全文获取类型
收费全文 | 60499篇 |
免费 | 5248篇 |
国内免费 | 2440篇 |
专业分类
电工技术 | 3379篇 |
技术理论 | 8篇 |
综合类 | 3405篇 |
化学工业 | 10368篇 |
金属工艺 | 3782篇 |
机械仪表 | 3640篇 |
建筑科学 | 4412篇 |
矿业工程 | 1992篇 |
能源动力 | 1886篇 |
轻工业 | 4194篇 |
水利工程 | 1064篇 |
石油天然气 | 4277篇 |
武器工业 | 479篇 |
无线电 | 6608篇 |
一般工业技术 | 7171篇 |
冶金工业 | 3445篇 |
原子能技术 | 750篇 |
自动化技术 | 7327篇 |
出版年
2024年 | 306篇 |
2023年 | 1038篇 |
2022年 | 1952篇 |
2021年 | 2754篇 |
2020年 | 2019篇 |
2019年 | 1678篇 |
2018年 | 1924篇 |
2017年 | 2079篇 |
2016年 | 1835篇 |
2015年 | 2416篇 |
2014年 | 3157篇 |
2013年 | 3552篇 |
2012年 | 3782篇 |
2011年 | 4150篇 |
2010年 | 3616篇 |
2009年 | 3292篇 |
2008年 | 3184篇 |
2007年 | 3154篇 |
2006年 | 3227篇 |
2005年 | 2790篇 |
2004年 | 1782篇 |
2003年 | 1537篇 |
2002年 | 1450篇 |
2001年 | 1142篇 |
2000年 | 1309篇 |
1999年 | 1629篇 |
1998年 | 1269篇 |
1997年 | 1090篇 |
1996年 | 1059篇 |
1995年 | 951篇 |
1994年 | 730篇 |
1993年 | 487篇 |
1992年 | 390篇 |
1991年 | 316篇 |
1990年 | 251篇 |
1989年 | 204篇 |
1988年 | 178篇 |
1987年 | 112篇 |
1986年 | 96篇 |
1985年 | 64篇 |
1984年 | 56篇 |
1983年 | 39篇 |
1982年 | 33篇 |
1981年 | 30篇 |
1980年 | 18篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 14篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Shensong Wang Zheng Wu Jie Chen Jiangping Ma Jingshi Ying Shouchen Cui Shigang Yu Yongming Hu Jinhe Zhao Yanmin Jia 《Ceramics International》2019,45(9):11703-11708
In this work, the hydrothermally-synthesized sodium niobate nanowires were used to decompose Rhodamine B dye solution through the piezo-catalytic effect. With the sodium niobate catalyst, a high piezo-catalytic degradation ratio of ~80% was achieved under the excitation of vibration for the Rhodamine B dye solution (~5?mg/l). These active species in the catalytic process, hydroxyl radicals and superoxide radicals with the strong oxidation ability, were also observed, which confirmed the key role of piezoelectric effect for piezo-catalysis. The piezo-catalysis of sodium niobate nanowires provides a high-efficiency and reusable tool in application in depredating the dye wastewater. 相似文献
42.
Tong
Ma 《International Journal of Adaptive Control and Signal Processing》2020,34(9):1162-1181
A filtered adaptive constrained sampled-data controller for uncertain multivariable nonlinear systems in the presence of various constraints is synthesized in this paper. A piecewise constant adaptive law drives that estimation error dynamics to zero at each sampling time instant yields adaptive parameters. The filtered control scheme consists of two components. Based on an estimation/cancellation strategy, a disturbance rejection control law is designed to compensate the nonlinear uncertainties within the bandwidth of low-pass filters, whereas a constraint violation avoidance control law is designed to solve an online constrained optimization problem. Although a reduced sampling time helps to minimize the estimation error caused by the neglect of unknowns, the resulting aggressive signals put more restrictions on the control law. Greater sacrifice of tracking performance is required to satisfy the constraints. The constraints violation avoidance control law is in favor of a larger sampling time. Sufficient conditions are given to guarantee the stability of the closed-loop system with the sampled-data controller, where the input/output signals are held constant over the sampling period. Numerical examples are provided to validate the theoretical results, comparisons between the constrained sampled-data controller and unconstrained adaptive controller with the implementation of different sampling times are carried out. 相似文献
43.
Qun Ren Haijun Su Jun Zhang Haifang Liu Weidan Ma Guangrao Fan Di Zhao Min Guo Lin Liu Hengzhi Fu 《Ceramics International》2019,45(6):6632-6638
Directionally solidified microstructures of Al2O3-Er3Al5O12 eutectic and off-eutectic in situ composite ceramics were explored under abrupt-change pulling rate conditions. Corresponding temperature distributions and interface locations were studied. In eutectic composition, fluctuation of eutectic spacing occurred when the pulling rate increased abruptly. A gradually increase or abrupt increase in eutectic spacing was observed when the pulling rate decreased abruptly. In hypoeutectic and hypereutectic compositions, formation of the primary phases were suppressed when the pulling rate increased abruptly from 10?µm/s to 100?µm/s, while primary phases precipitated when the pulling rate decreased abruptly from 100?µm/s to 10?µm/s. The interface altitude decreased after the pulling rate increased abruptly, but increased after the pulling rate decreased abruptly. The liquid composition restriction (around the eutectic composition) at the eutectic interface plays an important role in the suppression of the primary dendrite and coupled eutectic oxides can be obtained in off-eutectic compositions even under higher solidification rate conditions. 相似文献
44.
45.
46.
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
47.
48.
Understanding semantic word shifts in scientific domains is essential for facilitating interdisciplinary communication. Using a data set of published papers in the field of information retrieval (IR), this paper studies the semantic shifts of words in IR based on mining per-word topic distribution over time. We propose that semantic word shifts not only occur over time, but also over topics. The shifts are examined from two perspectives, the topic-level and the context-level. According to the over-time word-topic distribution, stable words and unstable words are recognized. The diverging and converging trends in the unstable type reveal characteristics of the topic evolution process. The context-level shifts are further detected by similarities between word vectors. Our work associates semantic word shifts with the evolving of topics, which facilitates a better understanding of semantic word shifts from both topics and contexts. 相似文献
49.
50.
针对流体输送埋地管道泄漏问题,设计了一种利用管道机器人携带封堵气囊进行快速应急封堵修复的埋地管道泄漏内封堵装置。采用矩阵变换方法建立了牵引系统驱动轮过弯方程,利用MATLAB软件对过弯方程进行了验证,同时利用ADAMS软件仿真分析过弯路径与驱动轮转角对牵引系统行走速度的影响。研究结果表明:由两个串联封堵器组成的应急封堵系统可满足复杂工况下的管道泄漏封堵要求;牵引系统驱动轮在弯管内部行走时,单轮速度呈周期性变化,但三个驱动轮整体周期运动特性一致;驱动轮转角在25°~40°时,牵引系统行走速度与驱动轮转角成正比,且转角为30°时驱动效果最好。该内封堵装置的结构设计可为管道泄漏应急封堵领域装备的研发提供重要参考。 相似文献