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   15700篇
  免费   1251篇
  国内免费   625篇
电工技术   787篇
技术理论   1篇
综合类   1052篇
化学工业   2588篇
金属工艺   861篇
机械仪表   968篇
建筑科学   1488篇
矿业工程   472篇
能源动力   454篇
轻工业   885篇
水利工程   257篇
石油天然气   1007篇
武器工业   98篇
无线电   1830篇
一般工业技术   1963篇
冶金工业   757篇
原子能技术   178篇
自动化技术   1930篇
  2024年   62篇
  2023年   243篇
  2022年   431篇
  2021年   653篇
  2020年   489篇
  2019年   371篇
  2018年   422篇
  2017年   511篇
  2016年   415篇
  2015年   594篇
  2014年   717篇
  2013年   968篇
  2012年   931篇
  2011年   1000篇
  2010年   928篇
  2009年   831篇
  2008年   884篇
  2007年   795篇
  2006年   847篇
  2005年   760篇
  2004年   490篇
  2003年   458篇
  2002年   481篇
  2001年   403篇
  2000年   435篇
  1999年   457篇
  1998年   362篇
  1997年   299篇
  1996年   291篇
  1995年   243篇
  1994年   201篇
  1993年   124篇
  1992年   109篇
  1991年   111篇
  1990年   73篇
  1989年   63篇
  1988年   32篇
  1987年   27篇
  1986年   14篇
  1985年   11篇
  1984年   8篇
  1983年   12篇
  1982年   6篇
  1981年   4篇
  1980年   8篇
  1979年   1篇
  1978年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Organic–inorganic hybrid materials and mem branes were prepared through coating on Teflon plate or dip‐coating on microporous alumina substrates with the solution of glycidylmethacrylate (GMA) and γ‐methacryloxypropyl trimethoxy silane (γ‐MPS) copolymer, followed by ring‐opening of the GMA moiety with trimethylamine hydrochloric and sol–gel reaction of the γ‐MPS moiety. Composition of the GMA and γ‐MPS copolymer was varied by changing the feed ratio of GMA to γ‐MPS during the copolymerization. So the thermal stability, hydrophilicity, electrical properties, etc. of the hybrid materials and membranes were varied. Results showed that as the γ‐MPS amount increased in the copolymer, Td (the temperature on thermogram at 5% weight loss) value of the hybrid materials and water contact angle of the hybrid membrane generally increased, while the anion exchange capacity, water uptake (WR) and pure water flux decreased. The charge transition point of the hybrid membranes deduced from their streaming potential behavior decreased from pH > 12 to pH = 7–8 as the γ‐MPS amount increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3580–3589, 2006  相似文献   
102.
塑料挤出机主辅电机联动系统设计   总被引:1,自引:0,他引:1  
本文在分析国内外挤出机生产线主辅电机同步联调特点的基础上,提出了一种实用的联调控制系统设计方案,控制系统设计采用纯硬件方式,可以广泛适用于国内未采用同步联调技术的挤出生产线,进行技术改造,对原有设备改动极小,具有很高的性能/价格比。  相似文献   
103.
104.
以北京市妫水河为研究区,基于2011年9月25日和2012年9月30日的两期叶绿素a浓度实测数据和准同步的环境一号卫星(HJ-1A)多光谱数据,分别构建一元线性和多元支持向量机模型(SVMM),通过决定系数R2和平均相对误差对模型的精度进行检验,用模型进行水体叶绿素a浓度的反演,并分析其时空分布特征。研究表明:在样本数较少的情况下,SVM具有很强的非线性映射能力,能够取得较好的预测结果,更适用于反演叶绿素a浓度。时间分布上,研究区叶绿素a浓度呈增加趋势,均值上升了6.86 μg/L;空间分布上,深水区叶绿素a浓度值低于浅水区,上游高于下游。国产HJ-1A CCD2多光谱数据以其4 d的时间分辨率,在水质动态变化监测方面具有优势。  相似文献   
105.
电影的创作需要精湛的技术和创新性的思想作为基础,声音和动画更是其制作过程中不可缺少的重要组成部分。或悠扬或动感的音乐、或旋转或跳跃的动画的加入让影视作品更加充实完满,带给观看者关的享受。为方便影视多媒体的制作与传播,Micromedia公司以流程图标作为基本,研发了一套专门提供声音图标和数字视频图标、在交互式应用程序中仍可加栽多媒体信息,同时对播放使用参数不设置任何控制的交互式媒体编辑制作软件,即Authorware。本文就运用Authorware软件中控制电影图标的功能介绍,探究优秀影视作品制作背后的魅力与奇迹。  相似文献   
106.
随着现代化教学手段的不断发展,"微课"作为一种新的教学模式,在《计算机应用基础》课堂中的应用也越来越广泛。由于"微课"的特点与现代社会的发展节奏以及学生的认知特点等契合程度比较高,所以"微课"在高校教学中受到了广泛的欢迎。在本文中,我们试图通过对"微课"在高职《计算机应用基础》课程中的应用进行分析,以充分发掘"微课"在《高职计算机应用基础》课程教学中的优势作用。  相似文献   
107.
Magnetorheological (MR) elastomers, which are mainly composed of magnetic particles and elastic polymer, are a new kind of smart materials whose modulus can be controlled by changing the strength of magnetic fields. In this article, MR elastomers based on immiscible silicon rubber/polystyrene (SR/PS) blend matrix were fabricated successfully via cosolvent method and the MR effect, electric and mechanical properties, and the microstructures of the corresponding materials were studied. SEM studies showed that the dispersion of iron particles in blend matrix were different from that in single polymer, which could be further proved by the different electric conductivity. The MR effect of MR elastomers based on blend matrix varied with the different ratios of SR and PS, which was discussed in detail from the special dispersion of iron particles and of zero‐modulus of MR elastomers. In addition, the MR elastomers based on SR/PS blend matrix had enhanced mechanical properties, which made them more hopeful to be applied in practice. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3143–3149, 2007  相似文献   
108.
对中国石油吉林石化公司300 kt/a乙烯装置汽油加氢二段反应器接管与筒体焊接接头的缺陷进行详细分析。阐明了缺陷的产生是由于在焊接过程中焊缝熔合区内形成马氏体、增碳层并伴有δ-铁素体的分解而使熔合区内及焊缝处的材质脆化。由于选用焊接材料的错误,产生较高的焊接残余应力致使焊缝开裂。分析了焊缝马氏体、增碳层及δ-铁素体分解的原因。  相似文献   
109.
This paper presents the shear performance analysis of a heavy-duty universal hinged cast steel support with the largest bearing capacity. The effect of 9 parameters ( 52 specimens) ,i. e. height of the upper support,depth of the ring of the upper support,depth of the top plate of the bottom support,height of the ribs of the bottom support,depth of the ribs of the bottom support,bolt hole diameter,number of the ribs of the bowl,depth of the ribs of the bowl,and yield strength of the material,were analyzed with a 3-dimensional elastic-plastic finite element model in which the nonlinearities of geometry,material and contact were all considered. Analysis shows that height of the upper support,depth of the ring of the upper support and yield strength of the material have a great effect on the mechanical performance of the support. Height of the upper support has the largest effect on performance price ratio of the support,and the maximum effect can be up to 160% . Depth of the top plate of the bottom support,height of the ribs of the bottom support and depth of the ribs of the bottom support have a medium effect on performance price ratio of the support,and the effect is within the limit of 15% 19% .  相似文献   
110.
The structural evolution and optical characterization of hydrogenated silicon (Si:H) thin films obtained by conventional radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) through decomposition of silane diluted with argon were studied by X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), and ultraviolet and visible (UV-vis) spectroscopy, respectively. The influence of argon dilution on the optical properties of the thin films was also studied. It is found that argon as dilution gas plays a significant role in the growth of nano-crystal grains and amorphous network in Si:H thin films. The structural evolution of the thin films with different argon dilution ratios is observed and it is suggested that argon plasma leads to the nanocrystallization in the thin films during the deposition process. The nanocrystallization initiating at a relatively low dilution ratio is also observed. With the increase of argon portion in the mixed precursor gases, nano-crystal grains in the thin films evolve regularly. The structural evolution is explained by a proposed model based on the energy exchange between the argon plasma constituted with Ar* and Ar+ radicals and the growth regions of the thin films. It is observed that both the absorption of UV-vis light and the optical gap decrease with the increase of dilution ratio.  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