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491.
Summary The rates of iodination of Salicylate in the bis-(ethylenediamine)(salicylato)cobalt(lII) complex and free Salicylate have been measured in acetate buffer at 40° and I = 0.1 M. The reaction is catalysed by acetate and water. The reactivity order for both acetate- and water-catalysed paths is: [HSal]– < [(en)2CoSal]+ < [Sal]2–, where [HSaI]– and [Sal]2– stand for the phenol and phenate forms of Salicylate respectively. Chelation of [Sal]2– to cobalt(III) results in a rate reduction of its iodination by 107. 相似文献
492.
493.
J. G. Dash 《固体与材料科学评论》1976,6(2):209-222
Recent developments in the field of physisorption have brought about qualitative changes in this relatively hoary branch of surface science. Rapid advances have been under way for the last 10 years or so, comparable to the time scale of the revolution in the rest of surface science, and as in the case of the overall field, they involve improvements in experimental technique, materials technology, and theoretical understanding. The progress in physisorption carries wide-ranging implications for substrate characterization, chemisorption, and catalysis, and beyond surface science for certain aspects of general statistical mechanics, the physics of condensed matter, and superfluidity. This review is a survey of some of these developments. The focus here will be on results; details of experimental and theoretical technique are omitted for brevity's sake. 相似文献
494.
Dash K Thangavel S Rao SV Chandrasekaran K Chaurasia SC Arunachalam J 《Journal of chromatography. A》2004,1036(2):223-227
Trace levels of phosphorus in purified quartz are determined by ion chromatography. In situ reagent purification, matrix digestion and oxidation of phosphorus to orthophosphate ion are carried out simultaneously in a vapour phase digestion (VPD) assembly using a mixture of HF, HNO3 and H2O2. A drastic reduction (475 times) in phosphate blank from reagents (HF/H2O2) was achieved in the VPD through in situ purification of the reagent. The residues remaining after volatilisation (solvent/matrix), mostly consisting of insoluble phosphate/fluoride salts of divalent and trivalent cations, were solubilised by ion-exchange dissolution. Phosphate was analysed on the IonPac AS17 column with suppressed conductivity detection. The results of the ion chromatography (IC) method were compared with a spectrophotometric method. Accuracy was evaluated by analysing a certified reference material (silicon, NIST 57a). The method detection limit was 0.05 microg g(-1). 相似文献
495.
Thangavel S Dash K Dhavile SM Chaurasia SC Mukherjee T 《Journal of chromatography. A》2005,1074(1-2):229-233
A simple dual vessel in situ analyte distillation (IAD) system has been developed for suppressed ion chromatographic determination of chloride and fluoride ions in complex matrices. In IAD system, water vapours generated from the outer vessel reacts with sulfuric acid generating heat, thus favouring the quantitative distillation of chloride and fluoride within 30 min on water bath temperature (approximately 80 degrees C). The distilled analytes, as their respective acids in water, were directly injected into an ion-chromatograph. This newly developed method has been applied for analysis of trace impurities in H2SO4, H3PO4 and H3BO3. The detection limits for chloride is 8, 80 and 70ppb (w/w) for H2SO4, H3PO4 and H3BO3, respectively. For fluoride the detection limits are 6 and 60 ppb (w/w) for H2SO4 and H3PO4, respectively. The recovery of spikes for both the analytes ranged between 87 and 100%. 相似文献
496.
K. Dash 《Analytica chimica acta》2005,546(2):229-235
A method has been developed for the determination of Al, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Sb, Sn and Zn at trace levels in high purity di-boron trioxide using ETAAS. The boron trioxide matrix was eliminated as trimethyl borate ester in a multiplex vapor phase matrix extraction (MVPME) device using a mixture of glycerol and methanol. In this MVPME device, in situ reagent purification, sample digestion and simultaneous matrix elimination were achieved by a single step in closed condition, which in combined effect reduce the process blanks. The matrix extraction procedure allows determination of trace elemental impurities by electrothermal atomic absorption spectrometry (ETAAS) with fast furnace analysis (without an ashing step and modifier) and calibration against aqueous standards. The performance and accuracy of the vapor phase matrix elimination technique are compared to those of suprapur grade hydrofluoric acid solution in two ways; (i) matrix separation as BF3 over hot plate and (ii) in situ matrix elimination inside graphite furnaces. The method detection limits calculated from blank samples are in the range of 0.5 (Ni) and 2.9 (Al) ng g−1. Thus the MVPME-based sample preparation approach is well suited for the trace analysis of high purity di-boron trioxide used in microelectronics applications. 相似文献
497.
U.N. Dash D. Satyanarayan K.N. Panda S.C. Rath S.K. Mohanty 《Thermochimica Acta》1979,30(1-2):217-223
The solubility studies on silver salicylate at different temperatures were made to derive (a) the standard electrode potential of the silver—silver salicylate electrode, (b) the mean activity coefficient of silver salicylate, (c) the dissociation constant of salicylic acid, and (d) the standard thermodynamic quantities, ΔG0t, ΔH0t, ΔS0t, and δC0pt, for the transfer of silver salicylate from the standard state in water to the standard state in water + 10, + 20, and + 40 mass percent of dioxane. The results are discussed in terms of the preferential solvation of the ions. 相似文献
498.
The reversible complexation of the pentaammine(pyridine-2-carboxylato)cobalt(III) ion [N5Co{O2C-(2)-C5H4 N}]2+ [N5=5HN3 and
tetraethylenepentaammine (tetren)] with NiIIL(OH2)6-n [L=H2O (N5=tetren); L=bipy, ida2- (iminodiacetate) and nta3- (nitrilotriacetate),
N5=5NH3 and tetren] has been investigated by the stopped-flow technique at 20-40 degC, and I= 0.3mol dm-3. At 25degC, the
rate constants, kf(dm3 mol-1s-1), DeltaH(kJmol-1) and DeltaS(JK-1mol-1) for the formation of the ternary complexes [(tetren)-CoIII{O2C-(2)-C5H4N}
NiIIL(OH2)6-n] are as follows: L=H2O, 530+9, 53+2, -15+7, respectively; L=bipy, 640+30, 37+3, -65+9; L=ida2-, 3900+100, 47+3,
-18+11; L=nta3-, 10200+400, 49+1, −2+2. Nickel(II), in the ternary complexes, is chelated by the free pyridyl-N and the carboxylato
moiety of the pyridine-2-carboxylate bound to the cobalt centre. The formation rate constant (kf) and the associated activation
parameters are relatively insensitive to the N5 moieties for a given ligand L; kf increased in the order: Ni(OH2)62+Ni(bipy)(OH2)42+
Ni(ida)(OH2)3 (nta)(OH2)2-. Data analysis indicated that the mechanism shifted from the dissociative interchange (Id) to the
chelation-controlled one, with the decrease of the available sites for coordination in NiIIL(OH2)6−n. The rate constants (kr)
for the dissociation of [N5CoIII{O2C-(2)-C5 H4N}NiIIL(OH2) 6-(n+2)] to the parent reactants indicated steric acceleration
[krL(5NH3) <krL(tetren)] and followed the trend: krNi(nta)->kr Ni(ida) >krNi(bipy)2+ for both pentaammine substrates. The
chelate ring opening rate constants for the ternary complexes were estimated, from which it was apparent that the tetren envelope
of cobalt(III) exerted relatively greater steric pressure as compared with 5NH3 in favouring opening up of the chelate ring.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
499.
The silver—silver oxalate electrode has been employed by many workers1–3 in aqueous media as the second order reference electrode, but no work seems to have been done so far on the study of the behaviour of silver—silver malonate and silver—silver succinate electrodes. The present work deals with the study of these electrodes in ionic equilibria of malonate and succinate ions in aqueous media. These electrodes, in conjunction with a saturated calomel electrode, have been employed in the poten- tiometric determination of malonate and succinate ions in aqueous media. In additon, the effect of the added salts, such as, potassium nitrate and sucrose on the behaviour of these electrodes has also been examined in this media. 相似文献
500.
A number of mixed ligand complexes of the type [Co(en)2(Im)Cl]Cl2 (Im = imidazole or a substituted imidazole) have been synthesized by reaction of trans-[Co(en2Cl2]Cl with the imidazole ligands. Electrical conductivity measurements support the ionic (1:2) formulation of the compounds, the electronic spectra is in agreement with an octahedral stereochemistry, and the IR and NMR (1H and 13C) spectra strongly favour the cis configuration for the isolated complexes, [Co(en)2(Im)Cl]Cl2.Trans-[Co(en)2Cl2]Cl reacts with KNCS to form cis-[Co(en)2(NCS)2Cl, the crystal structure of which is briefly reported. This lends additional support in favour of the probable cis configuration of the above complexes. 相似文献