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71.
The magnetic hyperfine structure of atoms is studied. A new compact expression is introduced for the magnetic hyperfine anomaly. A theoretical foundation is given for an empirical formula discovered by Moskowitz and Lombardi. The effects of core polarization and mesonic exchange currents are discussed. There are two kinds of core polarization, Δl = 0 and Δl = 2. The latter is shown to be important to explain certain isotope shifts, though it is smaller than the former Δl = 0 effect. 相似文献
72.
73.
Tsutomu Kagiya Takehisa Matsuda Masanori Nakato Ryuichi Hirata 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):1631-1652
Abstract In order to elucidate the structure and the stability of the growing cationic end in the polymerization of 2-oxazolines, the reactions of 2-bromoethylbenzamide with silver salts such as silver perchlorate, tetrafluoroborate, nitrate, nitrite, cyanate, and acetate were investigated. The reactions with silver perchlorate and tetrafluoroborate gave the 2-phenyl-2-oxazolinium salt (intramolecular O-alkylation product) quantitatively, whereas the reaction with silver nitrate gave the corresponding alkyl nitrate (staight-chain product). For the reactions with silver nitrite, cyanate and acetate, both products were obtained. In order to elucidate the ring-opening reactivity of the oxazolinium cation, the ring-opening addition reaction of N-methyl-2-oxazolinium perchlorates with pyridine was investigated. It was found that N-methyl-2-phenyl-2-oxazolinium perchlorate was more reactive toward the nucleophilic ring-opening reaction than was N-methyl-2-methyl-2-oxazolinium perchlorate. The mutual copolymerization of 2-phenyl-2-oxazoline with the other 2-substituted-2-oxazoline such as 2-methyl-, 2-isopropyl-, and 2-benzyl-2-oxazoline indicated that the monomer reactivity ratio r2 was much larger than unity, whereas r1 was very much smaller. Based on these results, the influence of the structure and the reactivity of the monomer and the growing cationic end of the polymerizability of 2-oxazolines are discussed. 相似文献
74.
Gregory B. Kharas Emi Hanawa Jamie Lachenberg Beata Brozek Patricia Miramon Audris C. Mojica 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):420-424
Electrophilic trisubstituted ethylene monomers, some ring‐substituted 2‐phenyl‐1,1‐dicyanoethylenes, RC6H4CH?C(CN)2 (where R is 3‐Br, 4‐CH3O; 5‐Br, 2‐CH3O; 4‐Cl, 3‐NO2; 5‐Cl, 2‐NO2; 2‐CN, 3‐CN, 4‐CN, and 4‐(CH3)2N), were synthesized by piperidine catalyzed Knoevenagel condensation of ring‐substituted benzaldehydes and malononitrile, and characterized by CHN elemental analysis, IR, 1H‐ and 13C‐NMR. Novel copolymers of the ethylenes and vinyl acetate were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, 1H and 13C‐NMR, GPC, DSC, and TGA. High T g of the copolymers, in comparison with that of polyvinyl acetate, indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. The gravimetric analysis indicated that the copolymers decompose in the 190–800°C range. 相似文献
75.
Abstract Various kinds of the complexes of 2-phenyl-2-oxazoline with various Bronsted acids were prepared. From the elementary analysis and spectroscopic analysis of the complex, it was identified to be an equimolar oxazolinium salt. The monomer could be polymerized with the oxazolinium salt to give N-benzoyl-polyethylenimine. The polymer yield in bulk polymerization was linearly proportional to the reaction time, and the number-average degree of polymerization of the polymer obtained at the complete conversion was proportional to the initial molar ratio of the monomer to the complex. The catalytic activities of the oxazolinium salts increased with a decrease in the pKavalue of Bronsted acid in water. The results of the infrared spectroscopy and nuclear magnetic resonance spectroscopy of the oxazolinium salt at room temperature and elevated temperature indicated that the change of the double bond character of the imino and ether linkages is brought about by the complexation. On the basis of these results, the mechanism of the polymerization was proposed. 相似文献
76.
The pressure-volume (P-V) isotherms were measured for the poly(methy1 methacrylate) (PMMA)-methyl methacrylate (MMA) coexistence system polymerized by γ-ray irradiation at various pressures. The P-V isotherm of the coexistence system polymerized below 3000 kg/cm2 was similar to that of the monomer. The specific volume of the coexistence system polymerized above 3000 kg/cm2 hardly changes in the pressure range between 3000 kg/cm2 and the polymerization pressure when measurements are made with successively decreasing or successively increasing pressures. The compressibility was of the order of 10?6 (kg/cm2)?1 in this pressure range. This indicated that the coexistence system polymerized above 3000 kg/cm2 behaves like a solid in this pressure range. Above the polymerization pressure, the compressibility was of the order of 10?5 (kg/cm2)?1, indicating that the coexistence system behaves as liquid. We concluded that the solid-like behavior of the coexistence system polymerized above 3000 kg/cm2 is caused by a strong interaction between as-polymerized polymer chains and monomer molecules due to propagation through monomer clusters having short-range order. The present results support that MMA is aligned in short-range order at suitable pressure and temperature as reported in the preceding paper. 相似文献
77.
Tomoyasu Noji Masaharu Kondo Keisuke Kawakami Jian-Ren Shen Mamoru Nango Takehisa Dewa 《Research on Chemical Intermediates》2014,40(9):3231-3241
Photosystem II (PSII) has attracted a lot of attention for use in the construction of artificial photosynthetic materials due to its high activity of oxidation of water molecules. However, the robustness of PSII needs to be improved for in vitro application. In this study, we incorporated PSII (Thermosynechococcus vulcanus) into various phospholipid membranes to examine the activity and durability of oxygen evolution. PSII was incorporated into anionic 1,2-dioleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (PSII-DOPG), zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphocholine (PSII-DOPC), and cationic 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine (PSII-EDOPC). Structural integrity of PSII was examined by absorption and fluorescence spectroscopy. Compared with PSII dissolved in a micellar solution of n-dodecyl-β-d-maltoside (PSII-micelle), durability of PSII-DOPC and PSII-DOPG were enhanced by 1.3- and 1.5-fold, respectively. The activity and durability of PSII-EDOPC was significantly low. Lipid-dependent activity and durability were discussed in terms of kinetic parameters of V max and K m, and inhibition of the electron acceptor, phenyl-p-benzoquinone. 相似文献
78.
Tadao Seguchi Takeshi Suwa Naoyuki Tamura Masaaki Takehisa 《Journal of Polymer Science.Polymer Physics》1974,12(12):2567-2576
The original morphology of polytetrafluoroethylene prepared by radiation-induced emulsion polymerization was studied by electron microscopy. The morphology depends on molecular weight, which in turn depends on polymerization conditions, especially the emulsifier concentration. The molecular weight decreases with increasing emulsifier concentration. The morphology changes with molecular weight roughly as follows: fibrils below 105, rods between 105 and 5 × 105, and granular particle above 106. The crystallinity is high for all morphologies. 相似文献
79.
The molecular motion of unsintered polytetrafluoroethylene (PTFE) was studied by dynamic viscoelastic measurements. From results for variously heat treated suspension polymerized (molding powder) PTFE, the following conclusions are drawn. Molding powder, as received, has a high degree of crystallinity according to calorimetric results and lower magnitude of the γ relaxation, but the behavior of the β relaxation suggests that the crystals are disordered more than those of the sintered PTFE. The β relaxation peak for an emulsion polymerized PTFE (fine powder) occurs at a higher temperature and is sharper than that for the molding powder, so that the crystals of the fine powder are better ordered than that for the molding powder. The behavior of the β relaxation for the radiation induced-polymerized PTFE is affected by polymerization conditions, particularly concentration of emulsifier. It is concluded from the results for the unsintered PTFE polymerized by various methods that the nature of crystalline state is decided during the course of simultaneous polymerization and crystallization. Molding powder as received has a relatively high magnitude of relaxation between 30°C to 180°C, but with little temperature dependence in this temperature range. This relaxation is diminished by gamma-ray irradiation. Since the molding powder has a complicated morphology, the relaxation in this temperature range is attributed to inter-particle friction rather than a relaxation associated with motion on the molecular level. 相似文献
80.
Oikawa H Fujiyoshi S Dewa T Nango M Matsushita M 《Journal of the American Chemical Society》2008,130(14):4580-4581
The fluorescence excitation spectrum of a single chromophore molecule in a photosynthetic pigment-protein complex is known to change in time at liquid helium temperature. The spectral change reflects a conformational change of the protein to which the chromophore binds. This work follows the temporal behavior of the spectrum of a single chromophore in the temperature range between 5 adn 18 K. The temperature dependence reveals two types of conformational change of the protein, i.e., thermally activated motions over a potential barrier of ca. 0.1 kJ/mol and temperature-independent motions of tunneling of a proton. 相似文献