首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   34871篇
  免费   4547篇
  国内免费   885篇
电工技术   2403篇
技术理论   2篇
综合类   2393篇
化学工业   8002篇
金属工艺   391篇
机械仪表   555篇
建筑科学   1480篇
矿业工程   16447篇
能源动力   2523篇
轻工业   82篇
水利工程   264篇
石油天然气   925篇
武器工业   17篇
无线电   453篇
一般工业技术   627篇
冶金工业   2120篇
原子能技术   132篇
自动化技术   1487篇
  2024年   60篇
  2023年   187篇
  2022年   751篇
  2021年   1190篇
  2020年   1362篇
  2019年   773篇
  2018年   824篇
  2017年   780篇
  2016年   1054篇
  2015年   1267篇
  2014年   2595篇
  2013年   2251篇
  2012年   3696篇
  2011年   3061篇
  2010年   2162篇
  2009年   2197篇
  2008年   1997篇
  2007年   2182篇
  2006年   1870篇
  2005年   1599篇
  2004年   1234篇
  2003年   1203篇
  2002年   937篇
  2001年   927篇
  2000年   742篇
  1999年   573篇
  1998年   405篇
  1997年   400篇
  1996年   328篇
  1995年   274篇
  1994年   206篇
  1993年   122篇
  1992年   111篇
  1991年   68篇
  1990年   43篇
  1989年   33篇
  1988年   40篇
  1987年   32篇
  1986年   22篇
  1985年   187篇
  1984年   223篇
  1983年   169篇
  1982年   145篇
  1981年   2篇
  1980年   3篇
  1979年   3篇
  1978年   1篇
  1959年   3篇
  1951年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Using low-rank coals, the modifying activities of some petroleum, coal tar and aromatic hydrocarbon additives have been examined to find procedures for their utilization in the preparation of blast furnace coke. Petroleum pitch, especially after hydrogenation, exhibited excellent modifying activity even with non-fusible coals. In contrast, the activity of coal tar was very limited with such coals. The napththenic component, revealed by n.m.r. of the additives, appears to be important in the co-carbonization by inducing fusibility and anisotropic development in such coals. Co-carbonization to recover the dehydrogenated additives was attempted. However, there was no development of the anisotropy in the resultant coke by dissolution of the coal particles although the coal particles were firmly fixed in the matrix. Acid-refluxing treatment of non-fusible coals was found to enhance their modification susceptibility, indicating that some of the acid-soluble mineral matter is important in the thermal depolymerization or fusion process of the coal.  相似文献   
102.
57Fe Mössbauer spectroscopy has been used to characterize the iron-bearing minerals present in some British Columbia coals. The minerals observed in a range of samples include pyrite/marcasite, siderite, jarosite, rozenite or melanterite, and Fe2+ -bearing clay minerals such as illite. The presence of jarosite is confirmed through the magnetic hyperfine interaction observed at 4.2 K. The absence of magnetic ordering at 4.2 K for the ferrous sulphate component indicates the presence of rozenite, FeS04 · 4H20, or melanterite, FeS04 · 7H20, rather than szomolnokite, FeS04 · H20 or FeS04. The effects of ashing on two of the coals is also studied.  相似文献   
103.
Bituminous coal samples from 84 distinct sources were analysed by conventional British Standards (BS) methods for phosphorus, sulphur, chlorine, ash and the ash-forming elements (calcium, silicon, aluminium, iron, sodium, magnesium, potassium, titanium and manganese). In most cases four determinations were made per element per source. Samples were crushed to ?212 μm (72 BS mesh) and pressed into aluminium cups at 20 t in?2 (309 MPa) without binder or backing. Two pellets from each sample were analysed by wave-length dispersive X-ray fluorescence techniques, using a spectrometer equipped with a rhodium rube; the X-ray count took 60 s. The X-ray results were calibrated against the conventional results using multiple regression. The accuracy obtained was comparable with routine ‘wet chemical’ techniques. The X-ray technique is suitable for the routine determination of large numbers of samples.  相似文献   
104.
根据国家质量技术监督局的计划安排,国家标准GB/T15224-1994《煤炭质量分级》需要修订。本文主要讨论“煤炭硫分分级”方面的内容。  相似文献   
105.
在线煤灰分检测技术在中国的应用   总被引:1,自引:0,他引:1  
介绍了应用双能量γ射线透射法测量煤灰分的技术原理及特点;清华大学工程物理系采用该法研制的在线煤灰分仪应用在选煤厂可以指导生产,保证产品质量,提高选煤效率,还可用于介耗<2kg/t的重介质选煤厂及自动配煤系统,为企业创造了显著的经济效益。  相似文献   
106.
铂丝还原滴定法在测量干法脱硫后硫化物含量时,测量数据偏离实际结果,容易造成触媒中毒。提出了用气相色谱火焰光度检测器测定的方法,使数据更可靠、准确。  相似文献   
107.
Claus F.K. Diessel 《Fuel》1983,62(8):883-892
Widespread disagreement about the degree of reactivity of the inertinite group of macerais is related to variations in experimental conditions of assessment and failure to appreciate technological modifications imposed on similar macerals by dissimilar source materials and depositional conditions. This has resulted in the constant under-estimation of the coking potential of post-Carboniferous inertinite-rich coals by predictive methods developed for vitrinite-rich Carboniferous coals. Coking tests up to 1000 °C have been carried out on 20 coals of different rank in such a manner that coked portions of the samples could be correlated with their uncoked equivalents. It has been found that an inverse relationship exists between the level of precarbonization reflectance (PCR) of inertinite and the reflectance and bireflectance of its coke. The increase in the latter parameter is non-linear and involves a sudden jump which is taken as the boundary between reactive (high bireflectance) and non-reactive (low bireflectance) inertinite. In relation to coal rank a reactivity field for inertinite has been delineated which can be subdivided into two areas of high and moderate reactivity, respectively. On the whole, the proportion of reactive inertinite is larger than allowed for in most petrography-based coke stability calculations.  相似文献   
108.
吴迎 《化工设计通讯》2006,32(2):1-2,10
介绍气化效率高、有利于环保、具有一定竞争力的Shell煤气化工艺原理、技术特点及关键设备。建议尽快实现关键技术和设备的国产化。  相似文献   
109.
煤在高温条件下燃烧不利于固硫反应,并从热力学角度出发,得出了煤燃烧中钙基固硫剂反应自由能与温度的关系函数,由化学反应动力学得出院 硫酸钙分解反应的动力学方程及其相关参数,在还原性气氛中,从理论和实验上都证明了硫酸钙在较低温下会发生二次分解,理论分解温度与实际分解温度非常吻合,煤灰中氧化钙和三氧化二铝的存在,可以提高硫酸钙的分解温度同阳也给出了钙基固硫剂的应用条件。  相似文献   
110.
介绍用水煤浆代替轻油原料,改造年产30万吨合成氨装置,重点论述其制氨工艺单元的合理组合和国产化措施。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号