全文获取类型
收费全文 | 154302篇 |
免费 | 14560篇 |
国内免费 | 9096篇 |
专业分类
电工技术 | 11281篇 |
技术理论 | 5篇 |
综合类 | 12116篇 |
化学工业 | 22906篇 |
金属工艺 | 9669篇 |
机械仪表 | 10756篇 |
建筑科学 | 12521篇 |
矿业工程 | 4974篇 |
能源动力 | 4715篇 |
轻工业 | 10482篇 |
水利工程 | 3561篇 |
石油天然气 | 8374篇 |
武器工业 | 1794篇 |
无线电 | 17948篇 |
一般工业技术 | 16796篇 |
冶金工业 | 6186篇 |
原子能技术 | 2073篇 |
自动化技术 | 21801篇 |
出版年
2024年 | 340篇 |
2023年 | 2189篇 |
2022年 | 3915篇 |
2021年 | 5971篇 |
2020年 | 4622篇 |
2019年 | 3801篇 |
2018年 | 4180篇 |
2017年 | 4768篇 |
2016年 | 4363篇 |
2015年 | 6343篇 |
2014年 | 8191篇 |
2013年 | 9426篇 |
2012年 | 10958篇 |
2011年 | 12166篇 |
2010年 | 11143篇 |
2009年 | 10592篇 |
2008年 | 10604篇 |
2007年 | 10100篇 |
2006年 | 9733篇 |
2005年 | 7847篇 |
2004年 | 5757篇 |
2003年 | 4813篇 |
2002年 | 4709篇 |
2001年 | 4034篇 |
2000年 | 3358篇 |
1999年 | 2987篇 |
1998年 | 2137篇 |
1997年 | 1836篇 |
1996年 | 1577篇 |
1995年 | 1306篇 |
1994年 | 1041篇 |
1993年 | 762篇 |
1992年 | 604篇 |
1991年 | 419篇 |
1990年 | 326篇 |
1989年 | 271篇 |
1988年 | 183篇 |
1987年 | 129篇 |
1986年 | 113篇 |
1985年 | 60篇 |
1984年 | 51篇 |
1983年 | 51篇 |
1982年 | 44篇 |
1981年 | 36篇 |
1980年 | 29篇 |
1979年 | 14篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1959年 | 18篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
91.
Wang Hay Kan Chenxi Wei Dongchang Chen Tao Bo Bao‐Tian Wang Yan Zhang Yangchao Tian Jun‐Sik Lee Yijin Liu Guoying Chen 《Advanced functional materials》2019,29(17)
Lithium‐rich disordered rock‐salt oxides have attracted great interest owing to their promising performance as Li‐ion battery cathodes. While experimental and theoretical efforts are critical in advancing this class of materials, a fundamental understanding of key property changes upon Li extraction is largely missing. In the present study, single‐crystal synthesis of a new disordered rock‐salt cathode material, Li1.3Ta0.3Mn0.4O2 (LTMO), and its use as a model compound to investigate Li concentration–driven evolution of local cationic ordering, charge compensation, and chemical distribution are reported. Through the combined use of 2D and 3D X‐ray nanotomography, it is shown that Li removal accompanied by oxygen oxidation is correlated with the development of morphological defects such as particle cracking. Chemical heterogeneity, quantified by subparticle level distribution of Mn valence state, is minimal during Mn redox, which drastically increases upon the formation of cracks during oxygen redox. Density functional theory and bond valence sum mismatch calculations reveal the presence of local short‐range ordering in the pristine oxide, which gradually disappears along with the extraction of Li. The study suggests that with cycling the transformation into true cation–disordered state can be expected, which likely impacts the voltage profile and obtainable energy density of the oxide cathodes. 相似文献
92.
Biyun Fang Chuanfeng Zhang Zeliang Qi Chunyan Li Jun Ni Xiuyun Wang Jianxin Lin Chak-Tong Au Bingyu Lin Lilong Jiang 《American Institute of Chemical Engineers》2022,68(11):e17849
The design of an efficient non-noble metal catalyst is of burgeoning interest for ammonia synthesis. Herein, we report a Mo2C/CeO2 catalyst that is superior in ammonia synthesis activity. In this catalyst, molybdenum carbide coexisted with the ceria overlayers which is from the ceria support as the strong metal–support interaction. There is a high proportion of low-valent Mo species, as well as high concentration of Ce3+ and surface oxygen species. The presence of Mo2C and CeO2 overlayers not only leads to enhancement of hydrogen and nitrogen adsorption, but also facilitates the desorption and exchange of adsorbed species with the gaseous reagents. Compared with the Mo/CeO2 catalyst prepared without carbonization, the Mo2C/CeO2 catalyst is more than sevenfold higher in ammonia synthesis rate. This work not only presents an explicit example of designing Mo-based catalyst that is highly efficient for ammonia synthesis by tuning the adsorption and desorption properties of the reactant gases, but opens a perspective for other elements in ammonia synthesis. 相似文献
93.
以太阳纸业备料车间木片筛选碎料(筛余物)为原料,对其烧碱法半化学制浆的实验室工艺和生产试验进行了研究。结果表明,筛余物采用半化学法制浆可获得较高得率和环压强度的纸浆,且用碱量对纸浆性能有显著影响。相对8%NaOH (相对于绝干原料)化学预处理,采用14%NaOH化学预处理结合两段浆浓22%的高浓磨浆工艺,所制半化学浆抄造浆张的裂断长和环压指数分别达2.89 km和9.76 N·m/g,是前者的1.9倍和1.2倍,而且优于现用国内OCC废纸浆抄造浆张;生产试验得到的浆张性能指标与实验室相吻合,其中紧度和环压强度分别达到GB/T 13023—2008瓦楞芯(原)纸AA级和A级优等品要求。 相似文献
94.
Basins with various mineral resources coexisting and enriching often occupy an important strategic position. The exploration of various mineral resources is repetitive at present due to unshared data and imperfect management mechanism. This situation greatly increases the cost of energy exploitation in the country. Traditional data-sharing mode has several disadvantages, such as high cost, difficulty in confirming the right of data, and lack of incentive mechanism, which make achieving real data sharing difficult. In this paper, we propose a data-sharing mechanism based on blockchain and provide implementation suggestions and technical key points. Compared with traditional data-sharing methods, the proposed data-sharing mechanism can realize data sharing, ensure data quality, and protect intellectual property. Moreover, key points in the construction are stated in the case study section to verify the feasibility of the data-sharing system based on blockchain proposed in this paper. 相似文献
95.
油页岩矿物质催化半焦燃烧特性及机理 总被引:1,自引:0,他引:1
利用微型流化床反应分析仪(MFBRA)研究了油页岩矿物质催化半焦燃烧特性,重点考察了半焦内部矿物质和外部页岩灰床料对半焦燃烧的催化作用,揭示了流化床反应器中半焦燃烧过程和机理。结果表明:内部矿物质和外部床料对半焦燃烧均具有明显催化作用,而两者共同催化效果最为显著。矿物质中CaO和Fe2O3对半焦燃烧具有催化活性,CaO催化作用强于Fe2O3。油页岩半焦燃烧反应活化能在60.41~78.97 kJ/mol之间,矿物质的催化作用会明显降低反应活化能。流化床反应器中,矿物质对半焦燃烧的催化作用主要表现在四个反应,即:挥发分裂解和燃烧、半焦表面炭燃烧、半焦内部炭燃烧以及一氧化碳燃烧。 相似文献
96.
97.
98.
针对大型旋转机械通过临界转速时振动过大及运行中故障频发等问题,搭建转子试验台,模拟启停机过程和碰摩、不对中故障。不改变原有支撑形式,安装自主设计的磁流变阻尼器,在不停机的情况下,试验研究阻尼器抑制转子通过临界转速时振动过大及各类故障振动。试验结果表明,阻尼器可以有效抑制转子系统临界转速附近的振动,降幅在60%以上;转子发生碰摩或不对中故障时,阻尼器可以降低其高倍频振动。 相似文献
99.
Zhang Huawei Yang Zhi Wu Zhaoyu Hong Xiaoyu Li Zhong Xu Yulai Li Jun Ni Gaojin Xiao Xueshan 《Oxidation of Metals》2019,92(1-2):49-65
Oxidation of Metals - The isothermal oxidation behavior and oxide-scale evolution on a newly developed Ni–Fe-based superalloy were investigated. Three oxidation stages were generally... 相似文献