全文获取类型
收费全文 | 25101篇 |
免费 | 4116篇 |
国内免费 | 2885篇 |
专业分类
化学 | 14242篇 |
晶体学 | 240篇 |
力学 | 950篇 |
综合类 | 145篇 |
数学 | 1831篇 |
物理学 | 6902篇 |
无线电 | 7792篇 |
出版年
2024年 | 109篇 |
2023年 | 530篇 |
2022年 | 712篇 |
2021年 | 948篇 |
2020年 | 936篇 |
2019年 | 976篇 |
2018年 | 866篇 |
2017年 | 767篇 |
2016年 | 1134篇 |
2015年 | 1195篇 |
2014年 | 1423篇 |
2013年 | 1823篇 |
2012年 | 2065篇 |
2011年 | 2057篇 |
2010年 | 1537篇 |
2009年 | 1587篇 |
2008年 | 1761篇 |
2007年 | 1588篇 |
2006年 | 1419篇 |
2005年 | 1265篇 |
2004年 | 1016篇 |
2003年 | 998篇 |
2002年 | 1098篇 |
2001年 | 813篇 |
2000年 | 595篇 |
1999年 | 536篇 |
1998年 | 377篇 |
1997年 | 311篇 |
1996年 | 273篇 |
1995年 | 249篇 |
1994年 | 195篇 |
1993年 | 170篇 |
1992年 | 147篇 |
1991年 | 137篇 |
1990年 | 89篇 |
1989年 | 60篇 |
1988年 | 58篇 |
1987年 | 40篇 |
1986年 | 44篇 |
1985年 | 44篇 |
1984年 | 27篇 |
1983年 | 18篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1975年 | 10篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1971年 | 5篇 |
1936年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Nanocomposite hydrogel consisting of Na‐montmorillonite with enhanced mechanical properties 下载免费PDF全文
Ting Li Shuangfei Xiang Piming Ma Huiyu Bai Weifu Dong Mingqing Chen 《Journal of Polymer Science.Polymer Physics》2015,53(14):1020-1026
A new kind of nanocomposite (NC) hydrogel with Na‐montmorillonite (MMT) is presented in this article. The NC hydrogels were synthesized by free radical copolymerization of acrylamide and (3‐acrylamidopropyl) trimethylammonium chloride (ATC) in the presence of MMT and N,N′‐methylene‐bis‐acrylamide used as chemical cross‐linker. Due to the cation‐exchange reaction between MMT and ATC (cationic monomer) during the synthesis of NC hydrogels, MMT platelets were considered chemical “plane” cross‐linkers, different from “point” cross‐linkers. With increasing amount of MMT, the crosslinking degree enhanced, causing a decrease of the swelling degree at equilibrium. Investigations of mechanical properties indicated that NC hydrogels exhibited enhanced strength and toughness, which resulted from chemical interaction between exfoliated MMT platelets and polymer chains in hydrogels. Dynamic shear measurements showed that both storage modulus and loss modulus increased with increasing MMT content. The idea described here provided a new route to prepare hydrogels with high mechanical properties by using alternative natural Na‐MMT. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1020–1026 相似文献
2.
3.
4.
棋盘格图像在摄像机标定中有非常广泛的应用,对于复杂环境且测量精度要求非常高的场合,会需要特定的且有一定复杂度的算法,但通常情况下,使用这样的标定系统是没有必要的,且会让初次应用的人觉得困难。这里提供一套应用简单,快速,对棋盘格图像具有旋转不变性,良好的鲁棒性,且对非复杂环境具有高精度的标定系统。所有算法均是在前辈们的算法上稍作改变而来,应用效果非常好。 相似文献
5.
Sung Hwan Koo Dong Jun Li Taeyeong Yun Dong Sung Choi Kyung Eun Lee Gil Yong Lee Youngtak Oh Joonwon Lim Suchithra Padmajan Sasikala Ho Jin Lee In Ho Kim Hong Ju Jung Rishabh Jain Sang Ouk Kim 《Particle & Particle Systems Characterization》2019,36(7)
Efficient water electrolysis catalyst is highly demanded for the production of hydrogen as a sustainable energy fuel. It is reported that cobalt derived nanoparticle (CoS2, CoP, CoS|P) decorated reduced graphene oxide (rGO) composite aerogel catalysts for highly active and reliable hydrogen evolution reaction electrocatalysts. 7 nm level cobalt derived nanoparticles are synthesized over graphene aerogel surfaces with excellent surface coverage and maximal expose of active sites. CoS|P/rGO hybrid aerogel composites show an excellent catalytic activity with overpotential of ≈169 mV at a current density of ≈10 mA cm?2. Accordingly, efficient charge transfer is attained with Tafel slope of ≈52 mV dec?1 and a charge transfer resistance (Rct) of ≈12 Ω. This work suggests a viable route toward ultrasmall, uniform nanoparticles decorated graphene surfaces with well‐controlled chemical compositions, which can be generally useful for various applications commonly requiring large exposure of active surface area as well as robust interparticle charger transfer. 相似文献
6.
Facile fabrication of fast recyclable and multiple self‐healing epoxy materials through diels‐alder adduct cross‐linker 下载免费PDF全文
Xiao Kuang Guoming Liu Xia Dong Xianggui Liu Jianjun Xu Dujin Wang 《Journal of polymer science. Part A, Polymer chemistry》2015,53(18):2094-2103
A reversibly cross‐linked epoxy resin with efficient reprocessing and intrinsic self‐healing was prepared from a diamine Diels‐Alder (DA) adduct cross‐linker and a commercial epoxy oligomer. The newly synthesized diamine cross‐linker, comprising a DA adduct of furan and maleimide moieties, can cure epoxy monomer/oligomer with thermal reversibility. The reversible transition between cross‐linked state and linear architecture endows the cured epoxy with rapid recyclability and repeated healability. The reversibly cross‐linked epoxy fundamentally behaves as typical thermosets at ambient conditions yet can be fast reprocessed at elevated temperature like thermoplastics. As a potential reversible adhesive, the epoxy polymer with adhesive strength values about 3 MPa showed full recovery after repeated fracture‐thermal healing processes. The methodology explored in this contribution provides new insights in modification of conventional engineering plastics as functional materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2094–2103 相似文献
7.
8.
9.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents. 相似文献
10.