全文获取类型
收费全文 | 17567篇 |
免费 | 1570篇 |
国内免费 | 1154篇 |
专业分类
电工技术 | 614篇 |
综合类 | 985篇 |
化学工业 | 6406篇 |
金属工艺 | 1419篇 |
机械仪表 | 604篇 |
建筑科学 | 383篇 |
矿业工程 | 239篇 |
能源动力 | 496篇 |
轻工业 | 1051篇 |
水利工程 | 77篇 |
石油天然气 | 1317篇 |
武器工业 | 177篇 |
无线电 | 1940篇 |
一般工业技术 | 1475篇 |
冶金工业 | 848篇 |
原子能技术 | 443篇 |
自动化技术 | 1817篇 |
出版年
2024年 | 110篇 |
2023年 | 421篇 |
2022年 | 957篇 |
2021年 | 1035篇 |
2020年 | 778篇 |
2019年 | 500篇 |
2018年 | 405篇 |
2017年 | 530篇 |
2016年 | 605篇 |
2015年 | 598篇 |
2014年 | 794篇 |
2013年 | 987篇 |
2012年 | 1079篇 |
2011年 | 1382篇 |
2010年 | 918篇 |
2009年 | 1029篇 |
2008年 | 943篇 |
2007年 | 1012篇 |
2006年 | 961篇 |
2005年 | 779篇 |
2004年 | 604篇 |
2003年 | 553篇 |
2002年 | 496篇 |
2001年 | 487篇 |
2000年 | 415篇 |
1999年 | 363篇 |
1998年 | 275篇 |
1997年 | 231篇 |
1996年 | 187篇 |
1995年 | 163篇 |
1994年 | 135篇 |
1993年 | 121篇 |
1992年 | 108篇 |
1991年 | 73篇 |
1990年 | 67篇 |
1989年 | 26篇 |
1988年 | 24篇 |
1987年 | 29篇 |
1986年 | 14篇 |
1985年 | 20篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1974年 | 4篇 |
1959年 | 3篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Thorough washing of a VPI-5 synthesized with n-dipropylamine as template improves greatly its thermal stability while no major change is observed in the template content. A detailed study of the influence of the pretreatment conditions shows that in order to obtain a high thermal stability (up to at least 960 °C) two parameters are of importance. The removal of both the template and the adsorbed water requires either a low heating rate at atmospheric pressure or a low pressure (less than 3 Torr) when the heating rate is 300 ° per hour. 相似文献
52.
Investigation of the reaction mechanism of chloromethane on ZSM5 is a new topic. In this work an in situ FTIR technique was employed to study the conversion processes of chloromethane, the active sites on HZSM5, and the desorption state of surface species. The catalytic conversion of chloromethane to higher hydrocarbons was also studied. It is demonstrated that chloromethane can be reversibly adsorbed on acidic sites of HZSM5 at room temperature. At 100°C chloromethane is irreversibly and dissociatively adsorbed on the strong acidic sites of HZSM5, on which surface methoxyl is formed as proved by infrared characteristic C-H stretchings of-CH3 at 2960 and 2870 cm–1. Alkoxyls are produced and adsorbed on the catalyst surface as characterized by the infrared absorption bands of -CH2-groups at 1460 and 2930 cm–1. At 100°C the adsorbed methoxyl and alkoxyls are the main surface species, and a small amount of aromatics might exist as detected by a characteristic absorption band at 1510 cm–1. Between 100 and 200°C the adsorbed surface methoxyl and alkoxyls are converted to aromatics, and the occupied OH groups partially appear. At temperature higher than 300°C the adsorbed aromatics are thermally desorbed into the gas phase. Aromatics and alkanes are the main products in catalytic conversion. These results reveal that the formation of aromatics from methoxyl and alkoxyls is easier than the desorption of aromatics from HZSM5 catalyst. An alkoxyl mechanism is proposed for the conversion of chloromethane on HZSM5 based upon the experimental results and the three assumptions: (a) The primary C-C bond is formed from surface methoxyl groups via the methoxyl group polarization and C-H bond weakening, (b) The adsorbed alkoxyls are converted to aromatics via hydrogen transfer and bond rearrangement similar to the conventional carbenium ion mechanism for the aromatization of olefins and alkanes on HZSM5. The hydrogen atoms from the aromatization stimulate the desorption of alkoxyls to alkanes. (c) At temperature higher than 300°C surface reactions and desorption of adsorbed species take place simultaneously, determining the product distribution in the catalytic conversion. 相似文献
53.
54.
利用抽余碳五馏份制备TAME 总被引:4,自引:0,他引:4
探索了以抽余C5为原料经与甲醇醚化制TAME的过程。试验表明,在国产催化剂D54型大孔阳离子交换树脂存在下,在反应温度60℃、LHSV2.4h-1、甲醇/异戊烯物质的量比1.00、反应压力0.2MPa的条件下,抽余C5中的异戊烯可与甲醇反应生成醚,异戊烯的转化率达63.26%,TAME的选择性可达99.61%。 相似文献
55.
活性碳和5A分子筛的吸附特性及其在真空获得中的作用 总被引:1,自引:0,他引:1
评述了活性碳和5A分子筛的吸附等温线及其在真空佩温绝热夹层真空获得中的作用。分析了真空夹层抽真空除气时用N_2气置换以及用“多次吸附-脱附N_2气”方法活化吸附剂等先进工艺的机理。论述了根据吸附剂吸水的吸附等温线,合理确定活化工艺条件的方法。 相似文献
56.
本文分析了使用计数的原理来测量长度、转速的仪器,其误差产生的原因,并结合G3K-3型高准确度长度测量仪,着重介绍了消除误差的方法. 相似文献
57.
李天瑞 《稀有金属与硬质合金》1996,(3)
用2-(5-溴-2吡啶偶氮)-5-二乙氨基苯酚(5-Br-PADAP)为显色剂,采用多波长分光光度法测定钨精矿、难溶锡石矿中的铌、袒,方法快速、准确、灵敏度高,相对标准偏差≤0.021(n=16). 相似文献
58.
W. F. J. Sampers A. P. G. G. Lamers A. A. van STEENHOVEN 《Chemical Engineering Communications》1993,125(1):187-196
In many applications swirling flow is used to enhance heat and mass transfer. One of the problems of modelling a turbulent swirling flow is the choice of the turbulent closure model which is acceptable for engineering purposes. To evaluate which model performs best, numerical results are compared with experimental data. Local velocity measurements are carried out on a swirling flow in a circular tube. The measurement method is hot-wire anemometry combined with visualization techniques. The numerical analysis is carried out using the k-ε model and the Algebraic Stress Model. In the experiment a symmetrical swirl was observed, Comparing the experimental data with the numerical results shows that the Algebraic Stress Model represents the experimental data quite well, whereas the k-ε model fails. 相似文献
59.
通过对多种支持HTML5技术内核的分析,选取了Webkit内核Qtwebkit2.1。在对其进行深入分析的基础上,着重研究了它对HTML5的支持。最后选取并裁剪了基于Qtwebkit2.1内核的浏览器QtWeb,实现对MeeGo平台的移植。经实验表明,该嵌入式移动浏览器能部分支持HTML5技术规范,为以后的进一步研究奠定了良好的基础。 相似文献
60.