全文获取类型
收费全文 | 15876篇 |
免费 | 1428篇 |
国内免费 | 910篇 |
专业分类
电工技术 | 458篇 |
综合类 | 1306篇 |
化学工业 | 1359篇 |
金属工艺 | 2154篇 |
机械仪表 | 2827篇 |
建筑科学 | 1220篇 |
矿业工程 | 420篇 |
能源动力 | 438篇 |
轻工业 | 508篇 |
水利工程 | 239篇 |
石油天然气 | 284篇 |
武器工业 | 158篇 |
无线电 | 1042篇 |
一般工业技术 | 2384篇 |
冶金工业 | 895篇 |
原子能技术 | 164篇 |
自动化技术 | 2358篇 |
出版年
2024年 | 31篇 |
2023年 | 225篇 |
2022年 | 291篇 |
2021年 | 415篇 |
2020年 | 447篇 |
2019年 | 391篇 |
2018年 | 433篇 |
2017年 | 461篇 |
2016年 | 502篇 |
2015年 | 484篇 |
2014年 | 790篇 |
2013年 | 915篇 |
2012年 | 1006篇 |
2011年 | 1097篇 |
2010年 | 891篇 |
2009年 | 924篇 |
2008年 | 811篇 |
2007年 | 1151篇 |
2006年 | 959篇 |
2005年 | 883篇 |
2004年 | 769篇 |
2003年 | 691篇 |
2002年 | 621篇 |
2001年 | 481篇 |
2000年 | 412篇 |
1999年 | 387篇 |
1998年 | 325篇 |
1997年 | 295篇 |
1996年 | 239篇 |
1995年 | 207篇 |
1994年 | 160篇 |
1993年 | 112篇 |
1992年 | 84篇 |
1991年 | 59篇 |
1990年 | 54篇 |
1989年 | 59篇 |
1988年 | 34篇 |
1987年 | 24篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1964年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
1.
Optimization of room-temperature TCR of polycrystalline La0.9-xSrxK0.1MnO3 ceramics by Sr adjustment
Hongjiang Li Kaili Chu Xingrui Pu Xiaohan Yu Xiaoli Guan Shuaizhao Jin Xiang Liu 《Ceramics International》2021,47(1):94-101
High-density La0.9-xSrxK0.1MnO3 ceramics (LSKMO, A-site = La, Sr and K, 0 ≤ x ≤ 0.25) are successfully fabricated by using facile sol-gel method. Electrical properties are performed by using combination of phenomenological percolation (PP) model, double exchange (DE) mechanism, and Jahn-Teller (JT) effect. Moreover, X-ray diffraction and scanning electron microscopy are employed to analyze the structure and morphology of LSKMO ceramics. Valence states and ionic stoichiometry are assessed by using X-ray photoemission spectrometry. Results reveal that Sr2+ ions, substituting La3+ ions, significantly influenced DE mechanism and JT effect. In addition, Sr-doping plays essential role in improving electrical properties of LSKMO ceramics. At optimal doping content of x = 0.09, peak temperature coefficient of resistance (TCR) of the resistivity is found to be 11.56% K?1 at 297.15 K, which is optimal TCR for A-site K-occupied perovskite manganese oxides. These results confirm that polycrystalline LSKMO ceramics render high room-temperature TCR values due to Sr-doping. 相似文献
2.
3.
Shammya Afroze Nico Torino Md Sumon Reza Nikdalila Radenahmad Quentin Cheok Paul F. Henry Abul K. Azad 《Ceramics International》2021,47(1):541-546
The structural and electrochemical properties of the double perovskite-type oxide, PrBaMnMoO6-δ, was investigated using neutron diffraction with in-situ conductivity measurement under a dry Argon atmosphere from 25 °C to 700 °C. A Rietveld refinement of the neutron diffraction data confirmed monoclinic symmetry in the P21/n space group. Rietveld refinement also confirms the unit cell parameters of a = 5.6567 (1) Å, b = 5.6065 (2) Å, c = 7.9344 (1) Å and β = 84.43° with reliable atomic positions and refinement factors (R-factors). Neutron diffraction data refinement shows two minor phases (<5%), an orthorhombic AB2O5 type phase of PrMn2O5 in the Pbam (No. 32) space group with unit cell parameters, a = 7.9672 (1) Å, b = 8.9043 (2) Å and c = 5.8540 (1) Å and a scheelite phase of BaMoO4 in the tetragonal I41/a (88) space group with the unit cell parameters, a = b = 5.9522 (1) Å, and c = 12.3211 (2) Å. Morphological images revealed a porous and intertwined microstructure. In-situ conductivity measurement shows that the total conductivity of this material was 130.84 Scm?1 at 700 °C. 相似文献
4.
Wire arc additive manufacturing(WAAM)has been investigated to deposit large-scale metal parts due to its high deposition efficiency and low material cost.However,in the process of automatically manufacturing the high-quality metal parts by WAAM,several problems about the heat build-up,the deposit-path optimization,and the stability of the process parameters need to be well addressed.To overcome these issues,a new WAAM method based on the double electrode micro plasma arc welding(DE-MPAW)was designed.The circuit principles of different metal-transfer models in the DE-MPAW deposition process were analyzed theoretically.The effects between the parameters,wire feed rate and torch stand-off distance,in the process of WAAM were investigated experimentally.In addition,a real-time DE-MPAW control system was developed to optimize and stabilize the deposition process by self-adaptively changing the wire feed rate and torch stand-off distance.Finally,a series of tests were performed to evaluate the con-trol system's performance.The results show that the capability against interferences in the process of WAAM has been enhanced by this self-adaptive adjustment system.Further,the deposition paths about the metal part's layer heights in WAAM are simplified.Finally,the appearance of the WAAM-deposited metal layers is also improved with the use of the control system. 相似文献
5.
6.
In this communication, the structural, micro-structural, dielectric, electrical, magnetic, and leakage-current characteristics of a double perovskite (Y2CoMnO6) ceramic material have been reported. The material was synthesized via a high-temperature mixed-oxide route. The compound crystallizes in a monoclinic structure which is confirmed from preliminary X-ray structural study. The morphological study by using scanning electron micrograph reveals the almost homogeneous distribution of grains throughout the surface of the sample. The nature of frequency-dependence of dielectric constant has been described by the Maxwell-Wagner model. The occurrence of a dielectric anomaly in the temperature dependence of dielectric permittivity study demonstrates the ferroelectric-paraelectric phase transition in the material. From the Nyquist plots, we found the existence of both grain and grain boundary effects. The frequency dependence of conductivity was studied by the Jonscher’s Power law, and the conduction phenomenon obeys the large overlapping polaron tunneling model. By using the Arrhenius equation, the activation energy has been calculated which is nearly equal to the energy required for the hoping of the electron. Both impedance and conductivity analysis demonstrate that the sample exhibits negative temperature coefficient of resistance (NTCR) properties indicating the semiconducting type of material at high temperatures. The anti-ferromagnetic character of the material is observed from the nature of magnetic hysteresis loop. The leakage current analysis suggests that the conduction process in the material follows the space charge limited conduction phenomenon. Such material will be helpful for modern electronic devices and spintronic applications. 相似文献
7.
A Cooper(II) (Cu2+)-nitrogen coordination-crosslinked network is designed in poly(styrene-co-butadiene-co-styrene) (SBS) to change commercial elastomers into advanced soft materials. Herein, ligand groups into SBS molecular chains by the 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (DPT) click reaction are first introduced. The results from fourier transform infrared (FT-IR), 1H-nuclear magnetic resonance, and X-ray photoelectron spectroscopy (XPS) are verified the successful modification of SBS. The DPT-grafted SBS could then coordinate with copper sulfate (CuSO4) to form a Cu2+-nitrogen bond, which is further characterized using FT-IR, XPS, atomic force microscope, scanning electron microscope, and geometric structure calculations. After modifying SBS to form an SBS-DPT/CuSO4 composite (SBS-DPT2-Cu10), the tensile stress is improved from 11.43 to 23.25 MPa, while the elongation at break is remained almost unchanged, and the corresponding toughness is increased from 33.21 to 63.26 MJ m–3. Moreover, the dynamic nature of the Cu2+-nitrogen coordination bonds enables the SBS-DPT/CuSO4 composite to exhibit sustained thermoplastic performance and excellent shape memory behavior under an external thermal stimulus. 相似文献
8.
9.
Flash cosintering of a lanthanum strontium cobalt ferrite nanofibre/Gd-doped ceria bilayer structure
《Journal of the European Ceramic Society》2022,42(6):2870-2878
For solid oxide fuel cells, an important structural requirement is that the electrolyte layer needs to be dense and the electrode layer porous, which is difficult to obtain by conventional cosintering. In this work, flash cosintering of a double layer structure consisting of a Gd-doped ceria substrate with a lanthanum strontium cobalt ferrite nanofibre coating is investigated. Experimental and finite element modelling results reveal that when the LSCF layer is connected to the electrode, the heat is concentrated in the LSCF layer, which leads to a huge temperature gradient and introduces severe cracking. When the LSCF layer is electrically isolated from the electrode, the heat is concentrated in the GDC layer, and the temperature gradient is dramatically reduced. In this situation, the density of GDC can reach 92.86% while a high porosity of 52.26% is maintained in the LSCF layer, which is higher than that of the conventional cosintered sample. 相似文献
10.
《International Journal of Hydrogen Energy》2022,47(6):3781-3790
A novel heterostructure of g-C3N4/ZnO/Bi4O5Br2 (ZB-3) was designed, and used in the microbial coupled photocatalytic fuel cell (MPFC). It can effectively improve electron utilization efficiency and pollutant degradation using this double Z-scheme heterojunction structure. The current–time (I–t) curves demonstrated that the current density of ZB-3 was higher than that of ZnO, ZnO/Bi4O5Br2 (ZB-1), g-C3N4/ZnO (ZB-2). Electrochemical impedance spectroscopy (EIS) indicated ZB-3 possessed the minimum charge-transfer resistance. This MPFC for degrading rhodamine B (RhB) and tetracycline (TC) under different conditions were developed using these materials. Even in the dark condition, MPFC with g-C3N4/ZnO/Bi4O5Br2 demonstrated 93% and 82% degradation efficiency for RhB and TC, respectively. Furthermore, the electron transport mechanism of the MPFC and ZB-3 were proposed. It paves the approach for more efficient pollutant degradation via MFC photocatalysis. 相似文献