全文获取类型
收费全文 | 103篇 |
免费 | 1篇 |
专业分类
化学 | 65篇 |
力学 | 4篇 |
数学 | 18篇 |
物理学 | 17篇 |
出版年
2021年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 9篇 |
2012年 | 5篇 |
2011年 | 8篇 |
2010年 | 5篇 |
2009年 | 6篇 |
2008年 | 4篇 |
2007年 | 8篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有104条查询结果,搜索用时 78 毫秒
11.
Corneliu Balan 《Continuum Mechanics and Thermodynamics》2001,13(6):399-414
Received March 25, 2001 / Published online November 15, 2001 相似文献
12.
Marian Vîrgolici Corneliu Ponta Mihaela Manea Daniel Neguţ Mihalis Cutrubinis Ioan Moise Rareş Şuvăilă Eugen Teodor Costel Sârbu Andrei Medvedovici 《Journal of chromatography. A》2010,1217(12):1977-1987
Research on the chemical composition of fossil resins has evolved during the last decades as a multidisciplinary field and is strongly oriented toward the correlation with their geological and botanical origin. Various extraction procedures and chromatographic techniques have been used together for identifying the volatile compounds contained in the fossil resin matrix. Hyphenation between thermal desorption (TD), gas chromatography (GC) and mass spectrometry detection (MS) has been chosen to investigate the volatile compounds fraction from ambers with a focus on Romanite (Romanian amber) and Baltic amber species. A data analysis procedure was developed for the main purpose of fingerprinting ambers based on the MS identity of the peaks generated by the volatile fraction, together with their relative percentual area within the chromatogram. Chromatographic data analysis was based entirely on Automated Mass Spectral Deconvolution & Identification System (AMDIS) software to produce deconvoluted mass spectra which were used to build-up a mixed mass spectra and relative retention scale library. Multivariate data analysis was further applied on AMDIS results with successful discrimination between Romanite and Baltic ambers. A special trial was conducted to generate pyrolysis “like” macromolecular structure breakdown to volatile compounds by gamma irradiation with a high absorbed dose of 500 kGy. Contrary to our expectations the volatile fraction fingerprints were not modified after irradiation experiments. A complementary non-destructive new approach by ESR spectroscopy was also proposed for discriminating between Romanite and Baltic ambers. 相似文献
13.
14.
15.
Corneliu I. Oprea Fanica Cimpoesu Petre Panait Bogdan Frecuş Marilena Ferbinteanu Mihai A. Gîrţu 《Theoretical chemistry accounts》2011,129(6):847-857
We report the first band structure calculations of the quasi-one-dimensional [MnTPP][TCNE] compounds (TPP = meso-tetraphenylporphyrinato, TCNE = tetracyanoethylene), based on Density Functional Theory (DFT) methods, in order to interpret
the magnetic ordering in these prototypic systems. We compare and contrast the results of broken-symmetry DFT calculations
for extended systems, with periodic boundary conditions, and for finite systems, magnetic dimers modeling the actual molecular
magnets. By varying systematically the main angles, we are able to determine the geometry dependence of the exchange interaction.
Structure–properties correlations in these charge-transfer salts reveal the determinant role of the Mn-(N≡C)TCNE bond angle on the strength of the ferrimagnetic coupling between the S
1 = 2 spin located on the MnIII-porphyrin donor and the S
2 = 1/2 spin positioned on the cyanocarbon acceptor. When the Mn-(N≡C)TCNE angle is decreased, the intrachain magnetic coupling strengthens, correlated with the increase in the dz2 - p* d_{{z^{2} }} - \pi * orbital overlap. The exchange coupling constants resulting from DFT calculations of extended systems, with periodic boundary
conditions, were found to be consistent with those obtained for the dimers, but systematically smaller. The exchange constants
vary strongly with the functional used, hybrid functionals such as B3LYP leading to results that better correlate with the
experimental mean-field critical temperatures. The coupling constant varies significantly with the type of broken-symmetry
approach, depending on the overlap between magnetic orbitals, but weakly on the basis set once polarization effects are included.
The electronic structure calculations for the extended systems provide a density of states consistent with the energy spectrum
of the corresponding dimer, allowing for an intuitive explanation of the intrachain ferrimagnetic ordering. 相似文献
16.
Maria Bruma Corneliu Hamciuc Elena Hamciuc Frank Mercer Nataliya Belomoina Burkhard Schulz 《Macromolecular Symposia》1997,122(1):303-311
New heterocyclic polyamides have been synthesized by solution polycondensation of aromatic diamines containing phenylquinoxaline units with diacid chlorides having both imide and hexafluoroisopropylidene (6F) groups. These polymers are soluble in polar aprotic solvents, such as N-methylpyrrolidone (NMP) or N, N-dimethylformamide (DMF), and can be cast into flexible thin films from solutions. They show high thermooxidative stability with decomposition temperatures above 400°C and glass transition temperatures in the range of 225-300°C. The polymer films exhibit good chemical resistance towards diluted acids and good electrical insulating properties with dielectric constants in the range of 3.2–3.7. 相似文献
17.
A novel series of nitrile-containing polyimide-polydimethylsiloxane copolymers was prepared by polycondensation reaction of 4,4′-oxydiphthalic anhydride with a mixture of an aromatic diamine, namely 2,6-bis(3-aminophenoxy)benzonitrile, and bis(aminopropyl)oligodimethylsiloxane of controlled molecular weight, in different ratios. The polymers were easily soluble in polar organic solvents, such as N-methylpyrrolidone, N,N-dimethylformamide as well as in less polar solvents such as chloroform, and can be cast from solution into thin flexible films. The inherent viscosity was in the range of 0.43-0.55 dL/g. The polymers showed good thermal stability, the decomposition temperature being above 430 °C. They exhibited a glass transition temperature in the range of 149-219 °C, with reasonable interval between glass transition temperature and decomposition temperature. The surface morphology was investigated by scanning electron microscopy. The water dynamic contact angles were measured by tensiometric method. The free surface energy was evaluated based on Owens and Wendt equation. A composite film based on a polyimide-polydimethylsiloxane copolymer and pyrite ash powder has been prepared and its nanoactuation has been investigated. 相似文献
18.
Mihaela M. ManeaIoan V. Moise Marian VirgoliciConstantin D. Negut Olimpia-Hinamatsuri BarbuMihalis Cutrubinis Viorel FugaruIoana R. Stanculescu Corneliu C. Ponta 《Radiation Physics and Chemistry》2012,81(2):160-167
The degradation of cultural heritage objects by insects and microorganisms is an important issue for conservators, art specialists and humankind in general. Gamma irradiation is an efficient method of polychrome wooden artifacts disinfestation. Color changes and other modifications in the physical chemical properties of materials induced by gamma irradiation are feared by cultural heritage responsible committees and they have to be evaluated objectively and precisely. In this paper FTIR and FT-Raman spectroscopy methods were used to investigate the structural changes in some experimental models of tempera paint layers on wood following 11 kGy gamma irradiation at two dose rates. Radiation chemistry depends on the particular pigment, matrix formed by protein, resin (in case of varnished samples) and water presence. For the majority of painted layer in experimental models very small spectral variations were observed. Small changes in the FTIR spectra were observed for the raw sienna experimental model: for the higher dose rate the egg yolk protein oxidation peaks and the CH stretching bands due to lipids degradation products increased. 相似文献
19.
In this work we study a version of the three constant differential-type Oldroyd constitutive relation which allows distinct objective time derivatives for the extra stress and the stretching. We integrate the constitutive equation and determine an equivalent history integral representation for this model for the general class of viscometric motions. For certain choices of the material parameters and initial conditions, we find that this model allows for the development of shear rate discontinuities in the flow domain as a steady viscometric flow is achieved. Correspondingly, we also give evidence that intense shear rate oscillations may occur during the transient period as an impulsively started viscometric flow in a channel tends to a steady state under a constant critical shear stress. This critical shear stress lies in an interval of values for which the material experiences the phenomenon of “flow yielding”. A qualitative comparison with experimental data is made for certain creams and greases. The material instabilities inherent in this constitutive theory for viscometric motions are suggestive of the instabilities that occur in many viscoelastic fluids such as sharkskin patterns, wavy fracture, and spurt flow. 相似文献
20.
Corneliu Ciubotariu Carmen-Iuliana Ciubotariu Ciprian Ciubotariu 《General Relativity and Gravitation》1995,27(2):129-141
We show that it is possible, by a suitable choice of metrics and connections, to construct for a wide class of relativistic equations of motion a geometry wherein the interacting particles become free of nongravitational forces and move on autoparallels. Some examples prove the consistency of this extended geodesic principle. 相似文献