全文获取类型
收费全文 | 71388篇 |
免费 | 8337篇 |
国内免费 | 3494篇 |
专业分类
电工技术 | 4600篇 |
技术理论 | 3篇 |
综合类 | 5962篇 |
化学工业 | 13937篇 |
金属工艺 | 3274篇 |
机械仪表 | 2214篇 |
建筑科学 | 4049篇 |
矿业工程 | 16975篇 |
能源动力 | 4176篇 |
轻工业 | 3176篇 |
水利工程 | 1354篇 |
石油天然气 | 3282篇 |
武器工业 | 581篇 |
无线电 | 4249篇 |
一般工业技术 | 4769篇 |
冶金工业 | 4501篇 |
原子能技术 | 1050篇 |
自动化技术 | 5067篇 |
出版年
2024年 | 164篇 |
2023年 | 626篇 |
2022年 | 1685篇 |
2021年 | 2318篇 |
2020年 | 2577篇 |
2019年 | 1804篇 |
2018年 | 1850篇 |
2017年 | 2139篇 |
2016年 | 2604篇 |
2015年 | 2829篇 |
2014年 | 4946篇 |
2013年 | 4854篇 |
2012年 | 6577篇 |
2011年 | 6006篇 |
2010年 | 4377篇 |
2009年 | 4332篇 |
2008年 | 3893篇 |
2007年 | 4585篇 |
2006年 | 3875篇 |
2005年 | 3325篇 |
2004年 | 2735篇 |
2003年 | 2480篇 |
2002年 | 1996篇 |
2001年 | 1841篇 |
2000年 | 1531篇 |
1999年 | 1214篇 |
1998年 | 966篇 |
1997年 | 870篇 |
1996年 | 775篇 |
1995年 | 650篇 |
1994年 | 482篇 |
1993年 | 329篇 |
1992年 | 315篇 |
1991年 | 219篇 |
1990年 | 177篇 |
1989年 | 126篇 |
1988年 | 101篇 |
1987年 | 73篇 |
1986年 | 60篇 |
1985年 | 220篇 |
1984年 | 253篇 |
1983年 | 186篇 |
1982年 | 161篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1975年 | 9篇 |
1959年 | 8篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
101.
A coal-oil mixture (COM) was prepared from a South African coal and a synthetic oil derived from the same coal by hydroliquefaction. The settling and rheological properties of this mixture were compared with those of a mixture of the same coal with fuel oil. The synthetic oil mixture showed greater settling stability, comparable with that of a commercial COM containing additives. The increased stability may be related to polar compounds present in the oil and on the coal surface. 相似文献
102.
The copreheat-treatment of non-fusible and slightly fusible coals with A240 and hydrogenated A240 under high temperature-short contact-time conditions around 500 °C has been examined in an attempt to produce a formed coke with better anisotropic development. These conditions shortened the copreheat-treatment time and provided better anisotropic development in the resultant coke after carbonization. Effectiveness of short contact-time has been discussed in terms of the extent of depolymerization of coal molecules suitable for anisotropic development, this being related to coal liquefaction under similar conditions. 相似文献
103.
Two lignite samples, Beulah No. 3 and Big Brown No. 1, were liquefied at 420 °C using H2 and synthesis gas to determine the optimum beneficial amount of H2S in the batch autoclave reactor. Under the conditions employed, 50–100 psi partial pressure of H2S, nominally 4–10 wt% of daf lignite, was optimum for both samples. Synthesis gas outperformed H2 with and without H2S for the liquefaction of the two coals. 相似文献
104.
Erv J. Kuhlmann Dick Y. Jung Richard P. Guptill Charles A. Dyke Hyung K. Zang 《Fuel》1985,64(11):1552-1557
The presence of hydroaromatic, hydrogen donor components in a coal-derived solvent is one of the more important factors in the successful operation of a non-catalytic coal liquefaction process. Various hydrogen donor species present in a hydrogenated creosote oil have been identified. Their rate of disappearance under conditions that are consistent with a short residence time coal liquefaction process has been used to rank the reactivities of the various hydrogen donors. 1,2,3,10b-Tetrahydrofluoranthene was found to be an exceptional donor while 4,5-dihydropyrene, the hexahydropyrenes and 9,10-dihydrophenanthrene were found to be quite active. Sym.-octahydrophenanthrene and 2a,3,4,5-tetrahydroacenaphthene exhibited moderate activity. Tetralin and the four methyltetralin isomers were found to be unreactive under the coal liquefaction conditions employed. 相似文献
105.
Results for various types of polar compounds in SRC-11 coal-derived liquids and other fuels were obtained by one or more of the three analytical methods: non-aqueous titration, i.r. spectroscopy and h.p.l.c. Practical aspects as well as precision, accuracy and assumptions necessary for effective application of each of the methods are discussed. H.p.l.c. is applicable to the widest variety of compound types, is the most rapid, most sensitive and shows the best promise for increased development and improvement. Application and development of these techniques is a logical step toward improving process monitoring, catalyst development, toxicological screening and general fuel analysis. 相似文献
106.
The new structure of fibre glass reinforced plastics bolt 总被引:4,自引:0,他引:4
The develop actuality and direction of FRP (fibre glass reinforced plastics) bolt in the world are analyzed. The new type structure of FRP bolt was designed. Trial data indicate that, all kinds of capability target of this FRP bolt all achieve and exceed the country stand-ard, substitute present metal bolt, wood bolt and bamboo bolt and other side bolt, it can gain magnitude technology and economy benefit. FRP bolt mechanization product line produce ef-ficiency is high, its throughput a day are 750 base, this can meet demand of hit-small mining company. 相似文献
107.
介绍了PHS网呼入成功率和短消息流程,依据短消息模型和性能统计结果分析了群发短信对PHS网呼入成功率的影响,并建议选择合理的时间进行短消息群发以减少对网络负荷的影响。 相似文献
108.
软件无线电中采样率转换技术的实现及在3G中的应用 总被引:1,自引:0,他引:1
目前移动通信标准繁多,且新旧体制混杂,很难做到统一.为了实现互连互通,目前比较可行的方法是采用软件无线电.采样率转换技术是实现互连互通的关键.文中针对第三代移动通信系统(3G)中不同通信体制的带宽、速率要求,根据分级变换的思想,对3G中的CDMA2000和TDSCDMA的采样率转换方案进行了设计,并对3G中的5种制式的采样率转换方案进行了分析比较.实验表明,这一方案可以在采样率变换的高效网络结构基础上进一步降低滤波运算量和存储量. 相似文献
109.
Shuichi Yamamoto Teruaki Morihiro Koichi Ariyoshi Turkan Aktas 《Drying Technology》2005,23(6):1319-1330
As the surface properties of the drying materials are very important not only for the drying rate but also for the quality change during drying, the effects of surface concentration on the drying behavior of liquid foods (sugar solutions) were investigated by isothermal drying experiments and by numerical calculation experiments. The isothermal drying experiments with gelled sugar solution systems (sucrose and maltodextrin) were carried out at various relative humidity (RH) values (RH = 0 to 84%). Separate experiments were carried out for determination of the desorption isotherms.
The isothermal drying curves of sugar solutions at RH = 0 to 51% were very similar. Numerical simulations also showed that the drying curves of these sugars at the surface concentration = 0 and 0.1 are almost the same, although the concentration distributions are different.
When a small amount of gelatin was added to sugar solutions, the drying rate decreased remarkably as the gelatin might form a thin film (skin) near the surface, and consequently the retention of ethanol increased. 相似文献
The isothermal drying curves of sugar solutions at RH = 0 to 51% were very similar. Numerical simulations also showed that the drying curves of these sugars at the surface concentration = 0 and 0.1 are almost the same, although the concentration distributions are different.
When a small amount of gelatin was added to sugar solutions, the drying rate decreased remarkably as the gelatin might form a thin film (skin) near the surface, and consequently the retention of ethanol increased. 相似文献
110.