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   1574053篇
  免费   28467篇
  国内免费   7344篇
电工技术   34916篇
综合类   7007篇
化学工业   276208篇
金属工艺   65272篇
机械仪表   44656篇
建筑科学   48020篇
矿业工程   11741篇
能源动力   50727篇
轻工业   121144篇
水利工程   15900篇
石油天然气   37991篇
武器工业   179篇
无线电   198992篇
一般工业技术   293495篇
冶金工业   195979篇
原子能技术   34284篇
自动化技术   173353篇
  2021年   15975篇
  2020年   12175篇
  2019年   14945篇
  2018年   17426篇
  2017年   16750篇
  2016年   22361篇
  2015年   17814篇
  2014年   29151篇
  2013年   88609篇
  2012年   37603篇
  2011年   51298篇
  2010年   44409篇
  2009年   52320篇
  2008年   47452篇
  2007年   44822篇
  2006年   46287篇
  2005年   41204篇
  2004年   43213篇
  2003年   43182篇
  2002年   42286篇
  2001年   39293篇
  2000年   37076篇
  1999年   36639篇
  1998年   55659篇
  1997年   45655篇
  1996年   39409篇
  1995年   33071篇
  1994年   30650篇
  1993年   30634篇
  1992年   26739篇
  1991年   23821篇
  1990年   24115篇
  1989年   23191篇
  1988年   21699篇
  1987年   19945篇
  1986年   19264篇
  1985年   22579篇
  1984年   22527篇
  1983年   20470篇
  1982年   19460篇
  1981年   19629篇
  1980年   18232篇
  1979年   18632篇
  1978年   17918篇
  1977年   18123篇
  1976年   19841篇
  1975年   16086篇
  1974年   15544篇
  1973年   15665篇
  1972年   13129篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
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   
872.
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   
873.
874.
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   
875.
876.
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   
877.
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   
878.
879.
880.
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