全文获取类型
收费全文 | 218057篇 |
免费 | 22560篇 |
国内免费 | 12915篇 |
专业分类
电工技术 | 17450篇 |
技术理论 | 8篇 |
综合类 | 17657篇 |
化学工业 | 31323篇 |
金属工艺 | 13428篇 |
机械仪表 | 15004篇 |
建筑科学 | 18088篇 |
矿业工程 | 7187篇 |
能源动力 | 6650篇 |
轻工业 | 16230篇 |
水利工程 | 5327篇 |
石油天然气 | 10820篇 |
武器工业 | 2532篇 |
无线电 | 26084篇 |
一般工业技术 | 22684篇 |
冶金工业 | 8899篇 |
原子能技术 | 2663篇 |
自动化技术 | 31498篇 |
出版年
2024年 | 828篇 |
2023年 | 3429篇 |
2022年 | 6679篇 |
2021年 | 9588篇 |
2020年 | 7206篇 |
2019年 | 5710篇 |
2018年 | 6384篇 |
2017年 | 7336篇 |
2016年 | 6516篇 |
2015年 | 9674篇 |
2014年 | 12240篇 |
2013年 | 14463篇 |
2012年 | 16916篇 |
2011年 | 17623篇 |
2010年 | 16177篇 |
2009年 | 15288篇 |
2008年 | 14949篇 |
2007年 | 14102篇 |
2006年 | 12852篇 |
2005年 | 10249篇 |
2004年 | 7255篇 |
2003年 | 6236篇 |
2002年 | 6099篇 |
2001年 | 5409篇 |
2000年 | 4312篇 |
1999年 | 3617篇 |
1998年 | 2353篇 |
1997年 | 1900篇 |
1996年 | 1781篇 |
1995年 | 1527篇 |
1994年 | 1201篇 |
1993年 | 818篇 |
1992年 | 659篇 |
1991年 | 470篇 |
1990年 | 376篇 |
1989年 | 295篇 |
1988年 | 243篇 |
1987年 | 140篇 |
1986年 | 139篇 |
1985年 | 61篇 |
1984年 | 59篇 |
1983年 | 34篇 |
1982年 | 43篇 |
1981年 | 47篇 |
1980年 | 47篇 |
1979年 | 35篇 |
1977年 | 16篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1951年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
A novel CdS/CaFe2O4 (CS/CFO) heterogeneous p-n junction was created by thermal deposition of CaFe2O4 nanoparticles on CdS rods. The CS/CFO hetero-structured photocatalysts exhibited increasingly efficient visible light harvesting compared to the bare CdS. The CS/CFO composites also presented higher photocurrent and slower decay of photoluminescence, suggesting a better separation of the photo-generated electrons and holes. The photocatalytic H2 evolution quantity on the optimized CS/CFO composite from water in the presence of ethanol was up to 2200 μmol after 3-h visible light illumination, which is more than twice that of the pristine CdS. The chemical interaction between CdS and CaFe2O4 was confirmed by the shifts in the XPS peaks, which made it possible for the charge carriers to transfer across the p-n junction interface. This research highlights the importance of forming an interfacial p-n heterojunction between two semiconductors for efficient charge separation and improved photocatalytic performance. 相似文献
32.
Jieyi Yu Xianguo Liu Rui Su Xuefeng Zhang Xinglong Dong 《Ceramics International》2021,47(17):23950-23957
Increasing the dielectric loss capacity plays an important role in enhancing the electromagnetic absorption performance of materials. It remains a challenge to simultaneously introduce multiple types of dielectric losses in the material. In this work, we show that the atomic and interfacial dipole polarizations can be simultaneously enhanced by substituting N species into both carbon coating layers and bulk TiC lattices of a core-shell TiC@C material. Additionally, substitution of N species results more exposed TiC(111) facets and refines the TiC grain sizes in the bulk material, which is beneficial for enhancing the scattering of the external electromagnetic waves. The maximum reflection loss of the N substituted TiC@C material is measured as ?47.1 dB with an effective absorbing bandwidth of 4.83 GHz at 1.9 mm, which illustrates a valuable way to further tuning the electromagnetic absorption performance of this type of materials. 相似文献
33.
34.
35.
Virtual Reality - BRICKxAR is a novel augmented reality (AR) instruction method for construction toys such as LEGO®. With BRICKxAR, physical LEGO construction is guided by virtual bricks.... 相似文献
36.
Water Resources Management - The low impact development (LID) concept aims to control storm runoff and pollution through decentralized, small-scale source control to bring the development area as... 相似文献
37.
支承或连接构件对梁结构的动力学性能有至关重要影响,必须保证其在振动过程中不发生破坏或者失效。通过合理设计和布局附加弹性支承可以实现对这些重要连接构件所承受约束反力的控制。应用微分变换法推导含附加支承的梁结构支承约束反力及其对于附加支承位置和刚度的灵敏度表达式,并通过优化设计附加支承位置和刚度实现具有弹性约束端的简支梁结构各支承约束反力的平衡,可提高结构的动力学性能。 相似文献
38.
为了提升大型载货车、专用车用变速箱分离机构分离性能,满足大离合器盘分离需求,设计出一种分离机构.该机构通过机械原理实现放大输入端推力来满足离合器摩擦片分离.该分离机构结构简单、成本低廉,值得推广. 相似文献
39.
本文开发了一种新型的方舱夹芯板用室温固化高强度环氧结构胶黏剂,验证了其物化特性、相关力学性能和环境适应性。结果表明此胶黏剂具有优良性能,可以满足方舱用大板胶黏剂的使用需求。 相似文献
40.
Lili Hao Jiaxiang Li Peng Wang Zongliang Wang Zhenxu Wu Yu Wang Zixue Jiao Min Guo Tongfei Shi Qigang Wang Yoshihiro Ito Yen Wei Peibiao Zhang 《Advanced functional materials》2021,31(15):2009661
The degradation behavior of implants is significantly important for bone repair. However, it is still unprocurable to spatiotemporally regulate the degradation of the implants to match bone ingrowth. In this paper, a magneto-controlled biodegradation model is established to explore the degradation behavior of magnetic scaffolds in a magnetothermal microenvironment generated by an alternating magnetic field (AMF). The results demonstrate that the scaffolds can be heated by magnetic nanoparticles (NPs) under AMF, which dramatically accelerated scaffold degradation. Especially, magnetic NPs modified by oleic acid with a better interface compatibility exhibit a greater heating efficiency to further facilitate the degradation. Furthermore, the molecular dynamics simulations reveal that the enhanced motion correlation between magnetic NPs and polymer matrix can accelerate the energy transfer. As a proof-of-concept, the feasibility of magneto-controlled degradation for implants is demonstrated, and an optimizing strategy for better heating efficiency of nanomaterials is provided, which may have great instructive significance for clinical medicine. 相似文献