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861.
Piero Dalla Croce 《Journal of heterocyclic chemistry》1976,13(5):1109-1110
4-Arylmethylene-Δ2 -isoxazolin-5-ones react with carbonyl-stabilized sulfur ylides yielding spiro[cyclopropane-1,4′-Δ2-isoxazolin]-5′-ones identified from spectroscopic data and chemical behaviour. 相似文献
862.
Klimova EI Berestneva TK Cinquantini A Corsini M Zanello P Tuscano RA Hernández-Ortega S Martínez-García M 《Organic & biomolecular chemistry》2003,1(24):4458-4464
Reactions of 2,3-diferrocenylcyclopropenone 1 with ethyl- and benzylmagnesium chlorides afford 3,3-diethyl-and 3,3-dibenzyl- 1,2-diferrocenylcyclopropenes 2 and 3, respectively, and products of nucleophilic opening of the three-membered ring resulting from the addition of RMgCl to the carbonyl group, viz., saturated ketones(4,5-diferrocenylheptan-3-ones 4a,b and 3,4-diferrocenyl-1,5-diphenylpentan-2-ones 5a,b as ca. 3: 1 mixtures of two diastereomers) and other products. The spatial structures of compounds 2 and 4a were established by X-ray diffraction analysis of single crystals. Protonation of the cyclopropenes 2 and 3 with tetrafluoroboric acid at -40 degrees C yields the corresponding 3,3-dialkyl-1 ,2-diferrocenylcyclopropylium tetrafluoroborates. Transformation of the latter into diferrocenylallylic cations upon increasing the temperature to 20 degrees C and their eprotonation under the action of N,N-dimethylaniline were studied. Electrochemical investigation of 1 and 2 shows that in both complexes the cyclopropene spacer allows electronic communication between the two outer ferrocenyl groups, this being notably greater for 2 than for 1. 相似文献
863.
Giovanni Fronza Claudio Fuganti Piero Grasselli Giuseppe Pedrocchi-Fantoni 《Tetrahedron letters》1981,22(50):5073-5076
The synthesis of the N-benzoyl derivatives of - (10),- (13) and - (-vancosamine) (12) 2,3,6-trideoxy-3--methyl-3-aminohexose from the (2,3) diol (1) prepared in fermenting bakers' yeast from α-methylcinnamaldehyde and acetaldehyde is reported 相似文献
864.
Albano Vincenzo G. Calderoni Francesca Iapalucci Maria Carmela Longoni Giuliano Monari Magda Zanello Piero 《Journal of Cluster Science》1995,6(1):107-123
The oxidation of the [Fe(CO)4]2– dianion with Ag+ salts occurs through a particularinner-sphere mechanism, which involves an intermediate cascade of silver clusters stabilized by Fe(CO)4 ligands. The last detectable Ag-Fe cluster of the sequence is the [Ag13{-Fe(CO)4}8]3– trianion, which has been selectively obtained by using ca. 1.7 equivalents of Ag+ per mole of [Fe(CO)4]2–. The [Ag13{-Fe(CO)4}8]3–- trianion has been isolated in a crystalline state with several quaternary cations, and has been characterized by X-ray diffraction studies of its bis(triphenylphosphine)iminium salt. [N(PPh3)2]3 [Ag13{
3-Fe(CO)4}8]·2(CH3)2CO, monoclinic, space group P21 (No.4),a = 16.284(2) Å,b =18.767(5) Å,c = 25.905(4) Å, = 90.46(1)°,V = 7916(3) Å3,Z = 2,R = 0.0324. The molecular structure of the anion consists of a centered cuboctahedron of silver atoms with the triangular faces capped by Fe(CO)4 units. Chemical reduction of ( Ag13{
3-Fe(CO)4}8]3– affords the corresponding [Ag13{
3-Fe(CO)4)8]4–, which in turn gives [Ag13{
3-Fe(CO)4)8]5– and [Ag6{
3-Fe(CO)4}4]– upon further reduction. Electrochemical investigations confirm the reversibility of the [Ag13{
3-Fe(CO)4}8]3–/4– redox change. Furthermore, in spite of some electrode poisoning effects, evidence of the existence of the [Ag13{
3-Fe(CO)4}8]5– pentaanion was obtained. The yet structurally uncharacterized [Ag6{
3-Fe(CO)4)4]2– dianion is quantitatively obtained by reaction of [Fe(CO)4]2– with ca. 1.5 equivalents of Ag+ or by addition of one equivalent of Ag+ to solutions of the [Ag5{Fe(CO)4}4]3– trianion. All attempts to isolate its quaternary salts as crystalline materials failed owing to formation of amorphous insoluble precipitates. The above series of
3-Fe(CO)4 octa-capped cuboctahedral Ag13 clusters can be envisioned as the Ag+ . Ag and Ag– cryptates of the [Ag12{}3-Fe(CO)4}8]4– cryptand. respectively.Dedicated to Prof L. F. Dahl on his 65th birthday. 相似文献
865.
Claudio Fuganti Piero Grasselli Giuseppe Pedrocchi-Fantoni 《Tetrahedron letters》1981,22(40):4017-4020
The synthesis of N-benzoyl--daunosamine (14) from the C4 aldehyde (2b), prepared from -threonine, through the intermediacy of the C7 adduct (7a) is reported 相似文献
866.
Brenna E Fuganti C Grasselli P Serra S Zamboti S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(8):1872-1878
A general method for the synthesis of C-glycosyl amino acids is described here. The stereoisomerically pure tyrosine analogues alpha-L-4 and beta-L-6 are prepared in reasonable overall yields from allyl derivatives 10 and 11. The key step is a benzannulation procedure which is employed in the creation of the aromatic ring that bears the amino acid function. 相似文献
867.
Cembran A Gonzalez-Luque R Altoè P Merchan M Bernardi F Olivucci M Garavelli M 《The journal of physical chemistry. A》2005,109(29):6597-6605
The low-lying singlet states (i.e. S0, S1, and S2) of the chromophore of rhodopsin, the protonated Schiff base of 11-cis-retinal (PSB11), and of its all-trans photoproduct have been studied in isolated conditions by using ab initio multiconfigurational second-order perturbation theory. The computed spectroscopic features include the vertical excitation, the band origin, and the fluorescence maximum of both isomers. On the basis of the S0-->S1 vertical excitation, the gas-phase absorption maximum of PSB11 is predicted to be 545 nm (2.28 eV). Thus, the predicted absorption maximum appears to be closer to that of the rhodopsin pigment (2.48 eV) and considerably red-shifted with respect to that measured in solution (2.82 eV in methanol). In addition, the absorption maxima associated with the blue, green, and red cone visual pigments are tentatively rationalized in terms of the spectral changes computed for PSB11 structures featuring differently twisted beta-ionone rings. More specifically, a blue-shifted absorption maximum is explained in terms of a large twisting of the beta-ionone ring (with respect to the main conjugated chain) in the visual S-cone (blue) pigment chromophore. In contrast, the chromophore of the visual L-cone (red) pigment is expected to have a nearly coplanar beta-ionone ring yielding a six double bond fully conjugated framework. Finally, the M-cone (green) chromophore is expected to feature a twisting angle between 10 and 60 degrees. The spectroscopic effects of the alkyl substituents on the PSB11 spectroscopic properties have also been investigated. It is found that they have a not negligible stabilizing effect on the S1-S0 energy gap (and, thus, cause a red shift of the absorption maximum) only when the double bond of the beta-ionone ring conjugates significantly with the rest of the conjugated chain. 相似文献
868.
De Angelis F Di Tullio A Del Boccio P Reale S Savelli G Spreti N 《Organic & biomolecular chemistry》2003,1(17):3125-3130
The catalytic activity of alpha-chymotrypsin on a model and a peptide substrate, in the supramolecular system "enzyme-surfactant" in water solution, has been studied by electrospray ionization mass spectrometry. Hydrolysis of N-succinyl-L-phenylalanine p-nitroanilide as the model compound, catalysed by alpha-chymotrypsin in the presence of monomeric cetyltributylammonium bromide, has been followed by UV and ESI-MS detection. Kinetic data, which are essentially identical independent of their determination techniques, show a twelve fold improvement of the enzyme catalytic efficiency when compared with the reaction carried out in the absence of the additive. Once validated, the ESI-MS technique was used to study the hydrolytic activity of the enzyme on a peptide substrate like substance P: it is worth emphasising that the spectrophotometric detection cannot be employed on peptides, where the chromophores are untouched by the hydrolytic process. Substance P hydrolyses in aqueous surfactant following dichotomic kinetics, which are initially rapid but then slow down as the reaction progress. The results presented in this paper are expected to extend studies on biocatalysis in aqueous surfactant media to a wide range of substrates, independent of their spectroscopic properties. 相似文献
869.
Claudio Fuganti Piero Grasselli Giuseppe Pedrocchi-Fantoni 《Tetrahedron letters》1979,20(26):2453-2454
Feeding experiments with (4) [5-3H;5-14C]-leucine () and with the (4) [5-3H;2-14C]-isomer () show that incorporation into the isoprenylated tryptophan derivative echinuline (), produced by , involves, to a large extent, loss of the fragment enbodying the carbon atom at position 2 of the fed amino acid. 相似文献
870.
Giovanni Fronza Claudio Fuganti Piero Grasselli Giuseppe Pedrocchi-Fantoni Carlo Zirotti 《Tetrahedron letters》1982,23(40):4143-4146
The synthesis of the 2,6-dideoxy sugars -digitoxose (14), 2-deoxy--fucose (15) and -mycarose (16) from the C4 and C5 chiral synthons (1), (2) and (3), through the intermediacy of the C7 adducts (4), (8) and (12), obtained by addition of diallylzinc onto (1), (2) and (3), is reported. 相似文献