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排序方式: 共有143条查询结果,搜索用时 15 毫秒
61.
Masami Fukushima Mitsuo Yamamoto Takeshi Komai Kanako Yamamoto 《Journal of Analytical and Applied Pyrolysis》2009,86(1):200-206
Pyrolysis-gas chromatography/mass spectrometry using tetramethylammonium hydroxide (TMAH-py-GC/MS) was used to characterize the humic acids (HAs) produced during the composting of conifer bark. The syringyl to guaiacyl ratios of HAs during composting were estimated from the peak area ratios for 3,4,5-trimethoxy to 3,4-dimethoxy benzene derivatives (0.11–0.50), which are characteristic of conifer species. The peak areas for nitrogen-containing and fatty acid pyrolysate compounds increased significantly during composting, indicating the degree of humification during composting. HA samples from the bark composts contained higher levels of diterpene resin acids, monoterpenes and sesquiterpenes. To investigate the species of terpenes, the HA was extracted with ethanol, and the components of the extract classified into α-HA and hymatomelanic acid (HMA) fractions, respectively. The peak areas for terpenes in the α-HA fraction were much smaller than those in the original HA, indicating that the majority of terpenes were extracted into the HMA fraction. If terpenes were to bind to HMA via unspecified interactions, no peaks would be apparent for the direct injection of HMA in ethanol into the GC/MS without pyrolysis. A comparison of the total ion chromatograms of HMA for the TMAH-py-GC/MS and GC/MS revealed that terpenes in the HA had been incorporated into polymeric structures of HMA. These results indicate that terpenes are transferred from the raw bark and incorporated into HA fractions during the composting processes. 相似文献
62.
Yuki Odanaka Takuya Kanemitsu Kanako Iwasaki Yukiko Mochizuki Michiko Miyazaki Kazuhiro Nagata Masaru Kato Takashi Itoh 《Tetrahedron》2019,75(2):209-219
A highly enantioselective construction of an all-carbon quaternary stereogenic center at the α-position of malonic diesters has been achieved by Michael addition using phase-transfer catalysis. The reaction of α-monosubstituted malonates with acrylates in the presence of N-(9-anthracenylmethyl)quininium chloride as a phase-transfer catalyst afforded the corresponding α,α-disubstituted malonic diesters in high chemical yields (up to >95% yield) with high enantioselectivities (up to 95% ee). Furthermore, the product was amenable to chemoselective transformation and could be successfully converted to the corresponding α,α-disubstituted amino acid derivatives through Curtius rearrangement. 相似文献
63.
Naoyuki Kotoku Aoi Ito Shunichi Shibuya Kanako Mizuno Aki Takeshima Masaki Nogata Motomasa Kobayashi 《Tetrahedron》2017,73(10):1342-1349
An improved method for synthesizing structurally simplified analogs of cortistatin A (1), a novel anti-angiogenic steroidal alkaloid from a marine sponge, was developed. In contrast to previous methods, step- and redox-economical synthesis was achieved using a known α-bromoketone as the starting material. The structure-activity relationship study revealed that the isoquinoline portion was strictly recognized by the target molecule. Surprisingly, the introduction of the acetamide moiety on the A-ring structure dramatically enhanced the selective antiproliferative activity against endothelial cells. This new method can be easily applied to gram-scale synthesis and enabled us to prepare various analogs, which were focused on the participation of the side chain and A-ring structure. 相似文献
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The synthesis of miraziridine A, a pentapeptide derivative isolated from marine sponge, and its truncated analogs has been achieved. To construct the backbone of miraziridine A, a side-chain-unprotected vinylogous arginine was condensed with an aziridine-containing fragment prepared by a conventional solid-phase procedure. An analog lacking the vinylogous arginine site showed comparable inhibitory activity with miraziridine A, whereas an analog lacking the aziridine site showed remarkably weak inhibitory activity for cathepsin B. 相似文献
66.
The insecticidal tetrahydroisocoumarin, (3R,4S,4aR)-4,8-dihydroxy-3-methyl-3,4,4a,5-tetrahydro-1H-2-benzopyran-1-one, was synthesized as a racemate and as an optically active form using one-pot esterification-Michael addition-aldol reaction of δ-hydroxy-α,β-unsaturated aldehyde and diketene as a key step. 相似文献
67.
Thiagarajan G Shirao E Ando K Inoue A Balasubramanian D 《Photochemistry and photobiology》2002,76(3):368-372
We have been able to identify a blue fluorophore from the low-molecular weight soluble fraction of human adult nondiabetic brunescent cataract lenses as xanthurenic acid 8-O-beta-D-glucoside (XA8OG) (excitation = 338 nm and emission = 440 nm). To determine the role of this fluorophore in the lens, we have examined its photophysical and photodynamic properties. We found XA8OG to have a fluorescence quantum yield (phi) of 0.22 and a major emission lifetime of 12 ns. We found it to be a UVA-region sensitizer, capable of efficiently generating singlet oxygen species but little of superoxide. We also demonstrated that XA8OG oxidizes proteins when irradiated with UVA light, causing photodynamic covalent chemical damage to proteins. Its accumulation in the aging human lens (and the attendant decrease of its precursor O-beta-D-glucoside of 3-hydroxykynurenine) can, thus, add to the oxidative burden on the system. XA8OG, thus, appears to be an endogenous chromophore in the lens, which can act as a cataractogenic agent. 相似文献
68.
A phenol-based "end-off" compartmental ligand, 2-[N-[2-(dimethylamino)ethyl]iminomethyl]-6-[N,N-di(2-pyridylmethyl)aminomethyl]-4-methylphenol (HL), having a bidentate arm and a tridentate arm attached to the 2 and 6 positions of the phenolic ring, has afforded the following heterodinuclear M(a)(II)M(b)(II) complexes: [CuM(L)(AcO)(2)]ClO(4) (M = Mn (1), Fe (2), Co (3), Ni (4), Zn (5)), [ZnM(L)(AcO)(2)]ClO(4) (M = Co (6), Ni (7)), and [CuNi(L)(AcO)(NCS)(2)] (8). 1.MeOH (1'), 2.MeOH (2'), 3.MeOH (3'), 4.MeOH (4'), 5.MeOH (5'), and 7.MeOH (7') are isostructural and have a heterodinuclear core bridged by the phenolic oxygen atom of L(-) and two acetate groups. In 1'-5' the Cu(II) is bound to the bidentate arm and has a square-pyramidal geometry with one acetate oxygen at the apical site. The M(II) is bound to the tridentate arm and has a six-coordinate geometry together with two acetate oxygen atoms. In the case of 7' the Zn is bound to the bidentate arm and the Ni is bound to the tridentate arm. 8.2-PrOH (8') has a dinuclear core bridged by the phenolic oxygen atom of L(-) and one acetate group. The Cu bound to the bidentate arm has a square-pyramidal geometry with an isothiocyanate group at the apical site. The Ni bound to the tridentate arm has a six-coordinate geometry with further coordination of an isothiocyanate group. The site specificity of the metal ions is discussed together with the crystal structure of [Cu(4)(L)(2)(AcO)(3)](ClO(4))(3).H(2)O (9) prepared in this work. 相似文献
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70.
A selective anodic oxidation system in which a carbocation intermediate is generated exclusively by use of a temperature-controlled multiphase solution to separate the different stages of the reaction from each other and from the products is described. The formation of a thermomorphic middle layer in an electrolytic solution composed of c-Hex and LPC/MeNO2 results in enhanced interaction between aliphatic alkenes and polar unstable cation. 相似文献