全文获取类型
收费全文 | 2235篇 |
免费 | 395篇 |
国内免费 | 146篇 |
专业分类
电工技术 | 139篇 |
综合类 | 93篇 |
化学工业 | 624篇 |
金属工艺 | 238篇 |
机械仪表 | 31篇 |
建筑科学 | 17篇 |
矿业工程 | 198篇 |
能源动力 | 81篇 |
轻工业 | 16篇 |
水利工程 | 1篇 |
石油天然气 | 136篇 |
武器工业 | 2篇 |
无线电 | 169篇 |
一般工业技术 | 244篇 |
冶金工业 | 750篇 |
原子能技术 | 30篇 |
自动化技术 | 7篇 |
出版年
2024年 | 10篇 |
2023年 | 59篇 |
2022年 | 47篇 |
2021年 | 77篇 |
2020年 | 87篇 |
2019年 | 91篇 |
2018年 | 97篇 |
2017年 | 110篇 |
2016年 | 132篇 |
2015年 | 119篇 |
2014年 | 159篇 |
2013年 | 190篇 |
2012年 | 170篇 |
2011年 | 197篇 |
2010年 | 138篇 |
2009年 | 122篇 |
2008年 | 86篇 |
2007年 | 115篇 |
2006年 | 126篇 |
2005年 | 92篇 |
2004年 | 65篇 |
2003年 | 86篇 |
2002年 | 63篇 |
2001年 | 71篇 |
2000年 | 61篇 |
1999年 | 41篇 |
1998年 | 34篇 |
1997年 | 21篇 |
1996年 | 21篇 |
1995年 | 12篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 11篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1982年 | 4篇 |
1975年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有2776条查询结果,搜索用时 15 毫秒
1.
This paper reports an investigation on the structure-properties correlation of trivalent metal oxide (Al2O3)-doped V2O5 ceramics synthesized by the melt-quench technique. XRD patterns confirmed a single orthorhombic V2O5 phase formation with increasing strain on the doping of Al2O3 in place of V2O5 in the samples estimated by Williamson-Hall analysis. FTIR and Raman investigations revealed a structural change as [VO5] polyhedra converts into [VO4] polyhedra on the doping of Al2O3 into V2O5. The optical band gap was found in a wide semiconductor range as confirmed by UV–visible spectroscopy analysis. The thermal and conductivity behavior of the prepared samples were studied using thermal gravimetric analysis (TGA) and impedance analyzer, respectively. All the prepared ceramics exhibit good DC conductivity (0.22–0.36 Sm-1) at 400 ?C. These materials can be considered for intermediate temperature solid oxide fuel cell (IT-SOFC)/battery applications due to their good conductivity and good thermal stability. 相似文献
2.
Hiromichi Ichinose Masanori Taira Sachiko Furuta Hiroaki Katsuki 《Journal of the American Ceramic Society》2003,86(9):1605-1608
Niobium- or vanadium-doped anatase sols were prepared by hydrothermal treatment of 0.1 mol/dm3 peroxotitanium complex aqueous solutions dissolving 0–10 mol% niobium or vanadium at 100°C for 8 h. Niobium-doping caused the increase of lattice constants of anatase and the shape change of anatase crystal from spindle-like to cubic-like structure, but no change of the optical absorbance. Vanadium-doping caused the decrease of lattice constant of c -axis, the miniaturization of anatase crystal and the increase of optical absorbance at the wavelength from 350–700 nm. 相似文献
3.
Marcia Cristina Kaezer Fran a Rosane Aguiar da Silva San Gil Jean-Guillaume Eon 《Catalysis Today》2003,78(1-4):105-115
γ-Al2O3 supported vanadium oxides were modified by tungsten and molybdenum oxides in order to improve dispersion and selectivity towards olefins in propane oxidative dehydrogenation (ODH). Both vanadium–tungsten and vanadium–molybdenum catalysts were obtained by adsorption of mixed isopolyanions (VW5O195−, V2W4O194−, VMo5O195− and V2Mo4O194−) from aqueous solutions. The isopolyanion solutions were characterized by UV-Vis and 51V NMR spectroscopy. Vanadium, vanadium–tungsten and vanadium–molybdenum precursors and catalysts were also characterized by UV-Vis (diffuse reflectance) and solid state 51V NMR spectroscopy. An improved selectivity to propene in the presence of tungsten and molybdenum in VOx/γ-Al2O3 was observed and attributed to dilution of vanadium by tungsten or molybdenum oxides on the γ-Al2O3 surface. 相似文献
4.
TeMxMo1.7O mixed oxides (M = V and/or Nb; x = 0-1.7) have been prepared by calcination of the corresponding salts at 600 °C in an atmosphere of N2. A new crystalline phase, with a Te/V/Mo atomic ratio of 1/0.2-1.5/1.7, has been isolated and characterised by XRD and IR spectroscopy. This phase is observed in the TeVMo or TeVNbMo mixed oxide but not in the TeNbMo mixed oxide. The new crystalline phase shows an XRD pattern similar to Sb4Mo10O31 and probably corresponds to the M1 phase recently proposed by Aouine et al. (Chem. Commun. 1180, 2001) to be present in the active and selective MoVTeNbO catalysts. Although these catalysts present a very low activity in the propane oxidation, they are active and selective in the oxidation of propene to acrolein and/or acrylic acid. However, the product distribution depends on the catalyst composition. Acrolein or acrylic acid can be selectively obtained from propene on Nb-free or Nb-containing TeVMo catalysts, respectively. The presence of both V and Nb, in addition to Mo and Te, appears to be important in the formation of acrylic acid from propene. 相似文献
5.
Significant increases in the activity of vanadium(III) amidinate catalysts for ethylene polymerization have been obtained by immobilization on a MgCl2‐based support prepared by reaction of AlEt3 with a MgCl2/ethanol adduct. Catalyst immobilization and activation on this type of support prevents the rapid decay in activity observed under homogeneous polymerization conditions with unsupported catalysts. Stable polymerization activity is also observed with analogous titanium(III) complexes. Polyethylene with narrow molecular weight distribution and spherical particle morphology is obtained without reactor fouling. Copyright © 2005 Society of Chemical Industry 相似文献
6.
Satohiro Yoshida Tsunehiro Tanaka Tomoko Hanada Takeshi Hiraiwa Hiroyoshi Kanai Takuzo Funabiki 《Catalysis Letters》1992,12(1-3):277-285
XANES of vanadium and niobium oxide on silica or alumina have been analyzed quantitatively by a deconvolution technique. Based on the results for reference compounds, local structures of supported vanadium and niobium species were identified. The composition was estimated from difference spectra for the samples which consisted of two kinds of species. 相似文献
7.
介绍了热钾碱法脱碳钒化工艺技术改进的试验过程,开发了原始开车钒化,在一定条件下取消钒含量控制,实现了运行中不加钒、中修后开车不钒化的新工艺技术。本技术已通过化工部鉴定,处于国内领先水平,并具有可观的经济效益。 相似文献
8.
Gas-phase selective oxidation of toluene has been carried out on vanadium oxide systems (5–20 wt.% of V2O5, equivalent to 0.4–1.7 theoretical monolayers) supported on TiO2–sepiolite (with titania loading around the theoretical monolayer, 12 wt.%) and on sepiolite. A study has been made on both the influence of vanadia loading and of the support on the catalytic behaviour of the supported vanadium systems. The reducibility by H2 TPR was also studied as well as the acid and basic/redox sites from the results of conversion of the 2-propanol test reaction of the solids. Benzaldehyde, benzoic acid and several coupling products were the main ones detected, attaining over 50% selectivity towards the benzaldehyde and benzoic acid products at a total conversion around 10%. The activity and selectivity to the selective products exhibited by vanadium systems supported on mixed support were superior to those exhibited by the systems supported on sepiolite and increased notably in both series with the increase in vanadium loading. The best catalytic behaviour exhibited by the vanadium systems supported on mixed support, which also exhibited the highest density of sites capable of being reduced (as well as their reducibility) and of those responsible for propanone formation, could be attributed not only to the different balance of the vanadia species existing in the two supports (monomeric + oligomeric/polymeric), but also to such other factors as the nature of the support and, concretely, its chemical composition. 相似文献
9.
10.
三叶状钒催化剂的研制 总被引:1,自引:0,他引:1
介绍了三叶状钒催化剂的研制。工业宏观活性评价和通气测试表明,三叶状催化剂性能优良,其床层压力降介于圆柱状和环状催化剂之间,为圆柱状催化剂的70%左右。在相同的转化条件下,相对于环状催化剂,三叶状催化剂的装填量可减少16.7%。 相似文献