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   102419篇
  免费   13893篇
  国内免费   9662篇
电工技术   15335篇
技术理论   20篇
综合类   12353篇
化学工业   3509篇
金属工艺   1869篇
机械仪表   4922篇
建筑科学   5152篇
矿业工程   2573篇
能源动力   2102篇
轻工业   1470篇
水利工程   2135篇
石油天然气   1781篇
武器工业   972篇
无线电   20187篇
一般工业技术   4292篇
冶金工业   4354篇
原子能技术   254篇
自动化技术   42694篇
  2024年   722篇
  2023年   2104篇
  2022年   4059篇
  2021年   4515篇
  2020年   4537篇
  2019年   3264篇
  2018年   2740篇
  2017年   3225篇
  2016年   3392篇
  2015年   3934篇
  2014年   6764篇
  2013年   6060篇
  2012年   7623篇
  2011年   8046篇
  2010年   6312篇
  2009年   6640篇
  2008年   6870篇
  2007年   7624篇
  2006年   6456篇
  2005年   5764篇
  2004年   4816篇
  2003年   4300篇
  2002年   3359篇
  2001年   2870篇
  2000年   2196篇
  1999年   1793篇
  1998年   1257篇
  1997年   1020篇
  1996年   820篇
  1995年   622篇
  1994年   477篇
  1993年   326篇
  1992年   211篇
  1991年   136篇
  1990年   124篇
  1989年   109篇
  1988年   80篇
  1987年   47篇
  1986年   47篇
  1985年   50篇
  1984年   35篇
  1983年   33篇
  1982年   40篇
  1964年   56篇
  1963年   46篇
  1961年   43篇
  1959年   34篇
  1957年   33篇
  1955年   46篇
  1954年   28篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
介绍季戊四醇的超分子化学,包括超分子网状结构、螺环冠醚、非常规液晶、富勒烯衍生物、固相光催化反应、Janus树枝状分子等等。  相似文献   
992.
张娟  瞿金平 《中国塑料》2002,16(6):23-26
假设聚合物熔体的缠结网络形变是非仿射的,运用瞬态网络结构原理,采用在本课题第一部分^[1]中所建立的动态速率方程,并对上随体Maxwell本构方程加以修正来建立一个非仿射网络结构模型,利用这一模型来研究振动剪切作用下LDPE熔体的流变行为,研究表明,随着应变振幅和频率的增加,LDPE熔体的剪切应力也增加,同时指出了非仿射网络结构模型的精确变比仿射结构模型有较大提高,这表明在振动力场作用下,网络形变发生了非仿射形变,因此在建立振动力场作用下聚烯烃熔体本构方程时,不能假设其网络是仿射形变的。  相似文献   
993.
三峡库区已完成了百万移民的搬迁安置,进入了移民安稳致富的新阶段,库区社会和谐稳定对促进库区经济社会健康发展和实现全面建成小康社会的目标具有重要作用。本研究重点关注和谐库区建设思路及评价指标体系构建:一方面,从理论层面,重点论述与库区和谐社会相关的理论认识成果;另一方面,从实际管理运用层面,构建了库区和谐评价指标体系,可为移民动态管理提供有力的技术支撑。  相似文献   
994.
以N,N-二甲基苯胺,1%(按IPN质量计,下同)过氧化二苯甲酰和二丁基二月桂酸锡(简称有机锡)为固化剂,活性二氧化硅为填充剂(用量为总质量的30%),由47%的甲基丙烯酸甲酯与蓖麻油,2,4-甲苯二异氰酸酯型聚氨酯组成的IPN为基材,在25-30℃下经8-12h固化。固化材料的体积电阻率和表面电阻率可达10^13数量级,介电常数为5.5-6.0,介电损耗角正切为0.018-0.020,拉伸强度为  相似文献   
995.
It is well known that a so-called “three-dimensional filler network structure” will be constructed in the polymer/layered silicate nanocomposites when the content of layered clay reaches a threshold value, at which the silicate sheets are incapable of freely rotating, due to physical jamming and connecting of the nanodispersed layered silicate. In this article, the effect of such clay network on the mobility and relaxation of macromolecular chains in isotactic polypropylene(iPP)/organoclay nanocomposites was investigated in detail with a combination of DMTA, DSC, TGA, TEM, rheometry and melt flow index measurements. The main aim is to establish a relationship between the mesoscopic filler network structure and the macroscopic properties of the polymer nanocomposites, particularly to explore the role of the clay network on the mobility and relaxation of macromolecular chains. It was found that the nanodispersed clay tactoids and layers play less important or dominant roles on the mobility of iPP chains depending on the formation of percolating filler network. The turning point of macroscopic properties appeared at 1 wt% organoclay content. Before this point, the effect of organoclay can be negligible, and the increase of chain mobility was ascribed to the decrease of molecular weight of polymer chains, as commonly occurs during dynamic melt processing; after this point, however, a reduced mobility of chains and a retarded chain relaxation were observed and attributed to the formation of a mesoscopic filler network. The essential features of such a mesoscopic organoclay network were estimated and discussed on the basis of stress relaxation and structural reversion measurements. A schematic model was proposed to describe the different relaxation and motion behaviors of macromolecular chains in the unfilled polymer and the filled hybrids with partial and percolated organoclay networks, respectively.  相似文献   
996.
蔡冬梅 《上海涂料》2004,42(5):14-16
研制的环氧-聚氨酯互穿网络(IPN)防腐蚀涂料具有优异的防腐蚀性能和附着力。介绍了该涂料的制法。列举了IPN涂层的性能指标。讨论了影响涂层性能的各种因素。  相似文献   
997.
Social media are often argued to change political communication, decreasing the distance between politicians and citizens, and increasing citizens' influence on policymaking. This paper presents findings from a study of how the Norwegian Labour Party uses social media, focusing on the community platform MyLabourParty. Interviews with politicians and a survey with citizens as respondents were conducted to examine the experiences of online political discussions. Findings show that citizens and politicians expect MyLabourParty to strengthen citizen participation. Yet, citizens still experience communication asymmetry and politicians may find it challenging to participate to the extent citizens expect. Means for bridging the gap between expectations and experiences are called for, in particular redefinition of the offering, changes of user‐practices, and system improvements.  相似文献   
998.
The present study examines the tele‐cocooning hypothesis in the context of general trust using a nationally representative survey of Japanese youth. We find that although frequency of texting is positively correlated with general trust, this correlation is spuriously caused by how heavy mobile texters interpret the words “most people” in the general trust measurement. Heavy users assume that “most people” only refers to friends, family, and others going to the same school. When the effect of the “most people” assumption is controlled, the positive association between texting and general trust disappears. Further exploration of the data shows that heavy texting nevertheless has negative implications for social tolerance and social caution, both of which are theoretically proximate to general trust.  相似文献   
999.
1000.
Revisiting the medical and social models of disability, this study adopted the integrated biopsychosocial approach to examine experiences of 25 mobility‐impaired respondents in Singapore with using mobile phones. We found that mobile phones provided respondents a greater degree of mobility, a sense of control, and opportunities to escape the stigma of disability, thus challenging the boundaries between the able‐bodied and the disabled. Mobile phone appropriation allowed the management of personal identities and social networks, leading to a sense of empowerment. However, mobile phone usage might act as a double‐edged sword for disabled people, creating mobile dependencies and a spatial narrowing of social connections. Theoretical and practical implications are discussed.  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