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   78476篇
  免费   920篇
  国内免费   690篇
电工技术   1494篇
综合类   60篇
化学工业   11649篇
金属工艺   3501篇
机械仪表   2689篇
建筑科学   1997篇
矿业工程   506篇
能源动力   1947篇
轻工业   6886篇
水利工程   873篇
石油天然气   2306篇
武器工业   41篇
无线电   7418篇
一般工业技术   16896篇
冶金工业   13560篇
原子能技术   2682篇
自动化技术   5581篇
  2022年   609篇
  2021年   971篇
  2020年   723篇
  2019年   815篇
  2018年   1602篇
  2017年   1605篇
  2016年   1821篇
  2015年   994篇
  2014年   1619篇
  2013年   3655篇
  2012年   2474篇
  2011年   2988篇
  2010年   2486篇
  2009年   2747篇
  2008年   2741篇
  2007年   2825篇
  2006年   2268篇
  2005年   1999篇
  2004年   1917篇
  2003年   1870篇
  2002年   1783篇
  2001年   1734篇
  2000年   1739篇
  1999年   1651篇
  1998年   4041篇
  1997年   2813篇
  1996年   2068篇
  1995年   1632篇
  1994年   1413篇
  1993年   1433篇
  1992年   1029篇
  1991年   1092篇
  1990年   1114篇
  1989年   1094篇
  1988年   968篇
  1987年   904篇
  1986年   901篇
  1985年   968篇
  1984年   804篇
  1983年   787篇
  1982年   695篇
  1981年   719篇
  1980年   691篇
  1979年   681篇
  1978年   637篇
  1977年   807篇
  1976年   987篇
  1975年   598篇
  1974年   571篇
  1973年   568篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
162.
This paper introduces a methodology for symbolic pole/zero extraction based on the formulation of the time-constant matrix of the circuits. This methodology incorporates approximation techniques specifically devoted to achieve an optimum trade-off between accuracy and complexity of the symbolic root expressions. The capability to efficiently handle even large circuits will be demonstrated through several practical circuits.  相似文献   
163.
An audio recording/playback head using an amorphous (Fe-Co-Ru-Cr) 75(Si-B)25 alloy was developed. Compared with a commercial Sendust head, three excellent features were observed. The wear of the amorphous alloy head when used with γ-Fe2O 3 is two-thirds that of the Sendust head. The output level at high-frequency (14 kHz) is 5 dB higher than that of the Sendust head. The bias current for the amorphous alloy head is half that of the Sendust head  相似文献   
164.
165.
A one-dimensional mesoscopic ring with one input and two output leads acts as a spintronic beam splitter. The spatial degree of freedom, i.e., the presence of two different possible output channels, gets intertwined with the spin direction as a consequence of quantum interference and spin-orbit interaction. We investigate this kind of spatial-spin correlation, and show that the output density operator contains no quantum entanglement in the important special case when the device polarizes a perfectly random input spin state. However, the correlations are in general not purely classical, we also present specific input states with maximal spatial-spin entanglement after the ring.  相似文献   
166.
Occupational airway diseases are now receiving attention in industry, although study is hampered by a lack of readily-available data. The interpretation of the data that is available, and also of the root problems themselves, is itself a difficult problem. This paper has been written as a literature review which it is hoped that other researchers can take either as a starting point or as a refresher.  相似文献   
167.
Evaluating and monitoring nucleation and growth in copper foil   总被引:1,自引:0,他引:1  
The electrodeposition of copper foil for use in electronic materials applications is a complex and demanding process. The specific aspects of producing and controlling the structure-property-performance requirements of the foil are important because of the stringent demands placed on their use in printed circuit boards and similar products. In this paper, a brief review of the electrodeposition process for raw copper foil is presented. Since electrolyte additives play such a significant role in the copper-depositionprocess, the effects of two essential additives, chloride ion and an organic (e.g., glue or gelatine), on the foil are described. Also, the influence of other operating parameters on the initial nucleation, growth, and subsequent electrocrystallization are discussed. Selected characterization methods, such as polarization and scanning electron micrography techniques, are described as a means of monitoring the process, but universally accepted methods of evaluating and controlling the additives and foil quality during electrolysis are still being sought.  相似文献   
168.
The leakage mechanism for a top-gate thin-film transistor (TFT) produced using the fewest process steps in the industry is analyzed in order to achieve a high-contrast liquid crystal display (LCD). Using a T-shaped TFT structure, the OFF and ON channel lengths are defined independently, so that the leakage can be reduced with no ON current decrease  相似文献   
169.
170.
We report on measurements of charge changing cross-sections and energy losses in dependence on the initial and final charge state of Ne ions at an incident energy of 2 MeV/u penetrating thin carbon foils. Different initial charge states could be separated in energy by applying a high voltage in front of the carbon foils; the final charges and their energy loss were measured with a high-resolution magnetic spectrometer. We derived a consistent evolution of the charge state distribution solving the corresponding rate equations for the measured cross-sections. Including the charge state dependent energy losses, ΔE(qi,qf), stopping power values for frozen charge states, S(q), could be extracted. The experimental data are compared with different theoretical predictions.  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