全文获取类型
收费全文 | 276006篇 |
免费 | 33175篇 |
国内免费 | 10367篇 |
专业分类
电工技术 | 15671篇 |
技术理论 | 16篇 |
综合类 | 14743篇 |
化学工业 | 55740篇 |
金属工艺 | 13461篇 |
机械仪表 | 15428篇 |
建筑科学 | 21128篇 |
矿业工程 | 6544篇 |
能源动力 | 7876篇 |
轻工业 | 22163篇 |
水利工程 | 4721篇 |
石油天然气 | 12909篇 |
武器工业 | 1980篇 |
无线电 | 35448篇 |
一般工业技术 | 39898篇 |
冶金工业 | 12773篇 |
原子能技术 | 2793篇 |
自动化技术 | 36256篇 |
出版年
2024年 | 848篇 |
2023年 | 3595篇 |
2022年 | 6665篇 |
2021年 | 9870篇 |
2020年 | 8251篇 |
2019年 | 8586篇 |
2018年 | 9166篇 |
2017年 | 10485篇 |
2016年 | 10239篇 |
2015年 | 12628篇 |
2014年 | 15275篇 |
2013年 | 19268篇 |
2012年 | 17881篇 |
2011年 | 19287篇 |
2010年 | 17040篇 |
2009年 | 16683篇 |
2008年 | 15690篇 |
2007年 | 14973篇 |
2006年 | 14822篇 |
2005年 | 12888篇 |
2004年 | 9169篇 |
2003年 | 7966篇 |
2002年 | 7364篇 |
2001年 | 6563篇 |
2000年 | 6543篇 |
1999年 | 6533篇 |
1998年 | 5587篇 |
1997年 | 4610篇 |
1996年 | 4135篇 |
1995年 | 3439篇 |
1994年 | 2885篇 |
1993年 | 2284篇 |
1992年 | 1757篇 |
1991年 | 1327篇 |
1990年 | 1044篇 |
1989年 | 896篇 |
1988年 | 689篇 |
1987年 | 499篇 |
1986年 | 387篇 |
1985年 | 326篇 |
1984年 | 204篇 |
1983年 | 189篇 |
1982年 | 159篇 |
1981年 | 153篇 |
1980年 | 141篇 |
1979年 | 104篇 |
1978年 | 65篇 |
1977年 | 64篇 |
1976年 | 79篇 |
1975年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
991.
992.
Highly transparent and conducting fluorine (F) doped cadmium oxide (CdO) thin films were deposited on glass slides by the sol-gel method. The films were doped by the addition of ammonium fluoride to the precursor solution whose optimum concentration was determined. The films were fired in an open atmosphere at 350 °C and after that, exposed to annealing treatments in different atmospheres (N2, N2/H2 mixture and Ar) at the same temperature. The films were characterized by ultraviolet-visible spectroscopy, X‐ray diffraction and scanning electron microscopy. The resistivity was determined by the four probes method and current-voltage measurements in accordance with the standard Van der Pauw configuration. The CdO:F thin films obtained, showed high polycrystalline quality and high transmission in the visible region (≥ 90%), shifting towards the blue region of the absorption edge as the fluorine concentration in the precursor solution was increased from 0 to 30 at.%. The lowest resistivity values were reached for the samples with F content higher or equal to 5% and annealed in either N2 or a 96/4 N2/H2 gas mixture. Our resistivity value reached in the CdO:F layers was 4.5 × 10− 4 Ω cm (20 Ω/square). 相似文献
993.
The AlCoCrCuFeNi high-entropy alloy system was synthesized using a well-developed arc melting and casting method. Their elemental effect on microstructures and hardness was investigated with X-ray diffraction, scanning electron microscopy and Vickers hardness testing. The alloys exhibit quite simple FCC and BCC solid solution phases. Co, Cu and Ni elements enhance the formation of the FCC phase while Al and Cr enhance that of the BCC phase in the alloy system. BCC phases form a spinodal structure during cooling. Copper tends to segregate at the interdendrite region and forms a Cu-rich FCC phase. Low copper content renders the interdendrite as a thin film and the as-cast structure like recrystallized grain structure. The formation of BCC phases significantly increases the hardness level of the alloy system. The strengthening mechanism is discussed. 相似文献
994.
Hydrothermal process was applied to synthesize zinc oxide nanocrystals. X-ray powder diffraction and scanning electron microscopy were used to analyze the crystal structure and surface morphology. XRD pattern analysis showed that the ZnO clusters are single hexagonal phase of wurtzite structure (space group P63 mc) with no impurity of Zn and Zn(OH)2. Also, SEM images revealed that the size of a single ZnO crystal is between 200-500 nm in diameter and 2-5 μm in length. The influence of potassium iodide (KI) as a surfactant on the crystallinity of ZnO has been investigated. 相似文献
995.
新经济增长理论对我国人力资本发展的借鉴 总被引:3,自引:0,他引:3
新经济增长理论为人力资本理论注入了新的内容,为各国如何利用人力资本发展经济提供了理论指导。分析了新经济增长理论中有关人力资本的理论,以此对我国经济和人力资本的发展提出了一些借鉴;收益递增模型。 相似文献
996.
This paper presents an application of digital signal processing to data acquired by the radio imaging method (RIM) that was adopted to measure moisture distribution inside the human body. RIM was originally developed for the mining industry; we are applying the method to a biomedical measurement because of its simplicity, economy, and safety. When a two‐dimensional image was constructed from the measured data, the method provided insufficient resolution because the wavelength of the measurement medium, a weak electromagnetic wave in a VHF band, was longer than human tissues. We built and measured a phantom, a model simulating the human body, consisting of two water tanks representing large internal organs. A digital equalizer was applied to the measured values as a weight function, and images were reconstructed that corresponded to the original shape of the two water tanks. As a result, a two‐dimensional image containing two individual peaks corresponding to the original two small water tanks was constructed. The result suggests the method was applicable to biomedical measurement by the assistance of digital signal processing. This technique may be applicable to home‐based medical care and other situations in which safety, simplicity, and economy are important. 相似文献
997.
998.
999.
1000.
Composition Range of Amorphous Mg-Ni-Y Alloys 总被引:1,自引:0,他引:1
Based on the thermodynamic point of view, a method for predication of the composition range of amorphous ter-nary alloys was proposed. The composition range of amorphous ternary alloys is determined by the comparison of the excess free energy of the amorphous alloy and the free energy of competing crystalline states. The free energy is extrapolated from the data of three binary alloys by using Toop‘s model. The method was applied to predict the composition range of amor-phous Mg-Ni-Y alloys. The theoretical results are in good agreement with the available experimental results. It indicates that the present method can be used to predict the composition range for amorphous ternary alloys. 相似文献