全文获取类型
收费全文 | 39838篇 |
免费 | 3306篇 |
国内免费 | 1903篇 |
专业分类
电工技术 | 2583篇 |
技术理论 | 3篇 |
综合类 | 3589篇 |
化学工业 | 6058篇 |
金属工艺 | 2468篇 |
机械仪表 | 2843篇 |
建筑科学 | 3042篇 |
矿业工程 | 1082篇 |
能源动力 | 1056篇 |
轻工业 | 3418篇 |
水利工程 | 925篇 |
石油天然气 | 1756篇 |
武器工业 | 447篇 |
无线电 | 3896篇 |
一般工业技术 | 3909篇 |
冶金工业 | 1574篇 |
原子能技术 | 468篇 |
自动化技术 | 5930篇 |
出版年
2024年 | 32篇 |
2023年 | 333篇 |
2022年 | 821篇 |
2021年 | 1210篇 |
2020年 | 972篇 |
2019年 | 780篇 |
2018年 | 889篇 |
2017年 | 989篇 |
2016年 | 966篇 |
2015年 | 1557篇 |
2014年 | 2007篇 |
2013年 | 2447篇 |
2012年 | 2926篇 |
2011年 | 3204篇 |
2010年 | 3051篇 |
2009年 | 2989篇 |
2008年 | 2918篇 |
2007年 | 2826篇 |
2006年 | 2730篇 |
2005年 | 2285篇 |
2004年 | 1690篇 |
2003年 | 1284篇 |
2002年 | 1289篇 |
2001年 | 1161篇 |
2000年 | 791篇 |
1999年 | 677篇 |
1998年 | 436篇 |
1997年 | 366篇 |
1996年 | 315篇 |
1995年 | 241篇 |
1994年 | 209篇 |
1993年 | 161篇 |
1992年 | 115篇 |
1991年 | 107篇 |
1990年 | 63篇 |
1989年 | 66篇 |
1988年 | 44篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 15篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1959年 | 3篇 |
1958年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
1.
Microbiologically influenced corrosion induced by bacteria has been studied for many years. Corrosion is known to be sensitive to the presence of microalgae, such as Phaeodactylum tricornutum. However, the life activity of P. tricornutum that influences the general and localized corrosion of carbon steel is not fully understood. The current study uses a combination of immersion tests and electrochemical experiments with a detailed surface characterization to reveal the naturally formed corrosion products with/without the presence of P. tricornutum. The results show that samples suffer from pitting corrosion and the averaged pit depths are approximately 15 μm under a light–dark cycle condition or a 24-h constant light condition. Meanwhile, the corrosion products are mainly comprised of γ-FeOOH and Fe3O4 in a constant light condition. However, γ-FeOOH, Fe3O4, and FeCO3 are found in a light–dark cycle. This study proposes the fundamental mechanisms of the effect of P. tricornutum life activities on the corrosion performance of Q235 carbon steel, to fulfill the knowledge gaps of the presence of microalgae inducing the general and pitting corrosion of carbon steel. 相似文献
2.
A new aqueous slurry-based laminated object manufacturing process for porous ceramics is proposed: firstly, an organic mesh sheet is pre-paved as a pore-forming template before slurry layer scraping; secondly, the 2D pattern is built with laser outline cutting of the dried mesh–ceramic composite layer; finally, the pore structure is formed after degreasing and sintering. Alumina parts with porosities of 51.5 %, round hole diameters of 80 ± 5 μm were fabricated using 70 wt. % solid content slurry and 100 mesh nylon net. Using an organic mesh as the framework and template not only reduces the risk of damage of the green body but also ensures the regularity, uniformity and connectivity of the micron scaled pore network. The layer-by-layer drying method avoids the delamination phenomenon and improves the paving density. The new method can realize the flexible design of the pore structure by using various organic mesh templates. 相似文献
3.
Qi Xiao Xinyao Dong Xiumei Yin Hong Wang Hua Zhong Mingming Xing Ying Tian Yao Fu Bin Dong Xixian Luo 《Journal of the American Ceramic Society》2021,104(3):1415-1423
Multicolor upconversion luminescence materials show significantly applications in materials science. In this paper, the novel Yb3+-sensitized Na3La(VO4)2 upconversion luminescence crystals are synthesized by the solid-state reaction method. Three primary colors upconversion luminescence are successfully achieved in Na3La(VO4)2:Yb3+,Tm3+, Na3La(VO4)2:Yb3+,Er3+, and Na3La(VO4)2:Yb3+,Ho3+ crystals excited by the single 980 nm LD. Multicolor upconversion luminescence can be obtained by simply adjusting the combination ratios of these three samples. Luminescence mechanisms of the Yb3+-sensitized system are discussed in detail. In the Na3La(VO4)2 host material, the Yb3+/Ho3+ codoped system exhibits unusual red upconversion luminescence based on the short decay time of Ho3+ ion 5I6 level, which provides the possibility of three primary color luminescence under 980 nm excitation. 相似文献
4.
新型建筑工业化具有高质量、低消耗、可循环发展等特征,其推广已上升到国家战略层面。利用演化博弈方法,建立“政府-开发商-银行” 的三方动态演化博弈模型,进行各博弈主体策略的演化稳定性分析,并针对初始状态、奖惩力度、借贷风险和开发成本等对演化结果的影响进行动态仿真。在此基础上, 考虑开发商群体的网络拓扑特征对演化真实性的影响,引入复杂网络理论, 以无标度网络为载体描述开发商个体的连接偏好和决策机制,构建政府监管下的建筑工业化扩散模型,并通过仿真深入研究相关因素对扩散深度的影响作用,最后结合仿真结果给出相应对策建议。 相似文献
6.
8.
Hua Zhu Hai Zhang Tian-hao Zhang Shi-jin Yu Ping-chun Guo Yan-xiang Wang Zhi-sheng Yang 《Ceramics International》2021,47(12):16980-16985
Indium Tin Oxide (ITO) films were prepared, at room temperature, on a fluorphlogopite substrate using magnetron sputtering technology. At various temperatures of 500 °C, 600 °C, 700 °C, 800 °C, and 900 °C, the samples were (had) annealed for 2 h (a 2-h duration). The results showed improvement in the crystalline performance of ITO film at selected annealing temperatures, with a significant reduction in resistivity at 800 °C. The lowest resistivity is 4.08 × 10?4 Ω-cm, which is nearly an order of magnitude lower than the unannealed sample. All samples have an average light transmittance above 85% in the visible light range (400–800 nm), and with increasing annealing temperature, the average light transmittance tends to decrease. Besides, at the sensitive wavelength of 550 nm, the light transmittance is as high as 93.74%. The sheet resistance testing of the sample was through the number of bending times, which revealed that with the increase of the number of bending, the sheet resistance increases. However, after 1200 bending times, the change rate of the sheet resistance remains below 5%. Thus, the ITO film prepared on the flexible fluorphlogopite substrate revealed excellent optical and electrical properties, good flexibility, and improved stability after high-temperature annealing, which guarantees successful application in flexible electronic devices. 相似文献
9.
Novel reddish-orange-emitting Ca2GdNbO6:Sm3+ phosphors based on the emission of 4G5/2 → 6H9/2 transition at 651 nm with the chromatic coordinate of (0.633, 0.366) were synthesized. The crystal structure and chemical purity were identified in detail. Under the 407 nm excitation, the optimum concentration of Sm3+ ion was found to be 5 mol% dominated by the dipole-dipole interaction in the Ca2GdNbO6 host material. The color purity of the sample with optimum doping was estimated to be about 78.38%. Besides, the thermal stability was also studied, and it was further found that the emission intensity remained 65.32% at 423 K. The packaged white LED device exhibited excellent CRI and CCT values of 92.43 and 4896 K. Finally, the polydimethylsiloxane film with a stable structure and flexible property was prepared. These above results reveal that novel reddish-orange-emitting Ca2GdNbO6:Sm3+ phosphors can be applied in high CRI white communication and flexible display applications. 相似文献
10.
Millicent Appiah Hua Hao Zheng Liu Shefiu Kareem Marwa Emmanuel Naomi Addai Asante Zhonghua Yao Minghe Cao Hanxing Liu 《Ceramics International》2021,47(17):24360-24371
In this study, the intermediate rare-earth oxide Gd2O3 (Gd) was substituted in different amounts (x = 0.2–2 mol%) for the formulation of BaTi1-xGdxO3-x/2 (BTGx) dielectric materials. The effect of B-site substitution was confirmed by the additional Raman active A1g octahedral peak at ~835cm-1 strengthened at x ≥ 0.4 mol%. Additionally, properties of 0.9BTG0.007-0.1BA dielectric ceramics were analysed based on the influence of various processing methods as a function of sintering temperature. The focal samples were labelled Method-A (direct-mix) and Method-B (indirect-mix). As the sintering temperature (1075–1200 °C) increased, the 1 kHz response of the ε–T curves of Method-A samples transformed from a single peak to broad-narrow double peaks of high dielectric loss tangent (tan δ). Nonetheless, samples of Method-B possessed a clearly defined transmission electron microscopy (TEM) core-shell structure, flattened double-peak ε-T curves, optimised dielectric properties (ε = ~1563–1851 and tan δ < 1.5% at room temperature), and a wide-ranging temperature behaviour that meets the X8R dielectric standards (ΔC/C25°C < ±15%). The maximum dielectric breakdown strength of Method-B samples reached ~131 kVcm, while the energy storage density was ~0.726 J/cm3 at a maximum efficiency of ~80% at 1100 °C. Thus, exhibiting good potentials for balancing temperature stability with energy storage applications. 相似文献