全文获取类型
收费全文 | 258207篇 |
免费 | 20995篇 |
国内免费 | 11004篇 |
专业分类
电工技术 | 15392篇 |
技术理论 | 22篇 |
综合类 | 15977篇 |
化学工业 | 43126篇 |
金属工艺 | 13944篇 |
机械仪表 | 16088篇 |
建筑科学 | 20312篇 |
矿业工程 | 7262篇 |
能源动力 | 7539篇 |
轻工业 | 16839篇 |
水利工程 | 4648篇 |
石油天然气 | 14795篇 |
武器工业 | 1862篇 |
无线电 | 30879篇 |
一般工业技术 | 31359篇 |
冶金工业 | 13138篇 |
原子能技术 | 2676篇 |
自动化技术 | 34348篇 |
出版年
2024年 | 1171篇 |
2023年 | 4443篇 |
2022年 | 8229篇 |
2021年 | 11087篇 |
2020年 | 8319篇 |
2019年 | 6727篇 |
2018年 | 7644篇 |
2017年 | 8574篇 |
2016年 | 7769篇 |
2015年 | 10158篇 |
2014年 | 13004篇 |
2013年 | 15801篇 |
2012年 | 16931篇 |
2011年 | 17865篇 |
2010年 | 15507篇 |
2009年 | 14685篇 |
2008年 | 14069篇 |
2007年 | 13203篇 |
2006年 | 13650篇 |
2005年 | 11835篇 |
2004年 | 7888篇 |
2003年 | 6817篇 |
2002年 | 6073篇 |
2001年 | 5495篇 |
2000年 | 5705篇 |
1999年 | 6573篇 |
1998年 | 5714篇 |
1997年 | 4711篇 |
1996年 | 4373篇 |
1995年 | 3590篇 |
1994年 | 2972篇 |
1993年 | 2134篇 |
1992年 | 1665篇 |
1991年 | 1300篇 |
1990年 | 962篇 |
1989年 | 822篇 |
1988年 | 673篇 |
1987年 | 422篇 |
1986年 | 367篇 |
1985年 | 238篇 |
1984年 | 207篇 |
1983年 | 145篇 |
1982年 | 139篇 |
1981年 | 119篇 |
1980年 | 99篇 |
1979年 | 61篇 |
1978年 | 37篇 |
1977年 | 57篇 |
1976年 | 42篇 |
1975年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
101.
The In-Sn-Ni alloys of various compositions were prepared and annealed at 160°C and 240°C. No ternary compounds were found;
however, most of the binary compounds had extensive ternary solubility. There was a continuous solid solution between the
Ni3Sn phase and Ni3In phase. The Sn-In/Ni couples, made of Sn-In alloys with various compositions, were reacted at 160°C and 240°C and formed
only one compound for all the Sn-In alloys/Ni couples reacted up to 8 h. At 240°C, Ni28In72 phase formed in the couples made with pure indium, In-10at.%Sn and In-11at.%Sn alloys, while Ni3Sn4 phase formed in the couples made of alloys with compositions varied from pure Sn to In-12at.%Sn. At 160°C, except in the
In/Ni couple, Ni3Sn4 formed by interfacial reaction. 相似文献
102.
Guangbin Yang 《Reliability, IEEE Transactions on》2002,51(3):288-293
ESS (environmental stress screening) has been extensively used to reduce infant mortality by precipitating defects. The existing ESS plans precipitate defects by stressing all products for specified durations. The plans usually require long screen durations to allow nearly all defective items to fail, and thus generate excessive aging effects on good items. For some products, failures are defined in terms of performance characteristics exceeding their critical values. This paper describes the principles of using degradation measurements of performance characteristics to screen the products. In an ESS, the performance characteristics of defective items degrade considerably faster than those of good ones, yielding a bimodal distribution of the characteristics. As screen duration increases, the 2 modes of the distribution shift apart. It is possible to find a tightened critical value to weed out the defective items before they fail. This paper, based on these principles, further designs the optimal 2-level screen plans which minimize a segment of life-cycle cost and which simultaneously meet the reliability requirement. The minimum cost is achieved by choosing optimal part-level and unit-level screen durations and tightened critical values of parts. A numerical example is followed by discussion. Because the ESS regime of this paper allows defective parts to be screened out before they fail, the developed optimal ESS plans can reduce life-cycle cost, shorten part-level screen duration, and alleviate aging effects on good products 相似文献
103.
104.
105.
106.
107.
从范围、原材料要求、组分要求、物理力学性能等方面对比分析了我国现行油毡瓦标准与欧美标准的区别,提出了我国制订沥青油毡瓦国家标准的的原则。 相似文献
108.
109.
黄劲松 《石油化工管理干部学院学报》2002,(2):33-34
职业技能鉴定是推行职业资格证书制度的重要环节,鉴定的质量直接关系到职业资格证书的真实性、权威性。通过对试卷的有效性和可靠性的分析,以及对试题难度、区分度的分析,对职业技能鉴定质量的分析方法进行了探讨,阐述了质量分析在职业技能鉴定中的作用。 相似文献
110.
The flow and heat transfer characteristics of a pair of embedded counter-rotating vortices are studied experimentally. In order to control the strength of longitudinal vortices, angle of attack of the vortex generators is varied from ±20° to ±45°, and the spacing between the vortex generators is 4 cm apart. The heat transfer measurements using thermo-chromatic liquid crystal are made to provide the local surface distributions of heat transfer coefficients. The following conclusions are obtained from the present experiment. For the common-flow-down cases, two maximum values in the local heat transfer distributions exist for the three angles of attack. With the common-flow-up cases, only one maximum value exists. The common-flow-down cases show better heat transfer characteristics than the common-flow-up cases. 相似文献