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981.
Deglmann P Ember E Hofmann P Pitter S Walter O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(10):2864-2879
Ruthenium complexes, mer-[RuX(3)(MeCN)(3)] and cis/trans-[RuX(2)(MeCN)(4)] with X=Br, Cl, were investigated as precatalysts in homogeneously catalyzed hydrosilylation of CO(2). The oxidation state of ruthenium and nature of the halide in the precatalysts were found to influence the catalytic activity in the conversion of Me(2)PhSiH to the formoxysilane Me(2)PhSiOCHO, with Ru(III) having chloride ligands being most active. Monitoring the reactions by in-situ IR spectroscopy in MeCN as the solvent indicates an interaction of the precatalyst with the silane prior to activation of CO(2). In the absence of CO(2), hydrosilylation of the MeCN solvent occurs. Catalytic activity in CO(2) hydrosilylation is enhanced by Me(2)PhSiCl, generated during reduction of Ru(III) in mer-[RuX(3)(MeCN)(3)] to Ru(II) or, when added as promoter to Ru(II) precatalysts. The reaction mechanism for the catalytic cycle has been calculated by DFT methods for the reaction of Me(3)SiH. The key steps are: Transfer of the Me(3)Si moiety to a coordinated halide ligand, resulting in an L(n)RuH(XSiMe(3)) intermediate --> CO(2) coordination --> Me(3)Si transfer to CO(2) --> reductive elimination of formoxysilane product. This reaction sequence is more favorable energetically for chloride complexes than for the analogous bromide complexes, which accounts for their differences in catalytic activity. Calculations also explain the rate increase observed experimentally in the presence of Me(2)PhSiCl. A parallel reaction pathway leads to (Me(3)Si)(2)O as a minor byproduct which arises from the condensation of two initially formed Me(3)SiOH molecules. 相似文献
982.
Solution Layer Deposition: A Technique for the Growth of Ultra‐Pure Manganese Oxides on Silica at Room Temperature 下载免费PDF全文
Dr. Jérémy Cure Dr. Kilian Piettre Dr. Yannick Coppel Dr. Eric Beche Dr. Jérôme Esvan Vincent Collière Dr. Bruno Chaudret Dr. Pierre Fau 《Angewandte Chemie (International ed. in English)》2016,55(9):3027-3030
With the ever increasing miniaturization in microelectronic devices, new deposition techniques are required to form high‐purity metal oxide layers. Herein, we report a liquid route to specifically produce thin and conformal amorphous manganese oxide layers on silicon substrate, which can be transformed into a manganese silicate layer. The undesired insertion of carbon into the functional layers is avoided through a solution metal–organic chemistry approach named Solution Layer Deposition (SLD). The growth of a pure manganese oxide film by SLD takes place through the decoordination of ligands from a metal–organic complex in mild conditions, and coordination of the resulting metal atoms on a silica surface. The mechanism of this chemical liquid route has been elucidated by solid‐state 29Si MAS NMR, XPS, SIMS, and HRTEM. 相似文献
983.
Engineering a Chemical Switch into the Light‐driven Proton Pump Proteorhodopsin by Cysteine Mutagenesis and Thiol Modification 下载免费PDF全文
Dr. Daniel Harder Stephan Hirschi Zöhre Ucurum Roland Goers Prof. Dr. Wolfgang Meier Prof. Dr. Daniel J. Müller Prof. Dr. Dimitrios Fotiadis 《Angewandte Chemie (International ed. in English)》2016,55(31):8846-8849
For applications in synthetic biology, for example, the bottom‐up assembly of biomolecular nanofactories, modules of specific and controllable functionalities are essential. Of fundamental importance in such systems are energizing modules, which are able to establish an electrochemical gradient across a vesicular membrane as an energy source for powering other modules. Light‐driven proton pumps like proteorhodopsin (PR) are excellent candidates for efficient energy conversion. We have extended the versatility of PR by implementing an on/off switch based on reversible chemical modification of a site‐specifically introduced cysteine residue. The position of this cysteine residue in PR was identified by structure‐based cysteine mutagenesis combined with a proton‐pumping assay using E. coli cells overexpressing PR and PR proteoliposomes. The identified PR mutant represents the first light‐driven proton pump that can be chemically switched on/off depending on the requirements of the molecular system. 相似文献
984.
Gold(I)‐Catalyzed N‐Desulfonylative Amination versus N‐to‐O 1,5‐Sulfonyl Migration: A Versatile Approach to 1‐Azabicycloalkanes 下载免费PDF全文
Solène Miaskiewicz Boris Gaillard Dr. Nicolas Kern Prof. Dr. Jean‐Marc Weibel Prof. Dr. Patrick Pale Dr. Aurélien Blanc 《Angewandte Chemie (International ed. in English)》2016,55(31):9088-9092
Valuable 1‐azabicycloalkane derivatives have been synthesized through a novel gold(I)‐catalyzed desulfonylative cyclization strategy. An ammoniumation reaction of ynones substituted at the 1‐position with an N‐sulfonyl azacycle took place in the presence of a gold cation by intramolecular cyclization of the disubstituted sulfonamide moiety onto the triple bond. Depending on the size of the heterocyclic ring and substitution of the substrates, two unprecedented forms of nucleophilic attack on the sulfonyl group were exploited, that is, a N‐desulfonylation in the presence of an external protic O nucleophile (37–87 %, 10 examples) and a unique N‐to‐O 1,5‐sulfonyl migration (60–98 %, 9 examples). 相似文献
985.
Flavie Bidel Sophie Corvaisier Christelle Jozet‐Alves Ivannah Pottier François Dauphin Nadège Naud Cécile Bellanger 《Biomedical chromatography : BMC》2016,30(8):1175-1183
The cuttlefish belongs to the mollusk class Cephalopoda, considered as the most advanced marine invertebrates and thus widely used as models to study the biology of complex behaviors and cognition, as well as their related neurochemical mechanisms. Surprisingly, methods to quantify the biogenic monoamines and their metabolites in cuttlefish brain remain sparse and measure a limited number of analytes. This work aims to validate an HPLC‐ECD method for the simultaneous quantification of dopamine, serotonin, norepinephrine and their main metabolites in cuttlefish brain. In comparison and in order to develop a method suitable to answer both ecological and biomedical questions, the validation was also carried out on a phylogenetically remote species: mouse (mammals). The method was shown to be accurate, precise, selective, repeatable and sensitive over a wide range of concentrations for 5‐hydroxyindole‐3‐acetic acid, serotonin, dopamine, 3,4‐dihydroxyphenylacetic acid and norepinephrine in the both extracts of cuttlefish and mouse brain, though with low precision and recovery for 4‐hydroxy‐3‐methoxyphenylethylene glycol. Homovanillic acid, accurately studied in rodents, was not detectable in the brain of cuttlefish. Overall, we described here the first fully validated HPLC method for the routine measurement of both monoamines and metabolites in cuttlefish brain. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
986.
Back Cover: Retention of Native Protein Structures in the Absence of Solvent: A Coupled Ion Mobility and Spectroscopic Study (Angew. Chem. Int. Ed. 45/2016) 下载免费PDF全文
987.
The Morita-Baylis-Hillman reaction of cyclohexenone and p-nitro benzaldehyde is catalyzed by carrier proteins such as serum albumins or enzymes such as certain lipases, conversion of up to 35% and enantioselectivities of up to 19% being observed. 相似文献
988.
Holger Stephan Anika Röhrich Jörg Steinbach Jürgen Seidel 《Tetrahedron letters》2007,48(50):8834-8838
Two novel glycocluster ligands with cyclam core bearing thiourea-linked d-glucose and 2-acetamido-2-deoxy-d-glucose at the periphery have been synthesized. The interaction with concanavalin A has been studied by isothermal titration microcalorimetry for characterizing protein-ligand interactions. The sugar-containing multivalent ligands showed higher association affinity compared to the sugar monomers, which is attributed to an entropy driven glycoside clustering effect. 相似文献
989.
Chavagnac V Milton JA Green DR Breuer J Bruguier O Jacob DE Jong T Kamenov GD Le Huray J Liu Y Palmer MR Pourtalès S Roduhskin I Soldati A Trueman CN Yuan H 《Analytica chimica acta》2007,599(2):177-190
Ten international laboratories participated in an inter-laboratory comparison of a fossil bone composite with the objective of producing a matrix and structure-matched reference material for studies of the bio-mineralization of ancient fossil bone. We report the major and trace element compositions of the fossil bone composite, using in-situ method as well as various wet chemical digestion techniques.For major element concentrations, the intra-laboratory analytical precision (%RSDr) ranges from 7 to 18%, with higher percentages for Ti and K. The %RSDr are smaller than the inter-laboratory analytical precision (%RSDR; <15-30%). Trace element concentrations vary by ∼5 orders of magnitude (0.1 mg kg−1 for Th to 10,000 mg kg−1 for Ba). The intra-laboratory analytical precision %RSDr varies between 8 and 45%. The reproducibility values (%RSDR) range from 13 to <50%, although extreme value >100% was found for the high field strength elements (Hf, Th, Zr, Nb). The rare earth element (REE) concentrations, which vary over 3 orders of magnitude, have %RSDr and %RSDR values at 8-15% and 20-32%, respectively. However, the REE patterns (which are very important for paleo-environmental, taphonomic and paleo-oceanographic analyses) are much more consistent.These data suggest that the complex and unpredictable nature of the mineralogical and chemical composition of fossil bone makes it difficult to set-up and calibrate analytical instruments using conventional standards, and may result in non-spectral matrix effects. We propose an analytical protocol that can be employed in future inter-laboratory studies to produce a certified fossil bone geochemical standard. 相似文献
990.
Jacquemin D Perpète EA Scalmani G Frisch MJ Kobayashi R Adamo C 《The Journal of chemical physics》2007,126(14):144105
Using the long-range correction (LC) density functional theory (DFT) scheme introduced by Iikura et al. [J. Chem. Phys. 115, 3540 (2001)] and the Coulomb-attenuating model (CAM-B3LYP) of Yanai et al. [Chem. Phys. Lett. 393, 51 (2004)], we have calculated a series of properties that are known to be poorly reproduced by standard functionals: Bond length alternation of pi-conjugated polymers, polarizabilities of delocalized chains, and electronic spectra of extended dyes. For each of these properties, we present cases in which traditional hybrid functionals do provide accurate results and cases in which they fail to reproduce the correct trends. The quality of the results is assessed with regard to experimental values and/or data arising from electron-correlated wave function approaches. It turns out that (i) both LC-DFT and CAM-B3LYP provide an accurate bond length alternation for polyacetylene and polymethineimine, although for the latter they decrease slightly too rapidly with chain length. (ii) The LC generalized gradient approximation and MP2 polarizabilities of long polyphosphazene and polymethineimine oligomers agree almost perfectly. In the same way, CAM-B3LYP corrects the major part of the B3LYP faults. (iii) LC and CAM techniques do not help in correcting the nonrealistic evolution with chain length of the absorption wavelengths of cyanine derivatives. In addition, though both schemes significantly overestimate the ground to excited state transition energy of substituted anthraquinone dyes, they provide a more consistent picture once a statistical treatment is performed than do traditional hybrid functionals. 相似文献