全文获取类型
收费全文 | 288826篇 |
免费 | 32688篇 |
国内免费 | 10298篇 |
专业分类
电工技术 | 15251篇 |
技术理论 | 18篇 |
综合类 | 14791篇 |
化学工业 | 58450篇 |
金属工艺 | 13857篇 |
机械仪表 | 16123篇 |
建筑科学 | 21984篇 |
矿业工程 | 6651篇 |
能源动力 | 8162篇 |
轻工业 | 22753篇 |
水利工程 | 4607篇 |
石油天然气 | 13756篇 |
武器工业 | 1890篇 |
无线电 | 36671篇 |
一般工业技术 | 41811篇 |
冶金工业 | 13895篇 |
原子能技术 | 2928篇 |
自动化技术 | 38214篇 |
出版年
2024年 | 1115篇 |
2023年 | 4078篇 |
2022年 | 7360篇 |
2021年 | 10206篇 |
2020年 | 8631篇 |
2019年 | 8984篇 |
2018年 | 9542篇 |
2017年 | 10815篇 |
2016年 | 10582篇 |
2015年 | 12823篇 |
2014年 | 15587篇 |
2013年 | 19625篇 |
2012年 | 18148篇 |
2011年 | 19743篇 |
2010年 | 17328篇 |
2009年 | 16882篇 |
2008年 | 15732篇 |
2007年 | 15027篇 |
2006年 | 14994篇 |
2005年 | 13093篇 |
2004年 | 9469篇 |
2003年 | 8528篇 |
2002年 | 8060篇 |
2001年 | 7196篇 |
2000年 | 6968篇 |
1999年 | 7140篇 |
1998年 | 6052篇 |
1997年 | 4985篇 |
1996年 | 4534篇 |
1995年 | 3798篇 |
1994年 | 3125篇 |
1993年 | 2495篇 |
1992年 | 1947篇 |
1991年 | 1448篇 |
1990年 | 1160篇 |
1989年 | 966篇 |
1988年 | 779篇 |
1987年 | 545篇 |
1986年 | 453篇 |
1985年 | 363篇 |
1984年 | 236篇 |
1983年 | 217篇 |
1982年 | 177篇 |
1981年 | 154篇 |
1980年 | 139篇 |
1979年 | 106篇 |
1978年 | 67篇 |
1977年 | 72篇 |
1976年 | 83篇 |
1975年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
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
42.
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
43.
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
44.
Lingfang Zou Zhuan Li Zonglong Gao Fu Chen Wenjie Li Yong Yu Yimin Li Peng Xiao 《Ceramics International》2021,47(14):19328-19339
Improving the piezoelectric activity of lead zirconate titanate (PZT) ceramics is of great importance for practical applications. In this study, the influence of Pr3+ doping on the ferroelectric phase composition, microstructure, and electric properties on the A-site of (Pb1-1.5xPrx)(Zr0.52Ti0.48)O3 is extensively investigated. A dense and fine microstructural sample is obtained with the introduction of Pr3+. The results show that the morphotropic phase boundary (MPB) moves to the rhombohedral phase region. The rhombohedral and tetragonal phases exhibit an ideal coexistence in the 4 mol.% Pr3+ doped (PPZT4) samples. Lead vacancy and the reduction of the potential energy barrier are considered to be the key mechanisms for donor doping, which is upheld by the Pr3+ doping. Combining the I-E hysteresis loops with the P-E hysteresis loops, it becomes apparent that both contribution maximums of the domain switching and residual polarisation are in PPZT4. Moreover, the thermal aging resistance of PZT is improved by doping, and the temperature stability is optimised from 83% in PZT to 96% in PPZT4. Hence, an appropriate amount of Pr3+ doping can effectively improve the piezoelectric activity of PZT ceramics in the MPB area and optimise the performance stability of the material under application temperatures. 相似文献
45.
Jinshuang Wang Luyao Chen Mengdi Chen Yuyang Wu Yinghui Wang Yongsheng Yu Junbin Sun Bing Liu Qiangshan Jing 《Ceramics International》2021,47(16):22965-22975
In this study, the destabilization resistance of Sc2O3 and CeO2 co-stabilized ZrO2 (SCZ) ceramics was tested in Na2SO4 + V2O5 molten salts at 750°C–1100 °C. The phase structure and microstructure evolution of the samples during the hot corrosion testing were analyzed with X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). Results showed that the destabilization of SCZ ceramics at 750 °C was the result of the chemical reaction with V2O5 to produce m-ZrO2 and CeVO4, and little ScVO4 was detected in the Sc2O3-rich SCZ ceramics. The primary corrosion products at 900 °C and 1100 °C were CeO2 and m-ZrO2 due to the mineralization effect. The Sc2O3-rich SCZ ceramics exhibited excellent degradation resistance and phase stability owing to the enhanced bond strength and the decreased size misfit between Zr4+ and Sc3+. The destabilization mechanism of SCZ ceramic under hot corrosion was also discussed. 相似文献
46.
Hongli Liu Peng Wang Bo Zhang Hongyan Li Jing Li Yajing Li Zhong Chen 《Ceramics International》2021,47(5):6487-6495
A novel carbon/m-HNTs composite aerogel was synthesized by introducing the modified halloysite nanotubes (m-HNTs) into phenolic (PR) aerogels through chemical grafting, followed with carbonization treatment. In order to explore the best proportion of HNTs to phenolic, the micromorphology of PR/m-HNTs were investigated by SEM before carbonization, confirming 10 wt% of m-HNTs is most beneficial to the porous network of aerogels. The interaction between PR and HNTs was studied by FTIR spectra, and microstructure evolution of the target product-carbon/m-HNTs composite aerogel were illustrated by SEM and TEM techniques. SEM patterns indicated that the carbon/m-HNTs aerogels maintain a stable porous structure at 1000 °C (carbonization temperature), while a ~20 nm carbon layer was formed around m-HNTs generating an integral unit through TEM analysis. Specific surface area and pore size distribution of composite aerogels were analyzed based on mercury intrusion porosimetry and N2 adsorption–desorption method, the obtained results stayed around 500 m2g?1 and 1.00 cm3g?1 (pore volume) without significant discrepancy, compared with pure aerogel, showing the uniformity of pore size. The weight loss rate (26.76%) decreased greatly compared with pure aerogel, at the same time, the best volumetric shrinkage rate was only 30.83%, contributed by the existence of HNTs supporting the neighbor structure to avoid over-shrinking. The highest compressive strength reached to 4.43 MPa, while the data of pure aerogel was only 1.52 MPa, demonstrating the excellent mechanical property of carbon/m-HNTs aerogels. 相似文献
47.
Li Qian Chen Yan Sun Shikun Zhu Muyuan Xue Jing Gao Zihan Zhao Jinfeng Tang Yihe 《Water Resources Management》2022,36(12):4799-4817
Water Resources Management - Increasing water consumption in agriculture due to global climate change has posed considerable challenges to food security, thus improving the efficiency of water... 相似文献
48.
Water Resources Management - The low impact development (LID) concept aims to control storm runoff and pollution through decentralized, small-scale source control to bring the development area as... 相似文献
49.
50.