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排序方式: 共有467条查询结果,搜索用时 15 毫秒
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Yoshikazu Horino Miki Sugata Hitoshi Abe 《Advanced Synthesis \u0026amp; Catalysis》2016,358(7):1023-1028
A three‐component reaction of 3‐(tri‐n‐butylstannyl)allyl acetates, aldehydes, and triorganoboranes in the presence of a palladium‐Xantphos catalyst system predominately gave (E)‐anti‐homoallylic alcohols with high diastereoselectivity and good to high levels of alkene stereocontrol. An efficient chirality transfer was observed when an enantioenriched substrate was employed. The reaction was initiated by the formation of an allylic gem‐palladium/stannyl intermediate, which subsequently underwent allylation of the aldehyde by an allyltributyltin followed by a coupling reaction of the in‐situ‐generated (E)‐vinylpalladium acetate with the triorganoborane.
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Naoya Kanbayashi Arisa Yamazawa Koichiro Takii Taka‐aki Okamura Kiyotaka Onitsuka 《Advanced Synthesis \u0026amp; Catalysis》2016,358(4):555-560
We report the asymmetric allylic alkylation of allylic chlorides with silyl enolates as a carbon nucleophile using a planar‐chiral cyclopentadienyl‐ruthenium (Cp′Ru) catalyst. The reaction proceeds under unusually mild conditions to give the desired branched products with complete regioselectivity and high enantioselectivity, and reactive functional groups, such as aldehyde, can be tolerated. In this reaction system, Cp′Ru plays an important role in activating both silyl enolate and allylic chloride.
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Ming Huang Zhihang Peng Wen Zhang Yang Xiang Feng Cao 《International Journal of Applied Ceramic Technology》2022,19(5):2916-2924
Fused silica ceramic has become one of the most widely used radome materials in the world since the 1970s. But its poor mechanical properties restricted its application to some extent. To improve the mechanical properties of the fused silica ceramic and keep its characteristic for radome materials, silicon nitride (Si3N4) whisker-reinforced fused silica ceramics were prepared by a slip-casting method in the work. The influence of Si3N4 whisker contents on the properties of the slurry was studied, indicating that the preferable pH values of the slurry were 4–6 and whisker contents were 10 wt.%. The flexural strength of as-prepared Si3N4w/SiO2 ceramic was about 74.35 MPa, exhibiting an increase of 7.75% over that of the pure silica sample. Its dielectric constant in the range from 8 to 12 GHz and tanδ under 10 GHz were, respectively, 3.37 and .0011. It is of great interest to find that Si3N4w/SiO2 has excellent oxidization resistance and its mass maintains even at 1270°C. 相似文献
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本文通过从石墨原料、氧化剂、膨化温度和膨胀设备等4个方面进行分析,综述了膨胀石墨的化学氧化法制备的研究进展,并提出了膨胀石墨的研究方向:采用细鳞片石墨,在少用甚至不用硫酸、膨化温度较低的情况下,制备高倍率低硫甚至无硫低温膨胀石墨。 相似文献
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采用HClO4对石油焦进行氧化改性,按照碱碳比为3∶1的比例将改性石油焦活化成活性炭,产物标记为OAC-3.作为对比,按照碱碳比4∶1将石油焦活化成活性炭,产物标记为AC-4.采用XRD、I2吸附、N2吸附和循环伏安研究HClO4氧化对石油焦结构和产物活性炭性能的影响.结果表明,HClO4氧化将石油焦石墨微晶d(002)晶面层间距由0.344nm提高到0.353nm,同时将晶粒粒径由2.34nm减小到1.75nm.AC-4和OAC-3的比表面积分别为2 929和3 058m2/g,在0.5 mV/s的扫描速率下,其比电容分别为361.3和392.7 F/g;基于OAC-3的超级电容器具有更好的功率特性. 相似文献
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p-TsOH-mediated the direct α-substitution of cyclic Morita–Baylis–Hillman alcohols with aliphatic and aromatic thiols in refluxing THF. The reaction proceeded with complete α-regioselectivity and provided the corresponding allyl sulfides in moderate to good yields. 相似文献
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Systematic designs to achieve normally-off operation and improved device performance for Al0.26Ga0.74N/AlN/GaN high electron mobility transistors (HEMTs) grown on a Si substrate are investigated in this work. The step-by-step approach includes: (1) devising a thin AlGaN/AlN composite barrier, (2) introducing fluoride ions within the active region by using CF4 plasma treatment, (3) growing the Al2O3 oxide passivation layers within gate-drain/source regions by using a cost-effective ozone water oxidization technique, and (4) integrating a metal-oxide-semiconductor gate (MOS-gate) design with high-k Al2O3 gate dielectric. Devices with four different evolutionary gate structures have been compared and studied. Variations of threshold voltage (Vth), Hooge coefficients (αH), maximum drain-source current density (IDS, max), maximum extrinsic transconductance (gm, max), gate-voltage swing (GVS) linearity, two-terminal gate-drain breakdown/turn-on voltages (BVGD/Von), on/off current ratio (Ion/Ioff), and high-temperature characteristics up to 450 K are also investigated. 相似文献
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