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排序方式: 共有313条查询结果,搜索用时 62 毫秒
61.
Rai R Vasudev PG Ananda K Raghothama S Shamala N Karle IL Balaram P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(20):5917-5926
The beta turn segment in designed peptide hairpins has been expanded by the insertion of beta-, gamma- and delta-amino acids at the i+2 position. The model octapeptides Boc-Leu-Phe-Val-DPro-Ac6c-Leu-Phe-Val-OMe (1), Boc-Leu-Phe-Val-DPro-beta3-Ac6c-Leu-Phe-Val-OMe (2), and Boc-Leu-Phe-Val-DPro-Gpn-Leu-Phe-Val-OMe (3) have been shown to adopt beta hairpin conformations in methanol by the observation of key diagnostic nuclear Overhauser effects. Boc-Leu-Val-Val-DPro-delta-Ava-Leu-Val-Val-OMe (4) adopts a beta hairpin conformation in crystals; this is stabilized by three cross-strand hydrogen bonds as demonstrated by X-ray diffraction. The canonical C10 turn in an alpha-alpha segment is expanded to C11, C12, and C13 turns in alpha-beta, alpha-gamma, and alpha-delta segments, respectively. The crystal structures of Piv-LPro-beta3-Ac6c-NHMe (5) and Boc-Ac6c-Gpn-Ac6c-OMe (6) reveal intramolecularly hydrogen-bonded C11 and C12 conformations, respectively. Computer modeling of octapeptide sequences that contain centrally positioned hybrid-turn segments, by using turn parameters derived from the structures of peptides 5 and 6, establishes the stereochemical acceptability of the beta hairpins in the cases of peptides 2 and 3. Accommodation of omega-amino acids into the turn segments is achieved by the adoption of gauche conformations around the backbone C--C bonds. 相似文献
62.
63.
Luigi Coppola Mohamed Youssry Isabella Nicotera Luigi Gentile 《Journal of colloid and interface science》2009,338(2):550-557
The thermal behavior of unsonicated dispersions of a double-chained surfactant, Dioctadecyldimethylammonium bromide (DODAB), has been studied over a wide concentration range using DSC and dynamic rheology. All dispersions are characterized by the pre- and main transition peaks at 35 °C and 43 °C, respectively. But, only above 10 mM DODAB, a third endotherm at 52 °C appears which may correspond to the (ULVs + Lα fragments) → MLVs transition. The thermal-induced MLV’s size is proportionally dependent on the concentration. In addition, and in agreement with DSC data, dynamic rheology has proven to be an indirect way to elucidate the structural transitions in these DODAB vesicular dispersions. 相似文献
64.
Isabella Richter Mark R. Warren Jusaku Minari Souad A. Elfeky Wenbo Chen Mary F. Mahon Paul R. Raithby Prof. Tony D. James Kazuo Sakurai Simon J. Teat Steven D. Bull John S. Fossey Dr. 《化学:亚洲杂志》2009,4(1):194-198
The crystal structures of phenylpropylpyridine‐N‐oxide and N‐methyl‐phenylpropylpyridinium iodide are compared, revealing that hydrogen bonding with the solvent molecule plays an important role in the N‐oxide compound, whilst electrostatic interactions are predominant in controlling the solid‐state orientation of the N‐methylated compound. Fluorescence spectroscopy and NOESY indicate that in contrast to the previously reported pyridinium iodide, the N‐oxide is not subject to intramolecular π‐stacking, as judged by excimer emission and a lack of corresponding cross peaks, respectively. 相似文献
65.
Mustazza C Borioni A Sestili I Sbraccia M Rodomonte A Ferretti R Del Giudice MR 《Chemical & pharmaceutical bulletin》2006,54(5):611-622
Some spiro[piperidine-4,2'(1'H)-quinazolin]-4'(3'H)-ones 3 and spiro[piperidine-4,5'(6'H)-[1,2,4]triazolo[1,5-c]quinazolines] 4 were synthesized and evaluated as ligands of the nociceptin receptor. The examined compounds showed partial agonistic activity, except compounds 3, 4n that proved to be pure antagonists. 相似文献
66.
Isabella L. Karle Y. B. R. D. Rajesh Subramania Ranganathan 《Journal of chemical crystallography》2009,39(3):201-208
Abstract Individually prepared, equivalent amounts of 2,5-bis-(4-pyridyl)-1,3,4-oxadiazole (4-BPO) and benzenehexacarboxylic acid (mellitic
acid, MA) when mixed, deposited long rods, whose X-ray structure showed a unique assembly of 40 membered planar modules composed
from two alternating units each of MA and 4-BPO, rather than the anticipated helical profile. Several novel features of complexes
of MA with organic molecules are seen here. In almost all cases the intermolecular hydrogen bonding between MA anions is so
stable that the MA anions and the complementary cations lie in separate planes. This barrier is overcome in the present case.
The basic module associates to form quartets by very simple hydrogen bonding of the carboxylic groups of MA. The quartet assembly
is characterized by the rotation of the left hand pair compared to the right hand pair. The mode of the macromolecular assembly
is clear, that is, they are layered in alternating planes. Space group: P21/c with a = 9.181(1) ?, b = 9.624(1) ?, c = 29.390(2) ?, and β = 94.626(4)°. The modules are embedded in an extensively hydrogen bonded MA network. The assembly profile of MA and 4-BPO
is unique and should be a harbinger for the design of novel functional assemblies. The 40-membered module mimics the self-assemblies
of peptides and can be important in the design of “Haptens” from simple molecules.
Index Abstract Rod like crystals from water that are formed on mixing MA and 4-BPO are shown to consist of 4-molecule modules (MA–4-BPO–MA–4-BPO–)
that contain a 40-membered ring, MA–BPO.
相似文献
67.
Alessio Boldrin Steffen Foss Hansen Anders Baun Nanna Isabella Bloch Hartmann Thomas Fruergaard Astrup 《Journal of nanoparticle research》2014,16(6):1-19
Information related to the potential environmental exposure of engineered nanomaterials (ENMs) in the solid waste management phase is extremely scarce. In this paper, we define nanowaste as separately collected or collectable waste materials which are or contain ENMs, and we present a five-step framework for the systematic assessment of ENM exposure during nanowaste management. The framework includes deriving EOL nanoproducts and evaluating the physicochemical properties of the nanostructure, matrix properties and nanowaste treatment processes as well as transformation processes and environment releases, eventually leading to a final assessment of potential ENM exposure. The proposed framework was applied to three selected nanoproducts: nanosilver polyester textile, nanoTiO2 sunscreen lotion and carbon nanotube tennis racquets. We found that the potential global environmental exposure of ENMs associated with these three products was an estimated 0.5–143 Mg/year, which can also be characterised qualitatively as medium, medium, low, respectively. Specific challenges remain and should be subject to further research: (1) analytical techniques for the characterisation of nanowaste and its transformation during waste treatment processes, (2) mechanisms for the release of ENMs, (3) the quantification of nanowaste amounts at the regional scale, (4) a definition of acceptable limit values for exposure to ENMs from nanowaste and (5) the reporting of nanowaste generation data. 相似文献
68.
69.
The palladium-catalyzed electrocarbonylation of heteroaromatic iodides, performed in the presence of formic acid under one atmosphere of carbon monoxide, affords heteroaromatic aldehydes in moderate to good yields. It has been developed a new application of palladium-catalyzed formylation using carbon monoxide, formic acid and tertiary amines as ligands under electrochemical reducing conditions. 相似文献
70.
Heterologous Expression,Biosynthetic Studies,and Ecological Function of the Selective Gq‐Signaling Inhibitor FR900359
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Dr. Max Crüsemann Raphael Reher Isabella Schamari Dr. Alexander O. Brachmann Dr. Tsubasa Ohbayashi Markus Kuschak Dr. Davide Malfacini Alexander Seidinger Marta Pinto‐Carbó René Richarz Tatjana Reuter Dr. Stefan Kehraus Dr. Asis Hallab Misty Attwood Prof. Dr. Helgi B. Schiöth Dr. Peter Mergaert Dr. Yoshitomo Kikuchi Prof. Dr. Till F. Schäberle Prof. Dr. Evi Kostenis Prof. Dr. Daniela Wenzel Prof. Dr. Christa E. Müller Prof. Dr. Jörn Piel Prof. Dr. Aurélien Carlier Prof. Dr. Leo Eberl Prof. Dr. Gabriele M. König 《Angewandte Chemie (International ed. in English)》2018,57(3):836-840
The cyclic depsipeptide FR900359 (FR), isolated from the tropical plant Ardisia crenata, is a strong and selective inhibitor of Gq proteins, making it an indispensable pharmacological tool to study Gq‐related processes, as well as a promising drug candidate. Gq inhibition is a novel mode of action for defense chemicals and crucial for the ecological function of FR, as shown by in vivo experiments in mice, its affinity to insect Gq proteins, and insect toxicity studies. The uncultured endosymbiont of A. crenata was sequenced, revealing the FR nonribosomal peptide synthetase (frs) gene cluster. We here provide a detailed model of FR biosynthesis, supported by in vitro enzymatic and bioinformatic studies, and the novel analogue AC‐1, which demonstrates the flexibility of the FR starter condensation domains. Finally, expression of the frs genes in E. coli led to heterologous FR production in a cultivable, bacterial host for the first time. 相似文献