全文获取类型
收费全文 | 25471篇 |
免费 | 2401篇 |
国内免费 | 1492篇 |
专业分类
电工技术 | 1031篇 |
技术理论 | 1篇 |
综合类 | 1128篇 |
化学工业 | 5081篇 |
金属工艺 | 4416篇 |
机械仪表 | 1354篇 |
建筑科学 | 755篇 |
矿业工程 | 214篇 |
能源动力 | 1325篇 |
轻工业 | 1492篇 |
水利工程 | 68篇 |
石油天然气 | 248篇 |
武器工业 | 226篇 |
无线电 | 2888篇 |
一般工业技术 | 4124篇 |
冶金工业 | 1500篇 |
原子能技术 | 1428篇 |
自动化技术 | 2085篇 |
出版年
2024年 | 90篇 |
2023年 | 529篇 |
2022年 | 894篇 |
2021年 | 1044篇 |
2020年 | 966篇 |
2019年 | 933篇 |
2018年 | 880篇 |
2017年 | 1041篇 |
2016年 | 999篇 |
2015年 | 965篇 |
2014年 | 1381篇 |
2013年 | 1714篇 |
2012年 | 1450篇 |
2011年 | 1847篇 |
2010年 | 1312篇 |
2009年 | 1504篇 |
2008年 | 1374篇 |
2007年 | 1758篇 |
2006年 | 1514篇 |
2005年 | 1210篇 |
2004年 | 1083篇 |
2003年 | 890篇 |
2002年 | 663篇 |
2001年 | 548篇 |
2000年 | 474篇 |
1999年 | 403篇 |
1998年 | 304篇 |
1997年 | 278篇 |
1996年 | 266篇 |
1995年 | 195篇 |
1994年 | 157篇 |
1993年 | 147篇 |
1992年 | 121篇 |
1991年 | 99篇 |
1990年 | 65篇 |
1989年 | 67篇 |
1988年 | 45篇 |
1987年 | 23篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 36篇 |
1981年 | 24篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1959年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
本文讨论了在电子词典生产中的SMT工艺,着重阐述了SMT工艺流程,列举了一些不良焊接及其产生不良焊接的原因以供参考。 相似文献
22.
曹颜顺 《有色金属材料与工程》1994,15(2):97-100
运用扫描电子显微镜技术,对金线断口观察分析,讨论金线在拉伸过程中断裂时断口形貌及断裂的原因,发现,断裂是由于金锭中的气体和杂质引起的,并提出改进生产工艺的意见。 相似文献
23.
New accurate two-noded shear-flexible curved beam elements 总被引:2,自引:0,他引:2
There are two purposes of this work. One is to present two accurate two-noded finite elements which are derived from the
potential energy principle and the Hellinger–Reissner functional principle respectively. The second is to show the successful
application of the internal displacement parameters in developing a high-order related displacement-rotation interpolation
field. Because the derived interpolation field is capable of accurately modeling deformation modes in extreme thin curved
beams and nearly straight beams, both shear locking and membrane shocking are avoided. Several standard numerical tests display
superior behaviors of the present elements.
Received: 5 February 2002 / Accepted: 16 September 2002 相似文献
24.
25.
本文研究了LF6铝合金的超塑性/扩散连接组合工艺,用变形和再结晶的方法细化晶粒,成功地进行了SPF/DB工艺试验,利用电子探针观察了扩散连接接头的界面微观区域,并从机理上分析了金属的超塑性/扩散连接两种工艺之间的内部联系及其金属学行为。 相似文献
26.
In the research presented here, we explore the use of a low‐energy plasma to deposit thin silicone polymer films using tetramethyldisiloxane (TMDSO) (H(CH3)2? Si? O? Si? (CH3)2H) on the surface of an ethylene propylene diene elastomeric terpolymer (EPDM) in order to enhance the surface hydrophobicity, lower the surface energy and improve the degradation/wear characteristics. The processing conditions were varied over a wide range of treatment times and discharge powers to control the physical characteristics, thickness, morphology and chemical structure of the plasma polymer films. Scanning electron microscopy (SEM) shows that pore‐free homogeneous plasma polymer thin films of granular microstructure composed of small grains are formed and that the morphology of the granular structure depends on the plasma processing conditions, such as plasma power and time of deposition. The thicknesses of the coatings were determined using SEM, which confirmed that the thicknesses of the deposited plasma‐polymer films could be precisely controlled by the plasma parameters. The kinetics of plasma‐polymer film deposition were also evaluated. Contact angle measurements of different solvent droplets on the coatings were used to calculate the surface energies of the coatings. These coatings appeared to be hydrophobic and had low surface energies. X‐ray photoelectron spectroscopy (XPS) and photoacoustic Fourier‐transform infrared (PA‐FT‐IR) spectroscopy were used to investigate the detailed chemical structures of the deposited films. The optimum plasma processing conditions to achieve the desired thin plasma polymer coatings are discussed in the light of the chemistry that takes place at the interfaces. Copyright © 2004 Society of Chemical Industry 相似文献
27.
本文着重对微波等离子体化学气相沉积法高速沉积的 a-Si∶H 膜的物理性能进行评价研究.测量了沉积膜的光电性能、暗电导激活能、光禁带宽度、光吸收特性、沉积膜中悬键态密度以及氢含量等,并讨论沉积条件对膜性能的影响.结果表明,在沉积速率高达30~90(?)/s 情况下,膜的光电导(光照强度10~5Lux)与暗电导比值可达10~3~10~5,暗电导率从10~(-3)到10~(-11)((?)cm)~(-1),其激活能在0.23~0.88eV 之间(0~200℃温度范围内),光禁带宽度为1.40~2.20eV,氢含量约为2~20%. 相似文献
28.
29.
This paper mainly focuses on the influence of three kinds of media: air, air-10%PA (Nylon) and air-10% POM (polyoxymethylene) on low-voltage circuit breaker arcs. A threedimensional (3-D) model of arc motioa under the effect of external magnetic field is built based on magnetohydrodynamics (MHD) equations. By adopting the commercial computational fluid dynamics (CFD) package based on the control-volume method, the above MHD equations are solved. For the media of air-10%PA and air-10%POM, the distributions of stationary temperature and electrical potential and the transient motion processes are compared with those of air arc. The research shows that both air-10%PA and air -10% POM can cool the arc plasma and the former is more effective. Both of them can increase the stationary voltage as well. Moreover, the presence of the two mixtures can accelerate the arc motion toward the quenching area and ensures the arc quenched in time. 相似文献
30.
The electron spin resonance (ESR) spectra of end‐group spin labelled poly(ethylene oxide) (SLPEO) using 2,2,6,6‐tetramethyl‐piperdine‐1‐oxyl nitroxide and its blends with poly(styrene‐co‐4‐vinylphenol) (STVPhs) of different hydroxyl contents were recorded over a wide temperature range. For a blend of SLPEO and pure polystyrene (PS), the ESR spectrum was composed of a single motion component, indicating that PS was immiscible with PEO. For blends composed of SLPEO and different‐hydroxyl‐content STVPhs, two spectral components with different motion rates were observed over a certain temperature range. The difference between the motion rates should be attributed to micro‐heterogeneity in the blends, with the faster rate corresponding to a nitroxide radical motion trapped in the PEO‐rich domain and the slower rate corresponding to a nitroxide radical motion trapped in the STVPh‐rich domain. Variations in the values of a number of the ESR parameters (Ta, Td and T50G) and the apparent activation energy (Ea) with hydroxyl content in the blends indicated that the miscibility of the blends increased with increasing hydrogen‐bonding density due to specific interactions between the hydroxyl groups in STVPh and the ether oxygens in PEO. Copyright © 2004 Society of Chemical Industry 相似文献