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131.
Metallation-ribosylation of 2-bromothiophene 1 when conducted at room temperature afforded the original glycosylated dibromothiophene 3b following a regiocontrolled halogen transfer-based halogen-dance process. Then, stereocontrolled reduction-cyclization of hemiacetals 3a-c allowed straightforward access to the halogenated thiophenyl-C-nucleosides 6a-c. 相似文献
132.
Comminges C Barhdadi R Doherty AP O'Toole S Troupel M 《The journal of physical chemistry. A》2008,112(34):7848-7855
The mechanism of 2,2'6,6'-tetramethylpiperidin- N-oxyl (TEMPO)-mediated oxidation of alcohols to aldehydes and ketones in ionic liquids has been investigated using cyclic voltammetry and rotating disk electrode voltammetry. It is shown that the presence of bases (B) and their conjugate acids (BH (+)), as well as their p K as, strongly influences the rate of reaction. Data indicated that the first step in the oxidation is the formation of the alcoholate species via acid-base equlibrium with B. The alcoholate subsequently reacts with the active form of TEMPO (T (+), i.e., the one-electron oxidized form) forming an intermediate that further reacts with T (+) and B returning TEMPO catalytically, BH (+), and the carbonyl product. A kinetic model incorporating this pre-equilibrium step has been derived, which accounts for the experimentally observed reaction kinetics. Overall, the rate of reaction is controlled by the equilibrium constant for the pre-equilibrium step; as such, strong bases are required for more kinetically efficient transformations using this redox catalyst. 相似文献
133.
Ghanem A Bados P Perreau F Benabdallah R Plagellat C de Alencastro LF Einhorn J 《Analytical and bioanalytical chemistry》2008,391(1):345-352
A multiresidue method has been developed to analyze atrazine (ATZ), diuron (DIU), and their major degradation products, desethylatrazine
(DEA), desisopropylatrazine (DIA), and dichlorophenylmethylurea in sewage sludge. Liquid chromatography coupled to electrospray
tandem mass spectrometry (LC–ESI-MS–MS) allowed, in the multiple-reaction monitoring mode, the simultaneous analysis of these
pesticides in only one run after their extraction with ethyl acetate–dichloromethane 90:10 (v/v) and a cleanup on a Florisil column. Stable isotopically labeled ATZ and DIU were used as internal standards to overcome
matrix effects during the pesticide quantification. Using fortified samples, the method gave rise to 86–115% as mean recovery
values depending on the analyte. Limits of detection (LODs) and of quantification (LOQs) ranging from 0.3 (DIA) to 1.5 (DEA)
μg kg−1 dw and from 0.4 (DIA) to 2.0 (DEA) μg kg−1 dw, respectively, were sufficient to achieve the monitoring of these molecules in sludge from wastewater treatment plants
of the Ile-de-France region. 相似文献
134.
Dr. Dimitrios Koumoulis Jan P. Scheifers Rachid St. Touzani Prof. Boniface P. T. Fokwa Prof. Louis‐S. Bouchard 《Chemphyschem》2016,17(19):2972-2976
Crystal orbital Hamilton population (COHP) bonding analysis has predicted that ScPd3B0.5 is the least stable compound of the entire series Sc2Ir6?xPdxB. Here, we report a systematic study of Sc2Ir6?xPdxB (x=3, 5 and 6) by means of 11B nuclear magnetic resonance (NMR), Knight shift (K) and nuclear spin‐lattice relaxation rate (1/T1). NMR results combined with theoretical band structure calculations provide a measure of s‐ and non‐s‐character Fermi‐level density of states. We present direct evidence that the enhanced s‐state character of the Fermi level density of states (DOS) in ScPd3B0.5 reduces the strength of the B 2p and Pd 4d hybridized states across the entire Sc2Ir6?xPdxB series. This hybridization strength relates to the opening of a deep pseudogap in the density of states of Sc2IrPd5B and the chemical bonding instability of ScPd3B0.5. This study is an experimental realization of a chemical fine‐tuning of the electronic properties in intermetallic perovskites. 相似文献
135.
Dehbiya Gherdaoui Hafsa Bekdouche Said Zerkout Rachid Fegas Michel Righezza 《Journal of the Iranian Chemical Society》2016,13(12):2319-2323
A high-performance liquid chromatographic method for chiral separation of ketoprofen racemate was developed. (R)- and (S)-ketoprofen enantiomers were separated on a LiChrosorb NH2 column (250 mm × 4.6 mm, i.d 5 µm) at 20 °C, using 2-propanol/potassium dihydrogen phosphate buffer (pH 6.0, 0.05 M) (50:50 v/v). Containing vancomycin as the mobile phase, at a flow rate of 0.8 ml min?1 and detection wavelength of UV, the detector was set at 310 nm. Under these conditions, ketoprofen enantiomers could be separated with a selectivity factor (α) of 2.172 and a resolution (Rs) of 4.78 using extremely low concentrations of the vancomycin chiral additive. 相似文献
136.
Enrique Alvarez-Manzaneda Rachid Chahboun Esteban Alvarez Mohammed Hmamouchi 《Tetrahedron letters》2007,48(50):8930-8934
A new route to abietane and podocarpane-type terpenoids from labdane diterpenes is reported. The key step is the transformation of β-ketoester 9 into the corresponding O-acetylsalicylate ester 18, via a manganese(III)-based oxidative free-radical cyclization carried out in Ac2O. Utilizing this, the synthesis of the antitumor (+)-7-deoxynimbidiol (5) from (−)-sclareol (11) has been achieved. (+)-Nimbidiol (6) and the natural terpenoid 20 have also been synthesized. 相似文献
137.
Rachid Skouta 《Tetrahedron letters》2007,48(47):8343-8346
(±)-Pterocarpan and analogues (4a-c) have been synthesized efficiently via the annulation of salicylaldehydes (1a, 1b and 1c) and o-methoxymethoxylphenylacetylene (2a), followed by a one-pot reduction and acidic cyclization of the ketones (3a-c). In addition, isoflavone derivatives (5a-c) have been synthesized rapidly, in two steps, via the annulation of salicylaldehyde (1a) and arylacetylenes (2b, 2c and 2d), followed by IBX/DMSO oxidation of the isoflavanones (3d, 3e and 3f). 相似文献
138.
Recent developments in microscopy and image processing have made digital measurements on high-resolution images of fibrous materials possible. This helps to gain a better understanding of the structure and other properties of the material at micro level. In this paper SEM image segmentation based on mathematical morphology is proposed. In fact, paper models images (Whatman, Murillo, Watercolor, Newsprint paper) selected in the context of the Euro Mediterranean PaperTech Project have different distributions of fibers and fillers, caused by the presence of SiAl and CaCO3 particles. It is a microscopy challenge to make filler particles in the sheet distinguishable from the other components of the paper surface. This objectif is reached here by using switable strutural elements and mathematical morphology operators. 相似文献
139.
Pham Sy Hieu Pham Minh Doan Sane Abdoul Razac Nguyen Xuan Hoan Semlal Nawal Boulif Rachid Germeau Alain Toussaint Claudia Sharrock Patrick Nzihou Ange 《Journal of Thermal Analysis and Calorimetry》2021,146(5):2027-2033
Journal of Thermal Analysis and Calorimetry - Up-to-date, solar salt (a mixture of 60 mass% NaNO3 and 40 mass% KNO3) is practically the only media for thermal energy storage (TES) in concentrated... 相似文献
140.
Tapia R Guardia JJ Alvarez E Haidöur A Ramos JM Alvarez-Manzaneda R Chahboun R Alvarez-Manzaneda E 《The Journal of organic chemistry》2012,77(1):573-584
A new strategy for synthesizing taiwaniaquinoids, a group of terpenoids with an unusual rearranged 5(6→7) or 6-nor-5(6→7)abeo-abietane skeleton, which exhibit promising biological activities, is reported. The procedure, based on the cleavage of the C7-C8 double bond of abietane diterpenes, is the only one yet reported for synthesizing C(20) taiwaniaquinoids bearing a carbon function on the cyclopentane B ring; it is also applicable to the synthesis of the wide variety of existing taiwaniaquinoids. Utilizing this, (-)-taiwaniaquinone A, F, G, and H, (-)-taiwaniaquinol B, and (-)-dichroanone have been synthesized from (+)-abietic acid. The versatility of this strategy allows us to propose the abietane C7-C8 cleavage as a possible biosynthetic pathway to this type of rearranged diterpenes; this proposal seems to be supported by phytochemical evidence. 相似文献