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71.
Busygin I Nieminen V Taskinen A Sinkkonen J Toukoniitty E Sillanpää R Murzin DY Leino R 《The Journal of organic chemistry》2008,73(17):6559-6569
Structures and conformational behavior of several cinchona alkaloid O-ethers in the solid state (X-ray), in solution (NMR and DFT), and in the gas phase (DFT) were investigated. In the crystal, O-phenylcinchonidine adopts the Open(3) conformation similar to cinchonidine, whereas the O-methyl ether derivatives of both cinchonidine and cinchonine are packed in the Closed(1) conformation. Dynamic equilibria in solutions of the alkaloids were revealed by combined experimental-theoretical spin simulation/iteration techniques for the first time. In the (1)H NMR spectra in CDCl3 and toluene-d8 at room temperature, Closed(1) conformation was observed for the O-silyl ethers as a separate set of signals. For O-methyl ether derivatives Closed(1) could be separated only at -30 degrees C in CDCl3 or toluene-d8 and for O-phenylcinchonidine at -70 degrees C in CDCl3/CD2Cl2. The ratio between the Closed(2) and Open(3) conformers was estimated by analyzing the vicinal coupling constant (3)J(H9,H8) at ambient and low temperatures. The observed conformational equilibria of O-(tert-butyldimethylsilyl)cinchonidine in CDCl 3 and toluene-d8 are in good agreement with the theoretically estimated equilibrium populations of the conformations according to Boltzmann statistics. The conformational equilibria of four cinchona alkaloid O-ether solutes in CDCl3 and toluene-d8 are discussed in the light of their relevance to the mechanism of 1-phenyl-1,2-propanedione (PPD) hydrogenation over cinchona alkaloid modified heterogeneous platinum catalysts. It was demonstrated that the conformation found to be abundant in the liquid phase has no direct correlation with the enantioselectivity of the PPD hydrogenation reaction. 相似文献
72.
Atomic layer deposition as pore diameter adjustment tool for nanoporous aluminum oxide injection molding masks 总被引:2,自引:0,他引:2
Miikkulainen V Rasilainen T Puukilainen E Suvanto M Pakkanen TA 《Langmuir : the ACS journal of surfaces and colloids》2008,24(9):4473-4477
The wetting properties of polypropylene (PP) surfaces were modified by adjusting the dimensions of the surface nanostructure. The nanostructures were generated by injection molding with nanoporous anodized aluminum oxide (AAO) as the mold insert. Atomic layer deposition (ALD) of molybdenum nitride film was used to control the pore diameters of the AAO inserts. The original 50-nm pore diameter of AAO was adjusted by depositing films of thickness 5, 10, and 15 nm on AAO. Bis(tert-butylimido)-bis(dimethylamido)molybdenum and ammonia were used as precursors in deposition. The resulting pore diameters in the nitride-coated AAO inserts were 40, 30, and 20 nm, respectively. Injection molding of PP was conducted with the coated inserts, as well as with the non-coated insert. Besides the pore diameter, the injection mold temperature was varied with temperatures of 50, 70, and 90 degrees C tested. Water contact angles of PP casts were measured and compared with theoretical contact angles calculated from Wenzel and Cassie-Baxter theories. The highest contact angle, 140 degrees , was observed for PP molded with the AAO mold insert with 30-nm pore diameter. The Cassie-Baxter theory showed better fit than the Wenzel theory to the experimental values. With the optimal AAO mask, the nanofeatures in the molded PP pieces were 100 nm high. In explanation of this finding, it is suggested that some sticking and stretching of the nanofeatures occurs during the molding. Increase in the mold temperature increased the contact angle. 相似文献
73.
Heikki Haario Aki Kallonen Marko Laine Esa Niemi Zenith Purisha Samuli Siltanen 《Mathematical Methods in the Applied Sciences》2017,40(18):6649-6669
A two‐dimensional sparse‐data tomographic problem is studied. The target is assumed to be a homogeneous object bounded by a smooth curve. A nonuniform rational basis splines (NURBS) curve is used as a computational representation of the boundary. This approach conveniently provides the result in a format readily compatible with computer‐aided design software. However, the linear tomography task becomes a nonlinear inverse problem because of the NURBS‐based parameterization. Therefore, Bayesian inversion with Markov chain Monte Carlo sampling is used for calculating an estimate of the NURBS control points. The reconstruction method is tested with both simulated data and measured X‐ray projection data. The proposed method recovers the shape and the attenuation coefficient significantly better than the baseline algorithm (optimally thresholded total variation regularization), but at the cost of heavier computation. 相似文献
74.
Leskinen Anumaija Salminen-Paatero Susanna Räty Antti Tanhua-Tyrkkö Merja Iso-Markku Taneli Puukko Esa 《Journal of Radioanalytical and Nuclear Chemistry》2020,323(1):399-413
Journal of Radioanalytical and Nuclear Chemistry - Determination of 14C, 55Fe, 63Ni and gamma emitters in two different types of activated reactor pressure vessel (RPV) steel samples were carried... 相似文献
75.
76.
Holding pressure was expected to change the free flow of the liquid crystalline melt. Because of the complex mold used and the two variables, nozzle and mold temperature, the shear and elongational flow were in the injection molding study evaluated by means of the notched Charpy and Izod impact strength. The tensile modulus, the flexural strength and modulus mainly depended on the elongational flow induced skin. On the grounds of the microstructure composed of 4 distinct layers a free flow model of the liquid crystal polymer having a yield stress is proposed. 相似文献
77.
Dmitry Yu. Murzin Esa Toukoniitty Jan Hájek 《Reaction Kinetics and Catalysis Letters》2004,83(2):205-212
Importance of investigating catalyst deactivation in the synthesis of fine chemicals is illustrated by several examples in
three-phase hydrogenation reactions, performed in batch and continuous reactors.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
78.
79.
Alcohol1, the side chain of α-tocopherol, has been synthesized in a stereoselective route involving an aldol condensation-Claisen rearrangement sequence. The synthesis require 11 steps and produces1in 17% overall yield. A complementary sequence employing reagent14provides isomer18. 相似文献
80.
Esa Mki Kalevi Pihlaja Imre Huber Ferenc Fülp Gbor Bernth Pirjo Vainiotalo 《Journal of mass spectrometry : JMS》1993,28(1):18-22
The electron impact ionization mass spectra of dipyrido [1,2-a:4,3-d]pyrimidinones are strongly influenced by the degree of aromaticity of the fused rings. The molecular ions of the compounds are fairly stable. The main routes of fragmentation involve formation of the [M – H]+ ion and loss of substituents, H2CN˙, CO and alkyl radicals. 相似文献