全文获取类型
收费全文 | 102719篇 |
免费 | 9468篇 |
国内免费 | 5090篇 |
专业分类
电工技术 | 6275篇 |
技术理论 | 7篇 |
综合类 | 7344篇 |
化学工业 | 17046篇 |
金属工艺 | 5550篇 |
机械仪表 | 6718篇 |
建筑科学 | 8017篇 |
矿业工程 | 2496篇 |
能源动力 | 3055篇 |
轻工业 | 6759篇 |
水利工程 | 1950篇 |
石油天然气 | 5632篇 |
武器工业 | 826篇 |
无线电 | 12652篇 |
一般工业技术 | 13037篇 |
冶金工业 | 4381篇 |
原子能技术 | 1301篇 |
自动化技术 | 14231篇 |
出版年
2024年 | 418篇 |
2023年 | 1525篇 |
2022年 | 2811篇 |
2021年 | 3928篇 |
2020年 | 2915篇 |
2019年 | 2611篇 |
2018年 | 2801篇 |
2017年 | 3192篇 |
2016年 | 3060篇 |
2015年 | 4004篇 |
2014年 | 4972篇 |
2013年 | 6033篇 |
2012年 | 6334篇 |
2011年 | 7042篇 |
2010年 | 6272篇 |
2009年 | 5821篇 |
2008年 | 5887篇 |
2007年 | 5490篇 |
2006年 | 5615篇 |
2005年 | 4784篇 |
2004年 | 3522篇 |
2003年 | 3608篇 |
2002年 | 4119篇 |
2001年 | 3526篇 |
2000年 | 2810篇 |
1999年 | 2692篇 |
1998年 | 2048篇 |
1997年 | 1726篇 |
1996年 | 1652篇 |
1995年 | 1361篇 |
1994年 | 1156篇 |
1993年 | 889篇 |
1992年 | 629篇 |
1991年 | 484篇 |
1990年 | 361篇 |
1989年 | 303篇 |
1988年 | 282篇 |
1987年 | 167篇 |
1986年 | 113篇 |
1985年 | 78篇 |
1984年 | 55篇 |
1983年 | 33篇 |
1982年 | 43篇 |
1981年 | 35篇 |
1980年 | 26篇 |
1979年 | 16篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1959年 | 4篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
采用直流磁控溅射和后退火氧化工艺在p型GaAs单晶衬底上成功制备了n-VO_2/pGaAs异质结,研究了不同退火温度和退火时间对VO_2/GaAs异质结性能的影响,并分析其结晶取向、化学组分、膜层质量以及光电特性。结果表明,在退火时间2 h和退火温度693 K下能得到相变性能最佳的VO_2薄膜,相变前后电阻变化约2个数量级。VO_2/GaAs异质结在308 K、318 K和328 K温度下具有较好的整流特性,对应温度下的阈值跳变电压分别为6.9 V、6.6 V和6.2 V,该结果为基于VO_2相变特性的异质结光电器件的设计与应用提供了可行性。 相似文献
2.
Xin Li Yurui Wang Minxuan Xu Yueqin Shi Hemiao Wang Xin Yang Haoting Ying Qi Zhang 《应用聚合物科学杂志》2021,138(19):50406
Polymer electrets have revealed great potential application in electromechanical devices because of the low weight, large quasi-piezoelectric sensitivity, and excellent flexibility. For an electret, a permanent and macroscopic electric field exists on the surface, principally led by a macroscopic electrostatic charge on the surface or a net orientation of polar groups inside the object. Here, progress in the development of polymer electrets is reviewed. After a brief retrospect of the research courses and those typical polymer electrets that are classified into fluorine polymer and nonfluorine polymer, we present a survey on the charging methods, including corona, soft X-ray, contact, thermal and monoenergetic particle beams. The latest representative applications (i.e., power harvesting, sensors, field effect transistors, and biomedicine) based on polymer electrets are also summarized. Finally, we complete this review with a discussion on perspectives and challenges in this field. 相似文献
3.
International Journal of Speech Technology - With the development of multimedia technology and network technology applications, it is possible to implement online teaching systems in schools. This... 相似文献
4.
5.
Hong Sae Jin Park Nam Il Hwang Dae Keun Yi Tae Gyu Eum Hyang Lan 《Food science and biotechnology》2022,31(6):669-679
Food Science and Biotechnology - Various hilling materials (rice hulls, pine sawdust, and perlite) were compared to produce sprout vegetables using beach silvertop (Glehnia littoralis Fr. Schm. ex... 相似文献
6.
Kai Liu Chenyang Zhou Jiaming Hu Song Zhang Qingqing Zhang Ce Sun Yusheng Shi Huajun Sun Changxia Yin Yuzhen Zhang Yu Fu 《Journal of the European Ceramic Society》2021,41(12):5909-5917
A digital light processing (DLP) technology has been developed for 3D printing lead-free barium titanate (BTO) piezoelectric ceramics. By comparing the curing and rheological properties of slurries with different photosensitive monomer, a high refractive index monomer acryloyl morpholine (ACMO) was chosen, and a design and preparation method of BTO slurry with high solid content, low viscosity and high curing ability was proposed. By further selecting the printing parameters, the single-layer exposure time was reduced and the forming efficiency has been greatly improved. Sintered specimens were obtained after a nitrogen-air double-step debinding and furnace sintering process, and the BTO ceramics fabricated with 80 wt% slurry shows the highest relative density (95.32 %) and piezoelectric constant (168.1 pC/N). Furthermore, complex-structured BTO ceramics were prepared, impregnated by epoxy resin and finally assembly made into hydrophones, which has significance for the future design and manufacture of piezoelectric ceramic-based composites that used in functional devices. 相似文献
7.
8.
Xiaoyan Dong Xu Li Xiuli Chen Hongyun Chen Congcong Sun Junpeng Shi Feihong Pang Huanfu Zhou 《Ceramics International》2021,47(3):3079-3088
Dielectric capacitors with decent energy storage and fast charge-discharge performances are essential in advanced pulsed power systems. In this study, novel ceramics (1-x)NaNbO3-xBi(Ni2/3Nb1/3)O3(xBNN, x = 0.05, 0.1, 0.15 and 0.20) with high energy storage capability, large power density and ultrafast discharge speed were designed and prepared. The impedance analysis proves that the introducing an appropriate amount of Bi(Ni0·5Nb0.5)O3 boosts the insulation ability, thus obtaining a high breakdown strength (Eb) of 440 kV/cm in xBNN ceramics. A high energy storage density (Wtotal) of 4.09 J/cm3, recoverable energy storage density (Wrec) of 3.31 J/cm3, and efficiency (η) of 80.9% were attained in the 0.15BNN ceramics. Furthermore, frequency and temperature stability (fluctuations of Wrec ≤ 0.4% over 5–100 Hz and Wrec ≤ 12.3% over 20–120 °C) were also observed. The 0.15BNN ceramics exhibited a large power density (19 MW/cm3) and ultrafast discharge time (~37 ns) over the range of ambient temperature to 120 °C. These enhanced performances may be attributed to the improved breakdown strength and relaxor behavior through the incorporation of BNN. In conclusion, these findings indicate that 0.15BNN ceramics may serve as promising materials for pulsed power systems. 相似文献
9.
Xiao-juan Li Yi-xiang Xu Xiang Li Zhi-jiang Jin Jin-yuan Qian 《International Journal of Hydrogen Energy》2021,46(7):5537-5547
Ambient condition, especially the wind condition, is an important factor to determine the behavior of hydrogen diffusion during hydrogen release. However, only few studies aim at the quantitative study of the hydrogen diffusion in a wind-exist condition. And very little researches aiming at the variable wind condition have been done. In this paper, the hydrogen diffusion in different wind condition which including the constant wind velocity and the variable wind velocity is investigated numerically. When considering the variable wind velocity, the UDF (user defined function) is compiled. Characteristics of the FGC (flammable gas cloud) and the HMF (hydrogen mass fraction) are analyzed in different wind condition and comparisons are made with the no-wind condition. Results indicate that the constant wind velocity and the variable wind velocity have totally different effect for the determination of hydrogen diffusion. Comparisons between the constant wind velocity and the variable wind velocity indicate that the variable wind velocity may cause a more dangerous situation since there has a larger FGC volume. More importantly, the wind condition has a non-negligible effect when considering the HMF along the radial direction. As the wind velocity increases, the distribution of the HMF along the radial direction is not Gaussian anymore when the distance between the release hole and the observation line exceeds to a critical value. This work can be a supplement of the research on the hydrogen release and diffusion and a valuable reference for the researchers. 相似文献
10.
随着经济的发展,消防救援队伍承担的任务越来越繁重.重大灾害事故的发生,对消防战勤保障方面提出了更高的要求.文章主要从消防战勤保障的主要任务职能、消防战勤的任务分类以及消防战勤保障体系建设存在的问题与建议等几个方面进行了详细的阐述,以期消防战勤保障得到更好的发展. 相似文献