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81.
Yaw-Terng Chern Wan-Ho Chung 《Journal of polymer science. Part A, Polymer chemistry》1996,34(1):117-124
1,3-Diaminoadamantane (I) was used as a monomer with various aromatic dicarboxylic acyl chlorides and dianhydrides to synthesize polyamides and polyimides, respectively. Polyamides having inherent viscosities of 0.10–0.27 dL/g were prepared by low-temperature solution polycondensation. The polyamides were soluble in a variety of solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), pyridine, dioxane, and nitrobenzene. These polyamides had glass transition temperatures in the 179–187°C range and 5% weight loss temperatures occurred at up to 354°C. Polyimides based on diamine I and various aromatic dianhydrides were synthesized by the two-stage procedure that included ring-opening to form polyamic acids, followed by thermal conversion to polyimides. The polyamic acids had inherent viscosities of 0.14–0.38 dL/g. The glass transition temperature of these polyimides were in the 245–303°C range and showed almost no weight loss up to 350°C under air and nitrogen atmosphere. © 1996 John Wiley & Sons, Inc. 相似文献
82.
现有的测定镍的容量分析方法很多[1~3],但准确、简便、快速者不多。目前最常用的是将Ni2+先用丁二酮肟沉淀,过滤,洗涤后,重新溶解,再用EDTA滴定,以红紫酸铵或茜素S为指示剂[4,5],滴定时pH控制要求严格。用丁二肟为滴定剂测镍的安培滴定法也有报导[6-8],但由于操作麻烦,很少在实际中应用。另外,在氨性溶液中用丁二肟碱性溶液直接滴定镍的办法也有报导[9],但因使用外指示剂误差较大。 相似文献
83.
Effect of short-chain alcohols on the oil-in-water microemulsion polymerization of styrene 总被引:4,自引:0,他引:4
The influence of short-chain alcohols, 1-butanol (C4OH), 2-pentanol (C5OH) and 1-hexanol (C6OH), on the formation of oil-in-water styrene microemulsions and the subsequent free-radical polymerization was studied. Sodium
dodecyl sulfate was used as the surfactant. The overall performance of C4OH as the cosurfactant is quite different from C5OH and C6OH. The range of the microemulsion region in decreasing order is C4OH > C5OH > C6OH. The primary parameters selected for the microemulsion polymerization study were the concentrations of cosurfactant and
styrene. Only a small fraction of microemulsion droplets initially present in the reaction system can be successfully transformed
into latex particles and the remaining droplets serve as a reservoir to supply the growing particles with monomer. Limited
flocculation of latex particles also occurs during polymerization and the degree of flocculation is most significant for the
C4OH system.
Received: 24 August 1999/Accepted in revised form: 22 October 1999 相似文献
84.
Chorng‐Shyan Chern Jih‐Cheang Sheu 《Journal of polymer science. Part A, Polymer chemistry》2000,38(17):3188-3199
The effects of 2‐hydroxyalkyl methacrylates (HEMA and HPMA) on the styrene miniemulsion polymerizations stabilized by SDS/lauryl methacrylate (LMA) or SDS/stearyl methacrylate (SMA) were investigated. A mixed mode of particle nucleation (monomer droplet nucleation and homogeneous nucleation) is operative during polymerization. Homogeneous nucleation plays a crucial role in the polymerizations stabilized by SDS/LMA, whereas monomer droplet nucleation becomes more important in the polymerizations stabilized by SDS/SMA. The polymerization kinetics is insensitive to the type of 2‐hydroxyalkyl methacrylates, but the difference in the relative importance of monomer droplet nucleation and homogeneous nucleation is detected. Incorporation of 1‐pentanol (C5OH) into the reaction mixture also shows a significant influence on the polymerizations stabilized by SDS/LMA or SDS/SMA. This is attributed to the formation of a close‐packed structure of SDS and C5OH on the droplet surface, which acts as a barrier to the incoming oligomeric radicals. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3188–3199, 2000 相似文献
85.
Yaw-Terng Chern Wen-Liang Wang 《Journal of polymer science. Part A, Polymer chemistry》1998,36(13):2185-2192
A series of new polyamides 3 were synthesized by direct polycondensation of the 1,6-bis[4-(4-aminophenoxy)phenyl]diamantane (1) with various dicarboxylic acids. The polyamides had inherent viscosities of 0.45–1.90 dL/g and number-average molecular weights (Mn) of 24,000–110,000. Dynamic mechanical analysis (DMA) reveals that polymers 3 have two relaxations on the temperature scale between −100 and 400°C. Their α relaxations occurred at high temperatures, ranging from 338 to 389°C. Moreover, these polymers remained quite stable at high temperatures and maintained good mechanical properties (G′ = ca. 108 Pa) up to temperatures close to the main transition markedly exceeding 350°C. Due to the bulky diamantane elements and the flexible ether segments, the polymers 3 were amorphous and soluble in a number of organic solvents such as pyridine, N-methyl-2-pyrrolidone (NMP), and N,N-dimethylacetamide (DMAc). The polyamides 3 have tensile strengths of 56.7–90.2 MPa, elongation to breakage values of 7.5–27.7%, and initial moduli of 1.8–2.1 GPa. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2185–2192, 1998 相似文献
86.
Polymer miscibility was found for a blend system comprising of a new poly(aryl ether ketone) and a poly(ether imide). Phase homogeneity was preliminarily confirmed using optical and scanning electron microscopy, indicating that the scales of phase homogeneity in the blends were beyond the resolution limits of either microscopy. A composition-dependent, single glass transition temperature (Tg) in the PAEK/PEI blends within the full range of composition was observed using differential scanning calorimetry (DSC). The thermal transition breadth also suggests that the scales of mixing are fine and uniform. 相似文献
87.
Capability of the explicit algebraic stress models to predict homogeneous and inhomogeneous shear flows are examined. The importance of the explicit solution of the production to dissipation ratio is first highlighted by examining the algebraic stress models performance at purely irrotational strain conditions. Turbulent recirculating flows within sudden expanding pipes are further simulated with explicit algebraic stress model and anisotropic eddy viscosity model. Both models predict better stress–strain interactions, showing reasonable shear layer developments. The anisotropic stress field are also accurately predicted by the models, though the anisotropic eddy viscosity model of Craft et al. returns marginally better results. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
88.
R. T. Chern W. J. Koros H. B. Hopfenberg V. T. Stannett 《Journal of Polymer Science.Polymer Physics》1983,21(5):753-763
Permeability data are reported for carbon dioxide in Lexan polycarbonate at 35°C. Measurements were made for both pure carbon dioxide and for a mixed feed consisting of carbon dioxide with a 117.8-torr (0.155-atm) Partial pressure of isopentane. The effects of varying upstream CO2 driving pressure from 1 up to 20 atm were studied. The permeability to CO2 is reduced significantly in the presence of isopentane; however, the fractional depression of the CO2 permeability due to the isopentane at low driving pressures is much more significant than at high CO2 driving pressures. The well-known pressure dependence of carbon dioxide permeabilities in glassy polymers, therefore, is largely diminished by introducing isopentane to the pure carbon dioxide feed. These observations are consistent with a model for transport in glassy polymers which explains the observed trends in terms of competition between the two penetrants for microvoid sorption sites existing in the non-equilibrium glassy polymer. Exclusion of carbon dioxide from microvoid sorption sites by the more condensable isopentane preempts transport through the microvoid regions, resulting in the observed depression of the CO2 permeability. 相似文献
89.
In this paper we will present systolic algorithms for static versions of the convex hull problem and the half-plane intersection problem. The systolic algorithms are based on a cyclic shift operation that makes each object meet all the other objects. 相似文献
90.