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991.
992.
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
993.
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
994.
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
995.
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
996.
Dr. Matthew P. Conley Ruben M. Drost Dr. Mathieu Baffert Dr. David Gajan Prof. Dr. Cornelis Elsevier Dr. W. Trent Franks Prof. Dr. Hartmut Oschkinat Laurent Veyre Alexandre Zagdoun Dr. Aaron Rossini Dr. Moreno Lelli Dr. Anne Lesage Dr. Gilles Casano Dr. Olivier Ouari Prof. Dr. Paul Tordo Prof. Dr. Lyndon Emsley Prof. Dr. Christophe Copéret Dr. Chloé Thieuleux 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12234-12238
997.
Benjamin Briois Tsuguyuki Saito Christian Pétrier Jean-Luc Putaux Yoshiharu Nishiyama Laurent Heux Sonia Molina-Boisseau 《Cellulose (London, England)》2013,20(2):597-603
Aqueous suspensions of dispersed Glaucocystis cellulose microfibrils were sonicated at 4 °C for 3 h, using 24 kHz ultrasonic waves. This treatment induced a variety of ultrastructural defects, as the microfibrils became not only shortened, but also presented substantial damage materialized by kinks and subfibrillation. Upon analysis by X-ray diffraction and 13C solid-state NMR spectroscopy, it was found that the initial sample that contained 90 % of cellulose Iα allomorph became, to a large extent, unexpectedly converted into the Iβ phase, while the loss of crystallinity was only moderate during the sonication treatment. 相似文献
998.
Mihaela Mândru Constantin Ciobanu Stelian Vlad Maria Butnaru Laurent Lebrun Marcel Popa 《Central European Journal of Chemistry》2013,11(4):542-553
This paper is focused on the preparation and physicochemical characterization of two poly(ester ether urethane)s with rifampicin in their matrix and different molar concentrations of urethane groups. The polyurethanes with rifampicin were processed as asymmetrical microporous membranes by a phase inversion method and characterized by attenuated total reflection — Fourier transform infrared (ATR-FTIR) spectroscopy and differential scanning calorimetry (DSC). The influence of the surface morphology in the release of drug compounds was analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle, and water uptake. The release of rifampicin depends on the molar concentration of urethane groups and also on the surface morphology of the polyurethane membranes. The antibacterial activity was evaluated with S. Epidermidis RP 62 A and P. Aeruginosa ATCC 1544. Finally, the biocompatibility of the polyurethane membranes was studied with human dermal fibroblasts (HDF) to evaluate the potential biomedical applications. 相似文献
999.
Lutfi Arif Ngah Olivier Alibart Laurent Labont Virginia D'Auria Sbastien Tanzilli 《Laser \u0026amp; Photonics Reviews》2015,9(2):L1-L5
The realization of an ultra‐fast source of heralded single photons emitted at the wavelength of 1540 nm is reported. The presented strategy is based on state‐of‐the‐art telecom technology, combined with off‐the‐shelf fiber components and waveguide non‐linear stages pumped by a 10 GHz repetition rate laser. The single photons are heralded at a rate as high as 2.1 MHz with a heralding efficiency of 42%. Single‐photon character of the source is inferred by measuring the second‐order autocorrelation function. For the highest heralding rate, a value as low as 0.023 is found. This not only proves negligible multi‐photon contributions but also represents one of the best measured values reported to date for heralding rates in the MHz regime. These performances, associated with a device‐like configuration, are key ingredients for both fast and secure quantum communication protocols.
1000.
Isabelle Martiel Laurent Sagalowicz Raffaele Mezzenga 《Advances in colloid and interface science》2014
Phospholipids are ubiquitous cell membrane components and relatively well-accepted ingredients due to their natural origin. Phosphatidylcholine (PC) in particular offers a promising alternative to monoglycerides for lyotropic liquid crystalline (LLC) delivery system applications in the food, cosmetics and pharmaceutical industries, provided its strong tendency to form zero-mean curvature lamellar mesophases in water can be overcome. Higher negative curvatures are usually reached through the addition of a third lipid component, forming a ternary diagram phospholipid/water/oil. 相似文献