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   171726篇
  免费   12827篇
  国内免费   6370篇
电工技术   9291篇
技术理论   9篇
综合类   9041篇
化学工业   28152篇
金属工艺   10277篇
机械仪表   10465篇
建筑科学   10237篇
矿业工程   4103篇
能源动力   3803篇
轻工业   9700篇
水利工程   3318篇
石油天然气   9903篇
武器工业   1107篇
无线电   18050篇
一般工业技术   27220篇
冶金工业   11228篇
原子能技术   4871篇
自动化技术   20148篇
  2024年   767篇
  2023年   2472篇
  2022年   4906篇
  2021年   6587篇
  2020年   4943篇
  2019年   4203篇
  2018年   5356篇
  2017年   5862篇
  2016年   5360篇
  2015年   5962篇
  2014年   7677篇
  2013年   9256篇
  2012年   9904篇
  2011年   10655篇
  2010年   8990篇
  2009年   8805篇
  2008年   8667篇
  2007年   8126篇
  2006年   7591篇
  2005年   6441篇
  2004年   4888篇
  2003年   4804篇
  2002年   4838篇
  2001年   4426篇
  2000年   3818篇
  1999年   3391篇
  1998年   2677篇
  1997年   2264篇
  1996年   2016篇
  1995年   1754篇
  1994年   1495篇
  1993年   1253篇
  1992年   1220篇
  1991年   1081篇
  1990年   1096篇
  1989年   1015篇
  1988年   896篇
  1987年   843篇
  1986年   765篇
  1985年   717篇
  1984年   701篇
  1981年   668篇
  1979年   736篇
  1978年   777篇
  1977年   739篇
  1976年   755篇
  1975年   713篇
  1974年   719篇
  1973年   723篇
  1972年   705篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
It has been well known that the greening of Allium sativum cloves could be formed after immersed in acetic acid solution. Nonetheless, no investigation was reported on colour development of A. sativum in response to acetic acid vapour until now. In this study, the brief exposure of A. sativum to acetic acid vapour (200–400 ppm) was combined with controlled atmosphere (5%, 20% and 80% CO2) packaging storage to break cell membrane and green garlic. The garlic bulbs were fumigated with acetic acid before controlled CO2 atmosphere packaging for 25 days at 4 °C. Fumigation with 200 ppm acetic acid followed by high CO2 atmosphere packaging (80% CO2) facilitated the garlic greening. It was also verified that γ‐glutamyl transpeptidase was involved in garlic greening in present study, and the compromise of glacial acetic acid vapour fumigation and CO2 gas atmosphere in package stored at low temperature could result in garlic greening as well.  相似文献   
53.
54.
55.
56.
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (εr= 12.18, Q×f?=?170,130?GHz, τf?=??53.1?ppm/°C, x?=?0.2).  相似文献   
57.
58.
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   
59.
60.
The microstructure and properties of the functional coatings formed by impact friction processing of product surfaces with a flexible tool are studied. It is established that the processing produces a hard nanostructured surface layer with fragments up to 0.13 µm in size, as it is achieved by severe plastic deformation.  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