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721.
Hattori T Shimazumi Y Goto H Yamabe O Morohashi N Kawai W Miyano S 《The Journal of organic chemistry》2003,68(6):2099-2108
A naturally occurring 1,1'-biphenanthrene, blestriarene C (1), was prepared in 13 steps and 30% overall yield. The key steps are the ester-mediated nucleophilic aromatic substitution on 2,6-di-tert-butyl-4-methoxyphenyl 5-isopropoxy-2-methoxybenzoate (4) by 2-methoxy-4-methoxymethoxy-6-methylphenylmagnesium bromide (5) and a novel intramolecular cyclization of the resulting 4-isopropoxy-2'-methoxy-4'-methoxymethoxy-6'-methylbiphenyl-2-carboxylic ester 14 to 7-isopropoxy-4-methoxy-2-(methoxymethoxy)phenanthren-9-ol (15). The racemic blestriarene C was optically resolved by chiral HPLC on a preparative scale to give several 10-mg yields of both the enantiomers in up to 95% ee. The absolute stereochemistry was determined to be S(a)-(-) by the axial chirality recognition method, which was based on the stereospecific formation of a 12-membered cyclic diester containing two biaryl-o,o'-diyl unites joined by ester -CO(2)- linkages. The validity of the method was confirmed by an X-ray crystallographic analysis and ab initio conformational analyses of such 12-membered cyclic diesters. It was found that blestriarene C and its 7,7'-diisopropyl ether 2 underwent rapid photoracemization even under ambient light exposure. 相似文献
722.
The novel 9,10-epidithio-9,10-dihydroanthracene (
) was formed as an intermediate in the reaction of 9,10-dihydro-9,10-(1,3-epidithio-2-methano- 2-p-methoxyphenyl-1-oxide)propanoanthracene (
) with perchloric acid. Singlet diatomic sulfur was generated from endodisulfide
and trapped with conjugated dienes. 相似文献
723.
Dendrimer technology has enabled us to build macromolecules with nanosized defined structures. By introducing unsymmetrical
patched structures in dendrimers, sophisticated artificial receptors exhibiting nanoscale substrate recognition can be obtained.
In this review article, our recent studies on molecular recognition by porphyrin dendrimers with patched structures are summarized.
Three topics are presented: (1) oligopeptide-patched dendrimers as a nanoscale receptor of cytochrome c protein; (2) pocket dendrimers as a nanoscale receptor for bimolecular guest accommodation; and (3) energy transfer in unsymmetrical
dendrimers. These dendrimers nicely mimic proteins and enzymes, and also act as photofunctional artificial receptors, in which
porphyrin’s strong photoabsorption and intense fluorescence signals can respond sensitively to the substrate binding. 相似文献
724.
Reactions of several cyclic disulfides with carbenes generated by catalytic and photochemical decompositions of diazo compounds have been studied. Carbenes reacted with cyclic disulfides yielding 1,3-dithiane quantitatively as S-S insertion reaction, while the selective desulfurization results in the reaction of disulfides with bulky substituents. The carbene reaction is sensitive to bulkiness of disulfides. 相似文献
725.
π-Bonded silaacrylate was isolated in argon matrix at 10K by the photolysis (λ > 360 nm) of ethyl pentamethyldisilanyldiazoacetate. The silaacrylate immediately changed to (ethoxydimethylsilyl) (trimethylsilyl)-ketene at 10K by the brief irradiation with the light of shorter wavelength (λ > 240 nm). 相似文献
726.
Urata S Irisawa J Takada A Shinoda W Tsuzuki S Mikami M 《The journal of physical chemistry. B》2005,109(9):4269-4278
Molecular dynamics simulations of the swollen membrane of perfluorinated ionomer, which is composed of poly(tetrafluoroethylene) backbones and perfluosulfonic pendant side chains, have been undertaken to analyze the static and dynamic properties of the water and the side chain in the membrane. The calculations were carried out for four different water contents, 5, 10, 20 and 40 wt %, at 358.15 K and 0.1 MPa. The results are summarized as follows: (1) The sulfonic acid is the unique site to which water molecules can bind, and the other sites in the pendant side chain have no bound water even at high water concentration. (2) Sulfonic acids aggregate in the short range within 4.6-7.7 A despite the electrostatic repulsion between them. In such aggregates, a water molecule bridges two sulfonic acids. (3) Pendant side chains prefer to orient perpendicular to the hydrophilic/hydrophobic interface, and long-range correlation of side chain orientations is observed at 20 and 40 wt % water uptake membranes. (4) In a low water uptake membrane, the dynamics of water is substantially restricted due to strong attractive interactions with acidic sites. In contrast, at high water content, even the water locating near the sulfonic acid is relatively mobile. The short residence time of the bound water reveals that such water can frequently exchange position with relatively free water, which locates in the center of water cluster, in highly swollen membranes. 相似文献
727.
Koichi Mikami Masahiro YamanakaMd.Nazrul Islam Kenichi KudoNobuko Seino Masaki Shinoda 《Tetrahedron letters》2003,44(40):7545-7548
The reactivity of the Mukaiyama aldol reaction is significantly increased by ‘fluorous nano flow’ system even in the low concentration (<0.0001 M) of a lanthanide fluorous catalyst and the reaction completes within seconds as a contact time in the micro cell. 相似文献
728.
Kudo M Ohkawa H Sugimoto W Kumada N Liu Z Terasaki O Sugahara Y 《Inorganic chemistry》2003,42(14):4479-4484
The conversion process of an Aurivillius phase, Bi(2)W(2)O(9), into a layered tungstic acid by hydrochloric acid treatment has been investigated, and resultant H(2)W(2)O(7) x nH(2)O has been fully characterized. The c parameter of Bi(2)W(2)O(9) [2.37063(5) nm] decreases to 2.21(1) nm in an acid-treated product dried at ambient temperature. The a and b parameters of Bi(2)W(2)O(9) [a = 0.54377(1) nm and b = 0.54166(1) nm] also decrease slightly to a = 0.524(1) nm and b = 0.513(1) nm in the acid-treated product dried at ambient temperature, indicating structural changes in the ReO(3)-like slabs in Bi(2)W(2)O(9) upon acid treatment. Drying at 120 degrees C leads to a further decrease in the c parameter [1.86(1) nm] with no notable change in the a and b parameters [a = 0.5249(2) nm and b = 0.513(2) nm]. The formation of an expandable layered structure is demonstrated by the successful intercalation of n-octylamine [interlayer distance 2.597(9) nm] and n-dodecylamine [interlayer distance 3.56(2) nm]. The compositions of the acid-treated products are determined to be H(2)W(2)O(7) x nH(2)O typically with n = 0.58 for the air-dried product and n = 0 for the product dried at 120 degrees C. As a consequence, the composition of the layer is H(2)W(2)O(7), and the decrease in the c parameter upon drying is ascribable to the loss of interlayer water. Scanning electron microscopy reveals no morphological change during acid treatment, which strongly suggests a selective leaching of the bismuth oxide sheets as a reaction mechanism. High-resolution transmission electron microscopy (HREM) observation of the acid-treated product shows consistency with a structural model for H(2)W(2)O(7), derived from Bi(2)W(2)O(9) through removal of the bismuth oxide sheets and contraction along the c axis. HREM observation also reveals that the WO(6) octahedra arrangement changes slightly with acid treatment. A one-dimensional electron density map projected on the c axis for the product dried at 120 degrees C, H(2)W(2)O(7), shows good consistency with that calculated for the structural model. 相似文献
729.
Shinoda S Okazaki T Player TN Misaki H Hori K Tsukube H 《The Journal of organic chemistry》2005,70(5):1835-1843
Cholesterol-armed cyclens worked as octadentate receptors for Na+, Ca2+, and Y3+ complexes in which four chiral cholesterol-functionalized sidearms were bundled and asymmetrically twisted above cyclen-metal complex platforms. Since the resulting helical metal complexes included chiral, hydrophobic cholesterol residues and charged, hydrophilic metal sites as well as asymmetric coordination geometries, they exhibited unique amphiphilic properties and provided chiral self-aggregates in aqueous solutions. Light scattering, fluorescence, and TEM characterizations demonstrated that Na+ complex with cholesterol-armed cyclen gave a particularly stable self-aggregate in aqueous solution and offered supramolecular environments effective for sensing and detection of amino acid anions. Various dansylamino acid derivatives (dansyl = 5-(dimethylamino)-1-naphthalenesulfonyl) were nicely accommodated in the helicate aggregates to give highly enhanced fluorescence signals, which could be detected by the naked eye at 10(-7) mol/L level. Their inclusion behaviors were analyzed by a Langmuir-type equation, indicating that enantiomer-selective inclusion occurred. MM/MD calculations and circular dichroism (CD) studies further suggested that cholesterol-armed cyclen helicates have chiral and hydrophobic cavities upon self-aggregation, in which the dansylamino acid anions were specifically accommodated. Since these helicates exhibited nonselective binding abilities in solvent extraction experiments of dansylamino acid anions, uncommon chiral recognition and sensing functions were generated by supramolecular alignments of the chiral metal helicates in the aqueous solutions. 相似文献
730.
Hitoshi Tamiaki Satomi Unno Eiji Takeuchi Nobuyuki Tameshige Satoshi Shinoda Hiroshi Tsukube 《Tetrahedron》2003,59(52):10477-10483
Synthetic gadolinium(III)porphyrins with various achiral β-diketonates as axial ligands in benzene solutions extracted chiral -amino acids and dipeptides from aqueous phases to give intense induced CD peaks in the Soret region via 1:1 supercomplexation. Their CD spectral shapes were dependent on the stereochemistry at the -positions of amino acids and of the C-terminal components of dipeptides: a reverse S-shape for the
-form and an S-shape for the
-form. When chiral 3-acetylcamphorate was introduced as an axial ligand, Gd(III)porphyrins showed CD spectral changes by supercomplexation with chiral alanylalanine; (+)-acetylcamphorate ligating Gd(III)porphyrin offered larger CD signal with the
- or
-form than the corresponding (−)-type Gd(III)porphyrin did, while the former afforded smaller CD peaks by supercomplexation with the
- or
-form than the latter Gd(III)porphyrin. 相似文献