全文获取类型
收费全文 | 70486篇 |
免费 | 6835篇 |
国内免费 | 4163篇 |
专业分类
电工技术 | 5809篇 |
技术理论 | 4篇 |
综合类 | 5605篇 |
化学工业 | 9674篇 |
金属工艺 | 4198篇 |
机械仪表 | 5173篇 |
建筑科学 | 6465篇 |
矿业工程 | 2223篇 |
能源动力 | 2088篇 |
轻工业 | 4619篇 |
水利工程 | 1630篇 |
石油天然气 | 3320篇 |
武器工业 | 780篇 |
无线电 | 8255篇 |
一般工业技术 | 7214篇 |
冶金工业 | 2921篇 |
原子能技术 | 904篇 |
自动化技术 | 10602篇 |
出版年
2024年 | 229篇 |
2023年 | 954篇 |
2022年 | 2003篇 |
2021年 | 2915篇 |
2020年 | 2111篇 |
2019年 | 1677篇 |
2018年 | 1929篇 |
2017年 | 2133篇 |
2016年 | 1953篇 |
2015年 | 2821篇 |
2014年 | 3834篇 |
2013年 | 4429篇 |
2012年 | 5298篇 |
2011年 | 5597篇 |
2010年 | 5221篇 |
2009年 | 4896篇 |
2008年 | 4881篇 |
2007年 | 4692篇 |
2006年 | 4360篇 |
2005年 | 3747篇 |
2004年 | 2672篇 |
2003年 | 2129篇 |
2002年 | 1992篇 |
2001年 | 1728篇 |
2000年 | 1491篇 |
1999年 | 1264篇 |
1998年 | 831篇 |
1997年 | 733篇 |
1996年 | 700篇 |
1995年 | 512篇 |
1994年 | 446篇 |
1993年 | 281篇 |
1992年 | 239篇 |
1991年 | 155篇 |
1990年 | 123篇 |
1989年 | 120篇 |
1988年 | 82篇 |
1987年 | 53篇 |
1986年 | 31篇 |
1985年 | 23篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1962年 | 42篇 |
1961年 | 39篇 |
1960年 | 16篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
研制了用于远程激光脉冲测距机的板条激光器。使用半导体泵浦的MOPA激光结构实现了大于250 mJ的脉冲激光输出,输出脉冲宽度为12.83 ns,最终输出激光光束束散角为0.18 mrad。该激光测照器可应用于远程激光测距。对激光测距机的测距与照射能力进行了理论计算与分析。理论分析表明,应用于机载平台时,该激光测照器能够实现50 km距离的激光测距。该型激光测距机具有测距距离远,重量轻,结构紧凑等特点,具有广泛的应用前景。 相似文献
43.
Wang Qibin Zhao Bo Ma Hongbo Chang Jiantao Mao Gang 《Journal of Mechanical Science and Technology》2019,33(6):2561-2571
Journal of Mechanical Science and Technology - Real-time monitoring and rapid evaluation of bearing operating conditions, especially for the reliability evaluation and remaining useful life (RUL)... 相似文献
44.
In the early design stage, automotive modeling should both meet the requirements of aesthetics and engineering. Therefore, a vehicle CAD (computer aided design) model that can be easily adjusted by feedbacks is necessary. Based on CE-Bézier surface, this paper presents a set of algorithms for parametric segmentation and fairing surface generation in a car model. This model is defined by a simplified automotive template and relevant control points, shape parameters and segmentation parameters, which can be modified to alter the car form efficiently. With this model and the corresponding adjustment method, more than fifty various vehicle models are established in this research according to different parameters. And two methods for calculating similarity index between car models are constructed, which are suitable for brand design trend analysis and modelling design decisionmaking. 相似文献
45.
紫砂壶以造型为基本的载体,通过形神兼备的造型表现出深厚的文化情感,它将自然万物融汇其中,将各种不同的生命、思想和个性呈现其上,使人观壶如同与人交流,产生深刻的情感、精神共鸣,感受到内心的平静,这十分有益于舒缓当代人的精神心理压力,让人们通过泡茶品茗这种生活方式来获得暂时的悠闲,并通过对紫砂壶的把玩来感悟其中的文化内蕴,从而获得自由淡泊的心态,更好地面对生活。本文以紫砂壶“知竹”为例,浅谈其文化意境。 相似文献
46.
47.
Changwei Dun Guoxi Xi Ye Zhang Tingting Zhao Yumin Liu Xiaoying Heng Lu Yao 《Ceramics International》2018,44(17):20984-20991
In this study, we investigated the effects of substituting Li+ for Co2+ at the B sites of the spinel lattice on the structural, magnetic and magnetostrictive properties of cobalt ferrites. The Li+ substituted cobalt ferrites, Co1-xLixFe2O4, with x varying from 0 to 0.7 in 0.1 increments, were synthesized with a sol-gel auto-combustion method using the cathode materials of spent Li-ion batteries. X-ray diffraction analysis revealed that all the Co1-xLixFe2O4 nanopowders had a single-phase spinel structure and the lattice parameters decreased with increasing Li+ content, which can be proved by slight shifts towards higher diffraction angle values of the (311) peak. Field emission scanning electron microscopy was used to observe the fractured inner surface of the sintered cylindrical rods and the increased porosity resulted in a decreased magnetostriction. The oxidation states of Co and Fe in the cobalt ferrite samples were examined by X-ray photoelectron spectroscopy. High resolution transmission electron microscopy micrographs showed that most particles were roughly spherical and with sizes of 25–35?nm. Li+ substitution had a strong effect on the saturation magnetization and coercivity, which were characterized with a vibrating sample magnetometer. The Curie temperature was reduced due to the decrease in magnetic cations and the weakening of the exchange interactions. The magnetostrictive properties were influenced by the incorporation of Li+ at the B sites of the spinel structure and correlated with the changes in porosity, magnetocrystalline anisotropy and the cation distribution. 相似文献
48.
This paper presents two well-instrumented large-scale field tests of PVD-improved soft soil with vacuum and surcharge preloading, respectively. The two large-scale field tests were conducted adjacent to each other with the same preload. A comparative analysis was performed to investigate the performance of subsoil (i.e., the ground settlement, the layered settlement, the lateral displacement of subsoil and pore water pressure) under vacuum preloading and equivalent surcharge preloading. Some design methods were verified based on the field data. Cone Penetration Tests (CPT) and Vane Shear Tests (VST) were conducted to assess the improvement effects on subsoil after preloading. The results showed that as compared with surcharge preloading, vacuum preloading mitigated the differential settlement of the ground. The vacuum pressure transmitted into the soil with a minor loss through the PVD length. From a practical point of view, the improvement effects by vacuum preloading and surcharge preloading were similar in terms of influence depth and soil strength based on the in-situ tests. 相似文献
49.
50.
苏6井区下石盒子组高分辨率层序地层学特征 总被引:1,自引:0,他引:1
以高分辨率层序地层学理论和技术方法为指导,在苏里格气田苏6井区地表露头、钻井岩心、测井、地震资料综合研究的基础上,通过基准面旋回结构、叠加样式的沉积动力学分析,将该井区下石盒子组划分为2个长期、5个中期和14个短期旋回层序;并较为详细地讨论了各期旋回层序特征;建立了以长期旋回层序界面和最大洪泛面为等时年代地层框架,以中期旋回层序为等时地层单元的高分辨率层序地层格架;通过分析,认为下石盒子组盒8下段天然气储、盖条件最为有利;有利于储层发育的河道砂体主要出现在长、中期上升半旋回的中、下部,层序界面上相当短期旋回级别的单河道砂体是下石盒子组天然气勘探开发的主要目标。 相似文献