全文获取类型
收费全文 | 58762篇 |
免费 | 6492篇 |
国内免费 | 2101篇 |
专业分类
电工技术 | 2787篇 |
综合类 | 4252篇 |
化学工业 | 13161篇 |
金属工艺 | 6245篇 |
机械仪表 | 2601篇 |
建筑科学 | 6015篇 |
矿业工程 | 957篇 |
能源动力 | 9059篇 |
轻工业 | 2835篇 |
水利工程 | 546篇 |
石油天然气 | 2607篇 |
武器工业 | 368篇 |
无线电 | 1784篇 |
一般工业技术 | 8454篇 |
冶金工业 | 3604篇 |
原子能技术 | 1148篇 |
自动化技术 | 932篇 |
出版年
2024年 | 106篇 |
2023年 | 995篇 |
2022年 | 1661篇 |
2021年 | 1952篇 |
2020年 | 2045篇 |
2019年 | 1733篇 |
2018年 | 1582篇 |
2017年 | 1811篇 |
2016年 | 2035篇 |
2015年 | 2006篇 |
2014年 | 3497篇 |
2013年 | 3676篇 |
2012年 | 4078篇 |
2011年 | 4466篇 |
2010年 | 3249篇 |
2009年 | 3415篇 |
2008年 | 2655篇 |
2007年 | 3718篇 |
2006年 | 3356篇 |
2005年 | 2913篇 |
2004年 | 2541篇 |
2003年 | 2255篇 |
2002年 | 2076篇 |
2001年 | 1670篇 |
2000年 | 1325篇 |
1999年 | 1083篇 |
1998年 | 894篇 |
1997年 | 756篇 |
1996年 | 619篇 |
1995年 | 588篇 |
1994年 | 475篇 |
1993年 | 382篇 |
1992年 | 346篇 |
1991年 | 243篇 |
1990年 | 199篇 |
1989年 | 203篇 |
1988年 | 132篇 |
1987年 | 104篇 |
1986年 | 85篇 |
1985年 | 64篇 |
1984年 | 91篇 |
1983年 | 71篇 |
1982年 | 76篇 |
1981年 | 25篇 |
1980年 | 24篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1975年 | 4篇 |
1959年 | 30篇 |
1951年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Jun Wang Fushuo Wu Ruoan Zou Yueshu Wu Mengdi Gan Jing Feng Xiaoyu Chong 《Journal of the American Ceramic Society》2021,104(11):5873-5882
In this study, high-entropy rare-earth tantalate ceramics (Y0.2Ce0.2Sm0.2Gd0.2Dy0.2)TaO4 ((5RE0.2)TaO4) have been successfully fabricated. The possibility of formation of (5RE0.2)TaO4 was verified via first-principles calculations. In addition, the phase structure, ferroelastic toughening mechanism, thermophysical, and mechanical properties were systematically investigated. The (5RE0.2)TaO4 ceramics have lower phonon thermal conductivity (1.2–2.6 W·m–1·K–1) in the entire temperature range than that of RETaO4 and YSZ. (5RE0.2)TaO4 has a higher fracture toughness and lower brittleness index than YSZ. The thermal expansion coefficients of (5RE0.2)TaO4 are as high as 10.3 × 10-6 K–1 at 1200°C and Young's modulus is 66–189 GPa, and thus, (5RE0.2)TaO4 possesses great potential for application in thermal barrier coatings (TBCs). 相似文献
62.
63.
I.A. Anokhina I.E. Animitsa V.I. Voronin V.B. Vykhodets Т.Е. Kurennykh N.G. Molchanova A.I. Vylkov A.E. Dedyukhin Y.P. Zaikov 《Ceramics International》2021,47(2):1949-1961
The lithium-doped phases Gd1.7Li0.3Zr2O6.7 and Gd2Zr1.7Li0.3O6.55 with a pyrochlore structure were prepared by the modified Pechini method using citric acid and glycerol. Monitoring of the lithium content by using a nuclear microanalysis showed that a significant loss of lithium occurred after heat treatment above 1200 °C. Dense ceramics with a stoichiometric lithium content can be prepared by a low temperature microwave sintering (1100 °C). The introduction of lithium in the Gd-sublattice was accompanied by a decrease in the unit cell parameter (a = 10.5208 (1) Å vs 10.5346 (2) Å for Gd2Zr2O7) and during doping at the Zr-sites with lithium, the cell parameter increased (10.5720 (1) Å). The doping in both cases led to an increase in the free cell volume. The impedance spectroscopy results showed that the bulk conductivity can be enhanced by the Li+-doping at the Gd3+-site by almost an order of magnitude. The sample Gd2Zr1.7Li0.3O6.55 had a conductivity lower than that of Gd1.7Li0.3Zr2O6.7 due to the possible trapping of oxygen vacancies by a high-charged acceptor defect LiZr???. The conductivity?pO2 measurements showed that the Li-containing phase was a pure oxide-ion conductor at T < 800 °C. 相似文献
64.
Pengfei Wang Alson Kwun Leung Ng Alastair Dowler Heike Ebendorff-Heidepriem 《Journal of the American Ceramic Society》2021,104(2):833-850
For lead-germanate glass fibers, reducing the content of hydroxyl (OH) groups and the formation of metallic Pb species is essential to pave the way for their applications as low-loss mid-IR fiber optics since OH and metallic Pb species cause intense absorption and scattering loss, respectively, in the mid-IR spectral range. The first part of this study reported the optimization of the glass melting procedure to obtain low amount of OH while preventing formation of metallic Pb species in lead-germanate glass. Here, the second part of this study reports the investigation of the process conditions to fabricate low-loss lead-germanate glass fiber through further understanding of the co-effects of glass melting and heat treatment atmospheres on the formation of nano- and micron-scale metallic Pb species in both the as-produced and heat treated lead-germanate glasses. Finally, using this advance in knowledge, we successfully fabricated low-loss lead-germanate glass fibers with no presence of reduced metallic Pb particles by optimizing dehydration agent, glass melting, preform extrusion and fiber drawing conditions. The optimized fabrication conditions reduced the unstructured fiber loss by almost one order to <0.3 dB/m at 1.55 μm. 相似文献
65.
通过对42CrMo4风机主轴结构尺寸、性能要求、材质特点等方面进行分析,对原有锻后热处理工艺进行优化,制定出既能达到锻后热处理效果又经济节能的工艺参数。 相似文献
66.
67.
《Ceramics International》2022,48(11):15293-15302
The in situ temperature monitoring of hot components in harsh environments remains a challenging task. In this study, SiBCN thin-film resistance grids with thicknesses of 1.8 μm were fabricated on alumina substrates via direct writing. Owing to their dense microscopic morphology and extremely high graphitisation level, the produced SiBCN films exhibited large high-temperature oxidation resistance and electrical conductivity. The resistance–temperature, stability, and repeatability characteristics of these films were examined in an aerobic environment at temperatures up to 800 °C. The obtained results revealed that the thermistor resistance decreased monotonously with increasing temperature from room temperature to 800 °C. The SiBCN film resistance variations observed during repeated temperature cycling in the regions of 505–620 °C and 610–720 °C were 0.09% and 1.7%, respectively. The high cyclability and stability of the SiBCN thin film thermistor suggested its potential applicability for the in situ temperature monitoring of hot components in harsh environments. 相似文献
68.
《Ceramics International》2022,48(8):11304-11312
Li13.9Sr0.1Zn(GeO4+δ)4 (LSZG) materials can exhibit proton conduction by Li+/H+ ion exchange in hydrogen atmosphere. It can be used in solid oxide fuel cells (SOFCs) as an electrolyte. In this study, In3+ doped LSZG powders are synthesized by sol-gel method. X-ray diffraction, scanning electron microscopy, thermal gravimetric analyzer, and electrochemical impedance spectroscopy are used to investigate the effects of In doping on LSZG. All Li13.9-xInxSr0.1Zn(GeO4+δ)4 (LISZG, 0 ≤ x ≤ 0.3) ceramics exhibit the same phase with LSZG. The dopant of In promotes the sintering activity and Li+/H+ ion exchange rate of LSZG. The optimum doping of In is x = 0.2. At 600 °C, Li13.7In0.2Sr0.1Zn(GeO4+δ)4 (0.2LISZG) shows a proton conductivity of 0.094 S/cm under 0.9 V direct current bias voltage. In addition, the single cell based on 0.2LISZG electrolyte is prepared, and it has been demonstrated that the practical utilization of 0.2LISZG in IT-SOFCs is feasible. 相似文献
69.
《Journal of the European Ceramic Society》2022,42(4):1568-1575
Li7La3Zr2O12-based garnet-type solid electrolytes are promising candidates for use in all-solid-state lithium batteries (ASSLBs). However, their potential in large-scale commercial applications is largely hindered by the time/energy-consuming and lithium-wasting synthetic method which typically needs a long-duration high temperature solid state reaction process. Herein we invent a fast preparation route that involves a short-period thermal reaction (1100 °C for 10 min) in laboratory muffle furnaces following by conventional hot pressing technique to get almost fully dense (Al, Ga, Ta, Nb)-doped garnet-type electrolytes with high phase purity (>99.9 %). The large and compact grains, low porosity and high phase purities of garnet ceramic electrolytes synthesized in this study ensure superior electrochemical performance. Particularly, Ga-doped cubic Li7La3Zr2O12 shows extremely low Ea values (0.17?0.18 eV) and record-high lithium ionic conductivities (>2 × 10?3 S cm-1 at 25 °C). 相似文献
70.
Guishang Pei Junyi Xiang Qingyun Huang Xuewei Lv 《Journal of the American Ceramic Society》2022,105(10):6359-6369
A double pyrovanadate CaMgV2O7 sample was synthesized via a facile solid-state route under an air atmosphere. The nonequilibrium formation pathways of the CaMgV2O7 were investigated via powder X-ray diffraction. A multistep reactions path (metavanadates–pyrovanadates–double pyrovanadate CaMgV2O7) was proposed to describe the formation of the CaMgV2O7 considering the thermodynamic and kinetic factors. The cell unit parameters of the CaMgV2O7 sample indicated the crystallization according to a monoclinic system with space group P12/c1(14), and the lattice parameters of a = 6.756 Å, b = 14.495 Å, c = 11.253 Å, β = 99.12, and V = 108.806 Å3. X-ray photoelectron spectroscopy also confirmed the +5 oxidation state vanadium in CaMgV2O7. The endothermic effects at 1033 and 1143 K were related to the incongruent melting and liquidus temperatures of CaMgV2O7, respectively. The comprehensive thermodynamic properties of CaMgV2O7 were established in both low- and high-temperature regions, utilizing a physical property measurement system and multi-high-temperature calorimetry (96 lines). The heat capacity (200 J mol K−1) and entropy (198 J mol K−1) at 298.15 K were computed based on the low-temperature heat capacity values, and the enthalpy of formation at 298.15 K was also estimated. The fitted high-temperature capacity can be used to obtain the changes in the enthalpy, entropy, and Gibbs free energy. This study is part of building a reliable thermodynamic database of the CaO–MgO–V2O5 system. 相似文献