全文获取类型
收费全文 | 19765篇 |
免费 | 981篇 |
国内免费 | 1063篇 |
专业分类
电工技术 | 324篇 |
综合类 | 592篇 |
化学工业 | 5367篇 |
金属工艺 | 2636篇 |
机械仪表 | 570篇 |
建筑科学 | 225篇 |
矿业工程 | 171篇 |
能源动力 | 2192篇 |
轻工业 | 223篇 |
水利工程 | 352篇 |
石油天然气 | 572篇 |
武器工业 | 56篇 |
无线电 | 2100篇 |
一般工业技术 | 5479篇 |
冶金工业 | 368篇 |
原子能技术 | 348篇 |
自动化技术 | 234篇 |
出版年
2024年 | 45篇 |
2023年 | 364篇 |
2022年 | 454篇 |
2021年 | 609篇 |
2020年 | 615篇 |
2019年 | 580篇 |
2018年 | 529篇 |
2017年 | 653篇 |
2016年 | 562篇 |
2015年 | 527篇 |
2014年 | 874篇 |
2013年 | 1100篇 |
2012年 | 1110篇 |
2011年 | 1854篇 |
2010年 | 1415篇 |
2009年 | 1481篇 |
2008年 | 1301篇 |
2007年 | 1292篇 |
2006年 | 1192篇 |
2005年 | 843篇 |
2004年 | 766篇 |
2003年 | 700篇 |
2002年 | 585篇 |
2001年 | 356篇 |
2000年 | 330篇 |
1999年 | 255篇 |
1998年 | 264篇 |
1997年 | 206篇 |
1996年 | 193篇 |
1995年 | 194篇 |
1994年 | 129篇 |
1993年 | 81篇 |
1992年 | 72篇 |
1991年 | 61篇 |
1990年 | 53篇 |
1989年 | 38篇 |
1988年 | 26篇 |
1987年 | 19篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 6篇 |
1983年 | 12篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1974年 | 3篇 |
1959年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
We have grown helical nanowire assemblies of parylene C, thereby demonstrating that polymeric sculptured thin films (STFs) can be fabricated by a combination of physical and chemical vapor deposition processes. The deposition method is explained in detail and electron micrographs of 200-400 nm size sculptured thin film of parylene are given. The shapes of the submicron and nanowire assemblies can be engineered so that the polymeric STF acts as a template for preferential attachment of biomolecules. 相似文献
22.
碳沉积法制富氮用炭分子筛的研究 总被引:1,自引:0,他引:1
本文提出的碳沉积法是用煤焦油馏分油的有机溶液浸渍煤炭化物,然后热解以进行“孔调变”。确定了最佳工艺条件,制得富氮性能良好的炭分子筛。并用D-A方程求取了各种样品的微孔结构参数。 相似文献
23.
Robert J. Andrews 《Carbon》2006,44(2):341-347
Single walled nanotubes have been synthesized by chemical vapor deposition from camphor, camphor analogs (camphorquinone, norcamphor, norbornane, camphene, fenchone), and various other precursors (menthone, 2-decanone, benzene, methane). The high temperature conditions (865 °C) and Fe/Mo alumina catalyst used in the syntheses are archetypal conditions for the production of single walled carbon nanotubes. It has been shown that the mechanism of tube growth is unlikely to depend upon the production of reactive five- and six-member rings, as has been previously suggested. The results suggest that the presence of oxygen in the precursor does not significantly improve the quality of tubes by etching amorphous carbon: it is suggested that the control of the flux of the precursor to the catalyst is more important in the production of high quality tubes. There is, however, evidence for different distributions of tube diameter being produced from different precursors. 相似文献
24.
25.
26.
Utilising a pseudo-reference electrode in polymer electrolyte fuel cells allows for the separation of anodic and cathodic contributions to the entire cell impedance. Modelling the impedance responses by using equivalent circuits inhibits the investigation of kinetic parameters of the basic electrochemical reactions, which take place at single electrode-electrolyte interfaces. Therefore, we evaluate single electrode impedance measurements by a kinetic model, which is based on specific reaction pathways, either for the oxygen reduction reaction (ORR) or the hydrogen oxidation reaction (HOR). As a consequence, it is possible to obtain kinetic parameters for the specific reaction of interest. Furthermore, the information gained from the single electrode impedance measurements and the kinetic model can give insight into single reactions steps. In particular, the ORR has to include a chemical step in the reaction pathway. 相似文献
27.
Centimeter-size multi-branched tree-like carbon structures have been generated by the catalytic chemical vapor deposition of toluene using ferrocene as the catalyst precursor and investigated by means of SEM, TEM, and EDX. It is found that a temperature of 1000-1200 °C and a carrier gas flow rate of 1000-2500 ml/min are necessary for the generation of the carbon trees. Their morphologies and microstructures change greatly with the changing reaction conditions. The fractal dimensions of the trees are calculated to quantitatively investigate the influence of different reaction temperatures on the morphologies. 相似文献
28.
29.
Polyaniline emeraldine base/epoxy resin (EB/ER) coating was investigated for corrosion protection of mild steel coupled with copper in 3.5% NaCl solution. EB/ER coating with 5-10 wt% EB had long-term corrosion resistance on both uncoupled steel and copper due to the passivation effect of EB on the metal surfaces. During the 150 immersion days, the impedance at 0.1 Hz for the coating increased in the first 1-40 days and subsequently remained constant above 109 Ω cm2, whereas that for pure ER coating fell below 106 Ω cm2 after only 30 or 40 days. Immersion tests on coated steel-copper galvanic couple showed that EB/ER coating offered 100 times more protection than ER coating against steel dissolution and coating delamination on copper, which was mainly attributed to the passive metal oxide films formed by EB blocking both the anodic and cathodic reactions. Salt spray tests showed that 100 μm EB/ER coating protected steel-copper couple for at least 2000 h. 相似文献
30.
For the first time, graphite fibers have been electrochemically intercalated with Br− that have the same structure and properties as those intercalated from vapor phase Br2. This was accomplished by intercalating pitch-based Thornel® K-1100 graphite fibers at low temperature (near 0 °C) and high currents (2 A) for long times (6 h). The mechanism appears to be that Br− is oxidized to aqueous Br2 which, when sufficient local concentration builds up, intercalates the fiber. This was confirmed by intercalating K-1100 fiber in a saturated aqueous Br2 solution without passing an electrical current. The applied voltage does apparently lower the activation energy of the reaction as evidenced by the observation that P-120 and P-100 fibers will not intercalate in aqueous Br2 unless a voltage is applied. 相似文献