全文获取类型
收费全文 | 19883篇 |
免费 | 648篇 |
国内免费 | 2949篇 |
学科分类
工业技术 | 23480篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 3篇 |
2020年 | 13篇 |
2019年 | 2篇 |
2017年 | 53篇 |
2016年 | 6篇 |
2015年 | 33篇 |
2014年 | 259篇 |
2013年 | 175篇 |
2012年 | 325篇 |
2011年 | 2922篇 |
2010年 | 1494篇 |
2009年 | 814篇 |
2008年 | 849篇 |
2007年 | 579篇 |
2006年 | 794篇 |
2005年 | 837篇 |
2004年 | 3261篇 |
2003年 | 1517篇 |
2002年 | 1298篇 |
2001年 | 1008篇 |
2000年 | 481篇 |
1999年 | 1058篇 |
1998年 | 697篇 |
1997年 | 643篇 |
1996年 | 327篇 |
1995年 | 261篇 |
1994年 | 218篇 |
1993年 | 1052篇 |
1992年 | 830篇 |
1991年 | 450篇 |
1990年 | 472篇 |
1989年 | 381篇 |
1988年 | 196篇 |
1987年 | 35篇 |
1986年 | 33篇 |
1985年 | 27篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1977年 | 1篇 |
1973年 | 2篇 |
1965年 | 3篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
初始等轴组织Ti-55531合金在相变点以上经过0.01、0.1、1 s~(-1)不同应变速率的等温压缩变形,随后进行750℃×5 min/AC热处理。采用扫描电子显微镜和透射电子显微镜研究了后续热处理时变形α相和基体β相的静态再结晶机理。结果表明,随着应变速率的升高,残留等轴α相的含量增加。变形合金中拉长α相在经过热处理后有球化现象,同时在强度相对较高的拉长α相端部的基体β相中,位错储能较高,有助于β相再结晶形核和空冷过程中局部高密度次生α相析出。 相似文献
2.
目前由中国移动集团牵头研发的网优自动化服务平台,主要集成了如下功能:LTE自动邻区关系优化模块、基于智能算法的PCI自动优化模块、 LTE功率配置自动优化模块、LTE小区参数自动化推荐模块,以及TAC边界区域自动优化模块等,并支持其他新增工具的快速扩展。本文介绍的网优自动化平台包括了全流程数据预处理模块、即插即用的优化算法模块、灵活的Web Service接口调用模块、以及各工具通用的数据挖掘/机器学习算法库等等,这种基于模块化搭建的网优自动化服务平台,使得各类核心网优应用能够快速上线,并具有极强的可扩展性和可靠性。 相似文献
3.
The last decade has witnessed the convergence of three giant worlds:electronics,computer science and telecommunications.The next decade should follow this convergence in most of our activities with the generalization of sensor networks.In particular with the progress in medicine,people live longer and the aging of population will push the development of wireless person- 相似文献
4.
The rolling process is determined by the interaction of a number of different movements,during which the relative movement occurs between the vibrating roll system and the rolled piece,and the roll system’s vibration interacts with the strip’s deformation and rigid movement.So many parameters being involved leads to a complex mechanism of this coupling effect.Through testing and analyzing the vibration signals of the mill in the rolling process,the rolling mill’s coupled model is established with comprehensive consideration of the coupling interaction between the mill’s vertical vibration,its torsional vibration and the working roll’s horizontal vibration,and vibration characteristics of different forms of rolling mill’s vibration are analyzed under the coupling effect.With comprehensive attention to the relationship between the roll system,the moving strip and the rolling parameters’dynamic properties,and also from the strip thickness control point of view,further research is done on the coupling mechanism between the roll system’s movement and the moving strip’s characteristics in the rolling process.As a result,the law of inertial coupling and the stiffness coupling effect caused by different forms of the roll system’s vibration is determined and the existence of nonlinear characteristics caused by the elastic deformation of moving strip is also found.Furthermore,a multi-parameter coupling-dynamic model is established which takes the tandem strip mill as its research object by making a detailed kinematics analysis of the roll system and using the principle of virtual work.The coupling-dynamic model proposes the instruction to describe the roll system’s movement,and analyzes its dynamic response and working stability,and provides a theoretical basis for the realization of the strip thickness’dynamic control. 相似文献
5.
In this paper,we investigate the matched filter based spectrum sensing in a more reasonable cognitive radio(CR) scenario when the primary user(PU) has more than one transmit power levels,as regulated in most standards,i.e.,IEEE 802.11 Series,GSM,LTE,LTE-A,etc.This new multiple primary transmit power(MPTP) scenario is specialized by two different targets:detecting the presence of PU and identifying the power level.Compared to the traditional binary sensing where only the presence of PU is checked,SU may attain more information about the primary network(making CR more "intelligent") and design the subsequent optimization strategy.The key technology is the multiple hypothesis testing as opposed to the traditional binary hypothesis testing.We discuss two situations under whether the channel phase is known or not,and we derive the closed form solutions for decision regions and several performance metrics,from which some interesting phenomenons are observed and the related discussions are presented.Numerical examples are provided to corroborate the proposed studies. 相似文献
6.
Gehan M.K.Tolba Nasser A.M.Barakat A.M.Bastaweesy E.A.Ashour Wael Abdelmoez Mohamed H.El-Newehy Salem S.Al-Deyab Hak Yong Kim 《材料科学技术学报》2015,(1):97-105
Metal oxides have a higher chemical stability in comparison to metals,so they can be utilized as electrocatalysts if the activity could be enhanced.Besides the composition,the morphology of the nanostructures has a considerable impact on the electrocatalytic activity.In this work,zinc oxide nano branches-attached titanium dioxide nanofibers were investigated as an economic and stable catalyst for ethanol electrooxidation in the alkaline media.The introduced material has been synthesized by electrospinning process followed by hydrothermal technique.Briefly,electrospinning of colloidal solution consisting of titanium isopropoxide,poly(vinyl acetate) and zinc nanoparticles was performed to produce nanofibers embedding solid nanoparticles.In order to produce TiO_2 nanofibers containing ZnO nanoparticles,the obtained electrospun nanofiber mats were calcined in air at 600 °C.The formed ZnO nanoparticles were exploited as seeds to outgrow ZnO branches around the TiO_2 nanofibers using the hydrothermal technique at sub-critical water conditions in the presence of zinc nitrate and bis-hexamethylene triamine.The morphology of the final product,as well as the electrochemical measurements indicated that zinc nanoparticles content in the original electrospun nanofibers has a significant influence on the electrocatalytic activity as the best performance was observed with the nanofibers synthesized from electrospun solution containing 0.1 g Zn,and the corresponding current density was 37 mA/cm~2.Overall,this study paves a way to titanium dioxide to be exploited to synthesize effective and stable metal oxide-based electrocatalysts. 相似文献
7.
8.
A 25 Gbit/s clock and data recovery(CDR) circuit with 1:2 demultiplexer for 100 Gbit/s Ethernet(100 Gb E) optical interconnects has been designed and fabricated in Taiwan Semiconductor Manufacture Company(TSMC) 65 nm complementary metal-oxide-semiconductor(CMOS) technology. A novel quadrature voltage-controlled-oscillator(QVCO) structure adopts two pairs of transconductance cell and inverters to acquire rail-to-rail output swing. A half-rate bang-bang phase detector adopts four flip-flops array to sample the 25 Gbit/s input data and align the data phase, so the 25 Gbit/s data are retimed and demultiplexed into two paths 12.5 Gbit/s output data. Experimental results show that the recovered clock exhibits a peak-to-peak jitter of 7.39 ps and the recovered data presents a peak-to-peak jitter of 7.56 ps, in response to 312-1 pseudorandom bit sequence(PRBS) input. For 1.2 V voltage supply, the CDR circuit consumes 92 m W(excluding output buffers). 相似文献
9.
10.