全文获取类型
收费全文 | 5680篇 |
免费 | 594篇 |
国内免费 | 179篇 |
专业分类
电工技术 | 71篇 |
综合类 | 404篇 |
化学工业 | 3156篇 |
金属工艺 | 230篇 |
机械仪表 | 44篇 |
建筑科学 | 308篇 |
矿业工程 | 279篇 |
能源动力 | 89篇 |
轻工业 | 561篇 |
水利工程 | 52篇 |
石油天然气 | 268篇 |
武器工业 | 6篇 |
无线电 | 71篇 |
一般工业技术 | 435篇 |
冶金工业 | 430篇 |
原子能技术 | 34篇 |
自动化技术 | 15篇 |
出版年
2024年 | 7篇 |
2023年 | 80篇 |
2022年 | 163篇 |
2021年 | 179篇 |
2020年 | 167篇 |
2019年 | 158篇 |
2018年 | 175篇 |
2017年 | 184篇 |
2016年 | 202篇 |
2015年 | 219篇 |
2014年 | 326篇 |
2013年 | 354篇 |
2012年 | 413篇 |
2011年 | 434篇 |
2010年 | 301篇 |
2009年 | 313篇 |
2008年 | 253篇 |
2007年 | 322篇 |
2006年 | 301篇 |
2005年 | 298篇 |
2004年 | 248篇 |
2003年 | 244篇 |
2002年 | 203篇 |
2001年 | 172篇 |
2000年 | 152篇 |
1999年 | 137篇 |
1998年 | 104篇 |
1997年 | 65篇 |
1996年 | 66篇 |
1995年 | 42篇 |
1994年 | 42篇 |
1993年 | 25篇 |
1992年 | 22篇 |
1991年 | 18篇 |
1990年 | 13篇 |
1989年 | 5篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1962年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有6453条查询结果,搜索用时 18 毫秒
1.
《Ceramics International》2022,48(24):36620-36628
In order to solve the problem of low charging and discharging energy density of dielectric capacitors, the structure design of layered polymer matrix composites is carried out in this paper. Ba0.7Sr0.3TiO3, Ba0.8Sr0.2TiO3 and Ba0.9Sr0.1TiO3 nanoparticles were successfully prepared by the oxalate coprecipitation method. The surface of BaxSr1-xTiO3 was successfully coated with dopamine, which promoted the dispersion of the polymer matrix of the ceramic powder. Monolayer BaxSr1-xTiO3/PVDF composites containing BaxSr1-xTiO3 with different Ba/Sr ratios were successfully prepared by the casting method. Three-layer asymmetric composites with different fillers were successfully prepared by layer-by-layer casting. The phase and microstructure of the as-prepared materials were analyzed by XRD and SEM. The dielectric, electrical conductivity, ferroelectric and energy storage properties of the composites were tested. The effects and laws of the design of the three-layer asymmetric structure on the dielectric properties and energy storage properties of the layered composites are mainly studied. When the structure of the three-layer asymmetric composite is 1-2-3, the breakdown field strength reaches 330 kV/mm, the discharge energy density reaches 8.51 J/cm3, and the charge-discharge efficiency is 67%. This work demonstrates that layered composites with asymmetric properties can facilitate the development of electrical energy storage. 相似文献
2.
《International Journal of Hydrogen Energy》2022,47(42):18566-18575
In this study, a sulfidogenic reactor fed with microalgal biomass of Chlorella pyrenoidosa as an electron donor was operated in a continuous mode. This study evaluated the influence of various initial sulfate concentration from 1.0 to 2.5 g/L on anaerobic sulfate reduction kinetics by a sulfidogenic enrichment culture predominantly Desulfovibrio sp. VSV2. It was observed that volumetric sulfate reduction rate (VSRR) was consistently increasing with an increase in volumetric sulfate loading rate (VSLR) across the retention time of 7–10 days. For a retention time of 7 days, the maximum VSRR was noted as 0.0050 g/(L.h) with a corresponding VSLR of 0.0089 g/(L.h). When retention time was maintained for 10 days, a maximum sulfate reduction of 65% and a maximum bacterial concentration of 1.632 g/L were achieved for an initial sulfate concentration of 1.5 g/L. It was concluded that VSLR facilitated through both dilution rate and initial sulfate concentration had a significant influence over sulfate reduction kinetics. The results of the study suggested that the microalgal-fed sulfidogenic system could be effectively employed for reduction of sulfate from sulfate-rich wastewater. 相似文献
3.
《Ceramics International》2022,48(9):11988-11997
We have studied peculiarities in the formation of single-crystalline barium titanate (BaTiO3) nanorods from a glycolate-mediated complex via a single-step hydrothermal process under different supersaturation (SR) conditions. X-ray diffraction (XRD) showed the formation of pure BaTiO3 with an SR of above 19. The tetragonality for the BaTiO3 (c/a) reached 1.013 at SR = 19–29 and dropped to 1.010 for SR = 39. According to the transmission electron microscopy (TEM) and XRD analyses, the rod-shaped particles exhibited single crystallinity and crystal growth along the [001] plane. With scanning electron microscopy (SEM), the morphological evolution from a plate-shaped intermediate precursor (SR = 6–9) to a rod-shaped product with an aspect ratio of 6–9 (SR = 19–29), and to non-polar material with an irregular structure (SR = 39), was observed. The negative slope, linear dependence of the particles’ width and length on the supersaturation level in the range SR = 19–39 was established for the first time. The replacement of the prevailing crystallization mechanism from in-situ topotactic transformation into dissolution-precipitation above SR = 19 was observed. It was shown that with a simple regulation of the SR, the structural and morphological characteristics of the obtained BaTiO3 nanoparticle can be effectively tuned. 相似文献
4.
Ivan Kushkevych Blanka Hýov Monika Vítzov Simon K.-M. R. Rittmann 《International journal of molecular sciences》2021,22(8)
This paper is devoted to microscopic methods for the identification of sulfate-reducing bacteria (SRB). In this context, it describes various habitats, morphology and techniques used for the detection and identification of this very heterogeneous group of anaerobic microorganisms. SRB are present in almost every habitat on Earth, including freshwater and marine water, soils, sediments or animals. In the oil, water and gas industries, they can cause considerable economic losses due to their hydrogen sulfide production; in periodontal lesions and the colon of humans, they can cause health complications. Although the role of these bacteria in inflammatory bowel diseases is not entirely known yet, their presence is increased in patients and produced hydrogen sulfide has a cytotoxic effect. For these reasons, methods for the detection of these microorganisms were described. Apart from selected molecular techniques, including metagenomics, fluorescence microscopy was one of the applied methods. Especially fluorescence in situ hybridization (FISH) in various modifications was described. This method enables visual identification of SRB, determining their abundance and spatial distribution in environmental biofilms and gut samples. 相似文献
5.
《Ceramics International》2022,48(13):18925-18932
The dielectric properties of a novel polymer dielectric material were investigated. The conductive phase of RuO2 was synthesized for deposition on the surface of a nanosized BaTiO3 (nBT). The RuO2@nBT hybrid particles were incorporated into a poly (vinylidene fluoride) (PVDF) as a three-phase composite (RuO2@nBT/PVDF). The obtained dielectric constant (ε′) was significantly high (3837.16) for the composite with a volume fraction of = 0.50. The large interfacial polarization between the RuO2?nBT and RuO2?PVDF interfaces considerably increased the value of ε′. Therefore, interfacial polarization is a critical factor in improving the dielectric properties. The dielectric behavior of the RuO2@nBT/PVDF composites can be described using the effective medium percolation theory model, which indicates the significant contributions of the conductive RuO2 phase and high-permittivity nBT phase. 相似文献
6.
《Ceramics International》2022,48(7):9527-9533
In this work, a magnetodielectric coupling observed in barium titanate–cobalt ferrite composites synthesized using high-energy ball milling assisted via a thermal treatment is discussed. Vibrating sample magnetometry and dielectric spectroscopy showed that multiferroic composites possess both ferromagnetic and dielectric behaviors inherited from the parent ferromagnetic cobalt ferrite and ferroelectric barium titanate phases. The magnetocapacitance (up to 35%) recorded for x = 0.3, (1-x)BaTiO3–xCoFe2O4, can be attributed to the spin-dependent filtering mechanism. The composite with the aforementioned composition exhibited a homogeneous matrix–particle composite microstructure, which was achieved via high-energy ball milling during the mixing stage. 相似文献
7.
《Ceramics International》2022,48(14):20158-20167
Vacuum induction melting is a potential process for the preparation of TiAl alloys with good homogeneity and low cost. But the crucial problem is a selection of high stability refractory. In this study, a BaZrO3/Y2O3 dual-phase refractory was prepared and its performance for melting TiAl alloys was studied and compared with that of a Y2O3 refractory. The results showed the dual-phase refractory consisted of BaZr1-xYxO3-δ and Y2O3(ZrO2), exhibited a thinner interaction layer (30 μm) than the Y2O3 refractory (90 μm) after melting the TiAl alloy. Although the TiAl alloys melted in the dual-phase and Y2O3 refractory exhibited similar oxygen contamination (<0.1 wt%), the alloy melted in the dual-phase refractory had smaller Y2O3 inclusion content and size than that in the Y2O3 refractory, indicating that the dual-phase refractory exhibited a better melting performance than the Y2O3 refractory. This study provides insights into the process of designing highly stable refractory for melting TiAl alloys. 相似文献
8.
9.
Samson I. Eze Chidinma C. Ezeofor Nkiru V. Mmadubuike Francis K. Ojo 《Petroleum Science and Technology》2019,37(15):1830-1838
The abstraction of crude oil molecules from aqueous solution (produced water) and from real petroleum polluted water (collected from River State, Nigeria) by Dialium guineense Seed Husk (DGSH) and its ammonium sulfate functionalized form (AS-DGSH) was studied using a batch technique. The sorbents were characterized using Fourier transform infrared (FTIR), BET surface area analysis and the Scanning electron microscopy (SEM). Crude oil characterization revealed a light crude oil based on the API gravity of 35.60. The Langmuir and Freundlich models gave good fits for crude oil sorption on DGSH and AS-DGSH respectively. The sorbents were found to remove over 50% of crude oil from the real polluted water at the natural pH of 6.1 and showed increase in removal with increase in sorbent dose. The potential of DGSH and its ammonium sulfate modified derivative as effective low cost sorbents for oil spill treatment was established. 相似文献
10.
The precipitation of the water-leaching solution of Baotou mixed rare earth(RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewater because of the relatively low solubility of rare earth sulfate.To solve the serious problem of ammonia-nitrogen pollution,new precipitators need to be developed urgently so as to meet the requirements of environmental protection and impurities content of the product(SO_4~(2-)1.8 wt% in RE carbonates products).In this paper,we studied the effects of feeding modes on the behavior of SO_4~(2-) during the preparation of light RE carbonate(RE=La,Ce,Pr,Nd) from their sulfate solutions using Mg(HCO_3)_2 as a precipitant.The results indicate that the contents of SO_4~(2+) in the La and Ce precipitates using positive feeding mode exceed 16 wt% because of the formation of La2(CO_3)_(2.15)(-SO_4)_(0.85)·4 H_2 O and Ce2(CO_3)_(2.15)(SO_4)_(0.85)·3 H_2 O,while those of the Pr and Nd precipitates are 4 wt%-5 wt%since they exist in the form of n-carbonate.The precipitates prepared using synchronous feeding mode are all RE carbonate with only 4 wt%-5 wt% of SO_4~(2-) enclosed in the precipitation.The content of SO_4~(2-) in the RE carbonate obtained using reverse feeding mode is the lowest.Among them,the content of SO_4~(2-) in La precipitate is only 1.40 wt%.Both synchronous and reverse feeding modes can effectively reduce the content of SO_4~(2-)in RE carbonate,which provides theoretical guidance for the preparation of qualified light RE carbonate products by Mg(HCO_3)_2 precipitation method. 相似文献