全文获取类型
收费全文 | 25806篇 |
免费 | 3293篇 |
国内免费 | 1969篇 |
专业分类
电工技术 | 1845篇 |
综合类 | 1721篇 |
化学工业 | 3023篇 |
金属工艺 | 949篇 |
机械仪表 | 1597篇 |
建筑科学 | 147篇 |
矿业工程 | 332篇 |
能源动力 | 1402篇 |
轻工业 | 519篇 |
水利工程 | 40篇 |
石油天然气 | 284篇 |
武器工业 | 206篇 |
无线电 | 7647篇 |
一般工业技术 | 2711篇 |
冶金工业 | 195篇 |
原子能技术 | 136篇 |
自动化技术 | 8314篇 |
出版年
2024年 | 43篇 |
2023年 | 1245篇 |
2022年 | 1009篇 |
2021年 | 1152篇 |
2020年 | 1376篇 |
2019年 | 959篇 |
2018年 | 984篇 |
2017年 | 1622篇 |
2016年 | 1729篇 |
2015年 | 1726篇 |
2014年 | 2106篇 |
2013年 | 2093篇 |
2012年 | 2638篇 |
2011年 | 2527篇 |
2010年 | 1832篇 |
2009年 | 1834篇 |
2008年 | 1200篇 |
2007年 | 1491篇 |
2006年 | 1199篇 |
2005年 | 499篇 |
2004年 | 211篇 |
2003年 | 214篇 |
2002年 | 254篇 |
2001年 | 228篇 |
2000年 | 176篇 |
1999年 | 206篇 |
1998年 | 61篇 |
1997年 | 20篇 |
1996年 | 26篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 30篇 |
1976年 | 27篇 |
1975年 | 24篇 |
1974年 | 22篇 |
1973年 | 26篇 |
1972年 | 17篇 |
1971年 | 23篇 |
1970年 | 21篇 |
1968年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Wireless Personal Communications - This research work explores the neural network learning capabilities by using a multi-layer perceptron artificial neural network to predict signal power loss by... 相似文献
2.
《Ceramics International》2021,47(23):32747-32755
To investigate the nonstoichiometric effect of (Bi0.5Na0.5)TiO3 (BNT) ceramics on their properties, we propose a novel chemical expression, (Bi0.5+xNa0.5−3x)TiO3. The nonstoichiometric effect of BNT can be explored in compounds with this composition without being hampered by the charge imbalance problem. With x ranging from −0.02 to 0.02, we find that the morphological, dielectric, ferroelectric, and electrostrain properties differ considerably between Na-rich and Bi-rich ceramic samples. The average grain size (AGS) increased significantly in Na-rich samples compared to that in stoichiometric BNT, while it decreased slightly in Bi-rich samples. The dielectric characteristics measured from 30 °C to 500 °C indicate that conductivity is activated in Na-rich nonstoichiometric samples but is effectively suppressed in Bi-rich nonstoichiometric samples. The ferroelectric properties also show the same trend. In Na-rich samples, elliptical polarization against electric field (P-E) hysteresis loops were detected, indicating a conductive character induced by high electric field loading. However, saturated P-E loops are observed in Bi-rich samples with well-inhibited conductivity. Furthermore, compared to stoichiometric BNT and nonstoichiometric x = 0.02 Bi-rich samples, (Bi0.5+xNa0.5−3x)TiO3 samples with x = 0.01 exhibit higher electrostrain from 30 °C to 150 °C. Based on the assumption of charge balance, our findings indicated that the presence of 1 mol% excess Bi would facilitate significant improvement in the dielectric, ferroelectric, and electrostrain properties of BNT and BNT-based systems. 相似文献
3.
4.
Wireless Networks - TCP latency is critical to the performance of Web services. However, packet loss greatly impairs the TCP performance due to its poor loss recovery mechanisms. Recent work FUSO... 相似文献
5.
Shucheng Qin Zhenrong Jia Lei Meng Can Zhu Wenbin Lai Jinyuan Zhang Wenchao Huang Chenkai Sun Beibei Qiu Yongfang Li 《Advanced functional materials》2021,31(25):2102361
Organic solar cells (OSCs) have recently reached a remarkably high efficiency and become a promising technology for commercial application. However, OSCs with top efficiency are mostly processed by halogenated solvents and with additives that are not environmentally friendly, which hinders large-scale manufacture. In this study, high-performance tandem OSCs, based on polymer donors and two small-molecule acceptors with different bandgaps, are fabricated by solution processing with non-halogenated solvents without additive. Importantly, the two active layers developed from non-halogenated solvents show better phase segregation and charge transport properties, leading to superior performance than halogenated ones. As a result, a tandem OSC with high efficiency of up to 16.67% is obtained, showing unique advantages in future massive production. 相似文献
6.
《Journal of the European Ceramic Society》2021,41(15):7886-7892
To elucidate the crystal growth process of hematite in high-temperature lead-free multicomponent alkali borosilicate glass, which is essentially important to control the color of red overglaze enamels, frit and hematite mixture is heat-treated and subjected to microscopic observations. Hematite particles slightly grew due to sintering at low temperature. Once the glass matrix formed near the softening point of frit, hematite dissolved into glass fluid. Hematite crystal growth concomitantly ensued with decrease in the number of hematite particles via Ostwald ripening as the temperature increased. The grown particles exhibited an anisotropic morphology with straight outlines reflecting crystal planes, the morphology of which is completely different from those grown by sintering and particles prior to heating. These results suggest that comprehensive understanding of frit and hematite from the perspectives of glass science and chemistry as well as powder technology are important to truly control the color of red overglaze enamels. 相似文献
7.
Junqi Chen Weishuang Fang Yifan Zhai Feihu Li Ying Tang Jie Li Huanhuan Guo Liang Fang 《Journal of the European Ceramic Society》2021,41(8):4473-4477
Orthorhombic-structured CaIn2O4 ceramics with a space group Pca21 were synthesized via a solid-state reaction method. A high relative density (95.6 %) and excellent microwave dielectric properties (εr ~11.28, Qf = 74,200 GHz, τf ~ ?4.6 ppm/°C) were obtained when the ceramics were sintered at 1375 °C for 6 h. The dielectric properties were investigated on the basis of the Phillips–Van Vechten–Levine chemical bond theory. Results indicated that the dielectric properties were mainly determined by the InO bonds in the CaIn2O4 ceramics. These bonds contributed more (74.65 %) to the dielectric constant than the CaO bonds (25.35 %). Furthermore, the intrinsic dielectric properties of the CaIn2O4 ceramics were investigated via infrared reflectivity spectroscopy. The extrapolated microwave dielectric properties were εr ~10.12 and Qf = 112,200 GHz. Results indicated that ion polarization is the main contributor to the dielectric constant in microwave frequency ranges. 相似文献
8.
《Ceramics International》2021,47(24):34845-34850
The interfacial delamination of electrode/ceramic multilayer structure will seriously damage the reliability of low temperature co-fired ceramic (LTCC) module in practical applications. In this work, three kinds of glasses employed in Au electrode are designed and prepared to study the abnormal expansion and delamination process in the Au/ceramic LTCC multilayer structure. The interfacial delamination in the co-fired structure is found to be attributed to the abnormal expansion of glass in respect to Au electrode at high temperature, which is originated from the enlarged closed pores during the co-firing process. This conclusion is further confirmed by co-firing the sample in a low-pressure condition. The mechanism and elimination of interfacial delamination here provides a feasible solution for the design of novel glasses in Au electrode for LTCC applications. 相似文献
9.
A superhydrophobic ceria-based composite coating is developed to improve anticorrosion properties of AZ61 magnesium alloy, fabricating via chemical conversion method followed by hydrothermal treatment. The cerium conversion coating has a block structure with microcracks. After the hydrothermal treatment, a dense CeO2 layer, porous CeO2 nanorods, and stearic absorbing layers are grown stepwise on the conversion coating. And the composite coating is hydrophobic or even superhydrophobic and has almost no microcracks. As the hydrothermal reaction time increases, the water contact angle of the composite coating first increases and then decreases, and it reaches the maximum value of 152° after hydrothermal treatment for 4 h. Both the dense CeO2 layer and the superhydrophobic stearic absorbing layer can effectively prevent the electrolyte from contacting the substrate; the corrosion current density of the superhydrophobic composite coating is lower than that of the hydrophilic composite coating and the cerium conversion coating, and has the best corrosion resistance. 相似文献
10.
《International Journal of Hydrogen Energy》2022,47(6):3580-3586
Renewable electricity-powered hydrogen production is an attractive alternative to unsustainable industrial processes, but the large-scale implantation of such sustainable technology still requires efficient and noble-metal-free electrocatalysts for driving cathodic hydrogen evolution reaction (HER), especially under alkaline conditions. In this paper, CoP nanowire array was in-situ developed on porous graphite felt (CoP/GF) as a new 3D electrocatalyst in facilitating hydrogen evolution electrocatalysis. This CoP/GF presents outstanding HER activity, requiring a low overpotential of 130 mV to deliver a current density of 20 mA cm?2 as tested in 1.0 M KOH. Furthermore, this free-standing catalyst exhibits impressive long-term durability of up to 50 h under working conditions. 相似文献