全文获取类型
收费全文 | 470篇 |
免费 | 5篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 5篇 |
综合类 | 13篇 |
化学工业 | 134篇 |
金属工艺 | 117篇 |
机械仪表 | 10篇 |
矿业工程 | 19篇 |
能源动力 | 24篇 |
轻工业 | 3篇 |
武器工业 | 2篇 |
无线电 | 16篇 |
一般工业技术 | 98篇 |
冶金工业 | 37篇 |
原子能技术 | 10篇 |
自动化技术 | 7篇 |
出版年
2023年 | 17篇 |
2022年 | 28篇 |
2021年 | 17篇 |
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 15篇 |
2017年 | 14篇 |
2016年 | 12篇 |
2015年 | 9篇 |
2014年 | 29篇 |
2013年 | 18篇 |
2012年 | 14篇 |
2011年 | 40篇 |
2010年 | 27篇 |
2009年 | 24篇 |
2008年 | 31篇 |
2007年 | 14篇 |
2006年 | 19篇 |
2005年 | 14篇 |
2004年 | 27篇 |
2003年 | 21篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 16篇 |
1996年 | 4篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1988年 | 2篇 |
1984年 | 1篇 |
排序方式: 共有495条查询结果,搜索用时 15 毫秒
71.
S.Y. Chang L.C. TsaoY.H. Lei S.M. MaoC.H. Huang 《Journal of Materials Processing Technology》2012,212(1):8-14
Al-8.4Si-20Cu-10Ge and mixed rare-earth elements (Re) containing Al-8.4Si-20Cu-10Ge-0.1Re filler metals were used for brazing of 6061 aluminum alloy/Ti-6Al-4V. The addition of 20 wt.% copper and 10 wt.% germanium into the Al-12Si filler metal lowered the solidus temperature from 586 °C to 489 °C and the liquidus temperature from 592 °C to 513 °C. The addition of 0.1 wt.% rare-earth elements into Al-8.4Si-20Cu-10Ge alloy caused remarkable Al-rich phase refinement and transformed the needle-like Al2Cu intermetallic compounds into block-like shapes. Shear strengths of the 6061 aluminum alloy/Ti-6Al-4V joints with the two brazing filler metals, Al-8.4Si-20Cu-10Ge and Al-8.4Si-20Cu-10Ge-0.1Re, varied insignificantly with brazing periods of 10-60 min. The average shear strength of the 6061 aluminum alloy/Ti-6Al-4V joints brazed with Al-8.4Si-20Cu-10Ge at 530 °C was about 20 MPa. Rare-earth elements appeared to improve the reaction of the Al-8.4Si-20Cu-10Ge filler metal with Ti-6Al-4V. The joint shear strength of the 6061 aluminum alloy/Ti-6Al-4V with Al-8.4Si-20Cu-10Ge-0.1Re reached about 51 MPa. 相似文献
72.
Akihiko Ito Jun Endo Teiichi Kimura Takashi Goto 《Surface & coatings technology》2010,204(23):3846-246
Y-Si-O films were prepared by laser chemical vapor deposition (LCVD) with a Nd:YAG laser using TEOS (tetraethyl orthosilicate) and Y(dpm)3 precursors. The effects of laser power (PL), deposition temperature (Tdep) and total chamber pressure (Ptot) on the phase, microstructure and deposition rate of Y-Si-O films were investigated. At PL < 102 W (Tdep < 1140 K), amorphous Y-Si-O films were obtained independent of Ptot. At Ptot = 0.6 kPa, mixture phase films of Y2SiO5 (the X1 phase) and Y2Si2O7 (the α, β, δ and y phases) were obtained at PL = 102 W (Tdep = 1210 K), while single phase X1-Y2SiO5 films were prepared at PL > 139 W (Tdep > 1280 K). Y2Si2O7 mixture phase films were obtained at Ptot = 3.5 kPa and Y2Si2O7 and Y2SiO5 (the X2 phase) mixture phase films were obtained at Ptot = 7.5 kPa independent of Tdep. Amorphous Y-Si-O films showed a dense, glassy microstructure. Faceted columnar grains grew on the Y-Si-O films at Ptot = 0.6 kPa, whereas rounded cauliflower-like grains grew at Ptot = 7.5 kPa. The Rdep increased with increasing PL and Tdep and reached a maximum of 430 μm h−1 at Ptot = 0.6 kPa, PL = 186 W and Tdep = 1310 K. 相似文献
73.
The influence of various cerium (Ce) additions and starting temperature on the resistance to oxidation of AM50 alloy prepared by rapid solidification (RS, RS-AM50 alloy) has been investigated. The Ce addition has two opposite effects on the oxide scale. To the RS-alloy, the beneficial effect outweighs the detrimental one. However, when the alloy was prepared by slow solidification at the normal cooling rate (SS, SS-AM50 alloy), the detrimental effect was dominant. The improvement of oxide scale is closely related to the adherence of metal/oxide and tightness of oxide scale of the alloy. In addition, the reaction rate at the surface increased with starting temperature, which finally results in the formation of a protective oxide scale. 相似文献
74.
The effects of Ni and Co addition on the hydrogen storage properties of Mg3Mm alloy was studied by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) and pressure-composition isotherm (PCI) measurement. The hydrogen absorption kinetics and the thermodynamic parameters (apparent ΔH, ΔS) for Mg3Mm dehydrogenation reactions in Mg3Mm, Mg3MmNi0.1 and Mg3MmNi0.1Co0.1 alloys have been also investigated. The maximum hydrogen storage content of Mg3Mm, Mg3MmNi0.1 and Mg3MmNi0.1Co0.1 alloys was improved due to that the addition of Ni and/or Co further spurred the MmH3 phase transforming to MmH2 phase. On the other side, the kinetics curves show the addition of Co could enhance hydrogen absorption rate while the addition of Ni change the hydrogenation reaction mechanism. 相似文献
75.
B.A. Sava M. Elisa L. Boroica R.C.C. Monteiro 《Materials Science and Engineering: B》2013,178(20):1429-1435
The present work investigates alumino-phosphate glasses from Li2O–BaO–Al2O3–La2O3–P2O5 system containing Sm3+ and Eu3+ ions, prepared by two different ways: a wet raw materials mixing route followed by evaporation and melt-quenching, and by remelting of shards. The linear thermal expansion coefficient measured by dilatometry is identical for both rare-earth-doped phosphate glasses. Comparatively to undoped phosphate glass the linear thermal expansion coefficient increases with 2 × 10−7 K−1 when dopants are added. The characteristic temperatures very slowly decrease but can be considered constant with atomic weight, atomic number and f electrons number of the doping ions in the case of Tg (vitreous transition temperature) and Tsr (high annealing temperature) but slowly increase in the case of Tir (low annealing temperature–strain point) and very slowly increase, being practically constant in the case of TD (dilatometric softening temperature). Comparatively to undoped phosphate glass the characteristic temperatures of Sm and Eu-doped glasses present lower values. The higher values of electrical conductance for both doped glasses, comparatively to usual soda-lime-silicate glass, indicate a slightly reduced stability against water. The viscosity measurements, showed a quasi-linear variation with temperature the mean square deviation (R2) being ranged between 0.872% and 0.996%. The viscosity of doped glasses comparatively to the undoped one is lower at the same temperature. Thermogravimetric analysis did not show notable mass change for any of doped samples. DSC curves for both rare-earth-doped phosphate glasses, as bulk and powdered samples, showed Tg values in the range 435–450 °C. Bulk samples exhibited a very weak exothermic peak at about 685 °C, while powdered samples showed two weak exothermic peaks at about 555 °C and 685 °C due to devitrification of the glasses. Using designed melting and annealing programs, the doped glasses were improved regarding bubbles and cords content and strain elimination. 相似文献
76.
JOHN S. PRESTON ANNA C. DU PREEZ 《Mineral Processing and Extractive Metallurgy Review》2013,34(2):175-200
Abstract A novel process based largely on solvent-extraction methods has been developed for the recovery of rare-earth oxides from waste calcium sulphate sludges obtained during the manufacture of phosphoric acid from a South African apatite ore. A mixed rare-earth oxide (90-98% purity) was first recovered from calcium nitrate leach liquors by extraction with TBP or DBBP, after which it was dissolved in nitric acid to enable pure cerium dioxide (99.98%) to be prepared by selective extraction of cerium(IV) nitrate into TBP. The heavy (yttrium), middle, and light rare-earth fractions were then separated by sequential extraction into D2EHPA at controlled pH values. Pure europium oxide (99.98%) was isolated from the middle fraction by reductive precipitation of europim(II) sulphate, followed by conversion to soluble europium(II) chloride and removal of trivalent rare-earth impurities by extraction with D2EHPA or Versatic 10 acid. Finally, magnet-grade neodymium oxide (95-96%) was obtained from the light rare-earth fraction by extraction of the contained lanthanum, cerium and praseodymium into Aliquat 336 nitrate. 相似文献
77.
Microporous rare-earth coordination polymers constructed by 1,4-cyclohexanedicarboxylate 总被引:1,自引:0,他引:1
In this paper, three novel microporous materials of 1, 4-cyclohexanedicarboxylate Ln[(C8H10O4)1.5(H2O)] · 0.5(H2O) (Ln = Eu for 1, Nd for 2, Sm for 3) are synthesized by the hydrothermal method. The powder X-ray diffraction patterns demonstrate three complexes are isomorphism. The crystal structure of the coordination polymer 1 reveals that the Eu3+ ion center is located in the nine-coordinated environment and the carboxyl groups chelate Eu3+ ions to form 1-D channels through c-axis in μ1, μ2 and μ3 fashion. The properties of the microporous materials are all characterized by the adsorption and desorption of the nitrogen gas and show tremendous difference. TGA illustrate the open frameworks are stable to about 450 °C and they are retained upon removal of water molecules in channels. 相似文献
78.
We synthesized high-quality and oriented periodic mesoporous organosilica (PMO) monoliths through a solvent evaporation process using a wide range of mole ratios of the components: 0.17–0.56 1,2-bis(triethoxysilyl)ethane (BTSE): 0.2 cetyltrimethylammonium chloride (CTACl): 0–1.8 × 10−3 HCl: 0–80 EtOH: 5–400 H2O. X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images indicated that the mesoporous channels within the monolith samples were oriented parallel to the flat external surface of the PMO monolith and possessed a hexagonal symmetry lattice (p6mm). The PMO monolith synthesized from a reactant composition of 0.35 BTSE: 0.2 CTACl: 1.8 × 10−6 HCl: 10 EtOH: 10 H2O had a pore diameter, pore volume, and surface area – obtained from an N2 sorption isotherm – of 25.0 Å, 0.96 cm3 g−1 and 1231 m2 g−1, respectively. After calcination at 280 °C for 2 h in N2 flow, the PMO monolith retained monolith-shape and mesostructure. Pore diameter and surface area of the calcined PMO monolith sample were 19.8 Å, 0.53 cm3 g−1 and 1368 m2 g−1, respectively. We performed 29Si and 13C CP MAS NMR spectroscopy experiments to confirm the presence of Si–C bonding within the framework of the PMO monoliths. We investigated the thermal stability of the PMO monoliths through thermogravimetric analysis (TGA). In addition, rare-earth ions (Eu3+, Tb3+ and Tm3+) were doped into the monoliths. Optical properties of those Eu3+, Tb3+ and Tm3+-doped PMO monoliths were investigated by photoluminescence (PL) spectra to evaluate their potential applicability as UV sensors. 相似文献
79.
Qingbei Li Jianming Lin Jihuai Wu Zhang Lan Yue Wang Fuguo Peng Miaoliang Huang 《Electrochimica acta》2011,(14):4980
In order to increase of the photocurrent, photovoltage and energy conversion efficiency of dye-sensitized solar cell (DSSC), rare-earth doped oxide of Lu2O3:(Tm3+, Yb3+) is prepared and introduced into the TiO2 film in the DSSC. As a luminescence medium, Lu2O3:(Tm3+, Yb3+) improves incident light harvest via a conversion luminescence process and increases photocurrent; as a p-type dopant, the rare-earth ions elevate the energy level of the oxide film and increase the photovoltage. Under a simulated solar light irradiation of 100 mW cm−2, the light-to-electric energy conversion efficiency of the DSSC with Lu2O3:(Tm3+, Yb3+) doping reaches 6.63%, which is increased by 11.1% compared to the DSSC without Lu2O3:(Tm3+, Yb3+) doping. 相似文献
80.