全文获取类型
收费全文 | 515404篇 |
免费 | 7465篇 |
国内免费 | 1793篇 |
专业分类
电工技术 | 9852篇 |
综合类 | 526篇 |
化学工业 | 78699篇 |
金属工艺 | 17982篇 |
机械仪表 | 15075篇 |
建筑科学 | 14795篇 |
矿业工程 | 1174篇 |
能源动力 | 13706篇 |
轻工业 | 54750篇 |
水利工程 | 4060篇 |
石油天然气 | 2270篇 |
武器工业 | 17篇 |
无线电 | 68006篇 |
一般工业技术 | 95066篇 |
冶金工业 | 93354篇 |
原子能技术 | 7028篇 |
自动化技术 | 48302篇 |
出版年
2021年 | 3212篇 |
2019年 | 3035篇 |
2018年 | 4561篇 |
2017年 | 4650篇 |
2016年 | 4997篇 |
2015年 | 4133篇 |
2014年 | 6911篇 |
2013年 | 23852篇 |
2012年 | 12215篇 |
2011年 | 17673篇 |
2010年 | 13641篇 |
2009年 | 15636篇 |
2008年 | 16902篇 |
2007年 | 17353篇 |
2006年 | 15566篇 |
2005年 | 14556篇 |
2004年 | 14145篇 |
2003年 | 13809篇 |
2002年 | 13430篇 |
2001年 | 13632篇 |
2000年 | 12611篇 |
1999年 | 13150篇 |
1998年 | 28780篇 |
1997年 | 21302篇 |
1996年 | 16978篇 |
1995年 | 13449篇 |
1994年 | 12040篇 |
1993年 | 11490篇 |
1992年 | 8958篇 |
1991年 | 8502篇 |
1990年 | 8113篇 |
1989年 | 7860篇 |
1988年 | 7501篇 |
1987年 | 6414篇 |
1986年 | 6320篇 |
1985年 | 7712篇 |
1984年 | 7143篇 |
1983年 | 6371篇 |
1982年 | 5995篇 |
1981年 | 5878篇 |
1980年 | 5513篇 |
1979年 | 5394篇 |
1978年 | 5024篇 |
1977年 | 6118篇 |
1976年 | 8044篇 |
1975年 | 4260篇 |
1974年 | 4033篇 |
1973年 | 3941篇 |
1972年 | 3177篇 |
1971年 | 2792篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The Interplay of Modulus,Strength, and Ductility in Adhesive Design Using Biomimetic Polymer Chemistry 下载免费PDF全文
High‐performance adhesives require mechanical properties tuned to demands of the surroundings. A mismatch in stiffness between substrate and adhesive leads to stress concentrations and fracture when the bonding is subjected to mechanical load. Balancing material strength versus ductility, as well as considering the relationship between adhesive modulus and substrate modulus, creates stronger joints. However, a detailed understanding of how these properties interplay is lacking. Here, a biomimetic terpolymer is altered systematically to identify regions of optimal bonding. Mechanical properties of these terpolymers are tailored by controlling the amount of a methyl methacrylate stiff monomer versus a similar monomer containing flexible poly(ethylene glycol) chains. Dopamine methacrylamide, the cross‐linking monomer, is a catechol moiety analogous to 3,4‐dihydroxyphenylalanine, a key component in the adhesive proteins of marine mussels. Bulk adhesion of this family of terpolymers is tested on metal and plastic substrates. Incorporating higher amounts of poly(ethylene glycol) into the terpolymer introduces flexibility and ductility. By taking a systematic approach to polymer design, the region in which material strength and ductility are balanced in relation to the substrate modulus is found, thereby yielding the most robust joints. 相似文献
22.
23.
24.
25.
26.
27.
28.
Thin Film Thermoelectric Metal–Organic Framework with High Seebeck Coefficient and Low Thermal Conductivity 下载免费PDF全文
29.
30.
Quantitative UPLC‐MS/MS analysis of chlorogenic acid derivatives in antioxidant fractionates from dandelion (Taraxacum officinale) root 下载免费PDF全文
Owen Kenny Thomas J. Smyth Chandralal M. Hewage Nigel P. Brunton 《International Journal of Food Science & Technology》2015,50(3):766-773
While qualitative studies have identified chlorogenic acids in antioxidant extracts, particularly ethyl acetate‐derived extracts, of Taraxacum officinale, quantitative analysis of these phenolic compounds remains largely unreported for this species. In this study, bioactivity‐guided fractionation of an antioxidant crude ethyl acetate extract (DPPH = 295.481 ± 0.955 mg TE g?1 extract) from T. officinale root resulted in a number of reverse‐phase fractions that demonstrated high antioxidant activity (DPPH = 1058.733–1312.136 mg TE g?1 extract), stronger than that of the synthetic antioxidant Trolox®. UPLC‐MS/MS screening of these fractions for the presence of selected mono‐ and di‐caffeoylquinic acids revealed large quantities of 1,5‐dicaffeoylquinic acid present in several fractions (853.052–907.324 μg mg?1), respectively. Due to the antioxidant potency and high levels of 1,5‐dicaffeoylquinic acid observed in these fractions, it was concluded that specifically this chlorogenic acid derivative is a major contributor to the antioxidant efficacy of dandelion root. 相似文献