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871.
Norihiro Moriyama Hiroki Nagasawa Masakoto Kanezashi Kenji Ito Toshinori Tsuru 《Journal of Sol-Gel Science and Technology》2018,86(1):63-72
Based on their high performance in gas and liquid-phase separations, 1,2-bis(triethoxysilyl)ethane (BTESE)-derived organosilica membranes have attracted much attention. To improve performance, we focused on the acid molar ratio (AR) in sol preparation and its effect on the pore formation mechanism during sol-gel processing. BTESE-derived sols with AR?=?10?4–100 were prepared, and the effect of the AR on the gel structure was evaluated in detail via FT-IR, nuclear magnetic resonance (NMR), N2 adsorption, and positron annihilation lifetime (PAL) measurements. The chemical structure of the gels was confirmed by FT-IR and NMR and showed that sols with the largest number of silanol groups (AR?=?10?2) experienced a significant increase in condensation during the firing process. The porous structures of fired gels characterized by N2 adsorption and PAL measurement showed that the AR?=?10?2 fired gel consisted of a larger number of small pores that had formed during the firing process. Single-gas permeation experiments showed high H2 permeance (5–9?×?10?7?mol/(m2?Pa?s)) and H2/CF4 selectivity (700–20,000). The gas permselectivity (He/H2, H2/N2, and H2/CF4) was highest for the intermediate AR (=10?2), which corresponded to the greatest amount of silanol groups in unfired gels and confirmed that small pores had formed from the condensation of silanol groups during firing. 相似文献
872.
Katsukiyo Ito 《Journal of polymer science. Part A, Polymer chemistry》1969,7(9):2707-2710
By using the expression, kt = A1Ds for the chain termination rate constant (where A1 is a constant and Ds is the diffusion constant of radical chain end), a familiar chain termination rate constant, kt = A2/ηs (where A2 is a constant and ηs is solvent viscosity) was examined with variation of conversion x. It was found that the proportionality of chain termination rate constant and solution viscosity is a valid relation at conversion 0 but is approximate at conversion xc ≥ x > 0. Here xc denotes a critical conversion under the average distance around spherical polymers formed in polymerization solution is zero. At conversions above xc, the inverse relation between chain termination rate constant and solution viscosity is not correct. 相似文献
873.
Osamu Matsuda Jiro Okamoto Nobutake Suzuki Masayuki Ito Akibumi Danno 《Journal of polymer science. Part A, Polymer chemistry》1974,12(9):1871-1880
Radiation-induced emulsion copolymerization of tetrafluoroethylene with propylene was carried out by batch operation with an initial molar ratio of tetrafluoroethylene to propylene of 3.0 in the emulsifier concentration range of 0.1 to 3.0% and in the dose rate range of 2 × 104 to 2 × 105 R/hr. The effects of emulsifier concentration and dose rate on the polymerization rate and the number-average degree of polymerization are discussed in comparison with the Smith-Ewart theory. The polymerization rate is proportional to the 0.26 power of emulsifier concentration and to the 0.7 power of dose rate. The degree of polymerization is independent of the emulsifier concentration and the dose rate above the critical micelle concentration (CMC) of the emulsifier. These results are not in agreement with the Smith-Ewart theory. It is explained that the termination reaction is a degradative chain transfer of propagating radicals to propylene. On the other hand, the copolymerization in emulsion occurs either below the CMC or in the absence of emulsifier. Under these conditions, however, it is impossible to obtain a copolymer of high molecular weight at a high rate of polymerization because of the presence of a small number of polymer particles formed and the short interval of chain growth in the polymer particle. 相似文献
874.
875.
876.
877.
Csorna SE Mestayer MD Panvini RS Word GB Yi X Bean A Bobbink GJ Brock I Engler A Ferguson T Kraemer R Rippich C Sutton R Vogel H Bebek C Berkelman K Blucher E Cassel DG Copie T DeSalvo R DeWire JW Ehrlich R Galik RS Gilchriese MG Gittelman B Gray SW Halling AM Hartill DL Heltsley BK Holzner S Ito M Kandaswamy J Kowalewski R Kreinick DL Kubota Y Mistry NB Mueller J Nordberg E Ogg M Peterson D Perticone D Pisharody M Read K Riley D Silverman A Stein PC Stone S Sadoff AJ Avery P Besson D Bowcock T 《Physical review letters》1986,56(12):1222-1225
878.
The effects of γ radiation on glycylglycine, triglycine, and polyglycine have been studied using ESR spectroscopy. The radiation exposures have been performed under vacuum at room temperature. All those irradiated substances show a doublet absorption signal often ascribed to a radical formed on the α carbon of the peptide chain. The magnetic susceptibility has been found to depend on temperature according to the Curie-Weiss law. The radio-sensitivity parameter Gr , the hyperfine splitting constant Ah and the spectroscopic factor g nave been determinated as well as θ which is the temperature corresponding to the Curie temperature of the irradiated substance. The results on Cr , θ and Ah for all peptides studied here agree with the assumption of radiation induced free radicals located at the α carbon of the peptide chain, leading to conclude that the degree of delocalization of the unpaired electron increases for increasing number of glycine units in the peptide. Finally, from negative θ values obtained, a conclusion has been reached on the antiferromagnetic nature of the interaction between unpaired spins. 相似文献
879.
Diffraction patterns of wedges are studied with special attention to the finish of the samples. We assume that the sharply finished vertex should generate two hemispherical waves by the end effect of the cylindrical waves issued from two sides of the wedge under illumination of the coherent light. It is found that the assumption is valuable to the investigation of the diffraction pattern appearing in the shadow region of the wedge. 相似文献
880.
Kazuhiko Ichikawa Prof. Mitunori Izumi Prof. Daiju Goto Naohito Ito 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(23):5094-5098
Four macrotricyclic cage hosts which feature four positive binding sites oriented toward the center of the intramolecular cavity are presented as promising candidates for anion receptors and they have been expected to play a important role in the selective encapsulation of the halide ion Cl− or Br−. The complementarity between a macrotricyclic quaternary ammonium ion and Cl− was achieved by fine-tuning of the four ammonium nitrogen atoms and the endocyclic methylene groups. The cage hosts [R4N4(C5H10)4(C6H12)2]4+ (abbreviated as [556]) showed perfect encapsulation of all chloride ions in acetonitrile at 0<r=([Cl−]o/[[556]]o)≤1 within the sensitivity of the 1H NMR spectra in combination with a rather slow chemical exchange of the Cl− ion in an encapsulation/decapsulation equilibrium with [556]. Further, the selective encapsulation of all the chloride ions into [556] cage occurs unambiguously at r=1 in the presence of equimolar amounts of Br−. The structural complementarity of the newly designed [556] host prevails over the Hofmeister-series restraints determined by differences in Gibbs free energy of halide anion solvation. 相似文献