全文获取类型
收费全文 | 291篇 |
免费 | 24篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 1篇 |
综合类 | 6篇 |
化学工业 | 156篇 |
金属工艺 | 5篇 |
机械仪表 | 11篇 |
建筑科学 | 10篇 |
矿业工程 | 14篇 |
能源动力 | 10篇 |
轻工业 | 27篇 |
水利工程 | 2篇 |
石油天然气 | 8篇 |
武器工业 | 1篇 |
无线电 | 14篇 |
一般工业技术 | 44篇 |
冶金工业 | 2篇 |
原子能技术 | 8篇 |
自动化技术 | 4篇 |
出版年
2023年 | 13篇 |
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 15篇 |
2019年 | 12篇 |
2018年 | 12篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 10篇 |
2013年 | 18篇 |
2012年 | 11篇 |
2011年 | 12篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 12篇 |
2007年 | 17篇 |
2006年 | 11篇 |
2005年 | 14篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有323条查询结果,搜索用时 31 毫秒
311.
312.
Secondary ethers can be obtained from meadow-foam-derived delta lactones or 5-hydroxy fatty acids by using Lewis or Brønsted acid catalysts in good yield (70–90%). The conversion of δ-lactone or 5-hydroxy fatty acid to 5-ethers is performed under atmospheric pressure between 67 and 125°C with 0.5–6.4 mole equivalents of acid catalyst in the presence of 2–40 equivalents of alcohol and a reaction time of 1–140 h. Acid catalysts include mineral acids, such as perchloric and sulfuric; Lewis acids, such as boron trifluoride; and heterogeneous catalysts, such as clays and ion-exchange resins. Primary alcohols, such as methanol, butanol, decanol, and oleyl alcohol, or branched-chain alcohols, such as 2-ethylhexanol, can be used to make secondary ether fatty esters. The 5-ether fatty esters and the process for their formation have not been previously known and appear to be limited to structures where stabilized cations can be formed. The novel ethers were fully characterized by nuclear magnetic resonance and gas chromatography-mass spectrometry. 相似文献
313.
The results of 1H NMR binding studies of mole-cular tweezers 1a with various aliphatic and aromatic cations in organic solvents are described. By the use of the viologene substrates 11 and 12 bearing bulky endgroups and therefore having a dumb-bell topology it could be demonstrated that besides the obvious mechanism of complexation in which the guest molecule enters the tweezer's cavity through the open sides of the host, a second mechanism is available in which the substrate enters the cavity through a gap emerging after a substantial spreading of the tweezer's tips by at least of about 280 pm. 相似文献
314.
《Ceramics International》2023,49(1):565-570
Two novel low-εr Ca3Mg2CV2O12 (C = Si, Ti) ceramics with the garnet structure were synthesized by a traditional solid-state reaction method. Rietveld refinements based on XRD patterns show both the compounds crystallized into a cubic structure with the Ia-3d space group. Outstanding microwave dielectric properties (εr = 9.70, Q × f = 35,680 GHz, and τf = ?60.1 ppm/°C for Ca3Mg2SiV2O12 ceramic; εr = 11.70, Q × f = 48,530 GHz, and τf = ?43.7 ppm/°C for Ca3Mg2TiV2O12 ceramic) were obtained at 1240 °C and 1260 °C, respectively. The bond valence calculations reveal that Ca2+ at the A-site and Mg2+ at the B-site are slightly compressed, in combination with “rattling” Si4+ and “compressed” V5+ in the C-site of Ca3Mg2SiV2O12 compared to “rattling” V5+and “compressed” Ti4+ in Ca3Mg2TiV2O12, resulting in a negative deviation of ?7.16% for Ca3Mg2SiV2O12 and a positive value of 5.66% for Ca3Mg2TiV2O12 between the porosity corrected εr(Corr) (10.11 and 11.95) and theoretical εth (10.89 and 11.31) calculated by the C-M equation. The overall “rattling” effect in Ca3Mg2TiV2O12 results in a higher εr and a nearer to zero τf compared to Ca3Mg2SiV2O12. Besides, the Q × f values of Ca3Mg2CV2O12 (C = Si, Ti) ceramics were correlated with relative density and Raman mode (A1g). 相似文献
315.
《Ceramics International》2023,49(20):32816-32825
The hydrothermal synthesis method to produce calcium hydroxyapatite (HA) of controlled morphology without the use of organic additives is developed in this study. The influence of smaller (Mg2+, Mn2+) and larger (Sr2+, Ba2+) ions on the hydrolysis of α-TCP and crystal growth of HA particles was investigated. It was revealed that both the hydrothermal synthesis conditions (temperature, time) and the nature and concentration of the foreign ion affected the phase purity and morphology of the final products. Of all the ions investigated, Mn2+ had the highest, and Sr2+ had the lowest inhibiting effect on the hydrolysis process of α-TCP. Under certain synthesis conditions, we were able to obtain samples consisting of plate-like or rod-like particles only. The dye adsorption test revealed that the adsorption of plate-like particles for cationic dyes was more efficient, possibly, due to the higher surface area (SBET). Upon normalizing the test results to SBET, it became apparent that the electrostatic attraction between HA particles and dye molecules also impacted the adsorption efficiency. Rod-like particles had a higher ratio of exposed (a,m)-planes and hence lower zeta potential, resulting in increased adsorption of the cationic dye. 相似文献
316.
《Journal of the European Ceramic Society》2023,43(4):1639-1648
Stuffed aluminosilicate quartz solid solutions (Qss) represent the main functional component of state-of-the-art zero-thermal-expansion glass-ceramics. For the first time, we present the synthesis of Li-, Mg- and Zn-free Qss solely stuffed with transition metal cations (Fe2+, Ni2+, Co2+); partial Li+ co-doping enables also significant Mn2+ incorporation. They were obtained by glass powder crystallization; Qss crystals exhibit compositionally tunable coefficients of thermal expansion (CTEs), from ? 2 × 10?6 K?1 to ~10 × 10?6 K?1 in the range 30–300 °C. Co2+-bearing crystals exhibit the closest-to-zero CTE value (0.2 ×10?6 K?1) and the most isotropic behavior in the whole Qss family, opening up new perspectives for the development of Li-free low-expansion materials. From a structural point of view, we identified the unit cell volume (and not the pseudo-hexagonality of the aluminosilicate framework) as the key structural parameter leading to low or negative CTEs in Qss, with a linear correlation extending to non-stuffed non-silicate quartz-like phases. 相似文献
317.
Kwan Ho Ngai Xinwen Sun Yinping Wang Long Lin Zefeng Chen Qi Wei Mingjie Li Chuhao Luan Wenjun Zhang Jianbin Xu Mingzhu Long 《Advanced functional materials》2023,33(18):2211830
The delicate engineering of monovalent cations in perovskite material has led to continuous performance breakthroughs and stability improvement for the perovskite light-emitting diodes (PeLEDs). However, the exact role of A-site cations on the electroluminescence (EL) performance and degradation mechanism of PeLEDs has not been systematically answered yet. Herein, it is demonstrated that the most commonly used methylammonium cation (MA+) has an adverse effect on the electrochemical reaction at the interface between perovskite and metal-oxide layer, leading to deteriorated EL performance as compared to that of the formamidinium cation (FA+)-based perovskite. It reveals that the accelerated deprotonation process of MA+ under an electric field will aggravate the reaction between iodide and metal ion in oxide layer. The further substitution of a small portion of FA+ with inorganic cesium cation (Cs+) results in much enhanced crystallinity and enlarged crystal size, leading to an optimized peak external quantum efficiency of 21.3%. The ion migration process in the PeLEDs can be significantly suppressed with Cs+ incorporation, leading to a smaller roll-off under large current density and an elongated half-lifetime of 190.1 h under a current density of 20 mA cm-2, representing one of the most stable PeLEDs based on 3D perovskite layer. 相似文献
318.
Xueyi Lu Mohang Cai Xuemin Wu Yongfei Zhang Shuai Li Shijun Liao Xia Lu 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(9):2206702
2D materials have captured much recent research interest in a broad range of areas, including electronics, biology, sensors, energy storage, and others. In particular, preparing 2D nanosheets with high quality and high yield is crucial for the important applications in energy storage and conversion. Compared with other prevailing synthetic strategies, the electrochemical exfoliation of layered starting materials is regarded as one of the most promising and convenient methods for the large-scale production of uniform 2D nanosheets. Here, recent developments in electrochemical delamination are reviewed, including protocols, categories, principles, and operating conditions. State-of-the-art methods for obtaining 2D materials with small numbers of layers—including graphene, black phosphorene, transition metal dichalcogenides and MXene—are also summarized and discussed in detail. The applications of electrochemically exfoliated 2D materials in energy storage and conversion are systematically reviewed. Drawing upon current progress, perspectives on emerging trends, existing challenges, and future research directions of electrochemical delamination are also offered. 相似文献
319.
《Journal of the European Ceramic Society》2023,43(15):7111-7117
Hot-corrosion behavior of Ba1/3Sr1/3Ca1/3Al2Si2O8 (BSCAS) in the presence of molten calcium-magnesium-aluminum-silicate (CMAS) is investigated in the temperature range of 1250–1350 °C. In comparison, the hot corrosion behavior of Ba0.5Sr0.5Al2Si2O8 (BSAS) is also studied under the same conditions. The results indicate that CMAS corrosion of both BSCAS and BSAS is caused by the interdiffusion of Ba/Sr and Ca between CMAS and corroded samples. The presence of Ca cations in BSCAS lowers the diffusion driving force of Ca cations between CMAS and BSCAS, resulting in a reduced diffusion rate of Ca cations from CMAS into BSCAS. Moreover, the sluggish diffusion effect of multi-component cations hinders the outward diffusion of Ba/Sr cations from BSCAS. Thus, the BSCAS shows a better CMAS corrosion resistance than BSAS. 相似文献
320.
Wonryeol Yang Geonwoong Park Ao Liu Hock Beng Lee Jae-Wook Kang Huihui Zhu Yong-Young Noh 《Advanced functional materials》2023,33(36):2303309
2D tin-based perovskites have gained considerable attention for use in diverse optoelectronic applications, such as solar cells, lasers, and thin-film transistors (TFTs), owing to their good stability and optoelectronic properties. However, their intrinsic charge-transport properties are limited, and the insulating bulky organic ligands hinder the achievement of high-mobility electronics. Blending 3D counterparts into 2D perovskites to form 2D/3D hybrid structures is a synergistic approach that combine the high mobility and stability of 3D and 2D perovskites, respectively. In this study, reliable p-channel 2D/3D tin-based hybrid perovskite TFTs comprising 3D formamidinium tin iodide (FASnI3) and 2D fluorinated 4-fluoro-phenethylammonium tin iodide ((4-FPEA)2SnI4) are reported. The optimized FPEA-incorporated TFTs show a high hole mobility of 12 cm2 V−1 s−1, an on/off current ratio of over 108, and a subthreshold swing of 0.09 V dec−1 with negligible hysteresis. This excellent p-type characteristic is compatible with n-type metal-oxide TFT for constructing complementary electronics. Two procedures of antisolvent engineering and device patterning are further proposed to address the key concern of low-performance reproducibility of perovskite TFTs. This study provides an alternative A-cation engineering method for achieving high-performance and reliable tin-halide perovskite electronics. 相似文献