全文获取类型
收费全文 | 27225篇 |
免费 | 1600篇 |
国内免费 | 855篇 |
专业分类
电工技术 | 326篇 |
综合类 | 1030篇 |
化学工业 | 15438篇 |
金属工艺 | 1244篇 |
机械仪表 | 154篇 |
建筑科学 | 198篇 |
矿业工程 | 218篇 |
能源动力 | 2117篇 |
轻工业 | 552篇 |
水利工程 | 10篇 |
石油天然气 | 6006篇 |
武器工业 | 84篇 |
无线电 | 160篇 |
一般工业技术 | 1255篇 |
冶金工业 | 661篇 |
原子能技术 | 154篇 |
自动化技术 | 73篇 |
出版年
2024年 | 56篇 |
2023年 | 321篇 |
2022年 | 629篇 |
2021年 | 730篇 |
2020年 | 706篇 |
2019年 | 757篇 |
2018年 | 702篇 |
2017年 | 712篇 |
2016年 | 792篇 |
2015年 | 728篇 |
2014年 | 1417篇 |
2013年 | 1373篇 |
2012年 | 1399篇 |
2011年 | 1779篇 |
2010年 | 1386篇 |
2009年 | 1474篇 |
2008年 | 1388篇 |
2007年 | 1585篇 |
2006年 | 1557篇 |
2005年 | 1371篇 |
2004年 | 1232篇 |
2003年 | 1197篇 |
2002年 | 1057篇 |
2001年 | 947篇 |
2000年 | 836篇 |
1999年 | 677篇 |
1998年 | 582篇 |
1997年 | 408篇 |
1996年 | 408篇 |
1995年 | 329篇 |
1994年 | 279篇 |
1993年 | 201篇 |
1992年 | 158篇 |
1991年 | 115篇 |
1990年 | 107篇 |
1989年 | 83篇 |
1988年 | 52篇 |
1987年 | 34篇 |
1986年 | 17篇 |
1985年 | 21篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1951年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
详述了国内外最新渣油催化裂化、多产柴油催化裂化、低碳烯烃催化裂化、生产清洁燃料催化裂化及催化剂的技术进展,同时根据我国实际情况对今后催化裂化技术的发展提出了建议。 相似文献
53.
磷铝杂原子固体酸催化剂催化合成乙酸异丙酯 总被引:5,自引:0,他引:5
高文艺 《精细石油化工进展》2003,4(12):30-31
以丙烯和乙酸为原料 ,自制的磷铝杂原子固体酸作催化剂催化合成了乙酸异丙酯 ,考察了反应温度、反应压力、反应空速 (LHSV)及催化剂用量对酯化反应的影响 ,同时考察了固体酸催化剂的重复使用性。确定了最佳合成条件 :反应压力 1 5MPa,反应温度 1 60℃ ,反应空速2 0h-1,催化剂用量 2 0g。在此条件下 ,酯化率可达 91 5 % ,乙酸异丙酯选择性达 99 0 % ,且催化剂的重复使用性良好。 相似文献
54.
合成直链烷基苯环境友好固体酸催化剂的研究 Ⅲ .催化剂失活原因分析 总被引:1,自引:0,他引:1
采用固定床反应器,对催化剂的稳定性进行了初步评价。在120℃、空速相同、液固反应条件下,高苯烯比时催化剂的稳定性明显高于低苯烯比时;在苯烯比和空速相同、液固反应条件下,相对低温反应时,催化剂的稳定性明显高于高温反应。IR分析结果表明,同新鲜和反应后未失活的催化剂相比,失活后催化剂的活性组分特征衍射峰消失,出现的新的特征衍射峰可能同—CH基的振动有关。TG分析结果表明,失活后催化剂在空气流中焙烧,失重幅度比新鲜催化剂大。 相似文献
55.
56.
Masaru Kadoshima Masahiko HirataniYasuhiro Shimamoto Kazuyoshi ToriiHiroshi Miki Shinichiro KimuraToshihide Nabatame 《Thin solid films》2003,424(2):224-228
We investigated rutile-type titanium dioxide (TiO2) films for possible use as a high-k gate insulator. The TiO2 thin films were directly deposited on Si substrates using a RF magnetron sputtering method with a sintered oxide target. A single phase of rutile-type TiO2 whose dielectric constant of approximately 75 was obtained when the film was deposited in an inert gas atmosphere and annealed at 800 °C in an oxidizing gas atmosphere. The oxygen ions were deficient in the as-deposited film, and consequently, a sufficient oxygen supply was needed to crystallize the film to a single phase of rutile during the post-annealing. However, the interfacial SiO2 layer between the TiO2 and the Si substrate simultaneously grew thicker than 2 nm. As the interfacial SiO2 grew, the leakage current was decreased and the equivalent oxide thickness was increased, in the Au/rutile-type TiO2/Si capacitor. Therefore, we concluded that the growth of the interfacial SiO2 layer thicker than 2 nm is inevitable to form the single phase of rutile-type TiO2 and to decrease the leakage. 相似文献
57.
MoSi2-based intermetallics containing different volume fractions of MoB or Mo5Si3 were fabricated by hot-pressing MoSi2, MoB, and Mo5Si3 powders in vacuum. Both classes of alloys contained approximately 5 vol.% of dispersed silica phase. Additions of MoB or Mo5Si3 caused the average grain size to decrease. The decrease in the grain size was typically accompanied by an increase in flexure strength, a decrease in the room temperature fracture toughness, and a decrease in the hot strength (compressive creep strength) measured around 1200 °C, except when the Mo5Si3 effectively became the major phase. Oxidation measurements on the two classes of alloys were carried out in air. Both classes of alloys were protected from oxidation by an in-situ adherent scale that formed on exposure to high temperature. The scale, although not analyzed in detail, is commonly recognized in MoSi2 containing materials as consisting mostly of SiO2. The MoB containing materials showed an increase in the scale thickness and the cyclic oxidation rate at 1400 °C when compared with pure MoSi2. However, in contrast with the pure MoSi2 material, oxidation at 1400 °C began with a weight loss followed by a weight gain and the formation of the protective silica layer. The Mo5Si3 containing materials experienced substantial initial weight losses followed by regions of small weight changes. Overall, the MoB and Mo5Si3 additions to MoSi2 tended to be detrimental for the mechanical and oxidative properties. 相似文献
58.
On the basis of new concept using a solid disperse phase we have developed an efficient catalytic solid-phase-system for epoxidations of alkenes using urea–hydrogen peroxide (urea–H2O2) complex and cetylpyridinium dodecatungstate ((CetylPy)10[H2W12O42]) catalyst on fluorapatite (FAp). The recovered solid catalyst phase was reused to keep the catalytic activity after several times. In the conceptual idea it is a key point that in situ solid-phase-activation of the catalyst with urea–H2O2 proceeds to form microcrystals of the active species dispersed on the solid phase. The dispersion of the catalyst on FAp in the case of tungstic acid (H2WO4) was suggested by EPMA analysis. We proposed the peroxo type of species keeping the parent polyoxometalate framework as novel active species from FT-IR spectroscopic studies. FAp phase plays important roles of dispersing the active species on its surface to have high catalytic activity and of stabilizing the active species to lead to high reusability. 相似文献
59.
60.
A solid oxide fuel cell using a thin ceria-based electrolyte film with a Ru-catalyzed anode was directly operated on hydrocarbons, including methane, ethane, and propane, at 600 °C. The role of the Ru catalyst in the anode reaction was to promote the reforming reaction of the unreacted hydrocarbons by the produced steam and CO2, which avoided interference from steam and CO2 in the gas-phase diffusion of the fuels. The resulting peak power density reached 750 mW cm−2 with dry methane, which was comparable to the peak power density of 769 mW cm−2 with wet (2.9 vol.% H2O) hydrogen. More important was the fact that the cell performance was maintained at a high level regardless of the change in the methane utilization from 12 to 46% but was significantly reduced by increasing the hydrogen utilization from 13 to 42%. While the anodic reaction of hydrogen was controlled by the slow gas diffusion, the anodic reaction of methane was not subject to the onset of such a gas-diffusion process. 相似文献