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981.
982.
Laurent Blasco Lucie Duracher Jean‐Pierre Forestier Laurence Vian Gilberte Marti‐Mestres 《Journal of Dispersion Science and Technology》2013,34(6):799-810
This work presents the behavior of bio‐mimetic monoglycerides at the squalene/water interface. The study was done in the so‐called “static” mode using the “pendant drop method”, enabling us to characterize these molecules according to the value of their critical efficiency concentration (CEC), their maximum surface excess concentration (Γ∞), the efficiency of the surface tension reduction parameter (pC20), and the minimum value of their interfacial tension (γmin). It also permitted the study of the influence of the structure of the carbon chain of those monoglycerides on their interfacial behavior. The analysis of the different parameters shows that monoglycerides with small hydrocarbon chains, monoglycerides with one or more double bonds, and monoglycerides possessing a hydroxyl function grafted in the middle of the chain constitute excellent surfactants. Two different groups can be found: one group composed of short saturated hydrocarbon chain monoglycerides (C12∶0 to C16∶0) and long hydrocarbon chain monoglycerides (C18∶0 to C22∶0); the second group, composed of unsaturated hydrocarbon chain monoglycerides, also includes hydroxystearate and isostearate monoglycerides. The first group could be used for the formulation of “hydrating” cosmetic products having secondary droplets, the second group for W/O emulsions. 相似文献
983.
Shigella flexneri serotypes 6 and 6a are closely related bacteria causing shigellosis in humans. Their O-antigens are {→4)-β-d-GalpA-(1→3)-β-d-GalpNAc-(1→2)-[3Ac/4Ac]-α-l-Rhap-(1→2)-α-l-Rhap-(1→}n acidic polysaccharides ({ABAcCD}n), which only differ in the degree of O-acetylation. A concise synthesis of two disaccharides (BC, BAcC) and four trisaccharides, representing portions and/or analogs of the O-antigens, is described. A protected intermediate compatible with late stage 3C-O-acetylation, and/or galactosyl (A°) to galacturonic acid (A) conversion, was designed and assembled from trichloroacetimidate and thioglycoside donors tuned for high yielding glycosylation and excellent stereocontrol. The galacturonic moiety was efficiently introduced from galactose using a TEMPO/NaOCl/NaClO2-based oxidation protocol optimized for full compatibility with sensitive moieties, such as allyl ethers and acetates. Final Pd/C-mediated deprotection provided the targets, including the propyl glycoside ABAcC, its non O-acetylated counterpart ABC, and the non acidic analogs A°BAcC and A°BC. The BC and ABC oligosaccharides are also portions of the O-antigen from Escherichia coli O147, which causes diarrhea in pigs. 相似文献
984.
Sébastien Gottis Lara-Isabel Rodriguez Régis Laurent Inmaculada Angurell Miquel Seco Oriol Rossell Jean-Pierre Majoral Anne-Marie Caminade 《Tetrahedron letters》2013
The first association of carbosilane dendrons (having a phosphine at the focal point) with phosphorhydrazone dendrons (having a thiophosphoryl azide at the focal point) has been successfully carried out by ‘Staudinger click’ reaction. The corresponding Janus dendrimers possess the characteristics of both components; they are oily as the carbosilane dendrons, and they can be easily functionalized as the phosphorhydrazone dendrons. 相似文献
985.
Fouzia Jbilou Catherine Joly Sophie Galland Laurent Belard Valérie Desjardin Rémy Bayard Patrice Dole Pascal Degraeve 《Polymer Testing》2013,32(8):1565-1575
Plasticised corn flour/poly(butylene succinate-co-butylene adipate) (PBSA) materials were prepared by extrusion and injection in order to study the impact of PBSA ratio on their physicochemical properties and biodegradability. Scanning electron microscopy observations showed that corn flour and PBSA are incompatible. Three types of morphology have been observed: (i) starch dispersed in a PBSA matrix, (ii) a “co-continuous-like” morphology of starch and PBSA, and (iii) PBSA dispersed in a starch matrix. As expected, the extent of plasticised corn flour starch hydrolysis by amylolytic enzymes decreased when the amount of PBSA increased. Addition of a lipase to hydrolyse PBSA ester bonds enhanced enzymatic hydrolysis of starch by amylolytic enzymes in materials where PBSA formed a continuous phase. This suggests that PBSA formed a barrier restricting the access of amylolytic enzymes to starch. This was consistent with aerobic and anaerobic biodegradation assays, which also showed lower biodegradability of materials containing a majority of PBSA. 相似文献
986.
987.
Dr. Lingfang Wang Dr. Christos E. Kefalidis Dr. Sourisak Sinbandhit Dr. Vincent Dorcet Prof. Dr. Jean‐François Carpentier Prof. Dr. Laurent Maron Dr. Yann Sarazin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(40):13463-13478
The tin(II) complexes {LOx}Sn(X) ({LOx}?=aminophenolate ancillary) containing amido ( 1 – 4 ), chloro ( 5 ), or lactyl ( 6 ) coligands (X) promote the ring‐opening polymerization (ROP) of cyclic esters. Complex 6 , which models the first insertion of L ‐lactide, initiates the living ROP of L ‐LA on its own, but the amido derivatives 1 – 4 require the addition of alcohol to do so. Upon addition of one to ten equivalents of iPrOH, precatalysts 1 – 4 promote the ROP of trimethylene carbonate (TMC); yet, hardly any activity is observed if tert‐butyl (R)‐lactate is used instead of iPrOH. Strong inhibition of the reactivity of TMC is also detected for the simultaneous copolymerization of L ‐LA and TMC, or for the block copolymerization of TMC after that of L ‐LA. Experimental and computational data for the {LOx}Sn(OR) complexes (OR=lactyl or lactidyl) replicating the active species during the tin(II)‐mediated ROP of L ‐LA demonstrate that the formation of a five‐membered chelate is largely favored over that of an eight‐membered one, and that it constitutes the resting state of the catalyst during this (co)polymerization. Comprehensive DFT calculations show that, out of the four possible monomer insertion sequences during simultaneous copolymerization of L ‐LA and TMC: 1) TMC then TMC, 2) TMC then L ‐LA, 3) L ‐LA then L ‐LA, and 4) L ‐LA then TMC, the first three are possible. By contrast, insertion of L ‐LA followed by that of TMC (i.e., insertion sequence 4) is endothermic by +1.1 kcal mol?1, which compares unfavorably with consecutive insertions of two L ‐LA units (i.e., insertion sequence 3) (?10.2 kcal mol?1). The copolymerization of L ‐LA and TMC thus proceeds under thermodynamic control. 相似文献
988.
Michaël Lemoine Claire-Helene Brachais Gilles Boni Laurent Brachais Jean-Pierre Couvercelle 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(2):100-107
Extension of hydroxytelechelic polybutadiene oligomers ( 3200 g/mol) is performed in mild conditions, in order to avoid backbone modifications, using succinic anhydride or methylenedicyclohexyl diisocyanate. The two routes present significative extension of the initial oligomers. Extension through the anhydride route, in the presence of DCC and DMAP, leads to new hydroxytelechelic oligomers ( 8000 g/mol). Extension through the diisocyanate route, catalyzed by DBTL at 65°C leads to hydroxytelechelic oligomers of higher average molecular weight ( 20000 g/mol). New materials are characterized by FTIR/1H-NMR and changes in their Tg according to , are discussed. The influence of reaction time on the length of the macromolecular chains is also studied. 相似文献
989.
Aleer M. Yol David E. Dabney Shih-Fan Wang Boyd A. Laurent Mark D. Foster Roderic P. Quirk Scott M. Grayson Chrys Wesdemiotis 《Journal of the American Society for Mass Spectrometry》2013,24(1):74-82
[M + Ag]+ ions from cyclic and linear polystyrenes and polybutadienes, formed by matrix-assisted laser desorption ionization (MALDI), give rise to significantly different fragmentation patterns in tandem mass spectrometry (MS2) experiments. In both cases, fragmentation starts with homolytic cleavage at the weakest bond, usually a C–C bond, to generate two radicals. From linear structures, the separated radicals depolymerize extensively by monomer losses and backbiting rearrangements, leading to low-mass radical ions and much less abundant medium- and high-mass closed-shell fragments that contain one of the original end groups, along with internal fragments. With cyclic structures, depolymerization is less efficient, as it can readily be terminated by intramolecular H-atom transfer between the still interconnected radical sites (disproportionation). These differences in fragmentation reactivity result in substantially different fragment ion distributions in the MS2 spectra. Simple inspection of the relative intensities of low- versus high-mass fragments permits conclusive determination of the macromolecular architecture, while full spectral interpretation reveals the individual end groups of linear polymers or the identity of the linker used to form the cyclic polymer. Figure
Macrocyclic and linear polystyrene and polydiene architectures are conclusively distinguished by the MS2 fragmentation patterns of Ag+-cationized oligomers. 相似文献
990.
Dr. Nicolas Popoff Dr. Jeff Espinas Dr. Jérémie Pelletier Benoît Macqueron Dr. Kai C. Szeto Olivier Boyron Dr. Christophe Boisson Dr. Iker Del Rosal Dr. Laurent Maron Dr. Aimery De Mallmann Dr. Régis M. Gauvin Dr. Mostafa Taoufik 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):964-973
Homoleptic benzyl derivatives of titanium and zirconium have been grafted onto silica that was dehydroxylated at 200 and 700 °C, thereby affording bi‐grafted and mono‐grafted single‐site species, respectively, as shown by a combination of experimental techniques (IR, MAS NMR, EXAFS, and elemental analysis) and theoretical calculations. Marked differences between these compounds and their neopentyl analogues are discussed and rationalized by using DFT. These differences were assigned to the selectivity of the grafting process, which, depending on the structure of the molecular precursors, led to different outcomes in terms of the mono‐ versus bi‐grafted species for the same surface concentration of silanol species. The benzylzirconium derivatives were active towards ethylene polymerization in the absence of an activator and the bi‐grafted species displayed higher activity than their mono‐grafted analogues. In contrast, the benzyltitanium and neopentylzirconium counterparts were not active under similar reaction conditions. 相似文献