全文获取类型
收费全文 | 59821篇 |
免费 | 6575篇 |
国内免费 | 4019篇 |
专业分类
电工技术 | 4716篇 |
技术理论 | 1篇 |
综合类 | 5504篇 |
化学工业 | 8606篇 |
金属工艺 | 4056篇 |
机械仪表 | 4107篇 |
建筑科学 | 4884篇 |
矿业工程 | 2025篇 |
能源动力 | 1653篇 |
轻工业 | 5811篇 |
水利工程 | 1687篇 |
石油天然气 | 2194篇 |
武器工业 | 639篇 |
无线电 | 6414篇 |
一般工业技术 | 6309篇 |
冶金工业 | 2242篇 |
原子能技术 | 1031篇 |
自动化技术 | 8536篇 |
出版年
2024年 | 181篇 |
2023年 | 1065篇 |
2022年 | 2058篇 |
2021年 | 2871篇 |
2020年 | 2219篇 |
2019年 | 1607篇 |
2018年 | 1762篇 |
2017年 | 2121篇 |
2016年 | 1776篇 |
2015年 | 2534篇 |
2014年 | 3148篇 |
2013年 | 3883篇 |
2012年 | 4485篇 |
2011年 | 4827篇 |
2010年 | 4386篇 |
2009年 | 4146篇 |
2008年 | 4120篇 |
2007年 | 4051篇 |
2006年 | 3707篇 |
2005年 | 3076篇 |
2004年 | 2115篇 |
2003年 | 1640篇 |
2002年 | 1493篇 |
2001年 | 1362篇 |
2000年 | 1106篇 |
1999年 | 815篇 |
1998年 | 632篇 |
1997年 | 505篇 |
1996年 | 521篇 |
1995年 | 432篇 |
1994年 | 368篇 |
1993年 | 289篇 |
1992年 | 227篇 |
1991年 | 182篇 |
1990年 | 140篇 |
1989年 | 116篇 |
1988年 | 104篇 |
1987年 | 78篇 |
1986年 | 60篇 |
1985年 | 45篇 |
1984年 | 34篇 |
1983年 | 15篇 |
1982年 | 20篇 |
1981年 | 16篇 |
1980年 | 22篇 |
1979年 | 14篇 |
1978年 | 4篇 |
1976年 | 5篇 |
1959年 | 10篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Ming-Puu Chen Asta Y. Z. Lord Yu-Yao Cheng Ku-Chou Tai Wen-Harn Pan 《Journal of Computer Assisted Learning》2020,36(3):383-396
Reflective judgement is crucial for medical-related practitioners in dealing with controversial issues. However, the conformity phenomenon is likely to occur and interfere with reflective judgement learning during interactive activities. Effective strategies are required to moderate the conformity behaviour tendency (CBT) and improve reflective judgement performance (RJP). This study demonstrates two significant results: (a) Compared with the guided self-reflection learning strategy, the online collective reflection (OCR) learning strategy effectively weakened the learners' general CBT while dealing with professional controversial issues; and (b) a significantly negative correlation between the RJP achieved and the change of CBT in online environment was detected in the OCR group. The implications and potential applications in higher education were discussed. Further studies are needed to confirm the long-term effects and the extending application to other professional studies. 相似文献
42.
43.
44.
Thermal management and catalytic combustion stability characteristics of premixed methane/air in heat recirculation meso‐combustors 下载免费PDF全文
Yunfei Yan Shuai Feng Zizhen Huang Li Zhang Wenli Pan Lixian Li Zhongqing Yang 《国际能源研究杂志》2018,42(3):999-1012
In order to illuminate heat recirculation effect on catalytic combustion stability and further improve energy conversion efficiency in meso‐combustor, the catalytic combustion characteristics of the combustor with/without preheating channels are numerically studied at steady conditions. It is found that methane conversion rate and combustion efficiency increases by 2% to 3% and approximately 9% in the heat recirculation meso‐combustor, indicating that heat recirculation effect facilitates more complete combustion of methane and medium components. Preheating channels show positive effects on improving combustion stability in the heat recirculation meso‐combustor. On one hand, preheating channels facilitate heat recirculation effect, and heat recirculation rate exceeds 10% for all cases and reaches 31.8% with an inlet velocity of 0.5 m/s, leading to significant increment of methane‐specific enthalpy at the preheating channel outlet. On the other hand, Rh(s)/O(s) ratios of catalytic surface and catalytic surface temperature in main reaction zone are enlarged by the preheating channels, facilitating methane adsorption at catalytic surface. Specially, most of fuels are consumed in a shorter distance with higher methane conversion speed, which brings benefits to promote combustion efficiency and may be helpful to inhibit the combustion instability in heat recirculation meso‐combustors. 相似文献
45.
为提高中子诱发铀裂变时低产额裂变产物156Eu和161Tb产额测量的精度,需获得放化纯的156Eu和161Tb样品。本工作建立了氢氧化物共沉淀法除铝、氟化钙共沉淀法除铀、TRPO萃取法提取稀土元素、阳离子交换色谱法从混合稀土元素中分离Eu和Tb的流程,可用于大量铀、铝和裂变产物中微量Eu和Tb的分离。在待分离样品中含2 g铀、0.65 g铝和裂变产物的条件下,该流程对Eu、Tb的化学回收率均大于80%,对U、239Np、95Zr、103Ru、131I、132Te、140Ba、140La、141Ce、147Nd等主要干扰物质的去污因子达到106。该方法可满足中子诱发铀裂变时156Eu和161Tb产额精确测量的要求。 相似文献
46.
47.
48.
目的探讨多排螺旋CT(MSCT)多期增强扫描在肾脏透明细胞癌诊断中的规律性,提高对该肿瘤诊断水平。方法回顾性分析2016年1月~2018年6月14例均经手术切除病理证实为肾脏透明细胞癌患者的CT影像资料,所有病例均行MSCT平扫及多期动态增强扫描。结果14例肾脏透明细胞癌形态大多数呈圆形或者类圆形,瘤体最大径范围1.7cm^11.3cm,平均(4.8±1.4)cm,13例CT平扫时肿瘤密度不均匀,呈等低密度,1例呈等密度;12例出现坏死囊变,钙化1例,伴肾盂、肾盏侵犯2例;动态增强扫描可见12例包膜完整,1例均匀性强化,13例不均匀性强化;引入对比剂后皮质期,出现10例病灶强化幅度大于肾皮质,而仅4例低于肾皮质,三期平均CT值分别为110±30Hu,90±15Hu及75±14Hu,其中在实质期出现13例肿瘤强化幅度小于肾实质,仅1例大于肾实质。结论引入对比剂动态增强扫描后,肾脏透明细胞癌在皮质期明显不均匀强化,实质期强化幅度下降显著,呈现出典型的“快进快出”血流动力学强化方式,且肿瘤容易出现坏死、囊变为其特点。 相似文献
49.
叶片是风力机最重要的组成部分,在不同的风能资源情况下,翼型的选择对垂直轴风力机气动特性有着重要的影响。文章分别以NACA0018翼型(对称翼型)和NACA4418翼型(非对称翼型)建立3叶片H型垂直轴风力机二维仿真模型。应用数值模拟的研究方法,从功率系数、单个叶片切向力系数等方面比较两种风力机模型在不同叶尖速比下的气动特性,并采用风洞实验数据验证了流场计算的准确性。CFD计算结果表明:在低叶尖速比下,NACA4418翼型风力机气动特性优于NACA0018翼型风力机,适用于低风速区域;在高叶尖速比下,NACA0018翼型风力机气动特性较好,适用于高风速地区。而且在高叶尖速比时,NACA0018翼型在上风区时,切向力系数平均值要高于NACA4418翼型,在下风区时,NACA418翼型切向力系数平均值高。该研究可为小型垂直轴风力机翼型的选择提供参考。 相似文献
50.
Qiang Xia Tao Feng Xiaowei Lou Ying Wang Yangying Sun Daodong Pan Jinxuan Cao 《International Journal of Food Science & Technology》2020,55(2):669-680
As a decisive attribute, flavour could be influenced by HP treatments through multiple physical and chemical pathways within the high pressure (HP)-assisted meat curing process. This investigation aimed to identify the major pathway influencing volatile flavour patterns of two representative vinasse-cured duck (VCD) products with HP treatments (150–300 MPa/15 min), including wet and dry types, by employing headspace fingerprinting as an untargeted approach. Results suggested that HP treatments greatly lowered moisture contents and increased Warner-Bratzler shear force and thiobarbituric acid reactive substances of the cured samples. According to multivariate models, the volatile flavour patterns of the HP-processed VCD could be clearly separated from the unprocessed samples, but the VCD pressurised at different intensities represented similar volatile fingerprinting, which was validated by e-nose analysis. The discriminant analysis (OPLS-DA) model outlined vinasse-derived ethanol, acetic acid, 3-methyl-1-butanol, 2-methyl-1-butanol, phenethyl alcohol and 2-methyl-3-octanone as the major discriminant aromas across the unpressurised and pressurised samples. 相似文献