全文获取类型
收费全文 | 6957篇 |
免费 | 663篇 |
国内免费 | 328篇 |
专业分类
电工技术 | 381篇 |
技术理论 | 3篇 |
综合类 | 503篇 |
化学工业 | 1206篇 |
金属工艺 | 350篇 |
机械仪表 | 460篇 |
建筑科学 | 554篇 |
矿业工程 | 249篇 |
能源动力 | 205篇 |
轻工业 | 460篇 |
水利工程 | 141篇 |
石油天然气 | 441篇 |
武器工业 | 57篇 |
无线电 | 681篇 |
一般工业技术 | 892篇 |
冶金工业 | 330篇 |
原子能技术 | 79篇 |
自动化技术 | 956篇 |
出版年
2024年 | 35篇 |
2023年 | 134篇 |
2022年 | 230篇 |
2021年 | 345篇 |
2020年 | 254篇 |
2019年 | 204篇 |
2018年 | 244篇 |
2017年 | 264篇 |
2016年 | 239篇 |
2015年 | 318篇 |
2014年 | 366篇 |
2013年 | 411篇 |
2012年 | 439篇 |
2011年 | 469篇 |
2010年 | 416篇 |
2009年 | 383篇 |
2008年 | 337篇 |
2007年 | 335篇 |
2006年 | 351篇 |
2005年 | 321篇 |
2004年 | 206篇 |
2003年 | 228篇 |
2002年 | 217篇 |
2001年 | 179篇 |
2000年 | 191篇 |
1999年 | 171篇 |
1998年 | 115篇 |
1997年 | 91篇 |
1996年 | 100篇 |
1995年 | 81篇 |
1994年 | 61篇 |
1993年 | 39篇 |
1992年 | 41篇 |
1991年 | 41篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1975年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有7948条查询结果,搜索用时 15 毫秒
211.
在建筑工程中,混凝土是工程结构的重要组成部分,影响着建筑结构的使用与安全。混凝土是由多种外加剂和骨料等组成的人工材料,受多种因素的影响容易产生不同程度的温度裂缝。本文主要就民用建筑混凝土温度裂缝的预防提出建议。 相似文献
212.
H. Liu D.‐G. Shang Z.‐K. Guo Y.‐G. Zhao J.‐Z. Liu 《Fatigue & Fracture of Engineering Materials & Structures》2014,37(8):937-944
Fatigue crack growth behaviours in different welding zones of laser beam welded specimens were investigated using central crack tension specimens for 6156 aluminium alloy under constant amplitude loading at nominal applied stress ratio R = 0.5, 0.06, ?1. The experimental results showed that base metal (BM) exhibited superior fatigue crack resistance compared to weld metal (WM) and heat‐affected zone (HAZ). Crack growth resistance of WM was the lowest. The exponent m values for BM and HAZ at different stress ratios are close and around 2.6, while m for WM at different stress ratio is around 4.7. The discrepancy between crack growth rates for WM and BM is more evident with increasing stress ratio, while it is a little change for HAZ and BM. Change of the microstructure in WM deteriorates the resistance of fatigue crack growth compared to BM. It was mainly due to grain boundary liquation and dissolving of second‐phase particles in the weld region. It was also found that the variety of fatigue crack resistance for different welding zones is in conformity with the change of hardness. BM with the highest hardness exhibited the maximum resistance for fatigue crack, and WM with the lowest hardness exhibited the minimum fatigue crack resistance. 相似文献
213.
Lin Daming Yuan Renmao Shang Yanjun Bao Weixing Wang Kaiyang Zhang Zhongjian Li Kun He Wantong 《Bulletin of Engineering Geology and the Environment》2017,76(1):263-274
Bulletin of Engineering Geology and the Environment - The Yanmenguan Tunnel runs through Hengshan Mountain in Shanxi Province, China. The mountain is mainly composed of metamorphic rock cut by a... 相似文献
214.
215.
Novel heat‐resistant N‐substituted poly(benzimidazole imide)s (PBIIs) with good solubility were synthesized via a C ? N coupling reaction. A model reaction was carried out to assist in determining the optimal reaction conditions for the polymerization and to elucidate the chemical structures of the polymers. The structures of the resulting polymers were characterized by means of Fourier transform infrared and elemental analysis; the results showed good agreement with the proposed structures. The resulting PBIIs exhibited high glass transition temperatures (Tg > 290 oC) and good thermostability (T5% > 440 oC). The thermal behavior in air of the PBII polymers suggests that they can be considered as a new class of high performance polyimides. © 2016 Society of Chemical Industry 相似文献
216.
Highly refractive polyimides containing pyridine and sulfur units: synthesis and thermal,mechanical, solubility and optical properties 下载免费PDF全文
Two series of isomers containing pyridine and sulfur unit aromatic diamine monomers, 4,4′‐bis(5‐amino‐2‐pyridinylsulfanyl)diphenyl sulfide ( 2a ), 4,4′‐bis(6‐amino‐3‐pyridinylsulfanyl)diphenyl sulfide ( 2b ) and 4,4′‐bis(5‐amino‐6‐methyl‐2‐pyridinylsulfanyl)diphenyl sulfide ( 2c ), 4,4′‐bis(5‐amino‐4‐methyl‐2‐pyridinylsulfanyl)diphenyl sulfide ( 2d ), were designed and synthesized. Aimed at clarifying the structure–property relationships of pyridine‐ and sulfur‐containing high refractive polymers, 2a was polymerized with various dianhydrides to prepare polyimides PI ‐1?PI ‐7 and 2b , 2c , 2d were reacted with 4,4′‐[p ‐thiobis(phenylenesulfanyl)]diphthalic anhydride to prepare polyimides PI ‐8?PI ‐10. The polyimides showed excellent optical properties with average refractive indices ranging from 1.7006 to 1.7620 and birefringence as low as 0.0056. Meanwhile, comparative studies on their properties including solubility, thermal and mechanical, and optical transparency properties were performed. Some property differences of the isomers caused by the sequence changes were found. © 2017 Society of Chemical Industry 相似文献
217.
218.
Detection of salient object sequences from video data is challenging when the salient object changes between consecutive frames. In this study, we addressed the salient object sequence rebuilding problem with video segment analysis. We reformulated the problem as a binary labeling problem, analyzed the potential salient object sequences in the video using a clustering method, and separated the salient object sequence from the background by applying an energy optimization method. Our proposed approach determines whether temporal consecutive pixels belong to the same salient object sequence. The conditional random field is then learned to effectively integrate the salient features and the sequence consecutive constraints. A dynamic programming algorithm was developed to resolve the energy minimization problem efficiently. Experimental results confirmed the ability of our approach to address the salient object rebuilding problem in automatic visual attention applications and video content analysis. 相似文献
219.
220.
Artificial Photosynthesis: Ni‐Nanocluster Modified Black TiO2 with Dual Active Sites for Selective Photocatalytic CO2 Reduction (Small 2/2018) 下载免费PDF全文