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131.
Koskinen AM Helaja J Kumpulainen ET Koivisto J Mansikkamäki H Rissanen K 《The Journal of organic chemistry》2005,70(16):6447-6453
The motional restrictions of the proline pyrrolidine ring allow this secondary amine amino acid to act as a turn inducer in many peptides and proteins. The pyrrolidine ring is known to exhibit two predominant pucker modes (i.e., C-4 (Cgamma) exo and endo envelope conformers whose ratio can be controlled by proper substituents in the ring). In nature, the exo puckered 4(R)-hydroxy-l-proline plays a crucial role as a building block in collagen and collagen-like structures. It has been previously concluded that the electronegativity of the 4-cis-substituent increases the endo puckering while the electronegativity of the 4-trans-substituent favors the exo puckering. Here, we have introduced a sterically demanding tert-butyl group at C-4 in trans- and cis-configurations. In the case of trans-substitution, the induced puckering effect on the pyrrolidine ring was studied with X-ray crystallography and 1H NMR spectral simulations. Both cis- and trans-4-tert-butyl groups strongly favor pseudoequatorial orientation, thereby causing opposite puckering effects for the pyrrolidine ring, cis-exo and trans-endo for l-prolines, in contrast to the effects observed in the case of electronegative C-4 substituents. The syntheses and structural analysis are presented for the conformationally constrained 4-tert-butylprolines. The prolines were synthesized from 4-hydroxy-l-proline, substitution with t-BuCuSPhLi being the key transformation. This reaction gave N-Boc-trans-4-tert-butyl-l-proline tert-butyl ester in 94% ee and 57% de. Enantioselectivity was increased to 99.2% ee by crystallization of N-Boc-trans-4-tert-butyl-l-proline in the final step of the synthesis. 相似文献
132.
Kumpulainen AJ Persson CM Eriksson JC 《Langmuir : the ACS journal of surfaces and colloids》2004,20(24):10534-10541
Surface tension isotherms were recorded for n-decyl-beta-d-glucopyranoside (Glu) and n-decyl-beta-D-maltopyranoside (Mal) solutions at temperatures of 8, 22, and 29 degrees C. Comparison was made with isotherms of n-decyl-beta-D-thiomaltopyranoside (S-Mal) at 22 degrees C. In addition to the transition from the gaseous to the liquid-expanded (LE) state, a second transition was observed in the early stages of the LE regime for Glu, Mal, and S-Mal at room temperature. The adsorption isotherm of Mal and Glu obtained at 22 degrees C shows the presence of an adsorption step at an average area/molecule of about 79 A2 between, approximately, 0.02 and 0.1 mM (the critical micelle concentration (cmc) is 2 mM) and 0.015 and 0.03 mM (the cmc is 2 mM), respectively. Similarly, for S-Mal an adsorption plateau is observed at 70 A2 between 0.01 and 0.03 mM (the cmc is 0.7 mM). From the temperature dependence of the surface tension, we have seen that there are considerable differences in the adsorption of Glu and Mal. For Mal, the adsorption plateau is also observed at 29 degrees C at around 79 A2, whereas Glu exhibits no adsorption plateau at this temperature. At 8 degrees C, both Mal and Glu exhibit saturation behavior in the dilute part of the liquid-expanded range, but at this temperature the average molecular areas are lower than at 22 degrees C: around 66 A2 for Glu and 75 A2 for Mal. Thus, the temperature sensitivity of Glu is considerably greater than for Mal in this range. The saturation regime coincides with a pronounced surface entropy minimum for Mal. The transition in the dilute liquid-expanded range supposedly occurs from a state with deformed surface micelles arranged in a hexagonal pattern, referred to as the granular range, to a true LE monolayer with a fluid hydrocarbon tail layer covering the entire surface. 相似文献
133.
Jorma T. Kumpulainen Helena Hyvärinen Margareta Hägg Sirkka Plaami Raija Tahvonen 《Fresenius' Journal of Analytical Chemistry》1995,352(1-2):102-106
As part of the analytical assurance system of the FAO European Cooperative Research Network on Trace Elements programme an ARC/CL-coded carrot flakes powder (CFP) candidate reference material (RM) has been prepared from a lot of commercial carrot flakes. The candidate RM has been homogenized using a Robot Coupe blender fitted with titanium blades, carefully homogenized in large teflon/polypropylene containers, bottled in 1000 numbered polyethylene containers (20 g samples) and tested for homogeneity. Interlaboratory comparison studies for 9 essential elements, cadmium and total dietary fiber (TDF) based on the AOAC-method resulted in the characterization of the contents of those compounds in the above material. After exclusion of outliers, mean values from at least nine different laboratories based altogether on three independent analytical principles have been used to calculate the recommended concentration ranges for mineral elements. Testing of homogeneity and stability for -carotene over a period of one year has been additionally carried out. The mean water content in the material amounted to 4.97% and remained stable over a one-year period. Homogeneity of the RM was within 3.0% for almost all included mineral elements as tested for a sample size of 0.5 g. The 95% confidence limits for the mean values of the established recommended concentrations of mineral elements in the present ARC/CL Carrot Powder candidate RM fell within 5% for all the other elements and TDF except for Fe (6.3%) and B (5.7%). The stability of -carotene in the present candidate RM stored in darkness over a one-year period at room temperature was within 6.3%. 相似文献
134.
Alexander A. Kodentsov Jorma K. Kivilahti Frans J. J. van Loo 《Monatshefte für Chemie / Chemical Monthly》2005,36(1):1861-1869
The use of equilibrium thermodynamics in describing interfacial reactions between non-ionic inorganic solids is demonstrated
using examples of high-temperature interactions in the Ti–Si–N and Mo–Si–N systems. In the case of a diffusion-controlled
process, solid-state reactions can be interpreted with chemical potential (activity) diagrams. The role of volatile reaction
products formed during interaction in developing the diffusion zone morphology is analysed. The interfacial phenomena in systems
based on dense Si3N4 and non-nitride forming metals can be explained by assuming a nitrogen pressure build-up at the contact surface. This pressure
determines the chemical potential of Si at the interface and, hence, the reaction products in the diffusion zone. 相似文献
135.
Alexander A.?KodentsovEmail author Jorma K.?Kivilahti Frans J. J.?van Loo 《Monatshefte für Chemie / Chemical Monthly》2005,136(11):1861-1869
Summary. The use of equilibrium thermodynamics in describing interfacial reactions between non-ionic inorganic solids is demonstrated
using examples of high-temperature interactions in the Ti–Si–N and Mo–Si–N systems. In the case of a diffusion-controlled
process, solid-state reactions can be interpreted with chemical potential (activity) diagrams. The role of volatile reaction
products formed during interaction in developing the diffusion zone morphology is analysed. The interfacial phenomena in systems
based on dense Si3N4 and non-nitride forming metals can be explained by assuming a nitrogen pressure build-up at the contact surface. This pressure
determines the chemical potential of Si at the interface and, hence, the reaction products in the diffusion zone. 相似文献
136.
Blomberg E Kumpulainen A David C Amiel C 《Langmuir : the ACS journal of surfaces and colloids》2004,20(24):10449-10454
The purposes of this study are to utilize the interactions between an adamantane end-capped poly(ethylene oxide) (PEO) and a cationic polymer of beta-cyclodextrin to build polymer bilayers on negatively charged surfaces, and to investigate the interactions between such layers. The association of this system in solution has been studied by rheology, light scattering, and fluorescence measurements. It was found that the adamantane-terminated PEO (PEO-Ad) mixed with the beta-cyclodextrin polymer gives complexes where the interpolymer links are formed by specific inclusion of the adamantane groups in the beta-cyclodextrin cavities. This results in a higher viscosity of the solution and growth of intermolecular clusters. The interactions between surfaces coated with a cationized beta-cyclodextrin polymer across a water solution containing PEO-Ad polymers were studied by employing the interferometric surface force apparatus (SFA). In the first step, the interaction between mica surfaces coated with the cationized beta-cyclodextrin polymer in pure water was investigated. It was found that the beta-cyclodextrin polymer adsorbs onto mica and almost neutralizes the surface charge. The adsorbed layers of the beta-cyclodextrin polymer are rather compact, with a layer thickness of about 60 A (30 A per surface). Upon separation, a very weak attractive force is observed. The beta-cyclodextrin solution was then diluted by pure water by a factor of 3000 and a PEO-Ad polymer was introduced into the solution. Two different architectures of the PEO-Ad polymer were investigated: a four-arm structure and a linear structure. After the adsorption of the PEO polymer onto the beta-cyclodextrin layer reached equilibrium, the forces were measured again. It was found that the weak repulsive long-range force had disappeared and an attractive force caused the surfaces to jump into contact, and that the compressed layer thickness had increased. The attractive force is interpreted as being due to a specific recognition between the hydrophobic adamantane groups on the PEO-Ad polymer and the hydrophobic cavity in the beta-cyclodextrin molecules. Furthermore, the attractive force observed on separation has increased significantly, which is a further indication of a specific interaction between the beta-cyclodextrin polymer and the adamantane groups. 相似文献
137.
H. Kumpulainen 《Journal of Radioanalytical and Nuclear Chemistry》1980,59(2):635-640
Uranium analysis at trace levels from geological samples was performed by K X-ray fluorescence using a semiconductor detector
and radioisotope excitation. The exciting57Co-source was constructed in such a way as to produce a high peak to background ratio. Using 10 minutes counting times the
detection limit with a 0.26 GBq source was 24 μg/g improving to about 9 μg/g with a ten times stronger source. The detection
limits for tin, cerium, tungsten and thorium were also measured. 相似文献
138.
Vähäoja P Närhi J Kuokkanen T Naatus O Jalonen J Lahdelma S 《Analytical and bioanalytical chemistry》2005,383(2):305-311
A new infrared spectroscopic method suitable for determining total fatty alcohol and fatty acid ester concentrations in industrial
oils has been developed. Oil samples were diluted with toluene (1:3 w/w), the toxicity and volatility of which are relatively
low compared with more commonly used IR solvents, like carbon tetrachloride or carbon disulfide. Mixture standards were prepared
from dodecanol, tetradecanol, octadecanol, methyl stearate and methyl palmitate. Some analytical and statistical tests were
performed on the developed method. The recoveries and the repeatability of the method proved to be sufficient for the quantitative
determination of fatty alcohol and fatty acid ester additives in industrial oils. Reproducibility testing in another laboratory
also produced satisfactory results. The developed method also proved to be relatively quick and simple. This method was developed
to satisfy industry’s need to determine the concentrations of these oil additives, and it has already been applied successfully
in machinery oil analysis. 相似文献
139.
Luminescence emission and uv-excitation properties of LaOBr: Tb3+, LaOBr: Ce3+, and LaOBr: Tb3+, Ce3+ phosphors were studied. The visible emission spectra of La0.995Tb0.005OBr consists of5D3,4 →7F3–6 transitions in the wavelength range of 410–630 nm. The excitation of the Tb3+ ion gives a broad 4f → 5d transition band at 254 nm and weaker4f → 4f transition lines above 300 nm. The uv-excitation and emission of La0.995Ce0.005OBr at 290, 315, 355 (excitation), and 440 nm (emission) originate from transitions between the 4f-ground state and the four crystal field components of the5d2D excited state. The sensitization of Tb3+ luminescence in LaOBr with Ce3+ at varying concentrations is described and discussed. With increasing Ce3+ concentration the 5D3 →7F transitions of Tb3+ quench totally and the5D4 →7F transitions begin to quench gradually. The excitation spectrum of the5D4 →7F5 transition of Tb3+ consists of four bands due to Tb3+ and Ce3+, of which the three Ce3+ bands increase in intensity and the Tb3+ band decreases as the Ce3+ concentration is increased. 相似文献
140.
Jorma Kaarlo Merikoski 《BIT Numerical Mathematics》1979,19(1):39-42
A lower boundn
–1
i,k
aik for the Perron eigenvalue of a symmetric non-negative irreducible matrixA=(a
ik) is studied and compared with certain other lower bounds. 相似文献