全文获取类型
收费全文 | 3293篇 |
免费 | 268篇 |
国内免费 | 80篇 |
专业分类
电工技术 | 43篇 |
综合类 | 331篇 |
化学工业 | 639篇 |
金属工艺 | 89篇 |
机械仪表 | 83篇 |
建筑科学 | 1635篇 |
矿业工程 | 45篇 |
能源动力 | 106篇 |
轻工业 | 89篇 |
水利工程 | 158篇 |
石油天然气 | 21篇 |
武器工业 | 8篇 |
无线电 | 51篇 |
一般工业技术 | 275篇 |
冶金工业 | 29篇 |
原子能技术 | 13篇 |
自动化技术 | 26篇 |
出版年
2024年 | 3篇 |
2023年 | 65篇 |
2022年 | 70篇 |
2021年 | 105篇 |
2020年 | 99篇 |
2019年 | 81篇 |
2018年 | 83篇 |
2017年 | 97篇 |
2016年 | 87篇 |
2015年 | 80篇 |
2014年 | 173篇 |
2013年 | 238篇 |
2012年 | 231篇 |
2011年 | 224篇 |
2010年 | 189篇 |
2009年 | 239篇 |
2008年 | 221篇 |
2007年 | 260篇 |
2006年 | 208篇 |
2005年 | 165篇 |
2004年 | 121篇 |
2003年 | 119篇 |
2002年 | 89篇 |
2001年 | 68篇 |
2000年 | 74篇 |
1999年 | 42篇 |
1998年 | 50篇 |
1997年 | 30篇 |
1996年 | 23篇 |
1995年 | 18篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 4篇 |
1987年 | 11篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有3641条查询结果,搜索用时 187 毫秒
1.
地铁混凝土处于地下空间,容易受到地下水的碳酸性侵蚀;碱集料反应 (AAR)是一种严重的混凝土耐久性问题,既难以发现又难以修补,由两者共同作用引起的混凝土耐久性降低严重影响地铁隧道的正常使用.为研究纳米材料对地铁混凝土在碳酸性侵蚀和AAR共同作用下耐久性的影响,在普通混凝土中掺入适量纳米SiO2和纳米Fe2O3,利用自行研制的碳酸性侵蚀试验箱进行试验,采用碳酸性侵蚀深度、膨胀率和声速作为测试指标来评价纳米混凝土在碳酸性侵蚀和AAR共同作用下的耐久性.试验结果表明:掺入纳米颗粒后,混凝土的膨胀率和侵蚀深度有了明显降低,而声速有了明显提升,说明纳米混凝土的耐久性优于普通混凝土;在182 d龄期时,掺量为2%的纳米SiO2混凝土耐久性改善最明显,侵蚀深度和膨胀率最小,声速最大且声速下降幅度最小;其次是掺量为1%的纳米Fe2O3混凝土.由于纳米颗粒特殊的物理化学性质,改善了混凝土内部的微观结构和孔溶液的化学组成,使碳酸性侵蚀和碱集料反应共同作用下混凝土的耐久性得到了提高. 相似文献
2.
3.
Mechanical durability of extruded fish feed must be optimized to lower economic losses as well as emission of organic matter to aquatic environments. The glass transition hypothesis for viscoelastic biopolymers is demonstrated and confirmed experimentally to be valid for extruded fish feed pellets. It is proposed and demonstrated that it is important to avoid early glass transition onset, to optimize the obtained mechanical durability. From the proposed glass transition hypothesis, immediate process relevance to the pre-drying transport mechanism is demonstrated. Furthermore, measured mechanical durability is found to range from 1.5 to 5.0% loss, for different combinations of drying parameters. 相似文献
4.
Sustainable biocomposites have gained considerable interest as an alternative to conventional composites in recent years due to their cost-effectiveness and environmental friendliness. The aim of this study was to investigate the performance and durability behavior of biocomposites from sustainable biocarbon (BC) as compared to conventional established fillers. The poly(butylene terephthalate) (PBT) and its composites reinforced with BC, talc, and glass fiber (GF) were prepared and the durability performances was investigated. The study showed that BC/PBT biocomposites provided a lighter weight alternative to traditionally used fillers. After undergoes thermo-oxidative aging, the mechanical properties of BC/PBT biocomposite were deteriorated. The GF/PBT showed the most stable in retaining its mechanical properties in comparison to the talc/PBT and BC/PBT. The aging behavior and mechanism of the PBT composites were discussed. This study provides further insight on the durability-related properties progression of biocomposites as compared to traditional used fillers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47722. 相似文献
5.
Apoorva Karamchandani Hojae Yi Virendra M. Puri 《Particulate Science and Technology》2018,36(4):447-456
Mechanical and physical properties of ground corn stover, switchgrass, and willow were measured and compared in addition to the quality of pellets. Biomass was size-reduced with two different screen sizes (3.175 and 6.35?mm) and conditioned to obtain samples at two different moisture contents (17.5 and 20% on wet basis). Ground switchgrass had the smallest and willow had the highest D50 when size-reduced with the same screen size. Hydrostatic triaxial compression tests were performed using the cubical triaxial tester to determine the bulk modulus, compression index, and spring-back index at specific unloading pressures (20, 45, 70, and 95?kPa). The trends of pressure vs. volumetric strain and void ratio vs. natural log of pressure were similar for all three materials; however, the magnitudes were different. Willow, size-reduced with 3.175?mm screen size at 17.5% wet basis, had the highest bulk modulus among different conditions of all the three biomass. Pellet durability values for all the three materials were higher than 80%. Corn stover pellets formed with 3.175?mm screen size at 20% wet basis had the highest diametral tensile and axial compressive strengths among different conditions for all the three biomass, however the values were not significantly different (p?>?0.05). 相似文献
6.
Minh Truong Xuan Nguyen Minh-Kha Nguyen Phuong Thi Thuy Pham Ha Ky Phuong Huynh Son Truong Nguyen 《International Journal of Hydrogen Energy》2021,46(5):3909-3921
One-dimensional (1D) metal-coated Pd structures are efficient catalysts for the ethanol electro-oxidation and promising strategy for minimizing the Pd-loading toward commercialization of direct ethanol fuel cells (DEFCs). Herein, the decorated and core-shell architectures of a novel Pd coating on Ag nanowires (PdAg-NWs) are controllable by a two-step polyol method based on the galvanic replacement reaction. The integration of uniform shell with a low Pd concentration and partial hollow structure onto 1D PdAg-NWs exhibits the highest efficiency for ethanol oxidation reaction (EOR) in alkaline solution. In comparison with Pd nanoparticles (PdNPs/C), the PdAgNWs/C performes 11 times superior EOR activity, and the onset potential shifts 80 mV negatively. The presence of Ag in PdAg-NWs enhances the absorption capacity of ethanol molecules and hydroxyl ions on the active sites, and improves the catalyst tolerance to CO-like intermediates, making them a potential anodic catalyst for DEFCs. 相似文献
7.
《Ceramics International》2020,46(9):13549-13555
In this study, the effects of the pyrochlore content on the phase, structure, and properties of uranium-rich glass ceramics were studied by modifying the mass ratio of the uranium pyrochlore in the glass ceramics. The results indicate that U has a high occupancy rate of approximately 0.7 f.u. at the A position of pyrochlore, and the crystal pyrochlore phase in the glass matrix can increase or decrease according to the U amount in the waste. Specifically, at a high occupancy rate and crystallization amount, the U loads reach 20 wt% in the sample, which exceeds the reported 16 wt% maximal U loads of pyrochlore-based glass ceramics. Furthermore, all the samples have excellent mechanical properties and chemical stabilities. The bulk density of each sample is more than 90% the theoretical density, which is 10–20% higher than those of the glass ceramics prepared by pressure sintering. Moreover, the Vickers hardness values of all samples exceed 6 GPa, and the U leaching rate after 21 days is only 6.7 × 10−5 g m−2 d−1, which is an order of magnitude lower than those of brannerite glass ceramics under equal leaching conditions. 相似文献
8.
《Ceramics International》2020,46(9):13040-13046
Gd2Zr2O7 ceramics demonstrate important prospect in the immobilization of high-level radioactive wastes (HLWs). In this study, Gd2Zr2O7 nanoceramics were fabricated using two-step method, where Gd2Zr2O7 nanopowder was firstly synthesized by solvothermal method and Gd2Zr2O7 nanoceramics were subsequently sintered via self-propagating chemical furnace plus quick pressing (SCF/QP). The characterization results display that the Gd2Zr2O7 nanocrystalline ceramics with average grain size of 78 nm and bulk density of 5.53 g cm−3 were successfully prepared. The results of MCC-1 static leaching experiments show that the normalized release rate (LRi) of Gd is 2.2 × 10−2 g m−2•d−1 on the first day and converges to 1.2 × 10−3 g m−2•d−1 after 42 days. Zr shows superior chemical stability as the 21 days LRZr value is as low as 2.7 × 10−6 g m−2•d−1, which becomes constant as the leaching duration prolongs. 相似文献
9.
通过正交实验的方法,以地聚合物稠度、凝结时间、胶砂强度为研究依据,以偏高岭土、矿渣、磷渣、碱激发剂用量为研究对象,每个因素取3个水平,分析4个因素在各自水平上对地聚合物性能的影响。试验结果表明,偏高岭土用量是地聚合物稠度的最主要影响因素;偏高岭土和碱激发剂用量是初凝时间的主要影响因素,磷渣和偏高岭土用量是终凝时间的主要影响因素;偏高岭土用量是3 d 抗压强度的主要影响因素,矿渣用量是28 d 抗压强度的主要影响因素。按30%偏高岭土-40%矿渣-30%磷渣-10%碱激发剂制备的地聚合物具有良好的抗碳化性能,但收缩率较普通硅酸盐水泥高。 相似文献
10.
《International Journal of Hydrogen Energy》2020,45(40):20594-20604
Common carbon-blacks have shown insufficient stability as cathodic catalyst supports for proton exchange membrane fuel cells (PEMFCs). In this regard, alternative supports have been proposed and, specifically graphene or reduced graphene oxide (rGO), have attracted special attention. Herein, a set of electrocatalysts using reduced graphene oxide (rGO) as support is synthetized by a modified polyol method. The influence of Pt loading on the support is studied and compared with conventional supports, considering Pt particle morphologies and oxygen reduction reaction (ORR) performance in rotating disk electrode (RDE). Despite Pt average particle size typically increases with the Pt loading, 30 wt% of Pt on rGO is the optimal Pt loading, yielding the highest ORR activity among the rGO-supported electrocatalysts. These results show that both Pt loading and type of support greatly impact on the morphology and electrochemical performance of Pt nanoparticles. 相似文献