全文获取类型
收费全文 | 45512篇 |
免费 | 4213篇 |
国内免费 | 4538篇 |
专业分类
电工技术 | 769篇 |
综合类 | 2218篇 |
化学工业 | 3344篇 |
金属工艺 | 24931篇 |
机械仪表 | 2494篇 |
建筑科学 | 348篇 |
矿业工程 | 956篇 |
能源动力 | 969篇 |
轻工业 | 176篇 |
水利工程 | 14篇 |
石油天然气 | 389篇 |
武器工业 | 638篇 |
无线电 | 1170篇 |
一般工业技术 | 8869篇 |
冶金工业 | 5477篇 |
原子能技术 | 372篇 |
自动化技术 | 1129篇 |
出版年
2024年 | 245篇 |
2023年 | 781篇 |
2022年 | 1316篇 |
2021年 | 1554篇 |
2020年 | 1708篇 |
2019年 | 1269篇 |
2018年 | 1337篇 |
2017年 | 1698篇 |
2016年 | 1472篇 |
2015年 | 1588篇 |
2014年 | 2230篇 |
2013年 | 2349篇 |
2012年 | 2697篇 |
2011年 | 3387篇 |
2010年 | 2502篇 |
2009年 | 2786篇 |
2008年 | 2218篇 |
2007年 | 3134篇 |
2006年 | 3186篇 |
2005年 | 2552篇 |
2004年 | 2218篇 |
2003年 | 1896篇 |
2002年 | 1539篇 |
2001年 | 1429篇 |
2000年 | 1174篇 |
1999年 | 1035篇 |
1998年 | 790篇 |
1997年 | 785篇 |
1996年 | 737篇 |
1995年 | 548篇 |
1994年 | 495篇 |
1993年 | 351篇 |
1992年 | 326篇 |
1991年 | 233篇 |
1990年 | 214篇 |
1989年 | 171篇 |
1988年 | 98篇 |
1987年 | 40篇 |
1986年 | 21篇 |
1985年 | 15篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 25篇 |
1981年 | 23篇 |
1980年 | 13篇 |
1979年 | 5篇 |
1978年 | 12篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
N. C. W. Kuijpers W. H. Kool P. T. G. Koenis K. E. Nilsen I. Todd S. van der Zwaag 《Materials Characterization》2002,49(5)
During homogenisation of AA 6xxx aluminium alloys, the platelike β-AlFeSi intermetallic phase will transform to a less Si-rich and more spheroidised α-Al(FeMn)Si phase which is more favourable for extrusion. In this study, several quantitative methods, which determine the relative volume fraction of α-Al(FeMn)Si and β-AlFeSi, are compared and an assessment of each method is made. The methods used are optical microscopy, scanning electron microscopy (SEM) in combination with electron dispersive X-ray (EDX) using polished samples, and X-ray diffraction (XRD) on intermetallics, extracted through selective dissolution of the Al matrix. The highest accuracy is obtained by using SEM/EDX analysis and applying two criteria. 相似文献
102.
This investigation proposes a fixed collision rate (FCR) back-off algorithm for wireless networks. The proposed scheme takes advantage of the central unit (CU) in a wireless network to broadcast a common back-off window size to all the users, significantly alleviating the unfairness of bandwidth utilization in conventional binary exponential back-off (BEB) algorithms. It is shown that, when maximum throughput is achieved, collision rate is almost a constant for any traffic load. In the operation of the FCR, the CU dynamically adjusts the back-off window size to keep the collision rate at a constant level for maximum throughput. Simulation results demonstrate that the unfairness of bandwidth utilization in the BEB is significantly lessened and the throughput can be maintained at e-1≈0.368 when the number of users approaches infinity. The capture effect even further improves system performance. 相似文献
103.
D. Srinivasa Rao H. Suresh Hebbar M. Komaraiah 《Materials and Manufacturing Processes》2007,22(7):825-829
Burnishing is used increasingly as a finishing operation which gives additional advantages such as increased hardness, fatigue strength, and wear resistance. Experimental work based on 34 factorial design was carried out to establish the effects of ball burnishing parameters on the surface hardness of high-strength low alloy steels (HSLA) dual-phase (DP) steel specimens. Statistical analysis of the results shows that the speed, feed, lubricant and ball diameter have significant effect on surface hardness. 相似文献
104.
105.
NiTi形状记忆合金激光气体氮化层表面特征 总被引:2,自引:0,他引:2
为改善NiTi合金的表面性能,利用2kW连续波Nd:YAG对NiTi合金进行激光气体氮化处理。采用SEM、TEM、XRD、XPS和纳米压痕研究了氮化层的显微组织及表面特征.结果表明:激光气体氮化可以在NiTi合金表面制备连续、无裂纹、厚度为2μm的TiN表面层,该表面层中基本不合有Ni元素且具有很高的硬度,其纳米压痕硬度为29.28GPa. 相似文献
106.
107.
Jinhong Shin Wyatt A. Winkenwerder Kyriacos Agapiou Gyeong S. Hwang 《Thin solid films》2007,515(13):5298-5307
Chemical vapor deposition growth of amorphous ruthenium-phosphorus films on SiO2 containing ∼ 15% phosphorus is reported. cis-Ruthenium(II)dihydridotetrakis-(trimethylphosphine), cis-RuH2(PMe3)4 (Me = CH3) was used at growth temperatures ranging from 525 to 575 K. Both Ru and P are zero-valent. The films are metastable, becoming increasingly more polycrystalline upon annealing to 775 and 975 K. Surface studies illustrate that demethylation is quite efficient near 560 K. Precursor adsorption at 135 K or 210 K and heating reveal the precursor undergoes a complex decomposition process in which the hydride and trimethylphosphine ligands are lost at temperatures as low at 280 K. Phosphorus and its manner of incorporation appear responsible for the amorphous-like character. Molecular dynamics simulations are presented to suggest the local structure in the films and the causes for phosphorus stabilizing the amorphous phase. 相似文献
108.
The AlCoCrCuFeNi high-entropy alloy system was synthesized using a well-developed arc melting and casting method. Their elemental effect on microstructures and hardness was investigated with X-ray diffraction, scanning electron microscopy and Vickers hardness testing. The alloys exhibit quite simple FCC and BCC solid solution phases. Co, Cu and Ni elements enhance the formation of the FCC phase while Al and Cr enhance that of the BCC phase in the alloy system. BCC phases form a spinodal structure during cooling. Copper tends to segregate at the interdendrite region and forms a Cu-rich FCC phase. Low copper content renders the interdendrite as a thin film and the as-cast structure like recrystallized grain structure. The formation of BCC phases significantly increases the hardness level of the alloy system. The strengthening mechanism is discussed. 相似文献
109.
Composition Range of Amorphous Mg-Ni-Y Alloys 总被引:1,自引:0,他引:1
Based on the thermodynamic point of view, a method for predication of the composition range of amorphous ter-nary alloys was proposed. The composition range of amorphous ternary alloys is determined by the comparison of the excess free energy of the amorphous alloy and the free energy of competing crystalline states. The free energy is extrapolated from the data of three binary alloys by using Toop‘s model. The method was applied to predict the composition range of amor-phous Mg-Ni-Y alloys. The theoretical results are in good agreement with the available experimental results. It indicates that the present method can be used to predict the composition range for amorphous ternary alloys. 相似文献
110.
研究了元素含量变化对8011铝合金防盗盖板综合性能的影响,在8011合金中改变Cu、Mn元素含量后可提高防盗盖板的强度,同时研究了烘烤处理后的强度变化问题。本文研究出了8011铝合金防盗盖板新的生产工艺制度。 相似文献