全文获取类型
收费全文 | 1582974篇 |
免费 | 27696篇 |
国内免费 | 7059篇 |
专业分类
电工技术 | 35485篇 |
综合类 | 6467篇 |
化学工业 | 277334篇 |
金属工艺 | 67047篇 |
机械仪表 | 47135篇 |
建筑科学 | 47772篇 |
矿业工程 | 11987篇 |
能源动力 | 50504篇 |
轻工业 | 120943篇 |
水利工程 | 16152篇 |
石油天然气 | 38618篇 |
武器工业 | 149篇 |
无线电 | 200656篇 |
一般工业技术 | 300604篇 |
冶金工业 | 187685篇 |
原子能技术 | 34766篇 |
自动化技术 | 174425篇 |
出版年
2021年 | 15636篇 |
2020年 | 11937篇 |
2019年 | 14714篇 |
2018年 | 19771篇 |
2017年 | 19625篇 |
2016年 | 23295篇 |
2015年 | 17669篇 |
2014年 | 28780篇 |
2013年 | 88267篇 |
2012年 | 38138篇 |
2011年 | 53900篇 |
2010年 | 46781篇 |
2009年 | 54646篇 |
2008年 | 49282篇 |
2007年 | 47512篇 |
2006年 | 46274篇 |
2005年 | 42711篇 |
2004年 | 43653篇 |
2003年 | 43191篇 |
2002年 | 41843篇 |
2001年 | 38325篇 |
2000年 | 36648篇 |
1999年 | 35951篇 |
1998年 | 51978篇 |
1997年 | 43717篇 |
1996年 | 38079篇 |
1995年 | 32368篇 |
1994年 | 30100篇 |
1993年 | 29912篇 |
1992年 | 26634篇 |
1991年 | 23833篇 |
1990年 | 24151篇 |
1989年 | 23268篇 |
1988年 | 21766篇 |
1987年 | 20005篇 |
1986年 | 19381篇 |
1985年 | 22689篇 |
1984年 | 22609篇 |
1983年 | 20588篇 |
1982年 | 19456篇 |
1981年 | 19553篇 |
1980年 | 18193篇 |
1979年 | 18672篇 |
1978年 | 17909篇 |
1977年 | 18059篇 |
1976年 | 19447篇 |
1975年 | 16150篇 |
1974年 | 15630篇 |
1973年 | 15739篇 |
1972年 | 13209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.
Alice Maurer Prof. Dr. Florian P. Seebeck 《Chembiochem : a European journal of chemical biology》2020,21(20):2908-2911
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.
ABSTRACTIn 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.
Effect of Supports and Promoters on the Performance of Ni-Based Catalysts in Ethanol Steam Reforming
Thanh Khoa Phung Thong Le Minh Pham Anh-Nga T. Nguyen Khanh B. Vu Ha Ngoc Giang Tuan-Anh Nguyen Thanh Cong Huynh Hong Duc Pham 《化学工程与技术》2020,43(4):672-688
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.