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   1705951篇
  免费   38959篇
  国内免费   12832篇
电工技术   43000篇
技术理论   9篇
综合类   14986篇
化学工业   293474篇
金属工艺   72739篇
机械仪表   54502篇
建筑科学   57020篇
矿业工程   15087篇
能源动力   53639篇
轻工业   131567篇
水利工程   18649篇
石油天然气   43995篇
武器工业   1192篇
无线电   213316篇
一般工业技术   313833篇
冶金工业   203950篇
原子能技术   36200篇
自动化技术   190584篇
  2021年   20890篇
  2020年   15877篇
  2019年   17842篇
  2018年   22767篇
  2017年   23005篇
  2016年   26445篇
  2015年   22308篇
  2014年   34524篇
  2013年   94991篇
  2012年   46178篇
  2011年   62030篇
  2010年   53456篇
  2009年   60859篇
  2008年   55869篇
  2007年   53531篇
  2006年   52638篇
  2005年   47889篇
  2004年   47416篇
  2003年   46979篇
  2002年   45642篇
  2001年   42110篇
  2000年   39722篇
  1999年   39088篇
  1998年   57276篇
  1997年   47187篇
  1996年   40871篇
  1995年   34387篇
  1994年   31740篇
  1993年   31236篇
  1992年   27388篇
  1991年   24451篇
  1990年   24702篇
  1989年   23705篇
  1988年   22226篇
  1987年   20342篇
  1986年   19676篇
  1985年   22986篇
  1984年   22732篇
  1983年   20705篇
  1982年   19560篇
  1981年   19686篇
  1980年   18351篇
  1979年   18793篇
  1978年   17998篇
  1977年   18315篇
  1976年   20125篇
  1975年   16234篇
  1974年   15674篇
  1973年   15793篇
  1972年   13244篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Estimation of earth-fill dam height and dimension of spillway are strongly depend on accurate evaluation of dam overtopping reliability. Ideally, whole random and effective variables on overtopping should be considered for dam overtopping reliability assessment. However, taking into account all affecting random variables as well as overtopping reliability assessment using algorithms such as Monte Carlo (MC) could be excessively time consuming and impossible in some cases. In this study, new approach has been introduced as conditional reliability method and it has been tried to reduce the simulations time significantly by using combination of rainfall threshold theory, SUFI (Sequential Uncertainty Fitting) and MC methods. According two defined indexes, the obtain results shown, the relative error of new approach in computation of Jamishan dam overtopping reliability is less than 0.23%. Also, time saving in new method against to regular MC method is more than 87%. So, the new introduced method has more efficiency with acceptable accuracy for assessment of dam overtopping reliability. In addition, among hydrological and hydraulic uncertainties, hydrological uncertainties have more effect on overtopping reliability.  相似文献   
992.
Ergothioneine has emerged as a crucial cytoprotectant in the pathogenic lifestyle of Mycobacterium tuberculosis. Production of this antioxidant from primary metabolites may be regulated by phosphorylation of Thr213 in the active site of the methyltransferase EgtD. The structure of mycobacterial EgtD suggests that this post-translational modification would require a large-scale change in conformation to make the active-site residue accessible to a protein kinase. In this report, we show that, under in vitro conditions, EgtD is not a substrate of protein kinase PknD.  相似文献   
993.
994.
ABSTRACT

In recent times, the applications of multimedia are rising in a greedy mode and hence the amount of video transactions is also increasing exponentially. This has shouted great demands on effective models on video encoding and also for reducing the transmission channel congestion. This research work introduces a managing technique termed weighted encoding for High-Efficiency Video Coding (HEVC). HEVC, also termed as MPEG-H Part 2 and H.265 is a video compression standard that is widely utilized AVC (H.264 or MPEG-4 Part 10). When compared to AVC, HEVC grants double the ratio of data compression at a similar level of quality of the video or considerably enhanced video quality at a similar bit rate. This work intends to optimize the weight that adopted in HEVC for encoding. For this, this paper proposes a new Iterative based propagation update in the water wave Optimization Algorithm (IPU-WWO), which is the improved form of Water wave Optimization (WWO). The performance of proposed IPU-WWO is compared over other conventional methods like Artificial Bee Colony (ABC), Firefly (FF), Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) with respect to Peak Signal to Noise Ratio (PSNR). By doing the encoding process, it minimizes the video size with perceptually better quality video or PSNR.  相似文献   
995.
996.
997.
Ethanol steam reforming (ESR) is one of the potential processes to convert ethanol into valuable products. Hydrogen produced from ESR is considered as green energy for the future and can be an excellent alternative to fossil fuels with the aim of mitigating the greenhouse gas effect. The ESR process has been well studied, using transition metals as catalysts coupled with both acidic and basic oxides as supports. Among various reported transition metals, Ni is an inexpensive material with activity comparable to that of noble metals, showing promising ethanol conversion and hydrogen yields. Additionally, different promoters and supports were utilized to enhance the hydrogen yield and the catalyst stability. This review summarizes and discusses the influences of the supports and promoters of Ni-based catalysts on the ESR process.  相似文献   
998.
Technical Physics Letters - Using the method of DC magnetron sputtering, nonstructured amorphous metal coatings of Zr75Pd25 composition were obtained with an average deposition rate of 1.3 nm/s at...  相似文献   
999.
1000.
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