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191.
This study represents the first application of Ag(I) charge transfer complexation in nonaqueous capillary electrophoresis. This method applies the principles of argentation chromatography to nonaqueous electrophoretic separations and is termed “nonaqueous argentation electrophoresis”. Since the separations are performed in 100% nonaqueous media, the advantages of nonaqueous solvents, such as enhanced solubility and flexibility in selectivity enhancement, compared to an aqueous or mixed hydroorganic solvent, are realized. A variety of compounds were separated. Qualitatively, the separation of eleven sulfonamides in 100% acetonitrile is shown to improve greatly upon the addition of Ag(I). These results also show that nonaqueous argentation electrophoresis provides fast, well-resolved separations of compounds, such as N-containing heterocyclics, that can selectively complex with Ag(I). Migration data and separation selectivities of these compounds by nonaqueous argentation electrophoresis were compared to previous aqueous argentation electrophoresis results. Selectivities were found to be significantly different for the two separation media. Ag(I) complexation provides an effective means of manipulating selectivity in nonaqueous capillary electrophoresis. 相似文献
192.
Hussain HH Babic G Durst T Wright JS Flueraru M Chichirau A Chepelev LL 《The Journal of organic chemistry》2003,68(18):7023-7032
We are attempting to develop novel synthetic antioxidants aimed at retarding the effects of free-radical induced cell damage. In this paper we discuss the design strategy and report the synthesis of seven novel antioxidants, including six catechols and a benzylic phenol. The bond dissociation enthalpy (BDE) for the most active (weakest) OH bond in each molecule was calculated by theoretical methods, as well as the BDE for the semiquinone radical. Reaction rates with the nitrogen-centered free radical DPPH(*) were measured in ethyl acetate. The log of k(DPPH) for bimolecular reaction correlated well with the primary BDE. The correlation between rate constants and calculated BDEs shows that the BDE is a good predictor of antioxidant activity with DPPH(*), suggesting that our design criteria are useful and that these compounds should undergo further testing in cell cultures and in animal models. 相似文献
193.
Karen Wright Fernando FormaggioClaudio Toniolo Roland TörökAntal Péter Michel WakselmanJean-Paul Mazaleyrat 《Tetrahedron letters》2003,44(22):4183-4186
Resolution of trans 3-(9-fluorenylmethyloxycarbonylamino)-1-oxyl-2,2,5,5-tetramethylpyrrolidine-4-carboxylic acid (Fmoc-POAC-OH) was quickly achieved upon esterification with (aR)-1,1′-binaphthyl-2,2′-diol, chromatographic separation of the obtained diastereomers, and facile saponification of the aryl ester function with removal of the chiral auxiliary. 相似文献
194.
Deep eutectic solvents (such as the combination of either urea or glycerol with choline chloride) are effective solvents/organocatalysts for Pictet–Spengler condensations to form carbolines. The reaction conditions are quite mild and do not require additional Bronsted or Lewis acid catalyst. Given the inexpensive, non-toxic, and recyclable nature of the DES, these reaction conditions are simple and highly environmentally friendly. 相似文献
195.
Mixed‐Metal MIL‐100(Sc,M) (M=Al,Cr, Fe) for Lewis Acid Catalysis and Tandem CC Bond Formation and Alcohol Oxidation 下载免费PDF全文
Laura Mitchell Patrick Williamson Barbora Ehrlichová Amanda E. Anderson Valerie R. Seymour Sharon E. Ashbrook Nadia Acerbi Luke M. Daniels Richard I. Walton Matthew L. Clarke Paul A. Wright 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(51):17185-17197
The trivalent metal cations Al3+, Cr3+, and Fe3+ were each introduced, together with Sc3+, into MIL‐100(Sc,M) solid solutions (M=Al, Cr, Fe) by direct synthesis. The substitution has been confirmed by powder X‐ray diffraction (PXRD) and solid‐state NMR, UV/Vis, and X‐ray absorption (XAS) spectroscopy. Mixed Sc/Fe MIL‐100 samples were prepared in which part of the Fe is present as α‐Fe2O3 nanoparticles within the mesoporous cages of the MOF, as shown by XAS, TGA, and PXRD. The catalytic activity of the mixed‐metal catalysts in Lewis acid catalysed Friedel–Crafts additions increases with the amount of Sc present, with the attenuating effect of the second metal decreasing in the order Al>Fe>Cr. Mixed‐metal Sc,Fe materials give acceptable activity: 40 % Fe incorporation only results in a 20 % decrease in activity over the same reaction time and pure product can still be obtained and filtered off after extended reaction times. Supported α‐Fe2O3 nanoparticles were also active Lewis acid species, although less active than Sc3+ in trimer sites. The incorporation of Fe3+ into MIL‐100(Sc) imparts activity for oxidation catalysis and tandem catalytic processes (Lewis acid+oxidation) that make use of both catalytically active framework Sc3+ and Fe3+. A procedure for using these mixed‐metal heterogeneous catalysts has been developed for making ketones from (hetero)aromatics and a hemiacetal. 相似文献
196.
Torsten Roth Vladislav Vasilenko Callum G. M. Benson Hubert Wadepohl Dominic S. Wright Lutz H. Gade 《Chemical science》2015,6(4):2506-2510
A simple, “click” synthetic approach to a new type of hybrid phosph(III)azane/NHC system is described. The presence of the phosphazane P2N2 ring unit, with P atoms flanking the NCN fragment and with this ring perpendicular to the binding site of the NHC, provides unique opportunities for modifying the electronic and steric character of these carbenes. 相似文献
197.
Louise B. Wright J. Pablo Palafox-Hernandez P. Mark Rodger Stefano Corni Tiffany R. Walsh 《Chemical science》2015,6(9):5204-5214
Peptide sequences that can discriminate between gold facets under aqueous conditions offer a promising route to control the growth and organisation of biomimetically-synthesised gold nanoparticles. Knowledge of the interplay between sequence, conformations and interfacial properties is essential for predictable manipulation of these biointerfaces, but the structural connections between a given peptide sequence and its binding affinity remain unclear, impeding practical advances in the field. These structural insights, at atomic-scale resolution, are not easily accessed with experimental approaches, but can be delivered via molecular simulation. A current unmet challenge lies in forging links between predicted adsorption free energies derived from enhanced sampling simulations with the conformational ensemble of the peptide and the water structure at the surface. To meet this challenge, here we use an in situ combination of Replica Exchange with Solute Tempering with Metadynamics simulations to predict the adsorption free energy of a gold-binding peptide sequence, AuBP1, at the aqueous Au(111), Au(100)(1 × 1) and Au(100)(5 × 1) interfaces. We find adsorption to the Au(111) surface is stronger than to Au(100), irrespective of the reconstruction status of the latter. Our predicted free energies agree with experiment, and correlate with trends in interfacial water structuring. For gold, surface hydration is predicted as a chief determining factor in peptide–surface recognition. Our findings can be used to suggest how shaped seed-nanocrystals of Au, in partnership with AuBP1, could be used to control AuNP nanoparticle morphology. 相似文献
198.
Prof. Margaret A. Brimble Dr. Pat J. Edwards Dr. Paul W. R. Harris Dr. Gillian E. Norris Dr. Mark L. Patchett Tom H. Wright Dr. Sung‐Hyun Yang Dr. Sarah E. Carley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(9):3556-3561
The first total synthesis of glycocin F, a uniquely diglycosylated antimicrobial peptide bearing a rare S‐linked N‐acetylglucosamine (GlcNAc) moiety in addition to an O‐linked GlcNAc, has been accomplished using a native chemical ligation strategy. The synthetic and naturally occurring peptides were compared by HPLC, mass spectrometry, NMR and CD spectroscopy, and their stability towards chymotrypsin digestion and antimicrobial activity were measured. This is the first comprehensive structural and functional comparison of a naturally occurring glycocin with an active synthetic analogue. 相似文献
199.
A Family of Molecular Sieves Containing Framework‐Bound Organic Structure‐Directing Agents 下载免费PDF全文
Jun Kyu Lee Dr. Jiho Shin Nak Ho Ahn Alessandro Turrina Dr. Min Bum Park Dr. Youngchul Byun Prof. Sung June Cho Prof. Paul A. Wright Prof. Suk Bong Hong 《Angewandte Chemie (International ed. in English)》2015,54(38):11097-11101
Organic structure‐directing agents (OSDAs), such as quaternary ammonium cations and amines, used in the synthesis of zeolites and related crystalline microporous oxides usually end up entrapped inside the void spaces of the crystallized inorganic host lattice. But none of them is known to form direct chemical bonds to the framework of these industrially important catalysts and adsorbents. We demonstrate that ECR‐40, currently regarded as a typical silicoaluminophosphate molecular sieve, constitutes instead a new family of inorganic‐organic hybrid networks in which the OSDAs are covalently bonded to the inorganic framework. ECR‐40 crystallization begins with the formation of an Al–OSDA complex in the liquid phase in which the Al is octahedrally coordinated. This unit is incorporated in the crystallizing ECR‐40. Subsequent removal of framework‐bound OSDAs generates Al‐O‐Al linkages in a fully tetrahedrally coordinated framework. 相似文献
200.
Locating Gases in Porous Materials: Cryogenic Loading of Fuel‐Related Gases Into a Sc‐based Metal–Organic Framework under Extreme Pressures 下载免费PDF全文
Jorge Sotelo Dr. Christopher H. Woodall Dr. Dave R. Allan Eugene Gregoryanz Dr. Ross T. Howie Konstantin V. Kamenev Dr. Michael R. Probert Prof. Paul A. Wright Dr. Stephen A. Moggach 《Angewandte Chemie (International ed. in English)》2015,54(45):13332-13336
An alternative approach to loading metal organic frameworks with gas molecules at high (kbar) pressures is reported. The technique, which uses liquefied gases as pressure transmitting media within a diamond anvil cell along with a single‐crystal of a porous metal–organic framework, is demonstrated to have considerable advantages over other gas‐loading methods when investigating host–guest interactions. Specifically, loading the metal–organic framework Sc2BDC3 with liquefied CO2 at 2 kbar reveals the presence of three adsorption sites, one previously unreported, and resolves previous inconsistencies between structural data and adsorption isotherms. A further study with supercritical CH4 at 3–25 kbar demonstrates hyperfilling of the Sc2BDC3 and two high‐pressure displacive and reversible phase transitions are induced as the filled MOF adapts to reduce the volume of the system. 相似文献