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81.
Etienne MA Aucoin JP Fu Y McCarley RL Hammer RP 《Journal of the American Chemical Society》2006,128(11):3522-3523
We have prepared two peptides based on the hydrophobic core (Lys-Leu-Val-Phe-Phe) of amyloid beta-protein (Abeta) that contain alpha,alpha-disubstituted amino acids at alternating positions, but differ in the positioning of the oligolysine chain (AMY-1, C-terminus; AMY-2, N-terminus). We have studied the effects of AMY-1 and AMY-2 on the aggregation of Abeta and find that, at stoichiometric concentrations, both peptides completely stop Abeta fibril growth. Equimolar mixtures of AMY-1 and Abeta form only globular aggregates as imaged by scanning force microscopy and transmission electron microscopy. These samples show no signs of protofibrillar or fibrillar material even after prolonged periods of time (4.5 months). Also, 10 mol % of AMY-1 prevents Abeta self-assembly for long periods of time; aged samples (4.5 months) show only a few protofibrillar or fibrillar aggregates. Circular dichroism spectroscopy of equimolar mixtures of AMY-1 and Abeta show that the secondary structure of the mixture changes over time and progresses to a predominantly beta-sheet structure, which is consistent with the design of these inhibitors preferring a sheet-like conformation. Changing the position of the charged tail on the peptide, AMY-2 interacts with Abeta differently in that equimolar mixtures form large ( approximately 1 mum) globular aggregates which do not progress to fibrils, but precipitate out of solution. The differences in the aggregation mediated by the two peptides is discussed in terms of a model where the inhibitors act as cosurfactants that interfere with the native ability of Abeta to self-assemble by disrupting hydrophobic interactions either at the C-terminus or N-terminus of Abeta. 相似文献
82.
Cedric Samuel Yvan Chalamet Fernande Boisson Jean‐Charles Majesté Frédéric Becquart Etienne Fleury 《Journal of polymer science. Part A, Polymer chemistry》2014,52(4):493-503
A one‐step process is reported to directly synthesize blends of poly(trimethylene carbonate) (PTMC) with a modified granular starch. Trimethylene Carbonate (TMC) ring‐opening polymerization is performed in the presence of native starch particles in bulk conditions at 150 °C and the efficiency of metal‐free organic catalysts (TBD and phosphazene superbases P1‐t‐Oct, P2‐t‐bu, and P4‐t‐bu) are investigated to replace the organo‐metallic stannous octanoate initiator. TMC monomer is successively converted into PTMC and the robustness of organic catalysts is highlighted with significant activities at very low concentrations (<100 ppm), where stannous octanoate is inefficient. Reactivity of starch toward TMC ROP is deeply investigated by NMR techniques and a starch‐graft‐PTMC is indirectly evidenced. Starch substitution degree reaches 0.9% indicating that PTMC grafting only occurs at the surface of swollen granular starch. PTMC graft length from the starch surface remained low in the range 2–12 and model ROP reactions highlight the role of TMC hydrolysis on PTMC graft length. Despite low PTMC grafts, a fine dispersion of intact starch particles into the PTMC matrix is evidenced. Consequently, metal‐free organic catalysts at low concentrations are promising candidates for synthesizing blends of PTMC with high loadings of surface‐modified starch (32% by weight) in 2 min within a one‐step process. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 493–503 相似文献
83.
A Bioinspired Molybdenum Complex as a Catalyst for the Photo‐ and Electroreduction of Protons 下载免费PDF全文
Jean‐Philippe Porcher Thibault Fogeron Dr. Maria Gomez‐Mingot Dr. Etienne Derat Lise‐Marie Chamoreau Dr. Yun Li Prof. Marc Fontecave 《Angewandte Chemie (International ed. in English)》2015,54(47):14090-14093
A molybdenum–dithiolene–oxo complex was prepared as a model of some active sites of Mo/W‐dependent enzymes. The ligand, a quinoxaline–pyran‐fused dithiolene, mimics molybdopterin present in these active sites. For the first time, this type of complex was shown to be active as a catalyst for the photoreduction of protons with excellent turnover numbers (500) and good stability in aqueous/organic media and for the electroreduction of protons in acetonitrile with remarkable rate constants (1030 s?1 at ?1.3 V versus Ag/AgCl). DFT calculations provided insight into the catalytic cycle of the reaction, suggesting that the oxo ligand plays a key role in proton exchange. These results provide a basis to optimize this new class of H2‐evolving catalysts. 相似文献
84.
Michel Auriel Edmond De Hoffmann Philippe Scheers Etienne Deffense 《Journal of mass spectrometry : JMS》1989,24(1):1-7
The mass spectra of some 1,3,4-substituted azetidin-2-ones are measured. Fragmentation pathways are confirmed by use of both high-resolution and mass-analysed ion kinetic energy. They are consistent with the possible [2 + 2]- cycloadditions through which the azetidin-2-ones may be synthesized. More attention has to be paid to further fragmentations of the main fragments in assessing the preferred fragmentation mode. Influence of side-chain substituents is discussed. 相似文献
85.
Louguet S Kumar AC Sigaud G Duguet E Lecommandoux S Schatz C 《Journal of colloid and interface science》2011,359(2):413-422
The adsorption behavior of poly(ethylene oxide)-b-poly(L-lysine) (PEO(113)-b-PLL(10)) copolymer onto silica nanoparticles was investigated in phosphate buffer at pH 7.4 by means of dynamic light scattering, zeta potential, adsorption isotherms and microcalorimetry measurements. Both blocks have an affinity for the silica surface through hydrogen bonding (PEO and PLL) or electrostatic interactions (PLL). Competitive adsorption experiments from a mixture of PEO and PLL homopolymers evidenced greater interactions of PLL with silica while displacement experiments even revealed that free PLL chains could desorb PEO chains from the particle surface. This allowed us to better understand the adsorption mechanism of PEO-b-PLL copolymer at the silica surface. At low surface coverage, both blocks adsorbed in flat conformation leading to the flocculation of the particles as neither steric nor electrostatic forces could take place at the silica surface. The addition of a large excess of copolymer favoured the dispersion of flocs according to a presumed mechanism where PLL blocks of incoming copolymer chains preferentially adsorbed to the surface by displacing already adsorbed PEO blocks. The gradual addition of silica particles to an excess of PEO-b-PLL copolymer solution was the preferred method for particle coating as it favoured equilibrium conditions where the copolymer formed an anchor-buoy (PLL-PEO) structure with stabilizing properties at the silica-water interface. 相似文献
86.
Wayland E. Noland Christopher L. Etienne Nicholas P. Lanzatella 《Journal of heterocyclic chemistry》2011,48(2):381-388
Vinylindoles and vinylpyrroles were prepared from their corresponding aldehydes or ketones using the Peterson olefination, or by use of the Nysted reagent, a commercially available gem‐dimetallic compound. The two methods provide efficient and convenient access to these useful heterocyclic 1,3‐diene systems. J. Heterocyclic Chem., (2011). 相似文献
87.
In our continuous search for alpha-glucosidase inhibitors from plants, four new depsidones named brevipsidones A-D (1-4) were isolated from stem bark of Garcinia brevipedicellata together with known damnacanthal, scopoletin and a mixture of stigmasterol and beta-sitosterol. Structural elucidations were made by spectroscopic analyses including 2D-NMR data. 相似文献
88.
The present work reports on the synthesis and evaluation of a crosslinkable thiolated gelatin derivative. The effect of varying two parameters including the pH of the reaction buffer and the thiolating agent applied (i.e. N-acetylhomocysteine thiolactone versus Traut’s reagent) on the obtained modification degree was studied in a first part. The gelatin derivatives synthesized starting from N-acetylhomocysteine thiolactone and Traut’s reagent were characterized in depth using size exclusion chromatography and UV–VIS spectrophotometry. In a subsequent part of the present work, hydrogel films were prepared starting from the thiolated gelatin derivative developed using N-acetylhomocysteine thiolactone. The contributions of both the chemical and the physical crosslinking of the hydrogels developed were studied in depth using rheology, swelling experiments and texturometry. The results indicate that the physical structuring, inherent to gelatin, contributes to a large extent to the mechanical properties. However, the chemical crosslinking mostly determines the final hydrogel properties and can be controlled to a large extent. The gelatin-based gels are flexible, strong and transparent. A major advantage of disulfide-crosslinked hydrogels is the fact that the crosslinking is reversible. The latter could be interesting in view of future applications as cell carriers for tissue engineering. 相似文献
89.
The cytochrome P450 (P450) enzymes are mainly localized to the endoplasmic reticulum (ER), where they function within catalytic
complexes metabolizing xenobiotics and some endogenous substrates. However, certain members of families 1–3 were also found
in other subcellular compartments, such as mitochondria, plasma membrane, and lysosomes. The physiological function of these
enzymes in non-ER locations is not known, although plasma-membrane-associated P450s have been described to be catalytically
active and to participate in immune-mediated reactions with autoantibody formation that can trigger drug-induced hepatitis.
Several retention/retrieval mechanisms are active in the ER retention of the P450s and inverse integration of the translated
P450 into the ER membrane appears to be responsible for transport to the plasma membrane. Furthermore, hydrophilic motifs
in the NH2-terminal part have been suggested to be important for mitochondrial import. Phosphorylation of P450s has been described to
be important for increased rate of degradation as well as for targeting into mitochondria. It was also suggested that the
mitochondria-targeted P450s from families 1–3 could be active in drug metabolism using an alternative electron transport chain.
In this review we present an update of the field emphasizing studies concerning localization, posttranslational modification,
such as phosphorylation, and intracellular transport of microsomal P450s. 相似文献
90.
Kesara Na-Bangchang Etienne Anagalou Guirou Anurak Cheomung Juntra Karbwang 《Chromatographia》2014,77(7-8):561-569
Primaquine (PQ) is the only 8-aminoquinoline antimalarial drug in clinical use because of its unique action on hypnozoites and gametocytes of Plasmodium species. We report here simple, sensitive and specific assay methods for the determination of PQ in human whole blood and dried blood spot (DBS) samples using high-performance liquid chromatography and liquid chromatography-mass spectrometry, respectively. Sample preparation was performed by a single or two-step liquid-liquid extraction with organic solvents. For whole blood analysis, separation was obtained on a reversed-phase C18 column with the mobile phase consisting of 0.25 % diethylamine and acetonitrile (7:3, v:v) running at a flow rate of 1.0 ml min?1. UV detection was at the wavelength 263 nm. For DBS analysis, separation was obtained on a reversed-phase column with the mobile phase consisting of methanol and 0.1 formic acid (1:3, v:v) running at a flow rate of 0.5 ml min?1. The selected ions generated by electrospray ionization were detected using mass spectrometer. Good precision and accuracy (both within-day and day-to-day assays) were obtained at the concentration ranges under investigation. Limits of quantification for PQ were accepted as 25 ng ml?1 using 500 μl whole blood and 5 ng ml?1 using 80 μl DBS samples. The mean recoveries for PQ and internal standard pyrimethamine (PYR) for both whole blood and DBS were over 70 %. The methods were successfully applied for a clinical pharmacology study of PQ in patients with Plasmodium vivax. Excellent correlation (r 2 = 0.997) was observed between the analysis of PQ in paired whole blood and DBS samples. 相似文献