全文获取类型
收费全文 | 24460篇 |
免费 | 3231篇 |
国内免费 | 1882篇 |
专业分类
电工技术 | 3917篇 |
综合类 | 1316篇 |
化学工业 | 6311篇 |
金属工艺 | 1907篇 |
机械仪表 | 1045篇 |
建筑科学 | 747篇 |
矿业工程 | 563篇 |
能源动力 | 1171篇 |
轻工业 | 1270篇 |
水利工程 | 217篇 |
石油天然气 | 472篇 |
武器工业 | 82篇 |
无线电 | 3235篇 |
一般工业技术 | 4370篇 |
冶金工业 | 1076篇 |
原子能技术 | 1392篇 |
自动化技术 | 482篇 |
出版年
2024年 | 134篇 |
2023年 | 569篇 |
2022年 | 692篇 |
2021年 | 923篇 |
2020年 | 1071篇 |
2019年 | 996篇 |
2018年 | 891篇 |
2017年 | 1064篇 |
2016年 | 1098篇 |
2015年 | 1006篇 |
2014年 | 1364篇 |
2013年 | 1462篇 |
2012年 | 1687篇 |
2011年 | 1811篇 |
2010年 | 1318篇 |
2009年 | 1325篇 |
2008年 | 1179篇 |
2007年 | 1505篇 |
2006年 | 1387篇 |
2005年 | 1197篇 |
2004年 | 1034篇 |
2003年 | 964篇 |
2002年 | 815篇 |
2001年 | 692篇 |
2000年 | 584篇 |
1999年 | 448篇 |
1998年 | 344篇 |
1997年 | 281篇 |
1996年 | 279篇 |
1995年 | 239篇 |
1994年 | 247篇 |
1993年 | 158篇 |
1992年 | 157篇 |
1991年 | 142篇 |
1990年 | 96篇 |
1989年 | 81篇 |
1988年 | 72篇 |
1987年 | 50篇 |
1986年 | 58篇 |
1985年 | 36篇 |
1984年 | 29篇 |
1983年 | 16篇 |
1982年 | 25篇 |
1981年 | 12篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1974年 | 5篇 |
1959年 | 5篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Anionic copolymerizations of styrene (M1) with excess 1-(4-dimethyl-aminophenyl)-1-phenylethylene (M2) were conducted in benzene at 25°C for 24h, using sec-butyllithium as initiator. Narrow molecular weight distribution copolymers with M?;n = 16.1 × 103 g/mol (M?w/M?n = 1.04) and 38.2 × 103g/mol (M?w/M?n = 1.05), and 24 and 38 moles of M2 per macromolecule, respectively, were characterized by size exclusion chromatography, 1H NMR spectroscopy and DSC. The monomer reactivity ratio, r1 = 5.6, was obtained from the copolymer composition at complete consumption of M1, assuming that the rate constant k22 =0,i.e. r2 =0. The polymers exhibited Tg values of 128 and 119°C, respectively, which correspond to an estimated Tg = 217°C for the hypothetical homopolymer of M2. 相似文献
103.
Xiang Lu S. Sundar Kumar Iyer Jin Lee Brian Doyle Zhineng Fan Paul K. Chu Chenming Hu Nathan W. Cheung 《Journal of Electronic Materials》1998,27(9):1059-1066
We have demonstrated feasibility to form silicon-on-insulator (SOI) substrates using plasma immersion ion implantation (PIII)
for both separation by implantation of oxygen and ion-cut. This high throughput technique can substantially lower the high
cost of SOI substrates due to the simpler implanter design as well as ease of maintenance. For separation by plasma implantation
of oxygen wafers, secondary ion mass spectrometry analysis and cross-sectional transmission electron micrographs show continuous
buried oxide formation under a single-crystal silicon overlayer with sharp Si/SiO2 interfaces after oxygen plasma implantation and high-temperature (1300°C) annealing. Ion-cut SOI wafer fabrication technique
is implemented for the first time using PIII. The hydrogen plasma can be optimized so that only one ion species is dominant
in concentration and there are minimal effects by other residual ions on the ion-cut process. The physical mechanism of hydrogen
induced silicon surface layer cleavage has been investigated. An ideal gas law model of the microcavity internal pressure
combined with a two-dimensional finite element fracture mechanics model is used to approximate the fracture driving force
which is sufficient to overcome the silicon fracture resistance. 相似文献
104.
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
105.
106.
Jacques Landry Sonia Delhaye D G Jones 《Journal of the science of food and agriculture》1992,58(3):439-441
The tryptophan content of nine samples of commercial feed was determined using two procedures (I and II) differing mainly in the hydrolysis conditions used prior to analysis. With I, hydrolysis was performed with 4 M LiOH in the presence of maltodextrin with 5-methyltryptophan used as internal standard at 110°C for 24 h; with II. oxygen-free 1.3 M Ba(OH)2 was used at 125°C for 16 h. The two procedures gave identical results for a given sample indicating that the corrections for the incomplete recovery of tryptophan 5-methyltryptophan quantitation were satisfactory. 相似文献
107.
Zhang Xiumiao 《电子科学学刊(英文版)》1992,9(3):265-269
When a linear voltage ramp is applied to the gate of a MOS capacitor, a capacitancetime (C-t) transient is observed. The MOS capacitor is biased into strong inversion before applying the voltage ramp in order to eliminate
surface generation. FromC-t transient curve obtained experimentally the minority carrier generation lifetime in semiconductor can be determined. The
experimental results show that for the same sample the lifetimes extracted fromC-t curves under varying voltage sweep rates are close each other, and they are consistent with the lifetimes extracted by saturation
capacitance method. 相似文献
108.
Bob Eisenberg 《Journal of Computational Electronics》2002,1(3):331-333
Ion channels are proteins with a hole down their middle important in a wide range of biological functions yet simple enough to be analyzed as devices in the engineering tradition. 相似文献
109.
对投电容器扰动识别和定位的方法进行了改进。针对其他此类方法的不足,比如在电压幅值低时投电容器扰动的识别、定位“可信度不高”等,文中通过提取小波变换的特定层的系数,对需要识别的电容器扰动的分解信号相对增强,而其他扰动的分解信号相对减弱,然后再提取熵特征值,结果表明它可以作为识别低电压时投电容器扰动的依据。在对电容器扰动进行定位时,参考了功率和能量定位法,并对其进行了改进。仿真分析证明,在电压幅值较低时,可以准确和可靠地对电容器扰动进行识别和定位。 相似文献
110.
黄埔发电厂#6发电机转冷水铜离子含量超标,通过对缺陷原因进行分析,针对二级水封的特性对溢出的转冷水进行回收并利用化学凝结水处理去除溶出的铜离子,通过控制转冷水的pH值最终减缓铜管的腐蚀. 相似文献