全文获取类型
收费全文 | 6060篇 |
免费 | 658篇 |
国内免费 | 435篇 |
专业分类
电工技术 | 2549篇 |
综合类 | 317篇 |
化学工业 | 733篇 |
金属工艺 | 576篇 |
机械仪表 | 170篇 |
建筑科学 | 61篇 |
矿业工程 | 95篇 |
能源动力 | 244篇 |
轻工业 | 100篇 |
水利工程 | 25篇 |
石油天然气 | 162篇 |
武器工业 | 25篇 |
无线电 | 1013篇 |
一般工业技术 | 479篇 |
冶金工业 | 258篇 |
原子能技术 | 62篇 |
自动化技术 | 284篇 |
出版年
2024年 | 7篇 |
2023年 | 96篇 |
2022年 | 116篇 |
2021年 | 179篇 |
2020年 | 179篇 |
2019年 | 155篇 |
2018年 | 139篇 |
2017年 | 189篇 |
2016年 | 215篇 |
2015年 | 265篇 |
2014年 | 348篇 |
2013年 | 341篇 |
2012年 | 448篇 |
2011年 | 510篇 |
2010年 | 415篇 |
2009年 | 426篇 |
2008年 | 423篇 |
2007年 | 462篇 |
2006年 | 406篇 |
2005年 | 311篇 |
2004年 | 231篇 |
2003年 | 239篇 |
2002年 | 185篇 |
2001年 | 181篇 |
2000年 | 120篇 |
1999年 | 134篇 |
1998年 | 82篇 |
1997年 | 47篇 |
1996年 | 48篇 |
1995年 | 64篇 |
1994年 | 58篇 |
1993年 | 31篇 |
1992年 | 22篇 |
1991年 | 33篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有7153条查询结果,搜索用时 15 毫秒
1.
Qing Li Jun Wang Jie Ma Meng Ni Fan Yang Peng Liu Kuo Yang Lee Hsing-I Hsiang Deyuan Shen Dingyuan Tang 《Journal of the American Ceramic Society》2022,105(5):3375-3381
High-efficiency Yb:Y2O3 laser ceramics were fabricated using the vacuum-sintering plus hot isostatic pressing (HIP) without sintering additives. High-purity well-dispersed nanocrystalline Yb:Y2O3 powder was synthesized using a modified co-precipitation method in-house. The green bodies were first vacuum sintered at a temperature as low as 1430°C and then HIPed at 1450°C. Finally, the samples were air annealed at 800°C for 10 h. Although no sintering aids were used, full density of the samples with excellent optical homogeneity and an inline transmission of 80% at 400 nm could be obtained. Moreover, photodarkening phenomenon was not detected in the ceramics. Preliminary laser experiment with the fabricated ceramics in a two-mirror cavity has demonstrated 32 W continuous-wave (CW) output at ∼1077 nm with an optical-to-optical conversion efficiency of 58.2%. To the best of our knowledge, this is so far the highest CW output power and optical-to-optical conversion efficiency achieved with the Yb3+-doped sesquioxide ceramics in a simple two-mirror cavity. 相似文献
2.
《Ceramics International》2022,48(2):2377-2384
Bi2O3, Y2O3 and MgO co-doped BaTiO3 (BT)-based X8R ceramics were synthesized successfully for the first time. The effects of the sintering temperature and Bi2O3, Y2O3 and MgO dopants on the dielectric properties were investigated systematically. Bi2O3 doping can increase the Curie temperature (Tc), but reduces the overall dielectric permittivity. On the other hand, Y2O3 doping is beneficial to the formation of core-shell microstructure and the increase of Tc, whereas MgO can prevent excessive Y2O3 from diffusing into grain core, and thereby further contributes to the generation of the core–shell microstructure. The generation of the typical core-shell microstructure was confirmed and investigated in detail by using transmission electron microscopy (TEM). It is argued that the synergistic effects of Bi2O3, Y2O3 and MgO co-doping in terms of the formation of the core-shell structure and the increase of Tc, can help improve the temperature stability of the dielectric permittivity effectively. Increasing the sintering temperature leads to an increase in the grain size, which in turn leads to an increase in the overall dielectric permittivity due to the grain size effect. 相似文献
3.
Zhongchao Fu Xiaodong Li Mu Zhang Qi Zhu Ji-Guang Li Jiao He Xing'an Wang Xudong Sun 《Journal of the American Ceramic Society》2021,104(6):2689-2701
An easy albeit quite effective deionization suspension treatment was adopted to alleviate the detrimental effects related to the hydrolysis of Y2O3 in an aqueous medium. Fabrication of highly transparent Y2O3 ceramics with a fine grain size via air pre-sintering and post–hot isostatic pressing (HIP) treatment without using any sintering additive was achieved using the treated suspensions. The hydrolysis issue of Y2O3 powder in an aqueous medium was effectively alleviated by using deionization treatment, and a well-dispersed suspension with a low concentration of dissolved Y3+ species was obtained. The dispersed suspensions were consolidated by the centrifugal casting method, and the green bodies derived from the suspension of 35.0 vol% solid loading showed an improved homogeneity with a relative density of 52.1%. Fully dense Y2O3 transparent ceramic with high transparency was obtained by pre-sintering consolidated green compacts at a low temperature of 1400°C for 16 h in air followed by a post-HIP treatment at 1550°C for 2 h under 200 MPa pressure. The sample had a fine average grain size of 690 nm. The in-line transmittance of the sample reached 83.3% and 81.8% at 1100 nm and 800 nm, respectively, very close to the theoretical values of Y2O3. 相似文献
4.
《Ceramics International》2022,48(14):20237-20244
Composite anode materials with a unique architecture of carbon nanotubes (CNTs)-chained spinel lithium titanate (Li4Ti5O12, LTO) nanoparticles are prepared for lithium ion capacitors (LICs). The CNTs networks derived from commercial conductive slurry not only bring out a steric hindrance effect to restrict the growth of Li4Ti5O12 particles but greatly enhance the electronic conductivity of the CNTs/LTO composites, both have contributed to the excellent rate capability and cycle stability. The capacity retention at 30 C (1 C = 175 mA g?1) is as high as 89.7% of that at 0.2 C with a CNTs content of 11 wt%. Meanwhile, there is not any capacity degradation after 500 cycles at 5 C. The LIC assembled with activated carbon (AC) cathode and such a CNTs/LTO composite anode displays excellent energy storage properties, including a high energy density of 35 Wh kg?1 at 7434 W kg?1, and a high capacity retention of 87.8% after 2200 cycles at 1 A g?1. These electrochemical performances outperform the reported data achieved on other LTO anode-based LICs. Considering the facile and scalable preparation process proposed herein, the CNTs/LTO composites can be very potential anode materials for hybrid capacitors towards high power-energy outputs. 相似文献
5.
6.
For the defect that the mechanical properties of polypyrrole supercapacitors decrease with charge and discharge cycles, and
the cycle stability is poor, a compound method of polypyrrole electrode for supercapacitors based on multi-walled carbon nanotubes
is proposed. The structure of the formed polypyrrole coated multi-walled carbon nanotubes effectively increase the specific surface
area of the electrode material, the utilization rate of the active material and the electrical conductivity, improve the rapid charge and
discharge performance of the electrode material, and greatly improve cyclic stability of polypyrrole. The composite electrode materi-
al of polypyrrole and functionalized multi-walled carbon nanotubes for supercapacitors is prepared by pulse current deposition meth-
od. It is scanned at a scanning rate of 1000mV?s -1 in a 3mol?L -1 potassium chloride electrolyte, after 100,000-cycle, the capacity on-
ly declines by 16%. 相似文献
7.
研究了相变温度附近等温热处理温度和保温时间对含长周期结构Mg97Zn1Y2合金的组织的影响,并对演变机理进行了探讨。主要研究结论如下:500℃固溶处理时,随着时间的增加,长周期结构有增长的趋势。采用等温热处理可以将Mg97Zn1Y2合金中的枝晶组织转变为球状晶,当合金保温温度范围从540℃~600℃时,组织尺寸由大-小-大的顺序变化,即经过了粗化、分离及球化至最后粗化三个过程。在等温热处理温度为575℃的组织大致演变趋势为:枝晶态-不规则球形+块状-球形状,当保温时间15min,其组织为均匀、圆整的球状晶。 相似文献
8.
Shaohui Li Jingwei Chen Jiaqing Xiong Xuefei Gong Jinghao Ciou Pooi See Lee 《纳微快报(英文)》2020,(3):55-68
Sodium-ion capacitors(SICs)have received increasing interest for grid stationary energy storage application due to their affordability,high power,and energy densities.The major challenge for SICs is to overcome the kinetics imbalance between faradaic anode and nonfaradaic cathode.To boost the Na+reaction kinetics,the present work demonstrated a high-rate MnS-based anode by embedding the MnS nanocrystals into the N,S-co-doped carbon matrix(MnS@NSC).Benefiting from the fast pseudocapacitive Na+storage behavior,the resulting composite exhibits extraordinary rate capability(205.6 mAh g−1 at 10 A g−1)and outstanding cycling stability without notable degradation after 2000 cycles.A prototype SIC was demonstrated using MnS@NSC anode and N-doped porous carbon(NC)cathode;the obtained hybrid SIC device can display a high energy density of 139.8 Wh kg−1 and high power density of 11,500 W kg−1,as well as excellent cyclability with 84.5%capacitance retention after 3000 cycles.The superior electrochemical performance is contributed to downsizing of MnS and encapsulation of conductive N,S-co-doped carbon matrix,which not only promote the Na+and electrons transport,but also buffer the volume variations and maintain the structure integrity during Na+insertion/extraction,enabling its comparable fast reaction kinetics and cyclability with NC cathode. 相似文献
9.
Lingling Chen Hongxian Wang Peiyao Zhao Chaoqiong Zhu Ziming Cai Zhenyong Cen Longtu Li Xiaohui Wang 《Journal of the American Ceramic Society》2019,102(7):4178-4187
BaTiO3-(Bi0.5Na0.5)TiO3 (BTBNT)-based multilayer ceramic capacitor (MLCC) chips with the inner electrodes being Ag0.6/Pd0.4 are prepared by a roll-to-roll casting method. The BTBNT-based MLCC chips with ten-dielectric layers can be sintered very well at a low temperature of 1130°C via two-step sintering (TSS). X-ray diffraction (XRD) and transmission electron microscope (TEM) results show that MLCC chips are a core-shell structure with two phases coexistence. The core exhibits a tetragonal phase at room temperature and then gradually changes into a cubic phase when the temperature increases above Tc (175°C). While, the shell exhibits a pseudocubic phase at all tested temperature from 25°C to 500°C. BTBNT-based MLCC chips exhibit a broad temperature stability and meet the requirement of Electronic Industries Association (EIA) X9R specifications. In terms of energy storage performance, a large discharge energy density of 3.33 J/cm3 can be obtained at 175°C under the applied electric field of 480 kV/cm. Among all tested temperature ranging from −50°C to 200°C, the energy efficiency of all chips is higher than 80%, even under a high applied electric field. The experimental results indicate that this novel BTBNT-based X9R MLCCs can be one of the most promising candidates for energy storage applications, especially operated in high temperature. 相似文献
10.
Atsushi Tsujita Masashi Ohchi Takayuki Wakimoto 《Electrical Engineering in Japan》2019,208(1-2):17-26
We have been studying on estimating distribution of permittivity between measurement electrodes using capacitance and electric potential. Two arc electrodes were separated by long distance and there electrodes were surrounded by additional electrodes respectively. In past research work, we carried out numerical electric analysis for calculating the capacitance and electric potential using Finite Element Method (FEM) and compared with experimental and numerical results. The capacitance values were almost agreed with experimental and numerical results. However, the electric potential values were different between experimental and numerical results in conventional studies. In this paper, we proposed an equivalent circuit including the stray capacity and measurement method for capacitance, the electric potential in space between long distance electrodes was estimated. 相似文献