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41.
Ronaldo S. Nunes Felipe S. Semaan Alan T. Riga Éder T. G. Cavalheiro 《Journal of Thermal Analysis and Calorimetry》2009,97(1):349-353
The thermal properties of verapamil hydrochloride (VRP) and its physical association as binary mixtures with some common excipients
were evaluated. Thermogravimetry (TG) was used to determine the thermal mass loss, as well as to study the kinetics of VRP
thermal decomposition, using the Flynn-Wall-Ozawa model. Based on their frequent use in pharmacy, five different excipients
(microcrystalline cellulose, magnesium stearate, hydroxypropyl methylcellulose, polyvinylpyrrolidone and talc) were blended
with VRP. Samples were prepared by mixing the analyte and excipients in a proportion of 1:1 (m/m). DSC curves for pure VRP
presented an endothermic event at 143 ± 2 °C (ΔHmelt = 132 ± 4 J g−1), which corresponds to the melting (literature Tm = 143.7 °C, ΔHmelt = 130.6 J g−1). Comparisons among the observed results for each compound and their binary physical mixtures presented no relevant changes.
This suggests no interaction between the drug and excipient. 相似文献
42.
P. M. Carreira D. Nunes P. Valério M. F. Araújo 《Journal of Radioanalytical and Nuclear Chemistry》2009,281(1):153-156
The Nuclear and Technological Institute (Instituto Tecnológico e Nuclear—ITN) in cooperation with the International Atomic
Energy Agency (IAEA) has been conducting a nationwide survey of hydrogen (2H/1H) and oxygen (18O/16O) isotopic composition of monthly precipitation since 1988. This paper focuses on basic features of spatial and temporal
distribution of δ18O and δ2H in the precipitation over Continental Portugal derived from ITN database. Phenomenological relationships between stable
isotopes composition of precipitation and various climate-related parameters (local air temperature, distance to the Atlantic
coast, altitude, amount of precipitation) are established and discussed. 相似文献
43.
Tatiana Visnevschi-Necrasov Sara C. Cunha Eugénia Nunes M. Beatriz P.P. Oliveira 《Journal of chromatography. A》2009,1216(18):3720-3724
A method based on matrix solid-phase dispersion (MSPD) has been developed for the determination of 12 isoflavones in Trifolium pratense L. Dried leaf samples were blended with C18, placed in small columns and isoflavones extracted with dichloromethane–methanol. Analyses were performed by high performance liquid chromatography with diode array detection (HPLC-DAD) with 2-methoxyflavone as internal standard. Several dispersants, eluents and clean-up steps were tested during the optimization of the process in order to obtain the best selectivity and yields. Mean recoveries ranged from 70% to 119%, with relative standard deviations <18%. The limits of detection were between 0.006 mg/l for biochanin A and 0.108 mg/l for daidzin. The performance of the optimized method in real samples was compared with a conventional method based in solid–liquid extraction (SLE). 相似文献
44.
Lurdes M. Ciríaco Isabel M. da Silva Pereira Manuel R. Nunes Helena M. Mendonça Fernanda M. Costa 《Journal of Solid State Electrochemistry》2001,5(7-8):495-501
The effect of the partial substitution of tantalum by iron on the structural and electrical properties of the KTaO3 perovskite-type oxide powders has been studied. The powders were prepared by the standard ceramic method, and the respective
structural characterization performed by X-ray powder diffraction. From the synthesized oxide samples, iron-coated electrodes
were fabricated and tested as the anode for the oxygen evolution reaction in alkaline medium. An estimation of the electrode's
capacity has been calculated from the charging currents and the corresponding roughness factor evaluated. The electrocatalytic
activity/stability of the oxide electrodes in alkaline solutions has been analysed through the kinetic parameters.
Electronic Publication 相似文献
45.
The objective of the present research work was to develop a membrane with a high H2O/alcohol selectivity for pervaporation and for use in direct alcohol fuel cells. Sulfonated poly (ether ether ketone) (SPEEK) was coated with a thin continuous carbon molecular sieve (CMS) layer. The membranes obtained had 180- and 400-nm thick CMS layers that led to a clear reduction of alcohol crossover. The water/alcohol selectivity increased with the size of the alcohol molecules as follows: methanol < ethanol < n-propanol < iso-propanol. A water/n-propanol selectivity of up to 34,000 was obtained, confirming the molecular sieving effect. The system was tested in a direct methanol fuel cell using standard electrodes, and demonstrated a better performance than with plain membranes. In a later stage Pt was introduced in the CMS layer during the preparation of the membrane electrode assemblies, this had the advantage that the CMS layer not only acted as an alcohol barrier but also as a catalyst support. 相似文献
46.
Alexandra Mara De Amorim Ana Cristina Franzoi Paula Nunes Oliveira Alfredo Tibúrcio Nunes Pires Almir Spinelli José Roberto Bertolino 《Journal of Polymer Science.Polymer Physics》2009,47(22):2206-2214
The influence of molecular weight and the amount of the poly(vinylpyrrolidone) (PVP) on the growth of poly(vinylpyrrolidone)–based films on copper surfaces was studied by electrochemical, infrared and electronic spectroscopy, and thermogravimetric methods. Complex polymer/metal ions were deposited onto a copper surface, as the result of the electrochemically generated reaction of copper cations with PVP and SCN?, in sulfuric acid media. Spontaneous film growth on copper surfaces was generated and characterized as a Cu(II)/PVP/SCN? complex. Infrared spectra and thermal gravimetric curves of the films generated at + 0.7 V were compared with the chemically synthesized complex, and show the same patterns. The oxidation process can be described as: Cu(0)→Cu(I) and Cu(I)→Cu(II), and the copper complex formed at more positive potentials was characterized as Cu(II)/PVP/SCN?, with copper bonded to the oxygen atom of PVP and thiocyanate ligand N‐linked. This study focuses on the complex formation on a copper surface in acid media and its characterization through electrochemical and spontaneously generated reactions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2206–2214, 2009 相似文献
47.
Luisa Célia Melo Djenaine De Souza Pedro de Lima‐Neto Adriana Nunes Correia 《Electroanalysis》2010,22(21):2502-2510
The highly boron‐doped diamond electrode (HBDD) combined with square wave voltammetry (SWV) was used in the development of an analytical procedure for diquat determination in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices. Preliminary experiments realised in a medium of 0.05 mol L?1 Na2B4O7 showed the presence of two voltammetric peaks around ?0.6 V and around ?1.0 V vs. Ag/AgCl/Cl? 3.0 mol L?1, where the first peak could be successfully used for analytical proposes due the facility in the electrode surface renovation. After the experimental and voltammetric optimisation, the calculated detection and quantification limits were 1.6×10?10 mol L?1 and 5.3×10?10 mol L?1 (0.057 µg L?1 and 0.192 µg L?1, respectively), which are lower than the maximum residue limit established for fresh food samples by the Brazilian Sanitary Vigilance Agency. The proposed methodology was used to determine diquat residues in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices and the calculated recovery efficiencies indicated that the proposed procedure presents higher robustness, stability and sensitivity, good reproducibility, and is very adequate for diquat determination in complex samples. 相似文献
48.
da Silva JN Salcedo E de Oliveira AB Barbosa MC 《The Journal of chemical physics》2010,133(24):244506
Using molecular dynamic simulations, we study a system of particles interacting through a continuous core-softened potentials consisting of a hard core, a shoulder at closest distances, and an attractive well at further distance. We obtain the pressure-temperature phase diagram of this system for various depths of the tunable attractive well. Since this is a two length scale potential, density, diffusion, and structural anomalies are expected. We show that the effect of increasing the attractive interaction between the molecules is to shrink the region in pressure in which the density and the diffusion anomalies are present. If the attractive forces are too strong, particle will be predominantly in one of the two length scales and no density of diffusion anomaly is observed. The structural anomalous region is present for all the cases. 相似文献
49.
Paula Santos Nunes Marília Santos Bezerra L. P. Costa Juliana Cordeiro Cardoso R. L. C. AlbuquerqueJr. M. O. Rodrigues Gabriela Borin Barin Francilene Amaral da Silva A. A. S. Araújo 《Journal of Thermal Analysis and Calorimetry》2010,99(3):1011-1014
The purpose of this study was to evaluate the physical–chemical properties of collagen (CL) and usnic acid/collagen-based
(UAC) films, using differential thermal analysis (DTA), thermogravimetry (TG/DTG), infrared spectroscopy (FTIR), and scanning
electron microscopy (SEM). Both films were prepared by casting process using polyethylene glycol 1500 (PEG 1500) as plasticizer.
In the spectrum of UAC, similar bands of the usnic acid are observed, indicating that the polymerization (film formation)
did not affect the stability of the drug. Distinctly, DTA curve of UAC did not show an endothermic peak at 201 °C, indicative
that the drug was incorporated into the polymeric system. These results were corroborated by the scanning electron microscopy
(SEM). The TG/DTG curves of UAC presented a different thermal decomposition profile compared to the individual compounds and
CL. These findings suggest the occurrence of molecular dispersion or solubilization of the drug in the collagen film. 相似文献
50.
J. Canotilho R. A. E. Castro M. T. S. Rosado S. C. C. Nunes M. S. C. Cruz J. S. Redinha 《Journal of Thermal Analysis and Calorimetry》2010,99(2):423-429
The growth of atenolol, pindolol and betaxolol hydrochloride from melt was investigated by differential scanning calorimetry
(DSC) and polarized light thermal microscopy (PLTM). Phase transitions occurring on cooling and subsequent reheating runs
performed between −160 °C and a temperature above the respective melting points were studied by DSC. The thermal cycles were
also followed by PLTM. Details about the dynamic of the crystallization front taken from microscopic observations are given.
An explanation of the results on the basis of molecular supramolecular recognition is advanced. 相似文献