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121.
Luljeta Raka Andrea Sorrentino Gordana Bogoeva‐Gaceva 《Journal of Polymer Science.Polymer Physics》2010,48(17):1927-1938
The effect of organo‐modified clay (Cloisite 93A) on the crystal structure and isothermal crystallization behavior of isotactic polypropylene (iPP) in iPP/clay nanocomposites prepared by latex technology was investigated by wide angle X‐ray diffraction, differential scanning calorimetry and polarized optical microscopy. The X‐ray diffraction results indicated that the higher clay loading promotes the formation of the β‐phase crystallites, as evidenced by the appearance of a new peak corresponding to the (300) reflection of β‐iPP. Analysis of the isothermal crystallization showed that the PP nanocomposite (1% C93A) exhibited higher crystallization rates than the neat PP. The unfilled iPP matrix and nanocomposites clearly shows double melting behavior; the shape of the melting transition progressively changes toward single melting with increasing crystallization temperature. The fold surface free energy (σe) of polymer chains in the nanocomposites was lower than that in the PP latex (PPL). It should be reasonable to treat C93A as a good nucleating agent for the crystallization of PPL, which plays a determinant effect on the reduction in σe during the isothermal crystallization of the nanocomposites. The activation energy, ΔEa, decreased with the incorporation of clay nanoparticles into the matrix, which in turn indicates that the nucleation process is facilitated by the presence of clay. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1927–1938, 2010 相似文献
122.
Flowing microwave plasma of propylene and propylene with argon was studied by mass spectrometry. Plasma composition was investigated as a function of external parameters such as pressure, argon/propylene ratio, and microwave-induced power. It was found that the propylene broke down to C2H2 and CH4, or reacted further with propylene. Two main products, leading to the determination of three main chain reactions for the polymerization of propylene by ion-molecule interactions, were observed, namely, C2H2 and CH4. These were the propylene, acetylene, and ethylene chain reactions. It was also found that the propylene disappeared in a pseudo-first-order reaction. Consequently an overall rate constant for the polymerization was determined (50 sec–1 at 1 torr pressure for propylene plasma). This constant is found to be linearly dependent upon the propylene percent concentration, and nonlinearly dependent upon plasma pressure.Partly presented at the 157th meeting of the Electrochemical Society, St. Louis, Missouri, May 11–16, 1980. 相似文献
123.
Gholam‐Reza Nejabat Mehdi Nekoomanesh Hassan Arabi Hamid Salehi‐Mobarakeh Gholam‐Hossein Zohuri Mojtaba Omidvar Stephen A. Miller 《Journal of polymer science. Part A, Polymer chemistry》2013,51(3):724-731
Various elastomeric polypropylenes (PPs) are synthesized through homogeneous propylene polymerization with metallocene catalyst (2‐PhInd)2ZrCl2 in the presence of different cocatalyst mixtures: triethylaluminum (TEA)/methylaluminoxane (MAO) or triisobutylaluminum (TIBA)/MAO in the range of AlAlR3/AlMAO = 0.0–0.9. The cocatalyst formulation impacts the resultant polymer microstructure and the thermal and dynamic mechanical properties of the produced PPs. 13C NMR analysis of the polymers reveals essentially atactic PP, with mmmm = 7.9%, when AlAlR3/AlMAO = 0.0. The mmmm pentad content is maximized when AlAlR3/AlMAO = 0.8; for TIBA, mmmm = 23.5%; and for TEA, mmmm = 17.6%. Differential scanning calorimetry analysis and dynamic mechanical thermal analysis corroborate these findings. Specifically, Tm, ΔHm, and Tg are essentially maximized under these conditions, and the minimum damping is observed for AlAlR3/AlMAO = 0.6–0.8. 1H NMR analysis of the mixtures of catalyst and cocatalysts (without monomer) shows very minor differences for [Zr]:AlAlR3 in the range of 1:1–1:5. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
124.
125.
Carmen Bocchino Mariagrazia Napoli Chiara Costabile Pasquale Longo 《Journal of polymer science. Part A, Polymer chemistry》2011,49(4):862-870
The synthesis and characterization of a zirconium complex, having two alkoxide functionalized N‐heterocyclic carbene ligands, and its behavior as catalyst in the polymerization of ethylene and propylene, have been reported. NMR analysis showed that more than one species was obtained during synthesis. These data were confirmed by ethylene polymerization that gave rise to a linear polyethylene having a high Molecular weight and a polydispersity index (MDI) > 2 and often bimodal. The same catalytic system was able to produce highly isotactic polypropylene together with an atactic fraction. DFT studies on the complex stereoisomer stability gave indications on the species possibly involved in the polymerizations. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
126.
Xi Jiang Qi Liao Jianjun Zhou Zhaohui Wang Chiming Chan Lin Li 《Journal of Polymer Science.Polymer Physics》2013,51(11):907-914
We have developed a morphologic method to investigate the relaxation processing of the stretched polymer chains in melts, in which an atomic force microscope probe was used to shear the surface of an isotactic polypropylene melt to obtain the isolated shish‐kebab structure. We present the results of the time dependence of length of the isolated shish‐kebab structure and the stress dependence of the kebab density along the direction of shish in this paper. Our results demonstrate that the shear‐oriented polymer melts show the relaxation dynamics of worm‐like chain where the length deficit of the isolated shish‐kebab structure is scaled with the relaxation time as a power of 1/3. The melting behavior of shish‐kebab structure was also investigated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 907–914 相似文献
127.
Calcium malonate (Camt) is used to induce the β crystalline form in isotactic polypropylene (iPP) for the first time. The relative content of the β crystalline form (K value) increases markedly with the addition of Camt and attains the maximum value of 73.48% at 0.40% Camt. The amounts of bright and colorful β spherulites increase and the spherulitic sizes decrease with the increase in Camt contents. The tensile strength and the Izod notched impact strength of the nucleated iPP samples increase with the addition of Camt; in particular, the latter almost doubles at 0.40% Camt compared to that of the blank iPP sample. The β nucleation mechanism of Camt is analyzed by the dimensional lattice match criterion. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
128.
J. Weng R. H. Olley D. C. Bassett P. Jskelinen 《Journal of Polymer Science.Polymer Physics》2004,42(18):3318-3332
Of the three melting peaks typical of a propylene–ethylene random copolymer (with 5.1 wt % ethylene) crystallized between 110 and 140 °C, the two higher peaks result from primary and secondary isothermal crystallization, whereas the material crystallized on cooling gives the lowest peak. In contrast to polypropylene homopolymers, which show strong morphological changes developing from the center of a spherulite, copolymer specimens are uniformly crosshatched. The highest melting peak is related to an open crosshatched framework of primary lamellae, and the next lower peak is related to later forming subsidiary lamellae filling the intervening space. The origin and nature of these double peaks are discussed in terms of the fractional crystallization and the ensuing constraints placed on isothermal lamellar thickening as a result of the exclusion of the comonomer from the polypropylene lattice. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3318–3332, 2004 相似文献
129.
B. K. Annis Man‐Ho Kim R. Alamo M. Pyda 《Journal of Polymer Science.Polymer Physics》2001,39(22):2852-2859
We used inelastic neutron scattering to probe the low‐energy excitations in semicrystalline isotactic polypropylenes with different degrees of crystallinity. The contributions from the amorphous and crystalline regions to the total scattering intensity were extracted under the assumption of a weighted linear contribution of the two regions in a simplified two‐phase system. The resulting intensity from the amorphous region showed a peak at 1.2 meV that was in good agreement with the previously determined boson peak characteristic of atactic polypropylene. The possibility of a contribution to the boson peak region by longitudinal acoustic mode modes that are characteristic of semicrystalline polymers and appear in the same low‐frequency region is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2852–2859, 2001 相似文献
130.
Akio Tsuboi Petr Kol Takeshi Ishikawa Yoshinori Kamiya Hirokatsu Masuoka 《Journal of Polymer Science.Polymer Physics》2001,39(12):1255-1262
The sorption of C2 and C3 hydrocarbons in two ethylene–propylene copolymers and a propylene homopolymer and the simultaneous dilation of the polymers were measured at temperatures of 287–363 K and pressures up to 4 MPa. The sorption isotherms were well described by the Flory–Huggins theory of dissolution. Dilation isotherms in the form of elongation versus pressure were similar in shape to the corresponding sorption isotherms. Solubility coefficients, partial molar volumes, and Flory–Huggins interaction parameters were determined from these isotherms. The thermal expansivities of the hydrocarbons dissolved in the polymers were 0.002–0.005 K?1, and the Flory–Huggins interaction parameters depended not only on temperature but also on concentration. At 323 K, the calculated solubilities of propylene in the ethylene–propylene‐rubber regions of the copolymers were 1.8 times higher than in the amorphous regions of the propylene homopolymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1255–1262, 2001 相似文献