全文获取类型
收费全文 | 24155篇 |
免费 | 2010篇 |
国内免费 | 904篇 |
专业分类
电工技术 | 1184篇 |
技术理论 | 5篇 |
综合类 | 1366篇 |
化学工业 | 4302篇 |
金属工艺 | 1627篇 |
机械仪表 | 1474篇 |
建筑科学 | 1813篇 |
矿业工程 | 699篇 |
能源动力 | 790篇 |
轻工业 | 1610篇 |
水利工程 | 382篇 |
石油天然气 | 1662篇 |
武器工业 | 154篇 |
无线电 | 2480篇 |
一般工业技术 | 3035篇 |
冶金工业 | 1346篇 |
原子能技术 | 259篇 |
自动化技术 | 2881篇 |
出版年
2024年 | 89篇 |
2023年 | 475篇 |
2022年 | 640篇 |
2021年 | 1023篇 |
2020年 | 827篇 |
2019年 | 691篇 |
2018年 | 795篇 |
2017年 | 821篇 |
2016年 | 709篇 |
2015年 | 981篇 |
2014年 | 1162篇 |
2013年 | 1573篇 |
2012年 | 1542篇 |
2011年 | 1612篇 |
2010年 | 1403篇 |
2009年 | 1335篇 |
2008年 | 1280篇 |
2007年 | 1232篇 |
2006年 | 1309篇 |
2005年 | 1131篇 |
2004年 | 691篇 |
2003年 | 641篇 |
2002年 | 588篇 |
2001年 | 473篇 |
2000年 | 549篇 |
1999年 | 658篇 |
1998年 | 555篇 |
1997年 | 414篇 |
1996年 | 407篇 |
1995年 | 331篇 |
1994年 | 275篇 |
1993年 | 189篇 |
1992年 | 150篇 |
1991年 | 108篇 |
1990年 | 88篇 |
1989年 | 48篇 |
1988年 | 63篇 |
1987年 | 39篇 |
1986年 | 23篇 |
1985年 | 30篇 |
1984年 | 25篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1974年 | 3篇 |
1959年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
991.
Asymmetric bilayer membranes have been regarded as ideal wound dressings for skin regeneration. Our previous work reported the potential advantages of polydimethylsiloxane modified gelatin/silicone rubber (PGE/SR) asymmetric bilayer membrane as a wound dressing. However, it is still unknown whether the proportion of the two components of the bilayer membrane has a prominent influence on its relevant performance. Herein, various PGE/SR membranes with different PGE:SR weight ratios (100:25, 100:50 and 100:100) were fabricated through a self‐stratification method driven by surface tension gradients. Subsequently, the effects of the PGE:SR ratios on the relevant performance (i.e. porous structure, mechanical properties, degradability and biocompatibility) of PGE/SR membranes were systematically investigated. The current results demonstrate that the separating force between the PGE and SR components was reduced significantly on increasing the content of SR, and in particular the PGE/SR1 membrane (100:25) exhibited a well‐defined asymmetric bilayer structure with high porosity, appropriate toughness, water uptake, swelling ratio and water permeability. Concomitantly, the maximum weight loss for the PGE/SR1 membrane was ca 70.65% after 9 days of enzymatic degradation, which met the typical healing period of a normal skin wound. In addition, both the original and degraded PGE/SR1 membrane possessed favorable cytocompatibility in vitro, suggesting its potential application as a wound dressing. © 2019 Society of Chemical Industry 相似文献
992.
Chaojun Cui Ye Wang Xiangze Du Li Li Mouxiao Song Wenqing Zeng Guiying Li Changwei Hu 《International Journal of Hydrogen Energy》2021,46(40):20835-20847
xNi/HTASAO5 catalysts (x = 2.5, 3.3, 4.4, 5.8, 8.2) were prepared for CO2 reforming of methane. No crystalline nickel species formed on the catalysts with lower nickel content (≤4.4%), and large Ni0 crystallite formed on 5.8% (10 nm) and 8.2 wt%Ni/HTASAO5 (17 nm), whereas the surface concentration of Ce3+ decreased with Ni loading. The initial conversion of CH4 increased from 29.5% to 46.9% with Ni loading. The xNi/HTASAO5 (x ≤ 4.4%) performed stably in the reaction due to the presence of dispersed Ni species and high surface Ce3+ content without coke formation, however, 5.8% and 8.2 wt%Ni/HTASAO5 exhibited decreased activity with time on stream, because of the formation of large Ni particles with lower surface Ce3+, leading to carbon accumulation. Thus, CH4 conversion stabilized at about 43% and no carbon formed on 4.4 wt%Ni/HTASAO5 with optimum Ni loading. 相似文献
993.
994.
995.
996.
Yaofa Luo Haoliang Wang Hui Wang Linzhao Jin Zongliang Du Haibo Wang Xu Cheng 《应用聚合物科学杂志》2021,138(45):51331
A synergistic reactive flame-retardant polyol (AFeDH) containing ferrocene, phosphorus, and nitrogen elements was synthesized from ferro-formaldehyde, 5-amino-1,3, 4-thiadiazole-2-mercaptan, 9,10-dihydro-9-oxa-10-phos-phaphenanthrene-10-oxide and hydroxyl terminated polybutadiene acrylonitrile, and then applied for flame retarding waterborne polyurethane (WPU). The chemical structures of intermediates and final products were well characterized to confirm the successful preparation of ternary P-N-Fe flame retardant. The effects of incorporated AFeDH on thermal stability, flame retardancy and mechanical properties of AFeDH/WPU films were systematically studied. The results indicated that LOI value increased with the increase amount of AFeDH, while the value then decreased as the loading content above 6 wt%. This increase in flame retardancy results from the competition between the catalytic degradation of iron and the catalytic carbonization. Benefiting from the good synergistic effects among each element of AFeDH, the WPU/AFeDH films perform the decreased heat release and smoke production. Moreover, the flame retardant films also show the enhanced tensile strength of 33.8 MPa and elongation at break of 763.3%. Therefore, this novel halogen-free flame retardant shows an excellent synergistic effect among P, N, and Fe elements, which has a great potential in the application of flame retardant WPU. 相似文献
997.
Longquan Hou Jinyun Ju Xu Tang Renjie Chen Wenzong Yin Aru Yan Bin Chen Yeyuan Du 《中国稀土学报(英文版)》2021,39(8):993-997
A series of sandwiched structures with different near-surface mass fractions x(x=3 wt%,4 wt%,5 wt%)was employed to develop high-coercivity hot-deformed Nd-Fe-B magnets by the addition of 2 wt%Nd-Cu eutectic alloys via adjusting the middle thickness and near-surface thickness.The designed magnet with a pronounced composite structure shows a 23% increase in coercivity with a 6% loss of remanence by adjusting the sandwiched structure at 4 wt% Nd-Cu eutectic alloys in the near-surface regions.The results indicate that the near-surface Nd-Cu-rich "shell" structure can effectively suppress the magnetization reversal of overall magnets,enhancing the coercivity.With the help of loading stress,Nd-Cu liquid enriched at the near-surface regions of the sample is infiltrated into the Nd-Cu-lean middle region,resulting in a concentration gradient.Microstructure characterizations further demonstrate that the infiltrated Nd-Cu eutectic plays a critical role in inhibiting grain growth and intergranular magnetic interaction.The optimized microstructure features suppress the reversed magnetization process,which makes a positive contribution to coercivity. 相似文献
998.
Scientometrics - Breakthrough research in scientific fields usually comes as a manifestation of major development and advancement. These advances build to an epiphany where new ways of thinking... 相似文献
999.
Synthesis of blue-emitting AlN:Eu2+ spherical phosphors by carbothermal reduction nitridation method
Sen Li Jie Zhang Zhaobo Tian Xuanyi Yuan Songmo Du Qi Wang Wenbin Cao 《Journal of the American Ceramic Society》2020,103(6):3716-3725
In this study, blue-emitting AlN:Eu2+ spherical phosphors were successfully synthesized for the first time by the carbothermal reduction nitridation (CRN) method, assisted with high nitrogen pressure, appropriate synthesis temperature, and the addition of CaF2. The influence of typical experimental parameters, such as N2 pressure, heating temperature, CaF2 content and Eu2+ concentration on the morphologies and luminescence properties of AlN phosphors were comprehensively investigated. The formation mechanism of spherical morphology were significantly proffered, indicating that sufficient liquid Ca-aluminates during the AlN growth stage were essential for the spheroidization process under the action of surface tension. The synthesized AlN:Eu2+ spherical phosphors presented an intense blue emission band centered in the range of 427- 476 nm relative to the reaction temperature. The lifetime of AlN:Eu2+ phosphor was calculated to be around 1.89 μs. The temperature-dependent PL spectra suggested that the emission band did not shift until 225°C. In addition, the spectral analysis strongly suggested that the luminescence property of AlN:Eu2+ phosphors was significantly enhanced by the large particle size, spherical morphology, reduced impurity content, and appropriate Eu2+ concentration. 相似文献