全文获取类型
收费全文 | 412篇 |
免费 | 61篇 |
国内免费 | 56篇 |
专业分类
化学 | 223篇 |
晶体学 | 25篇 |
力学 | 68篇 |
综合类 | 5篇 |
数学 | 17篇 |
物理学 | 191篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 11篇 |
2017年 | 18篇 |
2016年 | 21篇 |
2015年 | 19篇 |
2014年 | 13篇 |
2013年 | 64篇 |
2012年 | 25篇 |
2011年 | 26篇 |
2010年 | 18篇 |
2009年 | 25篇 |
2008年 | 25篇 |
2007年 | 31篇 |
2006年 | 32篇 |
2005年 | 25篇 |
2004年 | 21篇 |
2003年 | 17篇 |
2002年 | 18篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 8篇 |
1998年 | 10篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有529条查询结果,搜索用时 140 毫秒
121.
Suresh K. Jewrajka Emel Yilgor Iskender Yilgor Joseph P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》2009,47(1):38-48
Novel segmented polyurea elastomers containing soft polyisobutylene (PIB) segments were synthesized and characterized. The key ingredient, primary amine‐telechelic PIB oligomers (NH2‐PIB‐NH2) with number average molecular weights of 2500 and 6200 g/mol were synthesized. PIB‐based polyureas were prepared by using various aliphatic diisocyanates and diamine chain extenders with hard segment contents between 9.5 and 46.5% by weight. All copolymers displayed microphase morphologies as determined by dynamic mechanical analysis. Tensile strengths of nonchain‐extended and chain‐extended polyureas showed a linear dependence on the urea hard segment content. PIB‐based polyureas prepared with NH2‐PIB‐NH2 of Mn = 2500 g/mol, 4,4′‐methylendbis(cyclohexylisocyantate), and 1,6‐diaminohexane containing 45% hard segment exhibited 19.5 MPa tensile strength which rose to 23 MPa upon annealing at 150 °C for 12 h. With increasing hard segment content, elongation at break decreased from ~ 450% to a plateau of 110%. The hydrolytic and oxidative stability of PIB‐based polyureas were unprecedented. Although commercial “oxidatively resistant” thermoplastic polyurethanes degraded severely upon exposure to boiling water or concentrated nitric acid, the experimental polyureas survived without much degradation in properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 38–48, 2009 相似文献
122.
Takahiro Gunji Yasuhito Iizuka Koji Arimitsu Yoshimoto Abe 《Journal of polymer science. Part A, Polymer chemistry》2004,42(15):3676-3684
Polysilsesquioxanes were prepared through the acid‐catalyzed hydrolytic polycondensation of triethoxy(methyl)silane, triisopropoxy(methyl)silane, or triisobutoxy(methyl)silane and subjected to dip coating to form coating films. The film formation depended on the polarity and crystallinity of the substrate, and a correlation was found between the substrate and polysilsesquioxane solubility parameters. When the coating film was heated, thermal condensation occurred at about 500 °C between hydroxy groups or between hydroxy and alkoxy groups. The methyl group attached to silicon decomposed, and siloxane bonding formed at about 800 °C. The adhesion and hardness of the coating films were evaluated with the Japanese Industrial Standard K5400 protocol, and they increased with increases in the heating time and heat‐treatment temperature. The refractive index of the coating films decreased when the heat‐treatment temperature was increased to 500 °C because of the combustion of organic groups. In contrast, the surface electric resistance increased with the heat‐treatment temperature up to 500 °C. The dielectric constant was 2.6–2.8 and decreased with an increases in the molecular weight and the degree of crosslinking of the polysilsesquioxanes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3676–3684, 2004 相似文献
123.
一种新型水硬度测定的进样装置 总被引:1,自引:0,他引:1
报道一种新型水硬度测定的进样装置,它是特殊的直接进样-混合-混合-排液系统,勿需预先显色,可直接进样测定。实验表明具有操作简便,快速的优点。 相似文献
124.
Lijiang?Hu Xingwen?Zhang Yi?Sun Roberto?J.?J.?WILLIAMSEmail author 《Journal of Sol-Gel Science and Technology》2005,34(1):41-46
Instrumented-indentation testing (IIT) provided with a continuous stiffness measurement (CSM) technique was employed to measure hardness and elastic modulus profiles of thin organic/inorganic hybrid coatings on glass surfaces. Hybrids were synthesized by the hydrolytic condensation of (3-methacryloxypropyl) trimethoxysilane (MPMS) or vinyltrimethoxysilane (VMS), with 5–30 wt% tetraethoxysilane (TEOS), in the presence of formic acid. Coatings of 600–800 nm on glass substrates were obtained by dip-coating solutions of these hybrids with benzoyl peroxide (BPO) addition, and curing in an oven following a thermal cycle up to 120C. Both hardness and elastic modulus showed a maximum value close to the surface, followed by a plateau and a significant increase at higher penetrations. Hybrids based on MPMS and 20–30 wt% TEOS exhibited a good combination of intrinsic values of hardness (0.50 GPa) and brittle index (0.06–0.07), that makes them suitable for coatings of plastic substrates. 相似文献
125.
《Journal of Chemical Sciences》2005,117(5):549-554
In earlier work, the present authors have shown that hardness profiles are less dependent on the level of calculation than
energy profiles for potential energy surfaces (PESs) having pathological behaviors. At variance with energy profiles, hardness
profiles always show the correct number of stationary points. This characteristic has been used to indicate the existence
of spurious stationary points on the PESs. In the present work, we apply this methodology to the hydrogen fluoride dimer,
a classical difficult case for the density functional theory methods. 相似文献
126.
TiAlN作为一种三元复合纳米涂层材料,具有非常好的性能.该涂层克服了TiN涂层所存在的一些缺陷,其硬度远远高于TiN涂层,最高可达47GPa, 并且具有很好的热稳定性,在700℃高温下仍很稳定,而TiN涂层在500℃时就已被氧化.TiAlN涂层还具有抗磨损,摩擦系数小,热膨胀系数及热传导系数低等特性,这些特性与涂层中Al含量的多少有关,Al含量的改变会导致涂层微观结构的改变,从而使其性能发生变化.氮分压和基底温度对TiAlN涂层的性质有着极其重要影响.本文结合国内外对TiAlN涂层的最新研究进展,对TiAlN涂层的应用,制备方法,结构,抗氧化性及硬度作了简要论述. 相似文献
127.
128.
129.
This paper examines and compares the effects of exposing commercial, off the shelf erasable programmable read-only memory (EPROM) and electrically erasable programmable read-only memory (E2PROM) components to gamma rays. Results obtained for CMOS-based EPROM (NM27C010) and E2PROM (NM93CS46) components provide evidence that EPROMs have a greater radiation hardness than E2PROMs. Moreover, the changes in EPROMs are reversible, and after erasure and reprogramming all EPROM components restore their functionality. On the other hand, changes in E2PROMs are irreversible. The obtained results are analyzed and interpreted on the basis of gamma ray interaction with the CMOS structure. 相似文献
130.
正Crystalline polymers exhibit their strong connections to our practical world.In synthetic polymer materials,crystallization brings fiber orientation-strengthening,rubber strain-hardening and plastic neck-toughening.Important properties such as hardness,thermal stability,anisotropic structures,etc.are endowed to the 相似文献