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排序方式: 共有136条查询结果,搜索用时 156 毫秒
71.
Jochem Struppe Regitze R. Vold 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,135(2):541-546
Deuterium NMR spectroscopy has been employed to characterize the concentration dependence of orientational order in DMPC/DHPC bicellar solutions with molar ratiosq= [DMPC]/[DHPC] = 3.3, 2.7, and 2.3. The stability of a discotic nematic phase can, in general, be predicted from a simple Onsager picture involving the size and concentration of the mesogenic unit, but for the bicellar solutions this model is not adequate. Specifically, macroscopic alignment is observed at total lipid concentrations well below that, 1–10% (w/w) predicted by Onsager's model. Thus the discotic nematic phase is stable to ≈3–5% (w/w) forq= 3.3–2.3, and the bicellar order is highest just before phase separation occurs at the minimum total phospholipid concentration. This implies the presence of a DHPCbic DHPCsolequilibrium in establishing bicellar size, thereby extending the range of concentrations for which alignment occurs. Bicellar morphology has been verified for a wide range of concentrations, temperatures, andq-values, but as viscosity measurements demonstrate, major morphological changes take place as the temperature is reduced below 30°C. 相似文献
72.
L. Campanella A. Bonanni R. Dragone A.L. Magrì A. Sorbo M. Tomassetti 《Microchemical Journal》2005,79(1-2):61
Unpublished analytical data obtained by recovery tests by ‘standard addition’ method, concerning lecithin determinations in human serum, bile and amniotic fluid, using new derivative enzymatic–spectrophotometric method, recently pointed out by the authors, are reported and shortly discussed. 相似文献
73.
Dr. Andrea Pannwitz Holden Saaring Dr. Nataliia Beztsinna Dr. Xinmeng Li Dr. Maxime A. Siegler Dr. Sylvestre Bonnet 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(9):3013-3018
Photosystem I (PS I) is a transmembrane protein that assembles perpendicular to the membrane, and performs light harvesting, energy transfer, and electron transfer to a final, water-soluble electron acceptor. We present here a supramolecular model of it formed by a bicationic oligofluorene 12+ bound to the bisanionic photoredox catalyst eosin Y (EY2−) in phospholipid bilayers. According to confocal microscopy, molecular modeling, and time dependent density functional theory calculations, 12+ prefers to align perpendicularly to the lipid bilayer. In presence of EY2−, a strong complex is formed (Ka=2.1±0.1×106 m −1), which upon excitation of 12+ leads to efficient energy transfer to EY2−. Follow-up electron transfer from the excited state of EY2− to the water-soluble electron donor EDTA was shown via UV–Vis absorption spectroscopy. Overall, controlled self-assembly and photochemistry within the membrane provides an unprecedented yet simple synthetic functional mimic of PS I. 相似文献
74.
The in vitro stability, under freeze–thawing procedures, and in vivo degradation, in rat spleen, of two types of polymerized liposomes were examined: 1,2‐bis‐[2E, 4E) ‐ octadecadienoyl] ‐ sn ‐ glycero ‐ 3 ‐ phosphocholine (DODPC) and 1‐acyl‐2‐[(2E, 4E)‐octadecadienoyl]‐sn‐glycero‐3‐phosphocholine (AODPC) were used as polymerizable phospholipids. The lipid composition of the liposomes was prepared as DODPC/Chol/SA (Chol = cholesterol, SA = stearicacid), AODPC/Chol/SA (7/7/2 by molar ratio), AODPC/DPPC/Chol/SA (3.5/3.5/7/2 by molar ratio). The liposomes were extruded through a 0.2 µm polycarbonate‐ filter to obtain the approximate particle size of 0.2 µm, and then irradiated with γ‐rays. Hemoglobin‐encapsulated liposomes were also prepared in the same manner with concentrated hemoglobin (Hb) solution. The DODPC/Chol/SA liposome exhibited no trace of particle size change nor Hb leakage. Although not as excellent as the former, the AODPC‐base liposome showed slightly diameter change (below 7.5%) with a substantial abatement of Hb leakage (<3.5%). Transmission electron microscopy observation of spleens also revealed more efficient degradability with AODPC/DPPC/Chol/SA liposome than with DODPC/Chol/SA liposome. Hb‐encapsulated AODPC/DPPC/Chol/SA liposome, after five freeze–thawing cycles, attained an Hb leakage below 3.5% with a particle size change of 0.7–7.5%, and reduced the spleen retention compared with the DODPC‐base liposome. These results suggest that AODPC/DPPC/Chol/SA liposome can be used as a long‐term preservable blood substitute. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
75.
We refined the united atom field for the simulations of phospholipid membranes. To validate this potential we performed 1000-ps constant pressure simulation of a dipalmitoylphosphatidicholine (DPPC) bilayer at T=50° C. The average area per head group (61.6±0.6) Å2 obtained in our simulation agrees well with the measured one of (62.9±1.3) Å2. The calculated SCD order parameters for the Sn-2 hydrocarbon tail also display a good agreement with the experiment. The conformations of head groups in our simulations of the liquid crystal phase are different than the ones observed in the crystal structure. ©1999 John Wiley & Sons, Inc. J Comput Chem 20, 531–545, 1999 相似文献
76.
Yan-Feng Wang Tian-Ming Chen Yu-Jun Li Masaya Kitamura Ikuko Sakurai Tadao Nakaya 《Journal of polymer science. Part A, Polymer chemistry》1997,35(14):3065-3074
Polyamides (4a-b and 5a-b) were synthesized from interfacial polycondensation of novel diamine containing phosphatidylcholine analogous moiety, hexamethylene diamine with adipoyl chloride, or sebacoyl chloride in the interface of water and carbon tetrachloride at room temperature. The characterizations of synthesized diamine and polyamides were carried out with FT-NMR, or IR spectral method, elemental analysis, and melting point measurements, respectively. These polyamides obtained are insoluble in any normal solvents. From the results of X-ray diffraction analysis and POM observation, it was revealed that the polyamide 4b was prepared with high molecular weight, while polyamide 4a obtained seemed to have low molecular weight. For copolymers 5a and 5b, X-ray reflections from only adipoyl or sebacoyl chloride parts were observed as in crystalline state. In addition, thermal properties were also studied by DSC and transmitted light intensity measurements. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3065–3074, 1997 相似文献
77.
78.
DMPC与蛋白质在气-液界面上复合组装过程研究 总被引:2,自引:0,他引:2
对磷脂DMPC与蛋白质(β-lactoglobulin,β-casein或humanserumalbumin)组成的复合单分子膜在压缩过程中的相变进行了研究,同时通过Brewster角显微镜观察了磷脂与蛋白质在空气-水界面处发生的自组装过程。发现当低表面压时在DMPC/β-casein,DMPC/humanserumalbumin和DMPC/β-lactoglobulin复合单分子膜上分别出现线状和块状微区,而在较高表面压时只有DMPC/β-casein体系出现钩状的微区。说明微区的形貌与蛋白质的种类及构象变化有关。 相似文献
79.
The structures and formation energies of nucleic acid—phospholipid complexes both in the absence and in the presence of Mg2+ ions were calculated taking double-stranded trinucleoside diphosphates NpNpN or heptanucleotides ApAp(NpNpN)pApA, composed
of 64 possible combinations of genetic code, and phosphatidylcholine as model compounds. The dependence of intramolecular
interactions on the primary structure of nucleic acid molecules and on the presence of a cationic bridge was revealed. The
formation energies and structure of oligonucleotides were found by molecular mechanics calculations with the AMBER force field.
The structures of phospholipid and MgCl2 molecules were calculated by the semiempirical PM3 method, while the energies of phospholipid—oligonucleotide complexes were
calculated by the molecular mechanics method. Calculations of complexes were carried our with consideration of solvation effects.
Considerable gain in the formation energy of triple complexes (13–14 kcal mol−1) is achieved due to the presence of the electroneural metal bridge. A tendency toward increasing the stability of triple
complexes containing guanosine-and cytidine-enriched triplets was revealed.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2068–2071, November, 1999. 相似文献
80.
Wanrong Song Xizhao Chen Chongshan Dai Degui Lin Xuelin Pang Di Zhang Gang Liu Yipeng Jin Jiahao Lin 《Molecules (Basel, Switzerland)》2022,27(9)
Curcumin is a natural acidic polyphenol extracted from turmeric with a wide range of biological and pharmacological effects. However, the application of curcumin for animal production and human life is limited by a low oral bioavailability. In this study, natural curcumin was prepared for the curcumin β-cyclodextrin inclusion complex (CUR-β-CD), curcumin solid dispersion (CUR-PEG-6000), and curcumin phospholipid complex (CUR-HSPC) using co-precipitation, melting, and solvent methods, respectively. Curcumin complex formations were monitored using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) techniques via the shifts in the microscopic structure, molecular structure, and crystalline state. Subsequently, twenty-four female beagle dogs were randomly divided into four groups to receive unmodified curcumin and three other curcumin preparations. The validated UPLC–MS assay was successfully applied to pharmacokinetic and bioavailability studies of curcumin in beagle dog plasma, which were collected after dosing at 0 min (predose), 5 min, 15 min, 30 min, 40 min, 50 min, 1.5 h, 3 h, 4.5 h, 5.5 h, 6 h, 6.5 h, 9 h, and 24 h. The relative bioavailabilities of CUR-β-CD, CUR-PEG-6000, and CUR-HSPC were 231.94%, 272.37%, and 196.42%, respectively. This confirmed that CUR-β-CD, CUR-HSPC, and especially CUR-PEG-6000 could effectively improve the bioavailability of curcumin. 相似文献