全文获取类型
收费全文 | 7312篇 |
免费 | 190篇 |
国内免费 | 129篇 |
专业分类
电工技术 | 120篇 |
技术理论 | 2篇 |
综合类 | 188篇 |
化学工业 | 1520篇 |
金属工艺 | 975篇 |
机械仪表 | 730篇 |
建筑科学 | 300篇 |
矿业工程 | 805篇 |
能源动力 | 532篇 |
轻工业 | 238篇 |
水利工程 | 33篇 |
石油天然气 | 181篇 |
武器工业 | 16篇 |
无线电 | 177篇 |
一般工业技术 | 913篇 |
冶金工业 | 541篇 |
原子能技术 | 119篇 |
自动化技术 | 241篇 |
出版年
2024年 | 8篇 |
2023年 | 64篇 |
2022年 | 112篇 |
2021年 | 100篇 |
2020年 | 137篇 |
2019年 | 115篇 |
2018年 | 103篇 |
2017年 | 115篇 |
2016年 | 122篇 |
2015年 | 132篇 |
2014年 | 305篇 |
2013年 | 362篇 |
2012年 | 307篇 |
2011年 | 538篇 |
2010年 | 404篇 |
2009年 | 462篇 |
2008年 | 411篇 |
2007年 | 463篇 |
2006年 | 482篇 |
2005年 | 391篇 |
2004年 | 325篇 |
2003年 | 321篇 |
2002年 | 269篇 |
2001年 | 216篇 |
2000年 | 208篇 |
1999年 | 233篇 |
1998年 | 189篇 |
1997年 | 137篇 |
1996年 | 127篇 |
1995年 | 146篇 |
1994年 | 100篇 |
1993年 | 43篇 |
1992年 | 58篇 |
1991年 | 30篇 |
1990年 | 21篇 |
1989年 | 25篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有7631条查询结果,搜索用时 15 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(90):38468-38476
The distribution of hydrogen entering an Fe sheet under a droplet of NaCl solution was successfully visualized using a hydrogenochromic sensor consisting of a polyaniline layer and a Ni intermediate layer. At the initial stage of corrosion, the hydrogen entry was barely confirmed. The hydrogen entry was observed as the corrosion proceeded, and the preferential hydrogen entry site corresponded to the rust-formed area. It was postulated that the hydrogen entry is promoted by the decrease in pH due to the hydrolysis reactions of Fe ions under the rust. The hydrogenochromic sensor paves the way for the visualization of the hydrogen entry into metals under corrosion conditions. 相似文献
2.
《Advanced Powder Technology》2022,33(12):103847
We investigate synthesis, phase evolution, hollow and porous structure and magnetic properties of quasi-amorphous intermediate phase (QUAIPH) and hematite (α-Fe2O3) nanostructure synthesized by annealing of akaganeite (β-FeOOH) nanorods. It is found that the annealing temperature determines the phase composition of the products, the crystal structure/size dictates the magnetic properties whereas the final nanorod morphology is determined by the starting material. Annealing of β-FeOOH at ~300 °C resulted in the formation of hollow QUAIPH nanorods. The synthesized material shows low-cytotoxicity, superparamagnetism and good transverse relaxivity, which is rarely reported for QUAIPH. The QUAIPH nanorods started to transform to porous hematite nanostructures at ~350 °C and phase transformation was completed at 600 °C. During the annealing, the crystal structure changed from monoclinic (akaganeite) to quasi-amorphous and rhombohedral (hematite). Unusually, the crystallite size first decreased (akaganeite → QUAIPH) and then increased (QUAIPH → hematite) during annealing whereas the nanorods retained particle shape. The magnetic properties of the samples changed from antiferromagnetic (akaganeite) to superparamagnetic with blocking temperature TB = 84 K (QUAIPH) and finally to weak-ferromagnetic with the Morin transition at TM = 244 K and high coercivity HC = 1652 Oe (hematite). The low-cytotoxicity and MRI relaxivity (r2 = 5.80 mM?1 s?1 (akaganeite), r2 = 4.31 mM?1 s?1 (QUAIPH) and r2 = 5.17 mM?1 s?1 (hematite)) reveal potential for biomedical applications. 相似文献
3.
《Advanced Powder Technology》2022,33(12):103872
We investigate the transition evolution from the initial state with the random packing of the particles to the stable state in which successive avalanches exhibit consistent characteristics under the slumping regime. It is found that there exist three distinct stages in the transition evolution, considering the change of the volume fraction. The coordination number is almost unchanged during the transition evolution, which indicates the particle contact form is consistent in the three stages. The pause phenomena are discovered in some avalanches, and the probability of pause occurrence increases continuously in the three consecutive stages. We also explore the distribution of particles in the passive layer at the stable state. The particles in the middle region of the passive layer have the closest packing status, and the deeper the region is located, the later it reaches the stable state. 相似文献
4.
Hiromi Eba Yuki Masuzoe Toru Sugihara Hayao Yagi Tian Liu 《International Journal of Hydrogen Energy》2021,46(18):10642-10652
Ammonia generation was studied in the reaction between water and nitrogen-containing iron at 323 K and atmospheric pressure. Similar to metallic Fe, the interstitial compound Fe3N reduced water through Fe oxidation to produce hydrogen gas, while the N combined with atomic hydrogen to produce ammonia as a byproduct. The addition of carbon dioxide to this system accelerated the reaction with concomitant consumption of carbon dioxide. The promoted ammonia production upon addition of carbon dioxide can be attributed to the generation of atomic hydrogen from the redox reaction of carbonic acid and Fe, as well as removal of used Fe from the reaction system through the formation of a soluble carbonato complex. When carbonate was added to the reaction system, the production rates of ammonia and hydrogen increased further. The results here confirmed that ammonia can be synthesized from iron nitride under mild conditions by utilizing carbon dioxide. 相似文献
5.
Qianying Hoo Xiaohu Wang Feng Yuan Xuewei Cao Tiewa Cao Maolin Zhang 《Journal of the European Ceramic Society》2021,41(6):3816-3822
Jingdezhen is famous for its bluish white (Qingbai) porcelains of the Song Dynasty, and those decorated with iron spots are distinctive among them. Herein, iron spots on a bluish white porcelain were investigated using a series of microscopic and spectroscopic characterizations. We found the decreasing iron content from more than 8 wt% to about 2 wt% during the glaze color transition from rusty to brown and finally into green, which built a connection on the coloring mechanism of iron-rich crystallized glaze and celadon glaze. We identified the rare ε-Fe2O3, a promising magnetic material, in both the dark brown crystals and the triangular crystals in the rusty area, which is its first discovery among bluish white porcelains. Based on these findings, we discussed the coloring mechanism of iron-spot decoration along with the physical form of the iron oxide crystals, indicating the partially reducing atmosphere during firing process. 相似文献
6.
A hybrid sorbent material for removal of hydrogen sulfide from air was developed. The material is based on activated carbon and iron compounds obtained from waste iron(II) sulfate(VI) heptahydrate. The iron salt is deposited on the carbonaceous support and subjected to oxidation (Fe2+ to Fe3+) using atmospheric oxygen under alkaline conditions. An effect of H2O2 addition to the process on the composition of the resultant material was also examined. X-ray diffraction (XRD) analyses confirmed easy conversion of waste FeSO4·7H2O to iron oxides Fe3O4 and FeOOH. The activated carbon supporting iron oxides revealed a higher efficiency in H2S elimination from air compared to the commercial activated carbon, without any modification. 相似文献
7.
The heat transfer and flow characteristics of MWCNT-R141b nanorefrigerant with different mass fractions have been studied through experiments. Experimental results were compared with existing correlations. A two-step method was used to prepare the nanorefrigerants. Span-80 was used as surfactant with an average particle diameter of 20 nm. Transmittance method was used to evaluate the stability of nanorefrigerants. Results showed that the stability of MWCNT-R141b nanorefrigerant, which is the added dispersant, was good during the experiments. The 0.3 wt% MWCNT-R141b nanorefrigerants had optimal heat transfer enhancement effects compared with pure refrigerants. The maximum Nusselt number increased by 40%. The specific pressure drop of nanorefrigerant increased as the Reynolds number (Re) increased, and the specific pressure drop of the pure refrigerant was minimum, which is similar to R141b. 相似文献
8.
ABSTRACTA mathematical model has been developed by coupling genetic algorithm (GA) with heat and material balance equations to estimate rate parameters and solid-phase evolution related to the reduction of iron ore-coal composite pellets in a multi-layer bed Rotary hearth Furnace (RHF). The present process involves treating iron ore-coal composite pellets in a crucible over the hearth in RHF. The various solid phases evolved at the end of the process are estimated experimentally, and are used in conjunction with the model to estimate rate parameters. The predicted apparent activation energy for the wustite reduction step is found to be lower than those of the reduction of higher oxides. The thermal efficiency is found to decrease significantly with an increase in the carbon content of the pellet. Thermal efficiency was also found to increase mildly up to three layers. Multilayer bed remains as a potential design parameter to increase thermal efficiency. 相似文献
9.
《Ceramics International》2022,48(8):10506-10515
The search for materials and methods capable of reducing human impacts on the environment is of utmost importance nowadays. This study's primary purpose was to analyze the technical feasibility of ceramic composites production utilizing Fundão Dam's Iron Ore Tailings (IOT), Blast Furnace Slag (BFS) from charcoal, and Foundry Sand (FS) as partial substitutes for the traditional raw materials – sand and clay – for application in building industry materials. The composites were molded in rectangular specimens and fired at temperatures of 900, 950, 1000, 1050, and 1200 °C. The developed materials were analyzed and characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Thermogravimetry (TGA), and Differential Thermal Analysis (DTA). The obtained materials had flexural strength modulus of up to 12.19 MPa, water absorption ranging from 2 to 22%, linear shrinkage ranging from 0.02 to 6.50%, and apparent density ranging from 2.03 to 1.63 g/cm3. The study of the internal structure formation process revealed the formation of amorphous structures in the composites. The results demonstrated that these waste materials may be jointly used in construction materials, contributing to the reduction of natural resource extraction, besides enabling their correct disposal, minimizing environmental impacts, and improving the life quality of the surrounding communities. 相似文献
10.
J. Grune K. Sempert M. Kuznetsov T. Jordan 《International Journal of Hydrogen Energy》2021,46(23):12487-12496
This paper presents results of experimental investigations on spherical and cylindrical flame propagation in pre-mixed H2/air-mixtures in unconfined and semi-confined geometries. The experiments were performed in a facility consisting of two transparent solid walls with 1 m2 area and four weak side walls made from thin plastic film. The gap size between the solid walls was varied stepwise from thin layer geometry (6 mm) to cube geometry (1 m). A wide range of H2/air-mixtures with volumetric hydrogen concentrations from 10% to 45% H2 was ignited between the transparent solid walls. The propagating flame front and its structure was observed with a large scale high speed shadow system. Results of spherical and cylindrical flame propagation up to a radius of 0.5 m were analyzed. The presented spherical burning velocity model is used to discuss the self-acceleration phenomena in unconfined and unobstructed pre-mixed H2/air flames. 相似文献