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91.
The molecular weight distributions were estimated for carbon fiber polymer precursors such as poly(acrylonitrile-co -itaconic acid) synthesized by semi batch solution polymerization in mixed solvents media with the azonitrile compounds as initiator under the different ratios of solvent and non solvent from 0.75 to 2.5 in weight.The copolymer was characterized by using Fourier transform infrared spectroscopy(FTIR) and nuclear magnetic resonance(1H-NMR) analyses.The molecular weight distributions were evaluated by Mv/Mn ratios estimated from viscosity and osmotic measurements,and Mw/Mn estimated from size exclusion chromatography.The molecular weight distributions of these polymers as determined from Mv/Mn and Mw/Mn are 2.9 to 3.2 and 2.0 to 2.5 respectively.The molecular distributions were close to a narrow distribution of 2.0 when the solvent/non-solvent ratio was varied between 1.4 and 2.0.Intrinsic viscosity[?]as a function of molecular weight of poly(acrylonitrile-co-itaconic acid) was evaluated by means of low angle laser light scattering with size exclusion chromatography(SEC-LALLS) and viscometry with SEC(SEC-VISCO).The relationship between[?]and Mw for poly(acrylonitrile-co-itaconic acid) in DMF at 50℃was[?]= 1.1×10-5Mw0.79,where[?]is obtained in dL/g. 相似文献
92.
Preeti Saluja Hemant Sharma Navneet Kaur Narinder Singh Doo Ok Jang 《Tetrahedron》2012,68(10):2289-2293
We synthesized an imine-linked, benzimidazole-based chemosensor that can be used for chromogenic recognition of Mg2+ and fluorescent recognition of Cr3+. The chemosensor shows sensitive, selective, and ratiometric recognition of Cr3+ through concurrent quenching at one wavelength and enhancement of fluorescence intensity at another wavelength. It can also be used to detect Mg2+ via UV–vis absorption spectroscopy. DFT calculations support these phenomena. The sensor can be used to strain microbe cells without breakage. 相似文献
93.
Hemant Bhate 《Linear and Multilinear Algebra》2013,61(3-4):395-402
We give a method for construction of finite, abelian hypergroups of matrices which, while including most previously known cases, also gives rise to a new family of hypergroups. 相似文献
94.
Let G be a finite non-abelian p-group, where p is a prime. Let Autc(G) and Autz(G) respectively denote the group of all class preserving and central automorphisms of G. We give a necessary and sufficient condition for G such that Autc(G) = Autz(G) and classify all finite non-abelian p-groups G with elementary abelian or cyclic center such that Autc(G) = Autz(G). We also characterize all finite p-groups G of order ≤ p 7 such that Autz(G) = Autz(G) and complete the classification of all finite p-groups of order ≤ p 5 for which there exist non-inner class preserving automorphisms. 相似文献
95.
Gabrielse G Kolthammer WS McConnell R Richerme P Wrubel J Kalra R Novitski E Grzonka D Oelert W Sefzick T Zielinski M Borbely JS Fitzakerley D George MC Hessels EA Storry CH Weel M Müllers A Walz J Speck A;ATRAP Collaboration 《Physical review letters》2010,105(21):213002
Centrifugal separation of antiprotons and electrons is observed, the first such demonstration with particles that cannot be laser cooled or optically imaged. The spatial separation takes place during the electron cooling of trapped antiprotons, the only method available to produce cryogenic antiprotons for precision tests of fundamental symmetries and for cold antihydrogen studies. The centrifugal separation suggests a new approach for isolating low energy antiprotons and for producing a controlled mixture of antiprotons and electrons. 相似文献
96.
Suthari Prashanthi P. Hemant Kumar Li Wang Arun Kumar Perepogu Prakriti Ranjan Bangal 《Journal of fluorescence》2010,20(2):571-580
Steady state and time resolved fluorescence quenching behaviors of meso-Tetrakis (pentafluorophenyl) porphyrin (H2F20TPP) in presence of different aliphatic and aromatic amines have been executed in homogeneous dichloromethane (DCM) solution.
At room temperature in DCM, free base (H2F20TPP) shows fluorescence with two distinct peaks at 640 and 711 nm and natural lifetime τ
f = 9.8 ns which are very similar to that of meso-tetraphenyl porphyrin (TPP). Unlike TPP, addition of both aliphatic and aromatic
amines to a solution containing H2F20TPP results in an efficient decrease in fluorescence intensity without altering the shape and peak position of fluorescence
emission. Upon addition of amines there was no change in optical absorption spectra of H2F20TPP. The fluorescence quenching rate constants ranged from 1 × 109 to 4 × 109 s−1, which are one order below to the diffusion control limit, and temperature dependent quenching rate constants yield the activation
energies which are found to be order of 0.1 eV. Femto second transient absorption studies reveal the existence of amine cation
radical and porphyrin anion radicals with very short decay time (15 ps). The fluorescence quenching reaction follows Stern–Volmer
kinetics. Steady state and time-resolved data are interpreted within general kinetic scheme of Marcus semi-classical model
which attributes bimolecular electron transfer process between amines and the lowest excited singlet state of H2F20TPP. Calculated internal reorganization energies are found to be in between 0.04 and 0.22 ev. Variation of electron transfer
rate as function of free energy change (∆G0) points the ET reactions in the present systems are in Marcus normal region. This is the first example of reductive fluorescence
quenching of free base neutral porphyrins in homogeneous organic solvent ever known. 相似文献
97.
Prashant Shukla Suhasini Mahata Hemant Kashyap Manorama Singh Vijai K. Rai Ankita Rai 《Tetrahedron letters》2019,60(30):1943-1948
Graphene oxide (GO)/GO-I2 co-catalyzed green synthesis of tosylaziridine bearing keto and nitrile/ester functional groups is reported. The strategy involves sequential GO-catalyzed oxidation of benzylic alcohol and GO-I2 catalyzed nitrene insertion into olefin of Morita-Baylis-Hillman adduct. Operational simplicity, use of water as solvent, ambient reaction conditions, excellent yield of products (88–96%) and recyclability of catalyst up to five times without any substantial change in morphology as well as catalytic efficiency are the salient features of the envisaged protocol. 相似文献
98.
We prove uniform consistency of Random Survival Forests (RSF), a newly introduced forest ensemble learner for analysis of right-censored survival data. Consistency is proven under general splitting rules, bootstrapping, and random selection of variables—that is, under true implementation of the methodology. Under this setting we show that the forest ensemble survival function converges uniformly to the true population survival function. To prove this result we make one key assumption regarding the feature space: we assume that all variables are factors. Doing so ensures that the feature space has finite cardinality and enables us to exploit counting process theory and the uniform consistency of the Kaplan–Meier survival function. 相似文献
99.
Piero Zanello Giuliana OpromollaLuca PardiKeith H. Pannell Hemant K. Sharma 《Journal of organometallic chemistry》1993,450(1-2):193-196
The electrochemical behaviour of the ferrocenylacyl derivatives [FcCOER3] (E = C, Si or Ge; R = Me or Ph) is examined. One-electron oxidations to the substantially stable monocations [FcCOER3]+ occur at potentials significantly higher than that observed with ferrocene, but only minor differences hold within the series, independent of the nature of both E and R. In contrast the EPR spectra of the monocations for E = C show that the unpaired electron resides mainly on the iron, whereas for E = Si or Ge the electron density is essentially localized on the C5H4COER3 fragment. 相似文献
100.
The reaction of N‐alkylbenzaldimines with carbon monoxide (CO) in the presence of cobalt (Co) catalysts resulted in the formation of N‐alkylphthalimidines (Table 1). Their formation is proposed to occur by C? H activation of the aryl ring, migratory insertion of the hydride species into the benzaldimine functionality, CO coordination, and insertion into the Co? C bond, followed by reductive elimination of the N‐alkylphthalimidine and regeneration of the starting Co species (Scheme 4). Deuterium (2H)‐labeling NMR studies are consistent with this mechanism (Scheme 5). 相似文献