全文获取类型
收费全文 | 96309篇 |
免费 | 7561篇 |
国内免费 | 6016篇 |
专业分类
电工技术 | 7977篇 |
技术理论 | 2篇 |
综合类 | 6845篇 |
化学工业 | 19482篇 |
金属工艺 | 6151篇 |
机械仪表 | 7593篇 |
建筑科学 | 2919篇 |
矿业工程 | 1418篇 |
能源动力 | 3419篇 |
轻工业 | 6315篇 |
水利工程 | 643篇 |
石油天然气 | 4409篇 |
武器工业 | 891篇 |
无线电 | 11903篇 |
一般工业技术 | 10411篇 |
冶金工业 | 2238篇 |
原子能技术 | 1138篇 |
自动化技术 | 16132篇 |
出版年
2024年 | 137篇 |
2023年 | 1212篇 |
2022年 | 1582篇 |
2021年 | 2513篇 |
2020年 | 2280篇 |
2019年 | 2315篇 |
2018年 | 2172篇 |
2017年 | 2813篇 |
2016年 | 3069篇 |
2015年 | 3194篇 |
2014年 | 4559篇 |
2013年 | 5354篇 |
2012年 | 5703篇 |
2011年 | 6838篇 |
2010年 | 5659篇 |
2009年 | 6517篇 |
2008年 | 6293篇 |
2007年 | 6879篇 |
2006年 | 6620篇 |
2005年 | 5468篇 |
2004年 | 4783篇 |
2003年 | 4493篇 |
2002年 | 3590篇 |
2001年 | 2834篇 |
2000年 | 2402篇 |
1999年 | 1891篇 |
1998年 | 1320篇 |
1997年 | 1108篇 |
1996年 | 1059篇 |
1995年 | 1087篇 |
1994年 | 930篇 |
1993年 | 806篇 |
1992年 | 634篇 |
1991年 | 384篇 |
1990年 | 247篇 |
1989年 | 243篇 |
1988年 | 167篇 |
1987年 | 113篇 |
1986年 | 111篇 |
1985年 | 84篇 |
1984年 | 71篇 |
1983年 | 46篇 |
1982年 | 50篇 |
1981年 | 56篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 23篇 |
1977年 | 20篇 |
1976年 | 26篇 |
1975年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Most protons in the solar wind belong to one of two different populations,the less dense beam protons and the denser core protons.The beam protons,with a velocity of(1-2)VA(VA is the local Alfvén speed),always drift relative to the core protons;this kind of distribution is unstable and stimulates several kinds of wave mode.In this study,using a 2D hybrid simulation model,we find that the original right-handed elliptically polarized Alfvén waves become linearly polarized,and eventually become right-handed and circularly polarized.Given that linearly polarized waves are a superposition of left-handed and right-handed waves,cyclotron resonance in the right-handed/left-handed component heats beam/core protons perpendicularly.The resonance between beam protons and right-handed polarized waves is stronger when the beam relative density is lower,resulting in more dramatic perpendicular heating of beam protons,whereas the situation is reversed when the beam relative density is larger. 相似文献
22.
Understanding on the hydrogen detection of plasma sprayed tin oxide/tungsten oxide (SnO2/WO3) sensor
《International Journal of Hydrogen Energy》2022,47(33):15120-15131
The plasma spray technique was well proven in producing metal oxide based gas sensors in the last two decades using different powder feedstocks. However, limited research was made to fabricate hydrogen gas sensor from tin oxide layer coated over tungsten oxide layer. This paper attempts to interpret the hydrogen gas sensing performances of plasma sprayed coating derived by depositing tin oxide layer over tungsten oxide (SnO2/WO3) layer. Plasma sprayed SnO2/WO3 sensor showed maximum response of 90% at 150 °C in contrast to stand-alone WO3 (89% at 350 °C) and stand-alone SnO2 (89% at 250 °C). The lower operating temperature of SnO2/WO3 sensor without compromising gas response was attributed to the WO3–SnO2 hetero-junction. SnO2/WO3 sensor showed selective sensing towards hydrogen with respect to carbon monoxide and methane gases. This sensor also possessed repeatable characteristics after 39 days from the initial measurement. In a nut-shell, plasma spayed SnO2/WO3 sensor showed stability of base resistance, repeatability after successive response and recovery cycles, selective sensing towards 500 ppm H2 with significant magnitude of gas response of 90%, response time of 35 s and recovery time of 269 s at a temperature of 150 °C. 相似文献
23.
《International Journal of Hydrogen Energy》2022,47(36):16165-16178
This study deals with the manufacturing of catalyst-coated membranes (CCMs) for newcomers in the field of coating. Although there are many studies on electrode ink composition for improving the performance of proton-exchange membrane fuel cells (PEMFCs), there are few papers dealing with electrode coating itself. Usually, it is a know-how that often remains secret and constitutes the added value of scientific teams or the business of industrialists. In this paper, we identify and clarify the role of key parameters to improve coating quality and also to correlate coating quality with fuel cell performance via polarization curves and electrochemical active surface area measurements. We found that the coating configurations can affect the performance of lab-made CCMs in PEMFCs. After the repeatability of the performance obtained by our coating method has been proved, we show that: (i) edge effects, due to mask shadowing - cannot be neglected when the active surface area is low, (ii) a heterogeneous thickness electrode produces performance lower than a homogeneous thickness electrode, and (iii) the origin and storage of platinum on carbon powders are a very important source of variability in the obtained results. 相似文献
24.
《International Journal of Hydrogen Energy》2022,47(52):22165-22179
Aluminum alloy bipolar plates have unique application potential in proton exchange membrane fuel cell (PEMFC) due to the characteristics of lightweight and low cost. However, extreme susceptibility to corrosion in PEMFC operation condition limits the application. To promote the corrosion resistance of aluminum alloy bipolar plates, a Ni–P/TiNO coating was prepared by electroless plating and closed field unbalanced magnetron sputter ion plating (CFUMSIP) technology on the 6061 Al substrate. The research results show that Ni–P interlayer improves the deposition effect of TiNO outer layer and increase the content of TiN and TiOxNy phases. Compared to Ni–P and TiNO single-layer coatings, the Ni–P/TiNO coating samples exhibited the lowest current density value of (1.10 ± 0.02) × 10?6 A·cm?2 in simulated PEMFC cathode environment. Additionally, potential cyclic polarization measurements were carried out aiming to evaluate the durability of the aluminum alloy bipolar plate during the PEMFC start-up/shut-up process. The results illustrate that the Ni–P/TiNO coating samples exhibit excellent stability and corrosion resistance. 相似文献
25.
《International Journal of Hydrogen Energy》2022,47(65):28152-28164
The combustion characteristics of ammonia/methanol mixtures were investigated numerically in this study. Methanol has a dramatic promotive effect on the laminar burning velocity (LBV) of ammonia. Three mechanisms from literature and another four self-developed mechanisms constructed in this study were evaluated using the measured laminar burning velocities of ammonia/methanol mixtures from Wang et al. (Combust.Flame. 2021). Generally, none of the selected mechanisms can precisely predict the measured laminar burning velocities at all conditions. Aiming to develop a simplified and reliable mechanism for ammonia/methanol mixtures, the constructed mechanism utilized NUI Galway mechanism (Combust.Flame. 2016) as methanol sub-mechanism and the Otomo mechanism (Int. J. Hydrogen. Energy. 2018) as ammonia sub-mechanism was optimized and reduced. The reduced mechanism entitled ‘DNO-NH3’, can accurately reproduce the measured laminar burning velocities of ammonia/methanol mixtures under all conditions. A reaction path analysis of the ammonia/methanol mixtures based on the DNO-NH3 mechanism shows that methanol is not directly involved in ammonia oxidation, instead, the produced methyl radicals from methanol oxidization contribute to the dehydrogenation of ammonia. Besides, NOx emission analysis demonstrates that 60% methanol addition results in the highest NOx emissions. The most important reactions dominating the NOx consumption and production are identified in this study. 相似文献
26.
Referring to the total surface existing in wheat dough, gluten–starch interfaces are a major component. However, their impact on dough rheology is largely unclear. Common viewpoints, based on starch surface modifications or reconstitution experiments, failed to show unambiguous relations of interface characteristics and dough rheology. Observing hybrid artificial dough systems with defined particle surface functionalization gives a new perspective. Since surface functionalization standardizes particle–polymer interfaces, the impact on rheology becomes clearly transferable and thus, contributes to a better understanding of gluten–starch interfaces. Based on this perspective, the effect of particle/starch surface functionality is discussed in relation to the rheological properties of natural wheat dough and modified gluten–starch systems. A competitive relation of starch and gluten for intermolecular interactions with the network-forming polymer becomes apparent during network development by adsorption phenomena. This gluten–starch adhesiveness delays the beginning of non-linearity under large deformations, thus contributing to a high deformability of dough. Consequently, starch surface functionality affects the mechanical properties, starting from network formation and ending with the thermal fixation of structure. 相似文献
27.
《Ceramics International》2022,48(6):7533-7549
(1-x)SrFe10Al2O19/(x)Co0.6Zn0.4Fe2O4-(SFAO/CZFO) hard/soft nanocomposite ferrite materials were synthesized by ‘one-pot’ self-propagating combustion route. The co-existence of the two magnetic phases were confirmed by XRD, FESEM, EDS and VSM. The prepared nanocomposite samples were also characterized by TGA/DSC, Raman spectroscopy and VNA. Exchange coupling between the hard and the soft magnetic grains was observed by determining the switching field distribution (SFD) curve. As a result of the competing effects of exchange interaction and dipolar interaction, magnetic parameters were observed to be sensitive to the incorporation of soft magnetic phase into the nanocomposite. Results showed that with the inclusion of soft magnetic phase, exchange coupling behaviour between the hard and the soft ferrite phases had significant influence on the microwave absorption capacity of the samples. Related electromagnetic parameters and impedance matching ratio of the nanocomposite system were discussed. A minimum reflection loss of ?42.9 dB with an absorber thickness of 2.5 mm was attained by the nanocomposite (90 wt%)SrFe10Al2O19/(10 wt %)Co0.6Zn0.4Fe2O4 at a matching frequency of 11.45 GHz. This assured the candidacy of SrFe10Al2O19/Co0.6Zn0.4Fe2O4 nanocomposite as a promising microwave absorption material in the X-band (8–12 GHz). 相似文献
28.
《Ceramics International》2022,48(7):9413-9425
Artificial bone fillers are essentially required for repairing bone defects, and developing the fillers with synergistic biocompatibility and anti-bacterial activity persists as one of the critical challenges. In this work, a new agarose/gadolinium-doped hydroxyapatite filler with three-dimensional porous structures was fabricated. For the composite filler, agarose provides three-dimensional skeleton and endows porosity, workability, and high specific surface area, hydroxyapatite (HA) offers the biocompatibility, and the rare earth element gadolinium (Gd) acts as the antibacterial agent. X-ray photoelectron spectroscopy detection showed the doping of Gd in HA lattice with the formation of Gd-HA interstitial solid solution. Attenuated total reflection Fourier transform infrared spectroscopy imaging suggested chemical interactions between agarose and Gd-HA, and the physical structure of agarose was tuned by the Gd-doped HA. Cytotoxicity testing and alizarin red staining experiments using mouse pro-osteoblasts (MC3T3-E1) revealed remarkable bioactivity and osteogenic properties of the composite fillers, and proliferation and growth rates of the cells increased in proportion to Gd content in the composites. Antibacterial testing using the gram-positive bacteria S. aureus and the gram-negative bacteria E. coli indicated promising antibacterial properties of the fillers. Meanwhile, the antibacterial properties of composite filles were enhanced with the increase of Gd content. The antibacterial fillers with porous structure and excellent physicomechanical properties show inspiring potential for bone defect repair. 相似文献
29.
《International Journal of Hydrogen Energy》2022,47(1):228-241
The construction of semiconductor heterojunction for photocatalytic H2 production from water splitting is an efficient and environment-friendly technology. In this work, ZnO/BiOCl (ZBC) and Sn-doped ZnO/BiOCl (ZBC-S) photocatalysts with Z-scheme heterojunction were successfully prepared by simple hydrothermal method. The photocatalytic H2 evolution from water splitting by the as-prepared photocatalysts was investigated. The formation of ZnO/BiOCl heterojunction reduces the recombination probability of the photogenerated carriers. The impurity levels originated from Sn doping reduce the band gap width of ZnO and BiOCl to some extent, thereby enhancing the light absorption ability. The ZBC-S composite exhibits the best photocatalytic activity. In addition, the photocatalytic efficiency of H2 production was improved by sensitization with Eosin Y (EY) dye. The H2 production rate under simulated sunlight reaches 4146.77 μmol g?1 h?1, which is 27 times higher than that of pure ZnO. Finally, the Z-scheme electron transfer route in ZnO/BiOCl heterojunction was determined, and the photocatalytic H2 production mechanism of EY sensitized ZBC-S was proposed. 相似文献
30.
《Ceramics International》2022,48(7):9164-9171
The light-trapping structure is an effective method to increase solar light capture efficiency in the solar cells. In this study, Al-doped ZnO (AZO)/polystyrene (PS)/AZO tri-layer transparent conductive film with light-trapping structure was fabricated by magnetron sputtering and liquid phase methods. The structural, optical and electrical properties of the AZO films could be controlled by different growth conditions. When the sputtering pressure of the under-layer AZO film was 0.2 Pa, the discharge voltage was around 80 V, which was within the optimal process window for obtaining AZO film with high crystallinity. The optimal under-layer AZO film had a large surface roughness and a very low static water contact angle of 75.71°, promoting the relatively uniform distribution of PS spheres. Under this sputtering condition, the prepared AZO/PS/AZO tri-layer film had the highest crystallinity and least point defects. The highest carrier concentration and Hall mobility are 3.0 × 1021 cm-3and 5.39 cm2 V-1 s-1, respectively. Additionally, a transparent conductive film with the lowest resistivity value (3.88 × 10-4 Ω cm) and the highest average haze value (26.5%) was obtained by optimizing the process parameters. These properties were comparable to or exceed the reported values of surface-textured SnO2-based as well as ZnO-based TCOs films, making our films suitable for transparent electrode applications, especially in thin-film solar cells. 相似文献