全文获取类型
收费全文 | 184630篇 |
免费 | 4458篇 |
国内免费 | 1844篇 |
专业分类
电工技术 | 4615篇 |
综合类 | 2118篇 |
化学工业 | 29983篇 |
金属工艺 | 7314篇 |
机械仪表 | 6819篇 |
建筑科学 | 7428篇 |
矿业工程 | 994篇 |
能源动力 | 4961篇 |
轻工业 | 19344篇 |
水利工程 | 1624篇 |
石油天然气 | 2456篇 |
武器工业 | 215篇 |
无线电 | 24426篇 |
一般工业技术 | 33090篇 |
冶金工业 | 25491篇 |
原子能技术 | 2770篇 |
自动化技术 | 17284篇 |
出版年
2022年 | 1216篇 |
2021年 | 1887篇 |
2020年 | 1380篇 |
2019年 | 1558篇 |
2018年 | 1878篇 |
2017年 | 2081篇 |
2016年 | 2126篇 |
2015年 | 2175篇 |
2014年 | 3233篇 |
2013年 | 8424篇 |
2012年 | 5129篇 |
2011年 | 6710篇 |
2010年 | 5354篇 |
2009年 | 5915篇 |
2008年 | 6362篇 |
2007年 | 6597篇 |
2006年 | 6086篇 |
2005年 | 5674篇 |
2004年 | 5077篇 |
2003年 | 4870篇 |
2002年 | 4881篇 |
2001年 | 4787篇 |
2000年 | 4630篇 |
1999年 | 4660篇 |
1998年 | 7568篇 |
1997年 | 5988篇 |
1996年 | 5217篇 |
1995年 | 4344篇 |
1994年 | 3843篇 |
1993年 | 3627篇 |
1992年 | 3093篇 |
1991年 | 2912篇 |
1990年 | 2861篇 |
1989年 | 2772篇 |
1988年 | 2591篇 |
1987年 | 2256篇 |
1986年 | 2191篇 |
1985年 | 2610篇 |
1984年 | 2358篇 |
1983年 | 2225篇 |
1982年 | 2098篇 |
1981年 | 2011篇 |
1980年 | 1879篇 |
1979年 | 1884篇 |
1978年 | 1774篇 |
1977年 | 2095篇 |
1976年 | 2572篇 |
1975年 | 1586篇 |
1974年 | 1436篇 |
1973年 | 1461篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Kelin Hu Feipeng Wang Yuyang Yan Hongcheng Liu Zijia Shen 《Ceramics International》2021,47(11):15228-15236
In this paper, a novel hybrid structure of Pd doped ZnO/SnO2 heterojunction nanofibers with hexagonal ZnO columns was one step synthesized from electrospun precursor nanofibers. Due to the synergistic effect of hexagonal ZnO, SnO2 and Pd, the structure exhibited excellent hydrogen (H2) gas sensing properties. At low-temperature of 120 °C, the response (Ra/Rg) to 100 ppm H2 gas exceeded 160, the response/recovery time was only 20 s and 6 s respectively and the limit of detection was only 0.5 ppm. Meanwhile, it also had good selectivity for H2 gas and excellent linearity. In addition, the materials were characterized by XRD, FESEM, HRTEM, XPS, and the synthesis mechanism and gas sensing mechanism were proposed. 相似文献
2.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration. 相似文献
3.
Reliable joints of Ti3SiC2 ceramic and TC11 alloy were diffusion bonded with a 50 μm thick Cu interlayer. The typical interfacial structure of the diffusion boned joint, which was dependent on the interdiffusion and chemical reactions between Al, Si and Ti atoms from the base materials and Cu interlayer, was TC11/α-Ti + β-Ti + Ti2Cu + TiCu/Ti5Si4 + TiSiCu/Cu(s, s)/Ti3SiC2. The influence of bonding temperature and time on the interfacial structure and mechanical properties of Ti3SiC2/Cu/TC11 joint was analyzed. With the increase of bonding temperature and time, the joint shear strength was gradually increased due to enhanced atomic diffusion. However, the thickness of Ti5Si4 and TiSiCu layers with high microhardness increased for a long holding time, resulting in the reduction of bonding strength. The maximum shear strength of 251 ± 6 MPa was obtained for the joint diffusion bonded at 850 °C for 60 min, and fracture primarily occurred at the diffusion layer adjacent to the Ti3SiC2 substrate. This work provided an economical and convenient solution for broadening the engineering application of Ti3SiC2 ceramic. 相似文献
4.
Kamar M. S. Shalan A. S. Youssef W. M. Hussein A. E. M. Khawassek Y. M. Taha M. H. 《Radiochemistry》2022,64(2):244-256
Radiochemistry - Ferrugination, sericitization, desulfitization, chloritization, and kaolinitization of hydrothermal origin are the main wall rock alterations occurring within the NNW shear zones... 相似文献
5.
Yajing Qi Yuying Yang Alkassoumi Hassane Hamadou Qiuyun Shen Bin Xu 《International Journal of Food Science & Technology》2022,57(4):2104-2112
Wheat bran is rich in functional ingredients, but the high level of lipase limits its applications. Tempering–preservation treatment (at 70–90 °C with moisture of 20%–40% for 1–4 h) was exploited for stabilising wheat bran and its effect on polyphenols was investigated. The results showed that more lipase was inactivated at higher tempering moisture, temperature and longer time. The optimum condition for inactivation of wheat bran lipase was 30% moisture and 90 °C for 4 h. The inactivation rate reached 93.8% with a residual enzyme activity of 0.264 U g−1. Under the optimum condition, the sum of free phenolic acids rose from 25.4 to 55.8 µg g−1. As for bound phenolic acids, there was a slight increase of hydroxybenzoic acid derivatives but a slight decrease of hydroxycinnamic acid derivatives. The total contents of phenolic acids before and after stabilisation were not significantly different. This study showed the possibility of using tempering–preservation as an efficient method for inactivation of wheat bran lipase while maintaining its phenolic compounds, which could be used in the production of whole wheat flour. 相似文献
6.
Tuladhar Sanira Alsadoon Abeer Prasad P. W. C. Ali Akbas Ezaldeen Alrubaie Ahmad 《Multimedia Tools and Applications》2022,81(17):23845-23865
Multimedia Tools and Applications - Gastrointestinal stromal tumor is one of the critical tumors that doctors do not suggest to get frequent endoscopy, so there is a need for a diagnosis system... 相似文献
7.
Telecommunication Systems - Machine to Machine technology has a broad application prospect in the 5G network, but there is a bottleneck in the energy consumption of intelligent devices powered by... 相似文献
8.
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
9.
Science China Technological Sciences - Accurate modelling of lithium ion batteries is crucial for battery management in electric vehicles. Recent studies have revealed the fractional order nature... 相似文献
10.