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591.
592.
We present a new tert-butanol force field parametrized to reproduce the mixture thermodynamics of tert-butanol/water over a wide range of solution compositions at room temperature and atmospheric pressure. The experimental Kirkwood-Buff integrals, which quantify preferential solvation of solution components by the same species or by the other components, were used as target values to be reproduced. Water was modeled using the simple point charge model. In the range of alcohol mole fractions between 0.02 and 0.98, our optimized model satisfactorily reproduces alcohol-alcohol, water-water, and alcohol-water aggregation behavior. As a consequence, the solution activity derivatives are reproduced as well. A comparison has been made with solution activities obtained by free energy calculations (i.e., thermodynamic integration). It clearly shows that the Kirkwood-Buff based approach performs superior in predicting solution activities of liquid mixtures. The new tert-butanol model has been used to examine the solution structure and hydrophobic interactions in aqueous tert-butanol at the various mixture compositions. A comparison is made with structural data obtained by neutron diffraction. 相似文献
593.
van Liempd SM Kool J Reinen J Schenk T Meerman JH Irth H Vermeulen NP 《Journal of chromatography. A》2005,1075(1-2):205-212
The development and validation of an online cytochrome P450 (CYP)-based bioreactor coupled to automated solid-phase extraction (SPE) and gradient HPLC separation is described. The analytical method was checked on intra- and inter-day repeatability of the ethoxyresorufin-O-demethylation (EROD) reaction with CYP 1Al/1A2 containing beta-NF induced rat liver microsomes as an enzyme source. These experiments showed that CYP activity was linearly decreased with 16% over an 11 h period. Inter-day measurements had a CV of 9.1%. Furthermore, Km and Vmax values of the EROD reaction, measured with the bioreactor, were 2.72 +/- 0.46 microM and 7.9 +/- 0.5 nmol/min/mg protein, respectively. These were in good correspondence with Km and Vmax values, measured with standard batch assay, which amounted 0.66 +/- 0.08 microM and 6.4 +/- 0.2 nmol/min/mg protein respectively. In conclusion the newly developed analytical method can be used effectively and at a microliter scale for online generation, extraction and separation of metabolites. 相似文献
594.
Adams N Bigmore HR Blundell TL Boyd CL Dubberley SR Sealey AJ Cowley AR Skinner ME Mountford P 《Inorganic chemistry》2005,44(8):2882-2894
Reactions of Ti(NMe(2))(2)Cl(2) with a wide range of primary alkyl and arylamines RNH(2) afforded the corresponding 5-coordinate imido titanium compounds Ti(NR)Cl(2)(NHMe(2))(2) (R = (t)Bu (1), (i)Pr (2), CH(2)Ph (3), Ph (4), 2,6-C(6)H(3)Me(2) (5), 2,6-C(6)H(3)(i)Pr(2) (6), 2,4,6-C(6)H(2)F(3) (7), 2,3,5,6-C(6)HF(4) (8), C(6)F(5) (9), 4-C(6)H(4)Cl (10), 2,3,5,6-C(6)HCl(4) (11), 2-C(6)H(4)CF(3) (12), 2-C(6)H(4)(t)Bu (13)). The compounds 1-13 are monomeric in solution but in the solid state form either N-H...Cl hydrogen bonded dimers or chains or perfluorophenyl pi-stacked chains, depending on the imido R-group. The compound 13 was also prepared in a "one-pot" synthesis from RNH(2) and Ti(NMe(2))(4) and Me(3)SiCl. Reaction of certain Ti(NR)Cl(2)(NHMe(2))(2) compounds with an excess of pyridine afforded the corresponding bis- or tris-pyridine analogues [Ti(NR)Cl(2)(py)(x)](y) (x = 3, y = 1; x = y = 2), and the structure of Ti(2)(NC(6)F(5))(2)Cl(2)(mu-Cl)(2)(py)(4) shows pi-stacking of perfluorophenyl rings. Reaction of Ti(NMe(2))(2)Cl(2) with cross-linked aminomethyl polystyrene gave quantitative conversion to the corresponding solid-supported titanium imido complex. This paper represents the first detailed study of how supramolecular structures of imido compounds may be influenced by simple variation of the imido ligand N-substituent. 相似文献
595.
Nico Leupold Philipp Ramming Irene Bauer Christina Witt Jennifer Jungklaus Prof. Dr. Ralf Moos Dr. Helen Grüninger Dr. Fabian Panzer 《欧洲无机化学杂志》2023,26(8):e202200736
Here, we investigate in detail the impact of the size of the methylammonium iodide (MAI) reactants in the mechanochemical powder synthesis of the halide perovskite methylammonium lead iodide (MAPbI3). Morphology and structural characterizations by scanning electron microscopy and X-ray diffraction reveal that with increasing MAI reactant size, the particle size of the perovskite powder increases, while its defect density decreases, as suggested by nuclear quadrupole resonance spectroscopy and photoluminescence investigations. The reason for this behavior seems to be associated to the sensitive influence of the MAI size on the time durations of MAPbI3 synthesis and delayed MAPbI3 crushing stage during ball milling. Thus, our results emphasize the high importance the reactant properties have on the mechanochemical synthesis of halide perovskites and will contribute to enhance the reproducibility and control of the fabrication of halide perovskites in powder form. 相似文献
596.
Lidija?Fras?Zemlji?Email author Du?ko??akara Nico?Michaelis Thomas?Heinze Karin?Stana Kleinschek 《Cellulose (London, England)》2011,18(1):33-43
The protonation behavior of 6-deoxy-6-(2-aminoethyl)amino cellulose as a novel soluble aminated derivate of cellulose was
studied by means of the potentiometric titration technique. The resulting proton binding isotherms exhibit two equivalent
steps, which can be described by the standard macroscopic two-pK model, in which the degree of protonation is averaged over
all the amine groups. In addition, a microscopic proton binding model was applied, in which the protonation sites are distinguished
and the protonation free energy is expanded into an intrinsic term and an electrostatic repulsion between the primary and
secondary amine groups. The protonation behavior of 6-deoxy-6-(2-aminoethyl)amino cellulose was compared with a model compound
(N-methylethylenediamine). 相似文献
597.
Steen Ingemann Els Kluft Nico M. M. Nibbering Colin E. Allison Peter J. Derrick Steen Hammerum 《Journal of mass spectrometry : JMS》1991,26(10):875-881
The intramolecular secondary isotope effects on the α-cleavage of deuterium-labelled N-methyldipentylamine radical cations have been studied as a function of ion lifetime by field ionization kinetics. The isotope effects observed are all normal and increase in magnitude with increasing ion lifetime, with the exception of the δ-labelled compound which shows an inverse effect (predominant loss of the labelled radical) at times shorter than 10?9 s, and a normal effect at longer times. The isotope effects reflect differences in zero-point energies of the transition states as well as the influence of slight reductions of isotope-dependent frequencies on the state sums–a statistical weight effect. The latter is particularly important at high ion energies and is the primary reason for the occurrence of the inverse isotope effect. The time dependence of the normal and inverse isotope effect is reproduced by QET/RRKM calculations. 相似文献
598.
Puchta R Galle M van Eikema Hommes N Pasgreta E van Eldik R 《Inorganic chemistry》2004,43(26):8227-8229
The ligand exchange mechanism of solvated lithium cations has been studied using DFT calculations (RB3LYP/6-311+G**). The water exchange mechanism on [Li(H(2)O)(4)](+) was found to be limiting associative (A) involving a five-coordinate intermediate, whereas ammonia exchange on [Li(NH(3))(4)](+) was found to follow an associative interchange (I(a)) mechanism. The suggested mechanisms are discussed in reference to available experimental and theoretical data. 相似文献
599.
The residue-specific 13C' CSA tensor principal components, sigma(11), sigma(22), sigma(33), and the tensor orientation defined by the rotation angles beta and gamma have been determined by solution NMR for uniformly labeled ubiquitin partially aligned in four different media. Spurious chemical shift deviations due to solvent effects were corrected with an offset calculated by linear regression of the residual dipolar couplings and chemical shifts at increasing alignment strengths. Analysis of this effect revealed no obvious correlation to solvent exposure. Data obtained in solution from a protein offer a better sampling of 13C' CSA for different amino acid types in a complex heterogeneous environment, thereby allowing for the evaluation of structural variables that would be challenging to achieve by other methods. The 13C' CSA principal components cluster about the average values previously determined, and experimental correlations observed between sigma(11), sigma(22) tensorial components and C'O...H(N) hydrogen bonding are discussed. The inverse association of sigma(11) and sigma(22) exemplify the calculated and solid-state NMR observed effect on the tensor components by hydrogen bonding. We also show that 13C' CSA tensors are sensitive to hydrogen-bond length but not hydrogen-bond angle. This differentiation was previously unavailable. Similarly, hydrogen bonding to the conjugated NH of the same peptide plane has no detectable effect. Importantly, the observed weak correlations signify the presence of confounding influences such as nearest-neighbor effects, side-chain conformation, electrostatics, and other long-range factors to the 13C' CSA tensor. These analyses hold future potential for exploration provided that more accurate data from a larger number of proteins and alignments become available. 相似文献
600.
Each family of Gauss hypergeometric functions for fixed (not all equal to zero) satisfies a second order linear difference equation of the form Because of symmetry relations and functional relations for the Gauss functions, many of the 26 cases (for different values) can be transformed into each other. In this way, only with four basic difference equations can all other cases be obtained. For each of these recurrences, we give pairs of numerically satisfactory solutions in the regions in the complex plane where , and being the roots of the characteristic equation.