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   4102篇
  免费   172篇
  国内免费   173篇
电工技术   36篇
综合类   220篇
化学工业   2001篇
金属工艺   606篇
机械仪表   57篇
建筑科学   57篇
矿业工程   29篇
能源动力   28篇
轻工业   405篇
水利工程   16篇
石油天然气   85篇
武器工业   16篇
无线电   73篇
一般工业技术   509篇
冶金工业   237篇
原子能技术   44篇
自动化技术   28篇
  2024年   17篇
  2023年   51篇
  2022年   69篇
  2021年   89篇
  2020年   92篇
  2019年   95篇
  2018年   69篇
  2017年   111篇
  2016年   97篇
  2015年   118篇
  2014年   155篇
  2013年   211篇
  2012年   228篇
  2011年   246篇
  2010年   180篇
  2009年   198篇
  2008年   174篇
  2007年   266篇
  2006年   272篇
  2005年   238篇
  2004年   222篇
  2003年   261篇
  2002年   200篇
  2001年   159篇
  2000年   122篇
  1999年   126篇
  1998年   72篇
  1997年   59篇
  1996年   46篇
  1995年   33篇
  1994年   39篇
  1993年   36篇
  1992年   24篇
  1991年   24篇
  1990年   9篇
  1989年   9篇
  1988年   5篇
  1987年   2篇
  1985年   8篇
  1984年   6篇
  1983年   1篇
  1982年   4篇
  1981年   1篇
  1978年   1篇
  1973年   1篇
  1959年   1篇
排序方式: 共有4447条查询结果,搜索用时 0 毫秒
1.
Copolyesters containing poly(ethylene terephthalate) and poly(hexamethylene terephthalate) (PHT) were prepared by a melt condensation reaction. The copolymers were characterised by infrared spectroscopy and intrinsic viscosity measurements. The density of the copolyesters decreased with increasing percentage of PHT segments in the backbone. Glass transition temperatures (Tg). melting points (Tm) and crystallisation temperatures (Tc) were determined by differential scanning calorimetry. An increase in the percentage of PHT resulted in decrease in Tg, Tm and Tc. The as-prepared copolyesters were crystalline in nature and no exotherm indicative of cold crystallisation was observed. The relative thermal stability of the polymers was evaluated by dynamic thermogravimetry in a nitrogen atmosphere. An increase in percentage of PHT resulted in a decrease in initial decomposition temperature. The rate of crystallisation of the copolymers was studied by small angle light scattering. An increase in percentage of PHT resulted in an increase in the rate of crystallisation.  相似文献   
2.
服装粘合衬布的生产需要低密度聚乙烯热熔胶的微细粉末,介绍了对该热熔胶的化学粉碎技术所进行的实验研究,表明采用适当的助剂种类和用量以及适宜的工艺过程,通过化学粉碎可以得到合格的粉末产品。  相似文献   
3.
In this study, an aluminum based metallic matrix (Al-2wt.% Cu) was reinforced with SiC particulates using a conventional casting technique and a new disintegrated melt deposition technique. Microstructural characterization studies conducted on the samples taken from disintegrated melt deposition technique revealed a more uniform distribution of SiC particulates and good interfacial integrity between SiC particulates and metallic matrix when compared to the conventionally cast composite samples. Results of ambient temperature mechanical tests demonstrate an increase in 0.2% YS and ultimate tensile strength of samples taken from disintegrated melt deposition technique when compared with the unreinforced and conventionally cast composite samples. The results of microstructural characterization and mechanical testing were finally rationalized in terms of the nature of processing technique employed to reinforce Al-2wt.% Cu metallic matrix with SiC particulates.  相似文献   
4.
Poly(ethylene aspartate) [PEA] was synthesized by the melt condensation of D,L-aspartic acid and ethylene glycol. PEA containing pendent amino and carbonyl groups in its repeating chain was used as the polymeric ligand for complexation with transition metal ions, viz. Co(II), Ni(II), Cu(II), Mn(II), Zn(II), Cd(II), Ca(II), Mg(II), Pb(II) and Hg(II). Complexation was found to be most effective in DMSO. The resulting polyester-metal complexes were solid coloured materials which have been characterized by IR spectroscopy, elemental analysis and magnetic susceptibility measurements. The thermal stability of the polyester-metal complexes was investigated by thermogravimetric analysis (TGA). On the basis of the physico-chemical studies, an oxygen and nitrogen coordinated structure for the polyester-metal complexes is proposed.  相似文献   
5.
Melt index is considered an important quality variable determining product specifications. Reliable prediction of melt index (MI) is crucial in quality control of practical propylene polymerization processes. In this paper a least squares support vector machines (LS‐SVM) soft‐sensor model of propylene polymerization process is developed to infer the MI of polypropylene from other process variables. Considering the use of a SSE cost function without regularization might lead to less robust estimates; the weighted least squares support vector machines (weighted LS‐SVM) approach of propylene polymerization process is further proposed to obtain a robust estimation of melt index. The performance of standard SVM model is taken as a basis of comparison. A detailed comparison research among the standard SVM, LS‐SVM, and weighted LS‐SVM models is carried out. The research results confirm the effectiveness of the presented methods. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 285–289, 2006  相似文献   
6.
提出了一种新的铝液夹杂物快速检测方法。导出了该法的检测原理方程。分析并试验研究了影响检测重复性和分辨率的因素。试验选择了较好的检测参数,并获得了较好的检测结果。  相似文献   
7.
分析了通信线缆用 YH- 4热熔胶组成原料的性能和作用 ,找出影响耐环境高温性能的主要原因 ,并对新研制出的耐环境高温性能 YH- 5热熔胶作了一些分析和探讨 .  相似文献   
8.
Hans R. Kricheldorf  Volker D  ring 《Polymer》1992,33(24):5321-5327
The homopolyester of 4-(4′-hydroxyphenoxy)benzoic acid (poly(4-HPBA)), was prepared under two different reaction conditions and compared with a sample provided by another research group. Depending on the synthetic route, different melting points, d.s.c. traces and crystal lattices were found. However, after repeated heating and cooling, one thermodynamically stable modification with a melting point of 370–375°C can be obtained. Copolyesters of 4-hydroxybenzoic acid and 4-(4′-hydroxyphenoxy)benzoic acid were prepared with various molar ratios either in the melt (condensation in bulk) or in solution. These copolyesters were characterized by elemental analyses, 1H n.m.r. spectroscopy, d.s.c. measurements, wide-angle X-ray scattering measurements at various temperatures, and optical microscopy. Whereas copolyesters prepared in solution do not melt below 500°C, those prepared by polycondensation in bulk show melting points down to approximately 260°C and form a nematic melt.  相似文献   
9.
单螺杆挤出机—熔体泵串联挤出系统的性能与应用   总被引:3,自引:0,他引:3  
李庆春  董磊 《中国塑料》2003,17(6):91-95
从原理与应用方面,分析、探讨了单螺杆挤出机-熔体泵串联挤出系统的优异性能以及在塑料挤出成型领域的高效应用。  相似文献   
10.
阐述了用AutoLisp程序模拟塑料熔体在2层复合膜机头内的流动情况,并介绍了复合膜机头的内部结构。  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