全文获取类型
收费全文 | 35058篇 |
免费 | 2925篇 |
国内免费 | 1350篇 |
专业分类
电工技术 | 1978篇 |
技术理论 | 2篇 |
综合类 | 2109篇 |
化学工业 | 5549篇 |
金属工艺 | 1774篇 |
机械仪表 | 2076篇 |
建筑科学 | 2733篇 |
矿业工程 | 897篇 |
能源动力 | 1113篇 |
轻工业 | 2400篇 |
水利工程 | 638篇 |
石油天然气 | 1996篇 |
武器工业 | 263篇 |
无线电 | 3987篇 |
一般工业技术 | 4344篇 |
冶金工业 | 1850篇 |
原子能技术 | 279篇 |
自动化技术 | 5345篇 |
出版年
2024年 | 141篇 |
2023年 | 592篇 |
2022年 | 983篇 |
2021年 | 1305篇 |
2020年 | 1038篇 |
2019年 | 834篇 |
2018年 | 1046篇 |
2017年 | 1105篇 |
2016年 | 1014篇 |
2015年 | 1327篇 |
2014年 | 1573篇 |
2013年 | 2123篇 |
2012年 | 2129篇 |
2011年 | 2424篇 |
2010年 | 2028篇 |
2009年 | 1961篇 |
2008年 | 1917篇 |
2007年 | 1723篇 |
2006年 | 1876篇 |
2005年 | 1745篇 |
2004年 | 1122篇 |
2003年 | 1074篇 |
2002年 | 1109篇 |
2001年 | 925篇 |
2000年 | 839篇 |
1999年 | 945篇 |
1998年 | 762篇 |
1997年 | 706篇 |
1996年 | 599篇 |
1995年 | 497篇 |
1994年 | 424篇 |
1993年 | 283篇 |
1992年 | 252篇 |
1991年 | 177篇 |
1990年 | 157篇 |
1989年 | 125篇 |
1988年 | 103篇 |
1987年 | 65篇 |
1986年 | 45篇 |
1985年 | 39篇 |
1984年 | 43篇 |
1983年 | 21篇 |
1982年 | 25篇 |
1981年 | 19篇 |
1980年 | 13篇 |
1979年 | 13篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 14篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
A novel CdS/CaFe2O4 (CS/CFO) heterogeneous p-n junction was created by thermal deposition of CaFe2O4 nanoparticles on CdS rods. The CS/CFO hetero-structured photocatalysts exhibited increasingly efficient visible light harvesting compared to the bare CdS. The CS/CFO composites also presented higher photocurrent and slower decay of photoluminescence, suggesting a better separation of the photo-generated electrons and holes. The photocatalytic H2 evolution quantity on the optimized CS/CFO composite from water in the presence of ethanol was up to 2200 μmol after 3-h visible light illumination, which is more than twice that of the pristine CdS. The chemical interaction between CdS and CaFe2O4 was confirmed by the shifts in the XPS peaks, which made it possible for the charge carriers to transfer across the p-n junction interface. This research highlights the importance of forming an interfacial p-n heterojunction between two semiconductors for efficient charge separation and improved photocatalytic performance. 相似文献
2.
A new aqueous slurry-based laminated object manufacturing process for porous ceramics is proposed: firstly, an organic mesh sheet is pre-paved as a pore-forming template before slurry layer scraping; secondly, the 2D pattern is built with laser outline cutting of the dried mesh–ceramic composite layer; finally, the pore structure is formed after degreasing and sintering. Alumina parts with porosities of 51.5 %, round hole diameters of 80 ± 5 μm were fabricated using 70 wt. % solid content slurry and 100 mesh nylon net. Using an organic mesh as the framework and template not only reduces the risk of damage of the green body but also ensures the regularity, uniformity and connectivity of the micron scaled pore network. The layer-by-layer drying method avoids the delamination phenomenon and improves the paving density. The new method can realize the flexible design of the pore structure by using various organic mesh templates. 相似文献
4.
5.
Huizhu Cai Bingbing Chen Xiao Zhang Yuchen Deng Dequan Xiao Ding Ma Chuan Shi 《Nano Research》2021,14(1):122-130
Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe3C/C and Fe2N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH4/H2and pure NH3,respectively.By acid leaching of Fe2N/C sample,only single sites of FeN4species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN4in ORR.A correlation was conducted between the concentration of FeⅡN4in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin FeⅡN4 species as highly active sites for the ORR. 相似文献
6.
Nitrile rubber (NBR) blends with excellent performance have always been a hot research topic in petroleum field. Due to the excellent performance and compatibility of polyamide 6 (PA6), it provides an opportunity for the preparation of high-performance NBR/PA6 blends. In this article, NBR/PA6 blends were prepared by the three-step molding process. Experimentally, it was found that PA6 has a prominent reinforcement effect in NBR matrix. The variation of this mechanical property was investigated from different aspects of the crystal structure, crystallinities, phase morphology, and so on. It can be cleared that the formation of fibrous structure of PA6 phase is the main factor for reinforcement of the polymer blends. Meanwhile, the formation mechanism of the special phase structure induced by the three-step process is deeply expounded and its structural evolution schematic is established. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47472. 相似文献
7.
Bo Wang Edison Huixiang Ang Yang Yang Yufei Zhang Hongbo Geng Minghui Ye Cheng Chao Li 《Advanced functional materials》2020,30(28)
Orthorhombic molybdenum trioxide (MoO3) is one of the most promising anode materials for sodium‐ion batteries because of its rich chemistry associated with multiple valence states and intriguing layered structure. However, MoO3 still suffers from the low rate capability and poor cycle induced by pulverization during de/sodiation. An ingenious two‐step synthesis strategy to fine tune the layer structure of MoO3 targeting stable and fast sodium ionic diffusion channels is reported here. By integrating partially reduction and organic molecule intercalation methodologies, the interlayer spacing of MoO3 is remarkably enlarged to 10.40 Å and the layer structural integration are reinforced by dimercapto groups of bismuththiol molecules. Comprehensive characterizations and density functional theory calculations prove that the intercalated bismuththiol (DMcT) molecules substantially enhanced electronic conductivity and effectively shield the electrostatic interaction between Na+ and the MoO3 host by conjugated double bond, resulting in improved Na+ insertion/extraction kinetics. Benefiting from these features, the newly devised layered MoO3 electrode achieves excellent long‐term cycling stability and outstanding rate performance. These achievements are of vital significance for the preparation of sodium‐ion battery anode materials with high‐rate capability and long cycling life using intercalation chemistry. 相似文献
8.
9.
10.
Yingcai Bi Menglu Lan Jiaxin Li Shupeng Lai Ben M. Chen 《Asian journal of control》2019,21(4):1732-1744
Micro Aerial Vehicles (MAVs) have great potentials to be applied for indoor search and rescue missions. In this paper, we propose a modular lightweight design of an autonomous MAV with integrated hardware and software. The MAV is equipped with the 2D laser scanner, camera, mission computer and flight controller, running all the computation onboard in real time. The onboard perception system includes a laser‐based SLAM module and a custom‐designed visual detection module. A dual Kalman filter design provides robust state estimation by multiple sensor fusion. Specifically, the fusion module provides robust altitude measurement in the circumstance of surface changing. In addition, indoor‐outdoor transition is explicitly handled by the fusion module. In order to efficiently navigate through obstacles and adapt to multiple tasks, a task tree‐based mission planning method is seamlessly integrated with path planning and control modules. The MAV is capable of searching and rescuing victims from unknown indoor environments effectively. It was validated by our award‐winning performance at the 2017 International Micro Air Vehicle Competition (IMAV 2017), held in Toulouse, France. The performance video is available on https://youtu.be/8H19ppS_VXM . 相似文献