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1.
2.
Mária Meiarová Katarína Hubinská tefan Toma Burkhard Koch Albrecht Berkessel 《Monatshefte für Chemie / Chemical Monthly》2007,138(11):1181-1186
Summary.
N-Toluensulfonyl-l-prolin amide was tested as catalyst in the enantioselective Michael addition of carbonyl compounds to (E)-β-nitrostyrene in nine ionic liquids under different reaction conditions. The reaction rates and enantioselectivities were
strongly dependent on the ionic liquids. Change of enantioselectivity was observed too and it is attributed to both the cation
and the anion of ionic liquid. The best yields (up to 98%) and enantioselectivity (70% ee) of product were obtained in a basic ionic liquid [bmim]BF4 at room temperature. 相似文献
3.
Rearrangement of Tertiary Allyl Alcohols Induced by Bromination: The Effect of a Fluorine Substituent on the Rate and the Outcome of the Reaction The allyl alcohol bearing a methyl and a t-butyl group at the hydroxylated position was found to undergo a rearrangement when treated with bromine (or N-bromosuccinimide) in an aqueous medium and to afford a product mixture containing two regioisomeric ketones and one oxirane. Introduction of an additional methyl group or a fluorine atom at the non-terminal olefinic center led to a more selective discrimination between potential migratory groups. As the result of an exclusive t-butyl shift only one product, a ketone, was formed in both cases. Whereas the reaction rate was only slightly affected by the additional methyl group, it was substantially decreased by the fluorine atom. 相似文献
4.
The Bis (trifluormethylmercapto) amino radical (CF3S)2N· has been prepared by oxidation of Bis (trifluormethylmercapto) amine, (CF3S)2NH with activated lead diooxide in CCl3F solution at room temperature. The 10?5 – 10?6 molar solution of the radical shows in the ESR- spectrum a triplett of septetts with a isotropic nitrogen hyperfine splitting constant a(14N) = 13,2 G, a(19F) = 1.95 G, indicating that the radical is a planar sp2 species where the unpaired electron is located predominantly in the nitrogen 2p orbital. It is suggested that in solution an thermal equilibrium exists between the (CF3S)2 N radical and its dimer Tetrakis (trifluormethylmercapto)-hydrazine: Aspects of preparation as well as thermodynamic and kinetic details of the hydrazine (NN bond strength 7 kcal/mol?1) and the equilibrium, which can be followed by ESR-spectroscopy will be given. 相似文献
5.
Unimolecular fragmentation reactions of peptides in low-energy collision-induced dissociation are reviewed in the mechanistic context of five-membered ring formation. This structure of intermediates or of fragment ions is recognized as a key element that governs unimolecular peptide fragmentation within the structural framework determined by the peptide backbone and its side-chains. A collection of collision-induced dissociation reactions is presented covering (i) b-ion formation, (ii) the fragmentation of N-terminally acylated peptides, (iii) neutral loss of the C-terminal amino acid in alkali or silver cationized peptides, (iv) the fragmentation of isoAsp-containing peptides and (v) the fragmentation of negatively charged Asp- or Glu-containing peptides. It appears that for all possible nucleophile-electrophile interactions leading to a five-membered ring structure an associated unimolecular peptide fragmentation reaction can be observed. 相似文献
6.
Trifluoromethoxy-substituted anilines undergo hydrogen/lithium permutation ("metalation") with optional site selectivity depending on the N-protective group employed. N-tert-Butoxycarbonyl-2- and -4-(trifluoromethoxy)aniline react with tert-butyllithium at the nitrogen-adjacent 6- and 2-position affording, after electrophilic trapping, products 1-6. In contrast, deprotonation of the para isomer occurs at the oxygen-neighboring 3-position, giving rise to the acid 12, when the amino group is carrying two trimethylsilyl groups. sec-Butyllithium attacks 3-trifluoromethoxy-N-mono(trimethylsilyl)aniline at the 2-position, but 3-trifluoromethoxy-N,N-bis(trimethylsilyl)aniline at the 4-position to provide respectively the acids 10 and 11 after carboxylation. The synthesis of two new benzodiazepines illustrates (19 and 22) the preparative potential of the aniline functionalization mediated by organometallic reagents. 相似文献
7.
Fluoro-organic Syntheses VI: The Solvolysis of Chlorofluoro-cyclopropanes 2-Fluoro-allylic carbocations, generated from 1-chloro-1-fluoro-cyclopropanes or 2-fluoro-allyl p-toluene-sulfonates in water or acetic acid, undergo either proton loss or addition of hydroxyl or acetoxyl. In the latter case, an alkyl-substituted 2-fluoro-allyl ion leads predominantly to the more branched product (e.g. 3-fluoro-2-methyl-3-buten-2-ol) which may be converted into the less branched one (e.g. 2-fluoro-3-methyl-2-buten-2-ol) through reversible reactions. 相似文献
8.
Štefan Marchalín Dušan Ilavský Milan Bruncko 《Monatshefte für Chemie / Chemical Monthly》1989,120(12):1101-1105
Summary Good yields of substituted 5-(5R-2-furyl)-4H-pyrano[2,3-d]pyrimidines4 were obtained in the reaction of 2-ethoxymethyleneamino-3-cyano-4H-pyranes2 with ammonia. Compounds2 were prepared by the condensation of the starting 2-amino-5-acetyl-3-cyano-6-methyl-4H-pyranes1 with ethyl orthoformate. Spectral properties of the bicyclic system4 in relation to compounds3 are discussed. 相似文献
9.
Simple catalytic systems for cross-coupling reactions of acyl chlorides with arylboronic acids under microwave conditions were tested. Microwave irradiation facilitated the reaction course. Mild reaction conditions afford the symmetrical and unsymmetrical aryl ketones in reasonable to high yields within a short time. A wide range of substrates bearing an electron-donating or an electron-withdrawing substituent on aryl ring of acid chloride as well as on boronic acid were examined and high yields of ketones were produced. 相似文献
10.
The NMR enhancement factor of a frozenCuMn spin glass has been measured at a temperatureT?T g /5. The measurements were performed as function of static magnetic fields of different directions. A two component model of a spin glass has been outlined. One component being a “system of single spins” and the other one being a “subsystem of clusters”. Both components were attributed to different kinds of interaction being RKKY and dipole interaction respectively. The effective anisotropy field of the single spin system consists of two unidirectional contributionsH a s andH a c , which have been measured for different conditions. A second anisotropy fieldH d binds the cluster system to the system of single spins. All anisotropy fields depend on the annealing temperature of the alloys. 相似文献