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631.
Simon Drescher Katrin Helmis Andreas Langner Bodo Dobner 《Monatshefte für Chemie / Chemical Monthly》2010,38(3):339-349
Abstract
General syntheses of novel symmetrical, single-chain, diacetylene-modified bolaphospholipids have been carried out in five steps. For the ω-alkynols, which have an important role as key intermediates, three different synthetic approaches were comprehensively investigated. For the final synthesis it is suggested that (1) alkylation of lithium (trimethylsilyl)acetylide with tetrahydropyranyl-protected ω-bromoalcohols, followed by (2) cleavage of the trimethylsilyl moiety and the tetrahydropyranyl protecting group, and (3) copper(II)-catalyzed Eglinton coupling is the best strategy for obtaining diacetylene-modified alkane-1,ω-diols, because higher yields were obtained while avoiding the formation of by-products. Moreover, conversion of the diols into bipolar phospholipids was achieved by bis-phosphorylation with β-bromoethylphosphoric acid dichloride and subsequent quaternization with trimethylamine or dimethylamine. Finally, spectral data are presented for novel single-chain, diacetylene-modified bolaphospholipids with promising potential as starting molecules in the formation of polymerizable and, thus, thermostable nanofibers. 相似文献632.
Mariano A. Fernández‐Zúmel Dr. Katrin Thommes Gregor Kiefer Andrzej Sienkiewicz Dr. Katarzyna Pierzchala Kay Severin Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(43):11601-11607
Kinetic and spectroscopic analyses were performed to gain information about the mechanism of atom‐transfer radical reactions catalyzed by the complexes [RuCl2Cp*(PPh3)] and [RuClCp*(PPh3)2] (Cp*=pentamethylcyclopentadienyl), in the presence and in the absence of the reducing agent magnesium. The reactions of styrene with ethyl trichloroacetate, ethyl dichloroacetate, or dichloroacetonitrile were used as test reactions. The results show that for substrates with high intrinsic reactivity, such as ethyl trichloroacetate, the oxidation state of the catalyst in the resting state is +3, and that the reaction is zero‐order with respect to the halogenated compound. Furthermore, the kinetic data suggest that the metal catalyst is not directly involved in the rate‐limiting step of the reaction. 相似文献
633.
Katrin Schuhen David Sieb Hubert Wadepohl Markus Enders Prof. Dr. 《无机化学与普通化学杂志》2009,635(11):1560-1567
Sodium cyclopentadienide reacts as nucleophile with 4,7‐dibromo‐2,1,3‐benzothiadiazole (BTZ) and leads to the new donor‐functionalized ligand CpBTZ. Related quinoxalyl Cp systems have been prepared using Pd‐catalyzed coupling with zincated Cp‐metal complexes. The new ligands comprise two N‐donor atoms; one of them is located in a distal position relative to the metal centre so that it cannotcoordinate in a chelating manner. With CpBTZ ligand derivatives severalmetal complexes have been synthesized. The new chromium(III) complex CpBTZCrCl2 ( 12 ) becomes upon activation an active catalyst for the polymerization of ethylene. Relying on DFT calculations and analysis of spin‐density distribution combined with paramagnetic NMR data a chelating coordination of the CpBTZ ligand is feasible in 12 . 相似文献
634.
Ines Raabe Katrin Wagner Gustavo Santiso‐Quiñones Ingo Krossing Prof. Dr. 《无机化学与普通化学杂志》2009,635(3):513-517
Exposure of the tetrameric, heterocubane‐like perfluorinated lithium alkoxide [Li{OC(CF3)3}]4 to humid air gaverise to the hydrolysis products [{(CF3)3CO}Li(H2O)2‐μ‐(H2O)‐Li(H2O)2{OC(CF3)3}], [{(CF3)3CO}Li(H2O)2‐μ‐(H2O)‐Li‐(H2O)3]+[OC(CF3)3]– and [Li(H2O)4]+[OC(CF3)3]– because of stepwise addition of water molecules in a gas‐solid reaction without solvent. All compounds were studied by X‐ray crystallography and their solid‐state structures are strongly influenced by hydrogen bonding and fluorophilic interactions. 相似文献
635.
Raffael Koller Kyrill Stanek Daniel Stolz Dr. Raphael Aardoom Katrin Niedermann Antonio Togni Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(24):4332-4336
A (fluor)ry of activity : The transfer of an intact trifluoromethyl group from a hypervalent iodine reagent to an aliphatic alcohol occurs smoothly upon activation by zinc bis(triflimide). This constitutes a straightforward method for the preparation of trifluoromethoxy alkyl derivatives, compounds otherwise difficult to access.
636.
Buergler JF Niedermann K Togni A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(2):632-640
Intermolecular nucleophilic substitution of a CF(3) group of bis(trifluoromethyl)phosphanes by a lithiated Ugi's amine (4) affords both diastereoisomers of the corresponding P-stereogenic trifluoromethylphosphanes 6 and 7. Separation of the isomers by column chromatography on silica gel followed by substitution of the dimethylamino group with phosphanes or pyrazoles yields the bidentate P^P (9 and 10) or P^N ligands (12 and 13) without epimerization at the stereogenic phosphorus center. The coordination properties of these bidentate ligands were investigated on the basis of crystal structures of the corresponding palladium and rhodium complexes. IR spectroscopic measurements of rhodium-carbonyl complexes 16-23 indicated the strongly electronic-withdrawing character of these phosphanes. The catalytic potential of these ligands was demonstrated in the rhodium-catalyzed hydrogenation of olefins as well as in the palladium-catalyzed allylic alkylation reaction, where high activities and enantioselectivities were observed. 相似文献
637.
Dillon TJ Tucceri ME Dulitz K Horowitz A Vereecken L Crowley JN 《The journal of physical chemistry. A》2012,116(24):6051-6058
Absolute (pulsed laser photolysis, 4-639 Torr N(2) or air, 240-357 K) and relative rate methods (50 and 760 Torr air, 296 K) were used to measure rate coefficients k(1) for the title reaction, OH + C(4)H(5)N → products (R1). Although the pressure and temperature dependent rate coefficient is adequately represented by a falloff parametrization, calculations of the potential energy surface indicate a complex reaction system with multiple reaction paths (addition only) in the falloff regime. At 298 K and 760 Torr (1 Torr = 1.33 mbar) the rate coefficient obtained from the parametrization is k(1) = (1.28 ± 0.1) × 10(-10) cm(3) molecule(-1) s(-1), in good agreement with the value of (1.10 ± 0.27) × 10(-10) cm(3) molecule(-1) s(-1) obtained in the relative rate study (relative to C(5)H(8), isoprene) at this temperature and pressure. The accuracy of the absolute rate coefficient determination was enhanced by online optical absorption measurements of the C(4)H(5)N concentration at 184.95 nm using a value σ(184.95nm) = (1.26 ± 0.02) × 10(-17) cm(2) molecule(-1), which was determined in this work. 相似文献
638.
639.
640.
Yarman A Gröbe G Neumann B Kinne M Gajovic-Eichelmann N Wollenberger U Hofrichter M Ullrich R Scheibner K Scheller FW 《Analytical and bioanalytical chemistry》2012,402(1):405-412
The aromatic peroxygenase (APO; EC 1.11.2.1) from the agraric basidomycete Marasmius rotula (MroAPO) immobilized at the chitosan-capped gold-nanoparticle-modified glassy carbon electrode displayed a pair of redox peaks
with a midpoint potential of −278.5 mV vs. AgCl/AgCl (1 M KCl) for the Fe2+/Fe3+ redox couple of the heme-thiolate-containing protein. MroAPO oxidizes aromatic substrates such as aniline, p-aminophenol, hydroquinone, resorcinol, catechol, and paracetamol by means of hydrogen peroxide. The substrate spectrum overlaps
with those of cytochrome P450s and plant peroxidases which are relevant in environmental analysis and drug monitoring. In
M. rotula peroxygenase-based enzyme electrodes, the signal is generated by the reduction of electrode-active reaction products (e.g.,
p-benzoquinone and p-quinoneimine) with electro-enzymatic recycling of the analyte. In these enzyme electrodes, the signal reflects the conversion
of all substrates thus representing an overall parameter in complex media. The performance of these sensors and their further
development are discussed. 相似文献