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181.
A combinatorial approach for the synthesis of supramolecular gelators as new organic materials is described herein. In the course of the development of a convenient and flexible solid-phase synthesis of the artificial glycolipids, some of these compounds were accidentally found to act as low molecular-weight gelators toward organic solvents. Using this combinatorial solid-phase synthesis of glycosylated amino acetates, screening and optimization of low molecular-weight organo/hydro-gelators were efficiently carried out. We found that an N-acetyl-galactosamine-appended amino acid ester (GalNAc-aa) efficiently gelates a broad spectrum of organic solvents. More interestingly, some GalNAc-aa derivatives displayed an excellent hydrogelation capability. Transmission electron microscopy, scanning electron microscopy, confocal laser scanning microscopy, and FT-IR were used for characterization of the gel structure. It is indicated that supramolecular fibers supported by strong hydrogen-bonding networks are entangled so that the resulting spaces can immobilize a number of solvent molecules effectively. In addition, the supramolecular hydrogel consisting of GalNAc-suc-glu(O-methyl-cyc-pentyl)(2) is stable even under high salt concentrations probably due to its nonionic character and as a result, a native protein is successfully entrapped in the gel matrix without denaturation. 相似文献
182.
Tamaru S Kiyonaka S Hamachi I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(24):7294-7304
Assays of hydrolytic enzyme activity, such as of glycosidases and phosphatase, as well as several proteases, using a semi-wet supramolecular hydrogel array composed of a glycosylated amino acetate are described. It has been demonstrated that the microcavity formed by gel fibrils is suitable to immobilize native enzymes without denaturation under semi-wet conditions, and thus the nanofiber has been rationally used as a sensing domain to monitor enzymatic reactions. By using a fluorogenic substrate, reducing the size of the hydrogel can significantly improve the problem of suppressed diffusion within the gel matrix thus making the hydrogel a promising semi-wet matrix for evaluating enzyme activity. Confocal laser scanning microscopy observations have shown that an environmentally sensitive fluorescent probe accumulates in the hydrophobic domain of the gel fiber and emits fluorescence more strongly upon hydrolytic cleavage of the substrate peptides. Not only a simple environmentally sensitive probe but also a FRET (fluorescence resonance energy transfer)-type read-out mode can be devised to analyze the enzymatic hydrolysis-triggered redistribution of the probe between the nanospace and the nanofiber to accomplish a more clearly distinguished enzyme assay. Thus, it is clear that three distinct read-out modes, that is, 1) fluorogenic substrates, 2) substrates bearing an environmentally sensitive probe, or 3) a substrate exhibiting FRET, can operate under the semi-wet hydrogel conditions used in these investigations. In addition, owing to the unique properties of the present supramolecular hydrogel in semi-wet conditions, that is, its phase-segregation properties and dynamics, the supramolecular substrate/enzyme array has successfully been used for high-throughput screening of single and multiple enzymes based on their activity, lysate analysis, and quantitative evaluation of inhibitor potency and selectivity. 相似文献
183.
Noboru Matsumura Ryuji Hirase Shigeki Kamitani Yasuyuki Okumura Kazuhiko Mizuno 《Journal of heterocyclic chemistry》2005,42(6):1175-1180
2,3‐Bis[(p‐isothiocyanatomethylphenyl)methyl]‐6,7‐dihydro‐5H‐2a‐thia(2a‐SIV)‐2,3,4a,7a‐tetraaza‐cyclopent[cd]indene‐1,4(2H,3H)‐dithione ( 3 ), prepared by the reaction of 2,3‐dimethyl‐6,7‐dihydro‐5H‐2a‐thia(2a‐SIV)‐2,3,4a,7a‐tetraazacyclopent‐[cd]indene‐1,4(2H,3H)‐dithione ( 1 ) with p‐xylylene diisothio‐cyanate, reacted with N,N′‐dialkyl substituted diamines to give macrocyclic compounds bearing hypervalent sulfur by a ring closure reaction in good yields. These macrocyclic compounds were converted into ring‐expanded macrocyclic compounds with release of the hypervalent sulfur by treating with NaBH4 and CF3COOH. 相似文献
184.
Shigeki Katogi Masami Yusa 《Journal of polymer science. Part A, Polymer chemistry》2002,40(22):4045-4052
The structural effects of amineimide derivatives on photobase generation and the use of the resultant base for thermal curing of an epoxide/thiol system are investigated. The results of UV spectral change and gas chromatographic‐mass spectrometric analysis indicated that amineimide derivatives undergo photolysis by UV irradiation and generate bases. The order of conversion of the photolysis for the functional groups introduced to amineimide derivatives was NO2 > N(CH3)2 > CN > OCH3 > H. By using aminimide derivatives with NO2 and N(CH3)2 groups, the curing of the epoxide/thiol system was shifted to lower temperature after UV irradiation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4045–4052, 2002 相似文献
185.
A flow injection method for the sequential determination of iron(II) and iron(III) was developed. It is based on the differential reaction kinetics of iron(II) and iron(III) with Tiron in a double-injection FI system. The proposed method employs the accelerating action of copper(II) for the oxidation of iron(II) in the presence of Tiron. A linear calibration graph is obtained for iron (II) and iron(III) in the concentration range 1.8 × 10–5– 1.8 × 10–4 mol/L; the throughput of samples is 30 injections/h. 相似文献
186.
Matsunaga S Kinoshita T Okada S Harada S Shibasaki M 《Journal of the American Chemical Society》2004,126(24):7559-7570
Synthesis and application of alpha,beta-unsaturated N-acylpyrroles as highly reactive, monodentate ester surrogates in the catalytic asymmetric epoxidation and Michael reactions are described. alpha,beta-Unsaturated N-acylpyrroles with various functional groups were synthesized by the Wittig reaction using ylide 2. A Sm(O-i-Pr)(3)/H(8)-BINOL complex was the most effective catalyst for the epoxidation to afford pyrrolyl epoxides in up to 100% yield and >99% ee. Catalyst loading was successfully reduced to as little as 0.02 mol % (substrate/catalyst = 5000). The high turnover frequency and high volumetric productivity of the present reaction are also noteworthy. In addition, a sequential Wittig olefination-catalytic asymmetric epoxidation reaction was developed, providing efficient one-pot access to optically active epoxides from various aldehydes in high yield and ee (96-->99%). In a direct catalytic asymmetric Michael reaction of hydroxyketone promoted by the Et(2)Zn/linked-BINOL complex, Michael adducts were obtained in good yield (74-97%), dr (69/31-95/5), and ee (73-95%). This represents the first direct catalytic asymmetric Michael reaction of unmodified ketone to an alpha,beta-unsaturated carboxylic acid derivative. The properties of alpha,beta-unsaturated N-acylpyrrole are also discussed. Finally, the utility of the N-acylpyrrole unit for further transformations is demonstrated. 相似文献
187.
The stereoselective Horner-Wadsworth-Emmons reaction of aryl alkyl ketones with bis(2,2,2-trifluoroethyl)phosphonoacetic acid utilizing lithium hexamethyldisilazide in DMF afforded (E)-α,β-unsaturated carboxylic acids as the major products. 相似文献
188.
Hattori T Matsukawa S Kuwata S Ishii Y Hidai M 《Chemical communications (Cambridge, England)》2003,(4):510-511
Treatment of [Cp*IrH(SH)(PMe3)] (Cp* = eta5-C5Me5) with [IrCl2(NO)(PPh3)2] in the presence of triethylamine yielded the sulfido-bridged Ir(II)Ir0 complex [Cp*Ir(PMe3)(mu-S)Ir(NO)(PPh3)], which further reacted with I2 and triflic acid to give the diiodo complex [Cp*Ir(PMe3)(mu-I)(mu-S)IrI(NO)(PPh3)] and the hydrido complex [Cp*Ir(PMe3)(mu-H)(mu-S)Ir(NO)(PPh3)][OSO2CF3], respectively. 相似文献
189.
Osamu Haba Isao Itakura Mitsuru Ueda Shigeki Kuze 《Journal of polymer science. Part A, Polymer chemistry》1999,37(13):2087-2093
A novel nonphosgene process for producing bisphenol-A polycarbonate (PC) was developed through a transesterification between bisphenol-A (BPA) and dimethyl carbonate (DMC) and a melt-polycondensation of the resulting bisphenol-A bismethylcarbonate (1). The transesterification was carried out by heating bisphenol A in dimethylcarbonate in the presence of Lewis acid catalysts, removing the by-producing methanol using molecular shieves 4A. Among various catalysts, a combination of (Bu2SnCl)2O and dimethylaminopyridine gave the best results to produce 1 in 22% yield for 48 h. Using a larger amount of the molecular sieves further improved the yield to 80% in 120 h. The resulting 1 was heated under reduced pressure in the presence of titanium catalysts to produce PC in good yields. The resulting PC had high weight average molecular weight (Mw) of 75,000. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2087–2093, 1999 相似文献
190.