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   237964篇
  免费   9707篇
  国内免费   4649篇
电工技术   8738篇
技术理论   2篇
综合类   5928篇
化学工业   36677篇
金属工艺   10625篇
机械仪表   10061篇
建筑科学   10933篇
矿业工程   2188篇
能源动力   6472篇
轻工业   23763篇
水利工程   2927篇
石油天然气   4395篇
武器工业   679篇
无线电   31996篇
一般工业技术   39983篇
冶金工业   28103篇
原子能技术   3347篇
自动化技术   25503篇
  2023年   1488篇
  2022年   2338篇
  2021年   4209篇
  2020年   2935篇
  2019年   2876篇
  2018年   3370篇
  2017年   3825篇
  2016年   3642篇
  2015年   4377篇
  2014年   6150篇
  2013年   12139篇
  2012年   9167篇
  2011年   11290篇
  2010年   9367篇
  2009年   9708篇
  2008年   10133篇
  2007年   10163篇
  2006年   9380篇
  2005年   8233篇
  2004年   6782篇
  2003年   6185篇
  2002年   6240篇
  2001年   5954篇
  2000年   5609篇
  1999年   5585篇
  1998年   8401篇
  1997年   6760篇
  1996年   5821篇
  1995年   4797篇
  1994年   4207篇
  1993年   3861篇
  1992年   3307篇
  1991年   3076篇
  1990年   2939篇
  1989年   2819篇
  1988年   2651篇
  1987年   2263篇
  1986年   2209篇
  1985年   2621篇
  1984年   2361篇
  1983年   2208篇
  1982年   2083篇
  1981年   1998篇
  1980年   1857篇
  1979年   1868篇
  1978年   1755篇
  1977年   2063篇
  1976年   2573篇
  1975年   1553篇
  1973年   1450篇
排序方式: 共有10000条查询结果,搜索用时 464 毫秒
41.
刘少龙  李仑升  曹琳 《电子测试》2020,(8):26-27,51
本文利用TI公司TMS320F28335芯片高效的浮点运算能力,结合片上丰富的外设,设计并实现了一种具有高可靠性的智能电源控制单元。该控制单元周期性地对各片上外设进行自检维护,完成多路负载通道控制、电压、电流的实时监控,并对故障进行指示、处理和上报,同时提供人机交互界面更新状态信息。经过验证,该控制单元工作稳定,具备良好的工程应用价值。  相似文献   
42.
Lin  Jun-You  Yang  Chih-Hai 《Scientometrics》2020,122(1):1-2
Scientometrics - University–industry R&;amp;D collaboration is a key driver of participating firms’ technological capability. However, there is still debate on the determinants of a...  相似文献   
43.
Colour remains one of the key factors in presenting an object and, consequently, has been widely applied in retrieval of images based on their visual contents. However, a colour appearance changes with the change of viewing surroundings, the phenomenon that has not been paid attention yet while performing colour‐based image retrieval. To comprehend this effect, in this article, a chromatic contrast model, CAMcc, is developed for the application of retrieval of colour intensive images, cementing the gap that most of existing colour models lack to fill by taking simultaneous colour contrast into account. Subsequently, the model is applied to the retrieval task on a collection of museum wallpapers of colour‐rich images. In comparison with current popular colour models including CIECAM02, HSI and RGB, with respect to both foreground and background colours, CAMcc appears to outperform the others with retrieved results being closer to query images. In addition, CAMcc focuses more on foreground colours, especially by maintaining the balance between both foreground and background colours, while the rest of existing models take on dominant colours that are perceived the most, usually background tones. Significantly, the contribution of the investigation lies in not only the improvement of the accuracy of colour‐based image retrieval but also the development of colour contrast model that warrants an important place in colour and computer vision theory, leading to deciphering the insight of this age‐old topic of chromatic contrast in colour science. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 361–373, 2015  相似文献   
44.
Removal of imidacloprid and acetamiprid in tea infusions by microfiltration membrane using dead‐end model was investigated in the present study. The results showed that microfiltration significantly promoted the removal of both pesticides (P < 0.05) in tea infusions. Furthermore, the extent of removal was strongly influenced by the pore size of membrane, operational pressure and the concentrations of tea infusions. The initial concentration of imidacloprid and acetamiprid showed no significant effect on their removal rates. The maximum removal rates were 79.7% for imidacloprid and 81.9% acetamiprid. The changes in major chemical components of tea infusions after microfiltration were evaluated. The results indicated that microfiltration caused no considerable changes in total polyphenols and total free amino acids, and small but statistically significant losses (6.3–18.0%) of eight catechins and three methylxanthines when filtration volume reached to 200 mL. The present study validated the application of microfiltration as a potentially feasible and promising method for the removal of imidacloprid and acetamiprid residues from tea infusions.  相似文献   
45.
46.
47.
48.
Costunolide (CE) and dehydrocostuslactone (DE) are derived from many species of medicinal plants, such as Saussurea lappa Decne and Laurus nobilis L. They have been reported for their wide spectrum of biological effects, including anti-inflammatory, anticancer, antiviral, antimicrobial, antifungal, antioxidant, antidiabetic, antiulcer, and anthelmintic activities. In recent years, they have caused extensive interest in researchers due to their potential anti-cancer activities for various types of cancer, and their anti-cancer mechanisms, including causing cell cycle arrest, inducing apoptosis and differentiation, promoting the aggregation of microtubule protein, inhibiting the activity of telomerase, inhibiting metastasis and invasion, reversing multidrug resistance, restraining angiogenesis has been studied. This review will summarize anti-cancer activities and associated molecular mechanisms of these two compounds for the purpose of promoting their research and application.  相似文献   
49.
50.
大气污染物排放清单是空气质量模拟和空气污染治理的重要依据.本研究比较分析了两套覆盖江苏省的2017年大气污染物排放清单,即分别由上海市环境科学研究院、江苏省环境科学研究院编制的"长三角清单"和"江苏省清单",并结合区域空气质量模型CMAQ评估不同清单对长三角地区2017年1、4、7、10月的空气质量模拟的影响.清单比较结果表明,除二氧化硫(SO2)以外,江苏省清单估算的各污染物排放量较长三角清单低.通过与观测数据比较,发现两套清单对SO2、氮氧化物(NOx)、臭氧(O3)和细颗粒物(PM2.5)的模型模拟性能均较好.江苏省清单与长三角清单两者的模拟结果空间分布接近,其中江苏省清单模拟的PM2.5和O3在长三角多数地区略低于长三角清单的模拟结果(1月O3除外).江苏省清单与长三角清单均能够用于空气质量模式模拟,可为江苏地区的细颗粒物和光化学烟雾污染的控制策略制定提供参考.  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