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   23319篇
  免费   3316篇
  国内免费   1048篇
电工技术   208篇
技术理论   2篇
综合类   1495篇
化学工业   8409篇
金属工艺   425篇
机械仪表   363篇
建筑科学   1844篇
矿业工程   444篇
能源动力   621篇
轻工业   3118篇
水利工程   519篇
石油天然气   1468篇
武器工业   317篇
无线电   3160篇
一般工业技术   4107篇
冶金工业   752篇
原子能技术   99篇
自动化技术   332篇
  2024年   138篇
  2023年   689篇
  2022年   642篇
  2021年   1005篇
  2020年   1097篇
  2019年   1025篇
  2018年   873篇
  2017年   1021篇
  2016年   1065篇
  2015年   967篇
  2014年   1516篇
  2013年   1533篇
  2012年   1718篇
  2011年   1706篇
  2010年   1284篇
  2009年   1308篇
  2008年   1068篇
  2007年   1415篇
  2006年   1356篇
  2005年   1102篇
  2004年   877篇
  2003年   771篇
  2002年   577篇
  2001年   530篇
  2000年   450篇
  1999年   355篇
  1998年   246篇
  1997年   217篇
  1996年   184篇
  1995年   164篇
  1994年   145篇
  1993年   107篇
  1992年   86篇
  1991年   72篇
  1990年   50篇
  1989年   44篇
  1988年   32篇
  1987年   50篇
  1986年   28篇
  1985年   48篇
  1984年   34篇
  1983年   23篇
  1982年   19篇
  1981年   4篇
  1980年   10篇
  1979年   5篇
  1976年   2篇
  1974年   2篇
  1964年   2篇
  1951年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A Ti/Si complex zeolite has been prepared. X-ray diffraction and infrared spectrometry study has shown that two structures, namely the ZSM-5 and MCM-41, exist in the sample. BET tests have revealed that the complex zeolite contains regular mesopores of 2.6 nm. Ultraviolet spectrometry analysis has shown that the Ti species exist in the zeolite skeleton in the form of tetra-coordinate valence. The Ti/Si complex zeolite (TS-1/Ti-MCM-41) has apparently improved catalytic activity with respect to the macromolecular organic compound oxidation as compared to individual components of either Ti or Si containing zeolites (TS-1 and Ti-MCM-41).  相似文献   
62.
63.
海洋钻井液有机物添加剂生物降解性评价   总被引:1,自引:0,他引:1  
随着海洋石油的勘探开发,钻井液有机添加剂不可避免地进入海洋.因此在海洋勘探开发过程中应选择环保性能好,即生物降解性能好的有机物添加剂。用累计耗氧量法测定了海洋钻井液有机添加剂的生物降解性,研究评价了有机添加剂的生物降解规律和机理,探讨了有机物生物降解性同其化学结构的内在联系,为海洋勘探开发过程中选择环保性能好的有机物添加剂提供理论依据。总结实验结果发现:淀粉类(如DFD-140和FI-E1等)最容易生物降解;其次是纤维素类(如MV-CMC等)和烯类单体聚合物(如PAM和PHP);而沥青类、两性离子类则难以生物降解,有的甚至对生物降解起抑制作用。  相似文献   
64.
简要介绍了全板电镀镍金加工过程中镀金面发白现象及改善措施。特别是针对高位发白(或粗糙)的产生原因和处理过程进行较为详细的描述,并对工艺在此处理过程中存在问题进行了简要剖析。  相似文献   
65.
By using Ni0‐mediated polymerization, we have systematically synthesized a series of fluorene‐based copolymers composed of blue‐, green‐, and red‐light‐emitting comonomers with a view to producing polymers with white‐light emission. 2,7‐Dibromo‐9,9‐dihexylfluorene, {4‐(2‐[2,5‐dibromo‐4‐{2‐(4‐diphenylamino‐phenyl)‐vinyl}‐phenyl]‐vinyl)‐phenyl}‐diphenylamine (DTPA), and 2‐{2‐(2‐[4‐{bis(4‐bromo‐phenyl)amino}‐phenyl]‐vinyl)‐6‐tert‐butyl‐pyran‐4‐ylidene}‐malononitrile (TPDCM) were used as the blue‐, green‐, and red‐light‐emitting comonomers, respectively. It was found that the emission spectra of the resulting copolymers could easily be tuned by varying their DTPA and TPDCM content. Thus with the appropriate red/green/blue (RGB) unit ratio, we were able to obtain white‐light emission from these copolymers. A white‐light‐emitting diode using the polyfluorene copolymer containing 3 % green‐emitting DTPA and 2 % red‐emitting TPDCM (PG3R2) with a structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonic acid)/PG3R2/Ca/Al was found to exhibit a maximum brightness of 820 cd m–2 at 11 V with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33,0.35), which are close to the standard CIE coordinates for white‐light emission (0.33,0.33).  相似文献   
66.
We describe the preparation of a dendrimer that is solution‐processible and contains 2‐ethylhexyloxy surface groups, biphenyl‐based dendrons, and a fac‐tris[2‐(2,4‐difluorophenyl)pyridyl]iridium(III ) core. The homoleptic complex is highly luminescent and the color of emission is similar to the heteroleptic iridium(III ) complex, bis[2‐(2,4‐difluorophenyl)pyridyl]picolinate iridium(III ) (FIrpic). To avoid the change in emission color that would arise from attaching a conjugated dendron to the ligand, the conjugation between the dendron and the ligand is decoupled by separating them with an ethane linkage. Bilayer devices containing a light‐emitting layer comprised of a 30 wt.‐% blend of the dendrimer in 1,3‐bis(N‐carbazolyl)benzene (mCP) and a 1,3,5‐tris(2‐N‐phenylbenzimidazolyl)benzene electron‐transport layer have external quantum and power efficiencies, respectively, of 10.4 % and 11 lm W–1 at 100 cd m–2 and 6.4 V. These efficiencies are higher than those reported for more complex device structures prepared via evaporation that contain FIrpic blended with mCP as the emitting layer, showing the advantage of using a dendritic structure to control processing and intermolecular interactions. The external quantum efficiency of 10.4 % corresponds to the maximum achievable efficiency based on the photoluminescence quantum yield of the emissive film and the standard out‐coupling of light from the device.  相似文献   
67.
In this work, we co‐formulated an oil‐borne copper naphthenate/permethrin wood preservative system with synthetic polymer‐based fire‐retardant additives prior to the impregnation of Pinus radiata sapwood. We evaluated what effect, if any, the preservative had upon the fire performance properties of the fire retardants and whether the fire retardants impacted on the fungicidal and termiticidal efficacy of the preservative. The fire retardants included halogenated and phosphorus‐based systems. A mass loss calorimeter, in conjunction with a thermopile, was used to measure the time to ignition and the peak heat release rate (PHRR) from which the fire performance index (FPI) was determined. The preservative properties were evaluated using termite and soil‐block decay bioassays. In summary, we found that the rate of fire growth was reduced when the fire retardants were used in combination with the wood preservative. We also found that the PHRR was a better determinant of fire performance than the FPI. The performance of the wood preservative was enhanced against fungal decay and termite attack when used in combination with the fire retardants. The fire retardants also demonstrated some wood preservative properties of their own. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
68.
铜硅取代的酞青材料LB膜气敏传感器的研究   总被引:2,自引:0,他引:2  
李岚  许琳 《功能材料》1998,29(2):188-191
采用LB膜技术对沉积在石英晶振的铜硅取代的酞青材料的气体敏感性进行了系统研究,结果表明,该方法所获得的敏感膜敏感度高,反应迅速,稳定性较好。  相似文献   
69.
A waterborne paint was applied to tin plated steel sheets with three different film thicknesses. The emission of volatile and semivolaile organic compounds ((S) VOCs) from the samples was measured in small climatic chambers under standard conditions over a two-week period. The purpose of the study was to evaluate the effect of the film thickness on the emission rate decay. First order decay models, including sink effects for the high boiling (S) VOCs, were fitted to the concentration versus time data. The results showed that the first order rate constants decrease with increasing film thickness. In uddition, the results indicated that the emissions of the (S)VOCs in the waterborne paint film seemed to be controlled by evaporation. The thicknesses of paint films used in climatic chamber tests to estimate emission rates for product compurison or emission prediction must be known in order to prevent erroneous conclusions  相似文献   
70.
The procedure of nebulization was studied with the introduction of ethanol into a lower power argon ICE It was found that as ethanol introduced, the physical properties of solutions changed, which results in an improvement on the nebulization efficiency. An empirical relationship between the concentration of the aerosol and the solution properties ( viscosity, density, and surface tension) is presented.  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