全文获取类型
收费全文 | 9830篇 |
免费 | 822篇 |
国内免费 | 507篇 |
专业分类
电工技术 | 466篇 |
技术理论 | 1篇 |
综合类 | 723篇 |
化学工业 | 829篇 |
金属工艺 | 963篇 |
机械仪表 | 1809篇 |
建筑科学 | 357篇 |
矿业工程 | 269篇 |
能源动力 | 202篇 |
轻工业 | 140篇 |
水利工程 | 135篇 |
石油天然气 | 188篇 |
武器工业 | 309篇 |
无线电 | 2023篇 |
一般工业技术 | 1105篇 |
冶金工业 | 247篇 |
原子能技术 | 228篇 |
自动化技术 | 1165篇 |
出版年
2024年 | 30篇 |
2023年 | 113篇 |
2022年 | 228篇 |
2021年 | 286篇 |
2020年 | 262篇 |
2019年 | 248篇 |
2018年 | 234篇 |
2017年 | 290篇 |
2016年 | 343篇 |
2015年 | 412篇 |
2014年 | 531篇 |
2013年 | 934篇 |
2012年 | 559篇 |
2011年 | 690篇 |
2010年 | 596篇 |
2009年 | 579篇 |
2008年 | 522篇 |
2007年 | 655篇 |
2006年 | 563篇 |
2005年 | 441篇 |
2004年 | 331篇 |
2003年 | 344篇 |
2002年 | 287篇 |
2001年 | 312篇 |
2000年 | 242篇 |
1999年 | 215篇 |
1998年 | 169篇 |
1997年 | 163篇 |
1996年 | 135篇 |
1995年 | 115篇 |
1994年 | 68篇 |
1993年 | 49篇 |
1992年 | 49篇 |
1991年 | 32篇 |
1990年 | 36篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1957年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Practice has proven that CrN performs better than TiN under some specific tribological applications. Nevertheless, the relatively soft nature of CrN still remains a problem. This paper reports experimental results on increases in hardness of sputtered PVD CrN coatings by means of additions of varying content of Ag or W. The resulting Cr-Ag-N and Cr-W-N coatings, grown on JIS SKH51 steel substrates, were characterized using SEM, EDS, WDS, XRD, micro-indentation hardness testing and scratch adhesion tests. Moreover, wear behavior was studied on two types of tribometer, employing different contact regimes — a ‘cylinder-on-disk’ line-contact reciprocating-sliding regime and a ‘ball-on-disk’ point-contact rotating-sliding regime.The experimental results can be summarized as follows: The hardness of Cr-W-N coatings increased with increasing W content; reversely, that of Cr-Ag-N coatings decreased with increasing Ag content. The additions of Ag and W resulted in a formation of secondary phases, elemental Ag and WN, respectively, uniformly embedded in the CrN coatings. With the two different types of tribometer, the observed trends for wear behavior, wear and friction coefficient, were nearly identical, indicating that both Ag and W additions to CrN coatings were beneficial. However, the Cr-W-N coatings were significantly more wear resistant than the Cr-Ag-N coatings. With the addition of W at 6.8 at.%, the largest wear improvement of 73%-85% was achieved. 相似文献
72.
A.D. Pogrebnjak Yu.A. Kravchenko Sh.M. Ruzimov P. Misaelides 《Surface & coatings technology》2006,201(6):2621-2632
New experimental results are presented on the structure and the elemental and phase composition of hybrid coatings, which were deposited on a substrate of AISI 321 stainless steel using a combination of plasma-detonation, vacuum-arc and subsequent High-Current Electron Beam (HCEB) treatment. We found that an increase in energy density intensified mass transfer processes and resulted in changes in aluminum oxide phase composition (γ → α and β → α). Also we observed the formation of a nanocrystalline structure in Al2O3 coatings. Electron beam treatment of a hybrid coating surface induced higher adhesion, decreased the intensity of surface wear and increased corrosion resistance in a sulphuric acid solution. The corrosion resistance of the coatings was studied in several electrolytic solutions (0.5 M H2SO4, 1 M HCl, 0.75 M NaCl) using electrochemical techniques. In most cases the corrosion resistance was improved, except those in NaCl solutions. The nano-hardness of the protecting coating was 13 GPa before electron beam melting and 9 GPa after it (as a result of TiN and Al2O3 sub-layers mixing). 相似文献
73.
Nanocrystallized Cr1−xAlxN films with various Al contents (0 to 68 at.%) were deposited by pulsed closed field unbalanced magnetron sputtering (P-CFUBMS). The effects of aluminum content on the microstructure, mechanical and tribological properties of the Cr1−xAlxN films have been investigated. It was found that the hardness and elastic modulus of Cr1−xAlxN films increased with increasing Al contents in the films and reached the highest value of 36 GPa and 370 GPa, respectively, at an Al content of 58.5 at.%. Addition of Al beyond 64.0 at.% resulted in a change in crystal structure from B1 cubic to B4 hexagonal phase. The wear resistance improved gradually with the increase of Al in the Cr1−xAlxN films. A combination of the abrasive and adhesive wear mechanism was proposed based on the SEM and EDS analysis of the wear track. The steady state dry coefficient of friction measured against a WC ball for the Cr1−xAlxN films were in the range of 0.36-0.55, and the wear rate was in the 10− 6 mm3 N− 1 m− 1 range. 相似文献
74.
Magnesium alloys are of increasing interest to the automobile industry for their potential in reducing vehicle weight, and in turn, improving fuel economy and lowering emissions. It follows that improving the magnesium manufacturing processes will promote greater use of magnesium alloys in automobiles. In recent years, diamond-like carbon (DLC) coatings have attracted attention for their low coefficient of friction (COF) and wear rates. The implementation of DLC coatings on tool and die surfaces may help increase the efficiency of magnesium component manufacturing processes (such as cutting and sheet forming) and also improve the surface quality of the finished products.In this study, the dry sliding wear behaviour of magnetron sputtered non-hydrogenated DLC coatings against Mg (> 99.9 wt.%) was investigated using a vacuum pin-on-disc tribometer. Tests were performed in ambient air (28% RH) and in argon, under a constant load of 5 N and at a sliding speed of 0.12 m/s. In argon, the non-hydrogenated DLC coatings showed a very low COF of 0.05 after an initial running-in period. Carbonaceous material transfer from the non-hydrogenated DLC to the contact surface of the Mg pin was observed in argon. Changing the test atmosphere from argon to ambient air increased the COF to 0.40, which was accompanied by the formation of oxidized Mg debris and an increased wear rate. The friction and wear mechanisms of non-hydrogenated DLC coatings against Mg are proposed to rationalize experimental observations. 相似文献
75.
本文利用理想缔合液液模型,计算了1300-1600K温度范围内,Ag-Ln(Ln=La,Ce,Gd)三个二元系的热力学数据;认为在液相中存在着Ag3Ln和AgLn得缔合物,并利用浓度相互作用函数Scc(O)对这种短程有序性进行了讨论。 相似文献
76.
MEI Xian-xiu HAD Sheng-zhi MA Teng-cai WANG Ying-min LIU Zhen-min State Key Laboratory for Materials Modification by Laser Ion Electron Beams Department of Physics Dalian University of Technology Dalian China 《材料热处理学报》2004,25(5)
INTENSITY pulsed ion beam(IPIB)technology hasbeen developed over the last two decades primarily fornuclear fusion and high-energy density physicsresearch,which is also named as high-intensity pulsedion beam technology(HPIB)and becomes a newmodification technique of materials surface such as inthe fields of metal materials modification,functionalfilms and nano-powder synthesis[1-5].Directdeposition of a beam into a solid surface results in arapid melt and resolidification with heating and… 相似文献
77.
78.
用铸造的方法制备了原位自生复合碳化物[(Ti,W,Cr,V,Nb)C]增强钢基复合材料,并对该复合材料的磨粒磨损性能及磨损机理进行了研究。结果表明,采用该方法制备的钢基自生复合材料中,自生碳化物颗粒细小、圆整、且分布均匀,碳化物颗粒增强相体积分数达到42.8%;原位自生钢基复合材料的耐磨性能优良。在磨粒磨损条件下,其磨损机制主要是显微切削、颗粒脱落和脆性剥落;稀土和合金元素能够提高原位自生钢基复合材料的耐磨性能。 相似文献
79.
研究了新型反应体系A359-Zr(CO3)2熔体反应法制备的(Al3Zr+Al2O3)p/A359复合材料边界油润滑条件下的滑动磨损性能。结果表明,由于颗粒的支撑减磨作用,复合材料的磨损量随载荷的增大和时间的延长均远小于基体材料,当载荷为1176N时体积分数为12%的复合材料磨损量为4.9mg,而基体材料的磨损量为27.5mg,复合材料比基体材料耐磨性提高了6倍;由磨损表面SEN观察表明:基体A359合金存在严重粘着和变形,表现为粘着磨损和剥层磨损,复合材料的磨损类型表现为磨粒磨损。 相似文献
80.
Surface hardening of Ti-6Al-4V alloy was achieved by carburization in a molten salt bath containing BaCO3 as the carbon-yielding agent with electrolysis within the temperature range 790–930°C. The hardness of the total carburizing layer (TCD) is influenced by the bath temperature, the applied current density and the carburizing period. The major hardening effect is considered to be the formation of a solid solution of carbon in -Ti. The oxide film wrapping at the outermost surface of cathodically charged specimens, identified to be mainly BaTiO3, was formed irrespective of the bath temperature during the quenching process and has no effect on the surface hardening. The optimal carburizing parameters obtained in this study for surface hardening are carburizing at 930±10°C (bath temperature) and 0.3 A/Cm2 (applied current density) for 90 min (carburizing period), while those for tribological properties improvement are carburizing at 860±5°C and 0.3 A/Cm2 for 90 min. 相似文献