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排序方式: 共有134条查询结果,搜索用时 15 毫秒
101.
Katariina Yliheikkilä Pascal M. Castro Adnan Abu-Surrah Timo Repo 《European Polymer Journal》2006,42(1):92-100
Octahedral iron(II) and cobalt(II) based complexes, [N,N′-di(quinoline-2-methylene)-1,2-phenylenediimine]MCl2, and [N,N′-di(quinoline-2-methylene)diiminocyclohexane]MCl2 (M = Co and Fe), bearing tetradentate diimino nitrogen ligands were prepared and used in tert-butylacrylate (t-BA) polymerization after activation with methylaluminoxane (MAO). In general, polyacrylates with high molar mass and narrow molar mass distribution (MMD ≈ 2) were obtained. In order to understand the influence of the ligand on the polymerization process, polymerization behaviour of the hexacoordinated complexes was compared to pentacoordinated iron(II) and cobalt(II) complexes, 2,6-bis[1-(cyclohexylimido)ethyl]pyridine MCl2 (M = Co and Fe), bearing tridentate diimine nitrogen ligands as well as to free iron(II) chloride. The ability of the MAO activated hexacoordinated complexes to polymerize methylacrylate (MA) and methyl methacrylate (MMA) was also considered, but reduced activities as well as lower molar mass polymers were obtained than in the experiments with t-BA. 相似文献
102.
103.
Francesco Ciardelli Osvaldo Pieroni Adriano Fissi Angelina Altomare Roberto Solaro Nicola Tirelli 《先进技术聚合物》1995,6(1):32-41
In this review paper the photoresponsiveness of photochromic macromolecules under different structural and environmental conditions is discussed with reference to results from the authors' laboratories. Polypeptides, in particular poly(L -glutamic acid) and poly(L -lysine), with spirobenzopyrane side chains show photoinduced conformational variations which are amplified by addition of organic acids or bases to hexafluoro-2-propanol (HFP) solutions. Thus combination of light and environment effects allows modulation of order–disorder conformational transitions. Such photoindiced conformational changes are not observed in the case of macromolecules with a hydrocarbon main chain and azobenzene or stilbene side chains, obtained by polymerization of acrylic monomers. However, even in these systems structural variations affect the dependence of optical properties on irradiation. Moreover, the combination of organic solvents and water shows that polymer solubility can be modulated by light. 相似文献
104.
An ionic liquid phase organic synthesis (IoLiPOS) has been developed for the preparation of 2-thioxo tetrahydropyrimidin-4(1H)-ones. Treatment of the starting poly(ethyleneglycol)ionic liquid phases (PEGn-ILPs) 1 with acryloyl chloride 2 afforded a serie of (PEGn)-ILPs bound acrylate 3 in quantitative yields. Michael addition of aliphatic primary amines 5 to the PEG1-ILPs 3(a,d) allowed the preparation of β-aminoesters 6 in high yields. Addition of alkyl isothiocyanates 7 to 6 gave the corresponding thioureido esters 8 in the third step. The final cyclization-cleavage under microwave/solventless strategy provides, under basic conditions, the expected 2-thioxo tetrahydropyrimidin-4(1H)-ones 9 in high purity after flash chromatography. According to the IoLiPOS methodology, the NMR method was used to establish loading of all the PEG-ionic liquid phases intermediates. 相似文献
105.
Junfeng Zhou Li Wang Qiang Yang Xiaochen Dong Haojie Yu 《Colloid and polymer science》2007,285(12):1369-1376
Comb-like amphiphilic block copolymers of maleic anhydride (MA) and stearyl methacrylate (SMA) were prepared through the reversible-addition-fragmentation-transfer
polymerization. The resultant copolymers were characterized by gel permeation chromatograph and 1H NMR. The aggregation behaviors of P(MA-alt-SMA)-b-PSMA were investigated in tetrahydrofuran/water. It is of great interest that the aggregates with different morphologies
and dimensions could be obtained by adjusting the polymer concentration, water content, and pH. The dimension and structure
of these aggregates were investigated by transmission electron microscopy and dynamic light scattering. The effect of the
copolymer–solvent interaction on these aggregations was discussed. 相似文献
106.
A major unsolved problem in polymer synthesis is the design of efficient metal-mediated systems for the copolymerization of alkenes with polar vinyl monomers, such as acrylates and methacrylates. There are several reasons for the absence of efficient transition metal-based insertion copolymerization catalysts. First, following insertion, the ester group of the acrylate coordinates to the metal thereby hindering subsequent monomer coordination. A second reason stems from the preferred 2,1-insertion of acrylates into metal-carbon bonds resulting in the placement of the ester group on the α-carbon. This makes the metal-alkyl species particularly prone to homolysis because of the enhanced stability of the resultant alkyl radical, one that is essentially the same as the propagating species in radical-initiated acrylate polymerization. In this perspective we focus on this issue of facile metal-carbon bond homolysis, especially following acrylate insertion, using examples from our own work. We suggest ways to circumvent these issues, for example forcing 1,2-insertion by imposing steric crowding at the metal. Finally, we discuss the danger of relying on radical traps as probes for polymerization mechanism. Radical traps can react with metal-hydrides and attenuate metal-centered nonradical reactions. However, even when radical traps fail to stop an observed polymerization, it may be wrong to conclude that a nonradical mechanism is at work since the traps can be destroyed under certain reaction conditions. 相似文献
107.
108.
Dong-ming Qi Yong-zhong Bao Zhi-ming Huang Zhi-xue Weng 《Colloid and polymer science》2008,286(2):233-241
Polyacrylate/silica nanocomposite latex particles were prepared by in situ emulsion polymerization of acrylate monomers initiated
by 2,2′-azobis(2-amidinopropane)dihydrochloride (AIBA) adsorbed by silica nanoparticles. The anchoring of polyacrylate (ACR)
onto silica nanoparticles was achieved through the physical absorption and chemical grafting reaction. The elution and HF
etching experiments showed that most silica nanoparticles were encapsulated by ACR to form the raspberry-like ACR/silica nanocomposite
latex particles. The silica nanoparticles with a greater grafting degree of ACR tended to locate in the bulk of the polymer,
and the silica particle with a lower grafting degree would not be combined with polymer latex particles and always remained
in water phase. The formation of the final ACR/silica nanocomposite latex particles included the anchoring of ACR onto silica
primary particles, aggregation of silica primary particles to form the silica-containing latex particles, and the growth of
latex particles. 相似文献
109.
表面活性单体存在下的MMA/BA乳液共聚合(Ⅲ)--乳液的稳定性 总被引:9,自引:1,他引:8
研究了ZC-L,ZD-L等表面活性单体存在下,MMA,BA和MMA/BA乳液聚合的稳定性,制得了不含游离乳化剂,固含量在40%以上RMMA,PBA以及P(MMA/BA)稳定乳液。 相似文献
110.
Summary. Rhodococcus AJ270 is adsorbed by Dowex 1 at 15.4 mg dry weight per g resin with maximum amidase specific activity observed at lower
loadings. Bacteria form a monolayer on the resin surface, and adsorption is complete within 2 min. AJ270 can be entrapped
in agar and agarose gels (optimum loading: 20 mg dry weight bacteria per cm3 gel). Adsorption and entrapment improve amidase thermal stability 3–4 fold, and entrapment shifts the pH optimum from 8 to 7. Adsorbed and free bacteria show similar values for K
m and V
max, but entrapped bacteria have higher K
m values. Compared with bacteria adsorbed to Dowex, the activity per cm3 of matrix of agar-entrapped AJ270 is eight-fold higher. In stirred-tank reactors, exposure to acrylic acid reduces the amidase
activity of the biocatalyst in the hydrolysis of acrylamide. In column reactors, entrapped AJ270 suffers little reduction
in amidase activity against 0.25 M acrylamide over 22 h continuous operation.
Received November 18, 1999. Accepted December 14, 1999 相似文献