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31.
Ashok K. Prasad Mofazzal Husain Brajendra K. Singh Vijay K. Manchanda Virinder S. Parmar 《Tetrahedron letters》2005,46(26):4511-4514
Lipase-catalyzed enantioselective amidation was performed by reacting the racemic amine with aliphatic acids in nonsolvent system. The reaction equilibrium was shifted towards amide synthesis by the removal of water under reduced pressure. This methodology avoids the use of activating agents and hazardous solvents. 相似文献
32.
A Gurtu P K Malhotra I S Mittra P M Sood SC Gupta VK Gupta GL Kaul LK Mangotra Y Prakash NK Rao ML Sharma 《Pramana》1974,3(5):311-322
This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR em = 〈n s〉/〈n ch〉, where 〈n ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R em = 1·71 implies an effectiveA-dependence ofR A =A 0.18,i.e., a very weak dependence. Predictions ofR em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production. 相似文献
33.
A quantification procedure of trace elements during colloid size fractionation was developed and validated. This procedure is based on the hyphenation between Asymmetrical Flow Field-Flow Fractionation (As-Fl-FFF) and Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The optimisation of the procedure was performed on a soil leachate spiked with six trace elements selected for their environmental and health impact (As, Cd, Sb, Se, Sn and Pb). The elements in the spiked sample were on-line monitored during the fractionation. The validation was carried out by comparison with a second off-line quantification procedure based on fraction collection and total element analysis by ICP-MS. This off-line one was previously validated using reference materials. Finally, the analytical performances of the two procedures were compared. 相似文献
34.
Viefhues M Manchanda S Chao TC Anselmetti D Regtmeier J Ros A 《Analytical and bioanalytical chemistry》2011,401(7):2113-2122
Surface modifications of microfluidic devices are of essential importance for successful bioanalytical applications. Here,
we investigate three different coatings for quartz and poly(dimethylsiloxane) (PDMS) surfaces. We employed a triblock copolymer
with trade name F108, poly(l-lysine)-g-poly(ethylene glycol) (PLL-PEG), as well as the hybrid coating n-dodecyl-β-d-maltoside and methyl cellulose (DDM/MC). The impact of these coatings was characterized by measuring the electroosmotic flow
(EOF), contact angle, and prevention of protein adsorption. Furthermore, we investigated the influence of static coatings,
i.e., the incubation with the coating agent prior to measurements, and dynamic coatings, where the coating agent was present
during the measurement. We found that all coatings on PDMS as well as quartz reduced EOF, increased reproducibility of EOF,
reduced protein adsorption, and improved the wettability of the surfaces. Among the coating strategies tested, the dynamic
coatings with DDM/MC and F108 demonstrated maximal reduction of EOF and protein adsorption and simultaneously best long-term stability concerning EOF.
For PLL-PEG, a reversal in the EOF direction was observed. Interestingly, the static surface coating strategy with F108 proved to be as effective to prevent protein adsorption as dynamic coating with this block copolymer. These findings will
allow optimized parameter choices for coating strategies on PDMS and quartz microfluidic devices in which control of EOF and
reduced biofouling are indispensable. 相似文献
35.
A. Bhattacharyya P. K. Mohapatra V. K. Manchanda 《Journal of Radioanalytical and Nuclear Chemistry》2011,288(3):709-716
Separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is a challenging task in the nuclear fuel cycle due to their similar charge and chemical behaviour. Some soft donor ligands show selectivity for An(III) over Ln(III) due to the formation of stronger covalent bonds with the former. The extraction behaviour of Am(III) and Eu(III) is studied in the present work with a mixture of Cyanex-301 (bis(2,4,4-trimethylpentyl)di-thiophosphinic acid) with several various ??N??, ??O?? or ??S?? donor neutral ligands. Comparison of the data was done with that of the oxygen donor analogue of Cyanex-301, i.e. Cyanex-272 (bis(2,4,4-trimethylpentyl)phosphinic acid). Effect of the organic diluent on the extraction behaviour of Am(III) using Cyanex-301 in presence of ??N?? donor synergists was also studied. Ab initio molecular orbital calculations were carried out using GAMESS software and charges on the donor atoms were calculated which helped in understanding the co-ordination chemistry of the ligands and explained the separation behaviour. 相似文献
36.
Arijit Sengupta V. C. Adya R. Acharya P. K. Mohapatra V. K. Manchanda 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(1):281-285
Americium is an important actinide element having versatile applications based on its alpha and gamma emissions. Multi-element
determination of radioactive samples using ICP-AES technique may be affected by the presence of americium due to its rich
emission spectra. With a view to characterize plutonium based fuels containing americium for trace metals by ICP-AES technique
accurately, a high purity 241Am (using a separation procedure developed in our laboratory) was prepared. To ascertain its chemical purity it is essential
to determine its impurity contents accurately. Instrumental neutron activation analysis (INAA), being a sensitive multi-elemental
technique, was employed to determine the concentrations of impurities in purified 241Am. Detection limits for the common elements and rare earth elements have also been determined. Comparison is made with the
analytical data obtained by the ICP-AES method. 相似文献
37.
Mandal M Manchanda AS Zhuang J Kruk M 《Langmuir : the ACS journal of surfaces and colloids》2012,28(23):8737-8745
Large-pore ethenylene-bridged (-CH═CH-) and phenylene-bridged (-C(6)H(4)-) periodic mesoporous organosilicas (PMOs) with face-centered-cubic structure (Fm3m symmetry) of spherical mesopores were synthesized at 7 °C at low acid concentration (0.1 M HCl) using Pluronic F127 triblock copolymer surfactant in the presence of aromatic swelling agents (1,3,5-trimethylbenzene, xylenes-isomer mixture, and toluene). In particular, this work reports an unprecedented block-copolymer-templated well-ordered ethenylene-bridged PMO with cubic structure of spherical mesopores and an unprecedented block-copolymer-templated face-centered cubic phenylene-bridged PMO, which also has an exceptionally large unit-cell size and pore diameter. The unit-cell parameters of 30 and 25 nm and the mesopore diameters of 14 and 11 nm (nominal BJH-KJS pore diameters of 12-13 and 9 nm) were obtained for ethenylene-bridged and phenylene-bridged PMOs, respectively. Under the considered reaction conditions, the unit-cell parameters and pore diameters were found to be similar when the three different methyl-substituted benzene swelling agents were employed, although the degree of structural ordering appeared to improve for phenylene-bridged PMOs in the sequence of decreased number of methyl groups on the benzene ring. 相似文献
38.
Vinit SharmaPriyanka Manchanda Pankaj K. SahotaRalph Skomski Arti Kashyap 《Journal of magnetism and magnetic materials》2012,324(5):786-791
Density-functional calculations are used to determine the electronic structure and magnetic properties of dilute magnetic semiconductors with the composition X1−xMnxN (X=Al, Ga, In, x=6.25% and 12.5%). Emphasis is on the interatomic exchange as a function of the Mn-Mn distance. Our superlattice calculations show that the Mn dopants are spin-polarized with a half-metallic band gap and a magnetic moment of 4 μB per Mn atom at x=6.25 and 12.5%. The Mn (3d) bands lie in the band gap but partially hybridize with valence band or N 2p electrons, depending on the group-III element and on the spin direction. To calculate the exchange interaction parameters Jij, we have used a Green-function approach. The interaction between Mn atoms extends over several interatomic interactions and is mediated by nitrogen (2p) electrons. The exchange is always ferromagnetic and largest for the first nearest neighbors, but substantial ferromagnetic interactions persist over Mn-Mn distances up to sixth nearest neighbors in the considered supercell. 相似文献
39.
H. Naik S. Singh A. V. R. Reddy V. K. Manchanda S. Ganesan D. Raj Md. Shakilur Rahman K. S. Kim M. W. Lee G. Kim Y. D. Oh H. -S. Lee M. -H. Cho I. S. Ko W. Namkung 《The European Physical Journal A - Hadrons and Nuclei》2009,41(3):323-334
The photo-fission yields and photo-neutron cross-sections of ( $ \gamma$ , 3n) and ( $ \gamma$ , 4n) on 209Bi induced by 50 and 65MeV bremsstrahlung have been measured by using a recoil catcher and an off-line $ \gamma$ -ray spectrometric technique. The mass-yield distribution of fission products in 209Bi induced by bremsstrahlung photons from the present work and literature data in the energy range 28-85MeV is symmetric around 103 mass units. However, the full width at half maximum of the yields distribution increases from 19 mass units at 28-40MeV to 23 mass units at 85MeV. The ( $ \gamma$ , 3n) reaction cross-section in the 50MeV and the ( $ \gamma$ , 4n) reaction cross-section in the 50 and 65MeV bremsstrahlung-induced reaction of 209Bi were determined for the first time. 相似文献
40.
C. S. Pawaskar P. K. Mohapatra V. K. Manchanda 《Journal of Radioanalytical and Nuclear Chemistry》1999,242(3):627-634
The extraction behavior of several metal ions viz., Am3+, Eu3+, UO2
2+, Th4+, Sr2+ and Cs+ was investigated from sulphate medium employing phosphotungstic acid (PTA) and polyethylene glycol (PEG). The influence of
various parameters such as pH, PTA concentration, PEG concentration and salt concentration was studied. The order of extraction
followed the trend: Am3+>Eu3+>>Th4+>UO2
2+>Sr2+>Cs+ which deviate significantly from the reported order with conventional solvents. The relatively poor extraction of UO2
2+, Sr2+ and Cs+ was ascribed to their lack of interaction with the phosphotungstate anion. The separation behaviour of Am3+ vis-a-vis Eu3+ was also investigated under different experimental conditions. 相似文献