全文获取类型
收费全文 | 98840篇 |
免费 | 20875篇 |
国内免费 | 4136篇 |
专业分类
电工技术 | 6173篇 |
技术理论 | 3篇 |
综合类 | 5294篇 |
化学工业 | 25300篇 |
金属工艺 | 4154篇 |
机械仪表 | 4908篇 |
建筑科学 | 7013篇 |
矿业工程 | 1655篇 |
能源动力 | 2623篇 |
轻工业 | 11659篇 |
水利工程 | 1781篇 |
石油天然气 | 2735篇 |
武器工业 | 700篇 |
无线电 | 14420篇 |
一般工业技术 | 17829篇 |
冶金工业 | 2927篇 |
原子能技术 | 837篇 |
自动化技术 | 13840篇 |
出版年
2024年 | 374篇 |
2023年 | 1110篇 |
2022年 | 2183篇 |
2021年 | 3206篇 |
2020年 | 3611篇 |
2019年 | 4717篇 |
2018年 | 4722篇 |
2017年 | 5348篇 |
2016年 | 5617篇 |
2015年 | 6470篇 |
2014年 | 7065篇 |
2013年 | 8715篇 |
2012年 | 7315篇 |
2011年 | 7170篇 |
2010年 | 6973篇 |
2009年 | 6782篇 |
2008年 | 6380篇 |
2007年 | 5814篇 |
2006年 | 5337篇 |
2005年 | 4313篇 |
2004年 | 3452篇 |
2003年 | 3154篇 |
2002年 | 3404篇 |
2001年 | 2995篇 |
2000年 | 2494篇 |
1999年 | 1484篇 |
1998年 | 712篇 |
1997年 | 617篇 |
1996年 | 486篇 |
1995年 | 384篇 |
1994年 | 315篇 |
1993年 | 223篇 |
1992年 | 202篇 |
1991年 | 156篇 |
1990年 | 116篇 |
1989年 | 98篇 |
1988年 | 65篇 |
1987年 | 59篇 |
1986年 | 37篇 |
1985年 | 34篇 |
1984年 | 20篇 |
1983年 | 17篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1959年 | 5篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
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
54.
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
55.
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
56.
57.
Tong Le Fan Ronggui Yang Shuangchun Zhang Qiushi Pan Yi 《Chemistry and Technology of Fuels and Oils》2022,57(6):991-999
Chemistry and Technology of Fuels and Oils - Application of water flooding technologies in the oilfield causes intensive heterogeneity of the oil reservoir and improper circulation of the injected... 相似文献
58.
This paper considers the state‐dependent interference relay channel (SIRC) in which one of the two users may operate as a secondary user and the relay has a noncausal access to the signals from both users. For discrete memoryless SIRC, we first establish the achievable rate region by carefully merging Han‐Kobayashi rate splitting encoding technique, superposition encoding, and Gelfand‐Pinsker encoding technique. Then, based on the achievable rate region that we derive, the capacity of the SIRC is established in many different scenarios including (a) the weak interference regime, (b) the strong interference regime, and (c) the very strong interference regime. This means that our capacity results contain all available known results in the literature. Next, the achievable rate region and the associated capacity results are also evaluated in the case of additive Gaussian noise. Additionally, many numerical examples are investigated to show the value of our theoretical derivations. 相似文献
59.
D.R. Santos‐Peñate C.M. Campos‐Rodríguez J.A. Moreno‐Pérez 《International Transactions in Operational Research》2019,26(1):340-363
The ‐centroid problem or leader–follower problem is generalized considering different customer choice rules where a customer may use facilities belonging to different firms, if the difference in travel distance (or time) is small enough. Assuming essential goods, some particular customer choice rules are analyzed. Linear programming formulations for the generalized ‐medianoid and ‐centroid problems are presented and an exact solution approach is applied. Some computational examples are included. 相似文献
60.
When solving a mathematical problem, students who do not have sufficient conceptual understanding may perform poorly and exhibit misconceptions. This study was aimed to examine students' conceptual understanding and significant misconceptions when solving number sense‐related problems. An online three‐tier diagnostic test was administered to 125 fifth‐grade students with varied socio‐economic backgrounds in Hong Kong. Only 14.40% of the students exhibited high performance with high confidence, indicating that these students had a profound conceptual understanding of number sense. In addition, the majority of the students (66.40%) did not demonstrate number sense; these students exhibited several significant misconceptions and could solve the questions only by using a rule‐based method or guessing. Accordingly, most students performed unsatisfactorily on number sense‐related problems. This study is imperative in identifying early predictors and provides information for further compatible interventions in the teaching and learning of number sense in Hong Kong in particular and worldwide in general. 相似文献