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81.
为研究高压条件下聚合物的流变性能,以熔融共混挤出的方法制备聚对苯二甲酸乙二醇酯-聚酰胺6嵌段共聚物(PET-PA6)与聚酰胺6(PA6)共混物,利用安装在反向压力腔末端的旋塞控制毛细管出口压力,研究该共混物在出口压力为5~50 MPa条件下,剪切速率和温度对PET-PA6/PA6共混物流变行为的影响。结果表明:PET-PA6/PA6共混物的剪切黏度随压力的变化规律符合Barus方程;在恒定剪切速率下,随着毛细管内平均压力的增加,剪切黏度逐渐增大;当剪切速率从108 s-1增加到1 080 s-1时,压力系数减小19.24%,当温度从265 ℃增加到 290 ℃ 时,压力系数减小32.33%,共混物熔体剪切黏度对压力的依赖性随剪切速率和温度的增加逐渐减小。 相似文献
82.
为探究经编间隔织物的缓压性能与结构参数之间的量化关系,从理论上分析了经编间隔织物压缩过程中人体受力与间隔织物之间的相互作用机制,以及人体所受压强与其结构参数之间的关系,获得间隔丝直径、间隔丝排列密度以及间隔织物的厚度等结构参数与间隔织物缓压性能的规律方程。采用自行设计球形压头对不同结构参数的间隔织物样品进行压缩实验,验证分析间隔织物的缓压性能与这3个主要影响因素之间的关系,并得出了各自的回归方程。研究结果表明,间隔织物压缩过程中人体所受压强与间隔丝直径呈幂函数变化,与织物的厚度和间隔丝的排列密度分别呈反比和正比函数关系。 相似文献
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窖泥细菌群落结构演替及其与环境因子的相关性 总被引:3,自引:0,他引:3
利用PCR-DGGE系统研究了剑南春不同窖龄(2~50年)窖泥的微生物群落结构、种群演替趋势及其与环境因子的相关性。结果表明,2年窖龄窖泥的细菌丰度和多样性指数与5年样品相似,而10年窖龄窖泥的细菌丰度和多样性指数则明显增加,之后的10年基本持平,但50年时又显著下降。相同窖龄的窖泥样品中,中层的物种丰度和多样性指数均高于上层和下层,特别是在2~5年样品中这一趋势更加明显。DGGE和序列分析显示,窖泥中优势种群均分布在厚壁菌门(Phylum Firmicutes)的杆菌纲(Class Bacill)和梭菌纲(Class Clostrida),其中耐酸乳杆菌(Lactobacillus acetotolerans)、芽孢菌(Bacillus fordii)、未培养的瘤胃菌(uncultured Ruminococcaceae bacterium)和梭菌(uncultured Clostridia bacterium)为窖泥样品中的主要优势种群。典型对应分析显示,窖泥微生物群落结构与环境因子具有显著的相关性,其中有效磷、氨氮、pH对微生物群落结构的影响较大,其次是腐殖质,而水分含量的影响较小。 相似文献
87.
This review highlights the synthesis, physical properties, and emerging technologies of state-of-the-art segmented copolymers containing amide hydrogen bonding sites. Amide hydrogen bonding plays a crucial role in the physical properties associated with amide-containing segmented copolymers. Amide hard segments are accessible in many different forms from amorphous alkyl amides to crystalline aramids and greatly influence copolymer morphology and mechanical properties. Variations in copolymer structure allow for the fine tuning of physical properties and the ability to predict mechanical performance based upon structural modifications. This review includes various synthetic methods for producing well-defined amide-containing segmented copolymers as well as common applications. Also, the morphological and mechanical properties associated with modifications in copolymer structure are discussed. 相似文献
88.
Effect of pyrolysis temperature on the mechanical evolution of SiCf/SiC composites fabricated by PIP
《Ceramics International》2020,46(2):1297-1306
Three types of SiCf/SiC composites with a four-step three-dimensional SiC fibre preform and pyrocarbon interface fabricated via precursor infiltration and pyrolysis at 1100 °C, 1300 °C, and 1500 °C were heat-treated at 1300 °C under argon atmosphere for 50 h. The effects of the pyrolysis temperature on the microstructural and mechanical properties of the SiCf/SiC composites were studied. With an increase in the pyrolysis temperature, the SiC crystallite size of the as-fabricated composites increased from 3.4 to 6.4 nm, and the flexural strength decreased from 742 ± 45 to 467 ± 38 MPa. After heat treatment, all the samples exhibited lower mechanical properties, accompanied by grain growth, mass loss, and the formation of open pores. The degree of mechanical degradation decreased with an increase in the pyrolysis temperature. The composites fabricated at 1500 °C exhibited the highest property retention rates with 90% flexural strength and 98% flexural modulus retained. The mechanism of the mechanical evolution after heat treatment was revealed, which suggested that the thermal stability of the mechanical properties is enhanced by the high crystallinity of the SiC matrix after pyrolysis at higher temperatures. 相似文献
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《Ceramics International》2022,48(7):9651-9657
Friction is a common clean energy and can be harvested and converted into electricity energy via triboelectricity, which can electrochemically drive dye decomposition in theory. In this work, the tribocatalytic Rhodamine B dye decomposition has been experimentally realized in strontium titanate (SrTiO3) nanofibers, which are synthesized via a hydrothermal method. In the tribocatalytic dye decomposition process, the friction is exerted in the interface between catalyst surface and a polytetrafluoroethylene (PTFE) Teflon rod setup with the different stirring speed. The RhB dye decomposition ratios of SrTiO3 nanofibers at these stirring speeds of 200 rpm, 400 rpm, 600 rpm, and 800 rpm are respectively 24.2%, 51.8%, 73.9% and 88.6%, yielding to these reaction rate constants of ~0.0112 h?1, ~0.0260 h?1, ~0.0562 h?1 and ~0.0877 h?1. The main active species, which play an important role in tribocatalytic process, are the superoxide radicals and holes on basis of the active species quenching experiment results. The excellent tribocatalysis activity makes SrTiO3 nanofibers potential for application in dye wastewater treatment through utilizing the environmental friction energy. 相似文献