全文获取类型
收费全文 | 220747篇 |
免费 | 28899篇 |
国内免费 | 26206篇 |
专业分类
电工技术 | 19781篇 |
技术理论 | 9篇 |
综合类 | 15602篇 |
化学工业 | 47067篇 |
金属工艺 | 10938篇 |
机械仪表 | 14512篇 |
建筑科学 | 11228篇 |
矿业工程 | 3167篇 |
能源动力 | 7312篇 |
轻工业 | 19816篇 |
水利工程 | 3243篇 |
石油天然气 | 5070篇 |
武器工业 | 2254篇 |
无线电 | 30112篇 |
一般工业技术 | 24879篇 |
冶金工业 | 5944篇 |
原子能技术 | 5119篇 |
自动化技术 | 49799篇 |
出版年
2024年 | 919篇 |
2023年 | 3628篇 |
2022年 | 6931篇 |
2021年 | 8691篇 |
2020年 | 7958篇 |
2019年 | 7369篇 |
2018年 | 6790篇 |
2017年 | 8862篇 |
2016年 | 9666篇 |
2015年 | 10941篇 |
2014年 | 11213篇 |
2013年 | 14957篇 |
2012年 | 16615篇 |
2011年 | 18666篇 |
2010年 | 13357篇 |
2009年 | 13295篇 |
2008年 | 14383篇 |
2007年 | 16313篇 |
2006年 | 15386篇 |
2005年 | 13179篇 |
2004年 | 11148篇 |
2003年 | 8855篇 |
2002年 | 6796篇 |
2001年 | 5201篇 |
2000年 | 4363篇 |
1999年 | 3683篇 |
1998年 | 3090篇 |
1997年 | 2508篇 |
1996年 | 2008篇 |
1995年 | 1654篇 |
1994年 | 1448篇 |
1993年 | 1120篇 |
1992年 | 905篇 |
1991年 | 729篇 |
1990年 | 602篇 |
1989年 | 460篇 |
1988年 | 350篇 |
1987年 | 224篇 |
1986年 | 215篇 |
1985年 | 261篇 |
1984年 | 235篇 |
1983年 | 164篇 |
1982年 | 230篇 |
1981年 | 124篇 |
1980年 | 126篇 |
1979年 | 37篇 |
1978年 | 21篇 |
1977年 | 26篇 |
1959年 | 24篇 |
1951年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We report here the identification of a new precipitate phase in thin-film Al-4wt.%Cu metallization used for interconnects
on integrated circuits. The phase is based on a trigonal distortion of a face centered cubic lattice. Computer simulation
of electron diffraction intensities suggests that the basis structure is isomorphous with Al2Ca but with a large and ordered population of vacancies on Cu sites. The reason for the formation of the new phase and its
implications for electromigration reliability are discussed. 相似文献
992.
A rapid and easy analysis method for polymers is presented. The method involves sample preparation by SFE, separation of the extracted compounds by SFC and simultaneous quantitative detection by FID, as well as identification of unknowns by MS. The applications illustrate how structural research work and routine polymer analysis can be done with this time saving method. 相似文献
993.
994.
Because of its high–temperature chemical stability, SiC ceramic is a promising material for high-temperature device applications such as thermoelectric energy converters. However, the electrical conductivity of SiC ceramic is too low for it to be used as a thermoelectric energy converter at the cold junction. Therefore, we propose a SiC-Si functionally gradient material (FGM) in order to improve the electrical conductivity of the SiC ceramic at the cold junction. An SiC rod was fired in a temperature gradient furnace. One end of the SiC rod was maintained at 2473 K and the other end was maintained at 1973 K for 30 min. After firing, the porous SiC edge fired at 1973 K was dipped into molten Si in order to infiltrate molten Si into the porous SiC. The microstructure of the FGM is classified into three regions: the SiC-Si composite material; the porous SiC ceramic; and the densified SiC ceramic. The electrical conductivity, the Seebeck coefficient and the thermal conductivity for each region of SiC-Si FGM was measured at 300 K; a figure of merit was calculated. The figure of merit of the SiC-Si FGM at the cold junction, at room temperature, was 108 times higher than that of a nongradient SiC ceramic. 相似文献
995.
树脂热解炭制备碳化硅晶须 总被引:6,自引:1,他引:5
用自制的配合醛树脂热解和炭源,用SIO2超细汾作原,根据碳热还原原理,利用常规加热和微波加热两种方式,分别制备了直径在纳米级的SiC晶须,X射线衍射、透射电检测结果表明:制备工艺和条件对SiC晶须的性质有较大的影响。 相似文献
996.
997.
Sylvia V A Uzochukwu Esther Balogh Owen G Tucknot Mervyn J Lewis Patrick O Ngoddy 《Journal of the science of food and agriculture》1994,64(4):405-411
Palm wine and pasteurised palm sap volatiles were collected, concentrated on a Tenax GC and analysed by gas chromatography and gas chromatography-mass spectrometry. Eighty-two components were identified: 47 esters, 9 alcohols, 5 acids, 6 carbonyls, 2 acetals, 4 terpenes and 9 hydrocarbons. These had all been found previously in conventional wines. Odour evaluation of the separated palm wine components as they eluted suggested that no one compound is responsible for the characteristic palm wine odour. The acetates of higher alcohols and the ethyl esters of straight-chain aliphatic C6-C10 acids seemed to be important and may play a big role in imparting the fruity nuances of characteristic palm wine odour. Their association with alcohols seemed also to be necessary for the expression of typical palm wine odour. The qualitative difference between palm sap aroma and palm wine aroma appeared to be due mainly to the presence of these esters and alcohols in palm wine and their apparent absence from palm sap, as well as to the presence of some low-boiling esters and alcohols in palm sap and their apparent absence from palm wine. 相似文献
998.
In building energy simulation, an integrated modelling of airflow in the building needed. Therefore, in this paper two approaches are used for building energy simulation: zonal network for modelling of the building segments and Computational Fluid Dynamics (CFD) for modelling of the airflow. It is noted that a synchronize solution process is needed for the building and the CFD equation-sets. For this purpose an iterative procedure is used to corresponding solution of these equations. 相似文献
999.
基于故障树与灰关联分析的鱼雷故障诊断 总被引:2,自引:0,他引:2
将灰色关联度与故障树联合运用于鱼雷故障诊断,为鱼雷的故障诊断提供了一种新途径。在鱼雷动力系统故障树诊断模式识别中,运用灰色系统理论中的灰关联分析,通过进行关联度计算及排序,对各种故障模式发生的可能性大小作出了判断,从而为处理故障的轻重缓急、控制故障的发生以及改进系统的可靠性提供了理论依据。实例诊断表明,这种方法是有效可行的,并且诊断结果可靠。 相似文献
1000.
4-(N-异丙氨基)-苯甲酸的合成研究 总被引:1,自引:0,他引:1
对分子中既具有吸电子基,又具有给电子基的化合物4-(N-异丙氨基)-苯甲酸进行了合成,具体的合成步骤和反应条件为:50mL水中加入3g(0.022mol)对氨基苯甲酸,再加入无水碳酸钾1.5g(0.011mol),调整pH约为8,使成羧酸盐,经过滤后加入2-溴丙烷2.5g(0.02mol),加热回流12h,直至下层的2-溴丙烷基本消失,冷却,得灰白色固体,重结晶并用活性炭脱色,得白色晶体4-(N-异丙氨基)-苯甲酸。 相似文献