全文获取类型
收费全文 | 108932篇 |
免费 | 10813篇 |
国内免费 | 4614篇 |
专业分类
电工技术 | 7233篇 |
综合类 | 6815篇 |
化学工业 | 19768篇 |
金属工艺 | 9261篇 |
机械仪表 | 5010篇 |
建筑科学 | 9698篇 |
矿业工程 | 3099篇 |
能源动力 | 5107篇 |
轻工业 | 10432篇 |
水利工程 | 2598篇 |
石油天然气 | 4789篇 |
武器工业 | 840篇 |
无线电 | 10018篇 |
一般工业技术 | 12360篇 |
冶金工业 | 7155篇 |
原子能技术 | 1784篇 |
自动化技术 | 8392篇 |
出版年
2024年 | 202篇 |
2023年 | 1836篇 |
2022年 | 3664篇 |
2021年 | 5296篇 |
2020年 | 3860篇 |
2019年 | 3358篇 |
2018年 | 3391篇 |
2017年 | 3576篇 |
2016年 | 4554篇 |
2015年 | 5213篇 |
2014年 | 6965篇 |
2013年 | 7456篇 |
2012年 | 7646篇 |
2011年 | 7340篇 |
2010年 | 5334篇 |
2009年 | 5439篇 |
2008年 | 4970篇 |
2007年 | 7074篇 |
2006年 | 6992篇 |
2005年 | 5776篇 |
2004年 | 4473篇 |
2003年 | 4010篇 |
2002年 | 3022篇 |
2001年 | 2317篇 |
2000年 | 1773篇 |
1999年 | 1429篇 |
1998年 | 1091篇 |
1997年 | 932篇 |
1996年 | 917篇 |
1995年 | 710篇 |
1994年 | 648篇 |
1993年 | 443篇 |
1992年 | 423篇 |
1991年 | 374篇 |
1990年 | 325篇 |
1989年 | 221篇 |
1988年 | 170篇 |
1987年 | 119篇 |
1986年 | 115篇 |
1985年 | 119篇 |
1984年 | 120篇 |
1983年 | 81篇 |
1982年 | 63篇 |
1981年 | 50篇 |
1980年 | 69篇 |
1979年 | 31篇 |
1966年 | 26篇 |
1964年 | 34篇 |
1962年 | 64篇 |
1959年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
《International Journal of Hydrogen Energy》2022,47(59):24843-24851
Lithium alanate (LiAlH4) is a material that can be potentially used for solid-state hydrogen storage due to its high hydrogen content (10.5 wt%). Nevertheless, a high desorption temperature, slow desorption kinetic, and irreversibility have restricted the application of LiAlH4 as a solid-state hydrogen storage material. Hence, to lower the decomposition temperature and to boost the dehydrogenation kinetic, in this study, we applied K2NiF6 as an additive to LiAlH4. The addition of K2NiF6 showed an excellent improvement of the LiAlH4 dehydrogenation properties. After adding 10 wt% K2NiF6, the initial decomposition temperature of LiAlH4 within the first two dehydrogenation steps was lowered to 90 °C and 156 °C, respectively, that is 50 °C and 27 °C lower than that of the аs-milled LiAlH4. In terms of dehydrogenation kinetics, the dehydrogenation rate of K2NiF6-doped LiAlH4 sample was significantly higher as compared to аs-milled LiAlH4. The K2NiF6-doped LiAlH4 sample can release 3.07 wt% hydrogen within 90 min, while the milled LiAlH4 merely release 0.19 wt% hydrogen during the same period. According to the Arrhenius plot, the apparent activation energies for the desorption process of K2NiF6-doped LiAlH4 are 75.0 kJ/mol for the first stage and 88.0 kJ/mol for the second stage. These activation energies are lower compared to the undoped LiAlH4. The morphology study showed that the LiAlH4 particles become smaller and less agglomerated when K2NiF6 is added. The in situ formation of new phases of AlNi and LiF during the dehydrogenation process, as well as a reduction in particle size, is believed to be essential contributors in improving the LiAlH4 dehydrogenation characteristics. 相似文献
4.
《Ceramics International》2022,48(2):1889-1897
SiC fiber reinforced ceramic matrix composites (SiCf-CMCs) are considered to be one of the most promising materials in the electromagnetic (EM) stealth of aero-engines, which is expected to achieve strong absorption and broad-band performance. Multiscale structural design was applied to SiCf/Si3N4–SiOC composites by construction of micro/nanoscale heterogeneous interfaces and macro double-layer impedance matching structure. SiCf/Si3N4–SiOC composites were fabricated by using SiC fibers with different conductivities and SiOC–Si3N4 matrices with gradient impedance structures to improve impedance matching effectively. Owing to its unique structure, SiCf/Si3N4–SiOC composites (A3-composites) achieved excellent EM wave absorption performance with a minimum reflection coefficient (RCmin) of ?25.1 dB at 2.45 mm and an effective absorption bandwidth (EAB) of 4.0 GHz at 2.85 mm in X-band. Moreover, double-layer SiCf/Si3N4–SiOC with an improved impedance matching structure obtained an RCmin of ?56.9 dB and an EAB of 4.2 GHz at 3.00 mm, which means it can absorb more than 90% of the EM waves in the whole X-band. The RC is less than ?8 dB at 2.6–2.8 mm from RT to 600 °C in the whole X-band, displaying excellent high-temperature absorption performance. The results provide a new design opinion for broad-band EM absorbing SiCf-CMCs at high temperatures. 相似文献
5.
《Ceramics International》2022,48(3):3669-3675
ZnAl2O4 nanocrystalline particles were prepared using the solution combustion method using a new combustion fuel, Leucine. The prepared samples' structural, microstructural–elemental composition, and optical characteristics were investigated using XRD, SEM-EDS, and UV–Visible spectroscopy. As-synthesized ZnAl2O4 nanoparticles are polycrystalline, with no secondary phases, and crystallized in a cubic - spinel structure. The polycrystalline nature of the prepared sample is due to the exothermicity of fuel and oxidizer, which demonstrate that the fuel utilized (Leucine) provided adequate energy for the production of nanoparticles in their as-synthesized form, as supported by adiabatic temperature through thermodynamic calculations. The thermodynamic calculations also include a universal method to estimate the specific heat capacity at constant pressure. Furthermore, even after 2 h of calcination at 600 °C, ZnAl2O4 exhibits a single phase with no secondary phases, indicating the material stability and single-phase nature. The crystallinity of ZnAl2O4 nanoparticles was observed to increase with increasing annealing temperature. SEM micrographs of as-synthesized samples exhibit the formation of dense particles, voids, and pores in the as-synthesized sample. In addition, tiny aggregates were detected on the surface of more prominent clusters, which reduced as the calcination progressed. In addition, calcined samples exhibit a greater optical reflectance than as-synthesized samples. Tauc's graphs were used to compute the optical energy bandgap. The calculated energy band gap is redshifted to that of the bulk material. The bandgap energy decreases upon calcination, suggesting that the prepared materials have a larger crystallite size or more crystallinity. Correlations were found between the Tad, and the structural and optical properties of the prepared samples. The findings suggest that Leucine could be used as a novel combustion fuel to produce crystalline ZnAl2O4 nanoparticles in their as-synthesis form. 相似文献
6.
益生菌可在肠道定植从而发挥抗炎或抗氧化活性,有利于宿主肠道健康。本实验研究了从新疆传统发酵乳制品中分离得到的8?株植物乳杆菌对大肠杆菌侵袭和过氧化氢刺激肠上皮细胞HT-29的保护作用。结果表明:在8?株植物乳杆菌中,植物乳杆菌35具有最高的黏附能力。植物乳杆菌35可通过取代、竞争、排阻的方式抑制大肠杆菌对HT-29细胞的黏附,抑制率分别为42.60%、59.17%、60.19%。植物乳杆菌35及其多糖可抑制大肠杆菌刺激HT-29细胞产生白细胞介素-8;同时保护HT-29细胞免受过氧化氢的损伤,增加超氧化物歧化酶、谷胱甘肽过氧化物酶活力水平并降低丙二醛含量。结论:植物乳杆菌35及其粗胞外多糖具有抑制大肠杆菌O157诱导的炎症性肠病的潜力。 相似文献
7.
《Ceramics International》2022,48(12):16730-16736
Recently, all-inorganic cesium lead-halide perovskites have shown their promise for light emission applications, due to the excellent optical performance. Herein, we report that the initially nonphosphorescent undoped lead-halide Cs4PbBr6 single crystals (SCs) exhibit an ultralong phosphorescence emission under X-ray excitation at low temperatures. It is shown that the dramatic change has been taken place in radioluminescence spectra and the broad-band emission gradually appeared with the decrease of temperature. Below 210 K, the radioluminescence spectra can be deconvoluted into one narrow peak located at 530 nm and two broad peaks centered at 595 nm and 672 nm respectively. Subsequently, the time-dependent radioluminescence spectra in undoped lead-halide Cs4PbBr6 SCs were investigated. The ultralong phosphorescence emission can persist over 120 min at 70 K. We consider that ultralong phosphorescence originates from defect-related emission. To the best of our knowledge, our finding is the first time that undoped Cs4PbBr6 SCs exhibit the phosphorescence emission, which will offer a paradigm to motivate revolutionary applications on perovskite. 相似文献
8.
目的:探讨姜黄素的主要肠道代谢物四氢姜黄素(tetrahydrocurcumin,THC)对血小板活化和聚集的影响及其可能的分子机制。方法:在体外实验中,用不同浓度的THC(0、0.5、1、10 μmol/L)提前与健康人纯化血小板共同孵育40 min,然后加入凝血酶激活血小板2 min,用流式细胞术测定血小板表面CD62P和CD63的表达量,用酶联免疫吸附法测定血小板释放血小板因子-4(platelet factor-4,PF4)和趋化因子配体-5(chemokine ligand 5,CCL5)水平,用血小板聚集仪检测血小板释放ATP水平和血小板最大聚集率,用Western blot蛋白免疫印迹法检测血小板磷酸肌醇-3-激酶(phosphoinositide 3-kinase,PI3K)和Akt蛋白的磷酸化水平。结果:与模型组(血小板悬液中加入0.05%二甲基亚砜)相比,THC能抑制凝血酶诱导的血小板表面CD62P和CD63的表达,抑制PF4、CCL5和ATP的释放,降低血小板最大聚集率,下调PI3K和Akt蛋白的磷酸化水平,且呈浓度依赖效应,其中10 μmol/L的浓度下作用效果显著(P<0.01、P<0.001)。PI3K的特异性激动剂740 Y-P可部分逆转THC对PF4和CCL5释放和血小板聚集的抑制作用(P<0.05、P<0.01)。结论:THC具有显著抑制血小板活化和聚集的作用,其机制可能是THC可下调PI3K/Akt介导的信号通路。 相似文献
9.
《International Journal of Hydrogen Energy》2022,47(48):20705-20717
Water electrolysis technologies aim to provide a significant increase in green hydrogen production efficiency. In this work, a framework was developed to explore the use of supercritical water for alkaline electrolysis. This framework was used to perform Arrhenius analysis as a function of potential, and to explore activation energies for sub- and supercritical water electrolysis. An analysis of the conductivity of solution unveiled a discontinuity in the trends between sub- and supercritical potassium hydroxide solution conductivity. Unlike prior work on supercritical water electrolysis, this work investigates trends in electrochemical parameters, the sources of these trends, and how they change between the sub- and supercritical regimes. 相似文献
10.
《International Journal of Hydrogen Energy》2022,47(65):27973-27985
Metal-support interaction and catalyst pretreatment are important for industrial catalysis. This work investigated the effect of supports (SiO2, CeO2, TiO2 and ZrO2) for Cu–Pd catalyst with high Cu/Pd ratio (Cu/Pd = 33.5) regarding catalyst cost, and the reduction temperatures of 350 °C and 550 °C were compared. The activity based on catalyst weight follows the order of Si > Ce > Zr > Ti when reduced at 350 °C. The reduction temperature leads to the surface reconstruction over the SiO2, CeO2 and TiO2 catalysts, while results in phase transition over Cu–Pd/ZrO2. The effect of reduction temperature on catalytic performance is prominent for the SiO2 and ZrO2 supported catalysts but not for the CeO2 and TiO2 ones. Among the investigated catalysts, Zr-350 exhibits the highest methanol yield. This work reveals the importance of the supports and pretreatment conditions on the physical-chemical properties and the catalytic performance of the Cu–Pd bimetallic catalysts. 相似文献