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101.
Copolymerization of methyl vinyl ketone (MVK) with styrene was carried out at 50°C in the presence of cobalt(II) nitrate. The resulting monomer reactivity ratios decreased with an increasing concentration of the cobalt salt. This finding suggests that the metal salt participates in the propagation step of the copolymerization. Absolute copolymerization parameters were determined by assuming a three-component system as free MVK (M1), MVK complexed with cobalt(II) nitrate (M2), and styrene (M3): k11/k12 = 0.184, k11/k13 = 0.235, k22/k21 = 7.18 × 10−2, k22/k23 = 6.79 × 10−4, k33/k31 = 0.380, and k33/k32 = 2.77 × 10−3, and Q2 = 19.65 and e2 = 2.83. The complexed MVK monomer is more reactive to the polymer radical with the terminal styrene unit than the free MVK. Very small values for the monomer reactivity ratios, k22/k23 and k33/k32, show the marked alternating tendency for the copolymerization of the complexed monomer with styrene. In practice, however, alternating copolymer could not be obtained because of the poor solubility of cobalt(II) nitrate. 相似文献
102.
103.
K. Fujii T. Yoshizawa T. Ohyama K. Oto S. Takaoka K. Murase K. Gamo 《Superlattices and Microstructures》2000,27(5-6):353-357
In a vertically coupled dot, it is expected that generalized Kohn theorem is invalid. Then electron–electron interaction can be observed in far-infrared absorption. This interaction depends on the coupling between dots. We fabricated a vertically aligned double-dot array using a double heterostructure to investigate the coupling. The strength of the coupling depends on the confine potential of the dot. In far-infrared magneto-optical absorption measurements under pulsed photoexcitation, we observed peak shift of asymmetry states and increasing of absorption intensity of symmetry states of the dot. This is a result of the confined potential modulation by light. This indicates the possibility of optical control of the coupling. 相似文献
104.
S. Matsuki K. Shimomura I. Ogawa K. Suzuki S. Hamada T. Nakamura H. Okuno M. Koizumi N. Inabe Y. Fukashiro H. Sunaoshi M. Wada T. Murayama T. Kohmoto M. Kitano T. Kubo T. Shinozuka K. Asahi Y. Kido T. T. Inamura T. Nomura M. Ishihara M. Fujioka H. T. Duong H. Haas 《Hyperfine Interactions》1992,74(1-4):223-239
Radiation-detected optical pumping in solids has been developed to investigate the structure of unstable nuclei. Appreciable
nuclear polarization of implanted or doped unstable-nuclei in a host crystal is achieved with the optical pumping in solids.
The nuclear polarization achieved is enhanced/reduced by applying a radio-frequency magnetic field together with the optical
pumping, radiation-detected magnetic resonance being thus observed to get information on electromagnetic properties of unstable
nuclei. Two schemes have been successfully developed for the optical pumping of unstable nuclei in solids. One is to directly
pump the atoms by the excitation from the ground state to a broad absorption band in visible and UV regions which shows a
large magnetic circular dichroism. This scheme is applicable to many rare-earth atoms in alkaline-earth fluoride host. The
other scheme is to pump the electrons in the conduction band of direct-type semiconductor and thus indirectly polarize the
nuclei in the host material via a hyperfine interaction between the nuclei and the polarized conduction electrons. This scheme
can be especially applied to the III to VI families of atoms in direct-type semiconductors. Principle of the methods, on-line
experimental system, and a few examples of the results obtained so far are presented and discussed. 相似文献
105.
106.
107.
Fabrication of a carbon nanotube device using a patterned electrode and a local electric field 总被引:1,自引:0,他引:1
Fujio Wakaya Jun Takaoka Kiyofumi Fukuzumi Mikio Takai Yoichi Akasaka Kenji Gamo 《Superlattices and Microstructures》2003,34(3-6):401
Suspensions of carbon nanotubes (CNTs) and organic solvent were dropped onto a substrate which had patterned electrodes while applying a DC voltage between the electrodes. Both multiwall and single-wall (SW) CNTs were purified from the mixture of CNTs and the undesirable particles of carbon when the solvent dichloromethane was used at high temperature. It is found that a SW CNT bridges the gap of the electrodes. This enables us to fabricate CNT devices at a controlled position. 相似文献
108.
W. Sato H. Ueno H. Watanabe H. Ogawa H. Miyoshi N. Imai A. Yoshimi K. Yoneda D. Kameda Y. Kobayashi K. Asahi 《Journal of Radioanalytical and Nuclear Chemistry》2003,255(1):183-186
A new 19F probe disintegrated from short-lived 19O has been developed for the first time for time-differential perturbed angular correlation method. The angular correlation coefficient for the relevant cascade has been experimentally estimated to be A22 = -0.17±0.01. As the first application of this technique to condensed matter physics, the probe was implanted in polycrystalline fullerene C60. We have observed two contrastive perturbations acting on the probe nuclei, which reflect electrostatic and dynamic interactions with the extranuclear field. 相似文献
109.
Takaoka LR Buckmelter AJ LaCruz TE Rychnovsky SD 《Journal of the American Chemical Society》2005,127(2):528-529
A synthesis of spiroacetals was developed using a reductive cyclization strategy that leads stereoselectively to spiroacetals with a single anomeric stabilization. The method begins with the synthesis of spiro ortho esters. The ortho ester is converted to a cyano acetal. Reductive lithiation of the cyano acetal generates an axial dialkoxylithium reagent, and intramolecular cyclization produces a new ring with retention of configuration. The strategy is convergent and produces complex spiro acetals in only a few steps. The method will be useful in the synthesis of natural products and will facilitate the synthesis of previously inaccessible contra-thermodynamic acetals. 相似文献
110.
The reaction of trifluoropyruvic acid hydrate with urea derivatives affords 5-hydroxy-5-trifluoromethylhydantoin derivatives in good yield. The product orientation is consistent with the initial attack on the most active center, in trifluoropyruvic acid hydrate, towards nucleophiles 相似文献