全文获取类型
收费全文 | 921670篇 |
免费 | 72328篇 |
国内免费 | 39264篇 |
专业分类
电工技术 | 56953篇 |
技术理论 | 100篇 |
综合类 | 64445篇 |
化学工业 | 146352篇 |
金属工艺 | 50910篇 |
机械仪表 | 58853篇 |
建筑科学 | 77790篇 |
矿业工程 | 30061篇 |
能源动力 | 25215篇 |
轻工业 | 59415篇 |
水利工程 | 18408篇 |
石油天然气 | 56351篇 |
武器工业 | 7971篇 |
无线电 | 101518篇 |
一般工业技术 | 99086篇 |
冶金工业 | 47614篇 |
原子能技术 | 9512篇 |
自动化技术 | 122708篇 |
出版年
2024年 | 3547篇 |
2023年 | 12203篇 |
2022年 | 23917篇 |
2021年 | 33378篇 |
2020年 | 25464篇 |
2019年 | 20297篇 |
2018年 | 23357篇 |
2017年 | 27143篇 |
2016年 | 24443篇 |
2015年 | 34641篇 |
2014年 | 44498篇 |
2013年 | 53480篇 |
2012年 | 57915篇 |
2011年 | 63825篇 |
2010年 | 57000篇 |
2009年 | 54130篇 |
2008年 | 53223篇 |
2007年 | 51457篇 |
2006年 | 52836篇 |
2005年 | 46405篇 |
2004年 | 31311篇 |
2003年 | 27283篇 |
2002年 | 25938篇 |
2001年 | 23195篇 |
2000年 | 23111篇 |
1999年 | 25474篇 |
1998年 | 20706篇 |
1997年 | 17596篇 |
1996年 | 16246篇 |
1995年 | 13459篇 |
1994年 | 11101篇 |
1993年 | 7892篇 |
1992年 | 6323篇 |
1991年 | 4825篇 |
1990年 | 3685篇 |
1989年 | 3057篇 |
1988年 | 2494篇 |
1987年 | 1588篇 |
1986年 | 1230篇 |
1985年 | 860篇 |
1984年 | 592篇 |
1983年 | 430篇 |
1982年 | 432篇 |
1981年 | 322篇 |
1980年 | 268篇 |
1979年 | 150篇 |
1978年 | 51篇 |
1977年 | 82篇 |
1976年 | 74篇 |
1975年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Fangjun Zhu You Shi Guorong Hu Zhongdong Peng Yanbing Cao Qian Sun Zhichen Xue Yinjia Zhang Ke Du 《Ceramics International》2021,47(3):3070-3078
Titanium and boron are simultaneously introduced into LiNi0.8Co0.1Mn0.1O2 to improve the structural stability and electrochemical performance of the material. X-ray diffraction studies reveal that Ti4+ ion replaces Li+ ion and reduces the cation mixing; B3+ ion enters the tetrahedron of the transition metal layers and enlarges the distance of the [LiO6] layers. The co-doped sample has spherical secondary particles with elongated and enlarged primary particles, in which Ti and B elements distribute uniformly. Electrochemical studies reveal the co-doped sample has improved rate performance (183.1 mAh·g-1 at 1 C and 155.5 mAh·g-1 at 10 C) and cycle stability (capacity retention of 94.7% after 100 cycles at 1 C). EIS and CV disclose that Ti and B co-doping reduces charge transfer impedance and suppresses phase change of LiNi0.8Co0.1Mn0.1O2. 相似文献
102.
A novel CdS/CaFe2O4 (CS/CFO) heterogeneous p-n junction was created by thermal deposition of CaFe2O4 nanoparticles on CdS rods. The CS/CFO hetero-structured photocatalysts exhibited increasingly efficient visible light harvesting compared to the bare CdS. The CS/CFO composites also presented higher photocurrent and slower decay of photoluminescence, suggesting a better separation of the photo-generated electrons and holes. The photocatalytic H2 evolution quantity on the optimized CS/CFO composite from water in the presence of ethanol was up to 2200 μmol after 3-h visible light illumination, which is more than twice that of the pristine CdS. The chemical interaction between CdS and CaFe2O4 was confirmed by the shifts in the XPS peaks, which made it possible for the charge carriers to transfer across the p-n junction interface. This research highlights the importance of forming an interfacial p-n heterojunction between two semiconductors for efficient charge separation and improved photocatalytic performance. 相似文献
103.
Lili Hou Axel Olesund Shameel Thurakkal Xiaoyan Zhang Bo Albinsson 《Advanced functional materials》2021,31(47):2106198
Developing high-performance visible-to-UV photon upconversion systems based on triplet–triplet annihilation photon upconversion (TTA-UC) is highly desired, as it provides a potential approach for UV light-induced photosynthesis and photocatalysis. However, the quantum yield and spectral range of visible-to-UV TTA-UC based on nanocrystals (NCs) are still far from satisfactory. Here, three different sized CdS NCs are systematically investigated with triplet energy transfer to four mediators and four annihilators, thus substantially expanding the available materials for visible-to-UV TTA-UC. By improving the quality of CdS NCs, introducing the mediator via a direct mixing fashion, and matching the energy levels, a high TTA-UC quantum yield of 10.4% (out of a 50% maximum) is achieved in one case, which represents a record performance in TTA-UC based on NCs without doping. In another case, TTA-UC photons approaching 4 eV are observed, which is on par with the highest energies observed in optimized organic systems. Importantly, the in-depth investigation reveals that the direct mixing approach to introduce the mediator is a key factor that leads to close to unity efficiencies of triplet energy transfer, which ultimately governs the performance of NC-based TTA-UC systems. These findings provide guidelines for the design of high-performance TTA-UC systems toward solar energy harvesting. 相似文献
104.
Pu Mao Jiping Wang Peng Xiao Lixue Zhang Fang Kang Hao Gong 《Ceramics International》2021,47(1):111-120
In this work, we developed a novel system of isovalent Zr4+ and donor Nb5+ co-doped CaCu3Ti4O12 (CCTO) ceramics to enhance dielectric response. The influences of Zr4+ and Nb5+ co-substituting on the colossal dielectric response and relaxation behavior of the CCTO ceramics fabricated by a conventional solid-phase synthesis method were investigated methodically. Co-doping of Zr4+ and Nb5+ ions leads to a significant reduction in grain size for the CCTO ceramics sintered at 1060 °C for 10 h. XRD and Raman results of the CaCu3Ti3.8-xZrxNb0.2O12 (CCTZNO) ceramics show a cubic perovskite structure with space group Im-3. The first principle calculation result exhibits a better thermodynamic stability of the CCTO structure co-doped with Zr4+ and Nb5+ ions than that of single-doped with Zr4+ or Nb5+ ion. Interestingly, the CCTZNO ceramics exhibit greatly improved dielectric constant (~105) at a frequency range of 102–105 Hz and at a temperature range of 20–210 °C, indicating a giant dielectric response within broader frequency and temperature ranges. The dielectric properties of CCTZNO ceramics were analyzed from the viewpoints of defect-dipole effect and internal barrier layer capacitance (IBLC) model. Accordingly, the immensely enhanced dielectric response is primarily ascribed to the complex defect dipoles associated with oxygen vacancies by co-doping Zr4+ and Nb5+ ions into CCTO structure. In addition, the obvious dielectric relaxation behavior has been found in CCTZNO ceramics, and the relaxation process in middle frequency regions is attributed to the grain boundary response confirmed by complex impedance spectroscopy and electric modulus. 相似文献
105.
Jieyi Yu Xianguo Liu Rui Su Xuefeng Zhang Xinglong Dong 《Ceramics International》2021,47(17):23950-23957
Increasing the dielectric loss capacity plays an important role in enhancing the electromagnetic absorption performance of materials. It remains a challenge to simultaneously introduce multiple types of dielectric losses in the material. In this work, we show that the atomic and interfacial dipole polarizations can be simultaneously enhanced by substituting N species into both carbon coating layers and bulk TiC lattices of a core-shell TiC@C material. Additionally, substitution of N species results more exposed TiC(111) facets and refines the TiC grain sizes in the bulk material, which is beneficial for enhancing the scattering of the external electromagnetic waves. The maximum reflection loss of the N substituted TiC@C material is measured as ?47.1 dB with an effective absorbing bandwidth of 4.83 GHz at 1.9 mm, which illustrates a valuable way to further tuning the electromagnetic absorption performance of this type of materials. 相似文献
106.
长平煤矿机掘三队针对53031巷掘进期间工作面安装的SSJ-800型带式输送机经常出现跑偏打滑现象,导致输送机运行负荷大、煤矸运输效率低等,通过技术研究,对输送机安装了一套电液防打滑张紧装置.通过实际应用效果来看,该装置具有动作保护灵敏、故障率低、防打滑效果好等优点,输送机采用该装置后打滑事故率降低了7%,取得了显著应用效果. 相似文献
108.
Juan José Burbano He/him Darío Marcelino Cabezas María Jimena Correa 《International Journal of Food Science & Technology》2022,57(8):4772-4781
Walnut flour (WF), a by-product of walnut oil production, is characterised by high polyunsaturated fatty acids, proteins, and fibre contents and presents suitability for bakery products. However, when using non-traditional ingredients, it is essential to evaluate the effect on the quality properties of the final product. So, this work aimed to assess the impact of WF on the technological, physicochemical, and sensory properties of gluten-free (GF) cakes. WF was added at a flour blend (cassava (CS) and maize (MS) starches and rice flour) at 0, 10%, 15%, and 20%. The results showed that WF modified starch gelatinisation, increased amylose–lipid complex (ALC) content, and made crumbs easier to chew. Besides, the total dietary fibre (TDF) and protein content significantly increased. Cakes with 15% WF presented the highest specific volume (SV) and no differences in overall acceptability with respect to control. Hence, WF is a suitable ingredient for gluten-free bakery products. 相似文献
109.
A new aqueous slurry-based laminated object manufacturing process for porous ceramics is proposed: firstly, an organic mesh sheet is pre-paved as a pore-forming template before slurry layer scraping; secondly, the 2D pattern is built with laser outline cutting of the dried mesh–ceramic composite layer; finally, the pore structure is formed after degreasing and sintering. Alumina parts with porosities of 51.5 %, round hole diameters of 80 ± 5 μm were fabricated using 70 wt. % solid content slurry and 100 mesh nylon net. Using an organic mesh as the framework and template not only reduces the risk of damage of the green body but also ensures the regularity, uniformity and connectivity of the micron scaled pore network. The layer-by-layer drying method avoids the delamination phenomenon and improves the paving density. The new method can realize the flexible design of the pore structure by using various organic mesh templates. 相似文献
110.
Yin-Feng Wang Meng Li Jin-Ming Teng He-Ye Zhou Chuan-Feng Chen 《Advanced functional materials》2021,31(49):2106418
Recently, circularly polarized organic light-emitting diodes (CP-OLEDs) fabricated with thermally activated delayed fluorescence (TADF) emitters are developed rapidly. However, most devices are fabricated by vacuum deposition technology, and developing efficient solution-processed CP-OLEDs, especially nondoped devices, is still a challenge. Herein, a pair of triptycene-based enantiomers, (S,S)-/(R,R)-TpAc-TRZ, are synthesized. The novel chiral triptycene scaffold of enantiomers avoids their intermolecular π–π stacking, which is conducive to their aggregation-induced emission characteristics and high photoluminescence quantum yield of 85% in the solid state. Moreover, the triptycene-based enantiomers exhibit efficient TADF activities with a small singlet-triplet energy gap (ΔEST) of 0.03 eV and delayed fluorescence lifetime of 1.1 µs, as well as intense circularly polarized luminescence with dissymmetry factors (|gPL|) of about 1.9 × 10−3. The solution-processed nondoped CP-OLEDs based on (S,S)-/(R,R)-TpAc-TRZ not only display obvious circularly polarized electroluminescence signals with gEL values of +1.5 × 10−3 and −2.0 × 10−3, respectively, but also achieve high efficiencies with external quantum, current, and power efficiency up to 25.5%, 88.6 cd A−1, and 95.9 lm W−1, respectively. 相似文献