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81.
The efficient synthesis of the iminoalditols derivatives 1 and 2 (nojirimycin alpha-C-glycosides) has been achieved in 10 steps from commercially available 2,3;4,6-di-O-isopropylidene-alpha-L-sorbofuranose in an overall yield of 23-27%. 相似文献
82.
Christophe Masson Daniel Scherman Michel Bessodes 《Journal of polymer science. Part A, Polymer chemistry》2001,39(22):4022-4024
A new and very convenient route to oxidized poly(ethylene glycol), with a catalytic nitroxyl radical oxidant (2,2,6,6‐tetramethyl‐1‐piperidinyl‐oxyl) regenerated in situ by stoichiometric amounts of [bis(acetoxy)‐iodo]benzene, is described. Under these conditions, the reaction is quantitative and leads to the pure product by a simple process such as precipitation and washing with diethyl ether. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4022–4024, 2001 相似文献
83.
Ramin Rabbani Sima Saeedi Md Nazimuddin Hctor Barbero Nathalie Kyritsakas Travis A. White Eric Masson 《Chemical science》2021,12(46):15347
A cucurbit[8]uril (CB[8])-secured platinum terpyridyl chloride dimer was used as a photosensitizer and hydrogen-evolving catalyst for the photoreduction of water. Volumes of produced hydrogen were up to 25 and 6 times larger than those obtained with the corresponding free and cucurbit[7]uril-bound platinum monomer, respectively, at equal Pt concentration. The thermodynamics of the proton-coupled electron transfer from the Pt(ii)–Pt(ii) dimer to the corresponding Pt(ii)–Pt(iii)–H hydride key intermediate, as quantified by density functional theory, suggest that CB[8] secures the Pt(ii)–Pt(ii) dimer in a particularly reactive conformation that promotes hydrogen formation.The cucurbit[8]uril macrocycle can secure a platinum terpyridyl complex into a particularly reactive dimer that catalyzes the photoreduction of water. 相似文献
84.
Tormos JR Wiley KL Wang Y Fournier D Masson P Nachon F Quinn DM 《Journal of the American Chemical Society》2010,132(50):17751-17759
In a previous communication, kinetic β-deuterium secondary isotope effects were reported that support a mechanism for substrate-activated turnover of acetylthiocholine by human butyrylcholinesterase (BuChE) wherein the accumulating reactant state is a tetrahedral intermediate ( Tormos , J. R. ; et al. J. Am. Chem. Soc. 2005 , 127 , 14538 - 14539 ). In this contribution additional isotope effect experiments are described with acetyl-labeled acetylthiocholines (CL(3)COSCH(2)CH(2)N(+)Me(3); L = H or D) that also support accumulation of the tetrahedral intermediate in Drosophila melanogaster acetylcholinesterase (DmAChE) catalysis. In contrast to the aforementioned BuChE-catalyzed reaction, for this reaction the dependence of initial rates on substrate concentration is marked by pronounced substrate inhibition at high substrate concentrations. Moreover, kinetic β-deuterium secondary isotope effects for turnover of acetylthiocholine depended on substrate concentration, and gave the following: (D3)k(cat)/K(m) = 0.95 ± 0.03, (D3)k(cat) = 1.12 ± 0.02 and (D3)βk(cat) = 0.97 ± 0.04. The inverse isotope effect on k(cat)/K(m) is consistent with conversion of the sp(2)-hybridized substrate carbonyl in the E + A reactant state into a quasi-tetrahedral transition state in the acylation stage of catalysis, whereas the markedly normal isotope effect on k(cat) is consistent with hybridization change from sp(3) toward sp(2) as the reactant state for deacylation is converted into the subsequent transition state. Transition states for Drosophila melanogaster AChE-catalyzed hydrolysis of acetylthiocholine were further characterized by measuring solvent isotope effects and determining proton inventories. These experiments indicated that the transition state for rate-determining decomposition of the tetrahedral intermediate is stabilized by multiple protonic interactions. Finally, a simple model is proposed for the contribution that tetrahedral intermediate stabilization provides to the catalytic power of acetylcholinesterase. 相似文献
85.
Dr. Lucie Jarrige Prof. Vincent Gandon Dr. Géraldine Masson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1406-1413
A stable asymmetric intramolecular Povarov reaction has been established to provide an efficient method to access structurally diverse trans,trans-trisubstituted tetrahydrochromeno[4,3-b]quinolines in high stereoselectivities of up to >99:1 diastereomeric ratio and 99 % enantiomeric excess, without any purification step. Additionally, to facilitate large-scale application of this method, a low catalyst loading protocol was employed, 0.2 mol % chiral phosphoric acid, which provided the cycloadducts without any loss in yield and enantioselectivity. Theoretical studies revealed that the reaction occurred through a sequential Mannich reaction and an intramolecular Friedel–Crafts reaction, wherein the phosphoric acid acted as a bifunctional catalyst to activate the para-phenolic dienophile and N-2-hydroxy-2-azadiene simultaneously. 相似文献
86.
Renaud Masson 《International Journal of Solids and Structures》2008,45(3-4):757-769
Except for particular cases, the classical expressions of the Eshelby or Hill polarization tensors, depend, respectively, on a simple or double integral for a fully anisotropic two-dimensional or three-dimensional elastic body. When the body is two-dimensional, we take advantage of Cauchy’s theory of residues to derive a new explicit expression which depends on the two pairs of complex conjugate roots of a quartic equation. If the body exhibits orthotropic symmetry, these roots are explicitly given as a function of the independent components of the elasticity tensor. Similarly, the double integral is reduced to a simple one when the body is three-dimensional. The corresponding integrand depends on the three pairs of complex conjugate roots of a sextic equation which reduces to a cubic one for orthotropic symmetry. This new expression improves significantly the computation times when the degree of anisotropy is high. For both two and three-dimensional bodies, degenerate cases are also studied to yield valid expressions in any events. 相似文献
87.
The aza-MBH reaction of imines 1 and beta-naphthyl acrylate 2 in the presence of C-6' modified beta-isocupreidine derivative 1c (0.1 equiv) and beta-naphthol 5 (0.1 equiv) afforded the corresponding (3S)-aza-MBH adducts 4 in high yield and excellent enantiomeric excess. These catalytic conditions allowed the aliphatic imines to be employed for the first time as electrophilic partners of the aza-MBH reaction. The coexistence of two H-bond donors with different acidic strengths was found to be crucial for the observed high enantioselectivity. 相似文献
88.
Absorption cross sections of argon for argon resonance radiation have been measured by several techniques. The apparent cross sections are small (0·1 to 1·6 × 10-18 cm2) for resonance absorption and the values depend on the technique used for measurement. These observations are interpreted in terms of extensive reversal and broadening in the source. The excitation and quenching of resonance fluorescence was studied to provide information about the rates of the processes The rate constants were estimated relative to k r, the rate constant for radiation. Radiation imprisonment leads to a reduction of k r from its natural value and observations of the decay of resonance fluorescence suggest that k r ~ 1·5 × 105 s-1 in our system at [Ar] = 2 × 1017 atom cm-3. Combining this value with the relative values for the quenching rate constants gives k 1 < 1·5 × 10-13, k 1′(M = N2) ~ 6 × 10-12, k 1′(M = NO) ~ 4 × 10-10, in units of cm3 s-1 molecule-1. 相似文献
89.
90.
Wang Z Masson G Peiris FC Ozin GA Manners I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(33):9372-9383
Facile synthetic routes have been developed that provide access to cationic and anionic water-soluble polyferrocenylsilane (PFS) polyelectrolytes with controlled molecular weight and narrow polydispersity. Living photolytic ring-opening polymerization of amino-functionalized [1]ferrocenophane (fc) monomers [fcSiMe{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)}] (3), [fcSi{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)}(2)] (10), [fcSiMe(C[triple chemical bond]CCH(2)NMe(2))] (14), and [fcSiMe(p-C(6)H(4)CH(2)NMe(2))] (20) yielded the corresponding polyferrocenylsilanes [(fcSiMe{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)})(n)](5), [(fcSi{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)}(2))(n)] (11), [{fcSiMe(C[triple chemical bond]CCH(2)NMe(2))}(n)] (15), and [{fcSiMe(p-C(6)H(4)CH(2)NMe(2))}(n)] (21) with controlled architectures. Further derivatization of 5, 15, and 21 generated water-soluble polyelectrolytes [(fcSiMe{C[triple chemical bond]CCH(2)N(CH(2)CH(2)CH(2)SO(3)Na)(2)})(n)] (6), [{fcSiMe(C[triple chemical bond]CCH(2)NMe(3)OSO(3)Me)}(n)] (7), and [{fcSiMe(p-C(6)H(4)CH(2)NMe(3)OSO(3)Me)}(n)] (22), respectively. The polyelectrolytes were readily soluble in water and NaCl aqueous solutions, with 6 and 22 exhibiting long-term stability in aqueous media. The PFS materials 6 and 22, have been utilized in the layer-by-layer (LbL) self-assembly of electrostatic superlattices. Our preliminary studies have indicated that films made from controlled low molecular-weight PFSs possess a considerably thinner bilayer thickness and higher refractive index than those made from PFSs that have an uncontrolled high molecular-weight. These results suggest that the structure and optical properties of LbL ultra-thin films can be tuned by varying polyelectrolyte chain length. The water-soluble low molecular weight PFSs are also useful materials for a range of applications including LbL self-assembly in highly confined spaces. 相似文献