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   205946篇
  免费   15829篇
  国内免费   7822篇
电工技术   11308篇
技术理论   14篇
综合类   11246篇
化学工业   35809篇
金属工艺   10586篇
机械仪表   12049篇
建筑科学   16463篇
矿业工程   4954篇
能源动力   5864篇
轻工业   12709篇
水利工程   3235篇
石油天然气   11137篇
武器工业   1350篇
无线电   25527篇
一般工业技术   26751篇
冶金工业   10964篇
原子能技术   2122篇
自动化技术   27509篇
  2024年   886篇
  2023年   3277篇
  2022年   5847篇
  2021年   7934篇
  2020年   5824篇
  2019年   5021篇
  2018年   5428篇
  2017年   6214篇
  2016年   5703篇
  2015年   7310篇
  2014年   9538篇
  2013年   12306篇
  2012年   12264篇
  2011年   13920篇
  2010年   11656篇
  2009年   11488篇
  2008年   10909篇
  2007年   10495篇
  2006年   10895篇
  2005年   9655篇
  2004年   6578篇
  2003年   5796篇
  2002年   5269篇
  2001年   4742篇
  2000年   4889篇
  1999年   5664篇
  1998年   5296篇
  1997年   4361篇
  1996年   3971篇
  1995年   3317篇
  1994年   2778篇
  1993年   2192篇
  1992年   1704篇
  1991年   1284篇
  1990年   1019篇
  1989年   881篇
  1988年   681篇
  1987年   498篇
  1986年   394篇
  1985年   334篇
  1984年   212篇
  1983年   198篇
  1982年   163篇
  1981年   145篇
  1980年   131篇
  1979年   97篇
  1978年   63篇
  1977年   63篇
  1976年   77篇
  1975年   38篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In this study, a simple hydrothermal synthesis method was adapted for the preparation of Co-doping Co2+/F-/TiO2 nanotubes photocatalyst, and the micro-nano structure of catalysts prepared by biomimetic technology which makes the catalyst have super-oleophilicity property. Co2+/F-/TiO2 revealed improved photocatalytic performance for denitrification of light oil compared to single TiO2 photocatalysts. The enhance of photocatalytic activity can be attributed to narrowing the band gap, increasing the light response wavelength and exposing more highly active crystal surfaces due to synergistic effects of Co2+ and F? in the photocatalyst.  相似文献   
32.
The extensive research interests in environmental temperature can be linked to human productivity / performance as well as comfort and health; while the mechanisms of physiological indices responding to temperature variations remain incompletely understood. This study adopted a physiological sensory nerve conduction velocity (SCV) as a temperature‐sensitive biomarker to explore the thermoregulatory mechanisms of human responding to annual temperatures. The measurements of subjects’ SCV (over 600 samples) were conducted in a naturally ventilated environment over all four seasons. The results showed a positive correlation between SCV and annual temperatures and a Boltzmann model was adopted to depict the S‐shaped trend of SCV with operative temperatures from 5°C to 40°C. The SCV increased linearly with operative temperatures from 14.28°C to 20.5°C and responded sensitively for 10.19°C‐24.59°C, while tended to be stable beyond that. The subjects’ thermal sensations were linearly related to SCV, elaborating the relation between human physiological regulations and subjective thermal perception variations. The findings reveal the body SCV regulatory characteristics in different operative temperature intervals, thereby giving a deeper insight into human autonomic thermoregulation and benefiting for built environment designs, meantime minimizing the temperature‐invoked risks to human health and well‐being.  相似文献   
33.
34.
35.
36.
37.
38.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015.  相似文献   
39.
40.
Understanding semantic word shifts in scientific domains is essential for facilitating interdisciplinary communication. Using a data set of published papers in the field of information retrieval (IR), this paper studies the semantic shifts of words in IR based on mining per-word topic distribution over time. We propose that semantic word shifts not only occur over time, but also over topics. The shifts are examined from two perspectives, the topic-level and the context-level. According to the over-time word-topic distribution, stable words and unstable words are recognized. The diverging and converging trends in the unstable type reveal characteristics of the topic evolution process. The context-level shifts are further detected by similarities between word vectors. Our work associates semantic word shifts with the evolving of topics, which facilitates a better understanding of semantic word shifts from both topics and contexts.  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