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871.
872.
Ling Chen In Yee Phang Shing-Chung Wong Peng-Fei Lv Tianxi Liu 《Materials and Manufacturing Processes》2006,21(2):153-158
Nylon 66 nanocomposites with different smectite clay loadings were prepared by conventional melt compounding process. The fracture toughness decreases with increasing clay content, which is a direct result of reduced plastic zone size at the crack tip region. The fracture mechanisms were studied using double-notched four-point-bending (DN-4PB) technique. A constraining effect from nanoclay fillers on plastic deformation of matrix is revealed by transmission electron microscopy (TEM). Micron-sized and submicron voids could be observed around the clay platelets. The voids coalesce and form premature cracks that promote crack propagation, thus reducing toughness. 相似文献
873.
The tribological properties of polyamide 66 (PA66) composites, filled with TiO2 nanoparticles, short carbon fibres, and graphite flakes, were investigated. Sliding tests were performed on a pin-on-disk apparatus under different contact pressures, p, and sliding velocities, v. It was found that nano-TiO2 could effectively reduce the frictional coefficient and wear rate, especially under higher pv (the product of p and v) conditions. In order to further understand the wear mechanisms, the worn surfaces were examined by scanning electron microscopy and atomic force microscopy. A positive rolling effect of the nanoparticles between the material pairs was proposed which contributes to the remarkable improvement of the load carrying capacity of polymer nanocomposites. 相似文献
874.
多孔n-HA/CS/PA66三元复合支架材料的制备及性能 总被引:3,自引:0,他引:3
采用常压共混复合法制备了纳米羟基磷灰石/壳聚糖/聚酰胺66(n-HA/CS/PA 66)三元复合材料,并以乙醇为溶剂,聚乙烯吡咯烷酮和氯化钠混合物为致孔剂的粒子沥滤法制备了n-HA/CS/PA 66三元复合多孔支架材料,用燃烧试验、IR、XRD、SEM、孔隙率及力学性能测试等手段对其进行了表征。结果表明,n-HA在复合材料中分布均匀且呈弱结晶状态,复合前后三组分的化学组成未发生显著变化,但三相间两两均发生了相互作用。在制备n-HA/CS/PA 66多孔材料时,加入少量的聚乙烯吡咯烷酮可使该多孔材料孔隙率更高,孔的贯通性更好。 相似文献
875.
n-HA晶体及n-HA/PA66复合材料与人皮质骨的定性和定量对比研究 总被引:5,自引:0,他引:5
用TEM、XRD、FT-IR、TG-DTA等测试手段对成熟的人股骨皮质骨、纳米羟基磷灰石n-HA及n-HA/聚酰胺66(PA66)复合材料的形貌、相组成、晶胞参数、微晶尺寸分布、微观应变、特征基团和离子以及组成等进行了定性和定量表征。提出了一种简单易行的制样方法以获得较为清晰的人骨磷灰石照片。定量比较了人骨与两种材料中磷灰石晶体的结构差异。结果表明,n-HA和n-HA/PA66均具有较高的仿生性能。n-HA和n—HA/PA66中磷灰石的结晶度高于人骨磷灰石,晶格较人骨磷灰石完善,晶格畸变程度较人骨磷灰石小,并且两者中水分含量和CO3^2-含量均低于人骨。本文的研究对于进一步优化现有的骨修复替代材料和进一步开发更接近于人骨的骨修复替代材料具有重要意义。 相似文献
876.
聚酰胺/聚苯硫醚共混物摩擦学性能研究--(Ⅱ)水润滑 总被引:3,自引:0,他引:3
研究了PA66/PPS共混物在水润滑条件下的摩擦磨损性能。结果表明,共混物显著降低了PA66和PPS的摩擦系数,并远远低于干摩擦条件下的摩擦系数。其中,70%φ(PA)/30%φ(PPS)共混物在水润滑条件下的摩擦磨损性能最好。扫描电子显微镜(SEM)分析表明,水的存在抑制了聚合物在对偶钢环上形成转移膜的能力,材料的摩擦磨损主要是由对偶面上的微突起在样品表面的犁耕作用造成的。同时,水也起到了冷却剂的作用。 相似文献
877.
《Contact lens & anterior eye》2023,46(4):101846
IntroductionKeratoconus is defined as central and/or paracentral corneal thinning and steepening with consequent irregular astigmatism. To date, no prospective study has reported its prevalence in Central Europe. This study aimed to evaluate the prevalence of keratoconus assessed with Scheimpflug imaging in a profile of general medicine practice in Poland.MethodsThis cross-sectional study collected data by inviting all patients aged 10–80 years subscribed to a single general practitioner in the Elbląg area, Poland. Corneal measurements were performed using a rotating Scheimpflug corneal tomography system. Three masked examiners established the diagnosis of keratoconus in the right or left eye. Fleiss’ kappa coefficient (κ) was used to qualitatively analyze the interexaminer agreement.ResultsOf 1,705 patients invited to the study, 771 agreed to participate (45.2%). The mean age of the 728 patients (60.6% female and 39.4% male) with gradable images in at least one eye was 53.6 ± 16.5 years. All of the examiners classified the same four cases as keratoconus (0.549%, 549 per 100,000, 95% confidence interval 150 to 1,400 per 100,000), of which two were bilateral. Fleiss’ kappa showed almost perfect agreement among the three examiners regarding the diagnostic decision (κ = 0.784, 95% confidence interval 0.750 to 0.817, p < 0.001). The keratoconus cases were all women (p = 0.106), aged 48, 69, 70, and 71 years old.ConclusionThe prevalence of keratoconus in this area was higher than that previously demonstrated in many European countries. Underestimation of the prevalence has been postulated but never demonstrated. 相似文献
878.
金属有机框架(MOFs)材料因具有比表面积大、孔隙率高及孔道易调、易功能化等特点而应用于各研究领域。然而,多数MOFs材料的化学稳定性和水热稳定性较差,极大地限制其应用。锆基MOFs材料UiO-66的骨架坍塌温度高于500 ℃、可承受1.0 MPa的机械压力并且具有超高稳定性从而引起了人们的关注。该文系统介绍了UiO-66制备方法的研究进展,其中干凝胶转化法具有产品收率高、反应体积小及可连续生产等优点更具优势;详细介绍了有机配体、金属节点和掺杂等改性方式对UiO-66结构的影响,结果表明对UiO-66结构进行改性可进一步提高其性能;总结了UiO-66在催化、气体储存和分离等方面的应用;最后,对UiO-66的未来发展方向进行了展望。 相似文献
879.
《International Journal of Hydrogen Energy》2023,48(38):14418-14432
This study was conducted to understand the effects of hydrogen (H2) addition on the combustion and emission characteristics of hydro-processed renewable diesel. Experiments were performed in a constant volume combustion chamber (CVCC) at varying H2 concentrations (0%, 5%, and 10% (by vol.)) relative to air (100%, 95%, and 90% (by vol.)), initial temperatures (Tini) of 600, 650 and 700 K, equivalence ratios (φ) of 0.5, 1.0, and 1.5 and a fixed initial pressure (Pini) of 10 bar. Overall, HRD has lower ignition delay (ID) and total ID. However, H2 addition to HRD delayed the fuel's auto-ignition due to excess H2 oxidation (H2+OHH2O + H) reaction taking place, which turns the chain reactions from branching to propagation, resulting from increasing in ID. Moreover, increasing of H2 concentrations enhanced the maximum pressure rise (Pmax) and heat release rate (HRR), whereas carbon dioxide (CO2) and unburned hydrocarbon (HC) were decreased due to the higher magnitude of the lower heating value of H2 than that of pure HRD. Since H2 itself is a carbon-free molecule, the carbon content of the fuel is reduced. H2 has the characteristics of fast combustion, resulting in a more flammable and complete mixture, which also makes HC emissions to become lower. However, the higher energy density of H2 significantly raises the combustion temperature, and subsequent nitrogen oxides (NOx) were increased. The kinetic modeling predictions revealed that the IDs for HRD-H2 were elongated due to the increased hydroperoxyl (HO2) and hydrogen peroxide (H2O2) mole fractions which led to improved stability. 相似文献
880.
《International Journal of Hydrogen Energy》2023,48(53):20419-20429
With the increasing depletion of conventional energy sources and their detrimental environmental hazards, it is imperative to search for sustainable alternative clean energy sources. In the recent decades, hydrogen has emerged as potential source of clean energy. One of the potential alternatives to achieve the objective is the designing and characterization of materials for hydrogen-storage energy applications. In this regard, metal-bearing hydrides are the most promising candidates. For instance, magnesium-bearing hydrides are the focus of current research work owing to high hydrogen capacity of 7.6 wt%. In this paper, we first time report density functional-based quantum theoretical analysis to explore the potential of Mo-doped magnesium hydrides MgH2:Mo for optoelectronic and hydrogen-storage applications. For the quantum computations of the required optoelectronics and energy storage properties, we employed all-electron methods within generalized gradient approximation (GGA). Besides applying GGA approximation to account for the electronic correlated effects, we employed the Hubbard potential U (= 4 eV) for onsite repulsive Coulomb force. We predict that 10% doping by weight of Mo into MgH2 suppresses its insulating band gap of 4.9 eV to semiconducting band gap of order 3.15 eV for spin up and 0.15 eV for spin down. As such the doping of Mo can tune the the bandgap, structural, electronic and optoelectronic properties of MgH2 considerably for potential applications. 相似文献