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   4160篇
  免费   302篇
  国内免费   195篇
电工技术   50篇
综合类   420篇
化学工业   1357篇
金属工艺   366篇
机械仪表   225篇
建筑科学   685篇
矿业工程   67篇
能源动力   68篇
轻工业   184篇
水利工程   54篇
石油天然气   160篇
武器工业   43篇
无线电   161篇
一般工业技术   584篇
冶金工业   91篇
原子能技术   18篇
自动化技术   124篇
  2024年   23篇
  2023年   68篇
  2022年   118篇
  2021年   129篇
  2020年   129篇
  2019年   113篇
  2018年   105篇
  2017年   115篇
  2016年   184篇
  2015年   169篇
  2014年   173篇
  2013年   377篇
  2012年   247篇
  2011年   269篇
  2010年   184篇
  2009年   197篇
  2008年   172篇
  2007年   269篇
  2006年   255篇
  2005年   207篇
  2004年   172篇
  2003年   148篇
  2002年   111篇
  2001年   110篇
  2000年   96篇
  1999年   88篇
  1998年   84篇
  1997年   49篇
  1996年   36篇
  1995年   46篇
  1994年   33篇
  1993年   38篇
  1992年   22篇
  1991年   31篇
  1990年   17篇
  1989年   25篇
  1988年   14篇
  1987年   5篇
  1986年   3篇
  1985年   3篇
  1984年   5篇
  1983年   6篇
  1982年   7篇
  1980年   3篇
  1974年   1篇
  1951年   1篇
排序方式: 共有4657条查询结果,搜索用时 15 毫秒
31.
本文对含CaO陶瓷结合剂的强度影响机理进行了进一步的研究。研究结果表明,含CaO结合剂的强度与结合剂的网络结构参数Y有关。CaO作为网络改变体对网络结构的破坏作用可能是使含CaO陶瓷结合剂强度降低的一个主要原因。  相似文献   
32.
The irreversibly bound interfacial layer deposited by the γ-aminopropysilanetriol adhesion promoter onto a crystalline silicon substrate, which remains even after profuse washing, was found by XPS to have resulted from the fragmentation and rearrangement of the original γ-aminopropylsilanetriol molecule. A mechanism is proposed, involving the homolytic scission of the terminal N-C bond. One of the subsequent reactions is believed to involve hydrogen loss by abstraction and the formation of a terminal vinyl group, which bonds to the substrate. Support for this mechanism is found in IR spectroscopy of this layer.  相似文献   
33.
An alternative test method to the traditional 180° “T” peel test has been developed for the measurement of interlaminar bonding in three-ply (polyester/aluminium/polypropylene) flexible-packaging, laminate materials. The new test is thought to involve mixed mode I (opening) and mode II (shearing) failure, and takes into account the yielding of the polypropylene layer during testing. The method allows more direct comparisons between materials to be made, and allows the measurement of strong bonds, where a peel test would result in yield or fracture of the substrate arms before debonding.  相似文献   
34.
In this article we describe our recent efforts in the area of palladium- and nickel-catalysed aromatic substitution reactions. Main focus is on low cost and low waste production methods. The use of aromatic carboxylic anhydrides in the Heck reaction leads to a waste-free protocol. In addition these reactions are easy to work up as no ligands or bases are used. For Heck reactions where substrates or products do not tolerate high temperatures we found that use of a bulky phosphoramidite (13b) as ligand for palladium leads to a very fast reaction at low temperatures. Recycle of palladium in ligand-free Heck and Suzuki reactions is easily accomplished by treating the palladium black that precipitates at the end of the reaction on a carrier material with a small excess of I2 prior to its re-use in the next run. Use of aryl chlorides in the palladium- and nickel-catalysed formation of biaryls can be accomplished by using the nickel-catalysed coupling with arylzinc chlorides. Better still, it was possible to make use of the arylgrignard and use a catalytic amount of ZnCl2. Whereas the strength of these aromatic substitution reactions lies in their broad tolerance of functional groups, one exception was the Sonogashira reaction on 3-bromoaniline. The problem was solved by making use of in situ catalytic protection of the NH2 group with benzaldehyde.  相似文献   
35.
For the flexural reinforcement of bridge and building structure, synthetic materials whose dynamic properties are superior and those containing the merit of corrosion‐proof are widely used as the substitute for a steel plate. Since FRP plate has improved bond strength owing to the fibers externally adhering to the plate, many researches regarding the bond strength improvement have been substantially performed. To search out such bond strength improvement, previous researchers had ever examined the bond strength of FRP plate through their experiment by setting up many variables. However, since the experiment for a research on the bond strength takes much of expenditure for setting up the equipment and is time‐consuming, also is difficult to be carried out, it is limitedly conducted. The purpose of this study was to develop the most suitable artificial neural network model by application of various neural network models and algorithm to the data of the bond strength experiment conducted by previous researchers. Many variables were used as input layers against bond strength: depth, width, modulus of elasticity, tensile strength of FRP plate and the compressive strength, tensile strength, and width of concrete. The developed artificial neural network model has been applied back‐propagation, and its error was learned to be converged within the range of 0.001. Besides, the process for the over‐fitting problem has been dissolved by Bayesian technique. The verification on the developed model was executed by comparison with the test results of bond strength made by other previous researchers, which was never been utilized to the learning as yet. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 5119–5127, 2006  相似文献   
36.
李望 《涂料工业》2005,35(9):36-38
以己二异氰酸酯(HDI)改性聚酯树脂与氨基树脂配制成家电用卷材涂料。阐述了氨酯键对涂膜性能的贡献。探讨了HDI用量对涂膜性能的影响。  相似文献   
37.
研究了热处理过程对聚对苯二甲酰对苯二胺(PPTA)结构与性能的影响。通过对PPTA纤维升温红外光谱分析可以看出:在较低的热处理温度下,随着温度的升高,发现在3 300 cm~(-1)处—NH—伸缩振动峰向高波数方向移动,峰型变宽,吸收峰强度减弱。采用傅里叶变换红外光谱仪和单丝强度仪、比浓对数黏度等研究发现:经热拉伸处理后的PPTA纤维内部分子间氢键作用力增加,自由氢键数减少,游离的—NH_2含量却增加,纤维比浓对数黏度和强度降低,说明纤维的拉伸强度是由分子间作用力以及分子链段的长度共同作用的。  相似文献   
38.
以四氢呋喃为溶剂 ,合成了含Sn、Fe的环戊烯基二羰基铁的异核双金属化合物 ,并对配合物进行了元素分析、IR光谱分析 ,使用SimensP4单晶衍射仪测定了配合物的晶体结构。结构分析表明 ,该配合物属于三斜晶系 ,空间群P - 1。晶胞参数 :a =10 0 79(2 )A° ,b =10 975 0 (10 )A°,c =17 14 5 (3)A° ;a =82 0 30 (10 )° ,β =77 770 (10 )°,γ =6 3 70 0 (10 )° ,Z =2  相似文献   
39.
为提高超高分子质量聚乙烯(UHMWPE)纤维复合材料中纤维与树脂基体之间的界面黏结强度,提出通过不同质量分数的硅烷偶联剂KH-570处理纳米SiO_2对UHMWPE纤维进行表面改性。对改性处理后的纤维与乙烯基酯树脂进行黏结强度试验,发现硅烷偶联剂处理纳米SiO_2能有效提高纤维的界面黏结强度,同时使纤维保持一定的断裂强度。  相似文献   
40.
对高炉主出铁沟用Al2O3-SiC-C质浇注料的结合相变化进行了分析,其中涉及到溶胶结合、氮化硅铁为添加物形成的sialon结合、水泥形成的水硬性结合。溶胶结合强度主要来自于化学结合;而sialon结合、水泥结合的强度仍然来自少量水泥形成的水硬性凝固相的作用,因此对烘烤工艺、使用效果的影响不同。  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