全文获取类型
收费全文 | 766篇 |
免费 | 11篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 262篇 |
金属工艺 | 21篇 |
机械仪表 | 7篇 |
建筑科学 | 7篇 |
矿业工程 | 1篇 |
能源动力 | 36篇 |
轻工业 | 17篇 |
水利工程 | 4篇 |
石油天然气 | 2篇 |
无线电 | 64篇 |
一般工业技术 | 214篇 |
冶金工业 | 87篇 |
原子能技术 | 1篇 |
自动化技术 | 42篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 6篇 |
2014年 | 17篇 |
2013年 | 36篇 |
2012年 | 24篇 |
2011年 | 28篇 |
2010年 | 27篇 |
2009年 | 26篇 |
2008年 | 17篇 |
2007年 | 19篇 |
2006年 | 17篇 |
2005年 | 18篇 |
2004年 | 18篇 |
2003年 | 18篇 |
2002年 | 26篇 |
2001年 | 13篇 |
2000年 | 8篇 |
1999年 | 14篇 |
1998年 | 30篇 |
1997年 | 12篇 |
1996年 | 17篇 |
1995年 | 18篇 |
1994年 | 20篇 |
1993年 | 24篇 |
1992年 | 14篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 13篇 |
1985年 | 19篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1981年 | 5篇 |
1980年 | 14篇 |
1979年 | 15篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 14篇 |
1975年 | 7篇 |
1974年 | 10篇 |
1973年 | 14篇 |
排序方式: 共有777条查询结果,搜索用时 0 毫秒
771.
Degradable polyethylene: fantasy or reality 总被引:4,自引:0,他引:4
Roy PK Hakkarainen M Varma IK Albertsson AC 《Environmental science & technology》2011,45(10):4217-4227
Plastic waste disposal is one of the serious environmental issues being tackled by our society today. Polyethylene, particularly in packaging films, has received criticism as it tends to accumulate over a period of time, leaving behind an undesirable visual footprint. Degradable polyethylene, which would enter the eco-cycle harmlessly through biodegradation would be a desirable solution to this problem. However, the "degradable polyethylene" which is presently being promoted as an environmentally friendly alternative to the nondegradable counterpart, does not seem to meet this criterion. This article reviews the state of the art on the aspect of degradability of polyethylene containing pro-oxidants, and more importantly the effect these polymers could have on the environment in the long run. On exposure to heat, light, and oxygen, these polymers disintegrate into small fragments, thereby reducing or increasing the visual presence. However, these fragments can remain in the environment for prolonged time periods. This article also outlines important questions, particularly in terms of time scale of complete degradation, environmental fate of the polymer residues, and possible accumulation of toxins, the answers to which need to be established prior to accepting these polymers as environmentally benign alternatives to their nondegradable equivalents. It appears from the existing literature that our search for biodegradable polyethylene has not yet been realized. 相似文献
772.
T. Ram Prabhu V. K. Varma Srikanth Vedantam 《Journal of Materials Engineering and Performance》2014,23(10):3666-3679
In this work, we studied the high-speed tribological and mechanical properties of layered SiC particulate reinforced iron matrix composites. The layered composites consisted of a surface layer with high volume fraction of the reinforcement particles and a layer with low volume fraction in the bulk. The layered composites are a form of functionally graded materials with high wear resistance near the surface and high thermal conductivity in the bulk. The composites were prepared by standard powder metallurgy techniques. The tribological behavior of the composites was evaluated at 25 to 35 m/s sliding speeds using a sub-scale dynamometer disk brake testing system. The properties of the layered composites were compared to those of uniform composites. The results showed that the layered composites have better wear resistance and braking effectiveness in the range of braking speeds considered. The layered composites also showed higher bending strength than the monolayer composites due to the presence of the interfaces between the layers. 相似文献
773.
Panchagnula R Gupta A Kandavilli S Varma MV 《Drug development and industrial pharmacy》2006,32(6):669-675
Drug release from controlled-release (CR) matrix tablets involves the permeation and diffusion of water through the system. In this study, a new methodology is proposed for the measurement of water permeation and simultaneous drug release from the inert, non-swellable CR matrix tablet of diltiazem (DLT) and a correlation is made between these two processes. Cylindrical matrices were readily prepared by direct compression of pellets obtained by extrusion-spheronization. Water transport was studied using tritiated water (HTO) as a permeant in a Franz-diffusion cell and simultaneously drug release was measured. Further, dissolution was performed on USP XXI/XXII dissolution apparatus I using demineralized water. Matrices showed a steady water-uptake up to 6 h and the steady state for HTO permeation lasting from 6-h to 24-h Flux of water permeated and flux of drug released correlated well. Thus, HTO permeation through the matrix tablet and the proposed methodology can be used as a tool and/or surrogate marker for evaluation of controlled release matrix tablets. This methodology can be coined as “high-throughput” in terms of amount of labor and resources required in comparison to that of dissolution. 相似文献
774.
Nasrollahzadeh Mahmoud Sajjadi Mohaddeseh Varma Rajender S. 《Clean Technologies and Environmental Policy》2020,22(2):423-440
Clean Technologies and Environmental Policy - The fabrication of aminotetrazole–palladium(II) complex immobilized on silica-encapsulated Fe3O4 magnetic nanoparticles is described with full... 相似文献
775.
776.
Sabrina Presto Pravin Kumar Salil Varma Massimo Viviani Prabhakar Singh 《International Journal of Hydrogen Energy》2018,43(9):4528-4533
Three different materials are prepared by chemical reaction route, Sr2NiMoO6 (SNM00), Sr1.96La004NiMoO6 (SLNM04) and Sr1.99Ce0.01NiMoO6 (SCNM01) and conductivity is measured under reducing atmosphere, in order to study their suitability as anode materials in SOFC application. Selected materials correspond to compositions reported with highest conductivity in air at operative temperatures of a SOFC among the systems SLNM (Sr2?xLaxNiMoO6, 0.02 ≤ x ≤ 0.10) and SCNM (Sr2?xCexNiMoO6, 0.01 ≤ x ≤ 0.05). The end member Sr2NiMoO6 (SNM) is also considered as reference.Their conductivities considerably increase in wet hydrogen and follow Arrhenius behavior with lower activation energy. Effects of reduction on microstructure and phase stability are also studied by scanning electron microscopy and X–ray diffraction.The enhancement in conductivity is discussed in terms of defects chemistry. Amongst all measured samples, SLNM04 shows the highest conductivity in reducing atmosphere without phase degradation, which makes it a promising anode material for Solid Oxide Fuel Cells (SOFC). 相似文献
777.
The entropy generation rate in a vertical porous channel with injection and suction walls and a uniform magnetic field provided at an angle to the flow direction is studied using an analytical perturbation technique in the presence of Navier slip and buoyancy force. The momentum and energy equations were solved for exemplary values of fluid convection's physical characteristics. Important parameters' impacts on adequate numbers are graphically portrayed and conveyed. 相似文献