全文获取类型
收费全文 | 157186篇 |
免费 | 2530篇 |
国内免费 | 827篇 |
专业分类
电工技术 | 3336篇 |
技术理论 | 2篇 |
综合类 | 525篇 |
化学工业 | 25118篇 |
金属工艺 | 6095篇 |
机械仪表 | 5259篇 |
建筑科学 | 4930篇 |
矿业工程 | 578篇 |
能源动力 | 4055篇 |
轻工业 | 17599篇 |
水利工程 | 1232篇 |
石油天然气 | 1024篇 |
武器工业 | 56篇 |
无线电 | 21116篇 |
一般工业技术 | 29484篇 |
冶金工业 | 24018篇 |
原子能技术 | 2374篇 |
自动化技术 | 13742篇 |
出版年
2021年 | 1017篇 |
2019年 | 1001篇 |
2018年 | 1261篇 |
2017年 | 1340篇 |
2016年 | 1448篇 |
2015年 | 1291篇 |
2014年 | 2077篇 |
2013年 | 6951篇 |
2012年 | 3568篇 |
2011年 | 5001篇 |
2010年 | 3923篇 |
2009年 | 4433篇 |
2008年 | 4930篇 |
2007年 | 5174篇 |
2006年 | 4649篇 |
2005年 | 4346篇 |
2004年 | 4169篇 |
2003年 | 4036篇 |
2002年 | 4053篇 |
2001年 | 4077篇 |
2000年 | 3834篇 |
1999年 | 3821篇 |
1998年 | 6751篇 |
1997年 | 5334篇 |
1996年 | 4539篇 |
1995年 | 3770篇 |
1994年 | 3406篇 |
1993年 | 3220篇 |
1992年 | 2811篇 |
1991年 | 2709篇 |
1990年 | 2642篇 |
1989年 | 2627篇 |
1988年 | 2465篇 |
1987年 | 2173篇 |
1986年 | 2120篇 |
1985年 | 2558篇 |
1984年 | 2321篇 |
1983年 | 2197篇 |
1982年 | 2071篇 |
1981年 | 1992篇 |
1980年 | 1863篇 |
1979年 | 1875篇 |
1978年 | 1770篇 |
1977年 | 2087篇 |
1976年 | 2562篇 |
1975年 | 1583篇 |
1974年 | 1430篇 |
1973年 | 1453篇 |
1972年 | 1196篇 |
1971年 | 1117篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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.
Nengbing Long Yanqing Fu Tianxiang Xu Dashuang Ding Shaoqian Zhang Shengzhi Sun Shiliang Kang Tiefeng Xu Shixun Dai Qiuhua Nie Changgui Lin 《Journal of the European Ceramic Society》2021,41(8):4584-4589
The confinement of CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) in a stabilized inorganic glass matrix is a new strategy for improving their long-term stability and promoting their applications in the optoelectronic field. Here, in situ nanocrystallization strategy is developed to precipitate CsPbBr3?xIx NCs with arbitrary I/Br ratio among an elaborately designed GeS2–Sb2S3-based chalcogenide glass matrix. Spherical CsPbBr3?xIx NCs are homogeneously distributed in the glass matrix after thermal treatment. The photoluminescence (PL) spectra show that the emission peaks of CsPbBr3?xIx NCs can be tuned from 570 nm to 722 nm with the replacement of Br by I. The fs transient absorption (TA) spectra reveal that there exists some structural defects in the NCs, leading to short PL decay life. This work would shed light on confining CsPbX3 NCs into glassy matrices, facilitating their future applications in photoelectronic fields. 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.
Fischer-Tropsch synthesis of the CO2 in biogas aims at producing light hydrocarbons and increasing its calorific value for feeding into the grid. Fe catalysts with Mn and K as promoters are supposed to yield high amounts of light hydrocarbons. Using a Fe-Mn-K/MgO catalyst, a parameter screening and long-term experiments were carried out. The catalyst shows, within the examined range, the highest selectivity to C2–C4 hydrocarbons at 450 °C, 8 bar(a), and a gas hourly space velocity of 350 h−1. Calcination of the catalyst resulted in a significant drop of activity and an almost complete loss of selectivity to hydrocarbons. Admixture of steam to the reactant gas lowers the tendency to carbon deposition but also promotes the water-gas shift reaction and results in lower yields of hydrocarbons. 相似文献
8.
9.
10.
Xiaoyan Qiu Yongqiang Zhang Haitao Wu Rui Yang Jun Yang Rongjuan Liu Yong Liu Zhiping Zhou Tongfan Hao Yijing Nie 《Polymer International》2019,68(2):218-224
The crystallization of capped ultrathin polymer films is closely dependent on film thickness and interfacial interaction. Using dynamic Monte Carlo simulations, the crystallization behaviors of polymer films confined between two substrates were investigated. The crystallization rate of confined polymers is reduced with high interfacial interactions. Above a critical strength of interfacial interaction, polymer crystallization in the thin film is inhibited within the simulation time scales. An increase in film thickness leads to a rise in critical interfacial interaction. In thicker films, the chains have more space to change conformation to form crystal stems. In addition, there are fewer absorbed segments in confined chains for the thicker films, and thus the chains have stronger ability to adjust their conformation. Therefore an increase in film thickness can cause a reduction in the entropic barrier required for the formation of crystals and thus an increase in the critical interfacial interaction. © 2018 Society of Chemical Industry 相似文献