全文获取类型
收费全文 | 4203篇 |
免费 | 383篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 49篇 |
化学工业 | 714篇 |
金属工艺 | 65篇 |
机械仪表 | 67篇 |
建筑科学 | 148篇 |
矿业工程 | 6篇 |
能源动力 | 730篇 |
轻工业 | 271篇 |
水利工程 | 31篇 |
石油天然气 | 10篇 |
无线电 | 363篇 |
一般工业技术 | 562篇 |
冶金工业 | 1267篇 |
原子能技术 | 21篇 |
自动化技术 | 285篇 |
出版年
2021年 | 24篇 |
2020年 | 24篇 |
2019年 | 27篇 |
2018年 | 24篇 |
2017年 | 24篇 |
2016年 | 38篇 |
2015年 | 23篇 |
2014年 | 49篇 |
2013年 | 157篇 |
2012年 | 148篇 |
2011年 | 136篇 |
2010年 | 211篇 |
2009年 | 205篇 |
2008年 | 294篇 |
2007年 | 264篇 |
2006年 | 79篇 |
2005年 | 105篇 |
2004年 | 98篇 |
2003年 | 94篇 |
2002年 | 96篇 |
2001年 | 85篇 |
2000年 | 63篇 |
1999年 | 82篇 |
1998年 | 304篇 |
1997年 | 207篇 |
1996年 | 154篇 |
1995年 | 125篇 |
1994年 | 89篇 |
1993年 | 110篇 |
1992年 | 66篇 |
1991年 | 43篇 |
1990年 | 50篇 |
1989年 | 50篇 |
1988年 | 51篇 |
1987年 | 51篇 |
1986年 | 39篇 |
1985年 | 52篇 |
1984年 | 46篇 |
1983年 | 42篇 |
1982年 | 53篇 |
1981年 | 48篇 |
1980年 | 45篇 |
1979年 | 42篇 |
1978年 | 36篇 |
1977年 | 52篇 |
1976年 | 96篇 |
1975年 | 52篇 |
1974年 | 38篇 |
1973年 | 40篇 |
1972年 | 21篇 |
排序方式: 共有4589条查询结果,搜索用时 15 毫秒
31.
Beardsley Patrick M.; Aceto Mario D.; Cook Charles D.; Bowman Edward R.; Newman Jennifer L.; Harris Louis S. 《Canadian Metallurgical Quarterly》2004,12(3):163
Despite oxycodone's (4,5-epoxy-14-hydroxy-3-methoxy-17-methylmorphinan-6-one) history of clinical use and the attention it has received as a drug of abuse, few reports have documented its pharmacology's relevance to its abuse or its mechanism of action. The purposes of the present study were to further characterize the analgesic effects of oxycodone, its mechanism of action, and its effects in terms of its relevance to its abuse liability. The results indicate that oxycodone had potent antinociceptive effects in the mouse paraphenylquinone writhing, hot-plate, and tail-flick assays, in which it appeared to be acting as a μ-opioid receptor agonist. It generalized to the heroin discriminative stimulus and served as a positive reinforcer in rats and completely suppressed withdrawal signs in morphinedependent rhesus monkeys. These results suggest that the analgesic and abuse liability effects of oxycodone are likely mediated through μ-opioid receptors and provide the first laboratory report of its discriminative stimulus, reinforcing, and morphine cross-dependency effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
32.
33.
Savalani MM Hao L Zhang Y Tanner KE Harris RA 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》2007,221(8):873-886
Hydroxyapatite, a ceramic with which natural bone inherently bonds, has been incorporated into a polymer matrix to enhance the bioactivity of implant materials. In order to manufacture custom-made bioactive implants rapidly, selective laser sintering has been investigated to fabricate hydroxyapatite and polyamide composites and their properties investigated. One objective of this research was to identify the maximum hydroxyapatite content that could be incorporated into the matrix, which was sintered at various parameters. The study focused on investigating the control of porosity and pore size of the matrix by manipulating the selective laser sintering parameters of the laser power and laser scan speed. The interception method was used to analyse the internal porous morphology of the matrices which were cross-sectioned through the vertical plane. Most notably, all structures built demonstrated interconnection and penetration throughout the matrix. Liquid displacement was also used to analyse the porosity of the matrices. The laser power showed a negative relationship between porosity and variation in parameter values until a critical power value was reached. However, the same relationship for laser scan speed matrices was inconsistent. The effects of the laser power and laser scanning speed on the features of porous structures that could influence cell spreading, proliferation, and bone regeneration are presented. 相似文献
34.
Studies using thin boron carbide (B4C) coatings have previously been performed in order to investigate their potential use as finite-life run-in coatings. Such coatings have been shown to polish the mating surface in a relatively short time. The inherent ability of these coatings to polish can potentially allow them to function as finite-life run-in coatings. Employing such coatings requires a thorough understanding of the parameters which directly influence the changes that occur in the coating abrasiveness throughout the duration of the polishing process. In past studies, changes in the coating abrasiveness during dry sliding wear under ambient conditions have been investigated. However, both lubrication and humidity can strongly influence the abrasive wear process. In this study, the influences of the operating environment, namely humidity and lubrication, on the coating abrasiveness are directly investigated. The coating abrasiveness decreases at a slower rate when a lubricant is added and when the humidity decreases. 相似文献
35.
G R Harris 《Medical instrumentation》1975,9(4):192-194
A method is described for measuring the ultrasonic frequency, modulation data, and exposure time of ultrasonic therapy equipment be detection and analysis of the ultrasonic radiation rather than direct measurement of the electrical rf signal. The equipment used in performing these measurements consists of a receiving piezoelectric transducer, ana electron counter/timer designed to accept and process the detected ultrasonic signal, and an oscilloscope. 相似文献
36.
J. O. Harris 《Journal of the Institute of Brewing》1968,74(6):500-510
The processes involved In wort separation are discussed in terms of the underlying mathematical principles as exemplified by the Carman-Kozeny equation, which is applicable to cake filtration, the Moncrieff equation, which is relevant to sparging, and Stokes' Law, which is concerned with settling of particles in regions of viscous flow. The behaviour of small-scale mashes of different types is illustrated photographically. Beer clarification, polishing and sterilization are discussed as further examples of filtration in brewing. 相似文献
37.
R. A. Aitken A. Bruce J. O. Harris J. C. Seaton 《Journal of the Institute of Brewing》1968,74(5):436-440
A simple thin-layer chromatographic procedure for the quantitative analysis of beer bittering substances is described. In the beers examined, 88–100% of the Brenner determination can be attributed to isohumulones A and B and the ratios of these two isomers show a real variation. Alpha-acids have been shown to be present in our beers. Thin-layer chromatography has also been adapted for analysis of hop resins and with fresh hops excellent agreement has been obtained with the conductometric method of analysis. 相似文献
38.
Mary F. Barbe Mamta Amin Michele Y. Harris Siva Tejaa Panibatla Soroush Assari Steven N. Popoff Geoffrey M. Bove 《International journal of molecular sciences》2022,23(12)
The effectiveness of manual therapy in reducing the catabolic effects of performing repetitive intensive force tasks on bones has not been reported. We examined if manual therapy could reduce radial bone microstructural declines in adult female Sprague–Dawley rats performing a 12-week high-repetition and high-force task, with or without simultaneous manual therapy to forelimbs. Additional rats were provided 6 weeks of rest after task cessation, with or without manual therapy. The control rats were untreated or received manual therapy for 12 weeks. The untreated TASK rats showed increased catabolic indices in the radius (decreased trabecular bone volume and numbers, increased osteoclasts in these trabeculae, and mid-diaphyseal cortical bone thinning) and increased serum CTX-1, TNF-α, and muscle macrophages. In contrast, the TASK rats receiving manual therapy showed increased radial bone anabolism (increased trabecular bone volume and osteoblast numbers, decreased osteoclast numbers, and increased mid-diaphyseal total area and periosteal perimeter) and increased serum TNF-α and muscle macrophages. Rest, with or without manual therapy, improved the trabecular thickness and mid-diaphyseal cortical bone attributes but not the mineral density. Thus, preventive manual therapy reduced the net radial bone catabolism by increasing osteogenesis, while rest, with or without manual therapy, was less effective. 相似文献
39.
40.
High-Performance Optical 3R Regeneration for Scalable Fiber Transmission System Applications 总被引:1,自引:0,他引:1
Zuqing Zhu Funabashi M. Zhong Pan Paraschis L. Harris D.L. Yoo S.J.B. 《Lightwave Technology, Journal of》2007,25(2):504-511
This paper proposes and demonstrates optical 3R regeneration techniques for high-performance and scalable 10-Gb/s transmission systems. The 3R structures rely on monolithically integrated all-active semiconductor optical amplifier-based Mach-Zehnder interferometers (SOA-MZIs) for signal reshaping and optical narrowband filtering using a Fabry-Peacuterot filter (FPF) for all-optical clock recovery. The experimental results indicate very stable operation and superior cascadability of the proposed optical 3R structure, allowing error-free and low-penalty 10-Gb/s [pseudorandom bit sequence (PRBS) 223-1 ] return-to-zero (RZ) transmission through a record distance of 1 250 000 km using 10 000 optical 3R stages. Clock-enhancement techniques using a SOA-MZI are then proposed to accommodate the clock performance degradations that arise from dispersion uncompensated transmission. Leveraging such clock-enhancement techniques, we experimentally demonstrate error-free 125 000-km RZ dispersion uncompensated transmission at 10 Gb/s (PRBS 223-1) using 1000 stages of optical 3R regenerators spaced by 125-km large-effective-area fiber spans. To evaluate the proposed optical 3R structures in a relatively realistic environment and to investigate the tradeoff between the cascadability and the spacing of the optical 3R, a fiber recirculation loop is set up with 264- and 462-km deployed fiber. The field-trial experiment achieves error-free 10-Gb/s RZ transmission using PRBS 223-1 through 264 000-km deployed fiber across 1000 stages of optical 3R regenerators spaced by 264-km spans 相似文献