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61.
Partha Sarathi Das Basudam Adhikari Sukumar Maiti 《Journal of polymer science. Part A, Polymer chemistry》1994,32(1):39-45
Fluorination of low-density polyethylene, polyacetylene, and poly(vinyl alcohol) was carried out using SF6 gas under electric discharge. The polymers were partially fluorinated and the extent of fluorination was more in the case of poly (vinyl alcohol) than the other two polymers. The fluorinated polymers were characterized by elemental analysis (Fluorine), IR, and x-ray diffraction. Optical transparency of the films was also measured. The fluorinated polymers show better solvent resistance and decreased transparency than the virgin polymer. © 1994 John Wiley & Sons, Inc. 相似文献
62.
Sylvie BertinJean-Jacques Robin 《European Polymer Journal》2002,38(11):2255-2264
Recycling of mixed plastic wastes composed of low-density polyethylene (LDPE) matrix and polypropylene (PP) was carried out by compounding using single-screw or twin-screw extruders. Blends of virgin polymers have been prepared to compare mechanical properties of both virgin and regenerated materials. First, a model composition of virgin LDPE/PP blend was prepared to study the effect of process parameters and that of different types of compatibilizers. Second, the results were applied to plastic wastes coming from industrial post-consumer plastic wastes. By adding compatibilizing agents such as ethylene-propylene-diene monomer, ethylene-propylene monomer, or PE-g-(2-methyl-1,3-butadiene) graft copolymer, elongation at break and impact strength were improved for all blends. The effect of these various copolymers is quite different and is in relation with their chemical structure. The recycled blends exhibit suitable properties leading to applications that require good mechanical properties. 相似文献
63.
IntroductionItiswellknownthatmetallocenesactivatedwithmethylaluminoxane (MAO)arehighlyactivehomogeneousZiegler Nattacatalyststhatproducepolyolefinwithcon trolledstereoregularityandnarrowmolecularweightdistri bution ,1 4 however,themolecularweightofthepolym… 相似文献
64.
Rheological investigation of the influence of molecular structure on natural and accelerated UV degradation of linear low density polyethylene 总被引:1,自引:0,他引:1
Ibnelwaleed A. Hussein 《Polymer Degradation and Stability》2007,92(11):2026-2032
Metallocene and Ziegler-Natta (ZN) linear low density polyethylenes (LLDPEs) of different branch types and contents as well as linear high density polyethylene (HDPE) were exposed to natural and accelerated weather conditions. The degree of UV degradation of exposed samples was measured by rheological techniques and results were compared with unexposed polymers. Dynamic shear measurements were performed in an ARES rheometer in the linear viscoelastic range. The degree of enhancement or reduction in viscosity and elasticity was used as a measure of the degree of cross-linking or chain scission, respectively. The degradation results of LLDPE suggest that both cross-linking and chain scission are taking place. Chain scission dominated the degradation at high levels of short chain branching (SCB) and long exposure times. The degradation mechanism of m-LLDPE and ZN-LLDPE is similar; however, m-LLDPE showed a higher degradation rate than ZN-LLDPE of similar Mw and average SCB. ZN-LLDPE was found to be more stable than a similar m-LLDPE. Comonomer type had little influence on degradation. Dynamic shear rheology was very useful in revealing the influence of different molecular parameters and it exposed the degradation mechanism. 相似文献
65.
Different grades of linear low density polyethylenes (LLDPEs) have been quenched cooled step-wise and crystallised isothermally
at (a series of increasing) temperatures in a DSC (thermal fractionated samples). These samples have been investigated by
temperature modulated DSC (MDSC). The heat flow curves of the thermal fractionated materials were compared with those obtained
from samples crystallised at a relatively slow cooling rate of 2 K min-1(standard samples).
The melting enthalpy obtained from the total heat flow of the thermal fractionated samples was 0-10 J g-1higher than those of standard samples. The melting enthalpy obtained from the reversing heat flows was 13-31 J g-1lower in the thermal fractionated samples than in the standard samples. The ratio of the reversing melting enthalpy to the
total melting enthalpy increased with decreasing density of the PE. The melting temperature of the endotherms formed by the
step-wise cooling was 9 K higher than the crystallisation temperature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
66.
Aiming to develop a high performance fiber reinforced rubber of SBR, a special technique using electron beam (EB) irradiation-induced graft-polymerization was applied to ultra-high molecular-weight polyethylene (UHMWPE) fibers. Although UHMWPE is chemically inert, N-vinyl formamide (NVF) could be graft-polymerized onto the UHMWPE fiber surface with this special technique. A maximum grafting percentage of 23.6% was achieved. The composite of SBR and grafted UHMWPE fibers with maximum grafting indicated a linear increase in the initial modulus and strength with the fiber content. At the fiber content of 10%, the initial modulus was improved about five times with respect to that of the pure SBR, while the strength was done about twice. At this moment, only a small reduction could be observed in the strain compared with that of pure SBR. The fiber reinforced rubber with a good performance was obtained in the system of SBR and grafted UHMWPE fibers. 相似文献
67.
M. Lundbäck 《Polymer Degradation and Stability》2006,91(5):1071-1078
Plaques of branched polyethylene stabilized with 0.1 wt.% 4,4′-thiobis(6-tert-butyl-3-methylphenol) [Santonox® R] were aged at different temperatures between 75 and 95 °C in anaerobic (nitrogen or water) and aerobic (air or water saturated with air) media. Antioxidant concentration profiles were obtained by oxidation induction time (OIT) measurements using differential scanning calorimetry. Results obtained by high performance liquid chromatography of extracts confirmed that the gradual decrease in OIT with increasing ageing time was due to migration of antioxidant to the surrounding medium. The antioxidant concentration profiles along the plaque thickness direction were flat in the plaques aged in the non-aqueous media indicating that the migration of antioxidant to the surrounding medium was controlled by the low evaporation rate at the material boundary. Crystals of antioxidant were detected by optical microscopy on the samples exposed to nitrogen. The similarity of the antioxidant concentration profiles obtained after ageing in nitrogen and in air suggested that the fraction of the antioxidant oxidized is negligible in comparison with the loss of antioxidant by migration to the surrounding media. The antioxidant concentration profiles along the plaque thickness direction obtained after ageing in water were less flat, suggesting faster dissolution in the water phase than evaporation in the case of non-aqueous ageing. The antioxidant diffusivity could be determined from the aqueous experiments and was in reasonable agreement with data reported by Moisan. For the samples exposed to water, the loss of antioxidant was faster from the samples exposed to water saturated with air. This difference is attributed to a faster degradation of the antioxidant in the oxygen-containing water phase increasing the mass transport from the polymer phase boundary to the water phase. 相似文献
68.
Kawaljeet Singh Samra Ravinder Singh Lakhwant Singh 《Journal of Macromolecular Science: Physics》2013,52(10):691-698
Polyethylene terephthalate (PET) films of 50?μm thickness were exposed to swift-heavy 50?MeV copper and 84?MeV oxygen ions, with fluence varying from 1?×?1011 to 1?×?1013 ions cm?2. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) and UV-visible spectroscopic techniques were used to characterize the irradiated samples. The XRD and DSC analysis indicated the loss of crystallinity during/after the irradiation. The FTIR spectra revealed the formation of alkyne end groups, C═C groups and structural deformation with increase of ion fluence. Considerable reduction in the value of the optical bandgap was inferred from the study of the UV-visible absorption curves. 相似文献
69.
70.