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991.
Lu C Kirsch B Zimmer C de Jong JC Henn C Maurer CK Müsken M Häussler S Steinbach A Hartmann RW 《Chemistry & biology》2012,19(3):381-390
The pqs quorum sensing communication system of Pseudomonas aeruginosa controls virulence factor production and is involved in biofilm formation, therefore playing an important role for pathogenicity. In order to attenuate P. aeruginosa pathogenicity, we followed a ligand-based drug design approach and synthesized a series of compounds targeting PqsR, the receptor of the pqs system. In vitro evaluation using a reporter gene assay in Escherichia coli led to the discovery of the first competitive PqsR antagonists, which are highly potent (K(d,app) of compound 20: 7 nM). These antagonists are able to reduce the production of the virulence factor pyocyanin in P. aeruginosa. Our finding offers insights into the ligand-receptor interaction of PqsR and provides a promising starting point for further drug design. 相似文献
992.
Ina Neunzig Maria Widjaja C?lin-Aurel Dr?gan Frank T. Peters Hans H. Maurer Matthias Bureik 《Applied biochemistry and biotechnology》2012,168(4):785-796
The use of human cytochrome P450 (CYP) enzymes is increasing for the production of drug metabolites used for drug safety testing and doping analysis. Major challenges are high-priced cofactors, poor stability, and comparatively low activities. We have shown previously that production of specific metabolites in milligrams to gram scale is feasible using human CYPs recombinantly expressed in fission yeast. In this study, we sought to improve the activities of human CYP3A enzymes by genetic engineering. Two side chains (Pro293 and Arg409) of known activating human CYP3A polymorphic variants were??separately or together??introduced into the wild-type forms of each of the three enzymes CYP3A4, CYP3A5, and CYP3A7, respectively. Different effects of the two mutations and their combination on enzyme activity were monitored using both polar and nonpolar substrates. Interestingly, the CYP3A7 double mutant displayed a strong increase in activity with respect to testosterone 6??-hydroxylation (300?% of wild-type activity) and luciferin-6??-pentafluoro-benzyl ether turnover (400?% compared to wild type), while the single mutant CYP3A5Pro293 showed 370 and 400?% of wild-type activity towards 6??-hydroxylation of testosterone and 16??-hydroxylation of dehydroepiandrosterone, respectively. Overall, six out of seven newly created mutants displayed increased activity with at least one of the tested substrates. These results support the notion that pharmacogenetic knowledge can directly contribute to the improvement of biotechnological processes. 相似文献
993.
Sereina Riniker Luzi J. Barandun François Diederich Oliver Krämer Andreas Steffen Wilfred F. van Gunsteren 《Journal of computer-aided molecular design》2012,26(12):1293-1309
Water molecules in the binding pocket of a protein and their role in ligand binding have increasingly raised interest in recent years. Displacement of such water molecules by ligand atoms can be either favourable or unfavourable for ligand binding depending on the change in free enthalpy. In this study, we investigate the displacement of water molecules by an apolar probe in the binding pocket of two proteins, cyclin-dependent kinase 2 and tRNA-guanine transglycosylase, using the method of enveloping distribution sampling (EDS) to obtain free enthalpy differences. In both cases, a ligand core is placed inside the respective pocket and the remaining water molecules are converted to apolar probes, both individually and in pairs. The free enthalpy difference between a water molecule and a CH3 group at the same location in the pocket in comparison to their presence in bulk solution calculated from EDS molecular dynamics simulations corresponds to the binding free enthalpy of CH3 at this location. From the free enthalpy difference and the enthalpy difference, the entropic contribution of the displacement can be obtained too. The overlay of the resulting occupancy volumes of the water molecules with crystal structures of analogous ligands shows qualitative correlation between experimentally measured inhibition constants and the calculated free enthalpy differences. Thus, such an EDS analysis of the water molecules in the binding pocket may give valuable insight for potency optimization in drug design. 相似文献
994.
Water-insoluble amines (dissolved in an organic solvent/organic solvent mixture) are often used for the extractive recovery of carboxylic acids from aqueous phases. The basic design of the extraction process requires a thermodynamic framework that should be able to describe the liquid–liquid phase equilibrium not only in the phase forming systems (water + carboxylic acid + organic solvent + reactive extractant), but also when the aqueous feed phase contains additionally small amounts of strong electrolytes. Even small amounts of strong electrolytes might considerably reduce the recovery rate. In part I of this series such a model was presented and discussed for methyl isobutyl ketone as organic solvent and tri-n-octylamine (TnOA) as the chemical extractant. The present part II is to demonstrate that the procedures/methods described for methyl isobutyl ketone as organic solvent can be applied also for other organic solvents. By way of example, here toluene is that organic solvent. New experimental results are reported for the influence of sodium chloride, sodium nitrate, sodium sulfate, sodium acetate and hydrochloric acid on the partitioning of acetic acid to coexisting aqueous/organic liquid phases of the system (water + toluene + tri-n-octylamine) at 25 °C. An extension/adaptation of the previously published thermodynamic framework is successfully applied to describe/predict the new experimental liquid–liquid phase equilibrium data. 相似文献
995.
Xiaonan Ma Jan Maier Michael Wenzel Alexandra Friedrich Andreas Steffen Todd B. Marder Roland Mitri Tobias Brixner 《Chemical science》2020,11(34):9198
Reactive ortho-benzyne derivatives are believed to be the initial products of liquid-phase [4 + 2]-cycloadditions between a 1,3-diyne and an alkyne via what is known as a hexadehydro-Diels–Alder (HDDA) reaction. The UV/VIS spectroscopic observation of o-benzyne derivatives and their photochemical dynamics in solution, however, have not been reported previously. Herein, we report direct UV/VIS spectroscopic evidence for the existence of an o-benzyne in solution, and establish the dynamics of its formation in a photoinduced reaction. For this purpose, we investigated a bis-diyne compound using femtosecond transient absorption spectroscopy in the ultraviolet/visible region. In the first step, we observe excited-state isomerization on a sub-10 ps time scale. For identification of the o-benzyne species formed within 50–70 ps, and the corresponding photochemical hexadehydro-Diels–Alder (hν-HDDA) reactions, we employed two intermolecular trapping strategies. In the first case, the o-benzyne was trapped by a second bis-diyne, i.e., self-trapping. The self-trapping products were then identified in the transient absorption experiments by comparing their spectral features to those of the isolated products. In the second case, we used perylene for trapping and reconstructed the spectrum of the trapping product by removing the contribution of irrelevant species from the experimentally observed spectra. Taken together, the UV/VIS spectroscopic data provide a consistent picture for o-benzyne derivatives in solution as the products of photo-initiated HDDA reactions, and we deduce the time scales for their formation.We report the transient ultraviolet/visible absorption spectrum of an o-benzyne species in solution for the first time. 相似文献
996.
Low resolution and high resolution MS for studies on the metabolism and toxicological detection of the new psychoactive substance methoxypiperamide (MeOP) 下载免费PDF全文
Markus R. Meyer Anna Holderbaum Pierce Kavanagh Hans H. Maurer 《Journal of mass spectrometry : JMS》2015,50(10):1163-1174
In 2013, the new psychoactive substance methoxypiperamide (MeOP) was first reported to the European Monitoring Centre for Drug and Drug Addiction. Its structural similarity to already controlled piperazine designer drugs might have contributed to the decision to offer MeOP for online purchase. The aims of this work were to identify the phase I/II metabolites of MeOP in rat urine and the human cytochrome P450 (CYP) isoenzymes responsible for the initial metabolic steps. Finally, the detectability of MeOP in rat urine by gas chromatography–mass spectrometry (GC‐MS) and liquid chromatography coupled with multistage mass spectrometry (LC‐MSn) standard urine screening approaches (SUSAs) was evaluated. After sample preparation by cleavage of conjugates followed by extraction for elucidating phase I metabolites, the analytes were separated and identified by GC‐MS as well as liquid chromatography‐high resolution‐tandem mass spectrometry (LC‐HR‐MS/MS). For detection of phase II metabolites, the analytes were separated and identified after urine precipitation followed by LC‐HR‐MS/MS. The following metabolic steps could be postulated: hydrolysis of the amide, N‐oxide formation, N‐ and/or O‐demethylation, oxidation of the piperazine ring to the corresponding keto‐piperazine, piperazine ring opening followed by oxidation of a methylene group to the corresponding imide, and hydroxylation of the phenyl group. Furthermore, N‐acetylation, glucuronidation and sulfation were observed. Using human CYPs, CYP1A2, CYP2C19, CYP2D6, and/or CYP3A4 were found to catalyze N‐oxide formation and N‐, O‐demethylation and/or oxidation. Mostly MeOP and N‐oxide‐MeOP but to a minor degree also other metabolites could be detected in the GC‐MS and LC‐MSn SUSAs. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
997.
Univalent Gallium Complexes of Simple and ansa‐Arene Ligands: Effects on the Polymerization of Isobutylene 下载免费PDF全文
Martin R. Lichtenthaler Steffen Maurer Robert J. Mangan Florian Stahl Florian Mönkemeyer Julian Hamann Prof. Dr. Ingo Krossing 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):157-165
Using [Ga(C6H5F)2]+[Al(ORF)4]?( 1 ) (RF=C(CF3)3) as starting material, we isolated bis‐ and tris‐η6‐coordinated gallium(I) arene complex salts of p‐xylene (1,4‐Me2C6H4), hexamethylbenzene (C6Me6), diphenylethane (PhC2H4Ph), and m‐terphenyl (1,3‐Ph2C6H4): [Ga(1,4‐Me2C6H4)2.5]+ ( 2+ ), [Ga(C6Me6)2]+ ( 3+ ), [Ga(PhC2H4Ph)]+ ( 4+ ) and [(C6H5F)Ga(μ‐1,3‐Ph2C6H4)2Ga(C6H5F)]2+ ( 52+ ). 4+ is the first structurally characterized ansa‐like bent sandwich chelate of univalent gallium and 52+ the first binuclear gallium(I) complex without a Ga?Ga bond. Beyond confirming the structural findings by multinuclear NMR spectroscopic investigations and density functional calculations (RI‐BP86/SV(P) level), [Ga(PhC2H4Ph)]+[Al(ORF)4]?( 4 ) and [(C6H5F)Ga(μ‐1,3‐Ph2C6H4)2Ga(C6H5F)]2+{[Al(ORF)4] ?}2 ( 5 ), featuring ansa‐arene ligands, were tested as catalysts for the synthesis of highly reactive polyisobutylene (HR‐PIB). In comparison to the recently published 1 and the [Ga(1,3,5‐Me3C6H3)2]+[Al(ORF)4]? salt ( 6 ) (1,3,5‐Me3C6H3=mesitylene), 4 and 5 gave slightly reduced reactivities. This allowed for favorably increased polymerization temperatures of up to +15 °C, while yielding HR‐PIB with high contents of terminal olefinic double bonds (α‐contents=84–93 %), low molecular weights (Mn=1000–3000 g mol?1) and good monomer conversions (up to 83 % in two hours). While the chelate complexes delivered more favorable results than 1 and 6 , the reaction kinetics resembled and thus concurred with the recently proposed coordinative polymerization mechanism. 相似文献
998.
Tatyana V. Balashova Dmitry M. Kusyaev Tatyana I. Kulikova Olga N. Kuznetsova Frank T. Edelmann Prof. Dr. Stephan Gießmann Steffen Blaurock Mikhail N. Bochkarev Prof. Dr. 《无机化学与普通化学杂志》2007,633(2):256-260
The reactivity of neodymium diiodide, NdI2 ( 1 ), towards organosilicon, ‐germanium and ‐tin halides has been investigated. Compound 1 readily reacts with Me3SiCl in DME to give trimethylsilane (6 %), hexamethyldisilane (4 %) and (Me3Si)2O (19 %). The reaction with Et3SiBr in THF results in formation of Et3SiSiEt3 (17 %) and Et3SiOBun (34 %). Alkylation of Me3SiCl with PrnCl in the presence of 1 in THF affords Me3SiPrn (10 %), Me3SiOBun (52 %) and Me3SiSiMe3 (1 %). The main product identified in the reaction mixture formed upon interaction of 1 with dichlorodimethylsilane Me2SiCl2 in THF is di‐n‐butoxydimethylsilane Me2Si(OBun)2 (54 %) together with minor amounts of Me2Si(OBun)Cl. The reaction of 1 with Me3GeBr under the same conditions produces Me3GeGeMe3 (44 %), Me3GeH (3 %), and Me3GeI (7 %). An analogous set of products was obtained in the reaction with Et3GeBr. Treatment of trimethyltin chloride with 1 causes reduction of the former to tin metal (74 %). Me3SnH (7 %) and hexamethyldistannane (11 %) were identified in the volatile products. The reaction of 1 with Me3SiI provides straightforward access to hepta‐coordinated NdI3(THF)4 ( 2 ), the structure of which was determined by X‐ray diffraction. 相似文献
999.
1000.
Fritz T Steinfeld G Käss S Kersting B 《Dalton transactions (Cambridge, England : 2003)》2006,(31):3812-3821
The preparation and characterization of mononuclear complexes of the dinucleating 24-membered hexazadithiophenolate macrocycles H2L2 and H2L3 and their open-chain N3S2 analogues H2L4 and H2L5 are reported. The highly crystalline compounds [Ni(L4)] (4), [Ni(L5)] (5), [Co(L5)] (6), [NiH2(L2)]2+ (7), [ZnH2(L2)]2+ (8), and [NiH2(L3)]2+ (9) could be readily prepared by stoichiometric complexation reactions of the hydrochlorides of the free ligands with the corresponding metal(II) dichlorides and NEt3 in methanolic solution. All complexes were characterized by X-ray crystallography. Monometallic complexes 4-6 of the pentadentate ligands H2L4 and H2L5 feature distorted square pyramidal MN3S2 structures (tau = 0.01 to 0.44). Similar coordination geometries are observed for the macrocyclic complexes 7-9 of the octadentate ligands H2L2 and H2L3. The two hydrogen atoms in 7-9 are attached to the noncoordinating benzylic amine functions and are hydrogen bonded to the metal-bound thiophenolate functions. A comparison of the structures of 4-9 reveals that the macrocycles L2 and L3 have a rather flexible ligand backbone that do not confer unusual coordination geometries on the metal ions. We also report on the ability of the monometallic complexes 7 and 8 to serve as starting materials for the preparation of dinuclear complexes. 相似文献