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201.
N‐alkoxypyridinium salts as coinitiators in radical polymerization: Synthesis and Photochemical Properties 下载免费PDF全文
Janina Kabatc Katarzyna Kostrzewska Robert Dobosz Łukasz Orzeł Katarzyna Jurek 《Journal of polymer science. Part A, Polymer chemistry》2017,55(17):2840-2850
A few N‐alkoxypyridinium salts are developed as photoinitiators for efficient polymerization reactions. They are characterized by absorption properties below 300 nm, and generate alkoxy radicals on UV‐Vis light exposure. The squarylium dye was used as a blue‐light photosensitizer. Polymerization results are correlated with the photochemistry of N‐alkoxypyridinium salts. The quenching of the excited singlet state of squarylium dye by pyridinium salt and the formation of the semioxidized species of squaraine suggests an electron transfer from an excited dye to a coinitiator, and that the resulting oxygen‐centered radical initiates the polymerization process. The chemical mechanism was investigated by steady state photolysis and nanosecond laser flash photolysis experiments. Photoinitiating activity of new photoinitiators for initiation of polymerization of trimethylolpropane triacrylate in the UV‐blue light region was compared with photoinitiating ability of selected commercially available initiators. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2840–2850 相似文献
202.
Iwona Rutyna Mieczyslaw Korolczuk 《International journal of environmental analytical chemistry》2015,95(11):1042-1053
A double accumulation and stripping steps were proposed to increase the sensitivity of Co(II) determination by catalytic adsorptive stripping voltammetry (AdSV). Electrodes with large and small surface area were used for the first and second accumulation step, respectively. As the accumulation of Co(II) complex at the first electrode was finished, the electrode was placed at a short distance opposite the second one. Then the Co(II) complex desorbed from the first electrode was accumulated at the second electrode. Taking into account the small volume of space between the electrodes, the concentration of the Co(II) complex in solution between the electrodes was drastically higher than that in the bulk solution. The accumulation step at the second electrode was performed from the solution with higher concentration of Co(II) and therefore the detection limit was lowered. The calibration graph of Co(II) determination for accumulation time of 120 s at both electrodes was linear from 1.18 to 58.9 ng L?1. The detection limit for Co(II) was equal to 0.47 ng L?1 and it is so far the lowest detection limit obtained for Co(II) using mercury-free electrodes. The proposed method was applied to Co(II) determination in water certified reference material. 相似文献
203.
A needle trap device (NTD) was developed for the extraction of polycyclic aromatic hydrocarbons (PAHs) from liquid samples followed by determination by gas chromatography–mass spectrometry (GC-MS). The extraction was performed using the dynamic sampling approach, in which a liquid sample was pumped through the system. Due to the flexibility and softness of graphene, its application in NTD may be difficult. Herein, the effectiveness of reduced graphene oxide (rGO) packed in NTD in dynamic extraction of PAHs was evaluated. Several experimental parameters, such as the adsorbent mass, eluent type and its volume, as well as the sample volume were optimized to achieve satisfactory performance for dynamic extraction. Comparative studies showed that the extraction performance of rGO-NTD was better than using NTDs packed with other sorbents such as activated carbon. The recovery rate for reduced graphene oxide exceeded 92%. Comparison of dynamic and headspace sampling showed comparable results but the dynamic mode is more suitable for field measurements. The recovery rates of PAHs spiked in water samples were from 76.5 to 100.2% and the relative standard deviation values were from 2.7 to 7.5% under the optimal conditions. This work reveals the potential of NTD with a graphene-based material for sample preparation before chromatographic analysis of liquid samples. 相似文献
204.
Tyrpień K Wielkoszyński T Janoszka B Dobosz C Bodzek D Steplewski Z 《Journal of chromatography. A》2000,870(1-2):29-38
A rapid procedure for the analysis of the main nicotine metabolites (cotinine, trans-3′-hydroxycotinine) in urine has been worked out. The procedure includes isolation of nicotine and its metabolites from urine by means solid–liquid extraction technique using resin Amberlite XAD-2 and then quantitation by the use of thin-layer chromatography with densitometry (in reflection mode). GC–MS was applied to confirm the results obtained by TLC. The procedure was applied to the analysis of cotinine concentrations in urine samples taken from children living in Upper Silesia region (Poland). Among 444 investigated children we did not find cotinine almost in 60% but in 15% of this population, there were children who could have been exposed to cigarette smoke. 相似文献
205.
Miros?aw Szafran Iwona Kowalczyk Andrzej Katrusiak 《Journal of Molecular Structure》2006,786(1):25-32
A novel betaine derivative, 3-(2-amino-pyridinium)-propionate monohydrate, has been synthesized and its structure studied by X-ray diffraction, FTIR, Raman, 1H and 13C NMR spectroscopies and by DFT calculations. The crystals are monoclinic, space group P21/c with a=8.0800(16), b=15.242(3), c=7.1698(14) Å, β=104.30(3)° and Z=4. Each oxygen atom of the carboxylate group is engaged in two intermolecular hydrogen bonds, one with water molecule and the other with amine group. The water molecules link the molecules of 3-(2-amino-pyridinium)-propionate into planar zigzag chains along the b axis. The screening constants for 1H and 13C atoms have been calculated by GIAO/B3LYP/6-31 G(d,p) and analyzed. Linear correlations between the experimental 1H and 13C chemical shifts and the computed screening constants have been obtained. Raman and FTIR spectra of the title betaine have been investigated. 相似文献
206.
Szłyk Edward Biniak Stanisław Surdykowski Andrzej Łakomska Iwona Barwiołek Magdalena Larsen Erik 《Transition Metal Chemistry》2002,27(5):501-505
The Schiff base prepared by reacting (–)-(1R,2R)-1,2-cyclohexanediamine with 2-hydroxyacetophenone was used as a ligand for CoII and CuII. The coordination compounds were studied by u.v.–vis. absorption and by circular dichroism (c.d.) spectroscopy in solution. The complexes are four-coordinated in a slightly distorted square planar symmetry. The distortion from planarity is a main factor influencing the chiral surroundings of the metal ion. The d–d and c.t. transitions are consistent with the observed distortion, which arises from intramolecular interactions between the methyl groups attached to the Schiff base imine carbon and hydrogen atoms of the cyclohexane ring. The electrochemical properties of the CoII and CuII complexes were observed in MeCN but investigations revealed weaker oxygen activation than of CoII analogue with salicylaldehyde. The CuII complex is reduced in H2O to CuI which disproportionates to CuII and Cu0. 相似文献
207.
Furuya H Fujimaki S Kambara S Suzuki S Hashimoto Y Okazaki S Wada A Beech IB Sunner J Hiraoka K 《Rapid communications in mass spectrometry : RCM》2005,19(17):2433-2442
Atmospheric pressure Penning ionization mass spectra of methanol were measured as functions of Ar or He gas pressure in the first vacuum chamber, the position of the skimmer, and the voltage applied between the orifice and the skimmer. When the orifice and the skimmer were coaxial with a distance of 4 mm, the distribution of CH3OH2+(CH3OH)n clusters was only weakly dependent on both Ar pressure (in the range of 19-220 Pa) and orifice-skimmer voltage (in the range of 1-45 V). The ion/molecule reaction CH3OH2+ + CH3OH --> CH3+(CH3OH) + H2O was observed in the free jet expansion, especially at high orifice-skimmer voltage values. When the orifice and the skimmer were off-centered and the distance between them was increased to 18 mm, the formation of large CH3OH2+(CH3OH)n clusters, as well as their dissociation, were seen. The endothermic proton transfer reaction, CH3+(CH3OH) + CH3OH --> CH3OH2+ + CH3OCH3, occurred at high orifice-skimmer voltage. The collision-induced dissociation of cluster ions by He gas in the first vacuum chamber was much more efficient than by Ar. These results demonstrated that the mass spectra are highly dependent on skimmer position and on orifice-skimmer voltage and that ions observed by mass spectrometry do not necessarily reflect the abundance of ions produced in the atmospheric pressure ion source. 相似文献
208.
Shiea J Huang MZ Hsu HJ Lee CY Yuan CH Beech I Sunner J 《Rapid communications in mass spectrometry : RCM》2005,19(24):3701-3704
A new method of electrospray-assisted laser desorption/ionization (ELDI) mass spectrometry, which combines laser desorption with post-ionization by electrospray, was applied to rapid analysis of solid materials under ambient conditions. Analytes were desorbed from solid metallic and insulating substrata using a pulsed nitrogen laser. Post-ionization produced high-quality mass spectra characteristic of electrospray, including protein multiple charging. For the first time, mass spectra of intact proteins were obtained using laser desorption without adding a matrix. Bovine cytochrome c and an illicit drug containing methaqualone were chosen in this study to demonstrate the applicability of ELDI to the analysis of proteins and synthetic organic compounds. 相似文献
209.
Kaluzna IA Matsuda T Sewell AK Stewart JD 《Journal of the American Chemical Society》2004,126(40):12827-12832
Eighteen key reductases from baker's yeast (Saccharomyces cerevisiae) have been overproduced in Escherichia coli as glutathione S-transferase fusion proteins. A representative set of alpha- and beta-keto esters was tested as substrates (11 total) for each purified fusion protein. The stereoselectivities of beta-keto ester reductions depended both on the identity of the enzyme and the substrate structure, and some reductases yielded both L- and D-alcohols with high stereoselectivities. While alpha-keto esters were generally reduced with lower enantioselectivities, it was possible in all but one case to identify pairs of yeast reductases that delivered both alcohol antipodes in optically pure form. Taken together, the results demonstrate not only that individual yeast reductases can be used to supply important chiral building blocks, but that GST-fusion proteins allow rapid identification of synthetically useful biocatalysts (along with their corresponding genes). 相似文献
210.
The nitroaldol reaction of (1R)-8-phenylmenthyl glyoxylate 6 with 1-nitro-2-phenylethane or with phenylnitromethane led stereoselectively to adducts 4 and 12, which where then transformed into (−)-bestatin hydrochloride and the Taxotere® side-chain in overall yields of 31 and 52%. 相似文献