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191.
Poly(γ‐glutamic acid)/Silica Hybrids with Calcium Incorporated in the Silica Network by Use of a Calcium Alkoxide Precursor 下载免费PDF全文
Dr. Gowsihan Poologasundarampillai Dr. Bobo Yu Dr. Olga Tsigkou Dr. Daming Wang Dr. Frederik Romer Dr. Vineet Bhakhri Dr. Finn Giuliani Prof. Molly M. Stevens Dr. David S. McPhail Prof. Mark E. Smith Prof. John V. Hanna Dr. Julian R. Jones 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(26):8149-8160
Current materials used for bone regeneration are usually bioactive ceramics or glasses. Although they bond to bone, they are brittle. There is a need for new materials that can combine bioactivity with toughness and controlled biodegradation. Sol‐gel hybrids have the potential to do this through their nanoscale interpenetrating networks (IPN) of inorganic and organic components. Poly(γ‐glutamic acid) (γ‐PGA) was introduced into the sol‐gel process to produce a hybrid of γ‐PGA and bioactive silica. Calcium is an important element for bone regeneration but calcium sources that are used traditionally in the sol‐gel process, such as Ca salts, do not allow Ca incorporation into the silicate network during low‐temperature processing. The hypothesis for this study was that using calcium methoxyethoxide (CME) as the Ca source would allow Ca incorporation into the silicate component of the hybrid at room temperature. The produced hybrids would have improved mechanical properties and controlled degradation compared with hybrids of calcium chloride (CaCl2), in which the Ca is not incorporated into the silicate network. Class II hybrids, with covalent bonds between the inorganic and organic species, were synthesised by using organosilane. Calcium incorporation in both the organic and inorganic IPNs of the hybrid was improved when CME was used. This was clearly observed by using FTIR and solid‐state NMR spectroscopy, which showed ionic cross‐linking of γ‐PGA by Ca and a lower degree of condensation of the Si species compared with the hybrids made with CaCl2 as the Ca source. The ionic cross‐linking of γ‐PGA by Ca resulted in excellent compressive strength and reduced elastic modulus as measured by compressive testing and nanoindentation, respectively. All hybrids showed bioactivity as hydroxyapatite (HA) was formed after immersion in simulated body fluid (SBF). 相似文献
192.
Wei Jiang Dong Wang Shaowei Guan Hong Gao Yili Zhao Zhenhua Jiang Weinan Gao Dan Zhang Daming Zhang 《Journal of photochemistry and photobiology. A, Chemistry》2008,197(2-3):426-433
Novel sul-containing fluorinated polyimides have been synthesized by the reaction of 2,2′-bis-(trifluoromethyl)-4,4′-diaminodiphenyl sulfide (TFDAS) with 1,4-bis-(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA), 2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 4,4′-oxydiphthalicanhydride (ODPA) or 3,4,3′,4′-biphenyl-tetracarboxylic acid dianhydride (s-BPDA). The fluorinated polyimides, prepared by a one-step polycondensation procedure, have good solubility in many solvents, such as N-methyl-2-pyrrolidinone (NMP), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), cyclohexanone, tetrahydrofuran (THF) and m-cresol. The molecular weights (Mn's) and polydispersities (Mn/Mw's) of polyimides were in the range of 1.24 × 105 to 3.21 × 105 and 1.59–2.20, respectively. The polymers exhibit excellent thermal stabilities, with glass-transition temperatures (Tg) at 221–275 °C and the 5% weight-loss temperature are above 531 °C. After crosslinking, these polymers show higher thermal stability. The films of polymers have high optical transparency. The novel sul-containing fluorinated polyimides also have low absorption at both 1310 and 1550 nm wavelength windows. Rib-type optical waveguide device was fabricated using the fluorinated polyimides and the near-field mode pattern of the waveguide was demonstrated. 相似文献
193.
多组元液体混合物的理论极限过热度 总被引:1,自引:0,他引:1
1引言纯物质液体的极限过热度问题研究,已引起人们充分重视。通常研究液体过热的方法分为热力学极限和动力学极限过热度方法。但这两种方法并不能真正确定液体的极限过热度。为此,本文作者之一提出了一个假说,并从统计热力学涨落理论出发,建立了一个确定液体极限过热度的新方法山。文献[2]中的计算证实了新方法的正确性。一定条件下,当多组元液体混合物中发生核化时,存在与纯质液体核化不同的效应,即气相也是混合物。气核内部各组元成份通常与液体对应组元的成份不同。其原因在于不同组元具有不同挥发性。因此,相平衡条件必须包括… 相似文献
194.
本文利用柱层析法从天然产物中提取分离了叶绿素a(Chl-a)和胡罗h素C(Car),并按Langmuir-Blodgett单分子膜技术制备了Chl-a单分子膜、Chl-a与Car的混合单分子膜。实验中还引入了硬脂酸起辅助支撑作用,选用的硬脂酸与Chl-a的摩尔比为10:1。挂膜载片为经过疏水处理的玻璃片。为制作模仿天然光合膜集光天线系统的功能,我们以Car为给体Chl-a为受体,Caf与Chl-a的摩尔比为5:1、50:1和125:1;这里选用的比例远大于集光天线的色素比例。用荧光光谱的测量发现,L-B膜内的色素分子有特殊的集聚态,这种状态有助于实现高效的激子转移。作者指出,由于二维的L-B膜上会发生Frster型和激子型两种能量转移的协同作用,所以在Car与Chl-a的摩尔比125:1时Chl-a的荧光无相应衰减。Chl-a单分子膜的荧光带为677nm和766nm。吸附在层析纸上Chl-a的荧光,仅长波带有明显位移。 相似文献
195.
We report a polymer-stabilised blue-phase liquid crystal (BPLC) in an in-plane-switching (IPS) cell with negligible hysteresis and good stability. Long ultraviolet (UV) wavelength and top-side (no IPS electrode) exposure create uniform polymer network, which in turn helps to suppress hysteresis. The effect of photoinitiator is also investigated. Although a BPLC precursor without photoinitiator requires a higher UV dosage to stabilise the polymer network, it is favourable for keeping high resistivity and reducing image sticking. 相似文献
196.
Ying Wan Xu Fei Zuosen Shi Juan Hu Xiaolong Zhang Lisha Zhao Changming Chen Zhanchen Cui Daming Zhang 《Journal of polymer science. Part A, Polymer chemistry》2011,49(3):762-769
A series of highly fluorinated polymers were synthesized by copolymerization of 2,3,4,5,6‐pentafluorostyrene (PFS) and fluorinated styrene derivate monomer (FSDM). Their chemical structure were confirmed by 1H NMR, 13C NMR, and 19F NMR spectra. The refractive index and cross‐linking density of the polymers can be tuned and controlled by monitoring the feed ratio of comonomers. A series of negative‐type low‐molecular‐weight fluorinated photoresists (NFPs) were prepared by composing of fluorinated polystyrene derivates (FPSDs), diphenyl iodonium salt as a photoacid generator (PAG) and solvent. The polymer films prepared from NFP by photocuring exhibited excellent chemical resistance and thermal stabilities (Td ranged from 230.5 to 258.1 °C). A clear negative pattern was obtained through direct UV exposure and chemical development. For waveguides without upper cladding, the propagation loss of the channel waveguides was measured to be 0.25 dB/cm at 1550 nm. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
197.
198.
干摩擦条件下Si3N4基和Ti(CN)基陶瓷对1Cr18Ni9Ti不锈钢的磨损机理 总被引:2,自引:1,他引:2
研究了Si3N4基陶瓷和Ti(CN)基陶瓷分别与1Cr18Ni9Ti不锈钢在干摩擦条件下对摩时的磨损行为,并且通过销-盘磨损试验和磨损表面形貌分析等,提出了这2种陶瓷的磨损机理:Si3N4基陶瓷主要是在磨损表面发生偶件材料1Cr18Ni9Ti粘着层的粘着与剥落,同时陶瓷中的Si向粘着层发生扩散转移,并在粘着层表面下20~30μm深度范围内产生裂纹和断裂而导致磨损;Ti(CN)基陶瓷在发生粘着层的粘着与剥落的同时,还由于摩擦温度很高引起陶瓷表面熔化,熔融状的陶瓷被挤走或冷凝收缩产生裂纹和断裂而导致磨损 相似文献