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81.
Ilko Bald Helga D. Flosadttir Janina Kopyra Eugen Illenberger Oddur Inglfsson 《International journal of mass spectrometry》2009,280(1-3):190
We present a detailed, collaborative study on the fragmentation of deprotonated native d-ribose and d-fructose and the isotopically labelled 1-13C-d-ribose, 5-13C-d-ribose and C-1-d-d-ribose. The fragmentation is studied in a matrix assisted laser desorption/ionization time of flight mass spectrometer (MALDI ToF MS), both in in-source decay (ISD) and post-source decay (PSD) mode and compared with fragmentation through dissociative electron attachment (DEA). Fragmentation of deprotonated monosaccharides formed in the MALDI process, as well as their transient molecular anions formed upon electron attachment are characterized by loss of different numbers of H2O and CH2O units. Two different fragmentation pathways leading to cross-ring cleavage are identified. Metastable decay of deprotonated d-ribose proceeds either via an X-type cleavage yielding fragment anions at m/z = 119, 100 and 89, or via an A-type cleavage resulting in m/z = 89, 77 and 71. A fast and early metastable cross-ring cleavage of deprotonated d-ribose observed in in-source decay is dominated by X-type cleavage leading mainly to m/z = 100 and 71. For dissociative electron attachment to d-ribose a sequential dissociation was identified that includes metastable decay of the dehydrogenated molecular anion leading to m/z = 89. All other fragmentation reactions in DEA to d-ribose are likely to proceed directly and on a faster timescale (below 400 ns). 相似文献
82.
Mohamed Abdel Salam Hooman Shadnia James S. Wright Robert Burk 《Journal of solution chemistry》2010,39(3):385-397
Multi-walled carbon nanotubes (MWCNTs) were chemically modified with octadecyl amine or polyethyleneglycol and then used as
solid phase adsorbents for the adsorption from aqueous solution of different polyhalogenated organic pollutants: pentachlorophenol,
2,4,5-trichlorophenol, 3,3′,4,4′-tetrachlorobiphenyl and 2,2′,5,5′-tetrabromobiphenyl from model aqueous solutions. The effects
of temperature were measured and thus the Gibbs energy, enthalpy, and entropy of adsorption were calculated. In general, the
Gibbs energy of adsorption was negative for the target analytes, indicating that adsorption was spontaneous at all temperatures.
On the other hand, the values of the enthalpy and entropy of adsorption were significantly dependent on the type of modified
MWCNTs as well as the analytes used. Computer modeling was used to simulate the adsorption process and calculate the Gibbs
energies of adsorption. The results showed moderate agreement with the experimentally determined values. 相似文献
83.
Janina Kabatc Magdalena Zasada Jerzy Pączkowski 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3626-3636
New three‐component photoinitiating systems consisting of a cyanine dye, borate salt, and a 1,3,5‐triazine derivative were investigated by measuring their photoinitiation activities and through fluorescence quenching experiments. Polymerization kinetic studies based on the microcalorimetric method revealed a significant increase in polymerization rate when the concentration of n‐butyltriphenylborate salt or the 1,3,5‐triazine derivative were increased. The photo‐induced electron transfer process between electron donor and electron acceptor was studied by means of fluorescence quenching and SrEt change of the fluorescence intensity. The experiments performed documented that an increase of the n‐butyltriphenylborate salt concentration dramatically increases the rate of dye fluorescence quenching, whereas the increasing of the 1,3,5‐triazine derivative concentration slows down the consumption of the dye. We conclude that the primary photochemical reaction involves an electron transfer from the n‐butyltriphenylborate anion to the excited singlet state of the dye, followed by the reaction of the 1,3,5‐triazine derivative with the resulting dye radical to regenerate the original dye. This reaction simultaneously produces a triazinyl radical anion derived from the 1,3,5‐triazine, which undergoes the carbon‐halogen bond cleavage yielding radicals active in initiation of a free radical polymerization chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3626–3636, 2007 相似文献
84.
Andrzej Fruziński Janina Karolak-Wojciechowska Sandrine Alibert-Franco Christiane Santelli-Rouvier Jacques Barbe 《Journal of chemical crystallography》1999,29(11):1201-1204
As a part of studies on MDR reversing agents, the structure of a benzylamido-9,10-dihydro-9,10-ethenoanthracene is reported: C24 H19 N O; orthorhombic; space group: Pca21; a = 9.214(2), b = 18.624(4), c = 10.170(2) Å; 1745.2(6) Å3; Z = 4. The three nonplanar rings from the 9,10-dihydro-9,10-ethenoanthracene skeleton of the molecule adopt a boat conformation. The benzamide side-chain is extended (conformation, trans-trans-gauche). The molecules in the crystal are joined by infinite chains of H-bonds N14–H14···O13. 相似文献
85.
86.
87.
Zhao L Han B Huang Z Miller M Huang H Malashock DS Zhu Z Milan A Robertson DE Weiner DP Burk MJ 《Journal of the American Chemical Society》2004,126(36):11156-11157
The discovery, from nature, of a diverse set of microbial epoxide hydrolases is reported. The utility of a library of epoxide hydrolases in the synthesis of chiral 1,2-diols via desymmetrization of a wide range of meso-epoxides, including cyclic as well as acyclic alkyl- and aryl-substituted substrates, is demonstrated. The chiral (R,R)-diols were furnished with high ee's and yields. The discovery of the first microbial epoxide hydrolases providing access to complementary (S,S)-diols is also described. 相似文献
88.
A general method of evaluation of configurational entropy of a liquid mixture is presented. It is based on a generalized lattice model with no restrictions due to particle shape being introduced. A general formula for the entropy is derived. Achieved results open a way for a rigorous analysis of particle shape effect on mixing process. As an example, a new formula for the entropy of mixing of hard spheres in continuous space is derived which may respect a physical bound for packing ratio. A systematic approach to improve the model accuracy is proposed. The resultant alternative models are discussed in details. A comparison with literature data and the Mansoori-Carnahan-Starling formula is presented. Very good agreement is shown. 相似文献
89.
Maria PC Gal JF Massi L Burk P Tammiku-Taul J Tamp S 《Rapid communications in mass spectrometry : RCM》2005,19(4):568-573
A concerted theoretical (density-functional theory) and experimental electrospray mass spectrometry study was conducted on the formation of cesium cation adducts with small molecules taken as models of specific interactions sites in humic substances. Electrospray experiments with phenol, benzoic acid, salicylic acid, and phthalic acid, in methanolic solution containing cesium nitrate, were performed using a quadrupole ion trap. The formation of positively charged mixed clusters, [Cs(CsNO3)(n)(CsA1)(m)(Cs2A2)(p)]+ (A1 = benzoate, salicylate, and hydrogenophthalate, A2 = phthalate), was observed. Calculations of structures and bonding energetics of Cs+ in simple adducts formed with NO3-, CsNO3, A-, AH, and CsA are reported. The observation of variable cluster stoichiometry (n, m and p values) was interpreted in terms of more or less favorable interaction energies between Cs+ and the neutral species constituting the clusters. Phenol did not form clusters in significant abundances, despite a strong calculated interaction between Cs+ and cesium phenolate. This was attributed to its weak acid dissociation in the electrospray solution. 相似文献
90.
He I photoelectron (PE) spectra of four carboxylic acids and five esters are measured. Semiempirical and ab initio quantum chemical calculations are used for the interpretation of the spectra. The complex approach which uses empirically established relationships (the dependence of valence electron ionization energies on proton affinities in the gas phase, on the core level ionization energies, and on the structure) was developed. © 1997 John Wiley & Sons, Inc. 相似文献