全文获取类型
收费全文 | 27084篇 |
免费 | 794篇 |
国内免费 | 880篇 |
专业分类
电工技术 | 641篇 |
综合类 | 290篇 |
化学工业 | 3158篇 |
金属工艺 | 2493篇 |
机械仪表 | 1183篇 |
建筑科学 | 810篇 |
矿业工程 | 176篇 |
能源动力 | 961篇 |
轻工业 | 1362篇 |
水利工程 | 208篇 |
石油天然气 | 637篇 |
武器工业 | 26篇 |
无线电 | 3164篇 |
一般工业技术 | 7079篇 |
冶金工业 | 4090篇 |
原子能技术 | 342篇 |
自动化技术 | 2138篇 |
出版年
2024年 | 19篇 |
2023年 | 115篇 |
2022年 | 239篇 |
2021年 | 346篇 |
2020年 | 266篇 |
2019年 | 352篇 |
2018年 | 524篇 |
2017年 | 511篇 |
2016年 | 557篇 |
2015年 | 485篇 |
2014年 | 761篇 |
2013年 | 1744篇 |
2012年 | 1139篇 |
2011年 | 1608篇 |
2010年 | 1286篇 |
2009年 | 1459篇 |
2008年 | 1482篇 |
2007年 | 1446篇 |
2006年 | 1333篇 |
2005年 | 1235篇 |
2004年 | 975篇 |
2003年 | 914篇 |
2002年 | 869篇 |
2001年 | 836篇 |
2000年 | 810篇 |
1999年 | 821篇 |
1998年 | 1546篇 |
1997年 | 1102篇 |
1996年 | 955篇 |
1995年 | 630篇 |
1994年 | 495篇 |
1993年 | 400篇 |
1992年 | 266篇 |
1991年 | 268篇 |
1990年 | 167篇 |
1989年 | 184篇 |
1988年 | 136篇 |
1987年 | 103篇 |
1986年 | 63篇 |
1985年 | 63篇 |
1984年 | 38篇 |
1983年 | 31篇 |
1982年 | 28篇 |
1981年 | 30篇 |
1980年 | 16篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 19篇 |
1975年 | 12篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Reliable joints of Ti3SiC2 ceramic and TC11 alloy were diffusion bonded with a 50 μm thick Cu interlayer. The typical interfacial structure of the diffusion boned joint, which was dependent on the interdiffusion and chemical reactions between Al, Si and Ti atoms from the base materials and Cu interlayer, was TC11/α-Ti + β-Ti + Ti2Cu + TiCu/Ti5Si4 + TiSiCu/Cu(s, s)/Ti3SiC2. The influence of bonding temperature and time on the interfacial structure and mechanical properties of Ti3SiC2/Cu/TC11 joint was analyzed. With the increase of bonding temperature and time, the joint shear strength was gradually increased due to enhanced atomic diffusion. However, the thickness of Ti5Si4 and TiSiCu layers with high microhardness increased for a long holding time, resulting in the reduction of bonding strength. The maximum shear strength of 251 ± 6 MPa was obtained for the joint diffusion bonded at 850 °C for 60 min, and fracture primarily occurred at the diffusion layer adjacent to the Ti3SiC2 substrate. This work provided an economical and convenient solution for broadening the engineering application of Ti3SiC2 ceramic. 相似文献
2.
Sijia Huo Yujin Wang Mianyi Yao Zhikun Zhang Lei Chen Hui Gu Jiahu Ouyang Yu Zhou 《Journal of the European Ceramic Society》2021,41(11):5466-5473
Novel TiC-based composites were synthesized by reactive hot-pressing at 1800 °C for 1 h with ZrB2 addition as a sintering aid for the first time. The effects of ZrB2 contents on the phase composition, microstructure evolution, and mechanical properties were reported. Based on the reaction and solid solution coupling effects between ZrB2 and TiC, the product ZrC may be partially or completely dissolved into the TiC matrix, and then phase separation within the miscibility gap is observed to form lamellar nanostructured ZrC-rich (Zr, Ti)C. The TiC-10 mol.% ZrB2 (starting batch composition) exhibits good comprehensive mechanical properties of hardness 27.7 ± 1.3 GPa, flexural strength 659 ± 48 MPa, and fracture toughness of 6.5 ± 0.6 MPa m1/2, respectively, which reach or exceed most TiC-based composites using ceramics as sintering aids in the previous reports. 相似文献
3.
4.
5.
As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided. 相似文献
6.
7.
8.
Spinel LiSr0·1Cr0·1Mn1·8O4 was synthesised by high temperature solid state method in order to enhance the electrochemical performance. The LiSr0·1Cr0·1Mn1·8O4 (LSCMO) materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The XRD and SEM studies confirm that LSCMO had spinel crystal structure with a space group of Fd3m, and the particle of LSCMO shows irregular shape. The cyclic voltammetry data illustrated that the heavy current charge–discharge performance of LMO was improved by Sr2+ and Cr3+ doping. The galvanostatic charge–discharge of LSCMO cathode materials was measured at 1, 5, 10 and 20 C. The results indicated that LSCMO improved the capacity retention. 相似文献
9.
Strength of Materials - A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation,... 相似文献
10.
Xiaopu Lyu Yunxi Huo Jin Yang Dawen Yao Kaimin Li Haoxian Lu Yangzong Zeren Hai Guo 《Indoor air》2021,31(5):1340-1352
Due to the high health risks associated with indoor air pollutants and long-term exposure, indoor air quality has received increasing attention. In this study, we put emphasis on the molecular composition, source emissions, and chemical aging of air pollutants in a residence with designed activities mimicking ordinary Hong Kong homes. More than 150 air pollutants were detected at molecular level, 87 of which were quantified at a time resolution of not less than 1 hour. The indoor-to-outdoor ratios were higher than 1 for most of the primary air pollutants, due to emissions of indoor activities and indoor backgrounds (especially for aldehydes). In contrast, many secondary air pollutants exhibited higher concentrations in outdoor air. Painting ranked first in aldehyde emissions, which also caused great enhancement of aromatics. Incense burning had the highest emissions of particle-phase organics, with vanillic acid and syringic acid as markers. The other noteworthy fingerprints enabled by online measurements included linoleic acid, cholesterol, and oleic acid for cooking, 2,5-dimethylfuran, stigmasterol, iso-/anteiso-alkanes, and fructose isomers for smoking, C28-C34 even n-alkanes for candle burning, and monoterpenes for the use of air freshener, cleaning agents, and camphor oil. We showed clear evidence of chemical aging of cooking emissions, giving a hint of indoor heterogeneous chemistry. This study highlights the value of organic molecules measured at high time resolutions in enhancing our knowledge on indoor air quality. 相似文献