全文获取类型
收费全文 | 60947篇 |
免费 | 4926篇 |
国内免费 | 2647篇 |
专业分类
电工技术 | 3212篇 |
技术理论 | 6篇 |
综合类 | 4116篇 |
化学工业 | 10141篇 |
金属工艺 | 3827篇 |
机械仪表 | 3832篇 |
建筑科学 | 4666篇 |
矿业工程 | 2171篇 |
能源动力 | 1950篇 |
轻工业 | 3492篇 |
水利工程 | 1056篇 |
石油天然气 | 4481篇 |
武器工业 | 482篇 |
无线电 | 6402篇 |
一般工业技术 | 7127篇 |
冶金工业 | 3293篇 |
原子能技术 | 720篇 |
自动化技术 | 7546篇 |
出版年
2024年 | 99篇 |
2023年 | 934篇 |
2022年 | 1372篇 |
2021年 | 2275篇 |
2020年 | 1786篇 |
2019年 | 1605篇 |
2018年 | 1808篇 |
2017年 | 2015篇 |
2016年 | 1795篇 |
2015年 | 2338篇 |
2014年 | 2997篇 |
2013年 | 3458篇 |
2012年 | 3679篇 |
2011年 | 4024篇 |
2010年 | 3691篇 |
2009年 | 3311篇 |
2008年 | 3274篇 |
2007年 | 3224篇 |
2006年 | 3208篇 |
2005年 | 2776篇 |
2004年 | 2052篇 |
2003年 | 2148篇 |
2002年 | 2491篇 |
2001年 | 2078篇 |
2000年 | 1588篇 |
1999年 | 1687篇 |
1998年 | 1239篇 |
1997年 | 1064篇 |
1996年 | 1103篇 |
1995年 | 842篇 |
1994年 | 628篇 |
1993年 | 467篇 |
1992年 | 361篇 |
1991年 | 272篇 |
1990年 | 204篇 |
1989年 | 164篇 |
1988年 | 151篇 |
1987年 | 86篇 |
1986年 | 69篇 |
1985年 | 37篇 |
1984年 | 30篇 |
1983年 | 23篇 |
1982年 | 23篇 |
1981年 | 13篇 |
1980年 | 20篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1965年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
To reveal the effect mechanism of CO atmosphere on coal pyrolysis, a study on raw and demineralized lignite was carried out in a horizontal tube furnace under N2 and CO/N2 atmosphere. CO had a negligible effect on the char yield at low temperatures, whereas it enhances the char yield at temperatures higher than 550 °C. The release of tar was higher in the presence of CO above 450 °C because of more free radicals, which reduced low‐temperature crosslinking, and higher selectivity of hydroxyl groups to phenols in the CO‐containing atmosphere. The yields of CO2 and H2 increased, water and CO yields decreased under CO/N2 atmosphere. Light hydrocarbon gases were not affected by changing the reaction atmosphere. The difference between product yields from raw and demineralized coal confirmed that the catalysis of inherent minerals had a great catalytic effect on the water‐gas shift reaction and Boudouard reaction. 相似文献
82.
Junqi Chen Weishuang Fang Yifan Zhai Feihu Li Ying Tang Jie Li Huanhuan Guo Liang Fang 《Journal of the European Ceramic Society》2021,41(8):4473-4477
Orthorhombic-structured CaIn2O4 ceramics with a space group Pca21 were synthesized via a solid-state reaction method. A high relative density (95.6 %) and excellent microwave dielectric properties (εr ~11.28, Qf = 74,200 GHz, τf ~ ?4.6 ppm/°C) were obtained when the ceramics were sintered at 1375 °C for 6 h. The dielectric properties were investigated on the basis of the Phillips–Van Vechten–Levine chemical bond theory. Results indicated that the dielectric properties were mainly determined by the InO bonds in the CaIn2O4 ceramics. These bonds contributed more (74.65 %) to the dielectric constant than the CaO bonds (25.35 %). Furthermore, the intrinsic dielectric properties of the CaIn2O4 ceramics were investigated via infrared reflectivity spectroscopy. The extrapolated microwave dielectric properties were εr ~10.12 and Qf = 112,200 GHz. Results indicated that ion polarization is the main contributor to the dielectric constant in microwave frequency ranges. 相似文献
83.
Machine Learning - Recently, some statistical topic modeling approaches have been widely applied in the field of supervised document classification. However, there are few researches on these... 相似文献
84.
Yuemei Wang Wei Feng Meiqi Chang Jiacai Yang Yuedong Guo Li Ding Luodan Yu Hui Huang Yu Chen Jianlin Shi 《Advanced functional materials》2021,31(6):2005093
2D monoelemental nanomaterials (Xenes) have shown tremendous potential for versatile biomedical applications. Bismuth, as a heavy element in pnictogens, has acquired massive research interest due to its unique optical performance, high biocompatibility, stability, and relatively low cost. However, the utilization of 2D bismuthene in nanomedicine has not been achieved because of the difficulty in engineering bismuthene with crucial structural/compositional characteristics for satisfying strict biomedical requirements. Herein, to address this Gordian knot, a facile strategy to intercalate and delaminate Bi bulk for generating mass few-layered 2D bismuthene with high yield by employing a water molecule mediated freezing–thawing process and sodium borohydride-triggered reduction treatment is proposed. The resulting 2D bismuthene displays good optical performance in the near-infrared (NIR) biowindow and can be excited via red light for reactive oxygen species generation, enabling applications in multiple photonic cancer nanomedicine settings, including photothermal hyperthermia and photodynamic therapy. Utilizing the intrinsic desirable optical absorbance and strong X-ray attenuation of bismuthene, dual photonic therapy can be conducted under the supervision of photoacoustic/computed tomography guided multimodal imaging. This research not only offers a potential mass-production ready, cost-effective, and eco-efficient methodology for engineering 2D Xenes, but also exploits an innovative 2D bismuthene based photonic cancer nanomedicine. 相似文献
85.
Jiadong Liu Di Yu Zhipeng Zheng Geng Huangfu Yiping Guo 《Ceramics International》2021,47(3):3573-3579
Constructing hybrid nanogenerators (NGs) based on triboelectric effect and piezoelectric effect can combine the merits of the individual type of NG thus have drawn great attention in flexible wearable electronics. Herein, we prepared flexible BiFeO3 (BFO) film in a simple and cost-effective way, which was used to fabricate a wearable hybrid piezoelectric-triboelectric nanogenerator (H–P/TENG) with silk fiber. By optimizing the experimental conditions, the highest open-circuit voltage of 110 V and short-circuit current density of 3.67 μA/cm2 were achieved under 1 Hz contact-separation movement. The device also showed the best output power density of 151.42 μW/cm2 with load resistance of 250 MΩ. Stimulating by moving body, the fabricated H–P/TENG successively realized the harvest and conversion of mechanical energy into electric energy, demonstrating great potential to monitor posture and establish a self-powered system. Moreover, the proposed H–P/TENG exhibited great stable output after 1800 contact-separation cycles, indicating the outstanding structure stability and fatigue resistance. This work will provide not only a facile and viable way to realize the application of ferroelectric materials in H–P/TENG but also new opportunities for developing monitor posture and self-powered systems. 相似文献
86.
Hua Zhu Hai Zhang Tian-hao Zhang Shi-jin Yu Ping-chun Guo Yan-xiang Wang Zhi-sheng Yang 《Ceramics International》2021,47(12):16980-16985
Indium Tin Oxide (ITO) films were prepared, at room temperature, on a fluorphlogopite substrate using magnetron sputtering technology. At various temperatures of 500 °C, 600 °C, 700 °C, 800 °C, and 900 °C, the samples were (had) annealed for 2 h (a 2-h duration). The results showed improvement in the crystalline performance of ITO film at selected annealing temperatures, with a significant reduction in resistivity at 800 °C. The lowest resistivity is 4.08 × 10?4 Ω-cm, which is nearly an order of magnitude lower than the unannealed sample. All samples have an average light transmittance above 85% in the visible light range (400–800 nm), and with increasing annealing temperature, the average light transmittance tends to decrease. Besides, at the sensitive wavelength of 550 nm, the light transmittance is as high as 93.74%. The sheet resistance testing of the sample was through the number of bending times, which revealed that with the increase of the number of bending, the sheet resistance increases. However, after 1200 bending times, the change rate of the sheet resistance remains below 5%. Thus, the ITO film prepared on the flexible fluorphlogopite substrate revealed excellent optical and electrical properties, good flexibility, and improved stability after high-temperature annealing, which guarantees successful application in flexible electronic devices. 相似文献
87.
Hailong Liang Bo Zhang Dayu Zhou Xintai Guo Yan Li Yanqing Lu Yuanyuan Guo 《Ceramics International》2021,47(9):12137-12143
In this work, we introduced a simple solution processing method to prepare yttrium (Y) doped hafnium oxide (HfO2) based dielectric films. The films had high densities, low surface roughness, maximum permittivity of about 32, leakage current < 1.0 × 10?7 A/cm2 at 2 MV/cm, and breakdown field >5.0 MV/cm. In addition to dielectric performance, we investigated the influence of YO1.5 fraction on the electronic structure between Y doped HfO2 thin films and silicon (Si) substrates. The valence band electronic structure, energy gap and conduction band structure changed linearly with YO1.5 fraction. Given this cost-effective deposition technique and excellent dielectric performance, solution-processed Y doped HfO2 based thin films have the potential for insulator applications. 相似文献
88.
Pengchao Kang Qiqi Zhao Shiqi Guo Wei Xue Hao Liu Zhenlong Chao Longtao Jiang Gaohui Wu 《Ceramics International》2021,47(3):3816-3825
Based on orthogonal experimental design (OED), the effects of the sintering pressure, sintering temperature and holding time on the mechanical properties of 50 vol% silicon carbide particle (SiCp)/2024Al composites prepared by spark plasma sintering (SPS) were investigated. The sintering pressure had the greatest effect on the density and bending strength of the material among these three factors, followed by sintering temperature and holding time. The optimised process conditions for producing the 50 vol% SiCp/2024Al were sintering at 550 °C for 5 min under 40 MPa, which resulted in a composite material with a density of 99.7% and good interface bonding with a comparatively high bending strength of 766.65 MPa. This work provides a promising method to produce high volume fraction composites that can meet high strength requirements. 相似文献
89.
90.
Wan-Li Tan Dr. Chun Zhang Yang Li Dr. Kai Guo Dr. Xiao-Wei Gao Dr. Jun Wei Dr. Dong Yi Prof. Lin Pu Prof. Dr. Qin Wang 《ChemMedChem》2021,16(23):3569-3575
Forty samples of optically active falcarindiol analogues are synthesized by using the easily available C2 symmetric (R)- and (S)-1,1’-binaphth-2-ol (BINOL) in combination with Ti(OiPr)4, Zn powder and EtI. Their anticancer activities on Hccc-9810, HepG2, MDA-MB-231, Hela, MG-63 and H460 cells are assayed to elucidate their structure-activity relationships. These results showed that the falcarindiol analogue (3R,8S)- 2 i with the terminal double bond has the most potent anti-proliferation effect on Hccc-9810 cells with IC50 value of 0.46 μM. The falcarindiol analogue (3R,8S)- 2 i can induce obvious Hccc-9810 cell apoptosis in a concentration-dependent manner by Hoechst staining and flow cytometry analysis. The proposed mechanism suggests that the falcarindiol analogue (3R,8S)- 2 i increases LDH release and MDA content, and reduces the levels of SOD activity, which lead to the accumulation of oxidative stress and induce apoptosis in Hccc-9810 cells. 相似文献