全文获取类型
收费全文 | 56232篇 |
免费 | 3466篇 |
国内免费 | 2362篇 |
专业分类
电工技术 | 1021篇 |
技术理论 | 1篇 |
综合类 | 2317篇 |
化学工业 | 17448篇 |
金属工艺 | 9860篇 |
机械仪表 | 3988篇 |
建筑科学 | 2026篇 |
矿业工程 | 1183篇 |
能源动力 | 1522篇 |
轻工业 | 4220篇 |
水利工程 | 304篇 |
石油天然气 | 1633篇 |
武器工业 | 326篇 |
无线电 | 2268篇 |
一般工业技术 | 9518篇 |
冶金工业 | 2324篇 |
原子能技术 | 462篇 |
自动化技术 | 1639篇 |
出版年
2025年 | 13篇 |
2024年 | 812篇 |
2023年 | 1086篇 |
2022年 | 1591篇 |
2021年 | 1720篇 |
2020年 | 1607篇 |
2019年 | 1365篇 |
2018年 | 1417篇 |
2017年 | 1710篇 |
2016年 | 1653篇 |
2015年 | 1755篇 |
2014年 | 2563篇 |
2013年 | 3274篇 |
2012年 | 3499篇 |
2011年 | 4212篇 |
2010年 | 3131篇 |
2009年 | 3307篇 |
2008年 | 2869篇 |
2007年 | 3567篇 |
2006年 | 3373篇 |
2005年 | 2860篇 |
2004年 | 2561篇 |
2003年 | 2119篇 |
2002年 | 1841篇 |
2001年 | 1463篇 |
2000年 | 1255篇 |
1999年 | 1055篇 |
1998年 | 884篇 |
1997年 | 744篇 |
1996年 | 583篇 |
1995年 | 498篇 |
1994年 | 372篇 |
1993年 | 317篇 |
1992年 | 263篇 |
1991年 | 177篇 |
1990年 | 134篇 |
1989年 | 113篇 |
1988年 | 74篇 |
1987年 | 39篇 |
1986年 | 49篇 |
1985年 | 33篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
Target differentiation with simple infrared sensors using statistical pattern recognition techniques
Billur Barshan Author Vitae Tayfun Aytaç Author VitaeAuthor Vitae 《Pattern recognition》2007,40(10):2607-2620
This study compares the performances of various statistical pattern recognition techniques for the differentiation of commonly encountered features in indoor environments, possibly with different surface properties, using simple infrared (IR) sensors. The intensity measurements obtained from such sensors are highly dependent on the location, geometry, and surface properties of the reflecting feature in a way that cannot be represented by a simple analytical relationship, therefore complicating the differentiation process. We construct feature vectors based on the parameters of angular IR intensity scans from different targets to determine their geometry and/or surface type. Mixture of normals classifier with three components correctly differentiates three types of geometries with different surface properties, resulting in the best performance (100%) in geometry differentiation. Parametric differentiation correctly identifies six different surface types of the same planar geometry, resulting in the best surface differentiation rate (100%). However, this rate is not maintained with the inclusion of more surfaces. The results indicate that the geometrical properties of the targets are more distinctive than their surface properties, and surface recognition is the limiting factor in differentiation. The results demonstrate that simple IR sensors, when coupled with appropriate processing and recognition techniques, can be used to extract substantially more information than such devices are commonly employed for. 相似文献
23.
R. van Tijum 《Surface & coatings technology》2007,201(8):4633-4639
This paper concentrates on revealing the local deformation as a function of applied strain in a polymer coating supported by a plastically deforming and roughening metal substrate. To this end in-situ birefringence microscopy measurements have been executed. The measurements are performed in reflection and an alternative unwrapping scheme for the optical path difference is proposed. From the characterization of PET (polyethylene terephthalate) coated stainless steel it is concluded that strain localization appears below the macroscopic strain at yield and that the surface roughness of the substrate is the driving force of the localization. 相似文献
24.
对FK6-600牵伸加弹机主传动中"格里森"制圆弧螺旋齿轮的失效情况进行了考察和研究。通过对德国DIN867和我国JB110标准的分析,采用了等顶隙收缩齿并对其进行了合理改进,同时在现场安装工作中采取了必要措施,取得了较好的技术经济效果。 相似文献
25.
26.
27.
Pipelines and heat exchangers using seawater as coolant suffer from biofouling. Biofouling not only reduces heat transfer performance significantly, but also causes considerable pressure drop, calling for higher pumping requirements. It would be much more desirable if surfaces with an inherently lower stickability for biofouling could be developed. In this paper, a cost-effective autocatalytic graded Ni-Cu-P-PTFE composite coating with corrosion-resistant properties was applied to reduce biofouling formation. The experimental results showed that the surface free energy of the Ni-Cu-P-PTFE coatings, which were altered by changing the PTFE content in the coatings, had a significant influence on the adhesion of microbial and mineral deposits. The Ni-Cu-P-PTFE coatings with defined surface free energy reduced the adhesion of these deposits significantly. The anti-bacterial mechanism of the composite coatings was explained with the extended DLVO theory. 相似文献
28.
Pellets containing metronidazole were produced in a centrifugal granulator, with hydroxypropylcellulose (Klucel LF®) as binding agent, and corn starch, microcrystalline cellulose (Vivapur 101®) and lactose as excipients. The wettability of the pharmaceutical powders was assessed by means of contact angle measurements, and the dispersive and polar surface energies were determined. The spreading coefficients, the work of adhesion and the work of cohesion were calculated and correlated with the pellet properties (friability, bulk and tapped density, and porosity). The aim was to investigate the role of the surface free energy of one- and two-component powder compositions in pellet production. The interactions between the particles were found to be connected with the measured pellet parameters. It was concluded that, in the course of the growth of the pellets, the particle sizes of the pharmaceutical powders and the interactions between them are important. If the work of cohesion of the binder is lower than the work of cohesion of the substrate and the work of adhesion, then the optimal amount of the binding agent is that which coats the particles uniformly in minimal quantity and in continuous layer. 相似文献
29.
30.
石化换热器许多设备都由碳钢制作,需要涂镀渗防腐,为保证防腐层质量,需要进行严格的表面预处理。概述了机械与化学表面预处理及相关的防腐工艺。 相似文献