全文获取类型
收费全文 | 219258篇 |
免费 | 19952篇 |
国内免费 | 10820篇 |
专业分类
电工技术 | 14421篇 |
技术理论 | 16篇 |
综合类 | 16082篇 |
化学工业 | 34760篇 |
金属工艺 | 12888篇 |
机械仪表 | 14279篇 |
建筑科学 | 16468篇 |
矿业工程 | 6716篇 |
能源动力 | 6365篇 |
轻工业 | 16151篇 |
水利工程 | 4399篇 |
石油天然气 | 12666篇 |
武器工业 | 1903篇 |
无线电 | 25709篇 |
一般工业技术 | 25085篇 |
冶金工业 | 10339篇 |
原子能技术 | 2480篇 |
自动化技术 | 29303篇 |
出版年
2024年 | 439篇 |
2023年 | 3596篇 |
2022年 | 6256篇 |
2021年 | 9322篇 |
2020年 | 7174篇 |
2019年 | 5759篇 |
2018年 | 6555篇 |
2017年 | 7259篇 |
2016年 | 6576篇 |
2015年 | 9092篇 |
2014年 | 11392篇 |
2013年 | 13825篇 |
2012年 | 15515篇 |
2011年 | 16322篇 |
2010年 | 14381篇 |
2009年 | 13700篇 |
2008年 | 13458篇 |
2007年 | 12651篇 |
2006年 | 12577篇 |
2005年 | 10683篇 |
2004年 | 7376篇 |
2003年 | 5968篇 |
2002年 | 5380篇 |
2001年 | 4780篇 |
2000年 | 4444篇 |
1999年 | 4744篇 |
1998年 | 3833篇 |
1997年 | 3260篇 |
1996年 | 3004篇 |
1995年 | 2484篇 |
1994年 | 2031篇 |
1993年 | 1440篇 |
1992年 | 1167篇 |
1991年 | 847篇 |
1990年 | 608篇 |
1989年 | 525篇 |
1988年 | 404篇 |
1987年 | 267篇 |
1986年 | 212篇 |
1985年 | 125篇 |
1984年 | 114篇 |
1983年 | 80篇 |
1982年 | 86篇 |
1981年 | 72篇 |
1980年 | 66篇 |
1979年 | 31篇 |
1978年 | 26篇 |
1977年 | 25篇 |
1976年 | 27篇 |
1975年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
53.
This article proposes an active balancer, which features bidirectional charge shuttling and adaptive equalization current control, to fast counterbalance the state of charge (SOC) of cells in a lithium-ion battery (LIB) string. The power circuit consists of certain bidirectional buck-boost converters to transfer energy among the different cells back and forth. Owing to the characterization of the open-circuit voltage (OCV) vs SOC in LIB being relatively smooth near the SOC middle range, the SOC-inspected balance strategy can achieve more precise and efficient equilibrium than the voltage-based control. Accordingly, a compensated OCV-based SOC estimation is put forward to take into account the discrepancy of SOC estimation. Besides, the varied-duty-cycle (VDC) and curve-fitting modulation (CFM) methods are devised herein to tackle the problems of slow equalization rate and low balance efficacy, which arise from the diminution in balancing current as the SOC difference between the cells decreases in the later duration of equalization especially. The proposed strategies have taken the battery nonlinear characteristic and circuit parameter nonideality into account and can adaptively modulate the duty cycle with the SOC difference to keep balancing current constant throughout the balancing cycle. Simulated and experimental results are given to demonstrate the feasibility and effectiveness of the same prototype constructed. Compared with the fixed duty cycle and the VDC methods, the proposed CFM has the best balancing efficiency of 81.4%, and the balance time is shortened by 27.1% and 18.6%, respectively. 相似文献
54.
Yang Zhi Yang Jian Wang Qiang Sun Fengjing 《Chemistry and Technology of Fuels and Oils》2022,58(3):554-560
Chemistry and Technology of Fuels and Oils - For shale gas wells, plunger lift is challenged by the difficulties like difficult tool tripping in and high operation risks due to the liquid phase... 相似文献
55.
赫哲族是我国北方人口较少的少数民族之一,分布于黑龙江省东部松花江、黑龙江与乌苏里江流域交汇处及完达山余脉.作为具有悠久历史的东北渔猎民族,其东北寒带地区得天独厚的地理位置,造就了其独特的民族文化与建筑居住形式与居室陈设艺术.陈设用品与生活用品既具有精神与审美层面的艺术装饰,也有易加工的便利取材或因寒冷且潮湿的季节气候而考虑的防潮保暖、夏季通风的选材需求,或学习其他民族的优秀技艺文化而发展起来的具有本民族特色的生活与陈设用品.通过对赫哲族历史起源、生活方式、建筑居室陈设传统纹饰及材质手法的介绍与分析,展现出赫哲族人民勤劳、乐观、豁达、创新的生活面貌与文化. 相似文献
56.
Linhui Lu Qingli Shu Guiru Zhang Qi Zhang Ping Du Xuedong Zhu 《American Institute of Chemical Engineers》2022,68(10):e17787
Palladium-based catalysts have been widely employed in the electro-Fenton process for in situ generation of H2O2. However, the process is still far from being practical on a large scale. In this work, a series of ClxFePd/γ-Al2O3/Al catalysts were prepared by a three-step-impregnation method. They exhibited excellent activity in H2O2 in situ synthesis and high efficiency in phenol degradation. The characterization results showed that Cl could assist in increasing the content of Pd0 and reducing the isoelectric point of catalysts, which led to the drastic promotion in the synthesis of H2O2. Theoretical calculations further demonstrated that Cl doping could facilitate the main reaction in H2O2 synthesis, as well as inhibit side reactions such as dissociation of the O O bond. Furthermore, kinetic models were proposed and fitted. A plausible reaction mechanism as well as degradation pathways were elaborated based on electron spin resonance and gas chromatography–mass spectrometry results. These findings illustrate the value of palladium-based ClxFePd/γ-Al2O3/Al catalysts for their application in the electro-Fenton process. 相似文献
57.
Yang Mengmeng Chen Zhaofeng Liu Tianlong Wu Qiong Yang Lixia 《Journal of Porous Materials》2022,29(2):523-530
Journal of Porous Materials - In recent years, oil spills and industrial organic pollutants have caused irreparable damage to the environment and biological ecosystems. Therefore, the treatment of... 相似文献
58.
目的:探讨茶叶水提液对大鲵肝的脱腥效果。方法:采用感官腥味值结合气相—离子迁移色谱(GC-IMS)分析经茶叶水提液处理不同时间(0,5,10,15,20 min)大鲵肝中挥发性成分的变化。结果:与未脱腥组相比,经茶叶水提液脱腥处理5 min后大鲵肝脏腥味值显著下降(P<0.05),处理10 min后腥味值基本稳定。不同脱腥时间下大鲵肝样品中共鉴定出32种挥发性有机物,包括10种醇类、8种醛类、5种酯类、5种酮类、3种烯烃类和1种醚类。经脱腥处理后,大鲵肝中醇、烯烃、醚、酯类物质相对含量下降,酮类和醛类物质相对含量增加。通过正交偏最小二乘法判别分析(OPLS-DA)结合变量投影重要性(VIP)筛选出10种潜在特征标志物(VIP>1),包括4种酮类、2种醇类、2种醛类、1种烯类和1种醚类。随着脱腥时间的延长,蘑菇醇、2-丁酮二聚体、异戊醇单体、2-丁酮单体相对含量呈降低趋势,而正己醛单体、异戊醛单体、丙酮相对含量呈增加趋势。结论:茶叶水提液处理5~10 min能够明显降低大鲵肝腥味,通过GC-IMS技术结合多元统计分析可以对脱腥过程中大鲵肝挥发性有机物进行区分。 相似文献
59.
Based on the premise that large bubbles are removed in larger cyclones and small bubbles in smaller cyclones, a combined degassing cyclone with main and subsidiary chambers was designed to enhance liquid degassing. The pressure loss, liquid flow rate at the gas outlet, split ratio, gas flow rate at the liquid outlet, and degassing efficiency of the degassing cyclone were measured and calculated. Pressure loss correlations were established which relates the Euler number to the gas and liquid Reynolds numbers in the main chamber. Most cases exhibit a degassing efficiency greater than 0.998 when the liquid flow rate is more than 0.7 m3h?1. The contours of pressure loss, split ratio, and degassing efficiency provide an effective guidance for designing a degassing cyclone. 相似文献