全文获取类型
收费全文 | 49933篇 |
免费 | 5029篇 |
国内免费 | 2775篇 |
专业分类
电工技术 | 3605篇 |
综合类 | 5347篇 |
化学工业 | 4736篇 |
金属工艺 | 2073篇 |
机械仪表 | 3655篇 |
建筑科学 | 7475篇 |
矿业工程 | 5857篇 |
能源动力 | 1552篇 |
轻工业 | 2015篇 |
水利工程 | 1778篇 |
石油天然气 | 1642篇 |
武器工业 | 644篇 |
无线电 | 3404篇 |
一般工业技术 | 2909篇 |
冶金工业 | 2398篇 |
原子能技术 | 358篇 |
自动化技术 | 8289篇 |
出版年
2024年 | 73篇 |
2023年 | 487篇 |
2022年 | 1064篇 |
2021年 | 1348篇 |
2020年 | 1420篇 |
2019年 | 1159篇 |
2018年 | 1075篇 |
2017年 | 1309篇 |
2016年 | 1626篇 |
2015年 | 1812篇 |
2014年 | 3336篇 |
2013年 | 2766篇 |
2012年 | 3956篇 |
2011年 | 4207篇 |
2010年 | 3320篇 |
2009年 | 3331篇 |
2008年 | 3107篇 |
2007年 | 3722篇 |
2006年 | 3244篇 |
2005年 | 2724篇 |
2004年 | 2243篇 |
2003年 | 1969篇 |
2002年 | 1558篇 |
2001年 | 1329篇 |
2000年 | 1028篇 |
1999年 | 870篇 |
1998年 | 621篇 |
1997年 | 593篇 |
1996年 | 490篇 |
1995年 | 428篇 |
1994年 | 365篇 |
1993年 | 256篇 |
1992年 | 186篇 |
1991年 | 145篇 |
1990年 | 118篇 |
1989年 | 103篇 |
1988年 | 68篇 |
1987年 | 67篇 |
1986年 | 32篇 |
1985年 | 24篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1977年 | 4篇 |
1970年 | 4篇 |
1959年 | 7篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
2.
Aiming at the performance degradation of the existing presentation attack detection methods due to the illumination variation, a two-stream vision transformers framework (TSViT) based on transfer learning in two complementary spaces is proposed in this paper. The face images of RGB color space and multi-scale retinex with color restoration (MSRCR) space are fed to TSViT to learn the distinguishing features of presentation attack detection. To effectively fuse features from two sources (RGB color space images and MSRCR images), a feature fusion method based on self-attention is built, which can effectively capture the complementarity of two features. Experiments and analysis on Oulu-NPU, CASIA-MFSD, and Replay-Attack databases show that it outperforms most existing methods in intra-database testing and achieves good generalization performance in cross-database testing. 相似文献
3.
《Ceramics International》2022,48(8):10579-10591
In present study, we report a V doping fabrication method for obtaining rod-like MgO crystals decorated with a nanoflake layer. This novel structure has only been minimally reported in literature. Pure MgO and Mg2V2O7–MgO composite materials were obtained by precipitation and impregnation methods, with vanadium added concentrations of 0–9%. The influence of V doping on crystal structure and particle morphology of MgO was investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis demonstrated that MgO has a cubic structure, while X-ray photoelectron spectroscopy (XPS) revealed that V5+ exists on the surface of MgO. The specific surface areas and pore sizes of MgO composites were calculated by BET and BJH analysis. These techniques revealed that specific surface area and pore size of MgO increased due to vanadium doping. The antibacterial effects of Mg2V2O7–MgO composite materials against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were assessed using a bacterial killing/colony-forming unit (CFU) assay and bacteriostatic ring method. Our results demonstrate that V doping dramatically improved antimicrobial properties of MgO, with 7 mol% doping inducing the best antibacterial activity. The antibacterial mechanisms of Mg2V2O7–MgO composite material were also proposed. 相似文献
4.
《International Journal of Hydrogen Energy》2022,47(54):22738-22751
Transition metal-based electrocatalysts supported on carbon substrates face the challenges of anodic corrosion of carbon during oxygen evolution reaction at high oxidation potential. The role of electrophilic functional groups (carbonyl, pyridinic, thiol, etc.) incorporated in graphene oxide has been studied towards the anodic corrosion resistance. Heteroatom functionalized carbon supports possess modified electronic properties, surface oxygen content, and hydrophilicity, which are crucial in governing electrochemical corrosion in the alkaline oxidative environment. Evidently, electron-withdrawing groups in NGO support (pyridinic, cyano, nitro, etc) and its lower oxygen content impart maximum corrosion resistance and anodic stability in comparison to the other sulfur-doped and co-doped graphene oxide support. In this report, we establish the baseline evaluation of carbon-supported OER electrocatalysts by a systematic analysis of activity and substrate corrosion resistance. The result of this study establishes the role of surface composition of the doped supports while for designing a stable, corrosion-resistant OER electrocatalyst. 相似文献
5.
6.
为应对"三软"煤层综放沿空掘巷围岩稳定性差的问题,通过数值模拟分析、揭示"三软"煤层中锚杆、锚索载荷变化规律及其与围岩变形相互作用关系,为"三软"煤层沿空掘巷锚网支护参数优化提供理论依据,改善了巷道支护状况,降低相邻工作面间保护煤柱压煤率,提高矿井经济效益和社会效益。 相似文献
7.
为了解破碎围岩分别采用锚杆支护、锚喷支护以及锚喷+锚索耦合三种支护方式下的支护效果,进而为破碎围岩巷道选择合理的支护方式提供参考。通过借助FLAC3D软件建立数值模型,分析不同支护条件下的破碎围岩巷道位移量、应力分布以及塑性区的时空演化特征。结果表明,采用锚喷+锚索耦合支护时,可以较好的控制巷道围岩的位移量、减小应力集中效应、缩小塑性区的影响范围。 相似文献
8.
9.