全文获取类型
收费全文 | 17060篇 |
免费 | 261篇 |
国内免费 | 353篇 |
专业分类
电工技术 | 492篇 |
综合类 | 257篇 |
化学工业 | 4707篇 |
金属工艺 | 1505篇 |
机械仪表 | 833篇 |
建筑科学 | 1023篇 |
矿业工程 | 99篇 |
能源动力 | 2454篇 |
轻工业 | 621篇 |
水利工程 | 45篇 |
石油天然气 | 341篇 |
武器工业 | 92篇 |
无线电 | 907篇 |
一般工业技术 | 2941篇 |
冶金工业 | 496篇 |
原子能技术 | 365篇 |
自动化技术 | 496篇 |
出版年
2024年 | 15篇 |
2023年 | 335篇 |
2022年 | 464篇 |
2021年 | 485篇 |
2020年 | 465篇 |
2019年 | 443篇 |
2018年 | 452篇 |
2017年 | 509篇 |
2016年 | 485篇 |
2015年 | 555篇 |
2014年 | 894篇 |
2013年 | 1346篇 |
2012年 | 730篇 |
2011年 | 1491篇 |
2010年 | 1009篇 |
2009年 | 1070篇 |
2008年 | 1080篇 |
2007年 | 917篇 |
2006年 | 717篇 |
2005年 | 672篇 |
2004年 | 577篇 |
2003年 | 472篇 |
2002年 | 376篇 |
2001年 | 261篇 |
2000年 | 265篇 |
1999年 | 262篇 |
1998年 | 269篇 |
1997年 | 222篇 |
1996年 | 177篇 |
1995年 | 150篇 |
1994年 | 109篇 |
1993年 | 73篇 |
1992年 | 57篇 |
1991年 | 56篇 |
1990年 | 42篇 |
1989年 | 38篇 |
1988年 | 30篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 11篇 |
1980年 | 4篇 |
1974年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
W. Claeys V. Quintard S. Dilhaire D. Lewis Y. Danto 《Quality and Reliability Engineering International》1994,10(4):289-295
We have recently developed an optical contactless method for testing the quality of solder joints during accelerated thermal cycling ageing processes.1 The method was based upon the measurement of the dynamic thermal behaviour of the joint to short bursts of Joule heating. It has proved to be efficient in revealing the formation of cracks at the lead-solder interface. We present a method to evaluate ageing at a much earlier stage in the cycling process. We have observed in earlier work,1 that before cracks appear, structural changes occur in the solder at the lead-solder interface. The thermal response of the solder joint is recorded over time to a Peltier heat perturbation produced by flowing a current pulse through the interface where structural changes occur. The key point in this method is to discriminate the Peltier effect from the Joule thermal response because both effects generate heat. The variation of the early Peltier response in the thermal cycling ageing tests is seen as a quantitative signature of the structural changes in the lead-solder interface. 相似文献
22.
Thermal Characterization of 1.3 μm InAsP/InGaAsP Ridge Waveguide MQW Lasers Based on Spectroscopy Method 总被引:1,自引:1,他引:0
An experimental way to analyze the thermal characterization of semiconductor lasers based on spectroscopy method under pulse driving conditions has been developed. By using this way the thermal characteristics of strain compensated 1.3 μm InAsP/InGaAsP ridge waveguide MQW laser diodes have been investigated. Results show that by measuring and analyzing the lasing spectra under appropriate driving parameters and temperature ranges, the thermal resistance of the laser diodes could be deduced easily. A higher thermal resistance of 640 K/W has been measured on a narrow ridge laser chip without soldering. Other thermal and spectral properties of the lasers have also been measured and discussed. 相似文献
23.
红外热成象技术可以有效地用于股骨头坏死疾病的诊断和针刺治疗效果的评价,效果优于其它常规方法。 相似文献
24.
本文报导了LEC法半绝缘砷化镓单晶中含碳量对SI-GaAs热稳定性的影响。在800℃以上退火,发现当晶体中C含量大于1.5×10~(16)cm~(-3)时,SI-GaAs的热稳定性变差;而C含量小于5×10~(15)cm~(-3)时,通常表现出良好的热稳定性。 相似文献
25.
本征吸除硅片特性研究 总被引:1,自引:0,他引:1
本文描述硅本征吸杂片的特性参数,如吸除区宽度、洁净度,氧沉淀密度、MOS电容寿命,介绍了表面态密度及残余间隙氧浓度的检测方法和工艺对参数的影响及参数之间的内在联系,文章还实验论证了不同参数水平对器件成品率的影响,建立了以MOS电容寿命为主导的参数控制方法,利用本文提供的控制参数,可使CCD-512器件成品率达60%,以上优品率≥85%。 相似文献
26.
27.
This study examines the comfort criteria of ASHRAE Standard 55-2004 for their applicability in hospital environments. Through an extensive field survey conducted in a university hospital in Taiwan, 927 sets of data have been collected. Above half of the measured samples failed to meet the specifications of Standard 55 comfort zone due to improper humidity control. Acceptability votes by patients exceeded the Standard's 80% criterion, regardless of whether the physical conditions were in or out of the comfort zone. Thermal neutrality, preference and comfort range are compared with other studies conducted in office environments and Standard 55 criteria. Results of chi-square tests revealed that patients’ physical strength significantly effected their thermal requirements. The net effect of health yields a marked difference in thermal neutrality and preference, and also in the comfortable temperature range. 相似文献
28.
Thermal analysis of a ceramic coating diesel engine piston using 3-D finite element method 总被引:1,自引:0,他引:1
In this study, firstly, thermal analyses are investigated on a conventional (uncoated) diesel piston, made of aluminum silicon alloy and steel. Secondly, thermal analyses are performed on pistons, coated with MgO-ZrO2 material by means of using a commercial code, namely ANSYS. Finally, the results of four different pistons are compared with each other. The effects of coatings on the thermal behaviors of the pistons are investigated. It has been shown that the maximum surface temperature of the coated piston with material which has low thermal conductivity is improved approximately 48% for the AlSi alloy and 35% for the steel. 相似文献
29.
Stratis V. Sotirchos 《Chemical Engineering Communications》1985,39(1):259-276
The effects of thermal radiation on the pseudosteady state and transient behavior of porous char particles exposed to an oxygen containing environment are investigated. The numerical simulation results show that particles that do not interchange radiant energy with their environment are characterized by wider ambient temperature regions where multiple steady states exist, higher combustion rates, and lower burning times 相似文献
30.
本文用不同的测试技术和方法测定了锗酸铋(BGO)单晶的比热(300~800K)热膨胀系数(100~1100K)和导温系数(140~700K),进而导出了 BGO 单晶不同温度下的导热系数、定容比热、德拜温度和格虑内森数。本文还对 BGO 单晶热物理性质的变化规律作了理论解释。 相似文献