全文获取类型
收费全文 | 5583篇 |
免费 | 604篇 |
国内免费 | 375篇 |
专业分类
电工技术 | 86篇 |
综合类 | 281篇 |
化学工业 | 1457篇 |
金属工艺 | 1187篇 |
机械仪表 | 300篇 |
建筑科学 | 485篇 |
矿业工程 | 63篇 |
能源动力 | 50篇 |
轻工业 | 137篇 |
水利工程 | 47篇 |
石油天然气 | 83篇 |
武器工业 | 66篇 |
无线电 | 878篇 |
一般工业技术 | 1014篇 |
冶金工业 | 251篇 |
原子能技术 | 18篇 |
自动化技术 | 159篇 |
出版年
2024年 | 21篇 |
2023年 | 114篇 |
2022年 | 173篇 |
2021年 | 204篇 |
2020年 | 180篇 |
2019年 | 190篇 |
2018年 | 152篇 |
2017年 | 211篇 |
2016年 | 212篇 |
2015年 | 185篇 |
2014年 | 282篇 |
2013年 | 416篇 |
2012年 | 315篇 |
2011年 | 359篇 |
2010年 | 295篇 |
2009年 | 329篇 |
2008年 | 282篇 |
2007年 | 412篇 |
2006年 | 395篇 |
2005年 | 285篇 |
2004年 | 265篇 |
2003年 | 198篇 |
2002年 | 172篇 |
2001年 | 157篇 |
2000年 | 137篇 |
1999年 | 111篇 |
1998年 | 76篇 |
1997年 | 64篇 |
1996年 | 75篇 |
1995年 | 59篇 |
1994年 | 42篇 |
1993年 | 35篇 |
1992年 | 30篇 |
1991年 | 33篇 |
1990年 | 16篇 |
1989年 | 23篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有6562条查询结果,搜索用时 16 毫秒
151.
152.
Self-association (i.e. interchain aggregation) behavior of atactic poly(ethacrylic acid) PEA in dilute aqueous solution as function of degree-of-neutralization by Na+ counter-ions (i.e. charge fraction f) was investigated by molecular dynamics simulations. Aggregation is found to occur in the range 0 ≤ f ≤0.7 in agreement with experimental results compared at specified polymer concentration Cp = 0.36 mol/l in dilute solution. The macromolecular solution was characterized and analysed for radius-of-gyration, torsion angle distribution, inter and intra-molecular hydrogen bonds, radial distribution functions of intermolecular and inter-atomic pairs, inter-chain contacts and solvation enthalpy. The PEA chains form aggregate through attractive inter-chain interaction via hydrogen bonding, in the range f < 0.7, in agreement with experimental observation. The numbers of inter-chain contacts decreases with f. A critical structural transition occurs at f = 0.7, observed via simulations for the first time, in Rg as well as inter-chain H-bonds. The inter-chain distance increases with f due to repulsive interactions between COO− groups on the chains. PEA-PEA electrostatic interactions dominant solvation enthalpy. The PEA solvation enthalpy becomes increasingly favorable with increase in f. The transition enthalpy change, in going from uncharged (acid) state to fully charged state (f = 1) is unfavorable towards aggregate formation. 相似文献
153.
154.
155.
Thermal conductivity measurements on the vapors of methanol, ethanol, isopropanol, and t-butanol are reported as a function of temperature (330–420 K) and pressure (11–240 kPa). The thermal conductivity versus pressure isotherms for all four alcohols exhibit upward curvatures at the lower temperatures and nearly linear increases at higher temperatures. This behavior is indicative of a dimeric species and one or more polymeric clusters in the vapor in addition to the monomer. Quantum mechanical calculations have indicated that tetramers are the most likely polymeric species. Detailed analyses of the data provide thermodynamic data (H,S) for the dimerization and tetramerization reactions and show interesting correlations with the size of the monomer unit. 相似文献
156.
157.
针对水库重力式大坝加高加固问题进行试验研究,对后帮式、前帮式、外包式以及戴帽式加高方式建立实验模型评价新旧混凝土结合面的粘结性能。抗折强度试验和微观电镜试验结果表明,四种类型的加高方式,外包式的结合面最大,抗折强度最高,粘结性能最强。采用水泥砂浆处理后增多了结合面的纤维状C-S-H凝胶,增强了新旧混凝土之间的粘结性能,合理的加固方式加上结合面处理有利于提高坝体的安全性能。 相似文献
158.
159.
为了研究多层膜的腐蚀性能,促进多层膜在生产中的应用,采用电弧离子镀技术,通过调整环境N2和Ar气的时间比例在铜衬底上成功制备了不同调制周期的Ti/TiN多层膜.利用x 射线衍射谱和交流阻抗谱研究了该多层膜的结构和腐蚀性能.表面形貌显示,沉积的Ti/TiN多层膜具有明显的周期性,环境中N2和Ar气的时间比例决定了多层膜的调制周期,N2气时间越长,多层膜中TiN相层越厚.腐蚀性能测定表明,多层膜的调制周期影响其耐蚀性,当调制周期为550nm时,沉积膜的耐腐蚀性最好. 相似文献
160.
《Behaviour & Information Technology》2012,31(8):760-781
ABSTRACTA majority of senior Internet users maintains persistent social connections with others through social media (SM), such as Facebook and Twitter. This research explores the impacts of helping, self-expression, and enjoyment on bonding social capital and bridging social capital which in turn influence SM involvement; it also explores the moderating effect of avoidance attachment among senior SM users. The results show that helping, self-expression, and enjoyment have significant impacts on bonding social capital and bridging social capital. Also, bonding social capital and bridging social capital have significant effects on SM involvement. Furthermore, relationships between helping and bonding social capital, between self-expression and bonding social capital, and between self-expression and bridging social capital are stronger for seniors with high avoidance attachment. Conversely, the relationships between enjoyment and bonding social capital as well as between enjoyment and bridging social capital are stronger for seniors with low avoidance attachment. Accordingly, the results of this study provide theoretical contributions to the literature of behaviour and information technology. In addition, some implications of the research and various strategies for practitioners and marketers that can be used to better increase users’ involvement in SM for tourism-related activities are discussed. 相似文献