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761.
As a new method, stable-isotope dilution activation analysis has been developed. When an element consists of at least two stable isotopes which are converted easily to the radioactive nuclides through nuclear reactions, the total amount of the element (xg) can be determined by irradiating simultaneously the duplicated sample containing small amounts of either enriched isotope (y g), and by using the following equation. $${{x = y\left( {{M \mathord{\left/ {\vphantom {M {M*}}} \right. \kern-\nulldelimiterspace} {M*}}} \right)\left[ {\left( {{{R*} \mathord{\left/ {\vphantom {{R*} R}} \right. \kern-\nulldelimiterspace} R}} \right)\left( {{{\theta _2^* } \mathord{\left/ {\vphantom {{\theta _2^* } {\theta _2 }}} \right. \kern-\nulldelimiterspace} {\theta _2 }}} \right) - \left( {{{\theta _1^* } \mathord{\left/ {\vphantom {{\theta _1^* } {\theta _1 }}} \right. \kern-\nulldelimiterspace} {\theta _1 }}} \right)} \right]} \mathord{\left/ {\vphantom {{x = y\left( {{M \mathord{\left/ {\vphantom {M {M*}}} \right. \kern-\nulldelimiterspace} {M*}}} \right)\left[ {\left( {{{R*} \mathord{\left/ {\vphantom {{R*} R}} \right. \kern-\nulldelimiterspace} R}} \right)\left( {{{\theta _2^* } \mathord{\left/ {\vphantom {{\theta _2^* } {\theta _2 }}} \right. \kern-\nulldelimiterspace} {\theta _2 }}} \right) - \left( {{{\theta _1^* } \mathord{\left/ {\vphantom {{\theta _1^* } {\theta _1 }}} \right. \kern-\nulldelimiterspace} {\theta _1 }}} \right)} \right]} {\left[ {1 - \left( {{{R*} \mathord{\left/ {\vphantom {{R*} R}} \right. \kern-\nulldelimiterspace} R}} \right)} \right]}}} \right. \kern-\nulldelimiterspace} {\left[ {1 - \left( {{{R*} \mathord{\left/ {\vphantom {{R*} R}} \right. \kern-\nulldelimiterspace} R}} \right)} \right]}}$$ Where M and M* are atomic weights of the element to be determined and the enriched isotope used as a spike,θ 1 andθ 2 are natural abundances of two stable isotopes in the element,θ 1 * andθ 2 * are isotopic compositions of the above isotopes in the enriched isotope, and R and R* are counting ratios of gamma-rays emitted by two radionuclides produced in the sample and the isotopic mixture. Neither calibration standard nor correction of irradiation conditions are necessary for this method. Usefulness of the present method was verified by photon activations of Ca, Zn and Ce using isotopically enriched48ca,68Zn and142Ce. 相似文献
762.
Ernó Kuzmann Attila Vértes Yusuke Ujihira Pál Kovács Hisamichi Kimura Tsuyoshi Masumoto 《Structural chemistry》1991,2(3-4):(87)295-(93)301
The effect of electrochemical hydrogenation was investigated in Fe90Zr10 and Fe89Zr11 amorphous alloys by means of57Fe Mössbauer spectroscopy. Significant changes in the Mössbauer spectra as well as in the hyperfine field distribution of hydrogenated samples were found with increasing hydrogen concentration. It was established that the dependence of Curie temperature on hydrogen content had a maximum, and the hydrogen had two mean localization sites. By comparing the Mössbauer spectra of hydrogenated samples as-quenched and annealed before hydrogenation it was shown that low-temperature relaxation processes were going on at aging temperature as low as 150°C in this amorphous alloy and the low-temperature relaxation processes modify the localization of hydrogen. The combination of the hydrogenation and Mössbauer techniques gives a very sensitive method for detecting structural changes. 相似文献
763.
Cytochrome P450 model and liver microsomal oxidations of drugs were compared using phencyclidine. In general, the chemical reaction systems produced many oxidation products. Besides the formation of the cyclohexane-4-hydroxyl compound (2), hydroxylation of the aromatic ring was favored in the Fenton reaction system (Fe2+ + H2O2). Formation of an m-hydroxylated product (m-5) was the main aromatic oxidation pathway in the Udenfriend reaction (Fe2+-ascorbic acid-O2), and 2, the piperidine-3-hydroxyl compound (3), and the piperidine-4-hydroxyl compound (4) were also formed. In the system using meso-tetraphenylporphinatoiron chloride (Fe(III)TPPC1) with an oxidant, the main product was the piperidine-3-oxo compound (8). In the liver microsomes system, 2, 4, 8, and m-5, which were all generated by the chemical oxidation reactions, were detected as metabolites of phencyclidine. They were formed by cytochrome P450-dependent reactions. Chemical oxidation systems can be used to study drug metabolism; they can reveal some tendencies of the real metabolic reactions, are easy to operate, and yield sufficient amounts of product. 相似文献
764.
In situ chemical aminoacylation with amino acid thioesters linked to a peptide nucleic acid 总被引:1,自引:0,他引:1
Ninomiya K Minohata T Nishimura M Sisido M 《Journal of the American Chemical Society》2004,126(49):15984-15989
tRNA-specific chemical aminoacylation was achieved with nonnatural amino acids. A nonnatural amino acid was activated as a thioester derivative, and the latter was linked through a spacer to the N-terminal of a 9-mer peptide nucleic acid that is complementary to the 3'-terminal region of yeast phenylalanine tRNA. Efficient aminoacylation was observed when the amino acid thioester-spacer-PNA conjugate was mixed with the tRNA. The PNA-assisted aminoacylation was also successful in an Escherichia coli in vitro protein synthesizing system that contained an orthogonalized tRNA. The in situ aminoacylation/in vitro translation gave a mutant protein in which the nonnatural amino acid was incorporated into the position directed by a CGGG 4-base codon/anticodon pair. 相似文献
765.
Tsuneo Matsuda Keiko Ishimatsu Masatoshi Sugimoto 《Reaction Kinetics and Catalysis Letters》1991,44(1):63-68
In order to find the cause of the high activity for hydrogenation of 1,3-butadiene over a magnesium oxide catalyst prepared by thermal decomposition of magnesium oxalate, ESR and poisoning techniques were used. The cause of the high activity was attributed to large surface area and electron donating properties, which might be related to the surface basicity.
, 1,3-, . - , .相似文献
766.
An-Pang Tsai Akihsia Inoue Tsuyoshi Masumoto 《Progress in Crystal Growth and Characterization of Materials》1997,34(1-4):221-236
Growth, stability and structure of icosahedral (i-) phases have been studied by electron diffraction and X-ray diffraction in relation with the phason strains. Three alloy systems; AlPdCr, AlPdMn and AlCuV were chosen in this study. An i- Al72Pd25Cr3 grain has been analysed to have a phason matrix toward to a tetragonal or orthorhombic structure. Stability of the i-phases correlated with the phason relaxation was discussed in Al-Pd-Mn system. A quenched i-Al74Pd17Mn9 close to but containing significant phason strains, revealed that the phason relaxation induced by precipitation of crystalline phases upon annealing. Phason disorder dominated by the chemical composition was evidenced in a composition study in Al-Pd-Mn system. A high density random phasons characterized the icosahedral glass phase was observed in AlCuV alloys. 相似文献
767.
Quasicrystals, including face-centered icosahedral (FCI), simple icosahedral (SI) and decagonal (D) phases with periodicities of 1.6 nm and 1.2 nm along periodic axis, are found to form over a wide composition range in the Al---Pd---Mn system. A very strong composition dependence of the chemical order is seen in icosahedral Al90−xPdxMn10 alloys alloys. A discontinuous change in the lattice parameter, aR, with the Pd content of the i-phases suggests that the replacement of Al by Pd is selective. The predominant occupation site for the Pd atoms is icosahedral structure varies between the FCI and SI lattices. It is proposed that the FCI phase can be constructed as a two-cell structure, originating from the Al---Pd and Al---Mn binary systems. 相似文献
768.
Wha-Nam Myung Sang-Jo Kim Dal-Hwan Jang
H. Okumura
A. Inoue T. Masumoto 《Journal of Non》1992,150(1-3):406-412Measurements of internal friction and dynamic modulus have been carried out on amorphous Fe83−xMnxP17(x=9,12, or 15) alloys in the temperature range 300–800 K, as a function of applied frequency, by a forced oscillation method. The characteristic transition temperatures and activation energies for crystallization were measured by differential scanning calorimetry (DSC). The viscous flow of the sample was measured using a thermomechanical analyzer (TMA) under continuous heating conditions. Internal friction increases rapidly with temperature starting from 450 K for 0.1 Hz, 474 K for 0.5 Hz, 486 K for 1.0 Hz, 511 K for 5 Hz, and 525 K for 10 Hz for the Fe74Mn9P17 specimen. It was found that the internal friction peak temperature was very closely the same as the steady state viscous flow temperature from the TMA curves for Fe74Mn9P17 and Fe68Mn15P17 but not for Fe71Mn12P17. It is assumed that the internal friction peak does not correspond to the glass transition temperature or crystallization temperature for these alloy systems. Two maxima in the free-volume fraction and two minima in the viscosity were also found for the samples which exhibit a ‘mid-contraction’ in their TMA displacement curves. The internal friction peak occurred at the steady state viscous flow temperature. This occurrence means that the origin of the internal friction peak is related to the viscous flow behavior and free-volume fluctuation for this alloy system. 相似文献
769.
The Young's modulus sound velocity (VE) and the Young's modulus of amorphous ribbons for (Ti, Zr, Hf)100?x (Si, Ge)x binary and (Ti, Zr, Hf)85?xMx(Si, Ge)15 (M = V ? VIII group transition metal) ternary systems were measured as a function of alloy composition. VE increases with increasing silicon or germanium content and with the replacement of titanium, zirconium or hafnium by M elements except tantalum or hafnium, and tends to increase with the Debye temperature of the constituent elements themselves. E increases linearly with increasing σf and Hv, and ratios of σf/E and Hv/3E show a nearly constant value (? 0.018) for Zr100?xSix and Zr85?xMxSi15(M = Ti, V, Nb, Ta or Mo) amorphous alloys. Considering the compositional dependence of these mechanical properties (E, σf and Hv) and the strong correlation among them, it is suggested that (1) the short-range ordering due to the strong interaction among constituent atoms causes an increase in E, σf and Hv, and (2) all the early transition metal-based amorphous alloys possess a common mechanism for plastic flow. 相似文献
770.