全文获取类型
收费全文 | 112349篇 |
免费 | 11047篇 |
国内免费 | 6929篇 |
专业分类
电工技术 | 8013篇 |
技术理论 | 10篇 |
综合类 | 9574篇 |
化学工业 | 16640篇 |
金属工艺 | 6866篇 |
机械仪表 | 7083篇 |
建筑科学 | 8817篇 |
矿业工程 | 3839篇 |
能源动力 | 3091篇 |
轻工业 | 10458篇 |
水利工程 | 2931篇 |
石油天然气 | 4984篇 |
武器工业 | 1304篇 |
无线电 | 12361篇 |
一般工业技术 | 12170篇 |
冶金工业 | 4989篇 |
原子能技术 | 1677篇 |
自动化技术 | 15518篇 |
出版年
2024年 | 321篇 |
2023年 | 1894篇 |
2022年 | 3740篇 |
2021年 | 5169篇 |
2020年 | 3821篇 |
2019年 | 2957篇 |
2018年 | 3220篇 |
2017年 | 3517篇 |
2016年 | 3263篇 |
2015年 | 4715篇 |
2014年 | 5816篇 |
2013年 | 7069篇 |
2012年 | 8297篇 |
2011年 | 8636篇 |
2010年 | 7479篇 |
2009年 | 7286篇 |
2008年 | 7356篇 |
2007年 | 6943篇 |
2006年 | 6301篇 |
2005年 | 5336篇 |
2004年 | 4008篇 |
2003年 | 3085篇 |
2002年 | 2804篇 |
2001年 | 2449篇 |
2000年 | 2435篇 |
1999年 | 2287篇 |
1998年 | 1773篇 |
1997年 | 1437篇 |
1996年 | 1395篇 |
1995年 | 1171篇 |
1994年 | 1020篇 |
1993年 | 724篇 |
1992年 | 566篇 |
1991年 | 405篇 |
1990年 | 356篇 |
1989年 | 321篇 |
1988年 | 236篇 |
1987年 | 162篇 |
1986年 | 117篇 |
1985年 | 85篇 |
1984年 | 57篇 |
1983年 | 44篇 |
1982年 | 49篇 |
1981年 | 34篇 |
1980年 | 44篇 |
1979年 | 20篇 |
1976年 | 13篇 |
1974年 | 11篇 |
1959年 | 12篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
Zdeněk Slanina Filip Uhlík Lipiao Bao Takeshi Akasaka Xing Lu Ludwik Adamowicz 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(7):565-570
AbstractRelative populations of four energy-lowest IPR (isolated-pentagon-rule) isomers of Eu@C86 are computed using the Gibbs energy based on characteristics from density functional theory calculations (M06-2X/3-21G?~?SDD entropy term, M06-2X/6-31G*~SDD or B2PLYP(D)/6-31G*~SDD energetics). The calculations confirm that the recently isolated Eu@C1(7)-C86 species is a major isomer in a relevant temperature region. Relationship to the empty C86 cages is discussed, too. 相似文献
84.
Shuang Shao Yong Liu Chun-Shui Xu Ying-Xuan Xu Bin Wu Xiao-Shu Zeng Xian-Feng Lu Xiang-Jie Yang 《金属学报(英文版)》2015,(1):7-14
The microstructure and mechanical properties of Mg–6Zn–1Y and Mg–6Zn–3Y(wt%) alloys under different cooling rates were investigated. The results show that the second dendrite arm spacing(SDAS) of Mg–6Zn–1Y and Mg–6Zn–3Y is reduced by 32 and 30% with increasing cooling rates(Rc) from 10.2 to 23 K/s, which can be predicted using a empirical model of SDAS=68 R 0:45:45cand SDAS=73 R 0c, respectively. The compressive strength of both alloys increases with increasing the cooling rate, which is attributed to the increase of volume fraction(Vf) of secondary phases under high cooling rate. The interaction of the cooling rate and component with SDAS has been theoretically analyzed using interdependence theory. 相似文献
85.
Wenjie Wu Yan Liu Dong Liu Wenxing Chen Zhaoyi Song Ximin Wang Yamin Zheng Ning Lu Chunxia Wang Junjie Mao Yadong Li 《Nano Research》2021,14(4):998-1003
The demand for high-performance non-precious-metal electrocatalysts to replace the noble metal-based catalysts for oxygen reduction reaction(ORR)is intensively increasing.Herein,single-atomic copper sites supported on N-doped three-dimensional hierarchically porous carbon catalyst(Cu1/NC)was prepared by coordination pyrolysis strategy.Remarkably,the Cu1/NC-900 catalyst not only exhibits excellent ORR performance with a half-wave potential of 0.894 V(vs.RHE)in alkaline media,outperforming those of commercial Pt/C(0.851 V)and Cu nanoparticles anchored on N-doped porous carbon(CuNPs/NC-900),but also demonstrates high stability and methanol tolerance.Moreover,the Cu1/NC-900 based Zn-air battery exhibits higher power density,rechargeability and cyclic stability than the one based on Pt/C.Both experimental and theoretical investigations demonstrated that the excellent performance of the as-obtained Cu1/NC-900 could be attributed to the synergistic effect between copper coordinated by three N atoms active sites and the neighbouring carbon defect,resulting in elevated Cu d-band centers of Cu atoms and facilitating intermediate desorption for ORR process.This study may lead towards the development of highly efficient non-noble metal catalysts for applications in electrochemical energy conversion. 相似文献
86.
以机械共混法制备亲水性聚对苯二甲酸乙二醇酯(PET)共混材料,并通过接触角测定仪、差示扫描量热仪(DSC)和电子万能材料试验机等对共混材料的亲水性能、热性能和力学性能等进行研究与分析。结果表明,亲水处理剂聚乙二醇(PEG)、聚丙烯酸钠(PAAS)、聚乙烯吡咯烷酮(PVP)均能改善PET的亲水性能,影响PET的结晶性能,但亲水处理剂对PET的力学性能影响较小,其中PET/PEG共混材料的亲水性最优;随着PEG含量的增加,PET/PEG共混材料的亲水性先逐渐增强,当PEG含量高于5 %后,共混材料的亲水性变化很小;且PET的结晶度随着PEG的加入呈现先增大后减小的趋势。 相似文献
87.
Multicellular tumor spheroid models (MCTS) are often coined as 3D in vitro models that can mimic the microenvironment of tissues. MCTS have gained increasing interest in the nano‐biotechnology field as they can provide easily accessible information on the performance of nanoparticles without using animal models. Considering that many countries have put restrictions on animals testing, which will only tighten in the future as seen by the recent developments in the Netherlands, 3D models will become an even more valuable tool. Here, an overview on MCTS is provided, focusing on their use in cancer research as most nanoparticles are tested in MCTS for treatment of primary tumors. Thereafter, various types of nanoparticles—from self‐assembled block copolymers to inorganic nanoparticles, are discussed. A range of physicochemical parameters including the size, shape, surface chemistry, ligands attachment, stability, and stiffness are found to influence nanoparticles in MCTS. Some of these studies are complemented by animal studies confirming that lessons from MCTS can in part predict the behaviour in vivo. In summary, MCTS are suitable models to gain additional information on nanoparticles. While not being able to replace in vivo studies, they can bridge the gap between traditional 2D in vitro studies and in vivo models. 相似文献
88.
Jianmou Lu Yanli Huang Shunyan Ren 《International Journal of Control, Automation and Systems》2020,18(5):1250-1263
This paper investigates the general decay synchronization and general decay H∞ synchronization problems of multi-weighted coupled reaction-diffusion 相似文献
89.
为了给海面溢油污染识别检测提供理论基础,根据菲涅尔反射公式的偏振反射系数,结合偏振双向反射率因子和粗糙海面的概率密度分布函数,建立了完善的pBRDF模型,仿真在不同太阳入射角度、不同探测器观测角度以及不同海面风速风向等条件下海水和油膜的偏振反射分布函数。结果表明:海水和油膜太阳天顶角为53°和56°时P偏振反射率分别为1.0×10^-5和2.5×10^-5,S偏振反射率随着太阳天顶角的增加而增加;海面风速越大偏振反射率峰值越小;海面风向只改变pBRDF的空间位置;海水和油膜线偏振度空间分布有明显差异。搭建实验平台相机以40°拍摄时,得出海水和油膜的线偏振度分别在0.2~0.4, 0.5~0.7之间,同时表明利用偏振探测获取目标场景的偏振度和偏振角图可提高图像质量。 相似文献
90.