全文获取类型
收费全文 | 220426篇 |
免费 | 27890篇 |
国内免费 | 8608篇 |
专业分类
电工技术 | 12329篇 |
技术理论 | 13篇 |
综合类 | 11909篇 |
化学工业 | 46373篇 |
金属工艺 | 10516篇 |
机械仪表 | 12202篇 |
建筑科学 | 15609篇 |
矿业工程 | 5519篇 |
能源动力 | 6220篇 |
轻工业 | 19768篇 |
水利工程 | 3603篇 |
石油天然气 | 10970篇 |
武器工业 | 1443篇 |
无线电 | 28134篇 |
一般工业技术 | 32459篇 |
冶金工业 | 9488篇 |
原子能技术 | 2000篇 |
自动化技术 | 28369篇 |
出版年
2024年 | 923篇 |
2023年 | 3516篇 |
2022年 | 6571篇 |
2021年 | 9004篇 |
2020年 | 7859篇 |
2019年 | 8018篇 |
2018年 | 8665篇 |
2017年 | 9691篇 |
2016年 | 9406篇 |
2015年 | 11422篇 |
2014年 | 13286篇 |
2013年 | 16228篇 |
2012年 | 15120篇 |
2011年 | 15512篇 |
2010年 | 13780篇 |
2009年 | 13012篇 |
2008年 | 12108篇 |
2007年 | 11132篇 |
2006年 | 11047篇 |
2005年 | 9454篇 |
2004年 | 6714篇 |
2003年 | 5799篇 |
2002年 | 5291篇 |
2001年 | 4728篇 |
2000年 | 4620篇 |
1999年 | 4644篇 |
1998年 | 3565篇 |
1997年 | 3032篇 |
1996年 | 2799篇 |
1995年 | 2260篇 |
1994年 | 1845篇 |
1993年 | 1334篇 |
1992年 | 1070篇 |
1991年 | 806篇 |
1990年 | 589篇 |
1989年 | 478篇 |
1988年 | 374篇 |
1987年 | 264篇 |
1986年 | 221篇 |
1985年 | 134篇 |
1984年 | 120篇 |
1983年 | 89篇 |
1982年 | 87篇 |
1981年 | 70篇 |
1980年 | 66篇 |
1979年 | 31篇 |
1978年 | 26篇 |
1977年 | 27篇 |
1976年 | 27篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall 总被引:1,自引:0,他引:1
Chia-Feng Lin Zhong-Jie Yang Jing-Hui Zheng Jing-Jie Dai 《Photonics Technology Letters, IEEE》2005,17(10):2038-2040
In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga/sub 2/O/sub 3/ layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga/sub 2/O/sub 3/-air layers, by a rough Ga/sub 2/O/sub 3/ surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications. 相似文献
102.
Gonzalo Martínez‐Barrera Enrique Vigueras‐Santiago Susana Hernndez‐Lpez Gonzalo Martínez‐Barrera Witold Brostow Carmina Menchaca‐Campos 《Polymer Engineering and Science》2005,45(10):1426-1431
Fiber reinforced concrete (FRC) contains fibers physically mixed with gravel, sand, cement, and water. So far, adequate mechanical performance of FRC has been obtained at high cost and using complex technologies; important here is the geometry and surface characteristics of the polymers. We have modified polymeric‐fiber surfaces by using gamma radiation. Irradiated polypropylene (PP) fibers were submitted to 0, 5, 10, 50, and 100 kGy of gamma irradiation dosages. First, tensile strength of PP fibers was evaluated, and then fibers blended at 0, 1.0, 1.5, and 2.0% in volume with Portland cement, gravel, sand, and water. The highest values of compressive strength were obtained with irradiated‐fibers at 10 kGy and 1.5% in volume of fiber. The result is 101 MPa, as compared to 35 MPa for simple concrete without fibers. POLYM. ENG. SCI., 45:1426–1431, 2005. © 2005 Society of Plastics Engineers 相似文献
103.
2008年6月,温家宝总理在省区市和中央部门主要负责同志会议上指出:今年以来,我国经济社会发展经受了最为严峻的重大挑战和考验。这也让我们更加关注企业生存和发展的国际国内环境。 相似文献
104.
中国橡胶工业协会力车胎分会4月15~16日在青岛市召开了第十五次会员大会,大会总结了第六届理事会工作,讨论并通过推荐第七届理事和总会理事名单、副理事长和总会常务理事名单,确认了分会理事长、秘书长。讨论通过了第七届理事会工作设想及安排。 相似文献
105.
我国工程机械现状及今后发展趋势 总被引:1,自引:0,他引:1
中国的工程机械行业建立于1961年。改革开放以后,由于国内对工程机械的需求量大,自1978年开始至20世纪末共引进近200项技术.发展了近500个新产品。使我国的工程机械迈上了一个新的台阶,当年引进的产品目前已成为我国工程机械的主导产品。 相似文献
106.
107.
Xue‐Bing Zhao Lei Wang De‐Hua Liu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(6):950-956
Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry 相似文献
108.
109.
On effective offloading services for resource-constrained mobile devices running heavier mobile internet applications 总被引:1,自引:0,他引:1
Kun Yang Shumao Ou Hsiao-Hwa Chen 《Communications Magazine, IEEE》2008,46(1):56-63
Rapid advances in wireless mobile network technologies and mobile handsets (MHs) facilitate ubiquitous infrastructure that can support a range of mobile services and applications in addition to conventional mobile Internet access. One recent trend is to effectively run desktop PC-oriented heavier applications on MHs. However, due to their miniature, portable size, MHs are resource-constrained and therefore, running these applications directly on an MH is not satisfactory given a user's expectations. To cope with this problem, this article proposes a novel offloading service that can seamlessly offload some of the tasks of a mobile application from an MH to nearby, resource-rich PCs (called surrogates). The system architecture and key components of the proposed offloading service are presented, prototyped, and evaluated. The results of experiments and simulations have demonstrated the effectiveness and efficiency of this offloading service for mobile applications. 相似文献
110.
In polyolefin processes the melt index (MI) is the most important control variable indicating product quality. Because of
the difficulty in the on-line measurement of MI, a lot of MI estimation and correlation methods have been proposed. In this
work a new dynamic MI estimation scheme is developed based on system identification techniques. The empirical MI estimation
equation proposed in the present study is derived from the 1
st
-order dynamic models. Effectiveness of the present estimation scheme was illustrated by numerical simulations based on plant
operation data including grade change operations in high density polyethylene (HDPE) processes. From the comparisons with
other estimation methods it was found that the proposed estimation scheme showed better performance in MI predictions. The
virtual sensor model developed based on the estimation scheme was combined with the virtual on-line analyzer (VOA) to give
a quality control system to be implemented in the actual HDPE plant. From the application of the present control system, significant
reduction of transition time and the amount of off-spec during grade changes was achieved 相似文献