全文获取类型
收费全文 | 1275篇 |
免费 | 45篇 |
国内免费 | 254篇 |
专业分类
化学 | 1314篇 |
晶体学 | 10篇 |
力学 | 33篇 |
综合类 | 4篇 |
数学 | 16篇 |
物理学 | 197篇 |
出版年
2024年 | 2篇 |
2023年 | 44篇 |
2022年 | 41篇 |
2021年 | 36篇 |
2020年 | 48篇 |
2019年 | 32篇 |
2018年 | 19篇 |
2017年 | 51篇 |
2016年 | 42篇 |
2015年 | 31篇 |
2014年 | 44篇 |
2013年 | 107篇 |
2012年 | 53篇 |
2011年 | 78篇 |
2010年 | 59篇 |
2009年 | 74篇 |
2008年 | 87篇 |
2007年 | 93篇 |
2006年 | 95篇 |
2005年 | 62篇 |
2004年 | 66篇 |
2003年 | 45篇 |
2002年 | 38篇 |
2001年 | 34篇 |
2000年 | 38篇 |
1999年 | 40篇 |
1998年 | 32篇 |
1997年 | 21篇 |
1996年 | 33篇 |
1995年 | 25篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有1574条查询结果,搜索用时 22 毫秒
941.
KE Jian-Hong LIN Zhen-Quan CHEN Xiao-Shuang 《理论物理通讯》2008,49(3):791-796
We propose a sequential monomer reaction model for a two-species predator-prey system, in which the aggregates of either species can spontaneously produce or lose one monomer and meanwhile, a type-B aggregate can prey upon one monomer of a type-A aggregate when they meet. Using the mean-field rate equation approach, we analytically investigate the kinetic behavior of the system. The results show that the evolution of the system depends crucially on the details of the rate kernels. The aggregate size distribution of either species approaches the conventional or modified scaling form in most cases. Moreover, the total size of either species grows exponentially with time in some cases and asymptotically retains a constant quantity in other cases, while it decays with time and vanishes finally in the rest cases. 相似文献
942.
Lijun Shen Tianjiao Zhou Yatong Fan Xin Chang Yi Wang Jianguo Sun Lei Xing Hulin Jiang 《中国化学快报》2020,31(7):1709-1716
Photodynamic therapy(PDT) is a promising alternative approach for effective cancer treatment,which can directly destroy local tumor cells due to the generation of cytotoxic singlet oxygen and reactive oxygen species(ROS) in the tumor cells.Intriguingly,PDT-mediated cell death is also associated with anti-tumor immune response.Howeve r,immunosuppre s sion of tumor microe nvironment is able to limit the immune response induced by PDT,it is therefore necessary to combine with immunocheckpoint inhib... 相似文献
943.
Louis Schutz Forouzan Kazemi Elby Mackenzie Jean-Yves Bergeron Eric Gagnon Jerome P. Claverie 《Journal of polymer science. Part A, Polymer chemistry》2021,59(4):321-328
Vast quantities of the natural terpene (R)-limonene can be collected from food waste. Epoxidation of its two double bonds provides limonene dioxide (LDO), a difunctional epoxy monomer. However, LDO is a mixture of four isomers, two of which (trans-LDO) are actually difunctional while the others (cis-LDO) have one epoxide group which is significantly less reactive, as revealed by Fourier transformed infrared spectroscopic analysis of formulations cross-linked with polyethylene imine. These results are also confirmed when preparing epoxy formulations using respectively cis or trans isomers. From DFT calculations, the reactivity of each epoxide group of LDO has been assessed in model reactions with primary and secondary amines, in the presence of amine or alcohol hydrogen-bond donors. The kinetics of cross-linking has also been probed by differential scanning calorimetry. As measured by dynamic mechanical analysis, the resulting epoxy resins based on trans isomers have a storage modulus of ca 1GPa at room temperature and a glass transition temperature (Tg) of 70°C. These results demonstrate that trans LDO is a promising bio-based epoxy monomer, which could be used as an alternative to petroleum-based epoxy monomers. 相似文献
944.
Cuiling Meng Man Chun Tseng Shu Tuen Tang Chen Xiang Zhao Sze Yan Yeung Hoi Sing Kwok 《Liquid crystals》2019,46(3):484-491
Smart windows which switch between transparent and scattering states can be used not only as privacy window in buildings and cars, but also as information displays, and motorcycle helmet visors. Here, we have proposed a reverse mode polymer-stabilised liquid crystals (PSLCs) smart window based on inhomogeneous alignment surface, which greatly enhances the haze by 42% when compared to device without inhomogeneity treatment. A 100-cm2 window that switches between the power-off clear state (~4% haze) and a power-on scattering state (64% haze at 15 V) in less than 3.5 ms is demonstrated. Since no high-temperature treatment (< 80°C) is involved in device fabrication, further development on plastic films is feasible. 相似文献
945.
Tugba Celiker Recep İsci Kerem Kaya Turan Ozturk Yusuf Yagci 《Journal of polymer science. Part A, Polymer chemistry》2020,58(17):2327-2334
We herein report photoinduced step-growth polymerization of highly conjugated 2,5-dithiophenyl (thieno[3,4-b] thiophene) (TTs) derivatives possessing 4-cyanophenyl or 4-methoxyphenyl or 3-(4-fluorophenyl) groups substituted at the terminal position. Upon irradiation at 350 nm, the excited state of these molecules forms exciplex with diphenyliodonium hexafluorophosphate (DPI) that undergoes electron transfer reaction forming radical cations. Successive proton release and radical coupling reactions yield corresponding oligothienothiophenes with overall yields varying between 19–74%. Structural and molecular weight characteristics of the oligomers thus formed were investigated by Ultraviolet, fluorescence, NMR (Nuclear Magnetic Resonance) and infrared (IR) spectroscopic methods, and GPC (Gel Permeation Chromatography), respectively. The effect of substitution and dithiophene side groups on the reactivity of the monomer and band gap of the oligomers formed was evaluated by using cyclic voltammetry. 相似文献
946.
947.
Akira Matsumoto Taisuke Tani Hiroyuki Aota Kazuhisa Fushihara Mikio Yamada 《Journal of polymer science. Part A, Polymer chemistry》2012,50(5):1018-1025
As an extension of our continuing studies concerned with the mechanistic discussion of network formation in the free‐radical crosslinking (co)polymerization of multivinyl monomers, this work refers to the skewered reactions in the crosslinking (co)polymerizations of liquid polybutadiene rubber (LBR) as an internal olefinic multivinyl monomer or crosslinker, especially focused on the competitive occurrence of both addition or skewered reaction to internal carbon–carbon (CC) double bonds and abstraction reaction of allylic hydrogens in LBR by growing polymer radical. Thus, LBR is regarded as an internal olefinic multiallyl monomer‐linked allyl groups (? CH?CH? CH2? ) with methylene units (? CH2? ). First, gelation in the polymerization of LBR was explored in detail, especially at elevated temperatures. The occurrence of intermolecular crosslinking was easier in the order LBR > LBR containing 20 mol % of 1,2‐structural units > liquid polyisoprene rubber. Then, we pursued the polymerization of LBR using dicumyl peroxide (DCPO) as typical organic peroxide used at elevated temperatures. The primary cumyloxy radical generated by the thermal decomposition of DCPO may add to CC double bond or abstract allylic hydrogen or undergo β‐scission to generate a secondary methyl radical. The initiation by the cumyloxy radical was omitted. The ratio of allylic hydrogen abstraction to β‐scission reaction was estimated; thus, only 39% of cumyloxy radical was used for the allylic hydrogen abstraction reaction. The addition of methyl radical to CC double bond was clearly observed. Finally, we pursued the intermolecular and intramolecular skewered reactions in free‐radical crosslinking LBR/vinyl pivalate copolymerizations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
948.
以(2-甲基丙烯酰氧乙基)三甲基氯化铵(DMC)为例,用分光光度法研究了丙烯酰胺(AM)与季铵类阳离子单体在聚乙二醇(PEG)水溶液中双水相共聚的二次相分离.提出了二次相分离的机理,认为是阳离子单体单元的电离使得聚合物带上了正电荷,大分子间的静电排斥作用增加了其在PEG相中的溶解性(增容作用).讨论了反应条件对体系二次相分离的影响,发现二次相分离在一定的单体浓度和PEG浓度、以及适当的单体比例和PEG分子量条件下才能发生.总单体用量或PEG用量增加,第二次分相先出现后消失;PEG分子量增大,第二次分相逐渐明显;反应温度升高,两次分相更快完成.DMC摩尔分率为0.25~0.60时,第一次分相的临界转化率很小,第二次分相的临界转化率则随DMC摩尔分率的增加而增大;DMC摩尔分率超过0.60后,聚合反应主要在过渡区完成,第二次分相难以发生. 相似文献
949.
950.
R. Velmurugan B. Krishnakumar Rajendra Kumar M. Swaminathan 《Arabian Journal of Chemistry》2012,5(4):447-452
Nano-TiO2 was synthesized by sol–gel method. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) images, transmission electron microscope (TEM), BET surface area measurement and DRS analysis. The formation of anatase phase nano-TiO2 was confirmed by XRD measurements and its crystalline size is found to be 15.2 nm. SEM images depict the crystalline nature of prepared TiO2. The BET surface area of prepared TiO2 is found to be 86.5 m2 g?1 which is higher than that of commercially available TiO2–P25. The photocatalytic activity of prepared anatase phase TiO2 has been tested for the degradation of two azo dyes: Reactive Red 120 (RR 120) and Trypan Blue (TB) using solar light. The photocatalytic activity of nano-TiO2 is higher than TiO2–P25 under solar light. The mineralization of dyes has been confirmed by chemical oxygen demand (COD) measurements. 相似文献