全文获取类型
收费全文 | 117087篇 |
免费 | 3569篇 |
国内免费 | 1748篇 |
专业分类
电工技术 | 2515篇 |
技术理论 | 2篇 |
综合类 | 4470篇 |
化学工业 | 17395篇 |
金属工艺 | 6746篇 |
机械仪表 | 4948篇 |
建筑科学 | 4709篇 |
矿业工程 | 1585篇 |
能源动力 | 1953篇 |
轻工业 | 5481篇 |
水利工程 | 1782篇 |
石油天然气 | 2890篇 |
武器工业 | 230篇 |
无线电 | 13147篇 |
一般工业技术 | 20247篇 |
冶金工业 | 4157篇 |
原子能技术 | 685篇 |
自动化技术 | 29462篇 |
出版年
2024年 | 164篇 |
2023年 | 578篇 |
2022年 | 977篇 |
2021年 | 1397篇 |
2020年 | 1061篇 |
2019年 | 887篇 |
2018年 | 15305篇 |
2017年 | 14404篇 |
2016年 | 10813篇 |
2015年 | 1855篇 |
2014年 | 1838篇 |
2013年 | 2195篇 |
2012年 | 5200篇 |
2011年 | 11652篇 |
2010年 | 10173篇 |
2009年 | 7291篇 |
2008年 | 8460篇 |
2007年 | 9357篇 |
2006年 | 1905篇 |
2005年 | 2819篇 |
2004年 | 2214篇 |
2003年 | 2092篇 |
2002年 | 1393篇 |
2001年 | 843篇 |
2000年 | 1043篇 |
1999年 | 1067篇 |
1998年 | 837篇 |
1997年 | 733篇 |
1996年 | 730篇 |
1995年 | 570篇 |
1994年 | 471篇 |
1993年 | 352篇 |
1992年 | 274篇 |
1991年 | 216篇 |
1990年 | 146篇 |
1989年 | 128篇 |
1988年 | 123篇 |
1987年 | 68篇 |
1986年 | 50篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
聚乙二醇-三聚氰胺甲醛和聚乙烯醇半互穿网络的构建及表征 总被引:1,自引:0,他引:1
为提高三聚氰胺甲醛(MF)树脂制品的柔韧性,以聚乙二醇接枝三聚氰胺(M-PEG)替代部分三聚氰胺,并与甲醛、聚乙烯醇(PVA)在碱性条件下合成了聚乙二醇-三聚氰胺甲醛(PEG-MF)与PVA的半互穿聚合物网络体系(SemiIPN)。采用红外光谱、拉曼光谱、热重分析、差示扫描量热法等手段对Semi-IPN的微观结构进行了剖析,并分析了PEG、PVA等柔性链段对Semi-IPN黏度、游离甲醛含量、柔韧性等性能的影响。结果表明,PVA作为线型结构贯穿于聚乙二醇-三聚氰胺甲醛树脂交联网络体系结构中,形成了半互穿网络结构;所形成的Semi-IPN的热分解温度比MF树脂降低了60℃左右;Semi-IPN的韧性比纯MF树脂提高了800%,最高可达到19.700kJ/m2。 相似文献
2.
3.
4.
Mobile software applications have to cope with a particular environment that involves small size, limited resources, high autonomy requirements, competitive business models and many other challenges. To provide development guidelines that respond to these needs, several practices have been introduced; however, it is not clear how these guidelines may contribute to solve the issues present in the mobile domain. Furthermore, the rapid evolution of the mobile ecosystem challenges many of the premises upon which the proposed practices were designed. In this paper, we present a survey of the literature on software assurance practices for mobile applications, with the objective of describing them and assessing their contribution and success. We identified, organized and reviewed a body of research that spans in three levels: software development processes, software product assurance practices, and software implementation practices. By carrying out this literature survey, we reviewed the different approaches that researchers on Software Engineering have provided to address the needs that raise in the mobile software development arena. Moreover, we review the evolution of these practices, identifying how the constant changes and modernization of the mobile execution environment has impacted the methods proposed in the literature. Finally, we introduced discussion on the application of these practices in a real productive setting, opening an area for further research that may determine if practitioners have followed the proposed assurance paradigms. 相似文献
5.
6.
7.
Variations of Incomplete Open Cubes is the major project by the twentieth-century conceptual artist Sol LeWitt. In this paper we interpret the enumerative component of the project as embeddings of graphs. This formulation permits use of an algorithm to check the completeness of the list of the structures produced by the artist. Our conclusion is that the artist found the correct number of structures (that is, 122), but that his list contains a mistake in the presentation of a pair of incomplete cubes, a discovery that appears not to have been noted before. 相似文献
8.
9.
为了实现对微小环片零件的自动化装配,搭建了自动装配系统.通过4根直线导向轴与4个直线轴承来提高系统的导向精度和刚度.采用直线导轨进行各装配作业模块之间的切换,保证了微小环片零件的自动装配与取出.在环片的装配方向上,螺旋升降机和光栅尺实现环片的位置精度控制.在Lab VIEW编程环境中,采用分层软件架构和模块化控制思想,避免了不必要的数据循环检测与丢失,能够达到环片组件的装配精度要求.控制系统分为系统初始化模块、参数设置模块、装配模块和取出模块,自动装配系统通过各个模块间的相互交流配合完成装配任务.采用本文中自动装配系统装配环片的实验结果表明,环片零件装配的最大位置误差为26μm,垂直度误差为17μm,平均装配时间为75 s/片,可满足环片组件所需的精度要求. 相似文献
10.
Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted
calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical
composition (CaO)0.75(La203)0.20(Fe2O3)6 was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO3)2 and (NH4)2HPO4 maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX
and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite
particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies
by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give
clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse
to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites
could be useful for hyperthermia. 相似文献