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   87314篇
  免费   7620篇
  国内免费   3613篇
电工技术   4878篇
技术理论   6篇
综合类   5624篇
化学工业   14626篇
金属工艺   4664篇
机械仪表   5618篇
建筑科学   6416篇
矿业工程   2700篇
能源动力   2592篇
轻工业   6920篇
水利工程   1357篇
石油天然气   5661篇
武器工业   598篇
无线电   9525篇
一般工业技术   10955篇
冶金工业   4330篇
原子能技术   912篇
自动化技术   11165篇
  2024年   167篇
  2023年   1532篇
  2022年   2284篇
  2021年   3743篇
  2020年   2943篇
  2019年   2502篇
  2018年   2838篇
  2017年   3175篇
  2016年   2685篇
  2015年   3605篇
  2014年   4513篇
  2013年   5500篇
  2012年   5632篇
  2011年   6238篇
  2010年   5309篇
  2009年   4884篇
  2008年   4785篇
  2007年   4523篇
  2006年   4512篇
  2005年   3945篇
  2004年   2604篇
  2003年   2353篇
  2002年   2131篇
  2001年   1881篇
  2000年   1933篇
  1999年   2119篇
  1998年   1795篇
  1997年   1458篇
  1996年   1436篇
  1995年   1225篇
  1994年   981篇
  1993年   746篇
  1992年   560篇
  1991年   446篇
  1990年   348篇
  1989年   279篇
  1988年   236篇
  1987年   158篇
  1986年   113篇
  1985年   97篇
  1984年   62篇
  1983年   41篇
  1982年   46篇
  1981年   36篇
  1980年   33篇
  1979年   23篇
  1977年   12篇
  1976年   13篇
  1975年   9篇
  1968年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
5G非地面网络(non-terrestrial network,NTN)技术是5G通信系统面向卫星通信和低空通信等新应用场景的重要技术,标志着5G技术应用从陆地通信走向了空间通信。首先分析了5G NTN和地面5G的差异点,包括网络架构、时频同步、HARQ和移动性管理等。进而介绍了3GPP Release 17的5G NTN标准进展及关键技术点与3GPP Release 18的5G NTN增强技术。最后展望了未来空、天、地一体化的技术演进。通过对5G NTN技术研究和标准分析,明确了5G和卫星通信融合的技术路线,并为后续6G空、天、地融合系统研究和设计提供基础。  相似文献   
3.
Journal of Materials Science: Materials in Electronics - The influences of the selenium (Se) growth condition on the electronic level structure including deep defects and further on the...  相似文献   
4.
5.
6.
7.
Hao  Shijie  Wang  Zhonghao  Sun  Fuming 《Neural Processing Letters》2022,54(4):2759-2782
Neural Processing Letters - Scale variation is one of the primary challenges in object detection. Recently, different strategies have been introduced to address this challenge, achieving promising...  相似文献   
8.
In this study, the effect of high-intensity ultrasound (HIUS) (200 and 400 W for 0, 5, 10 and 15 min respectively) on conformational changes, physicochemical, rheological and emulsifying properties of scallop (Patinopecten yessoensis) myofibrillar protein (SMP) was investigated. HIUS-treated SMP had lower α-helix content and higher β-sheet content compared with the native SMP. HIUS treatment induced the unfolding of SMP and increased the surface hydrophobicity. The particle size of SMP decreased and the absolute zeta-potential increased after ultrasonication, which in turn increased the solubility of SMP. The conformational changes and the improvement of physicochemical properties of SMP increased the ability for SMP to lower the interfacial tension at the oil–water interface and increased the percentage of adsorbed protein. As a result, the emulsifying properties, rheological properties of SMP and storage stability of emulsions were also improved. In conclusion, HIUS treatment has future potential for improving the emulsifying properties of SMP.  相似文献   
9.
The structural diversity of polyphenols and the inherent limitations of current extraction techniques pose a challenge to extract polyphenols using a simple and green method. Hence, in this study, a method was developed to simultaneously fractionate multiple classes of polyphenols by only varying ethanol-water solutions. Honeybush tea, which is rich in polyphenols, was selected as a model for this study. Solvent extraction followed by solid-phase extraction (SPE) was developed to obtain a polyphenol-rich fraction from six honeybush samples. Based on a gradient elution programme (10%, 30%, 50%, 70% and 90% (v/v) ethanol-water solution) of SPE, the Strata X cartridge showed a better recovery of most targeted polyphenols under 0.9 mL of the drying volume and 1 mL min−1 of the dispensing speed. The elution programme for fractionating most polyphenols was as follows: single elution with 50% ethanol, followed by twice elution with 70% ethanol. The antioxidant capacity was used to analyse the differences among the polyphenol-rich fractions from six honeybush samples. Principal component analysis (PCA) revealed that unfermented C. genistoides (GG) has the greatest antioxidant capacity among the honeybush species studied. Additionally, mangiferin, isomangiferin and vicenin-2 were the main contributors to the antioxidant capacity in six honeybush fractions according to the correlation study.  相似文献   
10.
Flesh colour, which is affected by cultivars and browning, can largely impact consumer acceptance in fresh-cut apples. The study profiled phenolic metabolites from apple flesh of twenty-three cultivars by widely targeted metabolomics. Comparison among white- and yellow-fleshed cultivars showed fifteen phenolics, mainly quercetin 3-O-glucoside, hyperoside, hesperetin 5-O-glucoside and cymaroside, in white-fleshed apples were significantly higher than those in yellow-fleshed apples. It may indicate a metabolite basis of yellow and white flesh colour, and better potential nutrition in white-fleshed apples. In addition, ten phenolic metabolites including five cyanidin glycosides showed significant differences between the highest and the lowest browning groups, indicating them may be crucial in browning of fresh-cut apple. This work elucidates the differences of phenolic profiles among apple cultivars with different flesh colour and provides useful data to evaluate the suitability of apple for fresh-cut processing.  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