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   199908篇
  免费   21287篇
  国内免费   14630篇
电工技术   17244篇
技术理论   10篇
综合类   18741篇
化学工业   26702篇
金属工艺   13102篇
机械仪表   12900篇
建筑科学   15904篇
矿业工程   6994篇
能源动力   5475篇
轻工业   20133篇
水利工程   6307篇
石油天然气   7421篇
武器工业   2497篇
无线电   22283篇
一般工业技术   19425篇
冶金工业   8498篇
原子能技术   3073篇
自动化技术   29116篇
  2024年   1170篇
  2023年   3330篇
  2022年   7058篇
  2021年   9236篇
  2020年   6833篇
  2019年   5073篇
  2018年   5450篇
  2017年   6165篇
  2016年   5539篇
  2015年   8376篇
  2014年   10503篇
  2013年   12289篇
  2012年   15077篇
  2011年   16181篇
  2010年   14738篇
  2009年   14538篇
  2008年   14711篇
  2007年   14419篇
  2006年   12829篇
  2005年   10604篇
  2004年   7887篇
  2003年   5567篇
  2002年   5120篇
  2001年   4762篇
  2000年   4192篇
  1999年   2870篇
  1998年   1969篇
  1997年   1567篇
  1996年   1517篇
  1995年   1258篇
  1994年   1098篇
  1993年   813篇
  1992年   643篇
  1991年   474篇
  1990年   400篇
  1989年   390篇
  1988年   273篇
  1987年   190篇
  1986年   141篇
  1985年   96篇
  1984年   74篇
  1983年   51篇
  1982年   62篇
  1981年   44篇
  1980年   66篇
  1979年   47篇
  1976年   13篇
  1974年   11篇
  1959年   25篇
  1951年   25篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
高收率合成DADE的新方法   总被引:4,自引:3,他引:4  
在比较DADE的3条文献合成路线基础上,研究了以2-甲基-4,6-嘧啶二酮为母体用硝硫混酸硝化生成中间体2-(二硝基亚甲基)-5,5-二硝基-2H-嘧啶-4,6-二酮、中间体水解合成DADE的方法。DADE总收率达到83%以上,用IR、MS、NMR及元素分析鉴定了其结构。  相似文献   
992.
项目经理在项目管理中的职能和作用   总被引:1,自引:0,他引:1  
周江宁 《煤化工》2003,31(1):56-60
介绍了项目经理在工程项目管理中的法律地位和所起的重要作用。以总承包项目管理为基础 ,从国际型工程公司项目管理方式、重视与业主等各方的协调工作以及运用先进管理手段对项目各阶段实施综合控制等方面阐述了项目经理在工程项目管理中应注意的问题和应掌握的方法  相似文献   
993.
贺永德  王克文  周妮娜 《应用化工》2006,35(Z1):367-380
阐述了盐化工发展现状,主要包括盐化工产品的生产、消费情况和技术水平,并论述了盐化工发展前景及发展趋势.  相似文献   
994.
Butan‐1‐ol modified toluene diisocyanate tri mer (TDI‐trimer) was synthesized and characterized with Fourier transform infrared spectroscopy, gel permeation chromatography, and thermal gravimetry analysis techniques. The modified TDI‐trimer showed good dissolvable ability with hydroxy resin and can be used to produce paints with acrylic polyol resin. The thermal stability of the modified TDI‐trimer was improved by simply increasing both the amount of catalyst and the ratio of ? NCO/? OH, less depended on the kind of catalyst. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4958–4962, 2006  相似文献   
995.
陆雷  张乐军  赵莹  王浩 《中国陶瓷》2007,43(8):38-41,25
以钢渣和粉煤灰为主要原料,采用烧结工艺,制得以透辉石为主晶相的微晶玻璃;通过热分析、X射线衍射、收缩率、扫描电镜等分析方法,阐述了烧结过程中晶化和致密化的关系;详细说明了由于在微晶玻璃热处理过程中二者发生的先后顺序不同,而使微晶玻璃结构和性质不同。  相似文献   
996.
聚合物流变性能对共注射成型的影响   总被引:3,自引:0,他引:3  
在共注射成型多相分层流动充模成型机理的基础上,揭示了芯壳层熔体对共注射成型的分层界面形貌和芯层熔体前沿突破的影响,并模拟了芯壳层熔体粘度比对共注射成型的影响,建立了芯壳层熔体粘度与分层界面和前沿移动界面菜貌的关系。本文的模拟研究结果与一些文献的实验结果相吻合。  相似文献   
997.
Chun-Guey Wu  Ming-I Lu 《Polymer》2005,46(16):5929-5938
Highly conducting porous polymer electrolytes comprised of poly(vinylidene-fluoride-co-hexafluoropropylene) (PVdF-HFP), polyethylene oxide-co-polypropylene oxide-co-polyethylene oxide (P123), ethylene carbonate (EC), propylene carbonate (PC), and LiClO4 were fabricated. The PVdF-HFP/P123 hybrid polymer membranes were made with a phase inverse method and the electrolyte solution uptake was carried out in glove box to avoid the moisture contamination. It was found that when a small amount of polymer surfactant (P123) was blended into the PVdF-HFP, mesopores with well-defined sizes were formed. Impedance spectroscopy showed that the room temperature conductivity of (PVdF-HFP)/P123 polymer electrolytes increased as the content of P123 increased up to 4×10−3 S/cm. Nitrogen adsorption isotherms, electrolyte solution uptake, porosity measurements, and SEM micrographs showed that the enhanced conductivity was due to increase the pore volume, pore density, and electrolyte uptake. The highest conduction was found when the weight ratio of P123 to PVdF-HFP was 70%, when big channels were formed in the hybrid polymer membrane. Furthermore, blending P123 in PVDF-HFP reduced the pore size of polymer membrane, therefore, the solution leakage was also reduced. These polymer electrolytes were stable up to 4.5 V (vs Li/Li+) and the performance of the model lithium ion battery made by sandwiching the polymer electrolyte between a LiCoO2 anode and a MCMB cathode, showed great promise for the use of these polymer electrolytes in lithium ion batteries.  相似文献   
998.
The coupling efficiency of seven coupling agents in wood–polymer composites (WPC) was investigated in this study. The improvement on the interfacial bonding strength, flexural modulus, and other mechanical properties of the resultant wood fiber/high‐density polyethylene (HDPE) composites was mainly related to the coupling agent type, function groups, molecular weight, concentration, and chain structure. As a coupling agent, maleated polyethylene (MAPE) had a better performance in WPC than oxidized polyethylene (OPE) and pure polyethylene (PPE) because of its stronger interfacial bonding. A combination of the acid number, molecular weight, and concentration of coupling agents had a significant effect on the interfacial bonding in WPC. The coupling agents with a high molecular weight, moderate acid number, and low concentration level were preferred to improve interfacial adhesion in WPC. The backbone structure of coupling agents also affected the interfacial bonding strength. Compared with the untreated composites, modified composites improved the interfacial bonding strength by 140% on maximum and the flexural storage modulus by 29%. According to the statistical analysis, 226D and 100D were the best of the seven coupling agents. The coupling agent performance was illustrated with the brush, switch, and amorphous structures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 93–102, 2005  相似文献   
999.
In this study, a series of T300 carbon fiber‐reinforced polyimide (CFRPI) composites were prepared by laminating premolding polyimide (PI) films with unidirectional carbon fiber (CF) layers. On the basis of PI systems design, the effect of CF volume fraction, processing conditions, and PI molecular structure on the properties of CFRPI composites was studied in detail. In addition, two kinds of nano‐particles, including carbon nano‐tube (CNT) and SiO2 were filled into the premolding PI films with different concentrations. And the effect of nano‐particles on the properties of CFRPI composites was also investigated. The surface characteristic of T300 CF was measured by X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The properties of premolding PI film and CFRPI composites were measured by dynamic mechanical analysis (DMTA), SANS testing machine, scanning electron microscopy (SEM), and so forth. These experimental results showed that the properties of CFRPI composites were mainly affected by the premolding PI film and molding condition. The change of CF volume fraction from 55% to 65% took little effect on the mechanical properties of CFRPI composites. In addition, the incorporation of nano‐particle SiO2 could further improve the properties of CFRPI composites, but CNT hardly improved the properties of CFRPI composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 646–654, 2006  相似文献   
1000.
Vanadium doped La9.33Si6−xVxO26+0.5x (x = 0.5, 1.0, 1.5) (LSVO) electrolyte powder was prepared by combustion method at 600°C for 5-7 min. The powder was sintered at 1500°C for 3 hours to prepare LSVO ceramics. XPS, IR, XRD, and EIS analysis show that V5+ doping replaces Si4+ in [SiO4] to form [Si(V)O4] tetrahedron. With the increase in x, the lattice volume increase. When x = 2.0, the LaVO4 phase was formed, indicating that the limit doping amount of V5+ replacing Si4+ is x ≤ 1.5. The conductivity of LSVO increases significantly with the increase in x (x ≤ 1.0), which attributed to the defect reaction caused by V5+ doping. The addition of the interstitial oxygen Oi* in 63 channels and the increase of lattice volume leads to increased conductivity. When x = 1.0, the highest conductivity is 1.46 × 10−2 S·cm−1 (800°C). The doping enhancement conductivity mechanism is the Interstitial oxygen defect-Lattice volume composite enhancement mechanism.  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