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41.
Noboru Kimizuka Motohiko Ishii Isao Kawada Masanobu Saeki Mitsuoki Nakahira 《Journal of solid state chemistry》1974,9(1):69-77
The effects of nonstoichiometry upon the behavior of vanadium dioxide single crystals in the vicinity of the semiconductor/metal transition temperature (Tc) were experimentally investigated. According to the electrical and thermal measurements, more stoichiometric vanadium dioxide exhibited the less electrical conductivity gap, the larger thermal and electrical hysteresis, and the lower transition temperature than the increased nonstoichiometric one near transition. Infrared absorptions and X-ray observations indicated the local and overall lattice distortion in the nonstoichiometric crystal due to the existence of V5+ ions. Furthermore, an intermediate phase between the low-temperature monoclinic and the high-temperature tetragonal phases was found in the nonstoichiometric VO2. On the other hand, no evidence for this intermediate phase was found in the stoichiometric one. Finally, some comparisons and discussions of our present data with the previously published ones were made. 相似文献
42.
Cornella I Pérez Sestelo J Mouriño A Sarandeses LA 《The Journal of organic chemistry》2002,67(14):4707-4714
A novel convergent synthetic approach to new analogues of calcitriol modified at the C-18 position is reported. The key step in the synthesis is the 20-hydroxyl-directed photochemical iodination of the 18-methyl group in the presence of (diacetoxyiodo)benzene. Using this methodology, two new analogues of calcitriol were prepared: the first contains a hydroxylated alkyl side chain attached at C-18 with the natural side chain replaced by an isopropylidene group; the second is a conformationally locked analogue due to an extra oxacycle between the C-18 and C-20 positions. 相似文献
43.
The T1,2 ← S0 spectra of benzaldehydes have been studied as a function of the energy separation between the vibrationless levels. It is shown that the spectra are very complicated in the region of ΔE[T20(nπ*)-T10(ππ*)] = 250–400 cm−1, reflecting effective vibronic interferences between T20(0-0) and each of the ν36-ν33 out-of-plane vibrational levels of T10(ππ*). The simulated spectra correspond to the observed spectra. In the case of T10 = 3nπ* and T20 = 3ππ* the spectral change is not so drastic as in the reverse case loc. cit. because the optical intensity generally concentrates in the longest wavelength band, i.e., the origin band of the T1(nπ*) ← S0 transition. The simulation spectra are useful for interpretation of the absorption spectra in similar electronic structure systems of substituted benzaldehydes. 相似文献
44.
T1 ← S0 absorption and T1 → S0 phosphorescence spectra of neat cystalline hexachloroacetone have been analyzed at 4.2°K. From the lifetime and energy the upper state is assigned as 3nπ*. The spectra are sharp compared to other aliphatic ketones, with the 0-0 band at 26 248 ± 2 cm ?1. The phosphorescence shows two strong progressions; one involving the CO stretching mode at 1784 cm?1 (x), the other a long progression of at least 8 bands involving a mode at 143 cmt-1 (a). The 143 cm?1 progression forming mode can best be asigned to the CO out-of-plane wagging vibration. The absorption shows the same two strong progressions, reduced in frequency to 1270 cmt-1 and 123 cm?1, respectively, but with the progression in mode a broadened with increasing n. The broadening is interpreted as arising from inversion doublets; the close harmonicity up to n = 5 allowing the potential barrier to inversion to be estimated as > 700 cm?1. A feature of the spectra is the absence of low frequency torsional modes suggesting lack of pseudo Jahn-Teller distortion of the triplet state potential surface. For comparison, the phosphorescence of crystalline hexafluoroacetone was also studied at 4.2°K. The spectrum exhibits broad bandedness with a 00 band tentatively assigned at 26 870 ± 20 cm?1. 相似文献
45.
Shuhei Yamada Emiko Mouri Kohji Yoshinaga 《Journal of polymer science. Part A, Polymer chemistry》2011,49(3):712-718
We report a novel strategy for incorporation of titanium dioxide (TiO2) particles into poly(methyl methacrylate) (PMMA) to exploit high refractive and transparent organic–inorganic hybrid materials. Formation of TiO2 particles of around 20 nm was conducted within hydrophilic core of block copolymer micelles of poly(methyl methacrylate‐block‐acrylic acid) (PMMA‐b‐PAA) in toluene via sol–gel process from titanium isopropoxide and hydrochloric acid. Subsequently, incorporation of TiO2 particles into PMMA matrix was carried out by casting toluene solution of TiO2 precursor‐loaded copolymer micelles, prepared from PMMA350‐b‐PAA93 and the precursor of mole ratio Ti4+/carboxyl 4.0, and PMMA. Hybrid films of TiO2/PMMA exhibited high transparency to achieve transmission over 87% at 500 nm at 30 wt % of TiO2 content. The refractive index of resulting hybrid films at 633 nm linearly increased with TiO2 content to attain 1.579 at 30 wt % TiO2, which was 0.1 higher than that of PMMA. Cross‐sectional transmission electron microscope images of TiO2/PMMA hybrid films showed existence of TiO2 clusters less than 100 nm, which were probably formed by aggregation or agglutination of TiO2 particles during a drying process. It was also observed that decomposition temperature of the hybrid films elevated with increasing TiO2 content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
46.
S. Mouri N. Ould Moussa G. Molnr J.A. Real A.B. Gaspar A. Bousseksou K. Tanaka 《Chemical physics letters》2008,456(4-6):215-219
A photo-magnetic effect is evidenced using near-infrared light in the binuclear complex [Fe(bpym)(NCS)2]2(bpym). This compound has a 5T2g–5T2g ground state and exhibits no thermal spin crossover – in contrast to the analogous [Fe(bpym)(NCSe)2]2(bpym). The estimated photo-conversion ratio is ca. 30%. By means of magnetic susceptibility measurements as well as Raman and infrared absorption spectroscopies, the nature of the photo-induced phase was established as the 5T2g–1A1g state, which means that only one iron center is converted to low-spin. The photo-induced state was completely converted back to the ground state either by visible light excitation or by heating. 相似文献
47.
Zhiguo Ma Miwa Watanabe Emiko Mouri Kohji Yoshinaga 《Colloid and polymer science》2010,288(5):519-525
Colloidal crystallization of copolymer-grafted silica containing ferrocenyl groups in organic solvents and effects of ferrocenyl
groups on effective refractive index of colloidal crystal systems were investigated. Poly(ferrocenyl metharylate (FeMA)-co-methyl methacrylate (MMA)-grafted silica gave colloidal crystallization in dimethylformamide and acetonitrile. The colloidal
crystals exhibited characteristic coloration due to cooperative effects of specific absorption at 400–500 nm by ferrocenyl
group and transmission of 700–800-nm light through the crystals. It was observed that effective refractive index of colloidal
crystals systems of poly(FeMA-co-MMA)-grafted silica was higher than that of poly(MMA)-grafted silica. Normalized effective refractive index of the system
linearly increased with mole fraction of FeMA in grafted copolymer. However, poly(FeMA-block-MMA) did not bring effective increase of the index because of bias formation of ferrocenyl group on silica. 相似文献
48.
Diego M. Carballa Antonio Rumbo Mercedes Torneiro Miguel Maestro Antonio Mouriño 《Helvetica chimica acta》2012,95(10):1842-1850
A convergent synthesis of an analogue of (1α)‐1,25‐dihydroxyvitamin D3 ( 1b ) with a C7 side chain at C(12), i.e., of 5 (Fig.), is described. A key step of the synthesis is the assembly of the triene system by a PdII‐catalyzed ring closure of an enol triflate (‘bottom’ fragment) followed by coupling of the resulting PdII intermediate with an alkenylboronate (‘upper’ fragment) (Scheme 2). The synthetic strategy allows isotopic labelling at the end of the synthesis. 相似文献
49.
Catalytic asymmetric conjugate addition of nitroalkanes to α,β-unsaturated thioamides is promoted by a mesitylcopper/(R)-DTBM-Segphos precatalyst, affording γ-nitrothioamides in moderate to high syn-selectivity and excellent enantioselectivity. The intermediate Cu-thioamide enolate functions as a soft Lewis acid/hard Br?nsted base cooperative catalyst to drive the catalytic cycle efficiently under proton transfer conditions. 相似文献
50.
Ezawa M 《Physical review letters》2010,105(19):197202
Motivated by a recent magnetization reversal experiment on a TbFeCo thin film, we study a topological excitation in the anisotropic nonlinear sigma model together with the Zeeman and magnetic dipole-dipole interactions. Dipole-dipole interactions turn a ferromagnet into a frustrated spin system, which allows a nontrivial spin texture such as a giant Skyrmion. We derive an analytic formula for the Skyrmion radius. The radius is controllable by the external magnetic field. It is intriguing that a Skyrmion may have already been observed as a magnetic domain. A salient feature is that a single Skyrmion can be created or destroyed experimentally. An analysis is made also on Skyrmions in chiral magnets. 相似文献