全文获取类型
收费全文 | 22193篇 |
免费 | 1777篇 |
国内免费 | 855篇 |
学科分类
工业技术 | 24825篇 |
出版年
2024年 | 40篇 |
2023年 | 330篇 |
2022年 | 487篇 |
2021年 | 741篇 |
2020年 | 616篇 |
2019年 | 457篇 |
2018年 | 591篇 |
2017年 | 648篇 |
2016年 | 576篇 |
2015年 | 804篇 |
2014年 | 968篇 |
2013年 | 1256篇 |
2012年 | 1308篇 |
2011年 | 1470篇 |
2010年 | 1273篇 |
2009年 | 1190篇 |
2008年 | 1248篇 |
2007年 | 1110篇 |
2006年 | 1260篇 |
2005年 | 1206篇 |
2004年 | 767篇 |
2003年 | 726篇 |
2002年 | 719篇 |
2001年 | 626篇 |
2000年 | 584篇 |
1999年 | 730篇 |
1998年 | 546篇 |
1997年 | 520篇 |
1996年 | 426篇 |
1995年 | 351篇 |
1994年 | 312篇 |
1993年 | 203篇 |
1992年 | 189篇 |
1991年 | 136篇 |
1990年 | 114篇 |
1989年 | 91篇 |
1988年 | 76篇 |
1987年 | 35篇 |
1986年 | 26篇 |
1985年 | 23篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
从苗木定植、田间管理、环境调控、病虫害防治、果实采收等方面,对凉州区红颜草莓设施栽培技术要点进行介绍,以期设施草莓栽培产业得到更好的发展。 相似文献
92.
Hongyu Lv Zhichao Liu Chao Wang Yiyu Cai Hao Zhang Ting Wang Xiuxia Yang Xue Yu Jianbei Qiu Xuhui Xu 《Journal of the American Ceramic Society》2022,105(2):966-976
The exploration of the high thermal stability near-infrared (NIR) phosphors is significantly crucial for the development of plant lighting. However, NIR phosphors suffer from the poor chemical and thermal stability, which severely limits their long-term operation. Here, the successful improvement of luminous intensity (149.5%) and thermal stability at 423 K of Zn3Ga2GeO8 (ZGGO): Cr3+ phosphors is achieved for the introduction of Al3+ ions into the host. The release of carriers in deep traps inhibits the emission loss for the thermal disturbance. Furthermore, an NIR light emitting diodes (LEDs) lamp is explored by combining the optimized Zn3Ga1.1675Al0.8GeO8: 0.0325Cr3+ phosphors with a commercial 460 nm blue chip, and the emission band can match well with the absorption bands of photosynthetic pigments and the phytochrome (PR and PFR) of plants. The explored LEDs lamp further determines the growth and the pheromone content of the involved plants for the participation of the NIR emission originated from Cr3+ ions. Our work provides a promising NIR lamp as plant light with improved thermal stability for long-term operation. 相似文献
93.
Yuzheng Lu Junjiao Li Ligang Ma Zhihang Lu Lei Yu Yixiao Cai 《International Journal of Hydrogen Energy》2021,46(15):9835-9846
Lowering the operational temperature of solid oxide fuel cells (SOFCs) is a vital research challenge for achieving broad commercialization of SOFCs. However, there is currently a lack of suitable electrolyte materials with sufficient ionic conductivity. In this review, the recent progress in semiconductor-ionic conductor composite strategies and related key technologies for low temperature SOFCs (LT-SOFCs) applications is highlighted, in particular, emphasizing the demonstration of such composite materials sandwiched between semiconductor electrodes in a symmetrical configuration that has delivered a potent solution. Despite the co-existence of electronic and ionic conduction in the composite membrane, no electronic short-circuiting was displayed, but rather an enhanced device power output was achieved. Here, the recent progresses in the development of SOFCs, from single-layer fuel cells, to two-phase semiconductor-ionic conductor membrane fuel cells with symmetrical electrodes, are discussed. This review will furnish researchers within the SOFC community and beyond with a broader understanding of the theory, development and significance of composite materials for LT-SOFCs. 相似文献
94.
95.
96.
Droplet impingement of urea water solution (UWS) is a common source for liquid film and solid deposits formed in the tailpipe of diesel engines. In order to better understand and predict wetting phenomena on the tailpipe wall, this study focuses on droplet spreading dynamics of urea water solution. Impingement of single droplets is investigated under defined conditions by high‐speed imaging using shadowgraphy technique. The experimental studies are complemented by numerical simulations with a phase‐field method. Computational results are in good agreement with experimental data for the advancing phase of spreading and the maximum and terminal spreading radius, whereas for the receding phase notable differences occur. For the maximum spreading radius, an empirical correlation derived for glycerol‐water‐ethanol mixtures is found to be valid for millimeter‐sized UWS droplets as well. A numerical simulation for a much smaller droplet however indicates that this correlation is not valid for the tiny droplets of UWS sprays in technical applications. 相似文献
97.
Cai Huanhuan Huang Lei Zhang Wenfeng Wei Zhiqiang 《Multimedia Tools and Applications》2022,81(2):1787-1809
Multimedia Tools and Applications - We focus on the one-example person re-identification (Re-ID) task, where each identity has only one labeled example along with many unlabeled examples. Since... 相似文献
98.
99.
Linfei Cai Charles S. Brennan Huirong Yang Wanying Li Haifeng Zhao 《International Journal of Food Science & Technology》2019,54(12):3166-3174
The evolution of oxidative and structural characteristics of proteins, especially lipid transfer protein 1 (LTP1), in beer during forced-ageing was examined. The oxidative characteristics of beer and proteins were evaluated by DPPH radical scavenging activity and ABTS radical cation scavenging activity. Results showed that the levels of proteins, thiols, LTP1 and antioxidant activity decreased gradually. This was accompanied by the degradation of macromolecular proteins in beer during forced-ageing. Results from circular dichroism (CD), Fourier-transform infrared spectroscopy (FTIR), surface hydrophobicity (S0) and ζ-potential further indicated that the secondary and tertiary structure of LTP1 changed drastically during forced-ageing, with the reduction of the S0, α-helix and β-sheet contents and the increase in negative ζ-potential and random coil. Thus, the proteins, especially LTP1, might play important roles in maintaining oxidative stability of beer. 相似文献
100.
Guoxiao Xu Shiji Xue Zenglv Wei Jing Li Konggang Qu Ying Li Weiwei Cai 《International Journal of Hydrogen Energy》2021,46(5):4301-4308
With PWA as proton transfer and silica as water retainer, stable phosphotungstic acid/silica/Nafion (PWA/Si–N) composite membrane is non-destructively fabricated and exhibits excellent stability and high temperature proton conductivity. Compared with pristine Nafion, high temperature proton conductivity is significantly enhanced due to the collaboration between –SO3H ionic clusters and the in-situ filled silica embedded PWA nanoparticles. PWA is stabilized in the ionic clusters via in-situ catalyzing the hydrolysis silica precursor targeted filled into the –SO3H ionic clusters. Stable proton conductivity of the PWA/Si–N membrane at 110 °C and 60% RH is high to 0.058 S/cm, which is 2.4 folds of that of Nafion. At the same time, the composite membrane still maintains good mechanical and thermal stability. As a result, high temperature fuel cell performance of the composite membrane is improved by 41% compared with the pristine Nafion membrane. The in-situ coating method proved to be an effective method to solve the stability of PWA in Nafion membrane, especially the inorganic oxide with good hygroscopicity as the modifier. 相似文献