全文获取类型
收费全文 | 12460篇 |
免费 | 679篇 |
国内免费 | 284篇 |
专业分类
电工技术 | 371篇 |
综合类 | 561篇 |
化学工业 | 3126篇 |
金属工艺 | 296篇 |
机械仪表 | 527篇 |
建筑科学 | 921篇 |
矿业工程 | 400篇 |
能源动力 | 2875篇 |
轻工业 | 1388篇 |
水利工程 | 328篇 |
石油天然气 | 1128篇 |
武器工业 | 10篇 |
无线电 | 214篇 |
一般工业技术 | 484篇 |
冶金工业 | 588篇 |
原子能技术 | 66篇 |
自动化技术 | 140篇 |
出版年
2024年 | 24篇 |
2023年 | 221篇 |
2022年 | 372篇 |
2021年 | 495篇 |
2020年 | 490篇 |
2019年 | 484篇 |
2018年 | 370篇 |
2017年 | 399篇 |
2016年 | 356篇 |
2015年 | 309篇 |
2014年 | 734篇 |
2013年 | 682篇 |
2012年 | 825篇 |
2011年 | 909篇 |
2010年 | 741篇 |
2009年 | 727篇 |
2008年 | 625篇 |
2007年 | 745篇 |
2006年 | 640篇 |
2005年 | 548篇 |
2004年 | 445篇 |
2003年 | 444篇 |
2002年 | 337篇 |
2001年 | 268篇 |
2000年 | 244篇 |
1999年 | 212篇 |
1998年 | 137篇 |
1997年 | 117篇 |
1996年 | 118篇 |
1995年 | 87篇 |
1994年 | 71篇 |
1993年 | 65篇 |
1992年 | 56篇 |
1991年 | 32篇 |
1990年 | 19篇 |
1989年 | 22篇 |
1988年 | 19篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 385 毫秒
51.
通过改进铅膏的配方及极板的独特处理工艺 ,提高了干电荷电摩托车电池的低温高率放电性能、充电接受能力和储存性能 ,完全可以满足国内外摩托车主机厂的各种要求。 相似文献
52.
53.
生物产量是提高经济产量的基础,而施肥是调控生物产量及其组分动态转化的重要手段。本研究通过不同施钾水平对玉米干物质积累动态变化的影响分析,确定出钾肥合理用量,为玉米高产高效栽培提供理论依据。 相似文献
54.
Dimitris K. Liguras Dimitris I. Kondarides Xenophon E. Verykios 《Applied catalysis. B, Environmental》2003,43(4):345-354
The catalytic performance of supported noble metal catalysts for the steam reforming (SR) of ethanol has been investigated in the temperature range of 600–850 °C with respect to the nature of the active metallic phase (Rh, Ru, Pt, Pd), the nature of the support (Al2O3, MgO, TiO2) and the metal loading (0–5 wt.%). It is found that for low-loaded catalysts, Rh is significantly more active and selective toward hydrogen formation compared to Ru, Pt and Pd, which show a similar behavior. The catalytic performance of Rh and, particularly, Ru is significantly improved with increasing metal loading, leading to higher ethanol conversions and hydrogen selectivities at given reaction temperatures. The catalytic activity and selectivity of high-loaded Ru catalysts is comparable to that of Rh and, therefore, ruthenium was further investigated as a less costly alternative. It was found that, under certain reaction conditions, the 5% Ru/Al2O3 catalyst is able to completely convert ethanol with selectivities toward hydrogen above 95%, the only byproduct being methane. Long-term tests conducted under severe conditions showed that the catalyst is acceptably stable and could be a good candidate for the production of hydrogen by steam reforming of ethanol for fuel cell applications. 相似文献
55.
山西省横泉水库在原有遗留工程基础上进行重新建设,以往的4次施工,填兢了长400m、高17m左右的左岸坝体,填土约120万m^3,但坝体填筑质量极差,干客重和渗透系数根本无法满足设计要求。此次重新建设,决定对这部分干客重不迭设计要求且具有湿陷性的左岸旧坝体以及左岸黄土台地进行强夯处理,对坝体进行强夯处理在省内还是首次进行,在国内也比较少见,通过处理,坝体质量达到了设计要求,并且节约了投资,效果明显。 相似文献
56.
The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH4 traces under lean-burn conditions was studied in the presence or the absence of water or H2S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H2S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H2S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H2S-poisoned Pd/Al2O3 catalyst was studied by TPD in O2/He. Poisoning species decompose above 873 K as SO2 and O2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O2/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H2S-poisoned Pd/Al2O3. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested. 相似文献
57.
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
58.
59.
Further evidence was delivered that certain impurities, which could be contained in MgO samples, might be responsible for observed variability in MgO basicity and catalytic performance in oxidative coupling of methane. The surface basicity/base strength distribution of a series of MgO samples containing or not containing Ca and Na impurities was determined by a temperature-programmed desorption of CO2. It was revealed that samples containing Ca and Na impurities have much more medium, strong and very strong basic sites. The surface basicity of MgO samples containing added alkali or alkaline earth compounds or water was characterized by a test reaction of transformation of 2-butanol. It was confirmed that the introduction of these compounds to a pure MgO enhanced both its basicity and activity in oxidative coupling of methane. 相似文献
60.
聚氨酯干法涂层的应用 总被引:1,自引:0,他引:1
潘云芳 《南通纺织职业技术学院学报》2002,2(3):37-39
介绍了涂层织物的特点及聚氨酯在涂层整理中的作用,并对干法直接涂层工艺进行了探讨. 相似文献