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31.
M. Ahmed S. Ahmed M. M. Saeed M. Z. Iqbal 《Journal of Radioanalytical and Nuclear Chemistry》1996,212(4):269-280
Extraction of Pr(III), Ho(III) and Er(III) has been studied in the pH range of 1–10 with N-benzoyl-N-phenylhydroxylamine (BPHA) in benzene. The separation was found to be quantitative in borate media from pH 7 to 10, at an ionic strength of 0.1M (H+, BO3
3–). The stoichiometric composition of the complexes under the optimal conditions of shaking time, pH and reagent concentration was formulated using slope analysis and found to be M(BPHA)3, where M=Pr(III), Ho(III) and Er(III). The effect of various masking agents shows that citrate, ascorbate, EDTA, oxalate, fluoride and phosphate form stable complexes with these rare earths as compared to BPHA. The decontamination factors for different cations with respect to these rare earths under the optimum conditions have been evaluated. 相似文献
32.
One‐pot synthesis of 1‐ and 5‐substituted 1H‐tetrazoles using 1,4‐dihydroxyanthraquinone–copper(II) supported on superparamagnetic Fe3O4@SiO2 magnetic porous nanospheres as a recyclable catalyst 下载免费PDF全文
An effective one‐pot, convenient process for the synthesis of 1‐ and 5‐substituted 1H‐tetrazoles from nitriles and amines is described using1,4‐dihydroxyanthraquinone–copper(II) supported on Fe3O4@SiO2 magnetic porous nanospheres as a novel recyclable catalyst. The application of this catalyst allows the synthesis of a variety of tetrazoles in good to excellent yields. The preparation of the magnetic nanocatalyst with core–shell structure is presented by using nano‐Fe3O4 as the core, tetraethoxysilane as the silica source and poly(vinyl alcohol) as the surfactant, and then Fe3O4@SiO2 was coated with 1,4‐dihydroxyanthraquinone–copper(II) nanoparticles. The new catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, dynamic light scattering, thermogravimetric analysis, vibration sample magnetometry, X‐ray photoelectron spectroscopy, nitrogen adsorption–desorption isotherm analysis and inductively coupled plasma analysis. This new procedure offers several advantages such as short reaction times, excellent yields, operational simplicity, practicability and applicability to various substrates and absence of any tedious workup or purification. In addition, the excellent catalytic performance, thermal stability and separation of the catalyst make it a good heterogeneous system and a useful alternative to other heterogeneous catalysts. Also, the catalyst could be magnetically separated and reused six times without significant loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
33.
Soap-free emulsion polymerization (SFEP) of methyl methacrylate, butyl acrylate was conducted in water/methanol media with sodium salts of four different acidic comonomers, namely styrene sulfonic acid (NaSS), 2-acrylamide-2-methyl-1-propane sulfonic acid (NaAmps), acrylic acid (NaAA), and itaconic acid (Na2ita). It was found that the introduction of methanol as co-solvent (35 wt%) to the medium greatly decreases the amount of water-soluble polyelectrolyte in the cases NaAA and Na2ita while it does not make difference for NaSS and NaAmps. Having employed the concept of conductance dependency to the ion mobility, the onset concentration in which soluble chains were formed was detected. The addition of sulfonic-based comonomers (NaSS and NaAmps), first decreased particle size and then led to predomination of solution polymerization over SFEP. On the contrary, the incorporation of carboxylic-based comonomers (NaAA and Na2ita) led to increase in particle size. Moreover, the particle size results were in good qualitative agreement with the classical Smith–Ewart theory. 相似文献
34.
Saeed Nojavan Tayebeh Gorji Saied Saeed Hosseiny Davarani Amin Morteza-Najarian 《Analytica chimica acta》2014
There are numerous published reports about dispersive liquid phase microextraction of the wide range of substances, however, till now no broadly accepted systematic and purpose oriented selection of extraction solvent has been proposed. Most works deal with the optimization of available solvents without adequate pre-consideration of properness. In this study, it is tried to compare the performances of low- and high-density solvents at the same conditions by means of novel type of extraction vessel with head and bottom conical shape. Extraction efficiencies of seven basic pharmaceutical compounds using eighteen common organic solvents were studied in this work. It was much easier to work with high-density solvents and they mostly showed better performances. This work shows that although exact predicting the performance of the solvents is multifaceted case but the pre-consideration of initial selection of solvents with attention to the physiochemical properties of the desired analytes is feasible and promising. Finally, the practicality of the method for extraction from urine and plasma samples was investigated. 相似文献
35.
Saeed Ketabchi Hossein Moosaei 《Journal of Optimization Theory and Applications》2012,154(3):1080-1087
In this paper, we give an algorithm to compute the minimum norm solution to the absolute value equation (AVE) in a special case. We show that this solution can be obtained from theorems of the alternative and a useful characterization of solution sets of convex quadratic programs. By using an exterior penalty method, this problem can be reduced to an unconstrained minimization problem with once differentiable convex objective function. Also, we propose a quasi-Newton method for solving unconstrained optimization problem. Computational results show that convergence to high accuracy often occurs in just a few iterations. 相似文献
36.
37.
Nanosized cationic and anionic manganese porphyrins as mesoporous catalysts for the oxidation of olefins: Nano versus bulk aggregates 下载免费PDF全文
In this study, catalytic activity of bulk and nano‐sized meso‐tetrakis(4‐sulfonatophenyl)porphyrinatomanganese(III) acetate, MnTPPS4(OAc), (ammonium salt) and meso‐tetrakis(3‐methylpyridyl)porphyrinatomanganese(III) acetate, MnT(3‐MePy)P(OAc) (tosylate salt) for the oxidation of olefins with tetra‐n‐butylammonium Oxone has been studied and compared with that of the bulk counterparts. The nanoparticles were prepared by mixing solvent techniques using water, (triethyleneglycol) monomethyl ether and dimethylsulfoxide or acetonitrile. The formation of nano‐sized catalysts was confirmed by UV‐Vis spectroscopy, DLS and AFM. Nitrogen porosimetry measurements indicated the homogeneous pore size distribution in the bulk and nano‐sized manganese porphyrins. In spite of the high oxidizability of Oxone, the heterogenized manganese porphyrins showed a significantly higher oxidative stability relative to their homogeneous counterparts within a reaction time of 6 h. The increase in the catalytic activity induced by the formation of nano‐sized catalysts was more pronounced in the case of MnT(3‐MePy)P(OAc). MnT(3‐MePy)P(OAc) may be recovered and reused for at least 4 times without any significant decrease in the catalyst efficiency. In the case of MnTPPS4(OAc) a large decrease in the catalytic activity was observed after the first use of the catalyst. The latter was attributed to higher degrees of catalyst degradation in the case of MnTPPS4(OAc). 相似文献
38.
39.
Composites of polyaniline with yttrium oxide (Y2O3) nanoparticles have been prepared by chemical polymerizations method by increasing the weight percentage of yttrium oxide. X-Ray diffraction (XRD) and Fourier Transform Infrared Spectra (FTIR) were used to characterize the composites. XRD and FTIR pattern indicate that Polyaniline (PANI) is intercalated into the layers of Y2O3 nanoparticles successfully by in situ polymerization and therefore the degree of crystallinity increases due to crystalline of yttrium oxide nanoparticles. The scanning electron micrographs (SEM) also confirm the formation of dual phase of platelet as well as of flaky structure in PANI-Y2O3. Temperature dependant DC conductivity showed three dimensional variable ranges hopping (3D VRH) model. Activation energy, density of states and hopping length are calculated and found to be influenced by intercalating PANI into the layers of Y2O3 clay. 相似文献
40.
Oxidation of cyclohexene and styrene with sodium periodate and tetra‐n‐butylammonium periodate (TBAP) catalyzed by MnT(3‐MePy)P(OAc), MnT(4‐SO3)PP(OAc) and MnTPP(OAc) has been studied in water, methanol, acetonitrile and dichloromethane as solvents. The results show significant dependence of the product distribution on the type of solvent and the electronic nature of the aryl substituents introduced at the porphyrin periphery. While the oxidation of cyclohexene and styrene in the presence of MnT(3‐MePy)P(OAc) and MnTPP(OAc) in water (also in methanol) gave the corresponding epoxides as nearly the sole product, performing the reactions in the presence of MnT(4‐SO3)PP(OAc) yielded the products of allylic oxidation, cyclohexene‐2‐ol and cyclohexene‐2‐one and acetophenone as the major products. In the case of styrene, performing the reaction in the presence of MnT(4‐SO3)PP(OAc), MnT(3‐MePy)P(OAc) and MnTPP(OAc) in acetonitrile gave a mixture of styrene oxide and acetophenone as the products. Under the same conditions, the oxidation of cyclohexene afforded cyclohexene oxide as approximately the exclusive product. Furthermore, the oxidation of olefins in dichloromethane gave the corresponding epoxide as the exclusive products. The product distributions observed in the protic and aprotic solvents were used to provide indirect evidence on the relative contribution and reactivity of high valent manganese oxo and periodato Mn(III) porphyrin species to the oxidation reactions. 相似文献