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11.
Daniel Townsend Prof. Dr. Kenneth Shankland Dr. Alex Weymouth-Wilson Dr. Zofia Komsta Dr. Tim Evans Dr. Alexander J. A. Cobb 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(16):3504-3508
A highly enantioselective, organocatalytic, and scalable synthesis of a very unusual cis-decalin-cis-hydrindane tricyclic diterpenoid system has been achieved. Despite the prevalent pharmacological space that the related trans,trans and trans,cis-systems occupy, there have been no reports of an asymmetric synthesis of the cis,cis systems in the literature until now. We demonstrate the flexibility of our approach not only through access to a diverse range of products, all of which are attained in exceptionally high selectivities, but also by showing their easy conversion to the corresponding trans,cis-system and other derivatives. 相似文献
12.
Zofia Kowalewska E. Bulska A. Hulanicki 《Fresenius' Journal of Analytical Chemistry》1998,362(1):125-129
Different methods for the determination of several metals in soils by flame atomic absorption spectrometry (FAAS) were investigated.
Different procedures for total dissolution of soil: I – HF+HClO4, H3BO3, HCl digestion (conventional heating), II – HF+HClO4, H3BO3 digestion followed by fusion with LiBO2 (conventional heating) and III – HF+HCl+HNO3, H3BO3 digestion (microwave heating), as well as a leaching procedure with HNO3+HClO4, HCl were tested and compared. For quality assessment, the certified reference material S-1 soil was used. For most of the
investigated metals, the best accuracy and precision were achieved when the procedure I or III were used. The developed procedure
was applied to the analysis of soil samples from crude oil refinery and dump of petroleum origin wastes regions.
Received: 22 Dezember 1997 / Revised: 9 February 1998 / Accepted: 12 February 1998 相似文献
13.
Nowicka AM Zabost E Donten M Mazerska Z Stojek Z 《Analytical and bioanalytical chemistry》2007,389(6):1931-1940
A method is presented for the electroanalytical characterization of interactions of dsDNA with a drug, under conditions that
both agents are dissolved in the phosphate buffer solution and both are electroactive. Normal pulse, square wave, differential
pulse, and cyclic voltammetries were employed in the measurements of the drug and dsDNA oxidation signals at carbon electrodes.
UV–Vis spectroscopy was used as a non-electrochemical method to support the electroanalytical data. An anticancer drug, C-1311
(5-diethylaminoethyl-amino-8-hydroxyimidazoacridinone), has been selected for the examination. Normal pulse voltammetry was
particularly useful in showing that under the conditions employed neither dsDNA nor the drug were adsorbed at the electrode
surface. Necessary conditions for the appearance of the well-defined dsDNA voltammetric signal (guanine peak) are: rigorous
chemical and biological purity in the cell and appropriate purity of DNA. An analysis of the obtained results confirmed that
there were two modes of interaction between C-1311 and dsDNA: by intercalation and electrostatically. In the presence of excess
NaCl the electrostatic interactions deteriorate. The binding constants (K
1 and K
2, respectively) and the number (n) of nucleic base pairs (bp) and the number (m) of phosphate groups (pg) interacting with one molecule of drug have been determined. For strong interactions (intercalation)
the values of the binding constant, K
1, and the binding-site size, n, equal 3.7 × 104 M−1 and 2.1, respectively. For the weak electrostatic interactions the K
2 and m parameters equal 0.28 × 104 M−1 and 4.7. The intercalation process is rather slow and its rate (the conditions of pseudo-first-order reaction) was estimated
to equal 7 × 10−4 s−1. The possibility of independent determination of both interacting agents was very useful in the study.
Figure Intercalation of C-1311 into a dsDNA fragment 相似文献
14.
Martyna Zagrska-Dziok Tomasz Bujak Aleksandra Ziemlewska Zofia Nizio-ukaszewska 《Molecules (Basel, Switzerland)》2021,26(4)
The skin is an organ that is constantly exposed to many external factors that can affect its structure and function. Due to the presence of different cannabinoid receptors on many types of skin cells, cannabinoids can interact directly with them. Therefore, as part of this work, the impact of two types of Cannabis sativa L. herb extracts on keratinocytes and fibroblasts was assessed. The content of biologically active compounds such as phenols, flavonoids, chlorophylls and cannabinoids was evaluated. The antioxidant capacity of prepared extracts using the DPPH radical, H2DCFDA probe and measurement of superoxide dismutase activity was also assessed. The cytotoxicity of hemp extracts was determined using the Alamar Blue, Neutral Red and LDH assays. The ability of the extracts to inhibit the activity of matrix metalloproteinases, collagenase and elastase, was assessed. Preparations of model hydrogels were also prepared and their effect on transepidermal water loss and skin hydration was measured. The obtained results indicate that hemp extracts can be a valuable source of biologically active substances that reduce oxidative stress, inhibit skin aging processes and positively affect the viability of skin cells. The analysis also showed that hydrogels based on cannabis extracts have a positive effect on skin hydration. 相似文献
15.
Sylwia Basąg František Kovanda Zofia Piwowarska Andrzej Kowalczyk Katarzyna Pamin Lucjan Chmielarz 《Journal of Thermal Analysis and Calorimetry》2017,129(3):1301-1311
The Co–Mg–Al mixed metal oxides were prepared by calcination of co-precipitated hydrotalcite-like precursors at various temperatures (600–800 °C), characterised with respect to chemical (AAS) and phase (XRD) composition, textural parameters (BET), form and aggregation of cobalt species (UV–vis-DRS) and their redox properties (H2-TPR, cyclic voltammetry). Moreover, the process of thermal decomposition of hydrotalcite-like materials to mixed metal oxide systems was studied by thermogravimetric method combined with the analysis of gaseous decomposition products by mass spectrometry. Calcined hydrotalcite-like materials were tested as catalysts for methanol incineration. Catalytic performance of the oxides depended on cobalt content, Mg/Al ratio and calcination temperature. The catalysts with lower cobalt content, higher Mg/Al ratio and calcined at lower temperatures (600 or 700 °C) were less effective in the process of methanol incineration. In a series of the studied catalysts, the best results, with respect to high catalytic activity and selectivity to CO2, were obtained for the mixed oxide with Co:Mg:Al molar ratio of 10:57:33 calcined at 800 °C. High activity of this catalyst was likely connected with the presence of a Co–Mg–Al spinel-type phases, containing easy reducible Co3+ cations, formed during high-temperature treatment of the hydrotalcite-like precursor. 相似文献
16.
The 1:1 and 2:1 complexes between water and trans- and cis-isomers of nitrous acid have been isolated in argon matrices and studied using FTIR spectroscopy and DFT(B3LYP) calculations with a 6-311++G(2d,2p) basis set. The analysis of the experimental spectra indicate that 1:1 complexes trapped in solid argon involve very strong hydrogen bond in which acid acts as the proton donor and water as the proton acceptor. The perturbed OH stretches are −248, −228 cm−1 red shifted from their free-molecules values in complexes formed by trans- and cis-HONO isomers, respectively. The calculated spectral parameters for the two complexes are in good agreement with experimental data. The calculations also predict stability of two more 1:1 weakly bound complexes formed by each isomer. In these the water acts as the proton donor and one of the two oxygen atoms of the acid as the acceptor. The experimental spectra demonstrate also formation of 2:1 complex between water and trans-HONO isomer in an argon matrix. The performed calculations indicate that the complex involves a seven-membered ring in which OH group of HONO forms very strong hydrogen bond with the oxygen atom of one water molecule and nitrogen atom acts as a weak proton acceptor for the hydrogen atom of the second water molecule of the water dimer. The observed perturbations of the OH stretch of trans-HONO (750 cm−1 red shift) is much larger than that predicted by calculations (556 cm−1 red shift); this difference is attributed to strong solvation effect of argon matrix on very strong hydrogen bond. 相似文献
17.
Zofia Stepien/snm> 《Geometriae Dedicata》2002,93(1):37-45
We prove the formality property of any homogeneous space G/G
generated by an automorphism of finite order of a compact simple Lie group G. 相似文献
18.
Anna Michnik K. Michalik A. Kluczewska Zofia Drzazga 《Journal of Thermal Analysis and Calorimetry》2006,84(1):113-117
The thermal denaturation process of bovine and human
both fatty acid containing and fatty acid free albumins in aqueous solution
was studied by use of differential scanning calorimetry. Human serum albumins
were found to be more stable than their bovine counterparts. Fatty acid free
albumins were characterized as generally less stable, more susceptible to
aggregation, their unfolding endothermic transition was less cooperative and
with the smaller degree of reversibility. Deconvolution analysis with using
a non-two-state model with two component transitions showed essential differences
in the thermodynamic parameters between all studied albumins, particularly
regarding the high-temperature component transition. 相似文献
19.
The complexes of glyoxal (Gly), methylglyoxal (MGly), and diacetyl (DAc) with water have been studied using Fourier transform infrared (FTIR) matrix isolation spectroscopy and MP2 calculations with 6-311++G(2d,2p) basis set. The analysis of the experimental spectra of the Gly(MGly,DAc)/H2O/Ar matrixes indicates formation of one Gly...H2O complex, three MGly...H2O complexes, and two DAc...H2O ones. All the complexes are stabilized by the O-H...O(C) hydrogen bond between the water molecule and carbonyl oxygen as evidenced by the strong perturbation of the O-H, C=O stretching vibrations. The blue shift of the CH stretching vibration in the Gly...H2O complex and in two MGly...H2O ones suggests that these complexes are additionally stabilized by the improper C-H...O(H2) hydrogen bonding. The theoretical calculations confirm the experimental findings. They evidence the stability of three hydrogen-bonded Gly...H2O and DAc...H2O complexes and six MGly...H2O ones stabilized by the O-H...O(C) hydrogen bond. The calculated vibrational frequencies and geometrical parameters indicate that one DAc..H2O complexes, two Gly...H2O, and three MGly...H2O ones are additionally stabilized by the improper hydrogen bonding between the C-H group and water oxygen. The comparison of the theoretical frequencies with the experimental ones allowed us to attribute the calculated structures to the complexes present in the matrixes. 相似文献
20.
Joanna Wiśniewska Hasan Marai Andrzej Karocki Konrad Szaciłowski Ewa Kita Zofia Stasicka 《Journal of photochemistry and photobiology. A, Chemistry》2010,209(2-3):121-127
Irradiation of chromium(III) complexes with oxalate and pyridinedicarboxylate ligands (pda = 2,3-, 2,4-, or 2,5-dicarboxylate) leads to diverse behaviors, dictated by light energy, presence of oxygen and the ligand nature. Irradiation within the MC bands is unaffected by O2 and results in ligand substitution. The LMCT excitation is effective only when oxalate is coordinated to Cr(III); then electron transfer from oxalate to central ion generates an intermediate, consisted of a Cr(II)species and the C2O4? radicals. The species undergo fast redox reactions dependent on the presence of O2 and the pda ligand.(1) In anoxic medium the fast outersphere electron transfer from Cr(II) to solvent, generates hydrated electrons and re-oxidizes the chromium centre to CrIII. Then geminate recombination regenerates substrate, whereas competitive release of the C2O4? radical leads to substitution of one oxalate ligand by two water molecules (aquation induced by the LMCT excitation). In the presence of the pda ligand the outersphere electron transfer is accompanied by the innersphere CT, generating Cr(III) coordinated to two radical ligands: C2O4? and pda3?; the intermediate releases also eaq?, but this reaction is slower than that of the homoleptic oxalate complex. Hydrated electrons are scavenged also by the released radicals. All these processes are completed within microseconds and in consequence, the Cr(III) complexes irradiated in deoxygenated solutions are insensitive to subsequent oxygenation.(2) When UV-irradiation is carried out in oxygenated medium reaction of Cr(II) species with molecular oxygen competes with the outer- or inner electron transfer observed in anoxic medium. Both these pathways result in generation of chromate(VI). Quantum yield of the Cr(VI) production is sensitive to the presence and structure of pda ligand, decreasing within the series 2,3-pda > 2,4-pda > 2,5-pda. 相似文献