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   117940篇
  免费   3493篇
  国内免费   1408篇
电工技术   2308篇
技术理论   4篇
综合类   3891篇
化学工业   17231篇
金属工艺   6285篇
机械仪表   4754篇
建筑科学   3875篇
矿业工程   1318篇
能源动力   2310篇
轻工业   5795篇
水利工程   1709篇
石油天然气   1365篇
武器工业   146篇
无线电   14555篇
一般工业技术   21203篇
冶金工业   5316篇
原子能技术   655篇
自动化技术   30121篇
  2024年   85篇
  2023年   443篇
  2022年   809篇
  2021年   1223篇
  2020年   940篇
  2019年   811篇
  2018年   15203篇
  2017年   14176篇
  2016年   10740篇
  2015年   1684篇
  2014年   1649篇
  2013年   2330篇
  2012年   5113篇
  2011年   11615篇
  2010年   10045篇
  2009年   7370篇
  2008年   8619篇
  2007年   9447篇
  2006年   1708篇
  2005年   2461篇
  2004年   2232篇
  2003年   2359篇
  2002年   1946篇
  2001年   1292篇
  2000年   1014篇
  1999年   793篇
  1998年   1047篇
  1997年   727篇
  1996年   640篇
  1995年   497篇
  1994年   411篇
  1993年   347篇
  1992年   265篇
  1991年   249篇
  1990年   226篇
  1989年   203篇
  1988年   179篇
  1987年   153篇
  1986年   127篇
  1985年   126篇
  1984年   109篇
  1983年   76篇
  1982年   70篇
  1981年   59篇
  1980年   81篇
  1978年   60篇
  1977年   58篇
  1976年   76篇
  1955年   71篇
  1954年   69篇
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
31.
32.
水是人们生存必不可少的资源,是生产与生活的基础,但水资源短缺,时间、空间分布不均,利用率低,已成为制约各地经济可持续发展的重要因素之一。本文所选研究区域——昌宁县正处于经济快速发展时期,水资源承载力将会影响其发展,文章综合文献分析和实际调研数据,运用科学的方法进行水资源的承载力分析,结果表明:昌宁县水资源承载力目前与社会经济的发展相适应,但远期将会有所不足,因而要求协调人与自然的矛盾,促进昌宁县的可持续发展。  相似文献   
33.
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   
34.
Journal of Mechanical Science and Technology - Real-time monitoring and rapid evaluation of bearing operating conditions, especially for the reliability evaluation and remaining useful life (RUL)...  相似文献   
35.
36.
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   
37.
Research funding has been seen as one of the most important resource in the reward system of science. And usage of publications denotes an interesting perspective of user behavior in scientific communication. This study aims to address the relationship between funding and Usage Count, which is a new metrics item established on the platform of Web of Science. Full records of 300,010 articles published in 2013 were downloaded in October 2015, and divided into six disciplines, including information science library science, education educational research, economics, computer science, materials science, and chemistry. Seven indicators were proposed to measure the impact, including Funding rate, Citation per paper, Usage rate, Usage per paper, Citation difference, Usage difference, and Conversion rate. It concluded funding has impact on usage and citation, and funded papers attract more usage, but varying in different disciplines. Usage Count can be used in the extension of citation metrics but with limits. This study originally engages with usage metrics and detected that there is positive correlation between usage and funding.  相似文献   
38.
Recent increase in the number of digital photos in the content sharing and social networking websites has created an endless demand for techniques to analyze, navigate, and summarize these images. In this paper, we focus on image collection summarization. Earlier methods in image collection summarization consider representativeness and diversity criteria while recent ones also consider other criteria such as image quality, aesthetic or appeal. In this paper, we propose a multi-criteria context-sensitive approach for social image collection summarization. In the proposed method, two different sets of features are combined while each one looks at different criteria for image collection summarization: social attractiveness features and semantic features. The first feature set considers different aspects that make an image appealing such as image quality, aesthetic, and emotion to create attractiveness score for input images while the second one covers semantic content of images and assigns semantic score to them. We use social network infrastructure to identify attractiveness features and domain ontology for extracting ontology features. The final summarization is provided by integrating the attractiveness and semantic features of input images. The experimental results on a collection of human generated summaries on a set of Flickr images demonstrate the effectiveness of the proposed image collection summarization approach.  相似文献   
39.
The physical mechanism of highly efficient photoluminescence (PL) emission from p-type silicon is described by a comparative study of the effectiveness of the etching parameters in an electrochemical anodization technique. Two series of porous silicon samples were prepared in a combination of anodization current and time, to maintain the total amount of anodic charge transfer constant. Photoluminescence studies show that irrespective of the amount of charge transfer, the samples prepared with comparatively higher current density show an efficient PL as well as stronger blueshift in the emission energy vis-à-vis the samples prepared for longer durations. An overall decrease in crystallite size, as estimated by Raman spectral analysis, was observed for both series of samples with the progress of charge transfer. Comparative analysis shows a marginal difference in crystallite size for both series of samples in the initial state of charge transfer, whereas major differences arise at higher values. This is explained with the formation of silicon suboxide on the porous surface at higher current density, leading to initiation of side wall reaction, and higher reduction rate in crystallite size as well as strong luminescence due to the carrier quantum confinement effect.  相似文献   
40.
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