全文获取类型
收费全文 | 16792篇 |
免费 | 1102篇 |
国内免费 | 841篇 |
专业分类
电工技术 | 1057篇 |
综合类 | 787篇 |
化学工业 | 5353篇 |
金属工艺 | 1628篇 |
机械仪表 | 614篇 |
建筑科学 | 915篇 |
矿业工程 | 175篇 |
能源动力 | 250篇 |
轻工业 | 947篇 |
水利工程 | 58篇 |
石油天然气 | 475篇 |
武器工业 | 108篇 |
无线电 | 1472篇 |
一般工业技术 | 1966篇 |
冶金工业 | 536篇 |
原子能技术 | 243篇 |
自动化技术 | 2151篇 |
出版年
2024年 | 58篇 |
2023年 | 241篇 |
2022年 | 557篇 |
2021年 | 600篇 |
2020年 | 447篇 |
2019年 | 397篇 |
2018年 | 321篇 |
2017年 | 389篇 |
2016年 | 518篇 |
2015年 | 531篇 |
2014年 | 761篇 |
2013年 | 953篇 |
2012年 | 991篇 |
2011年 | 1258篇 |
2010年 | 988篇 |
2009年 | 1061篇 |
2008年 | 963篇 |
2007年 | 1136篇 |
2006年 | 1075篇 |
2005年 | 828篇 |
2004年 | 681篇 |
2003年 | 606篇 |
2002年 | 533篇 |
2001年 | 412篇 |
2000年 | 355篇 |
1999年 | 288篇 |
1998年 | 231篇 |
1997年 | 181篇 |
1996年 | 164篇 |
1995年 | 109篇 |
1994年 | 95篇 |
1993年 | 108篇 |
1992年 | 85篇 |
1991年 | 74篇 |
1990年 | 64篇 |
1989年 | 64篇 |
1988年 | 45篇 |
1987年 | 41篇 |
1986年 | 54篇 |
1985年 | 56篇 |
1984年 | 46篇 |
1983年 | 39篇 |
1982年 | 35篇 |
1981年 | 33篇 |
1980年 | 34篇 |
1978年 | 35篇 |
1977年 | 39篇 |
1976年 | 43篇 |
1975年 | 48篇 |
1974年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
141.
142.
Fourier transform infrared spectroscopy was used to investigate PA6/clay nanocomposites (PA6CN) with various cooling histories from the melt, including rapid cooling (water-quenched), middle-rate cooling (air-cooling) and slow cooling (mold-cooling). In contrast to pure PA6 dominated by the α-phase, the addition of clay silicate layers favor the formation of the γ-crystalline phase in PA6CN.We focus on the reason why silicate layers favor the formation of γ-phase in PA6. Vaia et al. suggested that the addition of clay layers forces the amide groups of PA6 out of the plane formed by the chains. This results in conformational changes of the chains, which limits the formation of H-bonded sheets so that the γ-phase is favored. If this assumption is correct, PA6CN is expected to show some differences as compared with PA6 with respect to hydrogen bonding.The silicate layers were indeed found to weaken the hydrogen bonding both in the α- and γ-phases. This was also confirmed by X-ray diffraction studies. The γ-phase is most likely concentrated in regions close to the silicate layers, whereas the α-phase is favored in the bulk matrix. 相似文献
143.
144.
以2,6-二氯吡啶为原料,制得2,6-二溴吡啶(收率79%)或2,6-二碘吡啶(收率56%),再分别与三氟乙酸钾反应,均可得标题化合物,收率28%~53%。该合成路线的优点是原料易得,反应条件温和,收率较高。 相似文献
145.
146.
连续加压炔化反应合成脱氢芳樟醇 总被引:1,自引:0,他引:1
研究了以液氨为溶剂 ,在反应温度 35~ 4 0℃ ,压力 2 0~ 2 5MPa的条件下 ,6 甲基 5 庚烯 2 酮连续加压乙炔化反应制备脱氢芳樟醇工艺 ,考察了反应时间、物料量比对反应的影响 ,并对反应机理作了初步探讨。实验表明 ,反应温度 35~ 4 0℃ ,压力 2 0~ 2 5MPa ,n (6 甲基 5 庚烯 2 酮 )∶n (催化剂 )∶n(乙炔 )∶n(液氨 ) =7∶1∶5 1∶15 3,反应时间为 2 1h ,脱氢芳樟醇收率为 92 %~ 94 % ,产品经减压精馏后 ,脱氢芳樟醇质量分数大于 98% 相似文献
147.
This paper deals with the activity of the KCu and KCo catalysts supported on beta-zeolite for the simultaneous NOx/soot removal from a simulated diesel exhaust, containing C3H6 as model hydrocarbon. In order to reveal the effect of potassium, the corresponding monometallic catalysts (Co/beta and Cu/beta) were analyzed and different potassium loadings were used. In addition, for comparative purpose, the performance of a platinum based catalyst (Pt/beta) was studied. All noble-free catalysts show, at 450 °C, a high activity for the simultaneous NOx/soot removal. Among them, K1Cu/beta presents the best global performance at 350 and 450 °C achieving a high soot consumption rate (comparable to platinum catalysts) and the highest NOx reduction. In contrast to platinum catalysts, K1Cu/beta has the advantage that the main reaction products are N2 and CO2. 相似文献
148.
149.
150.
Ammoxidation of toluene over the perovskites YBa2Cu3O6.1, YBa2Cu2CoO6.7 and YBaCuCoO4.9 was investigated at 400 °C. At low partial pressures of O2 benzonitrile was selectively formed, while CO2 was the main product at high pressures of O2. Systematic differences in activity were observed for the three phases and are related to the crystal contents of Cu and Co. At low O2 pressures, Cu-sites are active for nitrile formation, while Co-sites give CO2. At high O2 pressures, the activity for CO2 of Cu-sites increases more than that of Co-sites due to filling of near-surface oxygen vacancies. 相似文献