全文获取类型
收费全文 | 10691篇 |
免费 | 1373篇 |
国内免费 | 189篇 |
专业分类
化学 | 1473篇 |
晶体学 | 11篇 |
力学 | 147篇 |
综合类 | 55篇 |
数学 | 1696篇 |
物理学 | 1816篇 |
无线电 | 7055篇 |
出版年
2024年 | 32篇 |
2023年 | 186篇 |
2022年 | 268篇 |
2021年 | 316篇 |
2020年 | 320篇 |
2019年 | 233篇 |
2018年 | 259篇 |
2017年 | 324篇 |
2016年 | 450篇 |
2015年 | 407篇 |
2014年 | 655篇 |
2013年 | 810篇 |
2012年 | 697篇 |
2011年 | 636篇 |
2010年 | 616篇 |
2009年 | 660篇 |
2008年 | 675篇 |
2007年 | 756篇 |
2006年 | 556篇 |
2005年 | 498篇 |
2004年 | 404篇 |
2003年 | 389篇 |
2002年 | 326篇 |
2001年 | 302篇 |
2000年 | 245篇 |
1999年 | 198篇 |
1998年 | 159篇 |
1997年 | 159篇 |
1996年 | 151篇 |
1995年 | 130篇 |
1994年 | 105篇 |
1993年 | 71篇 |
1992年 | 64篇 |
1991年 | 42篇 |
1990年 | 25篇 |
1989年 | 28篇 |
1988年 | 24篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 20篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Summary: A controlled fabrication of rod‐like nanostructures of cadmium sulfide (CdS) incorporated into polymer fiber matrices has been developed by an electrospinning method. Here, poly(vinyl pyrrolidone) (PVP) was used as a polymer capping reagent, utilizing the interactions of cadmium ions with the carbonyl groups in the PVP molecules. The formation of CdS nanorods inside the PVP was carried out via the reaction of Cd2+ with H2S. SEM images showed that the electrospun films of PVP/CdS are composed of fibers with a diameter between 100 and 900 nm. TEM proved that most of the CdS nanorods are incorporated in the PVP fibrous film. The diameter of the rod is about 50 nm and the length is from 100 to 300 nm.
92.
93.
Cross-linked epoxy matrices containing small amounts of semi-conductive phthalocyanine (Phthalcon) nanoparticles were prepared using different crosslinking agents and processing temperatures. A starting mixture containing an optimum dispersion of these nanoparticles and with an almost equal and large Hamaker constant was always used. Nevertheless large differences in the relation between the volume conductivity σv and the particle concentration φ were found and this relation appeared to be sensitive to small changes in processing temperature and the application of a post-cure. Also the amine crosslinker chosen and the initial amount of solvent (catalyst) in the starting dispersion had a major effect. It was shown that these changes influence strongly the formation of and the final conductive fractal particle network morphology through the polymer matrix. During processing a local relaxation of the initially formed fractal particle network into another fractal particle network was often observed, which introduced or enlarged the amount of isolating material between the particles of the conductive network and changed the fractality and structure of the conductive backbone of the particle network. This local relaxation lowered the σv at each phthalcon concentration and enlarged φc by several orders of magnitude. The occurrence of local relaxation is dependent on the rate of viscosity change during the crosslinking of the polymer matrix components, the way the fractal conductive particle network is formed during processing (universal or non-universal) and the amount of solvent present. Local relaxation may even occur after the gel point of the polymer matrix. A severe post-cure may be needed to stop this local relaxation. To our knowledge local relaxation of a (fractal) nanoparticle network in a polymer matrix during processing is a new phenomenon, not reported before for polymer composites containing (conductive) nanoparticles. 相似文献
94.
95.
Measurements of the equilibrium degree of swelling and of the equilibrium modulus were performed on poly(dimethylsiloxane) networks (PDMS) and on polyisoprene vulcanizates. The results support the concept that topological interactions between network chains, e.g. entanglements or the like, have a large influence on the rubber elastic behavior, at least within a certain range of network densities.PDMS networks having network chains of different lengths and varying functionlities of the crosslinks were prepared in bulk by endlinking fractionated ,-divinyl PDMS via multifunctional hydrogen-siloxanes (f=3 to 22). Natural rubber (NR) and synthetic liquid polyisoprene (IR) were cured in bulk with various amounts of dicumyl peroxide to give randomly crosslinked samples.The experimentally determined moduli and degrees of swelling were compared with theoretical predictions based on the phantom network theory and affine network theory, taking into account only chemical crosslinks. The observed discrepancies can be traced back to a contribution of topological interactions (trapped entanglements) to the total effective network density. The modulus and swelling data are consistent, thus ruling out non-equilibrium effects. 相似文献
96.
Polysiloxane Interpenetrating Network Materials as Electronic Device Encapsulants: Synthesis and Properties 总被引:1,自引:0,他引:1
Thermally curable interpenetrating networks employing short and long chain components were successfully prepared via the sol-gel
route. Their mechanical properties were assessed and correlated to their composition and structure. The role of the organic
cross-links was found to be a larger determinant of the mechanical properties than the inorganic network. Their low frequency
dielectric properties were investigated and found to be comparable to those of conventional encapsulation materials. Observed
mass losses at 523 K ranged between 3–5% after 1000 minutes, the suspected mechanism being the development of organic cross-links. 相似文献
97.
《Journal of Coordination Chemistry》2012,65(20):3296-3305
1-(2-Pyridyl)benzotriazole (L1) and 1-(4-pyridyl)benzotriazole (L2) with transition metal cations Co(II), Ni(II) and Cu(II) give four coordination complexes, [{Cu(L1)2(H2O)2} · 2NO3] (1), [{Co(L1)2(H2O)2} · 2NO3] (2), [Ni(L2)2(NO3)2(H2O)2] (3), and [Cu2(L2)2(CH3COO)4] (4). In 1–4, different supramolecular frameworks are formed through hydrogen bonding and/or π–π interactions. 相似文献
98.
99.
100.
《Journal of Polymer Science.Polymer Physics》2018,56(10):814-820
Thin‐film polymer solar cell consisting of [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) and poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]] (PTB7) demonstrates elastic stretchability with the aid of a high boiling point additive, 1,8‐diiodooctane (DIO). The usage of DIO not only helps to form uniformly distributed nanocrystalline grains, but may also create free volumes between the nano‐grains that allow for relative sliding between the nano‐grains. The relative sliding can accommodate large external deformation. Large dichroic ratios of the optical absorption of both PC71BM and PTB7 were observed under large‐strain deformation, indicating reorientation of the nanocrystalline PC71BM and PTB7 polymer chains along stretching direction. The dichroic ratio decreases to nearly 1.0 as the blend was relaxed to 0% strain. Therefore, the nanometer‐size grain blending morphology provides an approach to impart stretchability to organic semiconductors that are otherwise un‐stretchable. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 814–820 相似文献