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71.
The structure of zamamistatin, a novel bromotyrosine derivative from the Okinawan sponge Pseudoceratina sp. was revised by comparison of the 13C NMR data of zamamistatin with those of synthetic model compounds. 相似文献
72.
Yasuhiro Mizobuchi Junji Shinjo Satoru Ogawa Tadao Takeno 《Proceedings of the Combustion Institute》2005,30(1):611-619
This paper presents a numerical study on the formation of diffusion flame islands in a hydrogen jet lifted flame. A real size hydrogen jet lifted flame is numerically simulated by the DNS approach over a period of about 0.5 ms. The diameter of hydrogen injector is 2 mm, and the injection velocity is 680 m/s. The lifted flame is composed of a stable leading edge flame, a vigorously turbulent inner rich premixed flame, and a number of outer diffusion flame islands. The relatively long-term observation makes it possible to understand in detail the time-dependent flame behavior in rather large time scales, which are as large as the time scale of the leading edge flame unsteadiness. From the observation, the following three findings are obtained concerning the formation of diffusion flame islands. (1) A thin oxygen diffusion layer is developed along the outer boundary of the lifted flame, where the diffusion flame islands burn in a rather flat shape. (2) When a diffusion flame island comes into contact with the fluctuating inner rich premixed flame, combustion is intensified due to an increase in the hydrogen supply by molecular diffusion. This process also works for the production of the diffusion flame islands in the oxygen diffusion layer. (3) When a large unburned gas volume penetrates into the leading edge flame, the structure of the leading edge flame changes. In this transformation process, a diffusion flame island comes near the leading edge flame. The local deficiency of oxygen plays an important role in this production process. 相似文献
73.
A numerical verification method to confirm the existence and local uniqueness of a double turning point for a radially symmetric solution of the perturbed Gelfand equation is presented. Using certain systems of equations corresponding to a double turning point, we derive a sufficient condition for its existence whose satisfaction can be verified computationally. We describe verification procedures and give a numerical example as a demonstration. 相似文献
74.
To observe spin polarization in nonmagnetic layers sandwiched by magnetic layers,119Sn Mössbauer spectra of [Co(20 Å)/Cu(20-x Å)/119Sn(1.5 Å)/Cu(x Å)] (x=0, 5 and 10) multilayers were measured. A magnetic fraction is observed in every spectrum, and the average hyperfine field ¯H
f at Sn nuclei in a Cu layer changes from 14 kOe (x=0) to 8 kOe (x=10). It was also observed that the polarization is greatly reduced by adding a Cr layer of only 2 Å to the Co/Cu interfaces. The spectrum of thex=10 film, measured under an external field of 30 kOe, cannot be interpreted without assuming magnetic fractions both in parallel and antiparallel to the external field, which indicates an oscillation of spin polarization in a Cu layer. 相似文献
75.
Teruya Shinjo 《Hyperfine Interactions》1994,90(1):159-170
Recent topics in multilayer studies are the giant magnetoresistance phenomena and interlayer exchange couplings between magnetic layers through non-magnetic intervening layers. Several measurements have been carried out concerning these problems, utilizing197Au,119Sn and57Fe as Mössbauer probes. In this article, experimental results are described and the use of Mössbauer spectroscopy for these problems is discussed. 相似文献
76.
Magnetic anisotropy of Fe/RE multilayers (RE=Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) was studied using 57Fe Mössbauer spectroscopy. Perpendicular magnetic anisotropy was observed in Fe/Pr, Fe/Nd, Fe/Tb, and Fe/Dy multilayers. The external field dependence of the direction of magnetic moments was also examined for Fe/Tb multilayers. The results imply that the perpendicular magnetic anisotropy originates from the single ionic anisotropy of RE at the interfaces. 相似文献
77.
The identification of the stage of ionization for various kinds of one-center electron repulsion integrals, occurring when nonbonding or lone-pair electrons are considered explicitly as well as π-electrons, is discussed for conjugated organic molecules containing heteroatoms N. It is concluded that the value for the negative ions should be used for (πCπC | πCπC) in all the states but for (πNπN | πNπN) only in the π-π states. In the n-π states, the appropriate value of (πNπN | πNπN) is that of the neutral atom if the molecule contains only one N atom. If more than one N atom is involved in the molecule, some weighted mean of the values for the negative ion and for the neutral atom should be used. The value for the neutral atom is most adequate for one-center repulsion integrals other than the (ππ | ππ) type in both the π-π and the n-π states. The method of determining these integrals is also discussed. It is concluded that they are to be determined from the consideration of appropriate electron-transfer reactions except for exchange integrals. The exchange integrals are shown to have to be determined from the Slater–Condon parameters derived from the analysis of the experimental atomic energy levels. Illustrative calculations are given for the lower singlet levels of the formaldehyde, pyrazine, pyridine, and the p-benzoquinone molecule. It is found that the calculated energies of the n-π transitions become much too low unless the (ππ | ππ) values of the heteroatoms in the molecule are chosen differently in the n-π states and in the π-π states as pointed out theoretically in this article. 相似文献
78.
Simulation of liquid jet primary breakup: Dynamics of ligament and droplet formation 总被引:6,自引:0,他引:6
Primary atomization of liquid injected at high speed into still air is investigated to elucidate physical processes by direct numerical simulation. With sufficient grid resolution, ligament and droplet formation can be captured in a physically sound way. Ligament formation is triggered by the liquid jet tip roll-up, and later ligaments are also produced from the disturbed liquid core surface in the upstream. Ligament production direction is affected by gas vortices. Disturbances are fed from the liquid jet tip toward upstream through vortices and droplet re-collision. When the local gas Weber number is O(1), ligaments are created, thus the ligament or droplet scale becomes smaller as the bulk Weber number increases. Observation of droplet formation from a ligament provides insights into the relevance between the actual droplet formation and pinch-off from a slow liquid jet in laboratory experiments. In the spray, the dominant mode is the short-wave mode driven by propagative capillary wave from the ligament tip. An injection nozzle that is necessary for a slow jet is absent for a ligament, thus the long-wave (Rayleigh) mode is basically not seen without the effect of stretch. By the present simulation, a series of physical processes have been revealed. The present result will be extended to LES modeling in the future. 相似文献
79.
Toshiaki Teruya 《Tetrahedron letters》2005,46(23):4001-4003
Novel 2-alkylpyridine alkaloids, phormidinines A (1) and B (2), were isolated from cyanobacterium Phormidium sp. Their structures were determined by spectroscopic analysis. The absolute stereochemistry of 1 was established by the modified Mosher’s method. 相似文献
80.
T. Shinjo S. Nasu T. Mizutani K. Shintaku N. Hosoito K. Matsukuma T. Takabatake 《Hyperfine Interactions》1990,55(1-4):1379-1386
Mössbauer absorption measurements were carried out for119Sn and57Fe impurities in La2CuO4, La1.85Sr0.15CuO4 and La1.6Sr0.4CuO4. For all cases,57Fe spectra at 4.2 K show magnetic hyperfine splittings. On the other hand, a magnetic hyperfine field at Sn nucleus is observed only in the case of La1.85Sr0.15CuO4. The results indicate that the Cu magnetic spins are collectively fluctuating in the superconducting sample. 相似文献