全文获取类型
收费全文 | 96篇 |
免费 | 0篇 |
专业分类
化学 | 63篇 |
晶体学 | 2篇 |
数学 | 3篇 |
物理学 | 28篇 |
出版年
2022年 | 2篇 |
2019年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2014年 | 3篇 |
2013年 | 4篇 |
2012年 | 1篇 |
2011年 | 2篇 |
2008年 | 1篇 |
2007年 | 4篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1968年 | 1篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1962年 | 2篇 |
1943年 | 2篇 |
1942年 | 1篇 |
1941年 | 2篇 |
1938年 | 2篇 |
1934年 | 3篇 |
1932年 | 2篇 |
1931年 | 4篇 |
1930年 | 1篇 |
排序方式: 共有96条查询结果,搜索用时 31 毫秒
1.
Sanchez-sanz M; Blyth MG 《The Quarterly Journal of Mechanics and Applied Mathematics》2007,60(2):125-138
Unsteady, axisymmetric stagnation flow about a circular cylinderis examined when the far-field flow is a periodic function oftime with a fixed time average and an oscillatory part of prescribedamplitude and frequency. Solutions are computed for arbitraryvalues of the Reynolds number, quantifying the effects of surfacecurvature, and a frequency parameter based on the period ofthe far-field flow. It is found that solutions remain regularand periodic provided that the far-field amplitude lies belowa critical value. Above this value, solutions terminate in afinite-time singularity. The blow-up time is delayed by increasingthe curvature of the surface. These results are corroboratedby asymptotic predictions valid in the limits of small and largeamplitude and frequency. For large Reynolds number, the problemreduces to the two-dimensional stagnation-point flow againsta plane wall studied by previous authors. 相似文献
2.
Pure crystalline samples of HTaO3 and DTaO3 have been prepared. The crystal structure has been solved using powder X-ray and neutron diffraction (at 2 K and room temperature) and has been shown to consist of Ta(O,OH)6 octahedra sharing vertices with the oxygen atoms displaced toward the vacant perovskite A sites. The compound is isomorphous with HNbO3, DxWO3, and DxReO3 and contains hydrogen atoms as hydroxide groups. 相似文献
3.
Brian Dickens 《Polymer Degradation and Stability》1980,2(4):249-268
Factor-jump thermogravimetry has been used to study the activation energy of polystyrene degrading in a vacuum, in N2 flowing at 4 mm/s and in mixtures. The results show the activation energy to be 44·9 ± 0·2 kcal/mole (188 ± 0·8 kJ/mole) for degradation above 350°C in vacuum or in flowing N2. This agrees well with work reported in 1949 by Jellinek7 but with few results reported subsequently.The apparent activation energy for polystyrene losing weight above 280°C in an atmosphere of abundant O2 is 21·5 ± 0·2 kcal/mole (90·2 ± 0·8 kJ/mole). In all cases where O2 was deliberately introduced (partial pressures >4 mm Hg), the sample degraded to a black tar and the activation energy was ≤30 kcal/mole, depending on the amount of oxygen present and on the thermal history of the sample. 相似文献
4.
The crystal structures of the apatites Ba10(PO4)6F2(I), Ba6La2Na2(PO4)6F2(II) and Ba4Nd3Na3(PO4)6F2 (III) have been determined by single-crystal X-ray diffraction. All three compounds crystallize in a hexagonal apatite-like structure. The unit cells and space groups are: I, a = 10.153(2), c = 7.733(1)Å, Å, ; III, a = 9.786(2), c = 7.281(1)Å, . The structures were refined by normal full-matrix crystallographic least squares techniques. The final values of the refinement indicators Rw and R are: I, Rw = 0.026, R = 0.027, 613 observed reflections; II, Rw = 0.081, R = 0.074, 579 observed reflections; III, Rw = 0.062, R = 0.044, 1262 observed reflections.In I, the Ba(1) atoms located in columns on threefold axes, are coordinated to nine oxygen atoms; the Ba(2) sites form triangles about the F site and are coordinated to six oxygen atoms and one fluoride ion. The fluoride ions are statistically displaced ~0.25 Å from the Ba(2) triangles. This displacement of the F ions is analogous to the displacement of OH ion in Ca10(PO4)6(OH)2.The structures of II and III contain disordered cations. In II there is disorder between La and Na in the column cation sites as well as triangle sites. In III, Nd and Na ions are ordered in the column sites, but there is disorder among Ba and the remaining Nd and Na ions in the triangle sites to give an average site population of . The coordination of the rare earth ions and Na ions in the ordered column sites are nine and six oxygens, respectively, in accord with the greater charge of the rare earth ions as compared with Na. The F ions in both II and III suffer from considerable disorder in position, and their locations are not precisely known. 相似文献
5.
P.G. Dickens 《Molecular physics》2013,111(2):206-211
A calculation of vibrational relaxation times in gaseous cyanogen at 300°K is presented. It is suggested that two well separated dispersion regions should be found in sound velocity measurements at ultrasonic frequencies, the higher frequency region being associated with the relaxation of the combined vibrational specific heat contributions of the two lowest modes and the lower frequency region being associated with the relaxation of the corresponding contribution of the next highest mode. 相似文献
6.
T.J. Dickens J. Breaux D.O. Olawale W.G. Sullivan O.I. Okoli 《Journal of luminescence》2012,132(7):1714-1719
This paper investigates the feasibility of using zinc sulfide manganese (ZnS:Mn) concentrated vinyl ester resin as a photon emitter for damage monitoring of polymer composites under flexural loading. Unreinforced vinyl ester resins doped with optical emitting materials (ZnS:Mn phosphors) in ratios of 5–50% by weight were cast, and subjected to flexural loading using standard 3-point bend tests. The intent of this work was to observe the transient response of triboluminescence (TL) throughout the failure cycle. Results indicate TL crystals emit light at various intensities corresponding to crystal concentration and imminent matrix fracture. Consequently, concentrated samples showed nearly 50% reductions of mechanical moduli. Scanning electron microscopy (SEM) revealed particulate inclusions with shearing bands and semblance of particle to resin adhesion. Despite significant parasitic effect to mechanical properties, the triboluminescent properties occur at yielding and point of matrix fracture. 相似文献
7.
S -nitrosothiols have many biological activities and may act as nitric oxide (NO) carriers and donors, prolonging NO half-life in vivo. In spite of their great potential as therapeutic agents, most S -nitrosothiols are too unstable to isolate. We have shown that the S -nitroso adduct of N -acetylcysteine (SNAC) can be synthesized directly in aqueous and polyethylene glycol (PEG) 400 matrix by using a reactive gaseous (NO/O2 ) mixture. Spectral monitoring of the S–N bond cleavage showed that SNAC, synthesized by this method, is relatively stable in nonbuf-fered aqueous solution at 25°C in the dark and that its stability is greatly increased in PEG matrix, resulting in a 28-fold decrease in its initial rate of thermal decomposition. Irradiation with UV light (λ= 333 nm) accelerated the rate of decomposition of SNAC to NO in both matrices, indicating that SNAC may find use for the photogeneration of NO. The quantum yield for SNAC decomposition decreased from 0.65 ± 0.15 in aqueous solution to 0.047 ± 0.005 in PEG 400 matrix. This increased stability in PEG matrix was assigned to a cage effect promoted by the PEG microenvironment that increases the rate of geminated radical pair recombination in the homolytic S–N bond cleavage process. This effect allowed for the storage of SNAC in PEG at −20°C in the dark for more than 10 weeks with negligible decomposition. Such stabilization may represent a viable option for the synthesis, storage and handling of S -nitrosothiol solutions for biomedical applications. 相似文献
8.
A weighted phonon frequency distribution has been measured in PbF2 at temperatures 10, 302, 660 and 910 K, using a neutron scattering technique. At 10 K good agreement is found between the measured distribution and the phonon density-of-states calculated from the low temperature dispersion relation of PbF2. At the higher temperatures, near the ionic conductivity transition temperature, Tc ~ 700 K, the optic modes are observed to broaden into a high energy tail consistent with strong anharmonicity or extensive disorder. A low energy peak arising from transverse acoustic modes remains well defined even at temperatures above Tc. 相似文献
9.
G. Thanheiser P. Dickens J. Kassler H. Laur und Erich Müller 《Fresenius' Journal of Analytical Chemistry》1934,99(3-4):142-144
Ohne Zusammenfassung 相似文献
10.
A new method for preparing 1H-1,2-benzodiazepines is described. Hydrazones of generalised structure 1 undergo base catalysed cyclisation to form 4-imidazolyl-4,5-dihydro-1H-1,2-benzodiazepines of general structure 2 . These compounds readily eliminate imidazole to form 1H-1,2-benzodiazepines of general structure 3 . 相似文献