全文获取类型
收费全文 | 72220篇 |
免费 | 5483篇 |
国内免费 | 2719篇 |
专业分类
电工技术 | 3824篇 |
技术理论 | 6篇 |
综合类 | 4407篇 |
化学工业 | 12247篇 |
金属工艺 | 3922篇 |
机械仪表 | 4803篇 |
建筑科学 | 5162篇 |
矿业工程 | 2377篇 |
能源动力 | 2225篇 |
轻工业 | 4752篇 |
水利工程 | 983篇 |
石油天然气 | 5240篇 |
武器工业 | 461篇 |
无线电 | 7549篇 |
一般工业技术 | 9294篇 |
冶金工业 | 3771篇 |
原子能技术 | 740篇 |
自动化技术 | 8659篇 |
出版年
2024年 | 129篇 |
2023年 | 1195篇 |
2022年 | 1668篇 |
2021年 | 2764篇 |
2020年 | 2148篇 |
2019年 | 1897篇 |
2018年 | 2250篇 |
2017年 | 2475篇 |
2016年 | 2052篇 |
2015年 | 2687篇 |
2014年 | 3428篇 |
2013年 | 4203篇 |
2012年 | 4350篇 |
2011年 | 4859篇 |
2010年 | 4172篇 |
2009年 | 3957篇 |
2008年 | 3847篇 |
2007年 | 3712篇 |
2006年 | 3797篇 |
2005年 | 3436篇 |
2004年 | 2286篇 |
2003年 | 2086篇 |
2002年 | 1870篇 |
2001年 | 1638篇 |
2000年 | 1801篇 |
1999年 | 2035篇 |
1998年 | 1754篇 |
1997年 | 1390篇 |
1996年 | 1383篇 |
1995年 | 1175篇 |
1994年 | 938篇 |
1993年 | 708篇 |
1992年 | 539篇 |
1991年 | 420篇 |
1990年 | 323篇 |
1989年 | 248篇 |
1988年 | 219篇 |
1987年 | 139篇 |
1986年 | 102篇 |
1985年 | 89篇 |
1984年 | 59篇 |
1983年 | 34篇 |
1982年 | 42篇 |
1981年 | 28篇 |
1980年 | 22篇 |
1979年 | 13篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1945年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Cai Jun Wang Li Wu Ping Tong Lige Sun Shufeng 《Frontiers of Chemical Engineering in China》2007,1(3):271-276
This paper presents a novel method that uses the interception effect of gradient magnetic field on oxygen molecules to realize
enrichment. The use of two opposite magnetic poles of two magnets at a certain distance forms a magnetic space having a field
intensity gradient near its borders. When air injected into the magnetic space outflows from the magnetic space via its borders,
oxygen molecules in the air will experience the interception effect of the gradient magnetic field, but nitrogen molecules
will outflow from the magnetic space without hindrance. Thus, continuous oxygen enrichment is realized. The enrichment degree
of oxygen reaches 0.65% when the inlet and outlet air flows are 40 mL/min and 20 mL/min, respectively, and the gas temperature
is 298 K and the maximal product of magnetic flux density and its gradient is 563 T2/m (the distance between two magnetic poles is 1 mm). When the gas temperature rises to 343 K, the enrichment degree drops
to 0.32%; and when the maximal product of magnetic flux density and field intensity gradient drops to 101 T2/m (the distance between two magnetic poles is 4 mm), the enrichment degree drops to 0.23%. The experimental results show
that there is an optimal ratio between the inlet air flow and the outlet air flow. Under the experimental conditions in this
paper, the value is about 2.0. It is demonstrated that the method presented in this paper can continuously enrich oxygen and
has a higher enrichment degree than other oxygen-enrichment methods using magnetic separation.
Translated from Journal of Beijing University of Chemical Technology, 2006, 33(5): 62–66 [译自: 北京化工大学学报] 相似文献
994.
Xuping Sun 《Polymer》2004,45(7):2181-2184
Polyelectrolyte-protected gold nanoparticles have been facilely obtained by heating an amine-containing polyelectrolyte/HAuCl4 aqueous solution without the additional step of introducing other reducing agents. All experimental data indicate that different initial molar ratio of polyelectrolyte to gold can lead to the formation of dispersed nanoparticles, quasi one-dimensional aggregates of nanoparticles or bulk metal deposits. More importantly, the growth kinetics of gold particles thus formed can be tuned by changing the initial molar ratio of polyelectrolyte to gold. 相似文献
995.
国外陶瓷球加工技术及其应用 总被引:4,自引:0,他引:4
主要综述了国外陶瓷球的加工技术,加工陶瓷球使用的设备,研磨介质和研磨料的选择,介绍了陶瓷球及陶瓷球轴承的应用发展概况。 相似文献
996.
The chemical equilibrium for the coupling of ethylbenzene dehydrogenation with nitrobenzene hydrogenation, to produce styrene and aniline simultaneously, has been calculated on the basis of the Soave–Redlich–Kwong equation of state. The dehydrogenation of ethylbenzene in the presence of nitrobenzene over the catalysts -Al2O3, ZSM-5, activated carbon and platinum supported on activated carbon has been carried out at 400 °C. The effects of Pt loading and the pretreatment of the catalysts have been investigated. It has been revealed that the conversion of ethylbenzene can be greatly improved by the reaction coupling due to the elimination of the hydrogen produced in the reaction by the hydrogenation of nitrobenzene. Platinum supported on the activated carbon has been suggested as a suitable catalyst. The best results with ethylbenzene conversion of 33.8% and styrene selectivity of 99.2% were obtained over Pt(0.02 wt%)/AC at 400 °C. Moreover, such process is also energetically favored since the necessary process heat to drive the ethylbenzene dehydrogenation can be provided by the coupling with the exothermic nitrobenzene hydrogenation reaction. 相似文献
997.
By means of the molecular dynamics (MD) simulation, the crystallization mechanism of 22,8-polyurethane which contains hydrogen-bond units is investigated and the results show that the crystallization process at a fixed temperature can be characterized by three stages: (1) The extended chain collapses to a globular random coil; (2) The random coil reorganizes into an ordered lamellar structure; (3) Accompanied with the segments clustering due to the hydrogen-bond formation, the lamellar develops with local defects. Two kinds of hydrogen-bond, which are formed between NH group and CO group (N-H?OC), and between NH group and urethane alkoxy oxygen (N-H?O), respectively, are found to play an important role in the crystallization process of 22,8-polyurethane. Furthermore, the effect of temperature on the crystallization is also studied by selecting three temperatures 200, 300 and 400 K. The lower the crystal temperature is, the slower the crystallization rate is and the stronger the hydrogen-bonding interactions are presented. This is in harmony with the experimental results. 相似文献
998.
999.
1000.
利用废铅酸蓄电池中的废硫酸作为浸取剂,对硼泥中的镁进行回收并制备出高品质的氢氧化镁产品。实验得出了酸浸硼泥的最佳工艺条件:酸浸温度为80℃;酸浸时间为30 min;酸用量为硫酸与硼泥质量比为1.2∶1。利用不同金属水解pH的不同,将酸浸过程中从硼泥和废硫酸中引入的杂质依次去除,得到精制硫酸镁溶液。由精制硫酸镁制取氢氧化镁的工艺条件为:常温下,沉淀剂为氨水,反应终点pH为11,反应时间为2 h,反应物在50℃下陈化12 h,过滤、洗涤后105℃烘干。实验考察了不同沉淀剂对氢氧化镁形貌的影响。所得氢氧化镁纯度在97%以上,粒径在0.1~1μm之间,各项指标均优于中国化工行业标准。 相似文献