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排序方式: 共有371条查询结果,搜索用时 125 毫秒
81.
Miharu Eguchi Hiroshi Tachibana Shinsuke Takagi Haruo Inoue 《Research on Chemical Intermediates》2007,33(1-2):191-200
The intercalation behavior of cationic porphyrin derivatives within the interlayer spaces of nano-layered clay minerals has been investigated. The porphyrins were successfully intercalated by the newly adopted method of repeated freeze-thaw cycles. The absorption spectra of the porphyrins were compared in the solution phase, adsorbed onto the exfoliated clay nano-sheets, intercalated within the interlayer spaces of clay sheets dispersed in water and intercalated in dry films. Substantial red shifts of the λmax values in the absorption spectra of the porphyrins were observed on the exfoliated clay sheets, and further red shifts were induced within the interlayer space. The dry films of the intercalated samples exhibited the largest red shifts. X-ray diffraction studies revealed that the clearance space between the layers in these intercalated hybrid compounds is only large enough for the porphyrins to be rigidly packed parallel to the clay layer. For the exfoliated clay nano-sheets, theoretical calculations were carried out on the correlation between the dihedral angle of the meso-substituted pyridiniumyl plane vs. the porphyrin ring and the λmax of the porphyrin Soret band. An extrapolation of the experimental λmax value to the correlation curve, afforded the dihedral angle to be 61.6°. The microscopic structure of the adsorbed state of the cationic porphyrins on the exfoliated clay nano-sheets was, thus, proposed to involve an orientation parallel to the clay surface, with a distance of 0.15 nm from the surface, which implies the expulsion of the solvent water molecules. 相似文献
82.
Ifuku S Kamitakahara H Takano T Tanaka F Nakatsubo F 《Organic & biomolecular chemistry》2004,2(3):402-407
Cellulose was reacted with a series of 4-alkoxytrityl chlorides (C(n)TCl, n: number of carbon atoms in a saturated alkyl chain) under homogeneous reaction conditions in LiCl-N,N-dimethyl acetoamide to give a series of 6-O-(4-alkoxytrityl)celluloses (C(n)TC) with a high degree of substitution (DS), from 0.94 to 0.99, and with high regioselectivity at the 6-O position. Solubility of the C(n)TC in nonpolar solvents depended on the alkyl chain length: as the alkyl chain lengthens, cellulose derivatives become more hydrophobic and are readily soluble in nonpolar solvents, but not in polar solvents. Acetates of the C(4)-C(18)TC (C(4)-C(18)TCAc) showed anisotropic structures over melting temperatures (T(m)) examined under a polarized optical microscope (POM). Over isotropization temperatures (T(i)), flow birefringence were detected for C(12)-C(18)TCAc. The T(m) and T(i) decreased linearly with an increasing number of carbon atoms in the alkyl substituent. Wide-angle X-ray scattering (WAXS) studies of C(n)TC indicated that the fully extended side chains were perpendicular to the polymer backbone and interdigitated. These C(n)TC with the improved solubility may be used as starting materials for further derivatization focused on the secondary hydroxyl groups at the C-2 and C-3 positions. 相似文献
83.
Matsumoto A Tanaka T Tsubouchi T Tashiro K Saragai S Nakamoto S 《Journal of the American Chemical Society》2002,124(30):8891-8902
We now report the molecular and crystal structure design of muconic ester derivatives on the basis of crystal engineering using halogen-halogen contacts and CH/pi interactions. The solid-state photoreaction pathway of the dibenzyl (Z,Z)-muconates as the 1,3-diene dicarboxylic acid monomers depends on the structure of the ester groups. The substitution of a halogen atom for the aromatic hydrogen of a benzyl group induces topochemical polymerization to produce stereoregular polymers in a crystalline form, whereas the unsubstituted benzyl derivative isomerizes to yield the corresponding E,E isomer under similar conditions. The topochemical polymerization process is directly confirmed by the fact that the single-crystal structures before and after the polymerization are very similar to each other. From the crystal structure analysis for a series of substituted benzyl (Z,Z)- and (E,E)-muconates, it has been revealed that the planar diene moieties are closely packed to form a columnar structure in the crystals. The stacking of the polymerizable monomers is characterized by a stacking distance of 4.9-5.2 A along the columns. This structure is supported by a halogen-halogen interaction between the chlorine or bromine atoms introduced at the p position of the benzyl groups in addition to an aromatic stacking due to the CH/pi interaction between the benzylic methylene hydrogens and aromatic rings. The design of a monomer packing corresponds to the type and position of the introduced halogen atom and also the polymorphs. To make a stacking distance of 5 A using both halogen-halogen and CH/pi interactions as supramolecular synthons is important for the molecular design of muconic ester derivatives appropriate for topochemical polymerization. 相似文献
84.
85.
Yamamoto T Endo A Inagi Y Ohmori T Nakaiwa M 《Journal of colloid and interface science》2005,284(2):614-620
The accuracy of thermoporometry (TPM) in terms of the characterization of SBA-15 is examined based on a model that classifies the water in the mesopores into two different types: freezable pore water, which can form cylindrical ice crystals, and nonfreezable pore water, which cannot undergo a phase transition during a differential scanning calorimetry (DSC) measurement. Applying the empirical relationship between the sizes of the ice crystals formed in the mesopores and the solidification temperature of the freezable pore water to a thermogram (a recording of the heat flux during the solidification of the freezable pore water) yielded a size distribution of the ice crystals. The size of the ice crystals increased slightly with repetitive freezing, indicating that the mesopores were enlarged by formation of the ice crystals. Adding the thickness, t(nf), of the nonfreezable pore water layer to the ice crystal-size distribution calculated from the thermogram allowed for the determination of the porous properties of SBA-15. The porous properties attained from TPM experiments were compared with the results attained through the combination of Ar gas adsorption experiments and nonlocal density functional theory (NLDFT) analysis. The porous properties determined by TPM were confirmed to be quite sensitive to the t(nf) value. 相似文献
86.
87.
M. Iftekhar Shams Shinsuke Ifuku Masaya Nogi Takeshi Oku Hiroyuki Yano 《Applied Physics A: Materials Science & Processing》2011,102(2):325-331
This paper demonstrates the preparation of chitin nanofibers from crab shells using a simple mechanical treatment. The nanofibers
are small enough to retain the transparency of neat acrylic resin. Possessing hydroxyl and amine/N-acetyl functionalities, water suspension of chitin nanofibers was vacuum-filtered 9 times faster than cellulose nanofibers
to prepare a nanofiber sheet of 90 mm in diameter. This is a prominent advantage of chitin nanofibers over cellulose nanofibers
in terms of commercial application. Interestingly, chitin acrylic resin films exhibited much higher transparency than cellulose
acrylic resin films owing to the close affinity between less hydrophilic chitin and hydrophobic resin. Furthermore, the incorporation
of chitin nanofibers contributes to the significant improvement of the thermal expansion and mechanical properties of the
neat acrylic resin. The properties of high light transmittance and low thermal expansion make chitin nanocomposites promising
candidates for the substrate in a continuous roll-to-roll process in the manufacturing of various optoelectronic devices such
as flat panel displays, bendable displays, and solar cells. 相似文献
88.
Cover Picture: Controlled Synthesis of Nanoporous Nickel Oxide with Two‐Dimensional Shapes through Thermal Decomposition of Metal–Cyanide Hybrid Coordination Polymers (Chem. Eur. J. 9/2015)
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89.
Tatsuya Higashi Koichi Ito Misato Narushima Takahiro Sugiura Shinsuke Inagaki Jun Zhe Min Toshimasa Toyo'oka 《Biomedical chromatography : BMC》2011,25(11):1175-1180
A method for the quantification of progesterone (PROG) in human saliva using liquid chromatography–electrospray ionization–tandem mass spectrometry (LC‐ESI‐MS/MS) has been developed and validated. The saliva was deproteinized with acetonitrile, purified using a Strata™‐X cartridge, and subjected to LC‐ESI‐MS/MS. Quantification was based on selected reaction monitoring, and deuterated PROG was used as the internal standard. This method allowed the reproducible (intra‐ and inter‐assay relative standard deviations, <2.2%) and accurate (analytical recovery, 96.6–99.7%) quantification of the salivary PROG using a 400 μL sample, and the limit of quantification was 12.5 pg/mL. The developed method enabled detection of the variation in the salivary PROG concentrations of healthy volunteers during the menstrual cycle and measurement of the salivary concentrations of pregnant women. The method is expected to be an alternative to the blood PROG monitoring in clinical examinations, because saliva collection is easy, non‐invasive and repeatable. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
90.