene fragment and it was shown that only the molecular tube 7c with an adamantane-containing thiacalixarene unit is capable of quantitatively binding potassium (swiftly) and rubidium (slowly) cations. 相似文献
54.
Elvira Barbera Carmela Currò Giovanna Valenti 《Mathematical Methods in the Applied Sciences》2010,33(12):1504-1515
A hyperbolic predator–prey model is proposed within the context of extended thermodynamics. The nature of the steady state solutions for the uniform and non‐uniform perturbations are analyzed. The existence of smooth traveling wave‐like solutions, related to the invasion of the predator population into a prey‐only state is discussed. Validation of the model in point is also accomplished by searching for numerical solutions of the system, which also points out limit cycles in the populations. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
55.
Shakurova Elvira R. Salimova Elena V. Mescheryakova Ekaterina S. Parfenova Lyudmila V. 《Chemistry of Heterocyclic Compounds》2019,55(12):1204-1210
Chemistry of Heterocyclic Compounds - An efficient one-pot method was developed for the preparation of quaternary pyridinium salts and tetrahydropyridine derivatives of fusidane triterpenoids,... 相似文献
56.
Maria A. Simonova Elvira V. Tarasova Marina M. Dudkina Andrey V. Tenkovtsev Alexander P. Filippov 《International Journal of Polymer Analysis and Characterization》2019,24(1):87-95
Properties of individual molecules of star-like polystyrene with calix[8]arene core in dilute chloroform solutions were studied using methods of static light scattering, translation diffusion, and viscometry. The solution behavior of the polymer investigated significantly differs from the properties of linear polymers. Star-like polystyrene macromolecules in solutions are characterized by compact structure—the hydrodynamic radius is not higher than 5.5?nm at M?=?125,000?g?mol?1. The shape of star-like polystyrene macromolecules differs slightly from spherical. 相似文献
57.
Effect of annealing on the properties of N-doped ZnO films deposited by RF magnetron sputtering 总被引:1,自引:0,他引:1
Jinzhong Wang Elangovan Elamurugu François Jomard Ana M. Botelho do Rego Gonçalo Gonçalves Elvira Fortunato 《Applied Surface Science》2008,254(22):7178-7182
N-doped ZnO films were deposited by RF magnetron sputtering in N2/Ar gas mixture and were post-annealed at different temperatures (Ta) ranging from 400 to 800 °C in O2 gas at atmospheric pressure. The as-deposited and post-annealed films were characterized by their structural (XRD), compositional (SIMS, XPS), optical (UV-vis-NIR spectrometry), electrical (Hall measurements), and optoelectronic properties (PL spectra). The XRD results authenticate the improvement of crystallinity following post-annealing. The weak intensity of the (0 0 2) reflection obtained for the as-deposited N-doped ZnO films was increased with the increasing Ta to become the preferred orientation at higher Ta (800 °C). The amount of N-concentration and the chemical states of N element in ZnO films were changed with the Ta, especially above 400 °C. The average visible transmittance (400-800 nm) of the as-deposited films (26%) was increased with the increasing Ta to reach a maximum of 75% at 600 °C but then decreased. In the PL spectra, A0X emission at 3.321 eV was observed for Ta = 400 °C besides the main D0X emission. The intensity of the A0X emission was decreased with the increasing Ta whereas D0X emission became sharper and more optical emission centers were observed when Ta is increased above 400 °C. 相似文献
58.
Lidiya I. Kursheva Olga N. Kataeva Dmitry B. Krivolapov Aidar T. Gubaidullin Elvira S. Batyeva Oleg G. Sinyashin 《Heteroatom Chemistry》2008,19(5):483-489
Some Cu(I) halides complexes based on P(III) acid esters,{[(RE)3PCuBr] (where E = O, N, S); R = n‐Pr, i‐Pr, Et2N} were obtained and characterized using IR, 31P NMR spectroscopy, and single crystal X‐ray diffraction. The comparative structural characteristics of complexes with various donor atoms (E = O, N, S) are analyzed. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:483–489, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20459 相似文献
59.
Dual stimuli‐responsive polyamines derived from modified N‐vinylpyrrolidones through CuAAC click chemistry 下载免费PDF全文
Anselmo del Prado Rodrigo Navarro Pavel Levkin Alberto Gallardo Carlos Elvira Helmut Reinecke 《Journal of polymer science. Part A, Polymer chemistry》2016,54(8):1098-1108
The synthesis via copper(I)‐catalyzed azide alkyne cycloaddition (CuAAC) of three new monomer derivatives of N‐vinyl‐2‐pyrrolidone (VP) carrying cyclic pyrrolidine, piperidine, and piperazine groups and the corresponding copolymers with unmodified VP is shown. The systems bearing pyrrolidine and piperidine displayed both thermo‐ and pH‐response, which has not been reported previously for a polymer with polyvinylpyrrolidone (PVP) backbone. A broad modulation of the LCST with the copolymer composition and pH was observed in a temperature range 0–100 °C. The polymers carrying piperazine exhibited broad buffering regions and no thermosensitivity. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1098–1108 相似文献
60.
We report molecular dynamics simulation results of equilibrium and dynamical characteristics pertaining to the solvation of the dye coumarin 153 (C153) trapped within hydrophobic cavities of di- and trimethylated beta-cyclodextrins (CD) in aqueous solutions. We found that stable configurations of the encapsulated probe are characterized by a slanted docking, in which the plane of the C153 lies mostly parallel to one of the glucose units of the CD. "In and out" dynamical modes of the encapsulated probe present very small amplitudes. The rotational dynamics of the trapped coumarin can be cast in terms of a simple model that includes diffusive motions within a local restrictive environment coupled to the overall rotational motion of the CD. We have examined the early stages of the solvation response of the environment following a vertical excitation of the probe. Regardless of the degree of CD methylation, the water dynamical response seems to be completed within 2-3 ps and does not differ substantially from that observed for nonencapsulated probes. The CD response is characterized by a single, subpicosecond relaxation that involves intramolecular motions. We also explored dynamical modes that could account for the recently reported persistence of Stokes shifts in the nanosecond time domain. In all cases, the only sources of ultraslow dynamics that we detected were those associated with gauche-trans interconversions in primary hydroxyl chains of the CD, which do not seem to be directly connected to the electronic excitation of the probe. 相似文献