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   896篇
  免费   25篇
  国内免费   4篇
电工技术   38篇
综合类   1篇
化学工业   185篇
金属工艺   13篇
机械仪表   20篇
建筑科学   10篇
能源动力   26篇
轻工业   50篇
水利工程   1篇
无线电   95篇
一般工业技术   161篇
冶金工业   223篇
原子能技术   25篇
自动化技术   77篇
  2023年   11篇
  2022年   17篇
  2021年   16篇
  2020年   5篇
  2019年   9篇
  2018年   18篇
  2017年   10篇
  2016年   12篇
  2015年   9篇
  2014年   11篇
  2013年   38篇
  2012年   31篇
  2011年   47篇
  2010年   30篇
  2009年   34篇
  2008年   45篇
  2007年   28篇
  2006年   33篇
  2005年   21篇
  2004年   22篇
  2003年   16篇
  2002年   18篇
  2001年   25篇
  2000年   10篇
  1999年   30篇
  1998年   78篇
  1997年   65篇
  1996年   35篇
  1995年   24篇
  1994年   19篇
  1993年   23篇
  1992年   10篇
  1991年   6篇
  1990年   8篇
  1989年   5篇
  1988年   11篇
  1987年   5篇
  1986年   8篇
  1985年   14篇
  1984年   4篇
  1983年   8篇
  1982年   5篇
  1981年   5篇
  1980年   7篇
  1979年   9篇
  1978年   4篇
  1977年   11篇
  1976年   10篇
  1975年   2篇
  1971年   1篇
排序方式: 共有925条查询结果,搜索用时 15 毫秒
41.
Previously, we noted significant differences in the behavioral patterns of mice fed safflower oil with a very low alpha-linolenate/linoleate ratio and perilla oil with a high alpha-linolenate/linoleate ratio from mothers to offsprings. In this report, we compared the behavior and drug responses in mice fed diets containing six different vegetable oils-corn, rapeseed, soybean, safflower, perilla and a mixture of perilla and safflower oils- for a relatively short period: 8 months after weaning. Soybean oil is a component of most conventional diets and was used as a control. The alpha-linolenate/linoleate ratios of the oils appeared to affect the locomotor activities in a wheel cage: the activity decreased in the order of safflower, the mixture (1:1) and the perilla oil groups. However, the rapeseed oil group exhibited much higher locomotor activity than that expected from the alpha-linolenate/linoleate ratio. Additionally, the rapeseed oil group exhibited unusual behavior patterns, including higher ambulation and rearing activities, faster acquisition of the water maze task and slower habituation behavior as compared with the control group. Susceptibility to pentobarbital anesthesia tended to be higher in the rapeseed oil group. The differences in the alpha-linolenate/linoleate ratios of these oils alone do not account for the observed differences in the behavioral patterns among the six dietary groups. Although we cannot exclude the possibility that the observed behavioral anomaly is due to the unique fatty acid composition of rapeseed oil, we speculate that a factor(s) other than fatty acids in rapeseed oil affected nervous system functions.  相似文献   
42.
43.
44.
An optoelectronic self-oscillatory circuit with a constant time delay and its injection locking have been theoretically and experimentally described. The oscillation circuit incorporates a delayed feedback path by utilizing an optical fiber and is characterized by a differential-difference equation. The oscillation waveform and amplitude have been investigated by computing the equation. It is also shown that a stable frequency locking region exists and expands with an increase in the injection amplitude. By employing a carrier signal, two methods for optoelectronic oscillation, an AM and an FM type, are proposed and have been demonstrated to obtain more stable oscillation.  相似文献   
45.
46.
47.
48.
We have developed a high-throughput deep-ultraviolet (DUV) Raman microspectrometer with excitation from a continuous wave (cw) laser operated at 244 nm that enables us to characterize thin surface layers of wide-gap semiconductors. This spectrometer system consists of a filter spectrometer for the rejection of stray light and a high-dispersion spectrograph combined with a liquid nitrogen cooled charge-coupled device (CCD) detector and extends the low-frequency limit of the observable spectral range down to 170 cm(-1). In the microscope we use a Cassegrain reflective objective for the collection of the scattered light and an off-axis mirror for introduction of the excitation laser light. DUV Raman spectroscopy has been applied for studying wide-gap semiconductors including SiC and AlGaN epitaxial films and shallow implanted layers of these materials. Raman spectra of various crystals have also been measured for examining the performance of this system. Resonance enhancement of Raman bands has been observed for several semiconductors, and the results are discussed.  相似文献   
49.
50.
The attenuated total reflectance infrared (ATR-IR) spectra of several aqueous solutions have been measured by using a newly developed heatable rod-type ATR cell. The OH stretching bands showed systematic change with increasing solute concentrations and these changes can be explained by four different OH components based on curve-fitting results. NaCl solutions show longer H-bond distance character, while carbonate solutions present shorter ones. The Na2CO3 1 M solution conserves this shorter H-bond nature up to 100 degrees C. On the other hand, the loose nature of NaCl solutions becomes less pronounced at higher temperatures because of the dissociation of pure water clusters. These in situ observations of water structures are generally in agreement with the expected nature of fluids within the earth.  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