全文获取类型
收费全文 | 388篇 |
免费 | 2篇 |
国内免费 | 177篇 |
专业分类
化学 | 530篇 |
综合类 | 2篇 |
物理学 | 35篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 3篇 |
2015年 | 9篇 |
2014年 | 10篇 |
2013年 | 35篇 |
2012年 | 16篇 |
2011年 | 11篇 |
2010年 | 18篇 |
2009年 | 26篇 |
2008年 | 27篇 |
2007年 | 41篇 |
2006年 | 39篇 |
2005年 | 27篇 |
2004年 | 33篇 |
2003年 | 23篇 |
2002年 | 29篇 |
2001年 | 21篇 |
2000年 | 33篇 |
1999年 | 18篇 |
1998年 | 17篇 |
1997年 | 18篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 1篇 |
1987年 | 6篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有567条查询结果,搜索用时 15 毫秒
1.
Liu-Qiao Zhang Yang Gao Zhi-Hao Huang Wei Zhang Nian-Chen Zhou Zheng-Biao Zhang Xiu-Lin Zhu 《高分子科学》2021,39(1):60-69
The controlled and efficient synthesis of polymers with tailored topologies is challenging but important for exploring structure/property research. Herein, we proposed a concept of macro-latent monomer to achieve the controlled growth of polymer topologies.The macro-latent monomer was installed by a dynamic furan/maleimide covalent bond at the chain terminal. One-shot reversible additionfragmentation chain transfer(RAFT) polymerization of styrene and the macro-latent monomer created controlled growth of polymer topologies.Low temperature such as 40 ℃ could not activate the macro-latent monomer and thus the polymerization created the homo-polystyrene. By contrast, high temperature of ~110 ℃ activated the macro-latent monomer, and a maleimide-terminated macro-monomer was released via the retro-Diels Alder reaction. This macro-monomer immediately joined the cross polymerization with styrene and thus produced the side chains. By delicately manipulating the polymerization temperature, the predetermined placement of the macro-latent monomer-derived polymeric sidechains created controllably growing topologies, including star-, π-shaped, and density-variable grafting copolymers. This work paved a new way for creating on-demand topologies and would greatly enrich the topology synthesis. 相似文献
2.
The catalytic performance of rare-earth metal dialkyl complexes in combination with DMAO(dry methylaluminoxane)is explored.In the presence of 60 equivalents of DMAO,the half-sandwich complex(C13H8CH2Ph)Sc(CH2SiMe3)2(THF)(1)is inert for styrene polymerization,but(C5Me4Ph)Sc(CH2C6H4NMe2-o)2(2)converts 18%styrene into syndiotactic polystyrene.Under the same conditions,the constrained-geometry configuration sandium complex(C13H8CH2Py)Sc(CH2SiMe3)2(3a)displays extremely high catalytic activity(>6420 kg·molSC-1·h-1)and perfect syndiospecific(rrrr>99%)for styrene polymerization,while its lutetium(3b)and yttrium(3c)analogues are nearly inactive.Although the binary catalytic system 3a/DMAO exhibits very low activity for 4-methoxystyrene polymerization,it is an efficient catalyst for the syndioselective polymerization of other styrene derivatives such as 2-methoxystyrene,4-methylthiostyrene,4-fluorostyrene,4-dimethylhydrosilylstyrene,alkyne-susbstituted styrenes and 4-methylstyrene.In addition,the binary system 3a/DMAO can copolymerize ethylene and styrene to give alternating copolymers with a single glass transition at 80℃and 0.4 MPa ethylene pressures.By increasing styrene feed amount from 20 mmol to 60 mmol,the styrene content slight increases from 48.2 mol%to 53.8 mol%,but the polymerization activity is obviously promoted from 240 kg·molSc-1·h-1 to 532 kg·molSc-1·h-1. 相似文献
3.
A facile and practically applied protocol for synthesis of benzil derivatives using styrene and arene diazonium salts is reported. Pd(OAc)2/SeO2 catalytic system was found to be efficient for chemoselective synthesis of benzil. Selenium dioxide works well as an oxidant under milder reaction conditions. Moderate to very good yields of the desired products were obtained. 相似文献
4.
S. Munavalli D. K. Rohrbaugh G. W. Wagner F. R. Longo H. D. Durst 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4):781-789
Microwave catalyzed reaction of a neat mixture of styrene oxide and H-dimethylphosphonate furnished dimethyl methylphosphonate, trimethylphosphate, phenylacetaldehyde, 1-methoxy-2-phenylethanol, 1-phenylethleneglycol, cis- and trans-1,3-diphenylcyclobutanes, hydrogen 1-(2-phenylethyl)methylphosphinate, (1-phenylethyl)dimethylphosphonate, and (1-phenylethyl)dimethylphosphonate via free radical processes. 相似文献
5.
Thermoplastic elastomer was prepared from deproteinized natural rubber (DPNR) by graft-copolymerization of styrene, which was performed onto rubber particles of about 1 μm in diameter in latex stage with tert-butyl hydroperoxide/tetraethylenepentamine as an initiator. Suitable initiator concentrations were determined to be 3.3 × 10−2 and 20 × 10−2 mol/kg-rubber for the graft-coplymerization of styrene of 1.5 and 5.5 mol/kg-rubber, respectively, in which conversion and grafting efficiency of styrene were more than 90 mol% and 80 mol%, respectively. The resulting polystyrene, grafted onto the rubber particles, was characterized by size exclusion chromatography after ozonolysis. Morphology of the DPNR grafted with polystyrene (DPNR-graft-PS) was observed by transmission electron microscopy (TEM). Change in morphology after processing the DPNR-graft-PS at 150 °C was associated with change in mechanical properties, i.e. stress at strain of 1 and stress at break. The outstanding mechanical properties, maintained even after processing, were assigned to the thermoplasticity of the DPNR-graft-PS, based on the high conversion and high grafting efficiency. 相似文献
6.
以同向啮合双螺杆挤出机为反应器,采用苯乙烯和异戊二烯为聚合单体,以正丁基锂为引发剂,采用三次加料法合成苯乙烯/异戊二烯/苯乙烯(SIS)三嵌段热塑性弹性体.氢核磁共振(1H NMR)谱分析结果表明,共聚物中聚异戊二烯嵌段以1,4-结构为主.采用四氧化锇催化双氧水氧化降解聚合物分子链,利用凝胶渗透色谱对氧化降解后的聚苯乙烯碎片进行分析,证明共聚物分子为(聚苯乙烯-聚异戊二烯-聚苯乙烯)(PS-PI-PS)三嵌段结构.动态力学分析(DMA)及透射电子显微镜(TEM)分析结果表明,SIS具有两相分离结构.拉伸试验结果表明,共聚物拉伸强度与苯乙烯含量有关. 相似文献
7.
This paper presents the influence of graphene on the vulcanization kinetics of styrene butadiene rubber (SBR) with dicumyl peroxide. A curemeter and a differential scanning calorimeter were used to investigate the cure kinetics, from which the kinetic parameters and apparent activation energy were obtained. It turns out that with increasing graphene loading, the induction period of the vulcanization process of SBR is remarkably reduced at low graphene loading and then levels off; on the other hand, the optimum cure time shows a monotonous decrease. As a result, the vulcanization rate is suppressed at first and then accelerated, and the corresponding activation energy increases slightly at first and then decreases. Upon adding graphene, the crosslinking density of the nanocomposites increases, because graphene takes part in the vulcanization process. 相似文献
8.
Synthesis and thermal properties of a new styryl-functionalized pentafulvene glassy carbon precursor
The first preparation of a styryl-functionalized aryl pentafulvene 4 was carried out. In the crystal structure of 4, the packing of fulvene molecules results in the shortest intermolecular contacts between aligned vinyl groups. Thermal reactivity studies of 4 (DSC and TGA, under N2) revealed a small difference between the melting point (120 °C) and the Tonset for cross-linking (125 °C), and provided strong evidence for the production of a network material (net4) due to reactivity of the attached styryl group. Pyrolysis of net4 under N2 gave a glassy carbon product in low yield as revealed by powder X-ray and TGA analyses (carbon yield (TGA) of 38% (900 °C)). 相似文献
9.
Three new liquid crystal asymmetrical styrene monomers bearing diacetylenes, naphthyl, and nitrogen-containing groups were successfully synthesized from 2-(bromoethynyl)-6-(hexyloxy)naphthalene, 4-(4-bromo-2-vinylphenyl)-2-methylbut-3-yn-2-ol, and derivatives of 4-ethynylaniline. The molecular structures of these compounds were confirmed by FTIR, 1H NMR spectroscopy, elemental analysis, and mass spectrometry. The liquid crystalline properties of monomers were characterized by differential scanning calorimetry and polarized light microscopy. Results indicated that all the compounds exhibited the nematic phase in liquid crystal state and super high optical birefringence of 0.5-0.8. The change of terminal nitrogen-containing group affected the birefringence values in the order of -N(CH3)2<-NH2<-NCS. Moreover, measurements using UV-vis and fluorescence spectroscopy showed their good photoluminescence properties and high quantum efficiency of 0.4-1.0. 相似文献
10.
CATALYTIC COPOLYMERIZATION OF STYRENE AND ETHYLENE BY NEUTRAL NICKEL(Ⅱ) COMPLEXES IN EMULSION 总被引:1,自引:0,他引:1
Emulsion copolymerization of styrene and ethylene catalyzed by a series of neutral nickel(Ⅱ) complexes was carried out in an aqueous system to give high-molecular-weight copolymers.The copolymers and emulsions were characterized by an array of techniques including NMR,GPC,TEM,WAXD and DSC.The results indicate that the copolymers obtained are mostly block copolymers of polyethylene with random insertion of styrene units,and their M_W is in the range of 10~5-10~6.By enhancing the electron withdrawing of th... 相似文献