全文获取类型
收费全文 | 404158篇 |
免费 | 12040篇 |
国内免费 | 4905篇 |
专业分类
电工技术 | 10898篇 |
技术理论 | 11篇 |
综合类 | 6734篇 |
化学工业 | 65307篇 |
金属工艺 | 17664篇 |
机械仪表 | 15390篇 |
建筑科学 | 15870篇 |
矿业工程 | 4884篇 |
能源动力 | 9979篇 |
轻工业 | 33025篇 |
水利工程 | 4939篇 |
石油天然气 | 13225篇 |
武器工业 | 708篇 |
无线电 | 45520篇 |
一般工业技术 | 72094篇 |
冶金工业 | 58650篇 |
原子能技术 | 8866篇 |
自动化技术 | 37339篇 |
出版年
2022年 | 3808篇 |
2021年 | 6090篇 |
2020年 | 4651篇 |
2019年 | 4563篇 |
2018年 | 6719篇 |
2017年 | 7041篇 |
2016年 | 6943篇 |
2015年 | 6401篇 |
2014年 | 9284篇 |
2013年 | 18727篇 |
2012年 | 13658篇 |
2011年 | 16772篇 |
2010年 | 14083篇 |
2009年 | 15091篇 |
2008年 | 15383篇 |
2007年 | 14889篇 |
2006年 | 14167篇 |
2005年 | 12984篇 |
2004年 | 10708篇 |
2003年 | 9987篇 |
2002年 | 9648篇 |
2001年 | 9353篇 |
2000年 | 9157篇 |
1999年 | 9724篇 |
1998年 | 17727篇 |
1997年 | 13643篇 |
1996年 | 10925篇 |
1995年 | 8550篇 |
1994年 | 7531篇 |
1993年 | 7098篇 |
1992年 | 5539篇 |
1991年 | 5225篇 |
1990年 | 4936篇 |
1989年 | 4880篇 |
1988年 | 4723篇 |
1987年 | 3970篇 |
1986年 | 3873篇 |
1985年 | 4416篇 |
1984年 | 4149篇 |
1983年 | 3780篇 |
1982年 | 3562篇 |
1981年 | 3683篇 |
1980年 | 3516篇 |
1979年 | 3450篇 |
1978年 | 3539篇 |
1977年 | 3992篇 |
1976年 | 5119篇 |
1975年 | 3210篇 |
1974年 | 3046篇 |
1973年 | 3065篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is... 相似文献
12.
Jia Dai Xiang Cheng Xiaofeng Li Zhisheng Wang Yufeng Wang Jing Zheng Jun Liu Jiawei Chen Changjin Wu Jinyao Tang 《Advanced functional materials》2021,31(48):2106204
Synthetic active matters are perfect model systems for non-equilibrium thermodynamics and of great potential for novel biomedical and environmental applications. However, most applications are limited by the complicated and low-yield preparation, while a scalable synthesis for highly functional microswimmers is highly desired. In this paper, an all-solution synthesis method is developed where the gold-loaded titania-silica nanotree can be produced as a multi-functional self-propulsion microswimmer. By applying light, heat, and electric field, the Janus nanotree demonstrated multi-mode self-propulsion, including photochemical self-electrophoresis by UV and visible light radiation, thermophoresis by near-infrared light radiation, and induced-charge electrophoresis under AC electric field. Due to the scalable synthesis, the Janus nanotree is further demonstrated as a high-efficiency, low-cost, active adsorbent for water decontamination, where the toxic mercury ions can be reclaimed with enhanced efficiency. 相似文献
13.
Ahmed Fathy Mohammad Ali Abdelkareem A.G. Olabi Hegazy Rezk 《International Journal of Hydrogen Energy》2021,46(8):6087-6099
Cell temperature and water content of the membrane have a significant effect on the performance of fuel cells. The current-power curve of the fuel cell has a maximum power point (MPP) that is needed to be tracked. This study presents a novel strategy based on a salp swarm algorithm (SSA) for extracting the maximum power of proton-exchange membrane fuel cell (PEMFC). At first, a new formula is derived to estimate the optimal voltage of PEMFC corresponding to MPP. Then the error between the estimated voltage at MPP and the actual terminal voltage of the fuel cell is fed to a proportional-integral-derivative controller (PID). The output of the PID controller tunes the duty cycle of a boost converter to maximize the harvested power from the PEMFC. SSA determines the optimal gains of PID. Sensitivity analysis is performed with the operating fuel cell at different cell temperature and water content of the membrane. The obtained results through the proposed strategy are compared with other programmed approaches of incremental resistance method, Fuzzy-Logic, grey antlion optimizer, wolf optimizer, and mine-blast algorithm. The obtained results demonstrated high reliability and efficiency of the proposed strategy in extracting the maximum power of the PEMFC. 相似文献
14.
氢脆具有很强的微观组织敏感性,威胁着各类高强结构材料的安全服役.采用激光-电弧复合焊工艺对BS960E型高强钢进行焊接,并对接头在原位电化学充氢的条件下进行慢应变速率(10-5s-1)拉伸试验,结合微观组织和断裂特征进行分析并对接头的氢脆行为进行研究.结果 表明,焊接热循环所形成的富马氏体中的细晶区可以使接头表现出一定的氢脆敏感性,马氏体较大的氢扩散系数和较低的氢溶解度以及氢在晶界上的快速扩散是引起接头对氢脆敏感的主要原因,通过控制焊接工艺参数可抑制焊接热循环所引起的马氏体转变量,能够降低BS960E型高强钢激光-电弧复合焊接头的氢脆敏感性. 相似文献
15.
Olga Yu Kurapova Sergey M. Shugurov Evgenia A. Vasil'eva Daniil A. Savelev Vladimir G. Konakov Sergey I. Lopatin 《Ceramics International》2021,47(8):11072-11079
Ceria-based solid solutions are important materials for high- and medium-temperature electrochemical applications. However, the stabilities of both binary and ternary ceria-based solid solutions are insufficient at elevated temperatures, which limits their application as solid electrolytes or SOFC cathodes. Data on the high-temperature stability of ceria-based ceramics are unavailable in the literature. In the present study, we report a thermodynamic stability investigation of Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions. The thermal prehistories of binary and ternary systems were investigated using STA, XRD, and ESCA techniques. The vaporization processes were investigated in the temperature range of 1577–2227°С via the Knudsen effusion mass spectrometry technique. Using data on the component activity in solid-phase thermodynamic properties of Y2O3-CeO2 solid solutions, which is represented as the Gibbs energy, the excess Gibbs energy was calculated as a function of the ceria mol. %. It was shown that the reduction of Ce4+ to Ce3+ in Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions corresponds to less-negative Gibbs energy compared to ZrO2-CeO2 solid solutions. 相似文献
16.
Electric nanogenerators that directly convert the energy of moving drops into electrical signals require hydrophobic substrates with a high density of static electric charge that is stable in “harsh environments” created by continued exposure to potentially saline water. The recently proposed charge-trapping electric generators (CTEGs) that rely on stacked inorganic oxide–fluoropolymer (FP) composite electrets charged by homogeneous electrowetting-assisted charge injection (h-EWCI) seem to solve both problems, yet the reasons for this success have remained elusive. Here, systematic measurements at variable oxide and FP thickness, charging voltage, and charging time and thermal annealing up to 230 °C are reported, leading to a consistent model of the charging process. It is found to be controlled by an energy barrier at the water-FP interface, followed by trapping at the FP-oxide interface. Protection by the FP layer prevents charge densities up to −1.7 mC m−2 from degrading and the dielectric strength of SiO2 enables charge decay times up to 48 h at 230 °C, suggesting lifetimes against thermally activated discharging of thousands of years at room temperature. Combining high dielectric strength oxides and weaker FP top coatings with electrically controlled charging provides a new paradigm for developing ultrastable electrets for applications in energy harvesting and beyond. 相似文献
17.
18.
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
19.
Zhang Qi Wang Yujing Zhang Xueling Song Jun Li Yinlei Wu Xuehong Yuan Kunjie 《Journal of Materials Science》2022,57(14):7208-7224
Journal of Materials Science - Form-stable composite phase change materials (C-PCMs) prepared by microencapsulation method and porous matrix adsorption method need for compression molding after... 相似文献
20.