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   6551篇
  免费   704篇
  国内免费   263篇
电工技术   83篇
综合类   356篇
化学工业   3524篇
金属工艺   271篇
机械仪表   85篇
建筑科学   314篇
矿业工程   141篇
能源动力   152篇
轻工业   274篇
水利工程   51篇
石油天然气   275篇
武器工业   10篇
无线电   353篇
一般工业技术   1237篇
冶金工业   304篇
原子能技术   55篇
自动化技术   33篇
  2024年   14篇
  2023年   90篇
  2022年   164篇
  2021年   200篇
  2020年   215篇
  2019年   177篇
  2018年   205篇
  2017年   245篇
  2016年   239篇
  2015年   266篇
  2014年   403篇
  2013年   417篇
  2012年   487篇
  2011年   469篇
  2010年   348篇
  2009年   411篇
  2008年   341篇
  2007年   391篇
  2006年   365篇
  2005年   345篇
  2004年   278篇
  2003年   269篇
  2002年   235篇
  2001年   177篇
  2000年   144篇
  1999年   116篇
  1998年   78篇
  1997年   59篇
  1996年   59篇
  1995年   49篇
  1994年   40篇
  1993年   28篇
  1992年   40篇
  1991年   38篇
  1990年   44篇
  1989年   30篇
  1988年   3篇
  1987年   7篇
  1986年   5篇
  1985年   5篇
  1984年   5篇
  1983年   4篇
  1982年   3篇
  1980年   2篇
  1978年   1篇
  1977年   1篇
  1959年   2篇
  1951年   4篇
排序方式: 共有7518条查询结果,搜索用时 15 毫秒
91.
为了弄清鄂尔多斯盆地上三叠统延长组长7段和长9段泥页岩硅质来源与油气富集上的差异性,进行了主微量元素分析、全岩黏土X衍射、岩石热解、有机碳分析和扫描电镜观察研究。延长组泥页岩中长72亚段和长9段在硅质来源、矿物组成、元素组成和有机地化特征方面表现出更多相似之处,而长73亚段泥页岩与前面2套泥页岩则表现出一定的差异性。长72亚段和长9段泥页岩中的硅质主要来自于陆源碎屑物质,而长73亚段泥页岩硅质则表现出2种来源特征,即陆源碎屑来源和湖底热液喷流。延长组长7段和长9段泥页岩均是非常优质的烃源岩。但相比之下,受湖底热液作用的影响,长73亚段泥页岩残留烃和干酪根含量更高,干酪根类型也更好,页岩油饱和度指数更高。因此,长73亚段要优于长72亚段和长9段泥页岩,具有更高的开采价值。  相似文献   
92.
面对日益严峻的能源短缺和环境恶化问题,氢能作为绿色、高效且具有可持续性的柔性二次能源被广泛关注和研究。借鉴欧洲的电转气技术(power to gas),将可再生能源电解制成氢气后,以一定比例掺入到天然气管网中供给居民使用,被认为是改善城镇燃气质量与烟气排放的有效途径之一。因此,基于互换性理论分析了掺氢天然气作为家用燃气具燃料的掺氢比例,并基于12T基准天然气测试与验证了掺氢天然气在家用燃气具上燃烧的安全性能与排放性能。研究结果表明:①掺氢比例体积分数不应高于20%;②掺氢天然气在家用燃气具中燃烧的点火率、火焰稳定性与烟气排放性能全部合格,未发现安全性问题;③家用燃气具的烟气排放指标满足标准要求,并且随着氢气的体积分数增加,烟气中CO与NO_x排放量有所降低。  相似文献   
93.
This study addresses adsorption kinetics of silica nanoparticles on sandstone mineral surfaces and Enhanced oil recovery (EOR) by nanoparticles. It was shown that nanoparticle adsorption on quartz which is the major constituent of sandstone reservoirs was best described as second order process. Both rate and equilibrium adsorption increases with salinity. However, salinity reduces Intraparticle diffusion while enhancing film diffusion. Spontaneous imbibition with nanoparticles dispersed in low salinity water showed higher incremental recovery which may be due to increased structural disjoining pressure. This was supported by surface forces analysis based on particle size and zeta potential measurements of the nanofluids.  相似文献   
94.
利用自合成的碳硅凝胶为吸附材料,以铜试剂[二乙基二硫代氨基甲酸钠(NaDDTC)]为柱前衍生化试剂。在优化的实验条件下,于pH4.6的缓冲介质中在线预富集Al(Ⅲ),Cr(Ⅵ),Cu(Ⅱ),Fe(Ⅲ),Pb(Ⅱ),V(Ⅴ)和Zn(Ⅱ).采用停流技术洗脱,富集倍数可达8.1~12.6倍,检出限为ng/mL级。对高纯氧化铕(Eu2O3)中的非稀土杂质进行测定,可避免大量稀土基体对测定的干扰。  相似文献   
95.
无机热传导技术用于烟气余热再利用   总被引:1,自引:0,他引:1  
唐乐平  王晓明 《工业加热》2001,(5):25-26,30
无机热传导技术是以无机元素为导热介质,将其注入类金属或非金属管内,经密封形成导热元件。受热时间利用分子震荡、摩擦,将热能快速激发、传递。唐钢高速线材厂二车间就是将这种传热元件制成蒸汽发生器和煤气预热器,利用烟气二次余热产生蒸汽同时预热煤气,设备小巧,传热效率高。  相似文献   
96.
The effects of three types of fumed silica on the electrochemical properties of gelled electrolytes have been investigated by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), transmission electron microscope (TEM) and the Brunauer, Emmett and Teller (BET) technique. The CV and EIS results show that a moderate mechanical dispersion of fumed silica in the H2SO4 solution has important effects on the electrochemical properties of the gelled electrolyte. The optimal mechanical dispersion time is closely related to the operating temperature during preparation of gel, as well as the silica particle size and its distribution. A high stirring rate improves the electrode capacity and decreases the viscosity of the gelled electrolyte. With moderate mechanical dispersion, gelled electrolytes prepared from different fumed silica particles exhibit equal electrode capacities.  相似文献   
97.
The early stages of corrosion of AISI 314, HK 40, and Alloy 800H have been studied in a strongly carburizing (aC=0.8), weakly oxidizing atmosphere at 1098 K. Samples with electropolished and cold-worked surfaces were exposed for up to 400 min. at temperature, in a conventional corrosion rig or in a reaction vessel which was installed within an X-ray photoelectron spectrometer. The latter facility allowed the effects of the specimen heating rate and the rat of gas flow to be investigated. Examination of the corrosion products was accomplished with the aid of XPS, SEM, TEM, and conventional metallography. Initially, surface layers comprised of -Cr2O3, (Mn, Cr)3O4, and SiO2 formed, with layer structure, microstructure, and composition being functions of alloy composition and surface condition. Only on the cold-worked surfaces did a well-developed duplex oxide, consisting of an outer, Cr-rich oxide layer and an inner, SiO2 layer, form. In good agreement with the predicted value of 1.9 wt.%, between 1.4 and 2 wt.% Si in the alloy was required to form a complete SiO2 layer. After an incubation period, -Cr2O3 became unstable and transformed to M7C3; the carbides then grew by diffusion of metal from the alloy substrate. The presence of manganese, as (Mn, Cr)3O4, in the surface oxide influenced the mode of carbide growth, whereas the rate of carbide growth was severely suppressed by a continuous SiO2 layer which acted as a diffusion barrier both to metal and to carbon. It is argued that the SiO2 layer is most effective in reducing carburization when it is free from or contains very few structural defects.  相似文献   
98.
丁二酸改性电子墨水用球形SiO2颗粒的FTIR及XPS分析   总被引:2,自引:3,他引:2  
采用丁二酸对球状亚微米级SiO2颗粒进行表面改性,以提高SiO2颗粒于四氯乙烯溶剂中的电泳性能,制备适于电子墨水用的白色电泳颗粒。利用傅立叶红外光谱(FTIR)、X射线光电子谱(XPS)和Zeta电位粒度仪,研究了丁二酸改性SiO2颗粒的表面键合情况及其在四氯乙烯溶剂中的Zeta电位变化情况。研究发现,丁二酸仅有一端的羧基与SiO2颗粒表面的羟基发生酯化反应,而且当丁二酸的用量为3g(50mL乙腈中)时,接枝于SiO2颗粒表面的丁二酸的量达到最大值,此时C1s(O—CO)/Si(原子比)有最大值为5.77×10-2。Zeta电位测试结果表明,丁二酸改性后的SiO2颗粒在四氯乙烯中的Zeta电位比改性前的SiO2颗粒提高了约5.5倍。  相似文献   
99.
基于级联光纤的拉曼光纤放大器的研究   总被引:7,自引:0,他引:7  
文章利用光子转换理论给出了两种光纤的任意信道间隔、N信道单向受激拉曼散射(SRS)的稳态分析结果,提出了一种新型的具有平坦增益的宽带拉曼光纤放大器(FRA).对64信道的波分复用(WDM)系统进行了仿真,为FRA增益平坦化提供了一种新的实现方法.  相似文献   
100.
Mimicking the hierarchically anisotropic structure and excellent mechanical properties of natural tissues, such as tendons and ligaments, using biomaterials is challenging. Despite recent achievements with anisotropic hydrogels, limitations remain because of difficulties in achieving both structural and mechanical characteristics simultaneously. A simple approach for fabricating hybrid hydrogels with a hierarchically anisotropic structure and superior mechanical properties that are reminiscent of tendons or ligaments is proposed. Alginate–polyacrylamide double‐network (DN) hydrogels incorporated with high aspect ratio mesoporous silica microparticles are stretched and fixed via subsequent drying and ionic crosslinking to achieve multiscale structures composed of an anisotropically aligned polymer network embedded with aligned microparticles. The mechanical properties of hydrogels can be further controlled by the degree of stretching, quantities, and functional groups of inorganic microparticles, and types of crosslinking cations. The subsequent reswelling results in a high water content (>80%) similar to that of natural tendons while high strength, modulus, and toughness are maintained. The optimized anisotropic hybrid hydrogel exhibits a tensile modulus of 7.2 MPa, strength of 1.3 MPa, and toughness of 1.4 MJ m?3 even in the swollen state, which is 451‐, 27‐, and 2.2 times higher than that observed in the non‐swollen tough DN hydrogel. This study suggests a new strategy for fabricating anisotropic hydrogels with superior mechanical properties to develop new biomaterials for artificial tendons or ligaments.  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