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991.
Two highly sensitive and selective methods based on gas chromatography coupled to mass spectrometry (GC-MS) in the selected ion monitoring (SIM) mode have been developed for the quantification of 2,6-dichlorophenol (2,6-DCP), a sex pheromone of the tick females of Anocentor nitens. Standard addition method and calibration curve techniques using 5-bromine-4-hydroxy-3-methoxybenzaldehyde (5-BrV) as internal standard (IS) afforded detection limit of 0.1 ng ml−1. The calibration curve was linear over the concentration range from 0.5 to 500 ng ml−1 for 2,6-DCP. Results show that the concentration range of sex pheromone in the extracts samples was 1.08-10.35 ng ml−1. The methods developed provided reliable procedures to determine amounts of 2,6-DCP present in ticks. 相似文献
992.
993.
Liane Bianchin Daniela Nadvorny Alessandra Furtado da Silva Maria Goreti Rodrigues Vale Mrcia Messias da Silva Walter N.L. dos Santos Sergio L.C. Ferreira Bernhard Welz Uwe Heitmann 《Microchemical Journal》2006,82(2):174-182
Iridium and ruthenium, alone and in combination with tungsten, thermally deposited on the platform of a transversely heated graphite tube, were investigated for their suitability as permanent chemical modifiers for the determination of cadmium in coal slurries by electrothermal atomic absorption spectrometry (ET AAS). The conventional mixed palladium and magnesium nitrates (Pd–Mg) modifiers, added in solution, were also investigated for comparison. The latter one showed the best performance for aqueous solutions, and the mixed W–Ir and W–Ru permanent modifiers had the lowest stabilizing power. All of the investigated modifiers lost some of their stabilizing power when coal slurries were investigated. The Pd–Mg modifier, pure Ir and Ru, and a mixture of 300 μg W + 200 μg Ir could stabilize Cd at least to a pyrolysis temperature of 600 °C, whereas all the other combinations already failed at temperatures above 500–550 °C. Additional investigations of the supernatant liquid of the slurries supported the assumption that the high acid concentration of the slurries and/or a concomitant leaching out of the coal might be responsible for the reduced stabilizing power of the modifiers. The maximum applicable pyrolysis temperature of 600 °C was not sufficient to reduce the background absorption to a manageable level in the majority of the coal samples. High-resolution continuum source ET AAS revealed that the continuous background absorption was exceeding values of A = 2, and was overlapping with the analyte signal. Although the latter technique could correct for this background absorption, some analyte was apparently lost with the rapidly vaporizing matrix so that the method could not be considered to be rugged. A characteristic mass of 1.0 pg and a detection limit of 0.6 ng g− 1 could be obtained under these conditions. 相似文献
994.
Roqueline Rodrigues Silva de Miranda Grácia Divina de Fátima Silva Lucienir Pains Duarte Sidney Augusto Vieira Filho 《Helvetica chimica acta》2007,90(4):652-658
The triterpene ester (3β)‐olean‐18‐en‐3‐yl stearate ( 1 ), together with (3β)‐urs‐12‐en‐3‐yl stearate ( 2 ), and (3β)‐lup‐20(29)‐en‐3‐yl stearate ( 3 ) were isolated from leaves of Maytenus salicifolia Reissek (Celastraceae). The structure of 1 , a new compound, including its configuration, was established by 1H, 13C, and DEPT‐135 NMR data, including 2D experiments (HSQC, HMBC, COSY, and NOESY). The molecular mass (692 Da) was confirmed by gas chromatography coupled with mass spectrometry (CG/MS). 相似文献
995.
Sakata SK Taniguchi S Rodrigues DF Urano ME Wandermüren MN Pellizari VH Comasseto JV 《Journal of chromatography. A》2004,1048(1):67-71
Volatile compound biodegradation analysis usually requires the time-consuming step of extraction of the analytes from the matrix using organic solvents or costly radioactive-compounds. Thus, it is desirable to have a simple and fast technique to generate a good evaluation of bacterial biodegradation. The goal of this research was to develop a methodology on the basis of static headspace-gas chromatography/mass spectrometry (HS-GC/MS) to evaluate the level of volatile contaminant biodegradation. The effects of the following parameters were studied: temperature and time of equilibration. The biodegradation experiments were carried out with bacteria inoculation in mineral media in presence of volatile hydrocarbon compounds (toluene, p-xylene, nonane and naphthalene). Autoclaved inoculates were used as control and reference sample. The optimal headspace conditions were observed when the vials were heated at 80 degrees C for 20 min, the syringe at 81 degrees C and an injection volume of 0.4 mL was used. This methodology has the advantage of being relative free from matrix effects. 相似文献
996.
Optimization of inulinase production by Kluyveromyces marxianus using factorial design 总被引:4,自引:0,他引:4
Factorial design and response surface techniques were used to optimize the culture medium for the production of inulinase
by Kluyveromyces marxianus. Sucrose was used as the carbon source instead of inulin. Initially, a fractional factorial design (25–1) was used in order to determine the most relevant variables for enzyme production. Five parameters were studied (sucrose,
peptone, yeast extract, pH, and K2HPO4), and all were shown to be significant. Sucrose concentration and pH had negative effects on inulinase production, whereas
peptone, yeast extract, and K2HPO4 had positive ones. The pH was shown to be the most significant variable and should be preferentially maintained at 3.5. According
to the results from the first factorial design, sucrose, peptone, and yeast extract concentrations were selected to be utilized
in a full factorial design. The optimum conditions for a higher enzymatic activity were then determined: 14 g/L of sucrose,
10 g/L of yeast extract, 20 g/L of peptone, 1 g/L of K2HPO4. The enzymatic activity in the culture conditions was 127 U/mL, about six times higher than before the optimization. 相似文献
997.
B. J. Vieira M. C. Freitas A. F. Rodrigues A. M. G. Pacheco P. M. Soares 《Journal of Radioanalytical and Nuclear Chemistry》2007,271(2):377-385
Within an extensive survey of prevalent lower and higher plants in the Azores’ islands, with a view to their monitoring potential
for airborne elements at ground level, and then to an eventual use in evaluation routines for the archipelago, epiphytic lichens
were collected from Cryptomeria japonica (Japanese cedar) trunks all across Terceira and Santa Maria islands. After suitable procedures, thalli samples were put through
instrumental neutron activation analysis (INAA; k
0-variant) for elemental concentrations. Providing an overall view of micro-and trace-element levels in representative foliose-and
fruticose-type species, the data of high-level elements agree generally well for genera with distinct species, with a relatively
low interspecies variability. Principal-component analysis of the whole set of results discriminates clearly between two morphological
factors, corresponding to foliose and fruticose species, and likely among four major origins of elemental inputs: soil/dust
(two factors), sea spray and an antimony-related source. All things considered, and accounting for its availability and ubiquity,
Parmotrema bangii seems an adequate choice for further lichen-based, biomonitoring campaigns in the Azores archipelago. 相似文献
998.
Gessenildo Pereira Rodrigues Elizete Ventura Silmar Andrade do Monte Mario Barbatti 《Journal of computational chemistry》2016,37(7):675-683
The UV‐induced photochemistry of HCFC‐132b (CF2ClCH2Cl) was investigated by computing excited‐state properties with time‐dependent density functional theory (TDDFT), multiconfigurational second‐order perturbation theory (CASPT2), and coupled cluster with singles, doubles, and perturbative triples (CCSD(T)). Excited states calculated with TDDFT show good agreement with CASPT2 and CCSD(T) results, correctly predicting the main excited‐states properties. Simulations of ultrafast nonadiabatic dynamics in the gas phase were performed, taking into account 25 electronic states at TDDFT level starting in two different spectral windows (8.5 ± 0.25 and 10.0 ± 0.25 eV). Experimental data measured at 123.6 nm (10 eV) is in very good agreement with our simulations. The excited‐state lifetimes are 106 and 191 fs for the 8.5 and 10.0 eV spectral windows, respectively. Internal conversion to the ground state occurred through several different reaction pathways with different products, where 2Cl, C‐Cl bond breakage, and HCl are the main photochemical pathways in the low‐excitation region, representing 95% of all processes. On the other hand, HCl, HF, and C‐Cl bond breakage are the main reaction pathways in the higher excitation region, with 77% of the total yield. © 2015 Wiley Periodicals, Inc. 相似文献
999.
Bridging C−H Activation: Mild and Versatile Cleavage of the 8‐Aminoquinoline Directing Group
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Martin Berger Rajan Chauhan Dr. Catarina A. B. Rodrigues Prof. Dr. Nuno Maulide 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16805-16808
8‐Aminoquinoline has emerged as one of the most powerful bidentate directing groups in history of C?H activation within the last decade. However, cleavage of its robust amide bond has shown to be challenging in several cases, thus jeopardizing the general synthetic utility of the method. To overcome this limitation, we herein report a simple oxidative deprotection protocol. This transformation rapidly converts the robust amide to a labile imide, allowing subsequent cleavage in a simple one‐pot fashion to rapidly access carboxylic acids or amides as final products. 相似文献
1000.
Maria Inês F. Mota José Miguel Loureiro Alírio E. Rodrigues 《Separation & Purification Reviews》2016,45(3):227-259
Lignin is an underexploited side-stream of pulp and paper industry and biorefineries, being used for energy production at mill site or as low value material for dispersants or binding applications. However, an integrated process of reaction and separation can be implemented for the production of high added-value monomeric phenolic chemicals such as vanillin and syringaldehyde. In this review, the main research advances in the recovery of vanillin and syringaldehyde resulting from oxidation of lignin are addressed, covering various separation methodologies namely liquid-liquid extraction, supercritical fluid extraction, distillation, crystallization, membrane separation, and adsorption. Studies in this area started in the early years of the 20th century, but in the last decades several processes have been suggested, mainly for vanillin separation. Finding the ultimate industrially feasible process is still a necessary task and this review points out the most promising technologies and sequence of processes. 相似文献