全文获取类型
收费全文 | 1156篇 |
免费 | 13篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 8篇 |
综合类 | 2篇 |
化学工业 | 67篇 |
金属工艺 | 7篇 |
机械仪表 | 9篇 |
建筑科学 | 29篇 |
能源动力 | 41篇 |
轻工业 | 66篇 |
水利工程 | 6篇 |
石油天然气 | 5篇 |
无线电 | 119篇 |
一般工业技术 | 74篇 |
冶金工业 | 673篇 |
原子能技术 | 20篇 |
自动化技术 | 47篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 10篇 |
2018年 | 11篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 18篇 |
2013年 | 18篇 |
2012年 | 20篇 |
2011年 | 35篇 |
2010年 | 21篇 |
2009年 | 22篇 |
2008年 | 30篇 |
2007年 | 29篇 |
2006年 | 19篇 |
2005年 | 29篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 14篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 146篇 |
1997年 | 100篇 |
1996年 | 84篇 |
1995年 | 49篇 |
1994年 | 36篇 |
1993年 | 42篇 |
1992年 | 16篇 |
1991年 | 24篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 17篇 |
1987年 | 9篇 |
1986年 | 15篇 |
1985年 | 21篇 |
1984年 | 12篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 36篇 |
1976年 | 69篇 |
1975年 | 5篇 |
1973年 | 3篇 |
排序方式: 共有1173条查询结果,搜索用时 15 毫秒
1.
PURPOSE: Our goal was to review the CT findings and to help define the role of CT in the evaluation of appendicitis in children. METHOD: Of 730 children with surgically proven appendicitis, 22 underwent preoperative CT evaluation. Their CT scans and operative and pathology records were retrospectively reviewed. The CT scans were evaluated for appendiceal wall thickness, diameter, and location, appendicoliths, pericecal inflammation, phlegmon, abscess, free fluid, small bowel dilatation, and bowel wall thickening. Criteria for diagnosing appendicitis were (a) appendiceal wall thickening (> 1 mm) or (b) presence of abscess, phlegmon, or pericecal inflammation associated with appendicolith(s). Prospective reports of ultrasound examinations performed within 2 days of the CT scans were available in 14 children and were correlated with the CT findings. RESULTS: An abnormally thickened appendix, with a diameter ranging from 9 to 18 mm, was seen in four children. Three appendices were retrocecal and one was near the cecal tip, anterior to the iliac vessels. Appendicoliths were present in 10 children, multiple in 1. Abscesses were seen in 13 of 22 children, multiple in 5. Phlegmon was seen in five children and pericecal inflammation in two. Bowel wall thickening was present in seven children and small bowel dilatation was noted in six. Other findings included free fluid, hydronephrosis, thickening of urinary bladder wall, air in the uterus and vagina, adenopathy, and thickening of the abdominal wall musculature. CT was diagnostic of appendicitis in 11 of 22 children (50%). In 14 children with both ultrasound and CT studies, CT was slightly better in diagnosing appendicitis and visualizing the abnormal appendix and was superior in defining the presence and extent of abscess and inflammation in 9 of 14 children. CONCLUSION: CT is a useful adjunct in diagnosing appendicitis in children, with a major role in cases of complicated appendicitis. 相似文献
2.
D Averill D Blockus B Brabson J Brom C Jung H Ogren DR Rust M Derrick P Kooijman JS Loos B Musgrave LE Price J Repond K Sugano B Cork C Akerlof J Chapman D Errede MT Ken DI Meyer H Neal D Nitz R Thun R Tschirhart S Abachi P Baringer BG Bylsma R DeBonte D Koltick EH Low RL McIlwain DH Miller CR Ng EI Shibata 《Canadian Metallurgical Quarterly》1989,39(1):123-137
3.
4.
In 4 experiments, chronometric evidence for keypress schemata in typing was sought by presenting stimuli to be typed in positions that were displaced from a central fixation point. Reaction times were shorter when stimulus positions corresponded to keyboard locations of the letters to be typed, suggesting that position was an important part of the internal representation of the response. Experiment 1 presented single letters left and right of fixation. Experiment 2 presented single letters above and below fixation. Experiment 3 presented words left and right of fixation and found evidence of parallel activation of keypress schemata. Experiment 4 found no effect of the eccentricity of the keyboard locations and responding fingers, suggesting that response-location codes are categorical, not metric. The results are consistent with D. E. Rumelhart and D. A. Norman's (1982) theory of typewriting. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
5.
Buried heterostructure lasers with highly strained InGaAs-InGaAsP active regions, emitting at 2 μm have been fabricated and tested. The lasers exhibited threshold current densities of 500 A/cm2 for 1-mm-long cavities, an internal loss of 11 cm-1, and characteristic temperatures as high as 50°C. The gain characteristics were also investigated and a linewidth enhancement factor of 8 was determined 相似文献
6.
7.
Neudorf E.G. Kiguel D.L. Hamoud G.A. Porretta B. Stephenson W.M. Sparks R.W. Logan D.M. Bhavaraju M.P. Billinton R. Garrison D.L. 《Power Systems, IEEE Transactions on》1995,10(3):1667-1675
There is an emerging recognition that utility investments and other decisions that affect electric service reliability should be explicitly evaluated on the basis of their cost and benefit implications. A cost-benefit approach that quantifies the reliability benefits of alternatives in terms of the reduction in costs resulting from unserved energy enables the evaluation of generation and transmission capacity additions on a consistent, economic basis. This approach has been applied to two utility case studies. In a case study for Pacific Gas and Electric Company, it was used to evaluate three options for maintaining reliability in a major load center-two involving local generation, and the third, a new 230 kV transmission connection. In a case study for Duke Power Company, the approach was used to evaluate alternative designs for proposed additions to a transmission station. This paper describes the methodology and presents the two utility studies 相似文献
8.
9.
10.