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511.
Hirofumi Dohi Ryota Komai Hidetoshi Sakai Haruka Komuro Yoshihiro Nishida 《Journal of carbohydrate chemistry》2017,36(8-9):307-324
A facile methodology is proposed for regioselective conjugation between glycosyl donors and acceptors towards the development of regioselective 1,2-cis-glycosylation method. ortho-Formylphenyl 1-thio-β-d-galactopyranoside was regioselectively tethered to methyl α-d-glucopyranoside under acidic condition to furnish an 4,6-O-arylidene acetal-linked conjugate. This conjugate can be readily converted to an ether-linked 4-O- or 6-O-derivative by regioselective cleavage of the acetal ring. In the glycosylation reaction, the ether-linked 4-OH conjugate was found to show excellent 1,2-cis selectivity via an intramolecular 1,9-transfer. 相似文献
512.
Yuya Nishio Ryota Mifune Taisuke Sato Shin-ich Ishikawa Hiroshi Matsubara 《Tetrahedron letters》2017,58(12):1190-1193
A solution of hydrogen bromide (HBr) in 1,4-dioxane was prepared and investigated for its ability to brominate alcohols, and hydrobrominate alkenes. This study revealed that the brominating ability of this HBr/1,4-dioxane solution is equal or superior to that of hydrobromic acid or HBr in acetic acid. The solution of HBr in 1,4-dioxane is robust, exhibiting no decomposition of the solvent, and retaining 97% of its original concentration, when kept at ?25 °C for 30 days. This solution is a liquid alternative to HBr gas without protic solvents. 相似文献
513.
Shear-strain-thickening transition under oscillatory flow was observed in flocculated ferric-oxide suspensions in mineral oil. The value of the dynamic modulus of the suspensions that was measured at small strain amplitude after cessation of shear also became higher when the strain amplitude of the applied shear had been within or above the transition region.The ferric-oxide powders used were an acicular submicron maghemite (magnetic) and the hematite (non-magnetic) that was converted from the maghemite by heat treatment. The powders were treated with a dispersing agent and the suspensions were prepared in 33% by particle weight. The strain-thickening transition was observed in both the magnetic and the non-magnetic suspensions. However, the onset of the strain-thickening in the magnetic suspension was found at about one decade larger strain amplitude than that in the non-magnetic analog suspension, indicating particle interactions affect to the appearance of the phenomenon.A qualitative interpretation was made in view of site percolation for the enhancement of modulus at rest after the application of the large-amplitude oscillatory shear, where the process of the strain-thickening transition under shear and the development of the modulus after stopping the shear was described with a floc model in which the flocculation phase dilates as a result of the reduction of the particle linkages under higher shear. 相似文献
514.
Exfoliation of Graphite into Graphene in Polar Solvents Mediated by Amphiphilic Hexa‐peri‐hexabenzocoronene
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Ryota Kabe Prof. Xinliang Feng Prof. Chihaya Adachi Prof. Klaus Müllen 《化学:亚洲杂志》2014,9(11):3125-3129
A water‐soluble surfactant consisting of hexa‐peri‐hexabenzocoronene (HBC) as hydrophobic aromatic core and hydrophilic carboxy substituents was synthesized. It exhibited a self‐assembled nanofiber structure in the solid state. Profiting from the π interactions between the large aromatic core of HBC and graphene, the surfactant mediated the exfoliation of graphite into graphene in polar solvents, which was further stabilized by the bulky hydrophilic carboxylic groups. A graphene dispersion with a concentration as high as 1.1 mg L?1 containing 2–6 multilayer nanosheets was obtained. The lateral size of the graphene sheets was in the range of 100–500 nm based on atomic force microscope (AFM) and transmission electron microscope (TEM) measurements. 相似文献
515.
Attenuation of the Aggregation and Neurotoxicity of Amyloid‐β Peptides by Catalytic Photooxygenation
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Dr. Atsuhiko Taniguchi Dr. Daisuke Sasaki Azusa Shiohara Prof. Takeshi Iwatsubo Dr. Taisuke Tomita Dr. Youhei Sohma Prof. Motomu Kanai 《Angewandte Chemie (International ed. in English)》2014,53(5):1382-1385
Alzheimer’s disease (AD), a progressive severe neurodegenerative disorder, is currently incurable, despite intensive efforts worldwide. Herein, we demonstrate that catalytic oxygenation of amyloid‐β peptides (Aβ) might be an effective approach to treat AD. Aβ1–42 was oxygenated under physiologically‐relevant conditions (pH 7.4, 37 °C) using a riboflavin catalyst and visible light irradiation, with modifications at the Tyr10, His13, His14, and Met35 residues. The oxygenated Aβ1–42 exhibited considerably lower aggregation potency and neurotoxicity compared with native Aβ. Photooxygenation of Aβ can be performed even in the presence of cells, by using a selective flavin catalyst attached to an Aβ‐binding peptide; the Aβ cytotoxicity was attenuated in this case as well. Furthermore, oxygenated Aβ1–42 inhibited the aggregation and cytotoxicity of native Aβ. 相似文献
516.
Palladium‐Catalyzed CH Fluorosilylation of 2‐Phenylpyridines: Synthesis of Silafluorene Equivalents
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Dr. Qing Xiao Dr. Xiangtai Meng Prof. Dr. Motomu Kanai Prof. Dr. Yoichiro Kuninobu 《Angewandte Chemie (International ed. in English)》2014,53(12):3168-3172
Treatment of 2‐phenylpyridines with amino(1,3,2‐dioxaborolan‐2‐yl)diphenylsilane produced fluorosilylated 2‐phenylpyridines in good to excellent yields under palladium catalysis. This reaction is the first example of C? H fluorosilylation. Single‐crystal X‐ray structure analysis revealed a Lewis acid–base interaction between the silicon and nitrogen atoms, and the obtained fluorosilylated products are silafluorene equivalents. The fluorosilylated products showed stronger fluorescence than the corresponding silafluorene derivative. 相似文献
517.
Dr. Ryota Suwa Assoc. Prof. Masayuki Hatta Prof. Kazuhiko Ichikawa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(42):13656-13661
CaCO3‐saturated saline waters at pH values below 8.5 are characterized by two stationary equilibrium states: reversible chemical calcification/decalcification associated with acid dissociation, Ca2++HCO3??CaCO3+H+; and reversible static physical precipitation/dissolution, Ca2++CO32??CaCO3. The former reversible reaction was determined using a strong base and acid titration. The saturation state described by the pH/PCO2‐independent solubility product, [Ca2+][CO32?], may not be observed at pH below 8.5 because [Ca2+][CO32?]/([Ca2+][HCO3?]) ?1. Since proton transfer dynamics controls all reversible acid dissociation reactions in saline waters, the concentrations of calcium ion and dissolved inorganic carbon (DIC) were expressed as a function of dual variables, pH and PCO2. The negative impact of ocean acidification on marine calcifying organisms was confirmed by applying the experimental culture data of each PCO2/pH‐dependent coral polyp skeleton weight (Wskel) to the proton transfer idea. The skeleton formation of each coral polyp was performed in microspaces beneath its aboral ectoderm. This resulted in a decalcification of 14 weight %, a normalized CaCO3 saturation state Λ of 1.3 at PCO2 ≈400 ppm and pH ≈8.0, and serious decalcification of 45 % and Λ 2.5 at PCO2 ≈1000 ppm and pH ≈7.8. 相似文献
518.
Surface‐Junction Effects on Interfacial Electron Transfer between Bis(terpyridine)iron(II) and Hydrogen‐Terminated Silicon(111) Electrode
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Hiroaki Maeda Dr. Ryota Sakamoto Prof. Dr. Hiroshi Nishihara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(10):2761-2764
Interfacial electron transfer at bis(tpy)–iron(II) complexes (tpy=2,2′:6′,2′′‐terpyridine) on Si(111) electrodes was investigated by using four types of surface‐anchor terpyridine ligands. Despite the greater distance, electron transfer between the bis(tpy)–iron(II) unit and the electrode is accelerated in surface‐anchor ligands with an additional phenylene group. 相似文献
519.
520.
This review summarizes recent advances of catalytic chemoselective aerobic oxidations promoted by a metal/stable organoradical redox conjugate. The sophisticated system exhibits high activity and chemoselectivity and is recently applied to late-stage transformations for complex natural product synthesis and a polypeptide transformation. The characteristics of the catalytic system are likely due to the unique mechanism ([1e + 1e] oxidation), which takes intrinsic advantages of cooperative work of first-row transition metals and stable organoradicals (radical-conjugated redox catalysis). 相似文献