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   873篇
  免费   61篇
  国内免费   28篇
电工技术   56篇
综合类   54篇
化学工业   163篇
金属工艺   10篇
机械仪表   29篇
建筑科学   14篇
矿业工程   5篇
能源动力   8篇
轻工业   35篇
水利工程   5篇
石油天然气   7篇
武器工业   12篇
无线电   234篇
一般工业技术   47篇
原子能技术   11篇
自动化技术   272篇
  2024年   3篇
  2023年   4篇
  2022年   6篇
  2021年   17篇
  2020年   11篇
  2019年   13篇
  2018年   6篇
  2017年   15篇
  2016年   19篇
  2015年   27篇
  2014年   47篇
  2013年   49篇
  2012年   67篇
  2011年   73篇
  2010年   60篇
  2009年   56篇
  2008年   68篇
  2007年   76篇
  2006年   67篇
  2005年   63篇
  2004年   40篇
  2003年   55篇
  2002年   36篇
  2001年   23篇
  2000年   12篇
  1999年   13篇
  1998年   10篇
  1997年   6篇
  1996年   6篇
  1995年   4篇
  1994年   2篇
  1993年   2篇
  1992年   3篇
  1989年   1篇
  1984年   1篇
  1983年   1篇
排序方式: 共有962条查询结果,搜索用时 0 毫秒
1.
为了满足高帧频、大面阵CCD相机数字视频实时存储要求,设计出基于SCSI协议处理器-FAS466,脱离计算机平台的图像数据直接存储系统。利用VerilogHDL语言对FPGA芯片编程实现外部微处理器及DMA控制器功能,从而协调SCSI协议处理器实现数据的存储。本文着重介绍了利用FPGA芯片设计DMA控制器。由于FPGA芯片的内部速度很高,因此与单独使用微处理器芯片及DMA控制器芯片相比,不仅使得系统设计更加灵活,传输性能更好及反应时间更快,而且减小了存储设备的体积。  相似文献   
2.
The controlled hydrolysis of organosilanes has been shown to greatly influence both the surface adsorption of silanes on alumina powder, and the resultant dispersion stability of alumina in organic solvent slurries. Plateau adsorption concentrations from settling experiments show that complete surface coverage for hydrolyzed forms of both n-octyltrimethoxysilane (NOS) and N-2-aminoethyl-3-aminopropyltrimethoxysilane (AAPS) is typically achieved at concentrations of approximately 6 μmol/m2. Moreover, the settling densities of dispersions prepared with hydrolyzed silanes are consistently higher than densities achieved with monomeric silanes alone (as seen in case studies involving NOS in toluene, and AAPS in isopropyl alcohol). Similarly, ceramic slips prepared with polystyrene and alumina, or with poly(isobutyl methacrylate) and alumina also lead to ceramic green bodies with increased densities when the slips are prepared with hydrolyzed silanes. In addition, solid state NMR and dynamic mechanical analyses of resultant green bodies reveal that the molecular motional behavior of these polymers is strongly influenced by the presence of hydrolyzed silanes. These results collectively add to a growing body of evidence which supports the idea that not only is hydrolysis required for silanes to produce controllable and predictable effects in many industrial processes, but hydrolysis must be made to occur at the 'right time' within any sequence of steps that define an industrial process. In the case of ceramic slurries, the 'right time' is the period just prior to the mixing of the ceramic slip ingredients.  相似文献   
3.
为解决中国聚变工程实验堆316L不锈钢焊缝超声波检测时,探头扫查空间受限、检测信噪比低的难题,提出了基于双晶面阵探头的相控阵超声检测方案.通过CIVA仿真,分析了不同聚焦参数下DMA探头的声场特征,确定对接接头的检测工艺.参考NB/T47013.3-2015《承压设备无损检测第3部分:超声检测》附录I,设计并制作了对比试块,验证了检测工艺下的声束覆盖和φ2 mm侧横孔信噪比.结果表明,DMA探头可以在有限的扫查空间内实现焊缝声束全覆盖,对比试块中不同位置的φ2 mm侧横孔信噪比大于15 dB.试验结果可为316L类不锈钢对接焊缝相控阵超声检测工艺制定提供参考.  相似文献   
4.
三维算量软件现状及发展方向研究   总被引:3,自引:0,他引:3  
介绍了三维算量软件的现状,展望未来工程量计算软件的发展趋势,指出三维算量软件在应用中面临的问题和解决方法,并提倡行业软件走自主版权研发之路,将创新和技术领先作为民族软件品牌的根本.  相似文献   
5.
In this study,the permeabilities of Berea and Otway sandstones were measured under different confining pressures,and porosity was investigated through mercury intrusion porosimetry(MIP).The total porosities of the Berea and Otway sandstones were approximately 17.4%and 25%,respectively.Pore size distributions of each sandstone were almost the same,but the pores in the Otway sandstone were slightly narrower.However,the permeability of the Otway sandstone was smaller than that of the Berea sandstone by one order of magnitude.Three-dimensional(3D)void geometry and geometrical properties of the void spaces relevant to flow were compared to obtain the relation between the permeability differences and porosities of the two sandstones.The 3D geometrical analysis using microfocus X-ray computed tomography(CT)was performed,and the pore geometries of both sandstones were compared using the 3D medial axis(3DMA)method.Pore and throat radii,pore coordination number,tortuosity,number of connecting paths,connecting path volume,and other factors were determined using 3DMA.The Otway sandstone was characterized by a small effective throat/pore radius ratio.Based on the fluid flow mechanism,the lower effective throat/pore radius ratio results in a lower permeability induced by the fluid energy loss,which means that the 3D geometrical shape of void spaces affects the permeability value.  相似文献   
6.
胡昕 《化学建材》2005,21(2):39-41
采用热重分析和动态热机械分析方法研究了改性自粘沥青对三元乙丙防水片材热老化的影响。实验表明, 复合有改性自粘沥青层的三元乙丙片材热老化后,有机物含量明显增加,玻璃化转变温度明显提高而高弹态下的贮能模量明显下降。这表明老化后增塑剂和沥青质大量迁移到三元乙丙片材中,对材料的老化性能有不利的影响。  相似文献   
7.
Octa(aminophenyl)-T8-polyhedral silsesquioxane, 1, can serve as a cross-linking agent for organic polymeric resins. Amino functional groups of 1 can form chemical bonds or hydrogen-bonds to appropriate matrix polymers or resins. Various resole phenolic resin/1 nanocomposites (0, 1, 3, 6, and 12 wt% 1) were prepared. Hydrogen bonding between phenolic hydroxyls and the amino groups of 1 in these nanocomposites were investigated by FT-IR. The aggregation morphologies of 1 within these samples were examined using SEM, TEM, and Wide Angle X-ray Diffraction (WAXD) studies. Small quasispherical nanometer-sized POSS particles which were further aggregated into clusters, like individual grapes in a bunch, formed into phase-separated domains as large as 400 nm in diameter as the loading of 1 increased. These particles exhibited a broad 2θ = 5.8° WAXD peak indicating the presence of some crystalline order within the nanoparticles of 1 making up the aggregates. This corresponds to an average crystalline plane lattice distance of 17.5 Å. However, extraction of the finely powdered nanocomposites by refluxing THF failed to remove 1 indicating the vast majority of 1 must be chemically bound. Thus, the aggregates must have resin within their structure. The storage modulus (E') in both the glassy and rubbery regions, thermal stability, and glass transition temperature of the composites were improved by 1 wt% 1. However, at high loadings of 1, these properties gradually decreased. Surface extractions by THF removed only a portion of the 1 in the surface regions based on X-EDS analyses for Si, suggesting that a portion of 1 might chemically bond into the phenolic resin matrix during the cure. As the loading of 1 increased, the content of 1 at specific surface locations gradually tends to increase and confirmed excellent dispersion of 1 in the micron size-scale at all locations.  相似文献   
8.
Polyamide‐6/clay nanocomposites were prepared employing melt bending or compounding technique followed by injection molding using different organically modified clays. X‐ray diffraction and transmission electron microscopy were used to determine the molecular dispersion of the modified clays within the matrix polymer. Mechanical tests revealed an increase in tensile and flexural properties of the matrix polymer with the increase in clay loading from 0 to 5%. C30B/polyamide‐6 nanocomposites exhibited optimum mechanical performance at 5% clay loading. Storage modulus of polyamide‐6 also increased in the nanocomposites, indicating an increase in the stiffness of the matrix polymer with the addition of nanoclays. Furthermore, water absorption studies confirmed comparatively lesser tendency of water uptake in these nanocomposites. HDT of the virgin matrix increased substantially with the addition of organically modified clays. DSC measurements revealed both γ and α transitions in the matrix polymer as well as in the nanocomposites. The crystallization temperature (Tc) exhibited an increase in case of C30B/polyamide‐6 nanocomposites. Thermal stability of virgin polyamide‐6 and the nanocomposites has been investigated employing thermogravimetric analysis. POLYM. COMPOS., 28:153–162, 2007. © 2007 Society of Plastics Engineers  相似文献   
9.
Available literature reports wide variation of glass–rubber transition temperature (Tg) of polyaniline (PAni). The present study determines the Tg of doped PAni using different techniques such as differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), temperature dependent DC conductivity, and dilatometry, and it is found to vary between 30 and 40 °C. Apart from measurement techniques the Tg of PAni is found to depend on the water and dopant present in it. The Tg of PAni is again determined through molecular dynamic (MD) simulation technique and found to be in agreement with the experimentally obtained results.  相似文献   
10.
Polypropylene (PP) was modified utilizing two types of polyesteramide‐based hyperbranched polymers (amphiphilic PS and hydrophilic PH). A maleicanhydride‐modified PP (PM) was used as a reactive dispersing agent to enhance the modification by grafting the hyperbranched polymers onto the PP chains. Pure PP, two different non‐reactively modified samples, i.e. excluding PM, and two different reactively modified samples, i.e. including PM, were studied. Investigating the morphology of the samples was performed by scanning electron microscopy. To follow the effect of the modification on the dynamic mechanical properties, dynamic mechanical analysis experiments both in the melt (rheometric mechanical spectrometry) and in solid state (dynamic mechanical thermal analysis) were carried out. In the next step, the nanocrystalline structure of the samples was studied by small angle X‐ray scattering (SAXS) in two different modes, i.e. static and recrystallization. Hundreds of SAXS patterns were analyzed automatically using procedures written in PV‐WAVE image‐processing software. The chord distribution function (CDF) was calculated and the long period (lp) of the crystal lamellae was extracted from the CDFs. The rheometric mechanical spectrometry results show that both hyperbranched polymers decrease complex viscosity η* and enhance liquid‐like behavior. This happens more significantly when PM is included. The dynamic mechanical thermal analysis results reveal that Tg decreases when PS and PH are added. In the reactively modified samples this reduction is compensated most probably because of the crosslinked structure formed through the grafting reaction between the hyperbranched polymers and PM. Such structure is confirmed by SAXS data and calculated CDFs in the recrystallization mode. Static SAXS data also show enhancement in the crosshatched morphology of the crystalline lamellae of PP for reactively modified samples compared with non‐reactively modified samples. © 2013 Society of Chemical Industry  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