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141.
A 2D and variable-temperature 13C-NMR study indicates that a CO-site exchange occurs in the title complex via several consecutive processes, the first being a ‘merry-go-round’ of the basal CO's, the second a switch of basal face not involving unbridged intermediates. 相似文献
142.
Functionalized 1,3-enzynes of general formula 1 have been prepared in good yields by coupling reaction of 1-alkynes or ω-functionalized 1-alkynes halides in the presence of a catalytic amount of (PPh3)4Pd and Cul. The reactions, which were carried out under phase transfer conditions employing benzyltriethylammonium chloride as phase transfer agent, benzene as organic solvent and diluted aq NaOH as base, occurred with 100% stereospecificity when 1-halo-1-alkenes of defined configuration were used. Such coupling reactions have been employed to prepare some pure insect sex pheromone components or their precursors in high overall yield. 相似文献
143.
Giovanni Carturan Renzo Campostrini Lorenzo Tognana Sara Boninsegna Roberto Dal Toso Renzo Dal Monte 《Journal of Sol-Gel Science and Technology》2006,37(1):69-77
Solutions with Na-alginate concentrations ranging from 0.5 to 2.5% w/v are processed to prepare Ca-alginate beads using a
nozzle ejector under constant He-flow. Beads were spherical in shape and their size distributions were determined; in all
samples the average diameter fell in the 120–140 μm interval. Volumetric yields were found to be linearly dependent of the
original Na-alginate load whereas the bead diameters were almost constant, according to a constant hindrance of Ca-alginate
macromolecular units in the final Ca-alginate gel. The rheology of Na-alginate solutions was studied, with determination of
intrinsic viscosity; experimental evidence of microsphere formation, even at the lowest Na-alginate concentrations, indicated
that ejection processing changes the rheological parameters controlling bead formation in ordinary dropping processing.
Gaseous silicon alkoxides – Si(OEt)4 and MeSi(OEt)3 – carried by a He flow were deposited on Na-alginate droplets during ejection. The process was studied by continuous mass
spectrometry analysis before and after Na-alginate ejection during the 5-min treatment; in all cases results indicated a deposition
yield of 58%. Traces of alcohol in the mass spectrometry analysis of the out-flow gas excluded instantaneous formation of
sol-gel silica on the Na-alginate droplets during their residence in the gas phase. For various Na-alginate concentrations,
ethanol released by silica gel formation is constant as well as the amount of deposited SiO2; a siliceous layer ranging from 0.08 to 0.17 μm thick on the surface of the Ca-alginate beads was calculated. 相似文献
144.
Andrs Strawczynski Gianfranco Suardi Renzo Ros Raymond Roulet 《Helvetica chimica acta》1993,76(6):2210-2226
The fluxionality of [Ir4(CO)8(μ2-CO)3L] (L = Br?, I?, SCN?, NO2?, P(4-ClC6H4)3, PPh3, P(4-MeOC6H4)3, P(4-Me2NC6H4)3), as studied by 2D-13C-NMR in solution, is due to two successive scrambling processes: the merry-go-round of six basal CO's and CO bridging to alternative faces of the Ir4 tetrahedron. The basicity of the ligand L has no significant effect on the activation parameters. The scrambling process of lowest activation energy in [Ir4(CO)7(μ2-CO)3(PMePh2)2] correspond to the two possible synchronous CO bridging about a unique face of the metal tetrahedron swapping the relative axial and radial positions of the ligands L. The disubstituted clusters [Ir4(CO)10(μ2-L? L)] with one edge-bridging ligand have a ground-state geometry with three edge-bridging CO's (L? L = bis(diphenylphosphino)methane, bis(diphenylarsino)methane, bis(diphenylphosphino)propane) or with all terminal CO's (L? L = CH3SCH2SCH3). In all cases, the fluxional process of lowest activation energy in the merry-go-round of six CO's about a unique triangular face. For the P and As donor ligands, this process is followed by the rotation of terminal CO's bonded to two Ir-atoms residing on the mirror plane of the unbridged intermediate. 相似文献
145.
Renzo Ros Raymond Bataillard Raymond Roulet 《Journal of organometallic chemistry》1976,118(2):C53-C54
The preparation and reactions are described of some novel platinum(II) complexes with a hydride ligand group trans to an sp3 carbon, viz. [PtH(YCN)-(PPh3)2] with Y (CH2)n (n = 1—3) or o-CH2C6H4. 相似文献
146.
Renzo Ros Rino A. Michelin Raymond Bataillard Raymond Roulet 《Journal of organometallic chemistry》1979,165(1):107-116
The preparation and spectroscopic properties are described of some platinum(II) complexes having a hydride ligand cis or trans to an sp3 carbon, viz. trans-PtH(YCN)(PPh3)2 and cis-PtH(YCN)(LL) with YCN = C2H4CN, n-C3H6CN, o-CH2C6H4CN and LL = bis(diphenylphosphino)-ethene or -ethane. The complexes trans-PtH(YCN)(PPh3)2 can add a fifth ligand in solution; the resulting five-coordinate complex was observed by 31P NMR in the case of PtH(C3H6CN)(PPh3)3. Insertion of olefin (ethen, 1-cyanoethene, norbornadiene, allen) into the PtH bond of the trans-hydrido complexes occurs to give cis-dialkyl complexes, but the cis-hydrido complexes are unreactive. The mechanism of insertion is discussed in terms of the kinetics and the geometries of reactants and products. 相似文献
147.
Oxazolinyl allylic alcohols 2 convert smoothly into 3-alkylidene-2-iminooxetanes 3 and dienic carboxylic acids 7 simply upon treatment with aqueous HCl. 相似文献
148.
The addition reaction of α-lithiated oxazolinyloxiranes to nitrones has been investigated. 1,5,9-Trioxa-8,10-diazadispiro[2.0.4.3]undecanes formed in a completely diastereoselective manner upon treatment of α-lithiated oxiranes with nitrones. The lithiation of optically active trans and cis-oxazolinyloxiranes followed by the addition of a nitrone resulted in the formation of the same dispirocyclic compound. An explanation for the observed stereoselectivity is provided. 相似文献
149.
The antitumor drugs 1-nitro-9-[(2-(dialkylamino)ethyl)amino]acridines (alkyl = Me, A(1); Et, A(2)) with platinum(II) give tridentate coordination compounds in which the two nitrogens of the ethylenediamine side chain and the C(8) carbon atom of the acridine ring system act as donor atoms. An excess of triphenylphosphine displaces the residual chloride coordinated to platinum but leaves unaltered the tridentate acridine ligand. The structures of [Pt(A(1)-H)Cl], 1, and [Pt(A(1)-H)(PPh(3))]Cl, 3, have been solved by single-crystal X-ray diffraction. 1.CHCl(3) crystallizes in the orthorhombic system, space group P2(1)2(1)2(1) (no. 19), with a = 8.715(1) ?, b = 11.045(2) ?, c = 22.609(4) ?, Z = 4, R = 0.0559, and R(w) = 0.0561 for 1502 reflections with F > 3sigma(F). 3.(1)/(2)CH(2)Cl(2) crystallizes in the monoclinic system, space group P2(1)/c (no. 14), with a = 13.418(3) ?, b = 14.053(3) ?, c = 18.918(4) ?, beta = 97.21(3) degrees, Z = 4, R = 0.0591, and R(w) = 0.0611 for 3608 reflections with F > 4sigma(F). In both complexes the acridine ligand adopts an imino-type configuration with the proton of the exocyclic 9-amino group shifted on N(10). Because of a severe steric interaction between the nitro group in the 1-position and the chelate diamine chain in the 9-position, the acridine moiety is folded about the C(9)-N(10) vector with an average angle between outer rings of 12 degrees. Moreover, the acridine aromatic moiety and the platinum coordination planes are twisted, forming a dihedral angle of ca. 20 degrees. The steric repulsion between the nitro and the diamine groups appears to provide the driving force to metalation. The H(10) proton has a great tendency to be engaged in H-bonding as shown by X-ray and solution studies. The formation of a H-bond with a rather poor acceptor such as the chloride ion can cause a downfield shift of the H-resonance as large as 6 ppm. 相似文献
150.
Regioselectively nucleus and/or side-chain fluorinated 2-(phenanthr-1-yl)- and 2-(phenanthr-2-yl)propionic acids 1-5 were prepared using phenanthren-1(2H)-ones 6a-c as key intermediates. Thus, ethyl 2-(fluorophenanthryl)propionates 11 were obtained in good yields by Reformatsky reaction of 6a-c with ethyl 2-bromopropionate followed by dehydratation and DDQ-promoted aromatization of the resulting beta-hydroxyesters. Side-chain alkyl 2-hydroxy-2-(phenanthr-1-yl)propionates 14 were obtained by bromine/lithium permutation of dihydrophenanthryl bromides 12a-c with butyllithium followed by quenching of the lithiated intermediates with methyl pyruvate or ethyl 3,3,3-trifluoropyruvate and subsequent DDQ-promoted aromatization. The alkyl 2-hydroxy-2-(phenanthr-1-yl)propionates 25 were prepared by reacting 8-bromo-1,3-difluorophenanthrene 24 with butyllithium for 10 seconds at -110 degrees C and subsequent addition of the suitable pyruvate to the lithiated intermediates. Alkyl 2-hydroxy-2-(phenanthr-2-yl)propionates 26 and 29 were suitably obtained by site-selective metalation of 1,3-difluorophenanthrene 28 and the bromophenanthrene 24, respectively, with LDA followed by quenching of the metalated intermediates with the suitable alkyl pyruvate. Fluorination of the above alpha-hydroxypropionates with DAST, followed by the alkaline hydrolysis, allowed the expected 2-(phenanthryl)propionic acids 1-5 to be obtained in satisfactory overall yields. 相似文献