全文获取类型
收费全文 | 117893篇 |
免费 | 13078篇 |
国内免费 | 8522篇 |
专业分类
电工技术 | 9679篇 |
技术理论 | 2篇 |
综合类 | 10766篇 |
化学工业 | 16222篇 |
金属工艺 | 7476篇 |
机械仪表 | 8318篇 |
建筑科学 | 9732篇 |
矿业工程 | 3994篇 |
能源动力 | 3240篇 |
轻工业 | 11326篇 |
水利工程 | 3339篇 |
石油天然气 | 4864篇 |
武器工业 | 1405篇 |
无线电 | 13566篇 |
一般工业技术 | 11513篇 |
冶金工业 | 4777篇 |
原子能技术 | 1828篇 |
自动化技术 | 17446篇 |
出版年
2024年 | 670篇 |
2023年 | 2152篇 |
2022年 | 4526篇 |
2021年 | 5841篇 |
2020年 | 4361篇 |
2019年 | 3209篇 |
2018年 | 3371篇 |
2017年 | 3945篇 |
2016年 | 3562篇 |
2015年 | 5381篇 |
2014年 | 6751篇 |
2013年 | 8075篇 |
2012年 | 9198篇 |
2011年 | 9880篇 |
2010年 | 8898篇 |
2009年 | 8743篇 |
2008年 | 8644篇 |
2007年 | 8184篇 |
2006年 | 7250篇 |
2005年 | 5868篇 |
2004年 | 4090篇 |
2003年 | 2947篇 |
2002年 | 2742篇 |
2001年 | 2476篇 |
2000年 | 2061篇 |
1999年 | 1416篇 |
1998年 | 941篇 |
1997年 | 754篇 |
1996年 | 675篇 |
1995年 | 611篇 |
1994年 | 480篇 |
1993年 | 405篇 |
1992年 | 279篇 |
1991年 | 255篇 |
1990年 | 182篇 |
1989年 | 147篇 |
1988年 | 109篇 |
1987年 | 73篇 |
1986年 | 70篇 |
1985年 | 44篇 |
1984年 | 29篇 |
1983年 | 37篇 |
1982年 | 31篇 |
1981年 | 23篇 |
1980年 | 30篇 |
1979年 | 22篇 |
1976年 | 4篇 |
1967年 | 3篇 |
1959年 | 14篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Pengfei Liang Jie Zhu Di Wu Hui Peng Xiaolian Chao Zupei Yang 《Journal of the American Ceramic Society》2021,104(6):2702-2710
Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO2-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag+/Nb5+ co-doped (Ag1/4Nb3/4)xTi1−xO2 (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 103 and 1.6 × 104 at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics. 相似文献
2.
4.
边坡位移的时间序列曲线存在复杂的非线性特性,传统的预测模型精度不足以满足预测要求。为此提出了基于变分模态分解的鸟群优化-核极限学习机的预测模型,并用于河北省某水泥厂的边坡位移预测。该方法首先采用VMD把边坡位移序列分解为一系列的有限带宽的子序列,再对各子序列分别采用相空间重构并用核极限学习机预测,采用鸟群算法优化相空间重构的嵌入维度和KELM中惩罚系数和核参数三个数值,以取得最优预测模型。最后将各个子序列预测值叠加,得到边坡位移的最终预测值。结果表明:和KELM、BSA-KELM、EEMD-BSA-KELM模型相比,基于VMD的BSA-KELM预测精度更高,为边坡位移的预测提供一种有效的方法。 相似文献
5.
6.
7.
纤维素和几丁质具有相似的结构,是自然界中储量丰富的两类天然多糖。经2, 2, 6, 6-四甲基哌啶氮氧化物(TEMPO)氧化修饰制备的纤维素和几丁质纳米纤维,不仅具有多糖类物质的良好亲水性、生物可降解性、生物相容性及丰富的官能团(羟基、羧基、乙酰氨基和氨基等)所带来的特定化学性质,而且还具有纳米纤维的纳米尺寸效应、大比表面积、高表面活性、高结晶度和手性液晶相结构等特点,已成为生物质纳米材料领域的研究重点之一。本文对TEMPO氧化修饰制备天然多糖纳米纤维的方法及剥离机制进行了总结,同时重点综述了TEMPO氧化修饰的天然多糖纳米纤维在薄膜、凝胶、导电、医用、电磁屏蔽及环境等复合材料的增强和功能升级等方面的研究进展,强调了纤维素和几丁质纳米纤维的官能团及纳米尺寸在复合材料中的增效机制。最后,对天然多糖纳米纤维的发展方向及其在各领域应用的机遇与挑战进行了展望。 相似文献
8.
Oxide-based near infrared (IR)-shielding coatings consisting of quarter‐wave stacks of oxygen-deficient tantalum oxide (Ta2O5?x) and silicon oxide (SiO2) multilayers and tin-doped indium oxide (In2O3) (ITO) films with the thicknesses of 200–600 nm can block the passage of IR-A (wavelength: 760–1400 nm) and IR-B (wavelength: 1400–3000 nm) radiation, respectively. In this study, the optical properties and microstructure of these oxide-based IR-shielding coatings were investigated. Transmission electron microscopy images indicated that amorphous Ta2O5?x/amorphous SiO2 multilayers were uniform and dense. ITO films were found to be highly crystalline and show carrier concentrations of up to 7.1 × 1020 cm?3, resulting in the strong IR-B optical absorption due to the plasma excitation of the free carriers. Oxide-based IR-shielding coatings with an ITO thickness of 420 nm were found to have near-IR shielding rates of >90% and an average visible light transmittance of >70%. The effects of IR on human keratinocytes were studied to evaluate the IR-induced photoaging in human skin. It was found that the downregulation of cellular proliferation and the enhancement of senescence-associated β-galactosidase activity induced by IR irradiation were significantly inhibited by oxide-based IR-shielding coatings. Thus, this study provides a facile method for the development of coatings for smart windows with high IR-shielding ability and high visible light transmittance. 相似文献
9.
围绕人工智能与智慧海洋建设这条主线,论述人工智能、智慧海洋的概念,列举当前较为成熟的人工智能与海洋科技在海洋观测方面融合的切入点,初步展现一种海洋技术与装备智能化的发展路径,提出加快人工智能技术向智慧海洋建设赋能的几点建议。 相似文献
10.
Chunsheng Wang Yishuang Wang Mingqiang Chen Defang Liang Zhonglian Yang Wen Cheng Zhiyuan Tang Jun Wang Han Zhang 《International Journal of Hydrogen Energy》2021,46(7):5852-5874
Given the continuing issues of environment and energy, methane dry reforming for syngas production have sparked interest among researchers, but struggled with the process immaturity owing to catalyst deactivation. This review summarizes the recent advances in the development of efficient and stable catalysts with strong resistance to coking and metal sintering, including the application of novel materials, the assessment of advanced characterizations and the compatibility to improved reaction system. One feasible option is the crystalline oxide catalysts (perovskite, pyrochlore, spinel and LDHs), which feature a fine metal dispersion and surface confinement effect via a metal exsolution strategy and exhibit superior reactivity and stability. Some new materials (h-BN, clays and MOFs) also extend the option because of their unique morphology and microstructure. It also is elaborated that progresses were achieved in advanced characterizations application, leading to success in the establishment of reaction mechanisms and attributions to the formed robust catalysts. In addition, the perspective described the upgrade of reaction system to a higher reaction efficiency and milder reaction conditions. The combination of efficient reaction systems and robust catalysts paves a way for a scaling-up application of the process. 相似文献