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   271396篇
  免费   2815篇
  国内免费   664篇
电工技术   5083篇
综合类   229篇
化学工业   38031篇
金属工艺   14466篇
机械仪表   11459篇
建筑科学   6168篇
矿业工程   2014篇
能源动力   5777篇
轻工业   18255篇
水利工程   3336篇
石油天然气   5365篇
武器工业   8篇
无线电   29845篇
一般工业技术   58721篇
冶金工业   42919篇
原子能技术   6079篇
自动化技术   27120篇
  2021年   1607篇
  2019年   1578篇
  2018年   10868篇
  2017年   11460篇
  2016年   7394篇
  2015年   2320篇
  2014年   3171篇
  2013年   9006篇
  2012年   7630篇
  2011年   15127篇
  2010年   13340篇
  2009年   12981篇
  2008年   12819篇
  2007年   14858篇
  2006年   5664篇
  2005年   8722篇
  2004年   6943篇
  2003年   6510篇
  2002年   5175篇
  2001年   4726篇
  2000年   4722篇
  1999年   4758篇
  1998年   11434篇
  1997年   8158篇
  1996年   6448篇
  1995年   4700篇
  1994年   4318篇
  1993年   4115篇
  1992年   3244篇
  1991年   3107篇
  1990年   2873篇
  1989年   2955篇
  1988年   2844篇
  1987年   2407篇
  1986年   2318篇
  1985年   2727篇
  1984年   2521篇
  1983年   2354篇
  1982年   2099篇
  1981年   2211篇
  1980年   2039篇
  1979年   2132篇
  1978年   2129篇
  1977年   2375篇
  1976年   3201篇
  1975年   1837篇
  1974年   1771篇
  1973年   1778篇
  1972年   1448篇
  1971年   1342篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 1, pp. 25–28, January, 1993.  相似文献   
992.
We have examined acetaminophen (paracetamol) dosing for outpatient management of posttonsillectomy pain in children. Forty children, 5-15 years of age, undergoing tonsillectomy and their parents were randomly assigned to use a scheduled administration of acetaminophen in weight appropriate doses, 60 mg.kg-1.24h-1 orally, 90 mg.kg-1.24h-1 rectally, or to use acetaminophen 'as needed' according to present standards (control group). Postoperative pain was assessed by the child using the poker chip tool for the first three days after discharge. The prevalence of pain amongst all the children was high. The second day after discharge 22%-64% of the children in the study group and 36%-73% of the children in the control group rated severe pain. Recommended dose ranges of acetaminophen do not provide sufficient pain relief in children following tonsillectomy. Further studies are required to determine, whether higher doses of acetaminophen or analgesics with different analgesic properties will lead to improved analgesia in children following tonsillectomy.  相似文献   
993.
There is great interest today in massively parallel analytical strategies as a way to accelerate the rate of discovery in biological research; among them being 'biochips' and 'laboratories-on-a-chip'. The concept in the 'chip' approach is that minaturization will allow large numbers of operations to be performed in parallel in a small space, as in electronics. Proceeding with the semiconductor analogy, this paper demonstrates that in situ micromachining can be used to simultaneously fabricate millions of micrometer size, particle like structures in multiple liquid chromatography columns on a single wafer. Reduction of this widely used bioanalytical tool to the nanoliter volume, parallel processing, chip format is a significant step toward laboratories-on-a-chip.  相似文献   
994.
Data compiled by the American Psychological Association (APA) revealed that 7%–10% of ethics complaints filed were against custody evaluators. Comparative data from various state and provincial psychology boards remain too sketchy to permit an accurate appraisal of this problem at the local level. Nevertheless, vulnerability to ethics complaints remains an occupational hazard for the private practitioner who engages in custody assessment. This article offers practitioners who conduct custody evaluations suggestions for reducing their risk of incurring an ethics complaint and discusses variables to consider when responding to a review board inquiry. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
995.
996.
997.
Giving a case example of an male adolescent with radical right-wing attitudes, the lack of male identification as well as in unresolved dyadic fixation to the mother will be shown. Though the radical right-wing orientation the adolescent tries on the basis of a phallic narcissistic conflict to establish bordes against an unresolved dyadic fixation to his mother.  相似文献   
998.
Inflammation of a mixture of Furnon-3KhP refractory mortar prepared using a binary reducer consisting of metallic Al and Mg powders is considered. It is shown that the inflammation temperature can be decreased by 100 – 150°C. Mechanical characteristics of refractory bricks joined by the mortar are determined.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 10, pp. 16 – 19, October, 1996.  相似文献   
999.
A solution to autonomous lateral vehicle guidance using a neurocontroller that can learn from measured human-driving data without knowledge of the physical car parameters is discussed. Simulations and practical tests confirm that a small-size feedforward autonomous neural network (21 neurons) can learn to steer a vehicle at high speeds only from looking at human-driving examples. In this way, the network learns the total closed-loop behavior, including the nonlinear dynamics of the vehicle and the driver's individual driving style. The main result of practical investigations is that the neutral controller trained on human-driving examples exhibits an aperiodic behavior that does not vanish at higher speeds (tests performed up to 130 km/h) and produces fewer lateral deviations than the linear state controller  相似文献   
1000.
Scattering from blood limits the contrast between the vessel wall and the lumen in intravascular ultrasound imaging. This makes it difficult to localize the vessel wall, especially on still images. This paper presents a method for automatic detection of vessel walls and reduction of blood noise based on correlation of the RF-signal between adjacent frames. The ultrasound RF-signal is quadrature demodulated, digitized, stored in memory, and transferred to a computer for processing and analysis. The absolute value of the cross-correlation coefficient between two adjacent frames is used to differentiate between stationary and fluctuating signals. Models and numerical calculations presented in this work indicate that the cross-correlation coefficient obtained from a radially dilating vessel wall will be larger than 0.8 under standard 20 MHz imaging conditions. The corresponding value from blood is less than 0.2 for blood velocities exceeding 0.5 cm s-1 . The blood-noise filter is based on detecting this difference in correlation and displays vessel wall regions with no modifications, while regions detected as blood are rejected. A simplified vessel-wall detector that is suitable for real-time implementation is proposed. The performance of this detector and the blood noise filter are demonstrated by in vitro experiments  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