全文获取类型
收费全文 | 474161篇 |
免费 | 15484篇 |
国内免费 | 6963篇 |
专业分类
电工技术 | 14757篇 |
技术理论 | 9篇 |
综合类 | 8980篇 |
化学工业 | 70000篇 |
金属工艺 | 24796篇 |
机械仪表 | 21764篇 |
建筑科学 | 16950篇 |
矿业工程 | 5379篇 |
能源动力 | 11360篇 |
轻工业 | 31425篇 |
水利工程 | 6169篇 |
石油天然气 | 13392篇 |
武器工业 | 1064篇 |
无线电 | 56731篇 |
一般工业技术 | 91099篇 |
冶金工业 | 63421篇 |
原子能技术 | 10138篇 |
自动化技术 | 49174篇 |
出版年
2023年 | 2886篇 |
2022年 | 5977篇 |
2021年 | 8254篇 |
2020年 | 6143篇 |
2019年 | 5826篇 |
2018年 | 15254篇 |
2017年 | 16178篇 |
2016年 | 12408篇 |
2015年 | 8180篇 |
2014年 | 11136篇 |
2013年 | 20146篇 |
2012年 | 17764篇 |
2011年 | 25578篇 |
2010年 | 22147篇 |
2009年 | 21913篇 |
2008年 | 22137篇 |
2007年 | 23311篇 |
2006年 | 14529篇 |
2005年 | 15638篇 |
2004年 | 12576篇 |
2003年 | 12477篇 |
2002年 | 11202篇 |
2001年 | 10754篇 |
2000年 | 9710篇 |
1999年 | 9619篇 |
1998年 | 18993篇 |
1997年 | 13519篇 |
1996年 | 10692篇 |
1995年 | 8285篇 |
1994年 | 7335篇 |
1993年 | 7023篇 |
1992年 | 5276篇 |
1991年 | 5038篇 |
1990年 | 4848篇 |
1989年 | 4564篇 |
1988年 | 4369篇 |
1987年 | 3774篇 |
1986年 | 3626篇 |
1985年 | 3834篇 |
1984年 | 3520篇 |
1983年 | 3402篇 |
1982年 | 3230篇 |
1981年 | 3118篇 |
1980年 | 3017篇 |
1979年 | 2946篇 |
1978年 | 2782篇 |
1977年 | 3260篇 |
1976年 | 4235篇 |
1975年 | 2414篇 |
1974年 | 2346篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Chenxu Liu Shuguang Zhang Ruonan Ji Peng Wang Jin Zhang Yu Tian Yonggang Meng Yedong He 《Ceramics International》2019,45(4):4747-4755
Semiconductor particles doped Al2O3 coatings were prepared by cathode plasma electrolytic deposition in Al(NO3)3 electrolyte dispersed with SiC micro- and nano-particles (average particle sizes of 0.5–1.7?µm and 40?nm respectively). The effects of the concentrations and particle sizes of the SiC on the microstructures and tribological performances of the composite coatings were studied. In comparison with the case of dispersing with SiC microparticles, the dispersion of SiC nanoparticles in the coatings was more uniform. When the concentration of SiC nanoparticles was 5?g/L, the surface roughness of the composite coating was reduced by 63%, compared with that of the unmodified coating. Friction results demonstrated that the addition of 5?g/L SiC nanoparticles reduced the friction coefficient from 0.60 to 0.38 and decreased the wear volume under dry friction. The current density and bath voltage were measured to analyze the effects of SiC particles on the deposition process. The results showed that the SiC particles could alter the electrical behavior of the coatings during the deposition process, weaken the bombardment of the plasma, and improve the structures of the coatings. 相似文献
92.
Magnetic Resonance Materials in Physics, Biology and Medicine - To investigate the value of using diffusion-weighted imaging (DWI) and intravoxel incoherent motion DWI (IVIM-DWI) to assess the... 相似文献
93.
Babilas R. Łoński W. Młynarek K. Bajorek A. Radoń A. 《Metallurgical and Materials Transactions A》2020,51(8):4215-4227
Metallurgical and Materials Transactions A - The influence of the chemical composition on the crystallization process, amorphous phase formation, and the anticorrosion properties of Al-Zr-Ni-Fe-Y... 相似文献
94.
卫星导航地基增强系统(GBAS)是国际民航组织重点推进的新技术。为全面借鉴国际上 GBAS 技术的发展与应用,本文介绍了 GBAS 组成、原理和优缺点,研究了国内外 GBAS 研究与应用的发展,结合中国民航目前的运行需求提出了 GBAS 应用建议,为 GBAS 发展应用提供了参考。 相似文献
95.
Wireless Personal Communications - The existing long term evolution networks originally designed for human-to-human communications are hard to tackle numerous and bursty random access requests from... 相似文献
96.
Sustainable and efficient food supply chain has become an essential component of one’s life. The model proposed in this paper is deeply linked to people's quality of life as a result of which there is a large incentive to fulfil customer demands through it. This proposed model can enhance food quality by making the best possible food quality accessible to customers, construct a sustainable logistics system considering its environmental impact and ensure the customer demand to be fulfilled as fast as possible. In this paper, an extended model is examined that builds a unified planning problem for efficient food logistics operations where four important objectives are viewed: minimising the total expense of the system, maximising the average food quality along with the minimisation of the amount of CO2 emissions in transportation along with production and total weighted delivery lead time minimisation. A four objective mixed integer linear programming model for intelligent food logistics system is developed in the paper. The optimisation of the formulated mathematical model is proposed using a modified multi-objective particle swarm optimisation algorithm with multiple social structures: MO-GLNPSO (Multi-Objective Global Local Near-Neighbour Particle Swarm Optimisation). Computational results of a case study on a given dataset as well as on multiple small, medium and large-scale datasets followed by sensitivity analysis show the potency and effectiveness of the introduced method. Lastly, there has been a scope for future study displayed which would lead to the further progress of these types of models. 相似文献
97.
98.
Effects of different carbon sources and C/N values on nonvolatile taste components of Pleurotus eryngii 下载免费PDF全文
Wen Li Xiaobei Li Yan Yang Feng Zhou Yanfang Liu Shuai Zhou Hailong Yu 《International Journal of Food Science & Technology》2015,50(11):2360-2366
Pleurotus eryngii, the second largest industrial cultivation mushroom in China, is usually cultivated on substrates mainly consisting of sawdust and corncob. In this study, experiments were performed to determine the effects of different carbon sources and C/N values on nonvolatile taste components of P. eryngii. The effects of different carbon sources on nonvolatile taste components levels revealed that sawdust was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while corncob was beneficial to high contents of carbohydrate, polysaccharides and trehalose. At the similar C/N values, relatively higher sawdust content was beneficial to umami amino acid production, while relatively higher corncob content was beneficial to high contents of carbohydrate, polysaccharides and mannitol. Higher C/N value was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while lower C/N value was beneficial to high contents of carbohydrate, polysaccharides and trehalose. These results provided information for P. eryngii fruit body industrial cultivation to obtain specific nonvolatile taste components with high levels. 相似文献
99.
Colour remains one of the key factors in presenting an object and, consequently, has been widely applied in retrieval of images based on their visual contents. However, a colour appearance changes with the change of viewing surroundings, the phenomenon that has not been paid attention yet while performing colour‐based image retrieval. To comprehend this effect, in this article, a chromatic contrast model, CAMcc, is developed for the application of retrieval of colour intensive images, cementing the gap that most of existing colour models lack to fill by taking simultaneous colour contrast into account. Subsequently, the model is applied to the retrieval task on a collection of museum wallpapers of colour‐rich images. In comparison with current popular colour models including CIECAM02, HSI and RGB, with respect to both foreground and background colours, CAMcc appears to outperform the others with retrieved results being closer to query images. In addition, CAMcc focuses more on foreground colours, especially by maintaining the balance between both foreground and background colours, while the rest of existing models take on dominant colours that are perceived the most, usually background tones. Significantly, the contribution of the investigation lies in not only the improvement of the accuracy of colour‐based image retrieval but also the development of colour contrast model that warrants an important place in colour and computer vision theory, leading to deciphering the insight of this age‐old topic of chromatic contrast in colour science. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 361–373, 2015 相似文献
100.
Diffusional limitations (the gel, glass, and cage effects) are manifested in several bulk free radical homopolymerizations as well as in random copolymerizations. These are associated with decreases of several orders of magnitude of the rate constants of termination, propagation, and initiation (the initiator efficiency), respectively. These phenomena have been modeled earlier using the free volume theory for the diffusivities of primary radicals, macro‐radicals, and monomer molecules, and have been applied to homopolymerizations. In this study, a similar model is developed for random bulk copolymerizations. The parameters of the model are fitted using isothermal data on styrene acrylonitrile random copolymerization carried out in small ampoules. Thereafter, best‐fit global correlations have been developed for this system. This enables the model to be used for studying non‐isothermal copolymerizations, as well as for carrying out optimization of industrial reactors, where non‐isothermal conditions are a norm. POLYM. ENG. SCI., 55:2098–2110, 2015. © 2014 Society of Plastics Engineers 相似文献