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   160057篇
  免费   8818篇
  国内免费   4609篇
电工技术   5808篇
技术理论   2篇
综合类   9348篇
化学工业   23801篇
金属工艺   9143篇
机械仪表   7741篇
建筑科学   8124篇
矿业工程   2607篇
能源动力   2943篇
轻工业   12159篇
水利工程   2957篇
石油天然气   3594篇
武器工业   787篇
无线电   17641篇
一般工业技术   24125篇
冶金工业   5700篇
原子能技术   1177篇
自动化技术   35827篇
  2024年   345篇
  2023年   1286篇
  2022年   2605篇
  2021年   3376篇
  2020年   2645篇
  2019年   2155篇
  2018年   16473篇
  2017年   15681篇
  2016年   12142篇
  2015年   4023篇
  2014年   4744篇
  2013年   5273篇
  2012年   8884篇
  2011年   15415篇
  2010年   13816篇
  2009年   10771篇
  2008年   12006篇
  2007年   12679篇
  2006年   4765篇
  2005年   4927篇
  2004年   3756篇
  2003年   3304篇
  2002年   2732篇
  2001年   1945篇
  2000年   1646篇
  1999年   1170篇
  1998年   823篇
  1997年   617篇
  1996年   619篇
  1995年   477篇
  1994年   343篇
  1993年   247篇
  1992年   217篇
  1991年   183篇
  1990年   117篇
  1989年   96篇
  1988年   106篇
  1987年   53篇
  1986年   57篇
  1985年   35篇
  1968年   49篇
  1967年   39篇
  1966年   46篇
  1965年   51篇
  1959年   43篇
  1958年   38篇
  1957年   37篇
  1956年   34篇
  1955年   65篇
  1954年   69篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
41.
42.
43.
44.
Variations of Incomplete Open Cubes is the major project by the twentieth-century conceptual artist Sol LeWitt. In this paper we interpret the enumerative component of the project as embeddings of graphs. This formulation permits use of an algorithm to check the completeness of the list of the structures produced by the artist. Our conclusion is that the artist found the correct number of structures (that is, 122), but that his list contains a mistake in the presentation of a pair of incomplete cubes, a discovery that appears not to have been noted before.  相似文献   
45.
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   
46.
(1-x)Sr0.7Pb0.15Bi0.1TiO3-xBi4Ti3O12 ((1-x)SPBT-xBIT, x = 0-0.125) bulk ceramics were developed and calcined via the solid-state method, aimed at the application of pulsed power capacitors. The phase structures, temperature stability, hysteresis loop, and discharge properties were systematically investigated. Considering both the temperature stability and dielectric properties, 0.925SPBT-0.075BIT bulk ceramics with a capacitance variation satisfying the X7R specification were developed for pulsed power capacitors. The energy storage density was 0.252 J/cm3, and the ceramics showed high temperature stability at 80 kV/cm. The discharge current waveforms of the 0.925SPBT-0.075BIT ceramics were recorded. A high discharge power density of approximately 1.01 × 108 W/kg with an 8 Ω load resistor and short discharge period of 84 ns were achieved at 50 kV/cm. The good temperature stability properties and high power density show that the 0.925SPBT-0.075BIT ceramics are well suited for pulsed power capacitors with a wide temperature range.  相似文献   
47.
48.
49.
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   
50.
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   
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