全文获取类型
收费全文 | 1752605篇 |
免费 | 44462篇 |
国内免费 | 15985篇 |
专业分类
电工技术 | 46825篇 |
技术理论 | 18篇 |
综合类 | 18979篇 |
化学工业 | 303936篇 |
金属工艺 | 74772篇 |
机械仪表 | 55852篇 |
建筑科学 | 62275篇 |
矿业工程 | 17309篇 |
能源动力 | 55307篇 |
轻工业 | 138259篇 |
水利工程 | 19413篇 |
石油天然气 | 48339篇 |
武器工业 | 1766篇 |
无线电 | 218697篇 |
一般工业技术 | 315978篇 |
冶金工业 | 202136篇 |
原子能技术 | 35839篇 |
自动化技术 | 197352篇 |
出版年
2022年 | 16773篇 |
2021年 | 24335篇 |
2020年 | 18338篇 |
2019年 | 19726篇 |
2018年 | 21653篇 |
2017年 | 21643篇 |
2016年 | 27358篇 |
2015年 | 25327篇 |
2014年 | 38419篇 |
2013年 | 99446篇 |
2012年 | 50477篇 |
2011年 | 64421篇 |
2010年 | 55103篇 |
2009年 | 62060篇 |
2008年 | 57852篇 |
2007年 | 54841篇 |
2006年 | 56679篇 |
2005年 | 49653篇 |
2004年 | 48527篇 |
2003年 | 47427篇 |
2002年 | 45972篇 |
2001年 | 42713篇 |
2000年 | 40902篇 |
1999年 | 40757篇 |
1998年 | 57080篇 |
1997年 | 47609篇 |
1996年 | 41599篇 |
1995年 | 35051篇 |
1994年 | 32490篇 |
1993年 | 31541篇 |
1992年 | 27925篇 |
1991年 | 24837篇 |
1990年 | 24835篇 |
1989年 | 23847篇 |
1988年 | 22341篇 |
1987年 | 20387篇 |
1986年 | 19856篇 |
1985年 | 23111篇 |
1984年 | 23074篇 |
1983年 | 20898篇 |
1982年 | 19681篇 |
1981年 | 19775篇 |
1980年 | 18380篇 |
1979年 | 18958篇 |
1978年 | 18131篇 |
1977年 | 18478篇 |
1976年 | 20668篇 |
1975年 | 16265篇 |
1974年 | 15780篇 |
1973年 | 15858篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Basic insulating refractories were fabricated by the pressing route using dead-burned magnesia, pure calcined alumina, expanded perlite, and calcined waste serpentine as starting raw materials in four compositions from F1 to F4. Periclase and forsterite were major phases in F1 and F2 compositions, while spinel was also detected in the XRD patterns of F3 and F4 samples. Quantitative phase analysis showed that F4 sample sintered at 1450?°C has the highest forsterite content among all other samples. On the other hand, it has lower thermal conductivity compared to F1 to F3, and even lower than aluminosilicate IFBs with the same bulk density. It is concluded that forsterite is a highly insulating material, compared to periclase, corundum, periclase-spinel, aluminosilicates, such as mullite, etc. 相似文献
992.
Amun Amri Ahmad Fadli Zhong-Tao Jiang Chun-Yang Yin M. Mahbubur Rahman Hantarto Widjaja Syamsu Herman Silvia Reni Yenti M. Miftahul Munir Gadang Priyotomo M. Iqbal Neni Frimayanti 《Ceramics International》2018,44(13):15274-15280
The copper and cobalt oxides composites coatings on aluminum substrates have been successfully synthesized via sol-gel method using nitrate-based sol precursors. The composites were characterized by X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), and UV–Vis–NIR spectrophotometry. The sol-gel reactions were discussed and Molecular Dynamics (MD) simulation was integrated into the study to predict molecules assembly properties. The XRD analyses revealed that the CuO and the Co3O4 composites were formed after the annealing process with the average difference of the calculated lattice parameters compared to ICDDs was 1.17%. The surface electronic structure was mainly consisted of tetrahedral Cu(I), octahedral Cu(II), tetrahedral Co(II), octahedral Co(III) as well as surface, sub-surface and lattice oxygen O?. The XRD, XPS and MD simulation results showed that there was minimal (or possibly non-existing) indication of copper-cobalt mixed phase oxides formations. FESEM and AFM surveys revealed that the coating had a porous surface composed of interlinked nanoparticles in the range of ~?10 to ~?40?nm. UV–Vis–NIR reflectance spectra showed that the sol precursors concentration and the dip-drying cycle significantly influenced the absorptance value with optimum absorptance (α) of 88.7% exhibited by coating synthesized using sol concentration of 0.1?M and 10 dip-drying cycles. High absorptance value and simplicity in the synthesis process render the coatings to be very promising candidates for solar selective absorber (SSA) applications. 相似文献
993.
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
994.
995.
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
996.
997.
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
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.