全文获取类型
收费全文 | 130658篇 |
免费 | 12687篇 |
国内免费 | 7928篇 |
专业分类
电工技术 | 9566篇 |
技术理论 | 4篇 |
综合类 | 12015篇 |
化学工业 | 19635篇 |
金属工艺 | 7507篇 |
机械仪表 | 8591篇 |
建筑科学 | 10112篇 |
矿业工程 | 3217篇 |
能源动力 | 3660篇 |
轻工业 | 10727篇 |
水利工程 | 2923篇 |
石油天然气 | 5346篇 |
武器工业 | 1233篇 |
无线电 | 15876篇 |
一般工业技术 | 14031篇 |
冶金工业 | 4967篇 |
原子能技术 | 1747篇 |
自动化技术 | 20116篇 |
出版年
2024年 | 487篇 |
2023年 | 1712篇 |
2022年 | 3499篇 |
2021年 | 4921篇 |
2020年 | 3723篇 |
2019年 | 3064篇 |
2018年 | 3229篇 |
2017年 | 3664篇 |
2016年 | 3561篇 |
2015年 | 5031篇 |
2014年 | 6550篇 |
2013年 | 7817篇 |
2012年 | 9411篇 |
2011年 | 9945篇 |
2010年 | 9216篇 |
2009年 | 9071篇 |
2008年 | 9114篇 |
2007年 | 8473篇 |
2006年 | 8166篇 |
2005年 | 6713篇 |
2004年 | 5216篇 |
2003年 | 4634篇 |
2002年 | 5462篇 |
2001年 | 4775篇 |
2000年 | 3381篇 |
1999年 | 2420篇 |
1998年 | 1555篇 |
1997年 | 1300篇 |
1996年 | 1129篇 |
1995年 | 945篇 |
1994年 | 711篇 |
1993年 | 517篇 |
1992年 | 429篇 |
1991年 | 322篇 |
1990年 | 253篇 |
1989年 | 185篇 |
1988年 | 155篇 |
1987年 | 113篇 |
1986年 | 51篇 |
1985年 | 68篇 |
1984年 | 49篇 |
1983年 | 37篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 32篇 |
1979年 | 20篇 |
1977年 | 12篇 |
1976年 | 16篇 |
1959年 | 12篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
高光谱激光雷达谱位合一的角度效应分析 总被引:1,自引:0,他引:1
高光谱激光雷达以其谱位合一的技术优势为实现超三维精准遥感观测提供了可行途径,因此成为当前激光雷达与高光谱遥感领域共同大力推进的前沿发展方向。目前已有多型原型系统研发出来并得到了原理性验证,然而针对其数据处理核心环节问题的基础技术仍较为欠缺。典型问题之一是不同波段回波信号受激光入射角度的影响,该角度效应限制了高光谱激光雷达实现高性能遥感。以芬兰空间信息研究所高光谱激光雷达原型系统扫描桦树树干为例探讨了该角度效应,发现了不同激光波段对不同入射角度的回波强度响应模式,推导出了角度效应的基本规律及其精细尺度的统计规律,为后续该方向的系统研发、数据处理及信息提取等提供了可借鉴的底层机理与技术基础。 相似文献
43.
Process object is the instance of process. Vertexes and edges are in the graph of process object. There are different types of the object itself and the associations between object. For the large-scale data, there are many changes reflected. Recently, how to find appropriate real-time data for process object becomes a hot research topic. Data sampling is a kind of finding c hanges o f p rocess o bjects. There i s r equirements f or s ampling to be adaptive to underlying distribution of data stream. In this paper, we have proposed a adaptive data sampling mechanism to find a ppropriate d ata t o m odeling. F irst o f all, we use concept drift to make the partition of the life cycle of process object. Then, entity community detection is proposed to find changes. Finally, we propose stream-based real-time optimization of data sampling. Contributions of this paper are concept drift, community detection, and stream-based real-time computing. Experiments show the effectiveness and feasibility of our proposed adaptive data sampling mechanism for process object. 相似文献
44.
Wei-Fei Hu Shuo Chen Hong-Chao Hao Hong Jiang 《American Institute of Chemical Engineers》2022,68(11):e17879
Herein, we propose a novel method to enhance the photoreactivity of an MOF catalyst by grafting isocyanate bonds ( NCO) and sulfhydryl-complexed copper ( SCu) onto ZIF-8 (NIF-SCu). The grafting process intercalated interlayer bands between the conduction and valence bands of ZIF-8, thereby providing a “ladder” for facile electron transition. The extreme improvement in the photoreactivity of NIF-SCu could be attributed to the enhancement in light responses in the range of 350–450 nm by NCO groups and the widening of the visible light range of the MOF by SCu groups. The formation of staggered energy levels in NIF-SCu could also narrow the band gap, lower the resistance, and facilitate the transfer of photogenerated carriers, thereby generating electrons with strong reduction potential in the SCu conduction band. This study provides a new strategy for improving or even endowing the photoactivity of environmental functional materials with wide bandgaps. 相似文献
45.
46.
47.
Genki Saito Yuji Kunisada Takumi Watanabe Xuemei Yi Takahiro Nomura Norihito Sakaguchi Tomohiro Akiyama 《Journal of the American Ceramic Society》2019,102(1):524-532
Carbon-and-oxygen-doped AlN specimens were prepared by combustion synthesis using Al, graphite, and AlN. Graphite addition changed the product color from white to blue. By XRD, the lattice constant increased slightly with increasing carbon content. Blue AlN powder was synthesized with a molar ratio of the diluent AlN of 0.2-0.5 with a fixed graphite content of 0.05. At an AlN molar ratio exceeding 0.6, carbon was not successfully incorporated due to the lower reaction temperature. Calcination at 800°C in air removed residual graphite without changing the crystal structure or product color. Oxygen, nitrogen, and carbon analyses revealed that blue AlN powders contained 0.45-0.54 mass% carbon and 1.4-1.6 mass% oxygen, while the undoped AlN contained 0.021 mass% carbon and 0.94 mass% oxygen. The origin of the white-to-blue color change was investigated via reflection measurements. Blue AlN exhibits an absorption peak at 634 nm (1.96 eV). From first-principles electronic structure calculations, the C-doped AlN and carbon-and-oxygen-doped AlN with a 1:1 ratio could be classified as p-type, whereas the O-doped AlN and 1:3 carbon-and-oxygen-doped AlN were n-type. One reason for the absorption peak at 634 nm may be a transition from the conduction band to an upper unoccupied state. These results suggest the possible control of optical and electronic properties of AlN via carbon-and-oxygen doping. 相似文献
48.
49.
Wu Ge Mu Yi Susilo Willy Guo Fuchun Zhang Futai 《International Journal of Information Security》2019,18(3):321-331
International Journal of Information Security - Data integrity is a critical security issue in cloud storage. The data integrity checking schemes by a third-party auditor (TPA) have attracted a lot... 相似文献
50.
将环隙式离心萃取器(ACCs)与电喷雾飞行时间质谱(ESI-TOF-MS)相结合,在线监测了回收过程中的钨萃取行为(宏观)和钨形态的转化路径(微观),发现宏观萃取反应和微观离子形态转化同时发生并相互补充。伯胺N1923萃取钨在144 s内即可达到萃取平衡,萃取率高达98%以上,同时,酸钨比n(H)/n(W)是一个关键变量,当酸钨比n(H)/n(W)=2.4时,全流程钨回收率超过93%。最后,得到了基于钨形态监测的萃取机理,同时,减少原料液中W1含量,增加W10含量,可有效提高钨回收效率。 相似文献