全文获取类型
收费全文 | 314008篇 |
免费 | 9812篇 |
国内免费 | 4929篇 |
专业分类
电工技术 | 10262篇 |
技术理论 | 3篇 |
综合类 | 5455篇 |
化学工业 | 44850篇 |
金属工艺 | 13224篇 |
机械仪表 | 11753篇 |
建筑科学 | 11366篇 |
矿业工程 | 2507篇 |
能源动力 | 9015篇 |
轻工业 | 25757篇 |
水利工程 | 3692篇 |
石油天然气 | 5884篇 |
武器工业 | 714篇 |
无线电 | 41870篇 |
一般工业技术 | 56680篇 |
冶金工业 | 50588篇 |
原子能技术 | 5902篇 |
自动化技术 | 29227篇 |
出版年
2022年 | 3537篇 |
2021年 | 5099篇 |
2020年 | 3746篇 |
2019年 | 3594篇 |
2018年 | 5011篇 |
2017年 | 5304篇 |
2016年 | 5266篇 |
2015年 | 4859篇 |
2014年 | 7251篇 |
2013年 | 15351篇 |
2012年 | 10935篇 |
2011年 | 13445篇 |
2010年 | 11309篇 |
2009年 | 12208篇 |
2008年 | 12768篇 |
2007年 | 12188篇 |
2006年 | 11045篇 |
2005年 | 9449篇 |
2004年 | 8406篇 |
2003年 | 8389篇 |
2002年 | 8183篇 |
2001年 | 8413篇 |
2000年 | 7389篇 |
1999年 | 7395篇 |
1998年 | 17115篇 |
1997年 | 11935篇 |
1996年 | 9223篇 |
1995年 | 6950篇 |
1994年 | 6166篇 |
1993年 | 6033篇 |
1992年 | 4300篇 |
1991年 | 4139篇 |
1990年 | 3941篇 |
1989年 | 3726篇 |
1988年 | 3613篇 |
1987年 | 3059篇 |
1986年 | 2961篇 |
1985年 | 3227篇 |
1984年 | 2940篇 |
1983年 | 2834篇 |
1982年 | 2651篇 |
1981年 | 2552篇 |
1980年 | 2475篇 |
1979年 | 2311篇 |
1978年 | 2107篇 |
1977年 | 2604篇 |
1976年 | 3563篇 |
1975年 | 1764篇 |
1974年 | 1730篇 |
1973年 | 1665篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
2.
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
3.
4.
Multimedia Tools and Applications - Mammograms are the images used by radiologists to diagnose breast cancer. Breast cancer is one of the most common cancers in women. The early detection of breast... 相似文献
5.
Vijay Singh Sharanagat Prabhat K. Nema Lochan Singh Ankur Kumar 《International Journal of Food Science & Technology》2022,57(3):1654-1665
The effect of microwave roasting parameters (300, 450 and 600 W; 5, 10 and 15 min) on acrylamide content in sorghum grain was determined using High Pressure Liquid Chromatography (HPLC)-photo diode array (PDA) detector coupled with C-18 column. Samples roasted at 300 and 450 W did not possess acrylamide, whereas 600 W (15 min) favoured formation of 2740.19 µg/kg of acrylamide, levels far exceeding the defined European Union (EU) limits. The chronic daily intake (CDI) for acrylamide through consumption of such grain flour was 3.25–9.5-fold higher to Joint FAO/WHO Expert Committee on Food Additives (JECFA) defined high exposure limits. The margin of exposure (MOE) values ranged from 4.3 to 12.76 and from 11.07 to 32.27 for neoplastic and neurological effects, respectively, demonstrating high exposure and serious health concerns associated with dietary intake of this toxicant. This study assesses the risk for the Indian population and highlights the importance of optimising process parameters for food product to minimise such exposure risks. 相似文献
6.
F.T. Munna Vidhya Selvanathan K. Sobayel Ghulam Muhammad Nilofar Asim Nowshad Amin Kamaruzzaman Sopian Md. Akhtaruzzaman 《Ceramics International》2021,47(8):11003-11009
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell. 相似文献
7.
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
8.
针对现有的混凝土裂缝检测算法在各种复杂环境中检测精度不够、鲁棒性不强的问题,根据深度学习理论和U-net模型,提出一种全U型网络的裂缝检测算法。首先,依照原U-net模型路线构建网络;然后,在每个池化层后都进行一次上采样,恢复其在池化层之前的特征图规格,并将其与池化之前的卷积层进行融合,将融合之后的特征图作为新的融合层与原U-net网络上采样之后的网络层进行融合;最后,为了验证算法的有效性,在测试集中进行实验。结果表明,所提算法的平均精确率可达到83.48%,召回率为85.08%,F1为84.11%,相较于原U-net分别提升了1.48%,4.68%和3.29%,在复杂环境中也能提取完整裂缝,保证了裂缝检测的鲁棒性。 相似文献
9.
Yixuan ZHOU Huajie WANG Yi YU Yihang CHEN Rui KE Min XU Chijie XIAO Zhanhui WANG Jiquan LI Xuru DUAN Minyou YE 《等离子体科学和技术》2021,23(7):75105-52
In this article, we present the optical design of a novel diagnostic on the HL-2 A tokamak, i.e. the20-channel edge Lyman-alpha beam emission spectroscopy, which is a promising solution for edge density turbulence research on tokamaks, as it offers the possibility of density fluctuation measurement with a 3.3 mm spatial resolution while maintains a high temporal resolution of1 μs. The optical path, including the reflective collection optics, the high-dispersion spectrometer, and the linear detector array, is carefully optimized to obtain a good image quality and a high throughput. The maximum root mean square radius of the collection optics is 64 μm.The detected photon flux is estimated to be about 10~(11) photons/s/channel. 相似文献
10.
Wireless Personal Communications - Despite its various benefits, the Mobile Ad-hoc Network (MANET) has a number of obstacles due to its mobility, unstable topology, energy efficiency, and other... 相似文献