首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1515篇
  免费   20篇
  国内免费   6篇
电工技术   22篇
化学工业   138篇
金属工艺   6篇
机械仪表   19篇
建筑科学   39篇
矿业工程   2篇
能源动力   11篇
轻工业   58篇
水利工程   13篇
石油天然气   3篇
无线电   112篇
一般工业技术   142篇
冶金工业   905篇
原子能技术   2篇
自动化技术   69篇
  2023年   4篇
  2022年   5篇
  2021年   4篇
  2020年   7篇
  2019年   4篇
  2018年   10篇
  2017年   5篇
  2016年   10篇
  2015年   9篇
  2014年   9篇
  2013年   43篇
  2012年   14篇
  2011年   28篇
  2010年   24篇
  2009年   17篇
  2008年   32篇
  2007年   36篇
  2006年   30篇
  2005年   20篇
  2004年   19篇
  2003年   20篇
  2002年   23篇
  2001年   14篇
  2000年   12篇
  1999年   54篇
  1998年   278篇
  1997年   192篇
  1996年   104篇
  1995年   82篇
  1994年   71篇
  1993年   59篇
  1992年   14篇
  1991年   21篇
  1990年   18篇
  1989年   12篇
  1988年   24篇
  1987年   16篇
  1986年   21篇
  1985年   19篇
  1984年   9篇
  1983年   4篇
  1982年   8篇
  1981年   6篇
  1980年   20篇
  1979年   5篇
  1978年   10篇
  1977年   22篇
  1976年   49篇
  1975年   6篇
  1973年   5篇
排序方式: 共有1541条查询结果,搜索用时 15 毫秒
11.
This paper argues that shiftworkers may have gradually habituated to their problems and hence that they underestimate them. Some support for this view was obtained in a 'reminiscence' questionnaire study of retired UK Police Officers who had all subsequently taken on another (mainly day-time) job. They completed a specially constructed questionnaire, which included several measures of health and well being, and in which they were asked to reminisce about how they had felt while still a shiftworker. These reminiscence scores were compared to their current perception of how they were. The results clearly indicated that individuals in retrospect perceive their situation as being worse than they realised at the time. This effect was most marked for scores on the General Health Questionnaire and Chronic Fatigue scale. The results of this study draw attention to a potential confounding in much of the shiftwork literature which demands further, more detailed, investigation.  相似文献   
12.
The seasonal variation in the nutrient composition of Enhydra fluctuans and Marsilea quadrifolia, two edible semi-aquatic plants, was studied in order to promote their consumption as green leafy vegetables. Both plants had a high crude protein content throughout all harvesting seasons. Enhydra fluctuans had a low ash content and was a good source of beta-carotene (3.7 to 4.2 mg/100 g on a fresh weight basis). Marsilea quadrifolia exhibited wide fluctuations between seasons and was not very promising in nutrient composition when compared to other commonly used green leafy vegetables.  相似文献   
13.
14.
15.
16.
17.
Wavelength-agile photonic integrated circuits are fabricated using a one-step ion implantation quantum-well intermixing process. In this paper, we discuss, the issues in processing optimized widely tunable multisection lasers using this technique and present the results achieved using this process. This quantum-well intermixing process is general in its application and can be used to monolithically integrate a wide variety of optoelectronic components with widely tunable lasers.  相似文献   
18.
Although regulations on work hours usually include a minimum weekly rest period, there is little empirical evidence concerning recovery from work. Shift-working nurses (N?=?61) used a handheld computer for 28 days to complete self-ratings, cognitive-performance tasks, and a sleep diary. Many measures were worse on rest days that followed a night shift rather than a day shift and tended to be worse on 1st rest days compared with subsequent rest days. Alertness was lowest on the 1st rest day following a night shift. Social satisfaction was better on workdays that were preceded by 2 rather than 1 rest day. Reaction time (RT) decreased over consecutive night shifts and tended to increase over rest days following night shifts. The results are interpreted as being consistent with the combined adaptive costs of fatigue and adjustment to and from a nocturnal routine. The practical implications for scheduling rest days are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
19.
Narrow pulse measurement of drain characteristics of GaAs MESFETs   总被引:2,自引:0,他引:2  
A measurement technique is presented which uses narrow, fast-rise-time pulses applied to both the gate and the drain of a GaAs MESFET to obtain the drain characteristics of the device. This allows the characteristics of the device to be obtained which correspond to frequencies above those at which surface and substrate traps can respond. The resulting characteristics show significant departures from those obtained using conventional long pulse and DC measurement techniques.  相似文献   
20.
BACKGROUND: Endoscopic sclerotherapy (ST), widely used as treatment of bleeding esophageal varices, might cause motility disturbances of the esophagus as well as mucosal damage. We performed this study to evaluate the long-term effects of repeated sclerotherapy on esophageal motility and mucosa. METHODS: Ten patients with liver cirrhosis and bleeding esophageal varices treated with repeated ST were evaluated after the last ST, median 52 months, by esophageal manometry and gastroscopy where forceps biopsies were taken. RESULTS: We found a significant difference in the distal esophageal sphincter intraabdominal length. The distal esophageal sphincter pressure was somewhat lower in the ST group although the difference did not reach statistical significance. There was infiltration of neutrophil leukocytes in biopsies from four patients and normal findings in the rest. CONCLUSIONS: Long-term follow-up evaluation showed statistically longer distal esophageal intraabdominal length in the ST group. No mucosal alterations were found at the histopathological investigation.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号