全文获取类型
收费全文 | 1856篇 |
免费 | 40篇 |
国内免费 | 41篇 |
专业分类
电工技术 | 31篇 |
综合类 | 71篇 |
化学工业 | 258篇 |
金属工艺 | 166篇 |
机械仪表 | 588篇 |
建筑科学 | 13篇 |
矿业工程 | 14篇 |
能源动力 | 26篇 |
轻工业 | 89篇 |
水利工程 | 2篇 |
石油天然气 | 466篇 |
武器工业 | 4篇 |
无线电 | 8篇 |
一般工业技术 | 113篇 |
冶金工业 | 83篇 |
原子能技术 | 1篇 |
自动化技术 | 4篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 21篇 |
2021年 | 32篇 |
2020年 | 30篇 |
2019年 | 43篇 |
2018年 | 38篇 |
2017年 | 48篇 |
2016年 | 52篇 |
2015年 | 45篇 |
2014年 | 68篇 |
2013年 | 67篇 |
2012年 | 76篇 |
2011年 | 111篇 |
2010年 | 78篇 |
2009年 | 88篇 |
2008年 | 61篇 |
2007年 | 108篇 |
2006年 | 130篇 |
2005年 | 135篇 |
2004年 | 130篇 |
2003年 | 86篇 |
2002年 | 98篇 |
2001年 | 66篇 |
2000年 | 46篇 |
1999年 | 58篇 |
1998年 | 36篇 |
1997年 | 37篇 |
1996年 | 42篇 |
1995年 | 29篇 |
1994年 | 14篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
排序方式: 共有1937条查询结果,搜索用时 31 毫秒
21.
22.
The ultra-low friction coefficient (typically in the 10−2 range) of MoS2-based coatings is generally associated with the friction-induced orientation of ‘easy-shear’ planes of the lamellar structure parallel to the sliding direction, particularly in the absence of environmental reactive gases and with moderate normal loads. We used and AES/XPS ultra-high vacuum tribometer coupled to a preparation chamber, thus allowing the deposition of oxygen-free MoS2 PVD coatings and the performance of friction tests in various controlled atmospheres. Friction of oxygen-free stoichiometric MoS2 coatings deposited on AISI 52100 steel was studied in ultra-high vacuum (UHV: 5 × 10−8 Pa), high vacuum (HV: 10−3 Pa), dry nitrogen (105 Pa) and ambient air (105 Pa). ‘Super-low’ friction coefficients below 0.004 were recorded in UHV and dry nitrogen, corresponding to a calculated interfacial shear strength in the range of 1 MPa, about ten times lower than for standard coatings. Low friction coefficients of about 0.013–0.015 were recorded in HV, with interfacial shear strength in the range of 5 MPa. Friction in ambient air leads to higher friction coefficients in the range of 0.2. Surface analysis performed inside the wear scars by Auger electron spectroscopy shows no trace of contaminant, except after friction in ambient air where oxygen and carbon contaminants are observed. In the light of already published results, the ‘super-low’ friction behaviour (10−3 range) can be attributed to superlubricity, obtained for a particular combination of cystallographic orientation and the absence of contaminants, leading to a considerable decrease in the interfacial shear strength. 相似文献
23.
As the rotation rate of magnetic recording disks increases over the next few years, lubricant spin-off from the disk surface may be significant. Lubricant thickness was measured as a function of spin time at 10000 rpm on typical carbon overcoated magnetic recording disks initially lubricated with 10–135 Å of perfluoropolyether Zdol. The viscosity of the lubricant film increased as the film thickness decreased with spin time. Lubricant spin-off in response to air shear stress on the free surface was approximately described by viscous flow. The rate of lubricant removal by evaporation was compared to the spin-off removal rate in films between 10 and 50 Å thick. Dispersion interaction and chemisorption are expected to retain a molecularly thin film of lubricant on the disk surface. 相似文献
24.
A non-Newtonian rheological model to investigate theoretically the effects of lubricant additives on the steady state performance of hydrodynamically lubricated finite journal bearings is introduced. In this model, the non-Newtonian behavior resulting from blending the lubricant with polymer additives is simulated by Stokes couple stress fluid model. The formed boundary layer at the bearing surface is described through the use of a hypothetical porous medium layer that adheres to the bearing surface. The Brinkman-extended Darcy equations are utilized to model the flow in the porous region. A stress jump boundary condition is applied at the porous media/fluid film interface. A modified form of the Reynolds equation is derived and solved numerically using a finite difference scheme. The effects of bearing geometry, and non-Newtonian behavior of the lubricant on the steady-state performance characteristics such as pressure distribution, load carrying capacity, side leakage flow, and coefficient of friction are presented and discussed. The results showed that lubricant additives significantly increase the load carrying capacity and reduce both the coefficient of friction and the side leakage as compared to the Newtonian lubricants. 相似文献
25.
为进一步提高磁头飞行的稳定性,增加硬盘存储容量,采用分子动力学方法研究磁头磁盘接触条件下盘片上类金刚石薄膜(DLC)层粗糙度、DLC表层官能团比例及单个润滑剂分子中羟基数对润滑剂转移行为及润滑剂在盘片表面分布的影响.研究结果表明:降低DLC层粗糙度,增加DLC表层官能团比例都将降低磁头磁盘间的润滑剂转移量;当磁盘表面存在物理吸附态的润滑剂分子时,增加单个润滑剂分子中的羟基数也可降低润滑剂转移量;但降低DLC层粗糙度或同时增加DLC表层官能团的比例和单个润滑剂中羟基数会增加润滑剂在盘片表面堆积的高度,进而降低磁头飞行稳定性.综合考虑润滑剂转移量和润滑剂在磁盘表面堆积厚度对磁头飞行稳定性的影响,DLC层粗糙度应降低至约0.07 nm,DLC表层官能团比例增至约80%,单个润滑剂分子中的羟基数量应少于8个. 相似文献
26.
The present paper deals with the theoretical investigation of the influence of dimple geometry on fully textured hybrid thrust pad bearing and operating with non-Newtonian lubricant. The modified Reynolds equation which governs the flow of non-Newtonian lubricant in the clearance space has been solved using Finite Element Method. The simulated results indicate that the values of load carrying capacity, frictional power loss, maximum pressure and fluid film stiffness coefficient are significantly affected by the behavior of lubricant. The results presented in the study are expected to aid in determining the optimum value of dimple diameter and depth for the optimum bearing performance. 相似文献
27.
S.D. Supekar A.F. Clarens D.A. Stephenson S.J. Skerlos 《Journal of Materials Processing Technology》2012,212(12):2652-2658
This paper investigates the cooling and lubrication properties of supercritical carbon dioxide (scCO2) sprays as potential substitutes for aqueous emulsions and straight oils used in the metalworking industry today. Sprays of rapidly expanding scCO2 act to cool and lubricate machining and forming processes by delivering a mixture of dry ice and lubricant deep into the cutting/forming zone. In this work, experiments with turning, milling, drilling, thread cutting, and thread forming were performed with scCO2 and other metalworking fluids (MWFs) to evaluate their relative performance with respect to tool wear and machining torque. Observations reveal that scCO2–MWFs are more effective in removing heat from the tool-workpiece interface than conventionally delivered (flood) aqueous MWFs as well as other gas-based MWF sprays. In addition, scCO2–MWFs delivered in lubricant-expanded phase, where scCO2 is used to increase volume of lubricant in the spray field, are shown to provide better lubricity than straight oils and oil-in-air minimum quantity lubrication (MQL) sprays. As a result, scCO2–MWFs can reduce tool wear and improve machining productivity in a wide range of manufacturing operations leading to appreciable improvements in the economics of manufacturing. Also given that CO2 is a recovered waste gas that is non-toxic, scCO2–MWFs can improve the environmental and worker health performance of manufacturing operations. 相似文献
28.
聚α-烯烃合成油是所有合成润滑油基础油中性能最优异的一种,具有黏度指数高、低温性能和高温氧化安定性好、抗燃性好及挥发性低等优点,是未来应用广泛的合成基础油,市场需求持续增加。综述聚α-烯烃基础油及其加氢工艺、加氢精制催化剂的研究现状。传统聚α-烯烃合成油生产工艺有乙烯齐聚法和石蜡裂解法等,潞安煤制油工艺和天然气制油工艺等新工艺也开始兴起。加氢精制工艺对提高聚α-烯烃合成油的质量起着至关重要的作用,北京燕化聚华工贸有限公司两段加氢精制工艺和中国石油兰州润滑油厂聚α-烯烃合成油加氢精制处理工艺均极大改善了聚α-烯烃合成油的质量。聚α-烯烃合成油加氢精制效果很大程度取决于加氢精制催化剂性能,要求加氢精制催化剂具有较高的选择性和较好的稳定性。 相似文献
29.
The polymerization of 1-decene catalyzed by rac-Me2Si(1-indenyl)2ZrCl2/AliBu3/[C6H5NH(CH3)2][B(C6F5)4] system with hydrogen has been carried out in the paper. The influence of reaction conditions on catalytic activity and polymer properties was investigated. High activity (17.2 × 106 g molZr?1 h?1) was observed under the optimized reaction conditions. The introduction of hydrogen enhances the catalytic activity of the metallocene system. The 1H NMR spectra revealed the polymerization mechanism with the presence of hydrogen. The 13C NMR spectra of poly(1-decene) indicated that the polymer has a very tactic side chain structure, showing potential application of the system in the commercial production of lubricant base oil. 相似文献
30.
Zhu Liye; Chen Ligong; Xiang Shuo; Chen Guoxu; Yang Xin 《中国炼油与石油化工》2012,14(2):60-65
A series of functionalized ionic liquids (ILs) containing ester-group were synthesized and their tribological properties as lubricants for steel-steel contact were studied and compared with a non-functionalized ionic liquid and perfluoropolyethers (PFPE). The morphology and chemical composition of the worn scars were analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively, and the possible lubrication mechanism of ILs was discussed. As a result, all ILs demonstrated a better lubricity and a much higher load-carrying capacity than PFPE used as lubricants for the steel-steel tribomates system. The functionalized ILs with ester-group showed slightly worse friction reducing ability than their nonfunctionalized counterparts at relatively lower loads owing to their higher viscosity, but then exhibited better antiwear ability because the ester group they contained had not only physical but also strong chemical reactions with the freshly exposed steel surface and formed chemical adsorption boundary films on the worn surface during friction process. Under high loads, some tribochemical reactions took place between the active elements, such as fluorine which were released from the ILs, and fresh metal surfaces of rubbing pairs to form the admixture reaction films, which were mainly composed of ferric fluoride mixed with ferric oxide, leading to lower friction coefficients and good wear resistance. 相似文献