全文获取类型
收费全文 | 140862篇 |
免费 | 13439篇 |
国内免费 | 7860篇 |
专业分类
电工技术 | 9949篇 |
技术理论 | 6篇 |
综合类 | 12263篇 |
化学工业 | 21441篇 |
金属工艺 | 7946篇 |
机械仪表 | 9255篇 |
建筑科学 | 11336篇 |
矿业工程 | 4036篇 |
能源动力 | 3917篇 |
轻工业 | 11822篇 |
水利工程 | 3107篇 |
石油天然气 | 7075篇 |
武器工业 | 1453篇 |
无线电 | 15795篇 |
一般工业技术 | 14735篇 |
冶金工业 | 5732篇 |
原子能技术 | 1634篇 |
自动化技术 | 20659篇 |
出版年
2024年 | 500篇 |
2023年 | 1939篇 |
2022年 | 3983篇 |
2021年 | 5492篇 |
2020年 | 4161篇 |
2019年 | 3386篇 |
2018年 | 3748篇 |
2017年 | 4185篇 |
2016年 | 3836篇 |
2015年 | 5522篇 |
2014年 | 7484篇 |
2013年 | 8655篇 |
2012年 | 9964篇 |
2011年 | 10890篇 |
2010年 | 9935篇 |
2009年 | 9403篇 |
2008年 | 9655篇 |
2007年 | 9136篇 |
2006年 | 8746篇 |
2005年 | 7243篇 |
2004年 | 5297篇 |
2003年 | 4584篇 |
2002年 | 4764篇 |
2001年 | 4048篇 |
2000年 | 3242篇 |
1999年 | 2740篇 |
1998年 | 1848篇 |
1997年 | 1510篇 |
1996年 | 1461篇 |
1995年 | 1120篇 |
1994年 | 914篇 |
1993年 | 669篇 |
1992年 | 494篇 |
1991年 | 366篇 |
1990年 | 278篇 |
1989年 | 252篇 |
1988年 | 226篇 |
1987年 | 134篇 |
1986年 | 85篇 |
1985年 | 52篇 |
1984年 | 39篇 |
1983年 | 29篇 |
1982年 | 34篇 |
1981年 | 18篇 |
1980年 | 34篇 |
1979年 | 26篇 |
1976年 | 5篇 |
1971年 | 3篇 |
1959年 | 6篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
21.
Sun Yehan Su Qingtang Wang Huanying Wang Gang 《Multimedia Tools and Applications》2022,81(5):6091-6113
Multimedia Tools and Applications - With the rapid development of the Internet, the color digital image copyright protection is facing severe challenges. Simultaneously, the color digital images... 相似文献
22.
Yuan-Xia Wang Ying Shi Chen-Chen Wang Jia-Hui Cheng Ying Wang Wen-Jun Shao Li-Zhi Liu 《应用聚合物科学杂志》2021,138(27):50651
Crosslinking of polyolefin elastomer (POE, ENGAGE™ 8480) with Dicumyl Peroxide (DCP) can have effects on its crystallization dynamics, crystal structure, and properties. The POE crosslinked uniformly has significantly lower crystalline ability than the one with only amorphous phase crosslinked, which, in turn, has weaker crystalline ability than neat POE. The crystallinity and melting point depend on how the POE is crosslinked. The neat POE and POE crosslinked in amorphous phase only, are investigated with DSC and in-situ tensile/synchrotron radiation (WAXD/SAXS). In situ tensile/synchrotron X-ray during a uniaxial stretching process indicates that severe crystal fragmentation is observed at a strain around 45%, and with further increase in strain. The stress in the crosslinked POE is significantly larger than neat POE. For both samples, crystal orientation increases sharply within the strain range up to 88% where orientation-induced new crystals aligned in stretching direction are observed. The long period increases more in stretching direction for the crosslinked POE, consistent with larger stress in this sample, and the stress difference is more pronounced at large strains (27.3 vs. 10.9 MPa at a strain 435%). Permanent set of the crosslinked POE is smaller, consistent with less oriented crystals observed after the test for permanent set. 相似文献
23.
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
25.
Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB2provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB2and(1-100)NbB2surface can be substituted by Al to form(Al,Nb)B2intermedia layers.In addition,a layer of NbAl3-like compound(NbAl3')can cover the surface of NbB2with the orientation relation of(1-100)[11-20]NbB2//(110)[110]NbAl3'.Both of the(Al,Nb)B2and NbAl3'intermedia layers contribute to enhancing the nucleation potency of NbB2particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys. 相似文献
26.
Borazine rings act as a pivotal part in siliconboroncarbonitride ceramics (SiBCN) for high-temperature stability and great resistance to crystallization. A detailed investigation of the ring formation mechanism will guide the design and synthesis of SiBCN to meet application requirements under extreme conditions. Boron trichloride (BCl3) and hexamethyldisilazane (HN(SiMe3)2) are common raw materials for the synthesis of precursors for SiBCN. In this paper, quantum chemical calculation was used to study the cyclization reaction mechanism between BCl3 and HN(SiMe3)2 to form trichloroborazine (TCBZ) at the MP2/6-31G (d,p) level of theory. We discussed the structure properties, reaction pathways, energy barriers, reaction rates, and other aspects in detail. The results show that BCl3 and HN(SiMe3)2 alternately participate in the reaction process, accompanied by the release of trimethylchlorosilane (TMCS), and that the entire reaction shows an absolute advantage in terms of energy. In the Step by step reaction, lower reaction barriers are formed due to the introduction of BCl3 with more heat released compared to that for the introduction of HN(SiMe3)2. The final single-molecule cyclization and TMCS elimination steps are found to be faster compared to all previous bimolecular reactions. 相似文献
27.
28.
30.