全文获取类型
收费全文 | 102738篇 |
免费 | 7880篇 |
国内免费 | 3935篇 |
专业分类
电工技术 | 5333篇 |
技术理论 | 14篇 |
综合类 | 6052篇 |
化学工业 | 17340篇 |
金属工艺 | 5082篇 |
机械仪表 | 5524篇 |
建筑科学 | 7027篇 |
矿业工程 | 2567篇 |
能源动力 | 3086篇 |
轻工业 | 7472篇 |
水利工程 | 1731篇 |
石油天然气 | 4627篇 |
武器工业 | 671篇 |
无线电 | 13482篇 |
一般工业技术 | 13378篇 |
冶金工业 | 6106篇 |
原子能技术 | 1101篇 |
自动化技术 | 13960篇 |
出版年
2024年 | 412篇 |
2023年 | 1602篇 |
2022年 | 2912篇 |
2021年 | 4027篇 |
2020年 | 3120篇 |
2019年 | 2547篇 |
2018年 | 2894篇 |
2017年 | 3028篇 |
2016年 | 2916篇 |
2015年 | 3705篇 |
2014年 | 4707篇 |
2013年 | 5951篇 |
2012年 | 6219篇 |
2011年 | 6947篇 |
2010年 | 5671篇 |
2009年 | 5541篇 |
2008年 | 5546篇 |
2007年 | 5132篇 |
2006年 | 4793篇 |
2005年 | 4078篇 |
2004年 | 3203篇 |
2003年 | 3058篇 |
2002年 | 3109篇 |
2001年 | 2712篇 |
2000年 | 2489篇 |
1999年 | 2700篇 |
1998年 | 2665篇 |
1997年 | 2074篇 |
1996年 | 1941篇 |
1995年 | 1605篇 |
1994年 | 1383篇 |
1993年 | 1019篇 |
1992年 | 788篇 |
1991年 | 607篇 |
1990年 | 562篇 |
1989年 | 501篇 |
1988年 | 388篇 |
1987年 | 305篇 |
1986年 | 237篇 |
1985年 | 204篇 |
1984年 | 166篇 |
1983年 | 115篇 |
1982年 | 122篇 |
1981年 | 91篇 |
1980年 | 115篇 |
1979年 | 61篇 |
1978年 | 66篇 |
1977年 | 67篇 |
1976年 | 89篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
This study used different metals to modify Rh/Al2O3 catalysts for NO reduction in a simulated waste incineration flue gas containing 6% O2. The characteristics of the modified catalysts were analyzed using BET, TEM and XRD. The results of the experiment reveal that Na addition can significantly affect the properties of Rh/Al2O3 catalysts on the BET surface area and Rh metal dispersion. Furthermore, Na addition was found to significantly enhance the NO conversion of Rh/Al2O3 at 250–350 °C. On the contrary, Cu, Ni, and Co addition was found to have slight suppression effects. 相似文献
52.
Min Chan Kim Dong Won Lee Chang Kyun Choi 《Korean Journal of Chemical Engineering》2008,25(6):1239-1244
When a horizontal homogeneous solid is melted from below, convection can be induced in a thermally unstable melt layer. In
this study the onset of buoyancy-driven convection during time-dependent melting is investigated by using similarly transformed
disturbance equations. The critical Rayleigh numbers based on the melt-layer thickness are found numerically for various conditions.
For small superheats, the present predictions approach the well known results of classical Rayleigh-Bénard problems, that
is, critical Rayleigh numbers are located between 1,296 and 1,708, regardless of the Prandtl number. However, for high superheats
the critical Rayleigh number increases with an increase in phase change rate but with decrease in Prandtl number. 相似文献
53.
54.
陆建明 《数字社区&智能家居》2005,(17)
本文利用Windows的API函数将VB窗体前置,避免教师在CAI过程中频繁切换活动窗口,并通过VB控件将各种不同的电子文档内容在窗体中显示出来。 相似文献
55.
MIP-CGP工艺专用催化剂CGP-1的开发与应用 总被引:11,自引:3,他引:8
阐述了生产汽油组分满足欧Ⅲ排放标准并多产丙烯的催化裂化工艺(简称MIP-CGP)专用催化剂(简称CGP-1)的研究开发与工业应用结果。CGP-1催化剂的基质具有良好的容炭性能,使活性组元受到良好保护,其优势作用在第二反应区得以充分发挥,具有更高的氢转移活性和强的汽油小分子烯烃裂化活性。中国石化九江分公司和镇海炼化公司的MIP-CGP工业试验标定结果表明,与常规FCC相比,采用CGP-1催化剂的MIP-CGP技术在生产烯烃体积分数小于18%的汽油组分的同时,丙烯产率达到8%以上。此外,汽油诱导期大幅提高,抗爆指数增加;总液体收率有所提高,干气产率下降,焦炭选择性良好。 相似文献
56.
Jun-Guo Lu Hill D.J. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2008,55(6):586-590
Sampled-data feedback control for master-slave synchronization schemes that consist of identical chaotic Lur'e systems is studied. Sufficient conditions for global asymptotic synchronization of such chaotic Lur'e systems are obtained using the free-weighting matrix approach and expressed in terms of linear matrix inequalities (LMIs). With the help of the LMI solvers, the sampled-data feedback control law can easily be obtained to globally asymptotically synchronize Lur'e chaotic systems. The effectiveness of the proposed method is finally illustrated via numerical simulations of chaotic Chua's circuits. 相似文献
57.
Xin Sun Qiang Lu Moroz V. Takeuchi H. Gebara G. Wetzel J. Shuji Ikeda Changhwan Shin Tsu-Jae King Liu 《Electron Device Letters, IEEE》2008,29(5):491-493
A tri-gate bulk MOSFET design utilizing a low-aspect-ratio channel is proposed to provide an evolutionary pathway for CMOS scaling to the end of the roadmap. 3-D device simulations indicate that this design offers the advantages of a multi-gate FET (reduced variability in performance and improved scalability) together with the advantages of a conventional planar MOSFET (low substrate cost and capability for dynamic threshold-voltage control). 相似文献
58.
Effect of Thickness of the p-AlGaN Electron Blocking Layer on the Improvement of ESD Characteristics in GaN-Based LEDs 总被引:1,自引:0,他引:1
Chung-Hsun Jang Sheu J.K. Tsai C.M. Shei S.C. Lai W.C. Chang S.J. 《Photonics Technology Letters, IEEE》2008,20(13):1142-1144
The following letter presents a study regarding GaN-based light-emitting diodes (LEDs) with p-type AlGaN electron blocking layers (EBLs) of different thicknesses. The study revealed that the LEDs could endure higher electrostatic discharge (ESD) levels as the thickness of the AlGaN EBL increased. The observed improvement in the ESD endurance ability could be attributed to the fact that the thickened p-AlGaN EBL may partly fill the dislocation-related pits that occur on the surface of the InGaN-GaN multiple-quantum well (MQW) and that are due to the strain and the low-temperature-growth process. If these dislocation-related pits are not partly suppressed, they will eventually result in numerous surface pits associated with threading dislocations that intersect the InGaN-GaN (MQW), thereby reducing the ESD endurance ability. The results of the experiment show that the ESD endurance voltages could increase from 1500 to 6000 V when the thickness of the p-AlGaN EBL in the GaN LEDs is increased from 32.5 to 130 nm, while the forward voltages and light output powers remained almost the same. 相似文献
59.
60.
Many approaches have been proposed to enhance software productivity and reliability. These approaches typically fall into three categories: the engineering approach, the formal approach and the knowledge-based approach. But the optimal gain in software productivity cannot be obtained if one relies on only one of these approaches. This paper describes the work in knowledge-based software engineering conducted by the authors for the past 10 years. The final goal of the research is to develop a paradigm for software engineering which integrates the three approaches mentioned above. A knowledge-based tool which can support the whole process of software development is provided in this paper. 相似文献