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11.
The catalytic activity of Chromobacterium viscosum lipase (CV-lipase) was estimated across varying surfactant tail lengths (C-10-C-18) in water-in-oil (w/o) microemulsions of cationic surfactants containing four different hydroxyethyl-substituted head groups. An attempt to find a correlation, if any, between the activity of interfacially solubilized lipase and the varying surfactant tails was made for the first time in micellar enzymology. The second-order rate constant, k2, in lipase-catalyzed hydrolysis of p-nitrophenyl-n-hexanoate at pH 6.0 and 25 degrees C shows an improvement in enzyme activity (approximately 30-140%) across different head groups of amphiphiles with increasing tail lengths in varying solution compositions. Improvement of enzyme activity is prominent in ascending from C-10 to C-14/C-16, depending on the nature of polar head group. The hydrolytic activity of lipase in different surfactant (50 mM)/water/isooctane/n-hexanol with varying z= [alcohol]/[surfactant] (6.4 or 4.8) was amplified by 25-250% with increment in surfactant tail length in comparison with widely used cationic w/o microemulsions having solution compositions (z=16). As a notable outcome of this research, we found w/o microemulsions of 25 mM tetradecyltrimethylammonium bromide/water/isooctane/n-hexanol (z=8) producing the highest ever activity of lipase in any w/o microemulsions. 相似文献
12.
The sandwich cell described by Pavon et al. and a similar sandwich cell, except with angled (45 degrees, confocal) single strand optical fibers and a conventional Z-type cell of 6-mm path length have been studied with respect to their performance for absorbance detection. Both sandwich cells show less susceptibility by one order of magnitude to artifact absorbance signals from RI changes than the Z-cell. The light throughput in the sandwich cells increase by an order of magnitude when an inert metallized reflector is used and this improves S/N. The overall light throughput is substantially greater for the angled entrance single strand fiber optic cell rather than the cell with the bifurcated fiber optic. Attainable limits of detection with these cells appear to be related to the pathlength for the cell dimensions studied. 相似文献
13.
Background
Nitric oxide (NO) and oxygen free-radicals play an important part in the destruction of beta-cells in auto- immune diabetes although the precise mechanism of interaction is still not known. This study was designed to examine any possible diabetogenic effect of NO by investigating any differences in cellular binding of insulin to its receptor on the cell membranes of erythrocytes and mononuclear leucocytes of dogs treated with the NO donor, S-nitroso-N-acetylpenicillamine (SNAP) and controls treated with captopril.Results
The result obtained showed decreased binding of insulin to its receptor on the cell membranes of erythrocytes and mononuclear leucocytes. Mononuclear leucocytes from SNAP-treated dogs had decreased ability to bind insulin (16.30 ± 1.24 %) when compared to mononuclear leucocytes from captopril-treated controls (20.30 ± 1.93 %). Similar results were obtained for erythrocytes from dogs treated with SNAP (27.20 ± 1.33 %) compared with dogs treated with captopril (34.70 ± 3.58 %). Scatchard analysis demonstrated that this decrease in insulin binding was accounted for by a decrease in insulin receptor sites per cell, with mononuclear leucocytes of SNAP-treated dogs having 55 % less insulin receptor sites per cell compared with those of captopril-treated controls (P < 0.05). Average affinity and kinetic analysis revealed a 35 % decrease in the average receptor affinity, with mononuclear leucocytes from captopril-treated controls having an empty site affinity of 12.36 ± 1.12 × 10-8 M-1 compared with 9.64 ± 0.11 × 10-8 M-1 in SNAP-treated dogs (P < 0.05).Conclusion
These results suggest that acute alteration of the insulin receptor on the membranes of mononuclear leucocytes and erythrocytes occurred in dogs treated with S-nitroso-N-acetylpenicillamine. These findings suggest the first evidence of the novel role of NO as a modulator of insulin binding and the involvement of NO in the aetiology of diabetes mellitus. 相似文献14.
Nataša Pejić Slobodan Anić Vesna Kuntić Vladana Vukojević Ljiljana Kolar-Anić 《Mikrochimica acta》2003,143(4):261-267
A kinetic method is described for the microquantitative (microconcentration/microvolume) determination of rutin based on potentiometric monitoring of the concentration perturbations of the Bray-Liebhafsky (BL) oscillatory reaction being in a non-equilibrium stationary state close to a bifurcation point. The experiments are carried out in an open reactor. The response of the matrix system to perturbations by different concentrations of rutin ethanolic solutions is followed by a Pt-electrode. In the concentration range between 7.8×10–8moldm–3 and 9.1×10–6mol dm–3, we found a linear dependence of the maximal potential shift, Em, on the logarithm of the rutin concentrations. The unknown concentrations can be determined from the calibration curve up to an accuracy of ±5%. The detection limit is 3.6×10–8mol dm–3. The amount of required sample can be as small as 10µL. 相似文献
15.
Analyte transfer from the matrix in a thin layer distillation (TLD) cell and its subsequent measurement were investigated in a flow injection configuration. We designed the cell such that the donor and acceptor streams flowed in parallel channels separated by a thin dividing wall. The matrix transfer process involved room-temperature distillation of the analyte into the headspace of the TLD cell and its subsequent condensation/uptake by a concurrently flowing acceptor stream. There are no membranes; hence there are no membrane-related problems. The TLD system design was optimized with respect to its dimensions and operational parameters. Throughput and sensitivity were compared with a conventional pervaporation flow injection (PFI) system for ammonia and five different amines. For the higher molecular mass amines, the TLD approach provided comparable or superior performance. The TLD technique should be an attractive approach for online analysis of volatile chemical species in ‘dirty’ samples, especially for volatile analytes of higher molecular mass. 相似文献
16.
A fluorimetric flow-injection procedure with a single reagent solution containing p-hydroxyphenylacetic acid, peroxidase and ammonia permits the determination of aqueous hydrogen peroxide in the range 10?8?10?4 M; 30–60 samples can be processed per hour. The method exhibits a wide linear range and is insensitive to sample pH within the range 2–6. 相似文献
17.
Amino Acid based cationic surfactants in aqueous solution: physicochemical study and application of supramolecular chirality in ketone reduction 总被引:2,自引:0,他引:2
Roy S Das D Dasgupta A Mitra RN Das PK 《Langmuir : the ACS journal of surfaces and colloids》2005,21(23):10398-10404
The present study provides a molecular understanding of the origin of the chirality in aqueous micelles and its correlation with the proficiency of stereoselective ketone reduction. The effects of varied headgroup architecture on the surface-active properties as well as on other microstructural parameters were studied and correlated to the structural differences of these naturally occurring amino acid containing surfactants (1-4). Micropolarity sensed by pyrene showed that the micelles prepared using 1-4 are mostly hydrated; particularly large headgroup size surfactant produces more polar environment. A theoretical study was done to quantify the varied spatial dissymmetry for all four surfactants. Asymmetric reduction of prochiral ketones was carried out at the aqueous micellar interface of these chiral amphiphiles by exploiting the supramolecular chirality as evidenced from a circular dichroism study. The enantioselectivity of the reduction process is rationally improved through increase in spatial dissymmetry and steric constraint imposed at the micellar interface by the polar head of surfactants. 相似文献
18.
A system of sequential injection analysis (SIA) in capillary format based on an electroosmotic pump is introduced. The system exhibits excellent reliability and reproducibility (relative standard deviation 0.6-0.8%) for both simple and complex chemical reaction systems. The simplicity and flexibility of the field-decoupled electroosmotic pump has been found to be ideally suited for SIA. There is significant potential for miniaturizing the necessary instrumentation. 相似文献
19.
A spectrophotometric flow injection method for the determination of H(2)O(2) in aqueous solution is presented. The technique is based on the oxidative condensation reaction between 1-anilinonaphthalene-8-sulfonic acid (ANSA) and 4-aminoantipyrine (AAP) in the presence of H(2)O(2). Hematin is a good peroxidatic catalyst for this reaction; its effectiveness is significantly enhanced in an ammoniacal medium. If the yellow product formed in the alkaline medium is acidified, a blue chromophore (lambda(max) 592 nm) is formed; a surfactant is necessary to keep the blue compound in solution. Chemical and instrumental parameters for FIA were evaluated and optimized. A detection limit of 0.3muM was achieved with a linear dynamic range extending to 50muM. The typical relative standard deviation is 1.5% or better. The structure of the reaction product has been identified. 相似文献
20.
Lj. Kolar-Ani? Dj. Misljenovi? S. Ani? G. Nicolis 《Reaction Kinetics and Catalysis Letters》1995,54(1):35-41
The reduction of iodate ion by hydrogen peroxide, originally postulated by Liebhafsky, is considered as a possible step in the kinetic model proposed by Kolar-Ani and G. Schmitz for the overall Bray-Liebhafsky oscillatory process. 相似文献