全文获取类型
收费全文 | 87258篇 |
免费 | 7931篇 |
国内免费 | 4928篇 |
专业分类
电工技术 | 1489篇 |
技术理论 | 5篇 |
综合类 | 6372篇 |
化学工业 | 6056篇 |
金属工艺 | 27818篇 |
机械仪表 | 3986篇 |
建筑科学 | 16183篇 |
矿业工程 | 1627篇 |
能源动力 | 1136篇 |
轻工业 | 2153篇 |
水利工程 | 901篇 |
石油天然气 | 2203篇 |
武器工业 | 606篇 |
无线电 | 1273篇 |
一般工业技术 | 10994篇 |
冶金工业 | 16303篇 |
原子能技术 | 497篇 |
自动化技术 | 515篇 |
出版年
2024年 | 354篇 |
2023年 | 1260篇 |
2022年 | 2549篇 |
2021年 | 2788篇 |
2020年 | 3006篇 |
2019年 | 2324篇 |
2018年 | 2140篇 |
2017年 | 3049篇 |
2016年 | 2990篇 |
2015年 | 3349篇 |
2014年 | 5257篇 |
2013年 | 4813篇 |
2012年 | 6194篇 |
2011年 | 7119篇 |
2010年 | 5396篇 |
2009年 | 5606篇 |
2008年 | 4405篇 |
2007年 | 5786篇 |
2006年 | 5252篇 |
2005年 | 4315篇 |
2004年 | 3706篇 |
2003年 | 3143篇 |
2002年 | 2653篇 |
2001年 | 2239篇 |
2000年 | 1901篇 |
1999年 | 1557篇 |
1998年 | 1222篇 |
1997年 | 1174篇 |
1996年 | 992篇 |
1995年 | 737篇 |
1994年 | 673篇 |
1993年 | 468篇 |
1992年 | 431篇 |
1991年 | 298篇 |
1990年 | 283篇 |
1989年 | 236篇 |
1988年 | 126篇 |
1987年 | 70篇 |
1986年 | 45篇 |
1985年 | 38篇 |
1984年 | 24篇 |
1983年 | 21篇 |
1982年 | 34篇 |
1981年 | 18篇 |
1980年 | 46篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1975年 | 4篇 |
1959年 | 12篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and network ferrite are eliminated, the dislocation density and the quantity of dislocated martensite are increased remarkably, and the shape and distribution of inclusions are improved by the addition of RE. Therefore, the mechanical properties of the modified steel can be greatly increased, especially the toughness (αK) by 44%, yield strength (σs) by 10%, and elongation (δ5) by 42%. 相似文献
2.
选取具有代表性的碳钢、不锈钢、镀锌碳钢、铝、钛和铜挂片,在某企业不同部位投放后进行为期半年的大气腐蚀试验,得出了在半年期中的腐蚀规律。在此基础上,对每种金属材料的腐蚀特点进行总结,并对大气腐蚀的各种影响因素进行分析,提出了行之有效的防护措施。 相似文献
3.
4.
结合工程实例,阐述了在输水水质腐蚀性不大的情况下,输水钢管的内壁防腐采用水泥砂浆衬里的必要性和优点,并介绍了设计要点和安装施工注意事项。 相似文献
5.
This article presents a method that can be applied to molten AA-6101 alloy to improve electrical properties of the aluminium part of the optical ground wire (OPGW) used in overhead transmission lines to protect phase conductors from lightning strike and to transmit signals and data. AA-6101 alloy in casting of the log as 6 m length and 178 mm diameter for extrusion has been inoculated by AlB2 to decrease detrimental effects of Cr, Ti, V, and Zr on the conductivity of the material. After inoculation, improved billets were extruded as 9.5 mm diameter feedstock. Required wires drawn from the feedstock according to the construction types of OPGW to be tested were exposed to aging at 175°C, 6 h (T-8). Upon completion of the back-twist and performing-type stranding process, resistance, and short-circuit current capacity and breaking load of the OPGW 88/44 constructions with other metal combinations have been examined and tested to show improvement. Results are summarized in tables and graphically. 相似文献
6.
J. Gegner 《Materialwissenschaft und Werkstofftechnik》2003,34(3):290-297
Chemical Composition and Microstructure of Polymer‐Derived Glasses and Ceramics in the Si–C–O System. Part 2: Characterization of microstructure formation by means of high‐resolution transmission electron microscopy and selected area diffraction Liquid or solid silicone resins represent the economically most interesting class of organic precursors for the pyrolytic production of glass and ceramics materials on silicon basis. As dense, dimensionally stable components can be cost‐effectively achieved by admixing reactive filler powders, chemical composition and microstructure development of the polymer‐derived residues must be exactly known during thermal decomposition. Thus, in the present work, glasses and ceramics produced by pyrolysis of the model precursor polymethylsiloxane at temperatures from 525 to 1550 °C are investigated. In part 1, by means of analytical electron microscopy, the bonding state of silicon was determined on a nanometre scale and the phase separation of the metastable Si–C–O matrix into SiO2, C and SiC was proved. The in‐situ crystallization could be considerably accelerated by adding fine‐grained powder of inert fillers, such as Al2O3 or SiC, which permits effective process control. In part 2, the microstructure is characterized by high‐resolution transmission electron microscopy and selected area diffraction. Turbostratic carbon and cubic β‐SiC precipitate as crystallization products. Theses phases are embedded in an amorphous matrix. Inert fillers reduce the crystallization temperature by several hundred °C. In this case, the polymer‐derived Si–C–O material acts as a binding agent between the powder particles. Reaction layer formation does not occur. On the investigated pyrolysis conditions, no crystallization of SiO2 was observed. 相似文献
7.
8.
ABSTRACT: The objective of this work was to observe the microstructure of feta cheese using confocal scanning laser microscopy. Low fat cheese and cheese containing capsule-producing cultures were made. The protein network was observed using the reflectance mode of the confocal microscope. Fat was stained by Nile red dye diluted with whey. More even distribution of fat with a larger number of smaller globules was observed in cheese made with noncapsule-forming culture compared to that made with the capsule-forming culture. Nonfat cheese had compact structure when made with noncapsule-forming culture which contrasted with the open structure observed in cheese made with the capsule-forming culture 相似文献
9.
通过探讨、分析无缝钢管壁厚偏差产生的原因,提出了改善钢管壁厚偏差的一些措施,并结合实际生产,得出了比较满意的结果。 相似文献
10.