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81.
82.
Density functional theory (DFT) calculations were made on the hydrolysis of hydantoin (2,4-imidazolidinedione). In the neutral hydrolysis, reacting systems composed of hydantoin and (H2O)n with n = 1+3, 2+3, 3+3, and 4+3 were adopted. Three water molecules (“+3”) participate in the in-plane hydrogen-bond circuit, and the n–3 = 1, 2, 3 or 4 water cluster works for the out-of-plane nucleophilic attack onto the carbonyl carbon of hydantoin. Transition states (TSs) involving bond interchanges prompted by proton transfers were determined. The reaction path with n = 3+3 containing N-carbamoyl glycine, N-carboxy glycine and three tetrahedral intermediates was found to be most likely. In the acid-catalyzed hydrolysis, a reacting system composed of hydantoin and H3O+(H2O)7 was employed. Ten TSs and nine intermediates were obtained. N-carbamoyl glycine and N-carboxy glycine were confirmed to be detectable stable species. The product consists of glycine, carbonic acid (not CO2), NH4+, and (H2O)5. It has the exothermic energy, whereas the product in the neutral hydrolysis is of the endothermic one for all n values. For both neutral (n = 3+3) and acid-catalyzed hydrolyses, the rate-determining steps were calculated to be for formation of the tetrahedral intermediate, HOOC-CH2-NH-C(OH)2NH2. The pattern of proton transfers along hydrogen bonds was carefully investigated. 相似文献
83.
A synthesis of an advanced ABCDE ring system (24c) having characteristic substituents in both benzene rings of ecteinascidin marine natural products is described based on our model studies. 相似文献
84.
Shingo Katayama Keiji Iwata Yuji Kubo Noriko Yamada 《Journal of Sol-Gel Science and Technology》2003,26(1-3):397-401
Solid acid-base properties of methylsiloxane-based inorganic/organic hybrids were controlled by incorporation of inorganic components other than Si into methylsiloxane networks. The effect of different inorganic components on the solid acid-base properties was estimated by first-principles calculations based on density functional theory (DFT). The deprotonation tends to occur in the order Si < Al < Nb inorganic components, suggesting that the acidity increases in the same order. Methylsiloxane-based hybrids with solid acid-base properties were also synthesized by incorporating inorganic components derived from metal alkoxides. Hammett indicators revealed that the solid acidity increased in the order Si < Al < Nb inorganic components, which was consistent with the results of first-principles calculations. Preliminary experiments revealed that the methylsiloxane-based hybrids also provided a solid basic nature by containing Ca and Y inorganic components derived from metal alkoxides. The acidic hybrids were found to have Brønsted acid sites from the FT-IR experiments of adsorbed pyridine on the hybrids. 相似文献
85.
Shindou Takuya Katayama Shingo Yamada Noriko Kamiya Kanichi 《Journal of Sol-Gel Science and Technology》2003,27(1):15-21
Polydimethylsiloxane (PDMS)-based inorganic/organic hybrids films were prepared on polyimide sheets by the sol-gel method using silanol-terminated PDMS and titanium tetraisopropoxide as starting materials. The effect of heat-treatment temperature on the surface property of the hybrid films was examined in terms of contact angle of water and Tapping-Mode Atomic Force Microscopy (AFM). AFM phase images showed the presence of domains, 200–500 nm in size, on the surface of these films after heat-treatment below 300°C. These regions were more hydrophilic than the rest of the area. The domains disappeared at 300°C and the surface became homogeneous surface of the peak to valley value, about 10 nm. It is also uniformly hydrophobic and a maximum contact angle (about 115°C) was obtained. 相似文献
86.
Onuma K Watanabe A Kanzaki N Kubota T 《The journal of physical chemistry. B》2006,110(49):24876-24883
The intermolecular interaction and association dynamics of the Ynd1p protein were investigated using dynamic and time-resolved static light scattering measurements. The mutual diffusion coefficients of wild- and mutant-type (a single amino acid substitution) Ynd1p monomer were measured in 50 mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer with 5 mM MnCl2 and 7.5% (v/v) ethylene glycol. Both translational diffusion coefficients at a zero protein concentration were (40.3 +/- 0.2) x 10(-12) m2/s at 20 degrees C and a pH of 7.0, so the hydrodynamic radius of the monomers was 4.1 +/- 0.1 nm. The measured intermolecular interaction between monomers, however, showed that the mutant-type Ynd1p had a stronger attractive force. Time-resolved static light scattering measurements showed that the association of mutant-type Ynd1p yielded a larger number of aggregates than that of wild-type Ynd1p. The time dependence of aggregate gyration radius differed between the two types. Fractal dimension analysis using scattering intensity data suggested that the inner structure of the aggregates changed from loose to rigid with time. Although this phenomenon is common for wild and mutant types, the differences in the number of aggregates yielded in the initial stages and in the intermolecular interaction affected the quality of the final grown crystals. That is, single crystals of Ynd1p grew in the mutant-type protein solution and polycrystals of Ynd1p grew in the wild-type protein solution. 相似文献
87.
The first total synthesis of kazusamycin A, a potent antitumor compound from an actinomycete, has been achieved, and its absolute structure was determined. Paterson's stereoselective aldol reaction was successfully applied to construct the contiguous chiral centers by using an originally designed optically active 2-acyl-1,3-propanediol derivative. 相似文献
88.
Ando K Tsuji E Ando Y Kuwata N Kunitomo J Yamashita M Ohta S Kohno S Ohishi Y 《Organic & biomolecular chemistry》2004,2(4):625-635
Novel 3-acetoacetylaminobenzo[b]furan derivatives having a modified triene system at the 3-position were synthesized starting with 3-aminobenzo[b]furans. The enol isomers, 3-[(3-hydroxybut-2-enonyl)amino]benzo[b]furans (), of the 3-acetoacetylaminobenzo[b]furans were obtained as stable isomers owing to formation of a hydrogen bonding between the enol hydroxyl group and the amidocarbonyl group. The planarity of the C-2 substituent through the C-3 side chain suggested the existence of a modified conjugational triene system in the enol compound. Cysteinyl leukotriene 1 and 2 receptor antagonistic activities for these compounds were evaluated. 2-(4-Cyanobenzoyl or ethoxycarbonyl)-3-[(2-cyano-3-hydroxybut-2-enonyl)amino]benzo[b]furans (, ) were moderately active. 相似文献
89.
Density functional theory calculations of the title reaction, P(OCH?)? + (H?O)(n) in CH?CN, were conducted, where n is the number of water molecules. Two routes, the routes suggested by (A) Aksnes and (B) Arbuzov, were traced with various n values. Both routes consist of two transition states (TSs) and one intermediate. Route B was found to be more likely than route A. In the former, the activation free energy (ΔG(?)) of n = 3 is slightly smaller than that of n = 2. The n = 3 TS geometry is composed of a nucleophile H?O, a proton donor H?O, and an auxiliary one. Indeed, the geometry appears to be plausible for ready proton relays along hydrogen bonds, but it is inconsistent with the observed third-order rate constant. Catalytic water molecules were added to the n = 2 and 3 bond-interchange circuits. Then route B with n = 2 + 2 was found to be best. By n = 2 + 10 and n = 3 + 12 models, the n = 2 based route B was confirmed to be likely. 相似文献
90.
Yoshiyuki Kani Shigeru Ohba Seiji Amano Noriko Ogawa Masami Ohtsuka Noritaka Chida 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):e222-e222
The relative configuration was determined for the title compound, C26H34O6, which was prepared in a synthetic study on immunosuppressant FR65814. There is an intramolecular hydrogen bond between the hydroxy and epoxy groups. 相似文献