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   48132篇
  免费   5662篇
  国内免费   1773篇
电工技术   2810篇
技术理论   2篇
综合类   3239篇
化学工业   9555篇
金属工艺   1984篇
机械仪表   1273篇
建筑科学   1900篇
矿业工程   16958篇
能源动力   2903篇
轻工业   380篇
水利工程   297篇
石油天然气   1472篇
武器工业   75篇
无线电   3585篇
一般工业技术   4443篇
冶金工业   2657篇
原子能技术   117篇
自动化技术   1917篇
  2024年   80篇
  2023年   315篇
  2022年   879篇
  2021年   1398篇
  2020年   1618篇
  2019年   986篇
  2018年   1074篇
  2017年   1172篇
  2016年   1469篇
  2015年   1664篇
  2014年   3210篇
  2013年   3081篇
  2012年   4648篇
  2011年   4135篇
  2010年   2927篇
  2009年   3011篇
  2008年   2852篇
  2007年   3159篇
  2006年   2790篇
  2005年   2390篇
  2004年   1920篇
  2003年   1783篇
  2002年   1474篇
  2001年   1370篇
  2000年   1148篇
  1999年   896篇
  1998年   658篇
  1997年   591篇
  1996年   493篇
  1995年   435篇
  1994年   332篇
  1993年   228篇
  1992年   183篇
  1991年   119篇
  1990年   87篇
  1989年   54篇
  1988年   61篇
  1987年   43篇
  1986年   31篇
  1985年   195篇
  1984年   232篇
  1983年   173篇
  1982年   149篇
  1981年   10篇
  1980年   6篇
  1979年   8篇
  1978年   6篇
  1976年   5篇
  1974年   5篇
  1951年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
动筛跳汰系统设计中若干环节的探讨   总被引:1,自引:0,他引:1  
论述了动筛跳汰机的选型原则及技术要求,提出了4m2动筛跳汰机分选系统设计中各环节技术参数及所用设备的选择条件,同时对动筛跳汰系统各环节的布置进行了探讨。  相似文献   
32.
A general procedure is proposed for innovative research and development of gas-solid reactor systems, with a brief explanation of the significance of each step in the procedureBased upon the contacting mode between gas and solid phases, as well as the ways of supplying thermal energy to the reacting regions, various types of gas-solid reactor systems are classified by using tables of so called “matrix” form, for thermal cracking and gasification of heavy oils, gasification of coal, gasification of solid waste, calcination of limestone, clinkering of cement and reduction of iron ore.The importance of fundamental concepts is emphasized for successful research and development by presenting several examples; namely, calcination of limestone, thermal cracking of heavy oils and gasification of solid waste materials.In connection with the direction in which fundamental research should be oriented, four primary ways of thinking are proposed, which can be applied to obtain innovative ideas for further research and development in this field.One example of the author's practical experience was selected to show the role of the fundamental research in the course of large scale development. Finally the author outlines the role of chemical reaction engineering to innovate the novel gas-solid reactor systems which may be inevitable for simultaneous solution of the three big E's; namely, Energy, Environment and Economy.  相似文献   
33.
我国煤焦油加工的现状及发展趋势   总被引:6,自引:0,他引:6  
我国煤焦油加工的现状为:装置规模小;热能回收利用不合理;产品种类少;环境保护存在一定问题。从国内外焦炭市场和生产情况分析,认为我国机焦产量大幅增长是带动煤焦油加工业发展的主要因素。指出我国煤焦油集中加工格局已经形成.时机已经成熟。  相似文献   
34.
Given the conditions of residual coal from the boundary of a flat dipping open-pit mine,which uses strip areas mining and inner dumping with slope-covering,we propose an open-pit and underground integrated mining technology for residual coal of end slopes.In the proposal a conveyance road and ventilation conveyance near the slope are built,corresponding to the pit mining area and the surface coal mine dump,as well as an interval haulage tunnel and air-inlet tunnel.The outcome shows that such mining method may reduce the effect to slope stability from underground mining,it does not affect the dumping advance and has a high recovery rate of residual coal resources.The working face is timbered by single hydraulic props,transported by a scraper conveyor and supported by coal walls.This method of mining is one of layered top coal caving,with high resource recovery,low production cost where positive economic benefit can be realized.  相似文献   
35.
Potassium humate was extracted from brown coal.A novel super absorbent composite,poly (acrylic acid-co-acrylamide)/potassium humate (PAA-AM/KHA),was prepared by graft polymerization of acrylic acid,acrylamide and coal based potassium humate using N,N'-methylenebisacrylamide as a crosslinker and potassium peroxydisulfate as an initiator.The effects of reaction temperature,degree of neutralization of the poly (acrylic acid) and the amounts of crosslinker,initiator and potassium humate were investigated.Salt resistance tests were also carried out.The composite prepared under optimal conditions had a potassium humate content of 10% and exhibited a water absorption of 770 g/g in distilled water,and 349,286 and 41 g/g in 0.5 mol/L KC1,MgCl2 and AlCl3 solutions respectively.The results indicate that the salt resistance of PAA-AM/KHA was superior to that of poly (acrylic acid-co-acrylamide) because of the collaborative effect of functional groups of the coal based potassium humate.The PAA-AM/KHA micro powder was characterized by IR spectroscopy and the micrographic surface was characterized by scanning electron microscopy.Introduction of potassium humate into the poly (acrylic acid-co-acrylamide) structure creates a composite more suitable for use as a water-managing material in the renewal of arid and desert environments.The salt resisting property of the composite is improved,production costs are reduced and the growth stimulant effect is still present.  相似文献   
36.
Concrete structures in main coal cleaning plants have been rebuilt and reinforced in the coal mines of the Shanghai Da-tun Energy Sources Co. Ltd., the first colliery of the Pingdingshan Coal Co. Ltd. and the Sanhejian mine of the Xuzhou Mining Group Co. Ltd. In these projects, the operating environment and reliability of concrete structures in the main plants of the three companies were investigated and the safety of the structures inspected. Qualitative and quantitative analyses were made on the spe-cial natural, technological and mechanical environments around the structures. On the basis of these analyses, we discuss the long-term, combined actions of the harsh natural (corrosive gases, liquids and solids) and mechanical environments on concrete structures and further investigated the damage and deteriorating mechanisms and curing techniques of concrete structures in the main coal cleaning plants. Our study can provide a theoretical basis for ensuring the reliability of concrete structures in main coal cleaning plants.  相似文献   
37.
The effects of insoluble eutectic Si particles on the growth of anodic oxide films on ZL114A aluminum alloy substrates were in-vestigated by optical microscopy (OM) and scanning electron microscopy (SE...  相似文献   
38.
一维炉是一种研究煤的热解燃烧和结渣等方面的实验系统,可用于模拟电厂煤粉的燃烧特性。以元宝山褐煤为燃料,介绍了一维炉的结构和功能,并对系统的可靠性进行了验证,利用烟气分析仪及热重分析仪对燃烧后的尾部烟气及灰渣进行了分析测定。结果表明:尾部烟气含氧量与灰渣可燃部分剩余量均在理论计算值的误差允许范围内,说明一维炉密封良好,系统内各部分正常运行,对维炉的调试和研究具有一定的参考意义。  相似文献   
39.
40.
A Fe-Ni soft magnetic film was prepared in sulphate solution by electroplating. The influences of the molar ratio of n [Fe2+ ]/ n [Ni2+ ], current density, bath temperature, pH and L-ascorbic acid concentration on magnetic properties of Fe-Ni alloy film were investigated. The results show that the saturated flux density(BS) of the film increases initially and decreases after it reaches the specific value with the increase of n [Fe2+ ]/ n [Ni2+ ] molar ratio, current density, bath temperature and pH. However, the relationship between L-ascorbic acid concentration and B S keeps linear. It is observed that the coercive force( Hc) is enhanced with the increase of n [Fe2+ ]/ n [Ni2+ ] molar ratio, current density and pH. By comparison, when the bath temperature increases, Hc always decreases. With the increase of L-ascorbic acid concentration, the coercive force increases initially and then decreases.  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