全文获取类型
收费全文 | 23034篇 |
免费 | 650篇 |
国内免费 | 3874篇 |
学科分类
工业技术 | 27558篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 10篇 |
2020年 | 20篇 |
2019年 | 9篇 |
2018年 | 5篇 |
2017年 | 65篇 |
2016年 | 10篇 |
2015年 | 36篇 |
2014年 | 280篇 |
2013年 | 215篇 |
2012年 | 392篇 |
2011年 | 3388篇 |
2010年 | 1692篇 |
2009年 | 908篇 |
2008年 | 950篇 |
2007年 | 652篇 |
2006年 | 878篇 |
2005年 | 916篇 |
2004年 | 3600篇 |
2003年 | 1694篇 |
2002年 | 1500篇 |
2001年 | 1202篇 |
2000年 | 601篇 |
1999年 | 1212篇 |
1998年 | 816篇 |
1997年 | 772篇 |
1996年 | 387篇 |
1995年 | 324篇 |
1994年 | 263篇 |
1993年 | 1270篇 |
1992年 | 962篇 |
1991年 | 607篇 |
1990年 | 644篇 |
1989年 | 515篇 |
1988年 | 327篇 |
1987年 | 117篇 |
1986年 | 142篇 |
1985年 | 55篇 |
1984年 | 20篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 19篇 |
1979年 | 21篇 |
1973年 | 2篇 |
1965年 | 3篇 |
1956年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
103.
低强度超声波强化污水生物处理技术 总被引:1,自引:0,他引:1
国内外研究发现低强度的超声辐照可以有效促进微生物的活性,因此可将其用于强化污水的生物处理。通过增强反应器内微生物的活性来提高污水的处理效率。介绍了低强度超声波强化生物活性的机理以及主要影响因素。概述了利用该技术强化污水生物处理的研究现状,并对未来的应用前景进行了展望。 相似文献
104.
105.
106.
107.
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
108.
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
109.
TONG YaBo YANG ZhenYu PAN YongXin ZHENG Li i SUN ZhiMing PEI JunLing &ZHUANG ZhongHai Institute of Geomechanics Chinese Academy of Geological Sciences Beijing China 《中国科学:技术科学(英文版)》2011,(4)
Geomagnetic polarity transitions were the most important phenomena in the study of the geomagnetic field evolution and the earth's deep interior dynamics.The Miocene postcollisional ultrapotassic-potassic rocks are widely distributed in the Lhasa Block of southern Tibet.Paleomagnetic studies on the Wuyu Formation indicated that these volcanic rocks recorded the C5Bn.2n-C5Bn.1r and C5ACr-C5ACn geomagnetic polarity transitions.The virtual geomagnetic poles(VGPs) of these two polarity transitions were located ... 相似文献
110.
FANG JiaSong & ZHANG Li State Key Laboratory of Marine Geology Tongji University Shanghai China College of Natural Computational Sciences Hawaii Pacific University Kaneohe HI USA State Key Laboratory of Geological Processes Mineral Resources Faculty of Earth Sciences China University of Geosciences Wuhan 《中国科学:技术科学(英文版)》2011,(2)
Over the past two decades, scientific drilling into sediments and rocks in the ocean and the continent has revealed the presence of physiologically and phylogenetically complex microbial life in the deep subsurface. Microorganisms, most of which have no cultured or known relatives in the surface biosphere, have been discovered in sediments and rock at depth as deep as 1 km below the seafloor and more than 3 km deep in the continent. The deep biosphere probably represents the most voluminous part of the glob... 相似文献