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排序方式: 共有112条查询结果,搜索用时 15 毫秒
61.
In this study, biodegradable and antibacterial poly(azomethine‐urethane) (PAMU)‐ and chitosan (CS)‐based hydrogels have been prepared for controlled drug delivery applications. Structural and morphological characterizations of the hydrogels were performed via Fourier transform‐infrared and scanning electron microscopy analyses. Thermal stability, hydrophilicity, swelling, mechanical, biodegradation, protein absorption properties, and drug delivery application of PAMU‐ and CS‐based hydrogels were also investigated. The swelling performance of the hydrogels was studied in acidic, neutral, and alkaline media. Swelling results showed that the hydrogels have higher swelling capacity in acidic and alkaline media than neutral medium. Biodegradation experiments of the hydrogels were also studied via hydrolytic and enzymatic experiments. The drug release property of the hydrogel was carried out using 5‐fluoro uracil (5‐FU), and 5‐FU release capacity of the hydrogels was found in the range from 40.10% to 58.40% after 3 days. 相似文献
62.
63.
Geraldine J. M. Ler Dr. Weijun Xu Dr. Jeffrey Y. W. Mak Dr. Ligong Liu Prof. Paul V. Bernhardt Prof. David P. Fairlie 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(68):15594-15608
5-(2-Oxopropylideneamino)-6-d -ribitylaminouracil (5-OP-RU) is a natural product formed during bacterial synthesis of vitamin B2. It potently activates mucosal associated invariant T (MAIT) cells and has immunomodulatory, inflammatory, and anticancer properties. This highly polar and unstable compound forms a remarkably stable Schiff base with a lysine residue in major histocompatibility complex class I–related protein (MR1) expressed in antigen-presenting cells. Inspired by the importance of the ribityl moiety of 5-OP-RU for binding to both MR1 and the T cell receptor (TCR) on MAIT cells, each OH was removed in silico. DFT calculations and MD simulations revealed a very stable hydrogen bond between the C3′−OH and uracil N1H, which profoundly restricts flexibility and positioning of each ribityl-OH, potentially impacting their interactions with MR1 and TCR. By using deoxygenation strategies and kinetically controlled imine formation, four monodeoxyribityl and four monohydroxyalkyl analogues of 5-OP-RU were synthesised as new tools for probing T cell activation mechanisms. 相似文献
64.
We have calculated the frequencies of the normal vibrations of the complementary nucleic acid base pairs adenine–thymine,
guanine–cytosine, adenine–uracil, corresponding to the Watson–Crick structure, and the adenine–uracil pair, corresponding
to the Hoogsteen structure, in condensed states and we interpret the spectra. We determine the contributions of hydrogen bonds
to the vibrational modes of the complementary pairs. We have analyzed the nature of the relative displacements of the nucleic
acid bases as integral molecular units along the hydrogen bonds. We show the role of hydrogen bonds in tautomeric interconversions
of complementary nucleic acid base pairs.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 84–92, January–February, 2009. 相似文献
65.
5-Acetyl-1-(3,5-O-isopropylidene--D-xylofuranosyl) uracil monohydrate (-AXU·H2O) crystallizes in an orthorhombic cell of dimensionsa=7.286(6),b 14.281(10),c=15.852(11) Å. Its structure has been determined by direct methods from single-crystal CuK
X-ray data and refined to a conventionalR factor of 0.055 over 1708 unique reflections. The furanose ring has conformation C2'endo-C3'endo (rather than the uncommon C3'endo-C4'exo as in -AXU) and the glycosidic torsion angle is –31° (17° in -AXU). The oxygen of the water molecule in -AXU·H2O accepts a hydrogen bond (O 10...O 5=2.70 Å) from the sugar hydroxyl O5 and the hydrogens form hydrogen bonds to a uracil carbonyl (O 10...O 2=2.78 Å) and an isopropylidene oxygen atom (O 10...O 7=2.90 Å). 相似文献
66.
X. P. Fu H. A. Aisa M. Abdurahim A. Yili S. F. Aripova B. Tashkhodzhaev 《Chemistry of Natural Compounds》2007,43(2):181-183
The known compounds cappariloside A and stachydrin, an adenosine nucleoside, and for the first time from plants of the Capparidaceae
family the known compounds hypoxanthine and uracil were isolated from Capparis spinosa (Capparidaceae) fruit.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 149–151, March–April, 2007. 相似文献
67.
YingCAI JianYiWU NaWANG XiaoFengSUN XianFuLIN 《中国化学快报》2004,15(5):594-596
Michael addition reactions of uracil to acrylates were catalyzed by an alkaline protease from Bacillus subtilis in dimethyl sulfoxide at 55℃ for 72h. The adducts were determined by TLC, IR and ^1 H NMR. 相似文献
68.
嘧啶及其异构体的密度泛函理论研究 总被引:2,自引:2,他引:0
胞嘧啶、尿嘧啶和胸腺嘧啶都有酮式和烯醇式互变异构。有人认为DNA的错配频率,与酮,烯醇或氨,亚氨的互变异构平衡有关。迄今,在相同理论水平上同时对三种嘧啶互变异构体进行理论计算研究的文献较少, 相似文献
69.
Detailed chemical kinetic mechanisms for the synthesis of complex organic molecules in the interstellar medium are at an early stage of developement. That such synthesis must take place is well-known from chemical analysis of sampled asteroids. As molecular complexity increases the number of possible structural isomers also increases with the consequence that the nascent species may adopt a different spatial arrangement, to the lowest energy one. As part of a program of investigations of the hydrogen atom transfer reaction or tautomerization of imidic acid–amide species H-O=C-N- O=C-N-H we have studied the kinetics for a number of nucleobases, namely cytosine, thymine and uracil where a cyclic form of tautomerism (lactim–lactam) is encountered. Together with a fourth, 5-aza-uracil (1,3,5-triazine-2,4(1H,3H)-dione), we report on the rates of reaction at low temperatures 50–200 K for both the direct unimolecular process and the similar transformation mediated by an additional water molecule. We show that these tautomerization reactions can be categorized into three classes, and highlight the importance of quantum mechanical tunneling on the rate constants at these low temperatures. We further present some thermochemistry data, such as formation enthalpies, entropies, isobaric heat capacities and enthalpy functions. 相似文献
70.