全文获取类型
收费全文 | 10683篇 |
免费 | 1419篇 |
国内免费 | 655篇 |
专业分类
电工技术 | 2854篇 |
技术理论 | 1篇 |
综合类 | 1121篇 |
化学工业 | 524篇 |
金属工艺 | 884篇 |
机械仪表 | 755篇 |
建筑科学 | 247篇 |
矿业工程 | 566篇 |
能源动力 | 169篇 |
轻工业 | 265篇 |
水利工程 | 79篇 |
石油天然气 | 388篇 |
武器工业 | 339篇 |
无线电 | 2201篇 |
一般工业技术 | 947篇 |
冶金工业 | 446篇 |
原子能技术 | 154篇 |
自动化技术 | 817篇 |
出版年
2024年 | 65篇 |
2023年 | 219篇 |
2022年 | 286篇 |
2021年 | 387篇 |
2020年 | 411篇 |
2019年 | 311篇 |
2018年 | 250篇 |
2017年 | 370篇 |
2016年 | 404篇 |
2015年 | 487篇 |
2014年 | 718篇 |
2013年 | 636篇 |
2012年 | 854篇 |
2011年 | 932篇 |
2010年 | 700篇 |
2009年 | 708篇 |
2008年 | 611篇 |
2007年 | 780篇 |
2006年 | 682篇 |
2005年 | 549篇 |
2004年 | 442篇 |
2003年 | 432篇 |
2002年 | 316篇 |
2001年 | 244篇 |
2000年 | 245篇 |
1999年 | 143篇 |
1998年 | 95篇 |
1997年 | 96篇 |
1996年 | 89篇 |
1995年 | 67篇 |
1994年 | 58篇 |
1993年 | 34篇 |
1992年 | 35篇 |
1991年 | 14篇 |
1990年 | 22篇 |
1989年 | 25篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 6篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1965年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
61.
Feng Qin Zhiyang Yan Jinfeng Fan Jinliang Cai Xingzhong Zhu Xiaogang Zhang 《大分子材料与工程》2021,306(2):2000607
Electromagnetic interference (EMI) shielding materials, especially ones with excellent shielding effectiveness (SE), high optical transmittance, long-term stability as well as high uniformity, are urgently desired to meet the requirements of many applications. Herein, an extremely transparent, stable and uniform silver nanowire (Ag NW)–poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composite film as an EMI shielding material is prepared, which possess excellent shielding capability to both small signal and high power microwaves (HPM). The composite film exhibits SE of 30.5 dB in the frequency range of 1–12 GHz (small signal) and simultaneously has an optical transmittance of 91.0%. The SE continuously increases to 41.4 dB, while the optical transmittance still maintains at 81.1%. The composite film is very uniform, and its SE is almost unchanged even when exposed in air for a year. The SE of this composite film under the excitation of HPM is also thoroughly investigated. The HPM SE is much larger than that of small signal. As the power density of HPM is increased, the SE firstly remains unchanged, then continuously increases, and finally saturates. The SE exceeds 50 dB with the excitation power density of 40 W. More interestingly, the SE is saturated at a fixed HPM power density. 相似文献
62.
Synergistic Effect of PVDF-Coated PCL-TCP Scaffolds and Pulsed Electromagnetic Field on Osteogenesis
Yibing Dong Luvita Suryani Xinran Zhou Padmalosini Muthukumaran Moumita Rakshit Fengrui Yang Feng Wen Ammar Mansoor Hassanbhai Kaushik Parida Daniel T. Simon Donata Iandolo Pooi See Lee Kee Woei Ng Swee Hin Teoh 《International journal of molecular sciences》2021,22(12)
Bone exhibits piezoelectric properties. Thus, electrical stimulations such as pulsed electromagnetic fields (PEMFs) and stimuli-responsive piezoelectric properties of scaffolds have been investigated separately to evaluate their efficacy in supporting osteogenesis. However, current understanding of cells responding under the combined influence of PEMF and piezoelectric properties in scaffolds is still lacking. Therefore, in this study, we fabricated piezoelectric scaffolds by functionalization of polycaprolactone-tricalcium phosphate (PCL-TCP) films with a polyvinylidene fluoride (PVDF) coating that is self-polarized by a modified breath-figure technique. The osteoinductive properties of these PVDF-coated PCL-TCP films on MC3T3-E1 cells were studied under the stimulation of PEMF. Piezoelectric and ferroelectric characterization demonstrated that scaffolds with piezoelectric coefficient d33 = −1.2 pC/N were obtained at a powder dissolution temperature of 100 °C and coating relative humidity (RH) of 56%. DNA quantification showed that cell proliferation was significantly enhanced by PEMF as low as 0.6 mT and 50 Hz. Hydroxyapatite staining showed that cell mineralization was significantly enhanced by incorporation of PVDF coating. Gene expression study showed that the combination of PEMF and PVDF coating promoted late osteogenic gene expression marker most significantly. Collectively, our results suggest that the synergistic effects of PEMF and piezoelectric scaffolds on osteogenesis provide a promising alternative strategy for electrically augmented osteoinduction. The piezoelectric response of PVDF by PEMF, which could provide mechanical strain, is particularly interesting as it could deliver local mechanical stimulation to osteogenic cells using PEMF. 相似文献
63.
64.
65.
B. W. Zhang Z.M. Ren Y.B. Zhong K. Deng K.D. XuShanghai Enhanced Laboratory of Metallurgy Shanghai University Shanghai China 《金属学报(英文版)》2002,15(5):416-424
The electromagnetic field under applied AC and DC current in round and rectangular pipe was systematically investigated, then a concept of "equivalent current density" was proposed for evaluating the inhomogeneous electromagnetic pinch force, and the mono-component removal efficiency and the overall removal efficiency of inclusion were formulated. It is founded that flat pipe is superior to round pipe for the electromagnetic removal of inclusion, and DC current can get a higher removal efficiency than A C current due to absence of skin phenomenon. Under usual condition, a removal efficiency of 52% for 10μm inclusion or more than 92% for 20μm inclusion can be achieved by imposing a current density of 3×106A/m2 in a flat pipe. 相似文献
66.
磁性纤维随机混合媒质等效电磁参数的计算 总被引:1,自引:0,他引:1
为计及强散射偶极子间的相互作用,引入参量εh和μh,利用广义多重散射理论及MATLAB计算机软件对在2 GHz~18 GHz频率下的体积占空比为8%的铁纤维随机混合媒质等效磁导率的实验值进行曲线的拟合,导出了耦合系数εh和μh,并在此基础上,对体积占空比分别为30%和20%的铁纤维随机混合媒质等效磁导率进行了计算,计算结果与实验吻合良好. 相似文献
67.
水平电磁连铸空心铜管坯组织和性能研究 总被引:5,自引:0,他引:5
提出在中试水平的空心铜管坯水平连铸过程中施加工频电磁场,分析其对铜管坯组织和性能的影响.结果表明:与未施加电磁场时相比,施加电流强度为140A的工频电磁场后,水平连铸空心铜管坯的组织显著细化,平均晶粒度由未施加磁场时的3.1提高到8.3,周向组织均匀性也得到明显改善;抗拉强度提高40%左右,延伸率提高50%左右. 相似文献
68.
69.
Zhang Rongfeng He Jishan College of Resource Environment Civil Engineering Central South University of Technology Changsha 《中国有色金属学会会刊》1997,(2)
ANEWELECTROMAGNETICIMAGINGSCHEME①ZhangRongfeng,HeJishanColegeofResource,EnvironmentandCivilEnginering,CentralSouthUniversityo... 相似文献
70.