全文获取类型
收费全文 | 91623篇 |
免费 | 7788篇 |
国内免费 | 5111篇 |
专业分类
电工技术 | 6301篇 |
技术理论 | 2篇 |
综合类 | 6484篇 |
化学工业 | 22282篇 |
金属工艺 | 11096篇 |
机械仪表 | 5235篇 |
建筑科学 | 7406篇 |
矿业工程 | 2694篇 |
能源动力 | 2773篇 |
轻工业 | 6273篇 |
水利工程 | 1232篇 |
石油天然气 | 2399篇 |
武器工业 | 1232篇 |
无线电 | 5844篇 |
一般工业技术 | 13744篇 |
冶金工业 | 4534篇 |
原子能技术 | 750篇 |
自动化技术 | 4241篇 |
出版年
2024年 | 409篇 |
2023年 | 1551篇 |
2022年 | 2568篇 |
2021年 | 3042篇 |
2020年 | 2959篇 |
2019年 | 2478篇 |
2018年 | 2415篇 |
2017年 | 3036篇 |
2016年 | 2901篇 |
2015年 | 3021篇 |
2014年 | 4628篇 |
2013年 | 4682篇 |
2012年 | 5852篇 |
2011年 | 6484篇 |
2010年 | 5142篇 |
2009年 | 5375篇 |
2008年 | 4714篇 |
2007年 | 6522篇 |
2006年 | 6061篇 |
2005年 | 5210篇 |
2004年 | 4398篇 |
2003年 | 3866篇 |
2002年 | 3208篇 |
2001年 | 2685篇 |
2000年 | 2356篇 |
1999年 | 1830篇 |
1998年 | 1467篇 |
1997年 | 1148篇 |
1996年 | 1041篇 |
1995年 | 806篇 |
1994年 | 709篇 |
1993年 | 517篇 |
1992年 | 395篇 |
1991年 | 231篇 |
1990年 | 190篇 |
1989年 | 165篇 |
1988年 | 97篇 |
1987年 | 61篇 |
1986年 | 58篇 |
1985年 | 50篇 |
1984年 | 32篇 |
1983年 | 31篇 |
1982年 | 26篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 7篇 |
1959年 | 8篇 |
1957年 | 5篇 |
1955年 | 9篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
101.
H.P. Kuo P.C. KnightD.J. Parker A.S. BurbidgeM.J. Adams J.P.K. Seville 《Powder Technology》2003,132(1):1-9
The motion of sand particles close to a single moving blade was investigated using Positron Emission Particle Tracking (PEPT) during the period in which the free bed surface profile was evolving to an equilibrium shape. The area affected by the blade was divided into active and inactive regions and these were analysed separately. The characteristic heart-shape of the active region in the plan view was determined. An approximately 10-particle-diameter wide velocity transition zone is found between the two regions. While the tracer particle is in the inactive region moving away from the blade, the time dependence of the axial displacement is well described by a logarithmic relationship. The probability of particle movement towards the centre of the blade was quantified using a “central tendency” index. The calculated central tendency shows maxima at each side of the blade. The separation of the two maxima, which indicates the width of the active region, increases with fill level but is independent of rotational speed. 相似文献
102.
103.
一种零电压转换有源功率因数校正电路的研究 总被引:1,自引:0,他引:1
提出了一种基于UC3854的零电压转换有源功率因数校正(ZVT-APFC)的控制电路实现方案,介绍了ZVT电路工作原理,着重分析了由分立元件构成的辅助开关管的驱动电路,通过实验证实了驱动电路的稳定性和可靠性,并通过效率比较验证了ZVT-APFC电路的优良性能。与采用UC3855的电路相比,该电路方案具有简单、可靠、成本低等优点。 相似文献
104.
光学材料的激光微加工研究进展与应用前景 总被引:2,自引:1,他引:1
综述了国内外在光学材料激光微加工方面的研究成果和应用状况,并展望了其发展前景。 相似文献
105.
J. B. Quinn G. E. Schumacher L. W. Schultheis 《Journal of Failure Analysis and Prevention》2004,4(1):41-46
Several days after heart surgery, a patient discovered his upper right canine tooth had broken at the root. Such tooth damage,
recognized post-operatively, is usually assumed to be caused by blunt mechanical force from an instrument used by the anesthesiologist
during placement of a breathing tube at the start of surgery.
In this case, the patient had saved the crown portion of the broken tooth, and it was possible to examine the root fracture
characteristics. The curvature and direction of the crack path and natural tooth situation suggested that failure could be
described through a cantilever beam model. This was confirmed when a whole extracted sample tooth was embedded and broken
by a measured force in a manner consistent with the model. The resulting fracture surface matched that of the patient’s broken
canine tooth. However, the high load and force direction necessary to fracture the root was inconsistent with forces applied
during the anesthesia procedure. The failure analysis and further investigation indicated tooth clenching on the breathing
tube during recovery was the likely cause of fracture.
This paper presents an alternate explanation for intubation-related dental injury, demonstrates the practicality of fractographic
analysis of biological materials, and introduces a methodology for simulating in vitro tooth settings for mechanical testing. 相似文献
106.
We report on picosecond time resolved spectroscopy of photogenerated infrared active vibrations in thin films of 2,5-dioctyloxy poly(phenylene vinylene). We excited the films by ?4 ps long pulses of 565 nm laser light with 2×1013 photons/cm2 per pulse and repetition rate of 76 MHz. We then followed the temporal evolution of the infrared active vibrational (IRAV) spectrum using a subsequent, variably delayed, weak tunable IR probe pulses of similar temporal duration. Under these conditions, we show clear spectroscopic evidence for photogenerated infrared active vibrations at times which are shorter than our temporal resolution (<4 ps). We suggest that the transient IRAV absorption is due to secondary polarons formation following exciton dissociation. 相似文献
107.
基于Intranet/Internet的大坝安全监测信息查询系统 总被引:2,自引:2,他引:0
大坝安全监测信息的网上发布可以让人们了解各种实时、动态信息,文 中主要介绍了在Intranet/Internet下采用ASP(active server pages)结合VBScript,JavaS cript及ActiveX技术进行大坝安全监测信息查询系统开发的方法及步骤,并结合实际系统的 开发加以说明。 相似文献
108.
109.
Investigation into polishing process of CVD diamond films 总被引:1,自引:0,他引:1
A new technique used for polishing chemical vapor deposition (CVD) diamond films has been investigated, by which rough polishing of the CVD diamond films can be achieved efficiently. A CVD diamond film is coated with a thin layer of electrically conductive material in advance, and then electro-discharge machining (EDM) is used to machine the coated surface. As a result, peaks on the surface of the diamond film are removed rapidly. During machining, graphitization of diamond enables the EDM process to continue. The single pulse discharge shows that the material of the coated layer evidently affects removal behavior of the CVD diamond films. Compared with the machining of ordinary metal materials, the process of EDM CVD diamond films possesses a quite different characteristic. The removal mechanism of the CVD diamond films is discussed. 相似文献
110.