全文获取类型
收费全文 | 69825篇 |
免费 | 5359篇 |
国内免费 | 2789篇 |
专业分类
电工技术 | 3439篇 |
技术理论 | 10篇 |
综合类 | 4071篇 |
化学工业 | 12214篇 |
金属工艺 | 3779篇 |
机械仪表 | 4319篇 |
建筑科学 | 5946篇 |
矿业工程 | 2003篇 |
能源动力 | 2061篇 |
轻工业 | 4241篇 |
水利工程 | 1106篇 |
石油天然气 | 4364篇 |
武器工业 | 534篇 |
无线电 | 8215篇 |
一般工业技术 | 8943篇 |
冶金工业 | 3586篇 |
原子能技术 | 782篇 |
自动化技术 | 8360篇 |
出版年
2024年 | 250篇 |
2023年 | 1124篇 |
2022年 | 1852篇 |
2021年 | 2521篇 |
2020年 | 1999篇 |
2019年 | 1757篇 |
2018年 | 1922篇 |
2017年 | 2215篇 |
2016年 | 1996篇 |
2015年 | 2636篇 |
2014年 | 3252篇 |
2013年 | 3900篇 |
2012年 | 4279篇 |
2011年 | 4518篇 |
2010年 | 3936篇 |
2009年 | 3726篇 |
2008年 | 3656篇 |
2007年 | 3650篇 |
2006年 | 3844篇 |
2005年 | 3326篇 |
2004年 | 2296篇 |
2003年 | 2001篇 |
2002年 | 1928篇 |
2001年 | 1752篇 |
2000年 | 1756篇 |
1999年 | 2026篇 |
1998年 | 1810篇 |
1997年 | 1485篇 |
1996年 | 1418篇 |
1995年 | 1081篇 |
1994年 | 1034篇 |
1993年 | 716篇 |
1992年 | 549篇 |
1991年 | 440篇 |
1990年 | 329篇 |
1989年 | 262篇 |
1988年 | 238篇 |
1987年 | 149篇 |
1986年 | 105篇 |
1985年 | 80篇 |
1984年 | 38篇 |
1983年 | 36篇 |
1982年 | 40篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Zhen Wu Jing Yao Pengfei Zhu Fusheng Yang Xiangyu Meng Sandra Kurko Zaoxiao Zhang 《International Journal of Hydrogen Energy》2021,46(19):11183-11198
Advanced biogas power generation technology has been attracting attentions, which contributes to the waste disposal and the mitigation of greenhouse gas emissions. This work proposes and models a novel biogas-fed hybrid power generation system consisting of solid oxide fuel cell, water gas shift reaction, thermal swing adsorption and proton exchange membrane fuel cell (SOFC-WGS-TSA-PEMFC). The thermodynamic, exergetic, and thermo-economic analyses of this hybrid system for power generation were conducted to comprehensively evaluate its performance. It was found that the novel biogas-fed hybrid system has a gross energy conversion efficiency of 68.63% and exergy efficiency of 65.36%, indicating high efficiency for this kind of hybrid power technology. The market sensitivity analysis showed that the hybrid system also has a low sensitivity to market price fluctuation. Under the current subsidy level for the distributed biogas power plant, the levelized cost of energy can be lowered to 0.02942 $/kWh for a 1 MW scale system. Accordingly, the payback period and annual return on investment can reach 1.4 year and about 20%, respectively. These results reveal that the proposed hybrid system is promising and economically feasible as a distributed power plant, especially for the small power scale (no more than 2 MW). 相似文献
23.
Tingen Zhu Wenping Li Qiqing Wang Yanbo Hu Kaifang Fan Jiafa Du 《Mine Water and the Environment》2020,39(1):57-67
A method to calculate the height of a water-conducting fractured zone (HWCFZ) was developed based on the plate and shell theory, and the development of the HWCFZ in bedrock and Q2l loess strata is discussed in detail. First, the subsidence-deflection curve equation of the overlying stratum is theoretically derived, and then the ultimate deflection and free space height of rock strata are calculated. Moreover, the strata tensile strain is calculated by using integral calculus. In addition, the failure state of the rock is analyzed by comparing the theoretically calculated tensile strain with the experimentally measured yield tensile strain, allowing one to attain the maximum value of HWCFZ. This approach was tested at the Jinjitan coal mine; the theoretically predicted, experimentally measured, and numerically computed maximum HWCFZ values were 189.5, 187.3, and 188.5 m, respectively, demonstrating the accuracy of the proposed method. These results are highly significant for safe and environment-friendly coal mining in northwest Shaanxi, China. 相似文献
24.
25.
The red grape berry pigments, anthocyanins, were characterized in the early 20th century, but investigations of wine pigments were stymied during that era. The question of their identity was a major challenge for wine chemists. A number of techniques showed that the pigments were polymeric in nature. Some structures were postulated by mid-century based on reactions between anthocyanins and condensed tannin, and later postulated wine pigments were observed in model reactions. Some related compounds were then observed in wine. By the end of the 20th century, the ionization of non-volatiles for mass spectrometry opened the door to these compounds. In addition, a new class of compounds was observed, the pyranoanthocyanins, a product of fermentation and aging metabolites with anthocyanins. These compounds possess the pigment stability to SO2 and pH change that is characteristic of aged red wine. Aging experiments show a dynamic situation with shifts in the population of pigment classes over time. The very large number of diverse pigments explains why it has been so difficult to answer the century-old question of the structure of wine pigments. Our current understanding is founded on the use of mass spectral analysis using electrospray and related ionization techniques over the last 25 years. Future progress will rely on more sophisticated analysis of this very complex mixture of substances. © 2019 Society of Chemical Industry 相似文献
26.
27.
CO2激光治疗皮肤基底细胞癌14例临床观察 总被引:4,自引:0,他引:4
目的 :探求一种简单 ,安全 ,效果好的基底细胞癌的治疗方法。方法 :对 1 4例基底细胞癌患者在局麻下用CO2 激光行基底细胞癌切除术或切除 +气化术。结果 :患者术中、术后出血少 ,伤口恢复快 ,愈合良好 ,疤痕表浅 ,随访未见复发。结论 :CO2 激光用于治疗基底细胞癌效果良好 ,无明显副作用 ,操作简单值得推广。 相似文献
28.
29.
涡轮搅拌桨反应器混合过程的数值计算 总被引:1,自引:1,他引:0
利用CFD方法计算单层涡轮反应器搅拌槽内流体混合过程的速度场和浓度场,研究物料在搅拌槽内的混合过程,以及不同监测点对混合时间的影响。结果表明,搅拌槽内物料的混合主要受槽内流体的流动形式所影响;混合时间的长短与监测点位置有关;在搅拌桨的桨叶附近进行监测所得到的混合时间较短,在液面附近进行监测所得的混合时间较长。在实际生产和试验中,应注意对监测点位置的选取。 相似文献
30.
选取具有代表性的碳钢、不锈钢、镀锌碳钢、铝、钛和铜挂片,在某企业不同部位投放后进行为期半年的大气腐蚀试验,得出了在半年期中的腐蚀规律。在此基础上,对每种金属材料的腐蚀特点进行总结,并对大气腐蚀的各种影响因素进行分析,提出了行之有效的防护措施。 相似文献