全文获取类型
收费全文 | 42619篇 |
免费 | 3076篇 |
国内免费 | 2501篇 |
专业分类
电工技术 | 1111篇 |
综合类 | 3177篇 |
化学工业 | 6058篇 |
金属工艺 | 6501篇 |
机械仪表 | 3243篇 |
建筑科学 | 6771篇 |
矿业工程 | 1895篇 |
能源动力 | 2974篇 |
轻工业 | 1062篇 |
水利工程 | 1884篇 |
石油天然气 | 1069篇 |
武器工业 | 307篇 |
无线电 | 1500篇 |
一般工业技术 | 6723篇 |
冶金工业 | 2122篇 |
原子能技术 | 453篇 |
自动化技术 | 1346篇 |
出版年
2024年 | 101篇 |
2023年 | 717篇 |
2022年 | 1139篇 |
2021年 | 1386篇 |
2020年 | 1379篇 |
2019年 | 1166篇 |
2018年 | 1201篇 |
2017年 | 1459篇 |
2016年 | 1534篇 |
2015年 | 1617篇 |
2014年 | 2466篇 |
2013年 | 2909篇 |
2012年 | 2639篇 |
2011年 | 3581篇 |
2010年 | 2518篇 |
2009年 | 2641篇 |
2008年 | 2470篇 |
2007年 | 2621篇 |
2006年 | 2282篇 |
2005年 | 1927篇 |
2004年 | 1596篇 |
2003年 | 1438篇 |
2002年 | 1163篇 |
2001年 | 980篇 |
2000年 | 900篇 |
1999年 | 801篇 |
1998年 | 690篇 |
1997年 | 569篇 |
1996年 | 449篇 |
1995年 | 400篇 |
1994年 | 307篇 |
1993年 | 210篇 |
1992年 | 197篇 |
1991年 | 157篇 |
1990年 | 140篇 |
1989年 | 125篇 |
1988年 | 94篇 |
1987年 | 44篇 |
1986年 | 33篇 |
1985年 | 32篇 |
1984年 | 21篇 |
1983年 | 20篇 |
1982年 | 29篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
High Pressure Turbine (HPT) first stage blade is the most important rotational components of aero-engine. It operates at high temperature and under conditions of extreme environmental attack such as oxidation and corrosion, is especially subjected to degradation by oxidation, corrosion and wear. During the service of aero-engine, the HPT first stage blades made of
c 6 y nickel-based superalloy suffer from increasing blade tip cracks after hundreds of hours service. This significantly affects the whole engine function and, of course, safety of the aircraft. In this paper, the premature tip cracking of the HPT first stage blade is investigated. The research result shows that turbine blade tip is initially damaged by rubbing and corrosion over a period time, premature cracking of blade tip is caused by a combination mechanism of environment and thermal stress. During turbine blade maintenance and refurbishment, coating of both oxidation-resistance and abrasion-resistance should be applied in blade squealer tip to counteract the problem. 相似文献
992.
Guojian Wang Xiumei Han Mingjun Song Guofu Wang Xifa Long 《Materials Letters》2006,60(29-30):3710-3713
(Ba0.32Sr0.68)5Nb4O15 crystal with sizes of Ø 17 × 35 mm was grown successfully by Czochralski technique method. The thermal anisotropy was discussed. The principal coefficients of thermal expansion along (100), (010), (001) directions were precisely measured to be 1.308 × 10− 5, 1.288 × 10− 5, 1.478 × 10− 5 K− 1, respectively. Its optical transparency range has been measured and found to span from 323 to 5500 nm. The bands present in the IR spectra were identified and assigned to the corresponding vibration modes of NbO6 anions. 相似文献
993.
Koji Matsumoto Ken Oikawa Masashi Okada Yoshikazu Teraoka Tetsuo Kawagoe 《International Journal of Refrigeration》2006,29(6):1010
This study focuses on an emulsion as a new thermal storage material for ice storage. Two types of emulsions were formed using an oil–water mixture with a small amount of additive. A silicone, light and lump oils were used. The water contents of the emulsions were 70, 80 and 90%. The additive was an amino group modified silicone oil. No depression of freezing point was observed for the emulsions because of their hydrophobic properties. In order to determine the structure of the emulsions, their electrical resistances were measured. Moreover, components of the liquids separating from the emulsions were analyzed. The results indicated that one emulsion was a W/O type emulsion, while the other was an O/W type. Finally, adaptability of the two emulsions to ice storage was discussed, it was concluded that a high performance ice slurry could be formed by the W/O type emulsion. 相似文献
994.
A detachable thermosiphon, as a transient thermal switch for conduction-cooled superconducting magnet, is designed, fabricated and tested. A thermosiphon between the first and second stages of a cryocooler can reduce the cool-down time of a conduction-cooled superconducting magnet by using the large cooling capacity of the first stage. The thermosiphon is a very efficient heat transfer device until all the working fluid in it freezes (off-state). After the working fluid freezes and the second stage temperature becomes lower than that of the first stage, however, the thermosiphon then becomes a conduction heat leak path between two stages of the cryocooler. Considering a very small cooling capacity of the second stage of the cryocooler around 4.2 K, the conduction heat loss is not negligible. Therefore, a detachable thermosiphon, made of a metal bellows, is considered to be able to eliminate such a conduction heat leak. The mock-up magnet is cooled down with the thermosiphon and the thermodynamic states of the thermosiphon and the mock-up magnet are precisely examined during the whole cool-down process. At off-state, the thermosiphon is detached mechanically from the magnet. In this way, the conduction heat leak path through the thermosiphon wall is completely eliminated. This paper describes the detailed transient operation of the detachable thermosiphon using nitrogen as the working fluid. 相似文献
995.
Amorphous dihalonaphthalenes that are prepared by vacuum deposition onto a cold Al2O3 surface form electronically excited dimers when optically pumped, and their emission is characteristically red-shifted, broad and featureless compared to the monomeric fluorescence. If the surface is heated, the adlayer undergoes a disorder-to-order transition at a temperature characteristic of the molecule. Since pure crystalline dihalonaphthalenes typically fluoresce and do not exhibit excimeric features, the transition was studied by taking advantage of the changes in the spectral characteristics of the adlayer. These included transmittance, and emission from fluorescence and excimer. The combination of these methods allowed a close look at the surface dynamics of molecules on the surface of Al2O3 as the adlayer was heated from the deposition temperature to desorption.If a bilayer is formed by depositing water onto the surface with the organic adlayer on top, water, with its lower desorption energy, can be made to percolate into the organic layer. The optical probes indicate that the water clearly associates with the organic molecules while the excess water desorbs. By varying the coverage of either the water or the dihalonaphthalene, the stoichiometric composition of the cluster can be determined and are reported here. 相似文献
996.
The resistive type high temperature superconducting fault current limiter (HTSFCL) limits the fault current with the resistance that generated by fault current. The generated resistance by fault current makes large pulse power which makes the operation of HTSFCL unstable. So, the cryogenic cooling system of the resistive type HTSFCL must diffuse and eliminate the pulse energy very quickly. Although the best way is to make wide direct contact area between HTS winding and coolant as much as possible, HTS winding also need the impregnation layer which fixes and protects it from electromagnetic force. This paper deals with thermal conductivity and dielectric strength of some epoxy compounds for the impregnation of high temperature superconducting (HTS) winding at 77 K. The measured data can be used in the optimal design of impregnation for HTS winding. Aluminar filling increased the thermal conductivity of epoxy compounds. Hardener also affected the thermal conductivity and the dielectric strength of epoxy compounds. 相似文献
997.
煤粉燃烧炉膛沿程NOx释放规律的研究 总被引:3,自引:6,他引:3
对一维炉内煤粉燃烧,炉膛沿程NOx的释放规律进行了数值模拟和试验研究。研究结果表明:炉内温度升高,NOx的析出峰值升高,位置前移,温度达到一定值后,随温度的升高, NOx 的释放量又呈下降趋势;煤中含氮量越多,NOx释放量越大,NOx的析出峰值位置,随煤种碳化程度的增加而逐渐后移;随过量空气系数的增加,NOx释放量呈明显增加的趋势;NOx的释放量与煤粉粒度的关系中,存在一个煤粉平均粒度临界值dc,当煤粉粒度d≤dc时,随煤粉粒度的减小,NOx的释放量减小,当煤粉粒度d>dc时,随煤粉粒度的减小,NOx的释放量增大;模拟计算同试验结果吻合较好。 相似文献
998.
稠密气固两相流动是当前国际上的研究热点,常常采用将颗粒湍流模型和反映颗粒碰撞作用的动力学模型叠加的办法来构造稠密两相流动的湍流模型。但是,对颗粒湍流模型,国内外尚没有进行双尺度湍流模型的研究。该文基于将颗粒脉动分成湍流引起的大尺度脉动和颗粒间碰撞产生的小尺度脉动的概念,建立了一种新的双尺度二阶矩颗粒湍流模型,并对提升管内的稠密气固两相流动进行了模拟。所得颗粒浓度及速度分布和实验数据吻合较好,能揭示出提升管内的环-核流动结构。该模型的结果比单尺度二阶矩两相湍流模型的结果有所改进。 相似文献
999.
1000.
圆弧齿轮是凹形齿廓与凸形齿廓之间的啮合,具 有承载能力强、润滑性能好、加工方便等优点,广泛应 用于石油、煤炭、钢铁等行业.但在使用中,也暴露了其 噪音较高、动力性能较差的缺点,并阻碍了进一步的推 广应用.所以对其进行受力变形分析显得极为重要,而 精确建模却是进行 相似文献