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51.
Journal of Heuristics - In this paper, we present a method to identify forum posts expressing user intentions in online discussion forums. The results of this task, for example buying intentions,... 相似文献
52.
Journal of Sol-Gel Science and Technology - The aim of the study was to prepare magnetic photo-Fenton catalysts based on CoFe2O4 by polyethylene glycol-assisted sol-gel method for the degradation... 相似文献
53.
A Diazido Mannose Analogue as a Chemoenzymatic Synthon for Synthesizing Di‐N‐acetyllegionaminic Acid‐Containing Glycosides 下载免费PDF全文
Dr. Abhishek Santra An Xiao Dr. Hai Yu Wanqing Li Dr. Yanhong Li Linh Ngo Dr. John B. McArthur Prof. Dr. Xi Chen 《Angewandte Chemie (International ed. in English)》2018,57(11):2929-2933
A chemoenzymatic synthon was designed to expand the scope of the chemoenzymatic synthesis of carbohydrates. The synthon was enzymatically converted into carbohydrate analogues, which were readily derivatized chemically to produce the desired targets. The strategy is demonstrated for the synthesis of glycosides containing 7,9‐di‐N‐acetyllegionaminic acid (Leg5,7Ac2), a bacterial nonulosonic acid (NulO) analogue of sialic acid. A versatile library of α2‐3/6‐linked Leg5,7Ac2‐glycosides was built by using chemically synthesized 2,4‐diazido‐2,4,6‐trideoxymannose as a chemoenzymatic synthon for highly efficient one‐pot multienzyme (OPME) sialylation followed by downstream chemical conversion of the azido groups into acetamido groups. The syntheses required 10 steps from commercially available d ‐fucose and had an overall yield of 34–52 %, thus representing a significant improvement over previous methods. Free Leg5,7Ac2 monosaccharide was also synthesized by a sialic acid aldolase‐catalyzed reaction. 相似文献
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Achille B. Nouga Emmanuel M. Mpondo Judith Caroline Ngo Nyobe Alain Njoya Luc M. Meva'a 《Natural product research》2016,30(3):305-310
Fractionation of the methanol extract of the leaves of Oricia renieri and Oricia suaveolens (Rutaceae) led to the isolation of 13 compounds including the hitherto unknown furoquinoline alkaloid named 6,7-methylenedioxy-5-hydroxy-8-methoxy-dictamnine (1) and a flavanone glycoside named 5-hydroxy-4′-methoxy-7-O-[α-l-rhamnopyranosyl(1?→5″)-β-d-apiofuranosyl]-flavanoside (2), together with 11 known compounds (3–13). The structures of the compounds were determined by comprehensive analyses of their 1D and 2D NMR, mass spectral data and comparison. All compounds isolated were examined for their activity against human carcinoma cell lines. The alkaloids 1, 5, 12, 13 and the phenolic 2, 8, 11 tested compounds exhibited non-selective moderate cytotoxic activity with IC50 8.7–15.9 μM whereas compounds 3, 4, 6, 7, 9 and 10 showed low activity. 相似文献
57.
Zafiropoulos NA Ngo HL Foglia TA Samulski ET Lin W 《Chemical communications (Cambridge, England)》2007,(35):3670-3672
Recyclable and reusable heterogeneous diarylammonium catalysts are highly effective in catalyzing the esterification of the free fatty acid (FFA) present in greases to methyl esters to reduce the FFA content from 12-40 wt% to 0.5-1 wt%; the resulting ester-glyceride mixture (pretreated grease) could then be readily converted to methyl esters by base-catalyzed transesterification. 相似文献
58.
Marc Chardin Nguyen Cong Minh Ngo Viet Trung 《Proceedings of the American Mathematical Society》2007,135(6):1597-1606
This paper proves the formulae
for arbitrary monomial complete intersections and , and provides examples showing that these inequalities do not hold for general complete intersections.
for arbitrary monomial complete intersections and , and provides examples showing that these inequalities do not hold for general complete intersections.
59.
The acyl endoperoxide arteannuin H, recently reported as a novel natural product from Artemtsia annua, has been obtained in two steps from the photooxidation of dihydroartemisinic acid, thereby confirming biogenetic speculation regarding its derivation from a secondary allylic hydroperoxide. The little studied 3,2-rearrangement reaction of such allylic hydroperoxides is also discussed. 相似文献
60.
Photooxidation of 4-amorphen-11-ol (1), recently reported as one of the major sesquiterpene natural products from the medicinal plant Fabiana imbricata, results in three allylic hydroperoxides 6, 9 and 10, which are expected from the “ene-type” reaction of molecular oxygen with the tri-substituted double bond in 1. The tertiary allylic hydroperoxide 6 undergoes carbon-carbon bond cleavage and a second autoxidation reaction to yield the more highly oxygenated seco-amorphane 11 under very mild conditions. In acid, this compound may then undergo either a second carbon-carbon bond cleavage reaction to yield nor-sesquiterpenes 2 and 3 (reported as bona fide natural products from F. imbricata, or cyclize to the sesquiterpene peroxofabianane (5), which is a presumed precursor to the natural product fabianane (4). Some mechanistic investigations concerning the two chemical processes: viz:- carbon-carbon bond cleavage and autoxidation which would account for the formation of natural products 2, 3 and 4 from 1 are reported. Tertiary allylic hydroperoxide 32, which lacks the 11-hydroxyl functional group present in 1 undergoes only C-4/C-5 carbon-carbon bond cleavage under more forcing conditions, suggesting a role for this functional group in assisting the autoxidation reactions of 4-amorphen-11-ol. 相似文献