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81.
A strategy is presented for synthesis of optically active precursors derived from (S)-(-)-ethyl lactate for use in synthesis of chiral liquid crystals. 相似文献
82.
Ricardo O. Silva Ricardo A. W. Neves Filho Rodrigo Azevedo Rajendra M. Srivastava Hugo Gallardo 《Structural chemistry》2010,21(3):485-494
In this article, we describe the complete 1H and 13C NMR signal assignments of four 1,2,4-oxadiazoles possessing light-emitting liquid crystal properties. These results were
obtained by using one- and two-dimensional NMR techniques as well as GIAO (PCM) calculations at B3LYP/6-311++G(d,p) level
for compounds 1 and 2a–d. The computed values are in good agreement with the ones obtained experimentally. In addition, some previously unexplained
thermotropic features of compounds 2a–d could be clarified with the help of the geometry optimization calculations carried out by us. 相似文献
83.
Determination of parathion in biological fluids by means of direct solid-phase microextraction 总被引:1,自引:0,他引:1
Gallardo E Barroso M Margalho C Cruz A Vieira DN López-Rivadulla M 《Analytical and bioanalytical chemistry》2006,386(6):1717-1726
A new and simple procedure for the determination of parathion in human whole blood and urine using direct immersion (DI) solid-phase
microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS) is presented. This technique was developed using only
100 μL of sample, and ethion was used as internal standard (IS). A 65-μm Carbowax/divinylbenzene (CW/DVB) SPME fibre was selected
for sampling, and the main parameters affecting the SPME process such as extraction temperature, adsorption and desorption
time, salt addition, agitation and pH effect were optimized to enhance the sensitivity of the method. This optimization was
also performed to allow the qualitative determination of parathion’s main metabolite, paraoxon, in blood. The limits of detection
and quantitation for parathion were 3 and 10 ng/mL for urine and 25 and 50 ng/mL for blood, respectively. For paraoxon, the
limit of detection was 50 ng/mL in blood. The method showed linearity between the LOQ and 50 μg/mL for both matrices, with
correlation coefficients ranging from 0.9954 to 0.9999. Precision and accuracy were in conformity with the criteria normally
accepted in bioanalytical method validation. The mean absolute recoveries were 35.1% for urine and 6.7% for blood. Other parameters
such as dilution of sample and stability were also validated. Its simplicity and the fact that only 100 μL of sample is required
to accomplish the analysis make this method useful in forensic toxicology laboratories to determine this compound in intoxications,
and it can be considered an alternative to other methods normally used for the determination of this compound in biological
media. 相似文献
84.
D.C.J. Rezende F.O. Borges G.H. Cavalcanti M. Raineri M. Gallardo J. Reyna Almandos A.G. Trigueiros 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(12-13):2000-2006
The spectrum of four-times-ionized krypton (Kr V) has been observed in the 230–4900 Å wavelength range, resulting in 91 new classified lines. We were able to identify 21 new energy levels belonging to the 4s24p5d, 4s24p5s, 4s24p6s, 4s24p5p and 4s4p24d configurations. Relativistic Hartree–Fock calculations were used to predict energy levels and transitions. 相似文献
85.
Beatriz Casta?eda William Ortiz‐Cala Cecilia Gallardo‐Cabrera Norma Sbarbati Nudelman 《Journal of Physical Organic Chemistry》2009,22(9):807-814
An HPLC method was developed to determine the stability of alprazolam (AL) as a pure drug and in monodrug pharmaceutical tablets. The main degradation product of AL tablets was isolated and fully characterized as triazolaminoquinoleine (TAQ). For a quantitative evaluation of the excipient effects in the pharmaceutical formulations, a 2k fractionated factorial design was applied in the preparation of the different samples. The kinetic of degradation of AL in each formulation was followed by UV spectrophotometry. It was found that excipients like CMC and magnesium stearate favour degradation, while the rate of the reaction is decreased when lactose and starch were used as excipients. A mechanism for the interactions of AL with some excipients is postulated that explains the observed results. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
86.
87.
88.
Hilal M Parrado MF Rosa M Gallardo M Orce L Massa EM González JA Prado FE 《Photochemistry and photobiology》2004,79(2):205-210
UV-B radiation (280-320 nm) is harmful to living organisms and has detrimental effects on plant growth, development and physiology. In this work we examined some mechanisms involved in plant responses to UV-B radiation. Seedlings of quinoa (Chenopodium quinoa Willd.) were exposed to variable numbers of UV-B radiation doses, and the effect on cotyledons was studied. We analyzed (1) cotyledons anatomy and chloroplasts ultrastructure; (2) peroxidase activity involved in the lignification processes; and (3) content of photosynthetic pigments, phenolic compounds and carbohydrates. Exposure to two UV-B doses induced an increase in the wall thickness of epidermal cells, which was associated with lignin deposition and higher activity of the peroxidase. The chloroplast ultrastructure showed an appearance typical of plants under shade conditions, likely in response to reduced light penetration into the mesophyll cells due to the screening effect of epidermal lignin deposition. Exposure to UV-B radiation also led to (1) enhancement in the level of phenolics, which may serve a protective function; (2) strong increase in the fructose content, a fact that might be related to higher requirement of erythrose-4P as a substrate for the synthesis of lignin and phenolics; and (3) reduction in the chlorophyll concentration, evidencing alteration in the photosynthetic system. We propose that the observed lignin deposition in epidermal tissues of quinoa is a resistance mechanism against UV-B radiation, which allows growing of this species in Andean highlands. 相似文献
89.
Charge in ionic micelles determines the trends of their stability and their practical applications. Charge can be calculated from zeta potential (zeta) measurements, which, in turn, can be obtained by Doppler microelectrophoresis. In this study, the electrophoretic properties of dodecyltrimethylammonium bromide (DTAB) in KBr aqueous solution (0-6 mM) were determined by Doppler microelectrophoresis. At very low surfactant concentrations (up to 6 mM), zeta potential was quite constant and due to the ionized monomers (DTA+). Above 6 mM, zeta potential increased to a maximum at surfactant concentrations still below the critical micellar concentration (CMC). This increase could be explained by a formation of nonmicellar aggregates of DTAB. Then, above the CMC, zeta potential underwent an abrupt reduction, which was dependent qualitatively and quantitatively on KBr concentration, and which could be due to an increase of the number of counterions adsorbed on the micelle surface. Calculation of effective micellar charge from zeta potential gave the surface charge density. Comparing this value with the theoretical, obtained from geometrical considerations, a fraction of 0.29 of charged micellar headgroups was obtained when DTAB was in aqueous solution, which is consistent with the value obtained by conductivity measurements. 相似文献
90.
OK Yoon WG Hwang JC Choe MS Kim 《Rapid communications in mass spectrometry : RCM》1999,13(14):1515-1521
A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd. 相似文献