全文获取类型
收费全文 | 17073篇 |
免费 | 586篇 |
国内免费 | 363篇 |
专业分类
电工技术 | 729篇 |
综合类 | 574篇 |
化学工业 | 2685篇 |
金属工艺 | 1322篇 |
机械仪表 | 1428篇 |
建筑科学 | 898篇 |
矿业工程 | 444篇 |
能源动力 | 1371篇 |
轻工业 | 883篇 |
水利工程 | 143篇 |
石油天然气 | 960篇 |
武器工业 | 101篇 |
无线电 | 2055篇 |
一般工业技术 | 1727篇 |
冶金工业 | 769篇 |
原子能技术 | 458篇 |
自动化技术 | 1475篇 |
出版年
2024年 | 26篇 |
2023年 | 206篇 |
2022年 | 279篇 |
2021年 | 395篇 |
2020年 | 381篇 |
2019年 | 315篇 |
2018年 | 315篇 |
2017年 | 432篇 |
2016年 | 471篇 |
2015年 | 490篇 |
2014年 | 868篇 |
2013年 | 975篇 |
2012年 | 915篇 |
2011年 | 1369篇 |
2010年 | 920篇 |
2009年 | 935篇 |
2008年 | 833篇 |
2007年 | 920篇 |
2006年 | 886篇 |
2005年 | 856篇 |
2004年 | 747篇 |
2003年 | 683篇 |
2002年 | 562篇 |
2001年 | 430篇 |
2000年 | 407篇 |
1999年 | 422篇 |
1998年 | 407篇 |
1997年 | 320篇 |
1996年 | 287篇 |
1995年 | 226篇 |
1994年 | 207篇 |
1993年 | 115篇 |
1992年 | 119篇 |
1991年 | 71篇 |
1990年 | 60篇 |
1989年 | 40篇 |
1988年 | 40篇 |
1987年 | 21篇 |
1986年 | 24篇 |
1985年 | 17篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(45):19718-19731
Metals and alloys forming reversible hydrides with hydrogen gas are potential building blocks for compact, solid state hydrogen storage systems. Based on the materials’ thermodynamic characteristics, their use as temperature-swing gas compression and delivery systems in the hydrogen economy is also possible. Given the wide variety of materials developed and tested at laboratory and pilot scales, a harmonized method of selecting the feasible material(s) for a particular real-life application is required. This study proposes a system selection framework based on a normalized, multi-criteria metric. Using calculated values of multi-criteria metric, multi-criteria screening and ranking of potential materials has been demonstrated for a particular use case. It is found that the alloy TiMn1.52 having value of additive metric between 0.25 and 0.35 represents the best material for a single stage system. The alloy pair CaNi5–Ti1.5CrMn represents the best alternative for a two-stage system with additive metric values between 0.63 and 0.82. Energy and economic characteristics of the metal hydride gas compression and delivery systems are evaluated and compared with an equivalent mechanical compression system producing the same final effect (i.e., delivery of a given quantity of gas at a defined pressure). 相似文献
2.
《International Journal of Hydrogen Energy》2022,47(87):36749-36762
The main objective of the present investigation is to conduct the performance, combustion and emission analysis of CI engine operated using hydrogen enriched syngas (pyrolytic gas) and biodiesel (pyrolytic oil) as dual fuel mode condition. Both the pyrolytic oil and syngas is obtained from single feedstock delonix regia fruit pod through pyrolysis process and then pyrolytic oil is converted into biodiesel through esterification. Initially biomass is subjected to thermal degradation at various pyrolysis temperature ranges like 350–600 °C. During the pyrolysis process syngas, pyrolytic oil and char are produced. The syngas is directly used in the CI engine and pyrolytic oil is converted into biodiesel and then used in the CI engine. The pyrolytic oil and syngas is subjected to FTIR and GC/TCD analysis respectively. The syngas analysis confirms the presence of various gases like H2, CH4, CO2, CO and C2H4 in different proportions. The various proportions of the syngas is mainly depending upon the reactor temperature and moisture content in the biomass. The syngas composition varies with increase in the temperature and at 400 °C, higher amount of hydrogen is present and its composition are H2 28.2%, CO is 21.9%, CH4 is 39.1% and other gases in smaller amounts. The biodiesel of B20 and syngas of 8lpm produced from the same feedstock are considered as test sample fuels in the CI engine under dual fuel mode operation to study the performance and emission characteristics. The study reveals that BTE has slight increase than diesel of 1.5% at maximum load. On the another hand emission like CO, HC and smoke are reduced by 15%,25% and 32% respectively at full load condition, whereas NOx emission is increased at all loads in the range of 10–15%. Therefore B20+syngas of 8lpm can be used as an alternative fuel in CI engine without any modification and major products from pyrolysis process with waste biomass is fully used as fuel in the CI engine. 相似文献
3.
《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
4.
《Advanced Powder Technology》2022,33(8):103663
In this work, a new type of FeSi/FeNi soft magnetic powder core (SMPC) was successfully fabricated by coating FeNi nanoparticles on the surface of FeSi micrometer powder. The effects of different contents of FeNi nanoparticles on the micromorphology, internal structures, and soft magnetic properties of SMPCs were studied. The results show that FeNi nanoparticles adhere to the surface of FeSi powder, which can effectively fill the air gap between FeSi powder and is beneficial to the compaction of the powder cores during the pressing process. Thus, the density of the SMPCs is increased. Compared to FeSi SMPCs, the comprehensive soft magnetic properties of FeSi/FeNi SMPCs have been greatly improved. When adding 15 wt% FeNi nanoparticles, the SMPCs exhibit excellent magnetic properties with high effective permeability (increased by 43.8 %) and low core loss (decreased by 22.1 %). The high performance FeSi/FeNi SMPCs prepared in this work are expected to be widely used in power choke coils, uninterruptible power supplies, and boosts and inverter inductors. 相似文献
5.
《International Journal of Hydrogen Energy》2022,47(75):32303-32314
Membrane electrode assembly (MEA) is considered a key component of a proton exchange membrane fuel cell (PEMFC). However, developing a new MEA to meet desired properties, such as operation under low-humidity conditions without a humidifier, is a time- and cost-consuming process. This study employs a machine-learning-based approach using K-nearest neighbor (KNN) and neural networks (NN) in the MEA development process by identifying a suitable catalyst layer (CL) recipe in MEA. Minimum redundancy maximum relevance and principal component analysis were implemented to specify the most important predictor and reduce the data dimension. The number of predictors was found to play an essential role in the accuracy of the KNN and NN models although the predictors have self-correlations. The KNN model with a K of 7 was found to minimize the model loss with a loss of 11.9%. The NN model constructed by three corresponding hidden layers with nine, eight, and nine nodes can achieve the lowest error of 0.1293 for the Pt catalyst and 0.031 for PVA as a good additive blending in the CL of the MEA. However, even if the error is low, the prediction of PVA seems to be inaccurate, regardless of the model structure. Therefore, the KNN model is more appropriate for CL recipe prediction. 相似文献
6.
The slight-alkalization of generator internal cooling water (GICW) is widely used to inhibit the corrosion of hollow copper conductor and thereby ensure the safe operation of the generator. CO2 inleakage is increasingly identified as a potential security risk for GICW system. In this paper, the influence of CO2 inleakage on the slight-alkalization of GICW was theoretically discussed. Based on the equilibriums of the CO2-NaOH-H2O system, CO2 inleakage saturation was derived to quantify the amount of the dissolved CO2 in GICW. This parameter can be directly calculated with the measured conductivity and the [Na+] of GICW. The influence of CO2 inleakage on the slight-alkalization conditioning of GICW and the measurement of its water quality parameters were then analyzed. The more severe the inleakage, the narrower the water quality operation ranges of GICW, resulting in the more difficult the slight-alkalization conditioning of GICW. The temperature calibrations of the conductivity and the pH value of GICW show non-linear correlations with the amount of CO2 inleakage and the NaOH dosage. This study provides insights into the influence of CO2 inleakage on the slight-alkalization of GICW, which can serve as the theoretical basis for the actual slight-alkalization when CO2 inleakage occurs. 相似文献
7.
大型综合室内亲子乐园属于高大空间,设有游乐设施和游戏的特殊性使得对空间的舒适性要求一致,但是送风气流遇阻严重,室内存在较多气流死角,影响室内空气质量和儿童健康。因此其空调设计不仅需要考虑温度、风速的空间均匀度,还要考虑各点的空气龄和PMV-PPD指标。以天津某亲子乐园为研究对象,利用scSTREAM软件对适用于该房间的辐射供冷加新风、置换通风、混合通风三种空调方式的送风效果进行数值模拟分析,从流场的均匀性、人员的热舒适性等方面对模拟结果进行探讨,研究结果表明辐射供冷加新风方式的空间均匀性和PMV指标最佳,混合通风方式的空气龄最小。 相似文献
8.
本文针对典型高温气冷堆乏燃料厂房在双发商用飞机撞击载荷下的响应及结构完整性开展研究,并探讨结构特性对撞击损伤的影响。对乏燃料厂房及飞机分别建立有限元模型,通过弹体-目标相互作用分析模拟了飞机撞击过程,综合IAEA与NRC的评价准则对乏燃料厂房在飞机撞击下的损伤程度进行评估。数值结果表明:厂房上对应于机身及发动机的撞击位置发生可接受的局部损伤;乏燃料贮存井墙体对于提高构筑物抗飞机撞击能力有重要作用。此外,构筑物外形对损伤有很大影响,圆柱形壳体的抗飞机撞击能力显著强于方形厂房,是核电厂厂房设计的优化方向之一。 相似文献
9.
Dongdong Ji Zheng Liu Bailing Jiang Xiaofei Luo 《International Journal of Hydrogen Energy》2021,46(27):13960-13970
The evaluation of cell's weatherability is of practical interest. To further improve the soluble lead flow battery's weatherability, physiochemical properties of electrolytes containing fluoborate, perchlorate, methanesulfonate and trifluoromethanesulfonate are investigated from ?60 to 50 °C. Activities of CF3SO3H and HClO4 are poor in trifluoromethanesulfonate and perchlorate solutions due to common anion effect. The solubility of lead salt can be improved by increasing temperature, but worsened by increasing acid's content. With the temperature increasing, the conductivity is enhanced, and the viscosity is lowered for four solutions. The same results have been found by increasing acid's content except for CF3SO3H. The high energy efficiency can be achieved for cells over ?40–0 °C using fluoborate and perchlorate solutions, 73.2% at ?40 °C and 78.1% at ?30 °C respectively. Over the temperature range of 20–50 °C, the cells with methanesulfonate and trifluoromethanesulfonate solutions have good performance, 77.4% and 73.7% at 50 °C respectively. 相似文献
10.
《International Journal of Hydrogen Energy》2021,46(70):34970-34982
Alloy hardened steels offer excellent combination of mechanical properties, hardenability and corrosion resistance. 34CrMo4 is a medium carbon, low alloy steel widely used due to a good combination of high-strength, toughness and wear resistance. However, this steel experiences hydrogen embrittlement (HE), a complex phenomenon depending on the composition and microstructure. This work estimates de loss of the mechanical properties caused by hydrogen in electrochemically H-charged specimens in absence of mechanical stress but also, at low strain rate and constant load. H-charging for 2 and 6 h induce YS losses of about 40% and 71% and UTS losses of 39% and 59%, respectively. The synergistic effect of the stress and the H-charging process leads to a higher loss, 91%, and a faster brittle fracture even though hydrogen content is similar to those firstly H-charged and then tested in air. 相似文献