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91.
Pettersson K Kyrychenko A Rönnow E Ljungdahl T Mårtensson J Albinsson B 《The journal of physical chemistry. A》2006,110(1):310-318
Singlet excitation energy transfer is governed by two donor-acceptor interactions, the Coulombic and exchange interactions giving rise to the F?rster and Dexter mechanisms, respectively, for singlet energy transfer. In transfer between colliding molecules or between a donor (D) and acceptor (A) connected in donor-bridge-acceptor (D-B-A) system by an inert spacer (B), the distinction between these two mechanisms is quite clear. However, in D-B-A systems connected by a pi-conjugated bridge, the exchange interaction between the donor and acceptor is mediated by the virtual low-lying excited states (unoccupied orbitals) of that bridge and, as a consequence, becomes much more long-range in character. Thus, the clear distinction to the Coulombic mechanism is lost. This so-called superexchange mechanism for singlet energy transfer has been shown to make a significant contribution to the energy transfer rates in several D-B-A systems, and its D-A distance as well as D-B energy gap dependencies have been studied. We here demonstrate that in a series of oligo-p-phenyleneethynylene (OPE) bridged porphyrin-based D-B-A systems with varying D-A distances the F?rster and through-bond (superexchange) mechanisms both make considerable contributions to the observed singlet energy transfer rates. The donor is either a zinc porphyrin or a zinc porphyrin with a pyridine ligand, and the acceptor is a free base porphyrin. By comparison to a homologous series where only the D-B energy gaps varies, a separation between the two energy transfer mechanisms was possible and, moreover, an interplay between distance and energy gap dependencies was noted. The distance dependence was shown to be approximately exponential with an attenuation factor beta=0.20 A-1. If the effect of the varying D-B energy gaps in the OPE series was taken into account, a slightly higher beta-value was obtained. Ground-state absorption, steady-state, and time-resolved emission spectroscopy were used. The experimental study is accompanied by time-dependent density functional theory (TD-DFT) calculations of the electronic coupling, and the experimental and theoretical results are in excellent qualitative agreement (same distance dependence). 相似文献
92.
Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out to study the interaction between xenon atom and iodine molecule in a solid krypton matrix. Interference between the CARS polarizations of the "free" and complexed iodine molecules is observed, while the quantum beats of the complex are not detected due to low concentration. Vibrational analysis based on the polarization beats yields accurate molecular constants for the I2-Xe complex. The harmonic frequency of the I2-Xe complex is found to be redshifted by 0.90 cm-1 when compared to the free I2, whereas the anharmonicity is approximately the same. The dephasing rate of the complex is found to be somewhat higher than that of the free iodine molecule in solid Kr, showing that the complexation affects dephasing, although not dramatically. Molecular dynamics simulations are carried out to find the conformation of the complex, and wave packet simulations are used to reproduce the CARS signal to confirm the assignments of the observed beatings as quantum and polarization beats. The results show that the polarization beats are a useful tool for investigating weak interactions in condensed phase. 相似文献
93.
Oskar Werner Can Quan Charlotta Turner Bert Pettersson Lars Wågberg 《Cellulose (London, England)》2010,17(1):187-198
Paper samples were rendered superhydrophobic with Alkyl Ketene Dimer using (1) Airblasting with cryo ground micro particles,
(2) crystallizing from organic solvents and (3) spraying with Rapid Expansion of Supercritical Solutions (RESS) technique.
The papers were characterized using Scanning Electron Microscopy, contact angle to water measurements and X-ray Photoelectron
Spectroscopy (XPS). Advancing contact angles were in the region of 150°–160° and receding contact angles were in the region
of 110°–130°. Diagrams showing the drop base diameter vs. the contact angle when water is pumped into, and then withdrawn
from, a sessile drop show that a stick slip pattern is present in the advancing phase for a non coated internally sized paper.
Papers rendered superhydrophobic with the RESS technique showed a much less pronounced stick slip pattern in the advancing
phase but still a stick slip pattern in the receding phase. 相似文献
94.
Lejonthun LS Andersson PU Någård MB Pettersson JB 《The journal of physical chemistry. B》2006,110(46):23497-23501
The kinetics of chlorine interactions with ice at temperatures between 103 and 165 K have been studied using molecular beam techniques. The Cl(2) trapping probability is found to be unity at thermal incident energies, and trapping is followed by rapid desorption. The residence time on the surface is less than 25 microg at temperatures above 135 K and approaches 1 s around 100 K. Rate constants for desorption are determined for temperatures below 135 K. The desorption kinetics follow the Arrhenius equation, and activation energies of 0.24 +/- 0.03 and 0.31 +/- 0.01 eV, with corresponding preexponential factors of 10(12.08+/-1.19) and 10(16.52+/-0.38) s(-1), are determined. At least two different Cl(2) binding sites are concluded to exist on the ice surface. The observed activation energies are likely to be the Cl(2)-ice binding energies for these states, and the Cl(2)-surface interactions are concluded to be stronger than earlier theoretical estimates. The surface coverage of Cl(2) on ice under stratospheric conditions is estimated to be negligible, in agreement with earlier work. 相似文献
95.
Chromatographic sorbents used within the purification of peptide or protein based active pharmaceutical ingredients (APIs) are commonly subjected to caustic regeneration procedures, so-called CIP treatments. While polymeric materials remain unaffected by this treatment, silica-based sorbents are at an intrinsic risk of dissolution under high pH conditions, such as, e.g. 0.1M NaOH. It is common misconception that silica-based materials simply cannot be subjected to alkaline conditions above pH 9. Moreover, most studies covering the chemical stability of HPLC sorbents above pH 9 have been limited to the chromatographic conditions used for the separations themselves. Such studies have used buffered mobile phases up to pH 11 or 12. Very little focus has been put on the stability of the stationary phases when subjected to shorter but harsher pH conditions required for regeneration purposes, such as 0.1M NaOH (pH 13). Knowledge about the amount of so-called leachables, degradation products originating from the stationary phase, is of growing importance for the registration of pharmaceuticals for human use and is addressed in this work. This study compares the chemical stability of different commercially available reversed phase silica materials (C18) that are used in industrial scale preparative HPLC. The silica materials were subjected to NaOH regeneration conditions and it is shown that some materials are able to withstand 0.1M NaOH conditions without significant harm. It is demonstrated that contaminants present in the effluent in the range of 10-50 microg/mL can lead to significant contamination of API product fraction. 相似文献
96.
Josephs RD Krska R MacDonald S Wilson P Pettersson H 《Analytical and bioanalytical chemistry》2004,378(5):1182-1189
Several previous interlaboratory studies in the field of mycotoxin analysis have revealed considerable problems, apparent as high between-laboratory standard deviations, or rather non-comparable and non-traceable results. A major reason is lack of proper calibrants for external calibration. Public awareness of substances that mimic or interfere with the activity of natural hormones (endocrine disrupters) has led to increased interest in mycotoxins with estrogenic potential, e.g. zearalenone (ZON). During a large-scale standard measurement and testing (SMT) project of the European Commission (EC) dealing with the preparation and certification of reference materials for determination of the mycotoxin ZON in maize, a ZON calibrant in acetonitrile was prepared and intensively checked for purity, homogeneity, and stability. Preparation of the material, study of its homogeneity and stability, and characterisation of the calibrant on the basis of its preparation, with discussion of the results obtained, are described in this paper. The certified value of 9.95 µg mL–1 for ZON in acetonitrile and its corresponding expanded uncertainty of ±0.30 µg mL–1 were calculated in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM). 相似文献
97.
98.
99.
Lundell J Jolkkonen S Khriachtchev L Pettersson M Räsänen M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(8):1670-1678
The structure, energetics, and infrared spectrum of the H2O2-CO complex have been studied computationally with the use of ab initio calculations and experimentally by FTIR matrix isolation techniques. Computations predict two stable conformations for the H2O2-CO complex, both of which show almost linear hydrogen bonds between the subunits. The carbon-attached HOOH-CO complex is the lower-energy form, and it has an interaction energy of -9.0 kJmol(-1) at the CCSD(T)/6-311++G(3df,3pd)// MP2/6-311++G(3df,3pd) level. The higher-energy form, HOOH-OC, has an interaction energy of 4.7 kJmol(-1) at the same level of theory. Experimentally, only the lower-energy form, HOOH-CO, was observed in Ar, Kr, and Xe matrices, and the hydrogen bonding results in substantial perturbations of the observed vibrational modes of both complex subunits. UV photolysis of the complex species primarily produces a complex between water and carbon dioxide, but minor amounts of HCO and trans-HOCO were found as well. 相似文献
100.
Cavalleri M Näslund LA Edwards DC Wernet P Ogasawara H Myneni S Ojamäe L Odelius M Nilsson A Pettersson LG 《The Journal of chemical physics》2006,124(19):194508
We present a combined x-ray absorption spectroscopy/computational study of water in hydrochloric acid (HCl) solutions of varying concentration to address the structure and bonding of excess protons and their effect on the hydrogen bonding network in liquid water. Intensity variations and energy shifts indicate changes in the hydrogen bonding structure in water as well as the local structure of the protonated complex as a function of the concentration of protons. In particular, in highly acidic solutions we find a dominance of the Eigen form, H(3)O(+), while the proton is less localized to a specific water under less acidic conditions. 相似文献