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191.
Shinichi Kitamura Kazuya Nakatani Takeshi Takaha Shigetaka Okada 《Macromolecular rapid communications》1999,20(12):612-615
Complex formation of large cyclodextrins(CDs) having DP 21–32 with iodine in aqueous KI solution was studied by isothermal titration calorimetry. The curves obtained for the titration of the CDs with iodine cannot be analyzed by a model based on a single set of identical sites, but, rather, by a model assuming 1 : 2 complex formation with identical interacting sites. For the two identical interacting sites, the binding constants K1 and K2 (K1 < K2), defined relative to the progress of saturation, lie in the range 0.7 to 7.3×103 M–1 and 3.0 to 62.6×103 M–1, respectively. The values of ΔH2 and T ΔS2 lie in the range –34.9 to –136.4 kJ·mol–1 and –15.5 to –112.8 kJ·mol–1, respectively. The largest values of –T ΔS2 obtained for a CD of DP 26 can, in part, be attributed to a large decrease in conformational flexibility of the CD which occurs during complex formation. 相似文献
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Tatsuya Hiratoko Akira Yoshiasa Tomotaka Nakatani Maki Okube Akihiko Nakatsuka Kazumasa Sugiyama 《Journal of synchrotron radiation》2013,20(4):641-643
XANES (X‐ray absorption near‐edge structure) spectra of the Ti K‐edges of ATiO3 (A = Ca and Sr), A2TiO4 (A = Mg and Fe), TiO2 rutile and TiO2 anatase were measured in the temperature range 20–900 K. Ti atoms for all samples were located in TiO6 octahedral sites. The absorption intensity invariant point (AIIP) was found to be between the pre‐edge and post‐edge. After the AIIP, amplitudes damped due to Debye–Waller factor effects with temperature. Amplitudes in the pre‐edge region increased with temperature normally by thermal vibration. Use of the AIIP peak intensity as a standard point enables a quantitative comparison of the intensity of the pre‐edge peaks in various titanium compounds over a wide temperature range. 相似文献
194.
S Umemoto S Im J Zhang M Hagihara A Murata Y Harada T Fukuzumi T Wazaki S Sasaoka K Nakatani 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(32):9999-10008
A series of xanthone and thioxanthone derivatives with aminoalkoxy substituents were synthesized as fluorescent indicators for a displacement assay in the study of small-molecule-RNA interactions. The RNA-binding properties of these molecules were investigated in terms of the improved binding selectivity to the loop region in the RNA secondary structure relative to 2,7-bis(2-aminoethoxy)xanthone (X2S) by fluorimetric titration and displacement assay. An 11-mer double-stranded RNA and a hairpin RNA mimicking the stem loop IIB of Rev response element (RRE) RNA of HIV-1 mRNA were used. The X2S derivatives with longer aminoalkyl substituents showed a higher affinity to the double-stranded RNA than the parent molecule. Introduction of a methyl group on the aminoethoxy moiety of X2S effectively modulated the selectivity to the RNA secondary structure. Methyl group substitution at the C1' position suppressed the binding to the loop regions. Substitution with two methyl groups on the amino nitrogen atom resulted in reducing the affinity to the double-stranded region by a factor of 40%. The effect of methyl substitution on the amino nitrogen atom was also observed for a thioxanthone derivative. Titration experiments, however, suggested that thioxanthone derivatives showed a more prominent tendency of multiple binding to RNA than xanthone derivatives. The selectivity index calculated from the affinity to the double-stranded and loop regions suggested that the N,N-dimethyl derivative of X2S would be suitable for the screening of small molecules binding to RRE. 相似文献
195.
We have studied current-driven dynamics of domain walls when an in-plane magnetic field is present in perpendicularly magnetized nanowires using an analytical model and micromagnetic simulations. We model an experimentally studied system, ultrathin magnetic nanowires with perpendicular anisotropy, where an effective in-plane magnetic field is developed when current is passed along the nanowire due to the Rashba-like spin-orbit coupling. Using a one-dimensional model of a domain wall together with micromagnetic simulations, we show that the existence of such in-plane magnetic fields can either lower or raise the threshold current needed to cause domain wall motion. In the presence of the in-plane field, the threshold current differs for positive and negative currents for a given wall chirality, and the wall motion becomes sensitive to out-of-plane magnetic fields. We show that large non-adiabatic spin torque can counteract the effect of the in-plane field. 相似文献
196.
Nadja A. Simeth Shotaro Kobayashi Piermichele Kobauri Stefano Crespi Wiktor Szymanski Kazuhiko Nakatani Chikara Dohno Ben L. Feringa 《Chemical science》2021,12(26):9207
Short, complementary DNA single strands with mismatched base pairs cannot undergo spontaneous formation of duplex DNA (dsDNA). Mismatch binding ligands (MBLs) can compensate this effect, inducing the formation of the double helix and thereby acting as a molecular glue. Here, we present the rational design of photoswitchable MBLs that allow for reversible dsDNA assembly by light. Careful choice of the azobenzene core structure results in excellent band separation of the E and Z isomers of the involved chromophores. This effect allows for efficient use of light as an external control element for duplex DNA formation and for an in-depth study of the DNA–ligand interaction by UV-Vis, SPR, and CD spectroscopy, revealing a tight mutual interaction and complementarity between the photoswitchable ligand and the mismatched DNA. We also show that the configuration of the switch reversibly dictates the conformation of the DNA strands, while the dsDNA serves as a chiral clamp and translates its chiral information onto the ligand inducing a preference in helical chirality of the Z isomer of the MBLs.We present the rational design of photoswitchable DNA glue to trigger the reversible formation of duplex DNA by light. The supramolecular assembly shows a mutual interaction between ligand and DNA, which induces a preferred helicity in the switch. 相似文献
197.
Boron Difluoride Curcuminoid Fluorophores with Enhanced Two‐Photon Excited Fluorescence Emission and Versatile Living‐Cell Imaging Properties
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Dr. Kenji Kamada Tomotaka Namikawa Dr. Sébastien Senatore Dr. Cédric Matthews Dr. Pierre‐François Lenne Dr. Olivier Maury Dr. Chantal Andraud Dr. Miguel Ponce‐Vargas Dr. Boris Le Guennic Prof. Denis Jacquemin Dr. Peter Agbo Dr. Dahlia D. An Dr. Stacey S. Gauny Dr. Xin Liu Dr. Rebecca J. Abergel Prof. Frédéric Fages Dr. Anthony D'Aléo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(15):5219-5232
The synthesis of boron difluoride complexes of a series of curcuminoid derivatives containing various donor end groups is described. Time‐dependent (TD)‐DFT calculations confirm the charge‐transfer character of the second lowest‐energy transition band and ascribe the lowest energy band to a “cyanine‐like” transition. Photophysical studies reveal that tuning the donor strength of the end groups allows covering a broad spectral range, from the visible to the NIR region, of the UV–visible absorption and fluorescence spectra. Two‐photon‐excited fluorescence and Z‐scan techniques prove that an increase in the donor strength or in the rigidity of the backbone results in a considerable increase in the two‐photon cross section, reaching 5000 GM, with predominant two‐photon absorption from the S0–S2 charge‐transfer transition. Direct comparisons with the hemicurcuminoid derivatives show that the two‐photon active band for the curcuminoid derivatives has the same intramolecular charge‐transfer character and therefore arises from a dipolar structure. Overall, this structure–relationship study allows the optimization of the two‐photon brightness (i.e., 400–900 GM) with one dye that emits in the NIR region of the spectrum. In addition, these dyes demonstrate high intracellular uptake efficiency in Cos7 cells with emission in the visible region, which is further improved by using porous silica nanoparticles as dye vehicles for the imaging of two mammalian carcinoma cells type based on NIR fluorescence emission. 相似文献
198.
Suguru Motokucho Akito Yamaguchi Yu Nakayama Hiroshi Morikawa Hisayuki Nakatani 《Journal of polymer science. Part A, Polymer chemistry》2017,55(12):2004-2010
We have demonstrated a hydrolysis reaction of polyurethane (PU) under high pressure of carbon dioxide (CO2) in water. We employed the PU sample, poly(methylene bis‐(1,4‐phenylene)hexamethylene dicarbamate), denoted as M‐PU, which was synthesized from 4,4′‐diphenyl methane diisocyanate and 1,4‐butane diol (BD). The optimum hydrolysis reaction condition was 190 °C under CO2 pressures over 4.1 MPa in water medium, and 93% hydrolysis of M‐PU was achieved. After the reaction, the water‐soluble parts were obtained, and isolated by column chromatography. The isolated products were 4,4′‐methylenedianiline (MDA) and 1,4‐butane diol (BD), which were components of repeating unit of M‐PU. In addition, the hydrolysis reaction gave no byproduct. This hydrolysis under high pressure of CO2 with water is a reaction by which M‐PU is selectively hydrolyzed into MDA and BD by cleaving urethane linkage. Moreover, the resulting hydrolyzed products were easily obtained by evaporation of aqueous layer after the reaction, indicating an efficient chemical recycling of PU was achieved. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2004–2010 相似文献
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