全文获取类型
收费全文 | 2352篇 |
免费 | 258篇 |
国内免费 | 96篇 |
专业分类
电工技术 | 34篇 |
综合类 | 77篇 |
化学工业 | 374篇 |
金属工艺 | 595篇 |
机械仪表 | 78篇 |
建筑科学 | 7篇 |
矿业工程 | 26篇 |
能源动力 | 6篇 |
轻工业 | 12篇 |
水利工程 | 1篇 |
武器工业 | 6篇 |
无线电 | 1143篇 |
一般工业技术 | 266篇 |
冶金工业 | 47篇 |
自动化技术 | 34篇 |
出版年
2024年 | 1篇 |
2023年 | 36篇 |
2022年 | 70篇 |
2021年 | 62篇 |
2020年 | 54篇 |
2019年 | 53篇 |
2018年 | 77篇 |
2017年 | 83篇 |
2016年 | 58篇 |
2015年 | 68篇 |
2014年 | 105篇 |
2013年 | 110篇 |
2012年 | 139篇 |
2011年 | 170篇 |
2010年 | 138篇 |
2009年 | 187篇 |
2008年 | 173篇 |
2007年 | 193篇 |
2006年 | 204篇 |
2005年 | 154篇 |
2004年 | 128篇 |
2003年 | 91篇 |
2002年 | 74篇 |
2001年 | 65篇 |
2000年 | 48篇 |
1999年 | 44篇 |
1998年 | 30篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 15篇 |
1994年 | 31篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有2706条查询结果,搜索用时 46 毫秒
1.
Novel lead-free (1-x)Ba0·9Ca0·1Ti0·9Zr0·1O3-xSrNb2O6 ceramics were synthesized via a two-step high energy ball milling process. The evolution of microstructural properties, phase transformation, and energy storage characteristics was comprehensively investigated to assess the applicability of material in multi-layered ceramic capacitors. The substitution of SrNb2O6 (SNO) in Ba0·9Ca0·1Ti0·9Zr0·1O3 (BTCZ) has resulted in substantial improvement in materials density along with a small increase in the grain size of the synthesized ceramic. A thorough microstructural investigation indicates an excellent dispersibility and compatibility between BTCZ and SNO phases. With an increase in SNO substitution, a transition from typical ferroelectric to relaxor ferroelectric has been observed, which has led to a significantly slimmer ferroelectric loop along with frequency dispersive dielectric properties. The optimized composition (i.e., x = 0.10) exhibits an ultra-high recoverable energy density of 2.68 J/cm3 along with a moderately high energy efficiency of 83.4%. Further, SNO substituted samples have also shown an enhancement in breakdown strength. The improvement in energy storage performance and breakdown strength of SNO substituted BTCZ composites are mainly attributed to relatively homogeneous grain morphology, optimum grain size, microstructural density, and improved grain boundary interface. 相似文献
2.
《Ceramics International》2022,48(3):3368-3373
Over the recent past, lead-based halide perovskite materials have drawn significant attention due to their excellent optical and electrical properties for solar cells and optoelectronics applications. However, the toxicity of lead elements and instability under ambient conditions leads to develop alternative compositions. Herein, we report a novel mechanochemical synthesis of tin iodide-based double perovskites (A2SnI6; A = Rb+, Cs+, methylammonium, and formamidinium), and their structural, optical, and electrical properties are investigated. Importantly, we found that the hydrogen iodide (HI) addition during the ball-milling process minimizes secondary phase formation in the synthesized A2SnI6 powders. The effects of HI addition and the A-site substitution are investigated with respect to the lattice parameters, optical bandgaps, and electrical properties of the synthesized perovskite materials. Our results demonstrate essential information to improve the understanding of halide perovskite materials and develop efficient lead-free perovskite photoelectric devices. 相似文献
3.
《Ceramics International》2022,48(17):24716-24724
Dielectric capacitors show great potential in superior energy storage devices. However, the energy density of these capacitors is still inadequate to meet the requirement of energy storage applications. In this study, the Bi0.5Na0.47Li0.03TiO3-xNaNbO3 (BNLT-xNN) ceramics were prepared via conventional solid-phase reaction. Results showed that NN can efficaciously enhance the breakdown strength (Eb) and the relaxation behavior of the BNLT ceramic because of the broken ferroelectric long-range order. When x = 0.3, the maximum Eb reached 350 kV/cm, at which the 0.7BNLT-0.3NN ceramic exhibited the high recoverable energy storage density (Wrec) of 4.83 J/cm3 and great efficiency (η) of 78.9%. The ceramic demonstrated good temperature stability at 20 °C-160 °C and excellent fatigue resistance. Additionally, the 0.7BNLT-0.3NN ceramic presented high power density (PD; ~77.58 MW/cm3), large current density (CD; ~861.99 A/cm2), and quite short discharge time (t0.9; ~0.090 μs). These results indicated that the 0.7BNLT-0.3NN material has excellent energy storage properties and various application prospects. 相似文献
4.
《Ceramics International》2022,48(14):19527-19541
Ferroelectric lead-free NaNbO3-based ceramics are the most promising candidates to a wide range of advanced technological applications as sensors, transducers and actuators. In special, (K,Na)NbO3 (KNN) and (Ba,Na)(Ti,Nb)O3 (BTNN) show interesting structural properties, including morphotropic phase boundaries regions that lead to exceptional dielectric, piezoelectric and ferroelectric responses. Also, the biocompatibility of these compounds allows their application as biomedical sensors, medical devices, and bone tissue replacement. In this way, high impact applications can be achieved with ferroelectric lead free NaNbO3 – based (NN-based) ceramics. In this review, we will explore the strategies for the improvement of ferroelectric, dielectric and structural properties reviewing the effects of the synthesis process, microstructure and chemical composition of lead-free complex perovskite ceramics, specially KNN and BTNN, as well as, PVDF-KNN and PVDF-BTNN polymer-ceramic and the (PVDF-TrFE)-KNN copolymer-ceramic composites to provide new insights and research opportunities for the development and improvement of fundamental properties of such systems considering their potential for technological applications, especially for the biological ones. 相似文献
5.
《Ceramics International》2020,46(3):3311-3323
Materials with two distinct (magnetostrictive-ferroelectric) phases, i.e., x (Co0·9Ni0·1Fe2O4) -(1-x) [0.5 (Ba0·7Ca0·3TiO3) −0.5 (BaZr0·2Ti0·8O3)], combined at ratios of 10:90, 20:80, 30:70, and 40:60 were prepared using a hydroxide coprecipitation method. These multiferroic composites were subjected to sintering via the hybrid microwave sintering technique at 1200 °C for 20 min. Ni-substituted CFO exhibited excellent magnetic properties at room temperature, with Ms ≈ 80 emu/g, μB ≈ 3.37, Mr ≈ 19.05 emu/g, and Hc ≈ 599 Oe, as well as a high value of the magnetostriction coefficient (λ12 ≈ −118 ppm). The magnetostrictive-ferroelectric crystal phases in each composite were confirmed via X-ray diffraction analysis. The highest value of the linear magneto-electric coefficient was α = 21.6 mV/cm-Oe at a frequency of 1 kHz for the 40CNFO-60(BCT-BZT) composite, and a similar sample had the highest value of the magnetodielectric coefficient, which was approximately 3.3% at f = 1 kHz with an applied magnetic field of 1 T. The typical ferromagnetic and ferroelectric nature of each composite was confirmed by M − H and P–E hysteresis loops, respectively at room temperature. Two anomalies were observed in the temperature-dependent dielectric permittivity one at ~140 °C and another above 500 °C confirming the coexistence of two materials with distinct transition points, i.e., BCT-BZT and CNFO, respectively. 相似文献
6.
He Qi Ruzhong Zuo Jing-feng Li Longtu Li 《Journal of the European Ceramic Society》2018,38(16):5341-5347
A morphotropic phase boundary (MPB) between rhombohedral (R) and tetragonal (T) phases was identified in a few (0.9-x)NaNbO3-0.1BaTiO3-xABO3 (x?=?0–0.05) lead-free systems. Critical roles of R-phase inducers were specially evaluated in terms of phase boundary position, microstructure and piezoelectric responses. The results indicate not only the tolerance factor of the ABO3 additive but also its ferroelectricity and corresponding volume change would influence the formation of phase boundary and further determine dielectric and ferroelectric responses. The piezoelectric coefficient d33 of MPB compositions was compared with theoretically-calculated d33-cal according to d33?=?2Pr·ε33·Q33, demonstrating that the piezoelectric response of these systems should be determined by combined effects of the phase coexistence, nano-scale domains and particularly enhanced dielectric responses. The largest d33 ~305 pC/N, the highest ε33T/εo ~2815 and the lowest Pr ~14.7 μC/cm2 were achieved in the MPB composition with 3.75% SrZrO3. These experimental results provide a valuable reference for designing new NaNbO3-based lead-free piezoelectric materials. 相似文献
7.
Rizwan Ahmed Malik Ali Hussain Matias Acosta John Daniels Hyoung-Su Han Myong-Ho Kim Jae-Shin Lee 《Journal of the European Ceramic Society》2018,38(6):2511-2519
In this work, the relationship between the structural mechanisms and macroscopic electrical properties of the Nb-modified 0.96(Bi0.5Na0.84K0.16TiO3)–0.04SrTiO3 (BNKT–ST) system were elucidated by using temperature dependent and in situ synchrotron X-ray diffraction (XRD) techniques. For the composition x?=?0.0175, a large-signal piezoelectric coefficient (Smax/Emax?=?d33*) of 735 pm?V?1 at 6?kV mm?1 was observed at room temperature. Interestingly, at a higher temperature of 110?°C, the sample still showed a large d33* of 570 pm V?1. Furthermore, the temperature-invariant electrostrictive coefficient for this sample was found to be 0.0285?m4?C?2 over the temperature range of 25–170?°C. Moreover, the energy density for x?=?0.030 sample was ~1.0?J?cm?3 with an energy storage efficiency of ?70% in the temperature range of 25–135?°C. These results suggest that the synthesized Nb-modified BNKT–ST system is promising for the design of ceramic actuators as well as capacitor applications. 相似文献
8.
Li-Feng Zhu Bo-Ping Zhang Jia-Qi Duan Bo-Wei Xun Ning Wang Yu-Cheng Tang Gao-Lei Zhao 《Journal of the European Ceramic Society》2018,38(10):3463-3471
0.7BiFeO3-0.3BaTiO3 (BFO-0.3BT) ceramics were prepared to uncover the impacts of sintering temperature (TS) and dwell time (td) on the microstructure and electrical properties. With increasing the TS or td, the grain sizes increase along with the porosity decreases, which is in favor of the alignment of dipole. However, excess TS or td are inclined to cause the volatilization of Bi2O3, which deteriorates piezoelectric properties. Because of the R-T two-phase coexistence, low defect ions concentration and porosity, as well as appropriate grain size, the excellent d33?=?208?pC/N and kp?=?35.46% as well as Pr?=?28.52?μC/cm2 were achieved in BFO-0.3BT ceramics at TS?=?1000?°C and td?=?6?h. In addition,large unipolar strain 0.13% and d33*?=?256.2?pm/V also were obtained in BFO-0.3BT ceramics at TS?=?1000?°C and td?=?6?h. This research indicates that the porosity and defect ion concentration as well as grain size also play an important role in piezoelectric properties in BFO-BT ceramics. 相似文献
9.
Xiang Lv Jiagang Wu Jianguo Zhu Dingquan Xiao Xixiang Zhang 《Journal of the European Ceramic Society》2018,38(1):85-94
Although both the phase type and fraction of multi-phase coexistence can affect the electrical properties of (K,Na)NbO3 (KNN)-based ceramics, effects of phase fraction on their electrical properties were few concerned. In this work, through changing the calcination temperature of CaZrO3 powders, we successfully developed the 0.96 K0.5Na0.5Nb0.96Sb0.04O3-0.01CaZrO3-0.03Bi0.5Na0.5HfO3 ceramics containing a wide rhombohedral-tetragonal (R-T) phase coexistence with the variations of T (or R) phase fractions. It was found that higher T phase fraction can warrant a larger piezoelectric constant (d33) and d33 also showed a linear variation with respect to tetragonality ratio (c/a). More importantly, a number of domain patterns were observed due to high T phase fraction and large c/a ratio, greatly benefiting the piezoelectricity. In addition, the improved ferroelectric fatigue behavior and thermal stability were also shown in the ceramics containing high T phase fraction. Therefore, this work can bring a new viewpoint into the physical mechanism of KNN-based ceramics behind R-T phase coexistence. 相似文献
10.
Florian Weyland Thorsten Eisele Sebastian Steiner Till Frömling George A. Rossetti Jürgen Rödel Nikola Novak 《Journal of the European Ceramic Society》2018,38(2):551-556
The stability of the electrocaloric effect under electric field cycling is an important consideration in the development of solid-state cooling devices. Here we report measurements carried out on Ba(Zr0.2Ti0.8)O3 ceramics which reveal that the adiabatic temperature change, polarization-electric field hysteresis loops and dielectric permittivity/loss show stable behavior up to 105 cycles. We further demonstrate that the loss in electrocaloric response observed after 105 cycles is associated with the migration of oxygen vacancies. As a result, the electrical properties of the material are changed leading to an increase in leakage current and Joule heating. Reversing the polarity of the electric field after every 105 cycles changes the migration direction of oxygen vacancies, thereby preventing charge accumulation at grain boundaries and electrodes. By doing so, the electrocaloric stability is improved and the adiabatic temperature remains constant even after 106 cycles, much higher than achieved in commercially available barium titanate ceramics. 相似文献