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排序方式: 共有308条查询结果,搜索用时 78 毫秒
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B. Hannoyer A. A. M. Prince M. Jean R. S. Liu G. X. Wang 《Hyperfine Interactions》2006,167(1-3):767-772
Crystalline LiFePO4 has been synthesized using solid-state, spray pyrolysis, and wet chemical methods. The crystal parameters were obtained from Rietveld’s refinement methods of the X-ray diffraction patterns. A detailed investigation of the Fe valency carried out using Mössbauer spectroscopy at room temperature indicates that Fe is predominantly present in its bivalent state. 相似文献
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X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), rotating disc electrode-electrochemical impedance spectroscopy (RDE-EIS) and synchrotron radiation-grazing incidence X-ray diffraction (SR-GIXRD) have been used to study the response mechanism of the mercury(II) chalcogenide ion-selective electrode (ISE) in saline media. XPS and SIMS have shown that the chalcogenide surface is poisoned by silver chloride, or a mixture of silver halides, on continuous exposure to synthetic and real seawater. Significantly, the in-situ SR-GIXRD study demonstrated that electrode fouling in synthetic seawater is linked to the formation of poorly crystalline or amorphous silver chloride, and that the low level of free mercury(II) in a calibration buffer (i.e., 10(-14) M) is able to undergo metathesis with silver(II) sulfide in the membrane generating mercury(II) sulfide. Significantly, the results of this detailed surface study have shown that silver chloride fouling of the electrode is ameliorated in real seawater comprising natural organic ligands, and this has been attributed to the peptization of silver chloride by the surfactant-like nature of seawater ligands at pH 8. RDE-EIS aging studies have revealed that the chalcogenide membrane experiences a sluggish charge transfer reaction in seawater, and contrary to a previous report for a static electrode, the seawater matrix does not passivate the RDE. The results of this XPS, SIMS, RDE-EIS and SR-GIXRD study have elucidated the response mechanism of the mercury(II) ISE in saline media. 相似文献
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Emile Cherbuliez H. Moll F. Hunkeler R. Prince J. Rabinowitz 《Helvetica chimica acta》1967,50(7):2180-2187
(1) Monopotassium phosphite KH2PO3 heated at 300°C with CO[18O] exchanges one atom of oxygen after 3 hours, one to two atoms after 6 hours, and its three O atoms after 12 hours; the probable mecanism of this exchange is discussed. When the same treatment is carried out in the presence of o-phenylene diamine hydrochloride, the exchange is total (three O) after 3 hours at 300°C. Treated by this last procedure, benzenephosphonic acid C6H5PO(OH)2 undergoes equally a total exchange of its O atoms in 3 hours. 相似文献
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Abstract. Investigations on the bacterial photosynthetic reaction center have recently made several important steps forward. Progress has been made in measuring the time course of the light-driven reactions, and in understanding the thermodynamics of these processes, in determining the chemical-structural properties of the protein and its constituents, and in elucidating the functional relationship of the reaction center with the chromatophore membrane. Although the well-characterized Rhodopseudomonas sphaeroides reaction center has been the main exploratory vehicle in many of these studies, we now have an ever increasing body of information from bacteria of other species and genera. This work is providing information from which we can underline features that are common to bacterial reaction centers, but it also reveals differences which may reflect different selection pressures on the separate species.
In this report we shall describe the early photochemical events of the reaction center, summarize the comparative biology of the reaction center, and discuss some of the current physical-chemical problems pertaining to the redox components of the reaction center. 相似文献
In this report we shall describe the early photochemical events of the reaction center, summarize the comparative biology of the reaction center, and discuss some of the current physical-chemical problems pertaining to the redox components of the reaction center. 相似文献
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Determination of capsaicinoids in salsa by liquid chromatography and enzyme immunoassay 总被引:2,自引:0,他引:2
Perkins B Bushway R Guthrie K Fan T Stewart B Prince A Williams M 《Journal of AOAC International》2002,85(1):82-85
Two simple and rapid methods were developed to monitor pungency of salsa in production. Capsaicin (C) and dihydrocapsaicin (DHC) were quantitated in 17 commercially available tomato-based salsas by enzyme immunoassay (EIA) and liquid chromatography (LC) with fluorescent detection. Samples were extracted with methanol and the extracts were subjected to solid-phase extraction (SPE) using polystyrene-divinylbenzene columns. Analysis of SPE eluates showed good correlation (r2 = 0.953) between LC and EIA, with a slightly high bias for EIA. Salsa fortified with C and DHC from 0.118 to 103.2 microg/g resulted in recoveries of 90-112% (C) and 76-97% (DHC). Limits of detection by LC were 0.1 microg/g for each capsaicinoid and 0.1 microg/g by EIA for total capsaicinoids. The LC on-column response was linear from 0.2 to 100 ng for both C and DHC, whereas the working range for EIA was 0.1-2.0 ppm. Pungency varied between different salsa brands labeled mild, medium, and hot. 相似文献