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91.
Electrochemical impedance spectroscopy is used to characterize thin p-doped polypyrrole (PPy) films in propylene carbonate (PC) solutions and poly(trifluorophenyl)thiophene (PTFPT), in solutions based on sulfolane (SF). It appears that the latter film is much less swelled compared to the former one. One consequence of this difference is that the PTFPT film shows a much higher bulk resistance compared to that for the PPy film. Another important consequence is that the swelling of the PTFPT film is essentially physically non-homogeneous. Two parallel, uncoupled paths, with different chemical diffusion coefficients, model the experimental results adequately. In order to quantify the impedance spectra for both polymer films, we use a model proposed by Rubinstein et al. explaining the difference in the diffusion coefficients of Ru(bpy)3+/2+
3 within a thin Nafion film. The model can also predict the impedance spectra for composite powdery electrodes containing different particle sizes, such as composite cathodes and graphite anodes used in lithium batteries. 相似文献
92.
The stability constants and the partial molal volume and isentropic partial molal compressibility changes of complex formation between cations and crown ethers in water at 25°C are presented. The cations involved are Na+, K+, Rb+, Cs+, Ca2+, and Ba2+, and the crown ethers are 12-crown-4, 15-crown-5, and 18-crown-6. Values of V of complex formation have been discussed in terms of two simple models, one based on the scaled particle theory, and the others on the Drude-Nernst continuum model. The results indicate that the charge of the potassium cation in 18-crown-6 is especially well screened from the water. On this basis hydration numbers of complexed cations have been calculated. This shows that the size of the cation compared to the crown ether hole is important for the contacts between complexed cations and water. 相似文献
93.
Bromophenol blue indicator was used in UV-visible spectrophotometric measurements to study ion association constants of alkali metal fluorides. The equilibrium constants for the ion pair formation of the alkali metal fluorides were determined as a function of ionic strength at one atmosphere pressure and 25°C. The effect of pressure on these association constants was measured at a constant total ionic strength of 1.0 mol-kg–1 over a pressure range of 1 to 2000 atmospheres at 25°C. The pressure dependences of the stoichiometric association constants of the alkali metal fluorides are given by: lnK
LiF
*
=0.77–2.47×10–4P–2.12×10–8P2; lnK
NaF
*
=0.53–1.08×10–4P–1.66×10–8P2; lnK
KF
*
=0.24–4.41×10–5P–7.15×10–8P2; lnK
RbF
*
=–0.17–8.65×10–5P–4.51×10–8P2; and lnK
CsF
*
= –0.37–1.14×10–4P–6.82×10–8P2, where P is the pressure in atmospheres. The stoichiometric molar volume and compressibility changes for ion pair formation of the alkali metal fluorides were evaluated from the pressure dependence of K
MF
*
data. The thermodynamic association constants were also calculated making use of activity coefficient data from the Pitzer equations. The partial molal volume and compressibility changes for ion pair formation of each alkali metal fluoride are reported. 相似文献
94.
Concetta De Stefano Claudia Foti Antonio Gianguzza Frank J. Millero Silvio Sammartano 《Journal of solution chemistry》1999,28(7):959-972
The hydrolysis of trimethyltin(IV) has been studied by potentiometry (H+ -glass electrode) and calorimetry in various salt media (NaNO3, NaCl, KCl, Na2SO4, and NaNO3—NaCl mixtures). The effect of ionic strength on the hydrolysis constants is accounted for by a simple Debye–Hückel type equation and by Pitzer equations. The results allow us to obtain H for hydrolysis and the temperature dependence of the Pitzer parameters. The resulting coefficients can be used to examine the speciation of (CH3)3Sn+ in multicomponent electrolyte solutions, such as natural waters, over a wide range of temperature and ionic strength. 相似文献
95.
Gasanov R. G. Tumanskii B. L. Tsikalova M. V. Nuretdinov I. A. Gubskaya V. P. Zverev V. V. Fazleeva G. M. 《Russian Chemical Bulletin》2003,52(12):2675-2678
The addition of the ·But (R1) and ·P(O)(OPri)2 (R2) radicals to pyrrolidino[60]fullerenes C60CH2NMeCHX (X = C6H4N(CH2CH2Cl)2, 2,6-(But)2C6H2OH, PhC6H4, and indol-3-yl) was studied by ESR spectroscopy. The rate constants of R1 radical addition to these compounds and dimerization of spin-adducts of the R1 radicals with pyrrolidino[60]fullerenes were determined. Pyrrolidino[60]fullerenes manifest considerably higher reactivity toward the R1 radicals than fullerene C60 and methanofullerenes C60CX1X2 (X1 = X2 = CO2Et; X1 = CO2Me, X2 = OP(OMe)2, X1 = X2 = OP(OEt)2). 相似文献
96.
97.
B A Finnin M A A O'Neill S Gaisford A E Beezer J Hadgraft P Sears 《Journal of Thermal Analysis and Calorimetry》2006,83(2):331-334
Isothermal
calorimetry is becoming indispensable as a tool for the study of a wide variety
of systems. As with all scientific instruments it is essential that robust
calibration routines be developed in order to validate the data obtained.
Chemical test reactions offer many advantages over (the traditionally used)
joule effect heating methods, not least because they have the potential to
validate instrument performance (i.e. they can be used to assess all aspects
of calorimeter operation). In this work the results of a validation exercise,
conducted by Thermal Hazard Technology as part of an installation routine,
using the base catalysed hydrolysis of methyl paraben are discussed. In the
case described, a systematic misreporting of the reported temperature of a
calorimeter was identified, caused by an upgrade to the calorimeter's
firmware, a discrepancy which may not have been noted using traditional electrical
calibration methods and one which highlights the importance of both manufacturers
and end-users adopting chemical test reactions into their test and validation
routines. 相似文献
98.
Aacute;gnes Buvári-Barcza Antal Csámpai Lajos Barcza 《Journal of inclusion phenomena and macrocyclic chemistry》2002,42(3-4):209-212
Two guests reacting with cyclodextrins (CDs) may form ternary complexes, in addition to the common competition of 1:1 complexes. One of the guests can really be included into the cavity of the CD, while the second guest molecule is either inserted close to the first one or attached to the outer surface of the supramolecule by H-bonding. There is a further possibility when the included guest bears a substituent outside the cavity and the second guest can interact with it. The properties of the ternary species formed are highly influenced by the solely (or primarily) included guest. The changes are attributed to the altered properties of the hydrophilic domain of the CD. The phenomena can be proved by NMR data obtained for some binary systems of -CD inclusion complexes and acetic acid and by the stability constants of the ternary complexes formed. Allosteric effects as well as coenzyme/apoenzyme/substrate interactions could be well modelled by these types of CD complexes. 相似文献
99.
Jiří Horský Josef Pitha 《Journal of inclusion phenomena and macrocyclic chemistry》1994,18(3):291-300
The stability constants were measured of inclusion complexes formed from aromatic amino acids and their oligopeptides with - and-cyclodextrin, hydroxypropyl-cyclodextrin, and partially methylated-cyclodextrin. The method of competitive spectrophotometry withp-nitrophenol as a competing reagent was used, and measurements were made at pH 7.4-Cyclodextrin formed complexes of higher stability than the other hosts. The stability of complexes of oligopeptides containing L-phenylalanine was invariably higher than that of L-phenylalanine itself. A model for interaction of proteins with cyclodextrins is proposed, in which the most stable complexes are formed when the native functional form of proteins is unfolded and the nonpolar residues that are buried inside the structure are exposed to water. The complexation of the unfolded structure favors its formation; thus thermal denaturation of proteins is easier in the presence of cyclodextrins. On the other hand, this complexation prevents the intermolecular association of unfolded structures by noncovalent hydrophobic bonding between the exposed nonpolar residues; furthermore, the unfolded complexed forms may revert to the native functional form. This prevention of intermolecular association may explain the stabilizing effect of cyclodextrins on solutions of proteins: a return to the native form is achieved more easily from the complexed, unfolded form than from the unfolded, aggregated forms.Dedicated to Professor József Szejtli. 相似文献
100.
We have studied the basicity of 2-phenyl-5-R-1,3,4-oxadiazoles (R = H, Me, CH2Ph, t-Bu, CH2Cl, CCl3, CF3) in aqueous sulfuric acid solutions. These compounds are weak organic bases (pKBH
+ is −1.8 to −5.2). The values of pKBH
+ determined on the H0 and X acidity function scales agree well with each other. The substituent at the 5 position has a substantial effect on the
basicity of the 1,3,4-oxadiazole ring.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 748–756, May, 2006. 相似文献