全文获取类型
收费全文 | 68929篇 |
免费 | 6138篇 |
国内免费 | 3031篇 |
专业分类
电工技术 | 3861篇 |
技术理论 | 5篇 |
综合类 | 4111篇 |
化学工业 | 11595篇 |
金属工艺 | 4291篇 |
机械仪表 | 4504篇 |
建筑科学 | 5268篇 |
矿业工程 | 1990篇 |
能源动力 | 1927篇 |
轻工业 | 4482篇 |
水利工程 | 1052篇 |
石油天然气 | 3872篇 |
武器工业 | 542篇 |
无线电 | 8267篇 |
一般工业技术 | 9143篇 |
冶金工业 | 3487篇 |
原子能技术 | 744篇 |
自动化技术 | 8957篇 |
出版年
2024年 | 244篇 |
2023年 | 1231篇 |
2022年 | 1852篇 |
2021年 | 3140篇 |
2020年 | 2334篇 |
2019年 | 2037篇 |
2018年 | 2233篇 |
2017年 | 2309篇 |
2016年 | 2142篇 |
2015年 | 2810篇 |
2014年 | 3404篇 |
2013年 | 4132篇 |
2012年 | 4357篇 |
2011年 | 4833篇 |
2010年 | 4027篇 |
2009年 | 3879篇 |
2008年 | 3838篇 |
2007年 | 3590篇 |
2006年 | 3650篇 |
2005年 | 3113篇 |
2004年 | 2208篇 |
2003年 | 1969篇 |
2002年 | 1911篇 |
2001年 | 1601篇 |
2000年 | 1661篇 |
1999年 | 1713篇 |
1998年 | 1439篇 |
1997年 | 1193篇 |
1996年 | 1117篇 |
1995年 | 899篇 |
1994年 | 717篇 |
1993年 | 516篇 |
1992年 | 432篇 |
1991年 | 330篇 |
1990年 | 253篇 |
1989年 | 233篇 |
1988年 | 166篇 |
1987年 | 122篇 |
1986年 | 88篇 |
1985年 | 63篇 |
1984年 | 50篇 |
1983年 | 48篇 |
1982年 | 39篇 |
1981年 | 27篇 |
1980年 | 34篇 |
1979年 | 18篇 |
1978年 | 16篇 |
1976年 | 18篇 |
1975年 | 10篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Wenyun Yang Qiwei Hu Guanyi Qiao Liang Zha Shunquan Liu Jingzhi Han Honglin Du Yan Zhang Yingchang Yang Changsheng Wang 《中国稀土学报(英文版)》2019,37(10):1102-1107
In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2Fe17 compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2Fe17 compounds, making the R2Fe17–xSix-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (fRL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ ?10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm1.5Y0.5Fe15Si2-paraffin composite (d = 1.0 mm) and the maximum RL of ?53.6 dB is achieved for Nd2Fe15Si2-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites. 相似文献
82.
根据新平大红山铁铜矿床探采工程揭露控制情况和以往地质工作成果,结合矿区成矿地质条件及矿床地质特征,系统分析了大红山铁铜成矿控制因素及其控矿作用。研究表明:大红山铁、铜矿成矿物质主要来源于古海底火山活动,此后矿床又经后期变质作用、构造及与岩体侵入有关的热液活化等多期地质作用改造;在诸多成矿控制因素中,地层、构造控制着矿体的产出和分布;岩性岩相控制着矿体及矿石类型;火山喷发—沉积旋回、火山活动中心控制了矿床类型及规模;岩体侵入相关的热液活动对矿床起到进一步的改造和富集作用。 相似文献
83.
84.
Mohammad Reza Gaeeni Morteza Sasani Ghamsari Abbas Majd Abadi Mohammad Hossein Majles Ara Wooje Han Hyung‐Ho Park 《Journal of the American Ceramic Society》2015,98(6):1818-1822
A facile sol–gel procedure has been developed for the synthesis of colloidal alumina nanocrystals. For the first time, optical characterization procedures were employed to study the quantum confinement effects in optical properties of the prepared Al2O3 sol. Accordingly, the hyperbolic band model was used to determine the optical band gap of colloidal alumina nanocrystals. X‐Ray diffraction pattern was used to study the crystallographic phase of the dried gel. Morphological characterization was performed using scanning electron microscopy (SEM). Inductively Coupled Plasma (ICP) emission spectroscopy was used to determination purity of the Al2O3 powder. High‐resolution TEM showed that the diameter of colloidal nanocrystals is about 10 nm. Photoluminescence spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 68% with 300 nm excitation wavelength. The experimental observations confirm that highly stable alumina sol with strong UV emission was synthesized. The mentioned optical properties have not been reported before. 相似文献
85.
Shuaishuai Ding Yuan Tian Xiang Liu Ye Zou Huanli Dong Wenbo Mi Wenping Hu 《Nano Research》2021,14(1):304-310
The spinterface formed between ferromagnetic(FM)electrode and organic materials is vital for performance optimization in organic spin valve(OSV).Half-metallic Fe3O4with drastic change in structure,conductivity and magnetic property near Verwey transition can serve as an intrinsic spinterface regulator.However,such modulating effect of Fe3O4in OSV has not been comprehensively investigated,especially below the Verwey transition temperature(Tv).Here,we highlight the important role of Fe3O4electrode in reliable-working and controllable Fe3O4/P3HT/Co polymer spin valves by investigating the magnetoresistance(MR)above and below 7V.In order to distinguish between different contributions to charge transport and related MR responses,the systematic electronic and magnetic characterizations were carried out in full temperature range.Particularly,the first-order metal-insulator transition in Fe3O4has a dramatic effect on the MR enhancement of polymer spin valves at 7V.Moreover,both the conducting mode transformation and MR line shape modulation could be accomplished across 7V.This research renders unique scenario to multimodal storage by external thermodynamic parameters,and further reveals the importance of spin-dependent interfacial modification in polymer spin valves. 相似文献
86.
Natural Computing - The fiber stretching process plays the key role in the process of fiber production and its effects is measured by the stretching ratio. The stretching ratio is determined by the... 相似文献
87.
88.
89.
介绍了如何配置与优化水电厂的自动化元件,其配置选型应以可靠实用、结构简单、便于维护为原则,同时还应结合电厂的各种介质特点、设备运行方式、控制方式等因素综合考虑. 相似文献
90.