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81.
Density measurements of dodecyl- (C12DBACl), tetradecyl- (C14DBACl), hexadecyldimethylbenzylammonium chloride (C16DBACl) and of decyl- (C10DBABr) and dodecyldimethylbenzylammonium bromide (C12DBABr) in aqueous solutions at T=15 °C and T=25 °C have been carried out. From these results, apparent and partial molar volumes were calculated. Positive deviations from the Debye-Hückel limiting law provide evidence for limited association at concentrations below the critical micelle concentration. The change of the apparent molar volume upon micellization was calculated. The relevant parameters have been presented in function of the alkyl chain length. Apparent molar volumes of the present compounds in the micellar phase, Vφm, and the change upon micellization, ΔVφm, have been discussed in terms of temperature and type of counterion. 相似文献
82.
Marcelle Gaune-Escard A. Bogacz L. Rycerz W. Szczepaniak 《Journal of Thermal Analysis and Calorimetry》1995,45(5):1117-1124
Present work is a part of thermodynamic research program on the MX?LnX3 system (M=alkali metal,X=Cl, Br andLn=lanthanide). Molar enthalpies of mixing in the LiBr?NdBr3, NaBr?NdBr3 and KBr?NdBr3 liquid binary systems have been determined at temperature 1063 K by direct calorimetry in the whole range of composition. Investigated systems are generally characterized by negative enthalpies of mixing with minimum atX NdBr3≈0.3–0.4. These enthalpies decrease with decrease of ionic radii of alkali metals. Molar enthalpies of solid-solid and solid-liquid phase transitions of K3NdBr6 and Cs3NdBr6 have been also determined by differential scanning calorimetry (DSC). K3NdBr6 is formed at 689 K from KBr and K2NdBr5 with enthalpy of 44.0 kJ·mol?1 whereas Cs3NdBr6 is stable at ambient temperature and undergoes phase transition in the solid state at 731 K with enthalpy of 8.8 kJ·mol?1. Enthalpies of melting have been also determined. 相似文献
83.
Enthalpies of Transfer of Tetraalkylammonium Bromides and CsBr from water to Aqueous DMF at 298.15 K
G. Rezaei Behbehani 《Journal of solution chemistry》2007,36(8):939-945
Enthalpies of transfer of tetraalkylammonium bromides and CsBr from water to aqueous DMF mixtures are reported and analyzed
in terms of a new solvation theory. It was found that a previous equation could not reproduce these data over the whole range
of solvent compositions. Using a new solvation theory to model the enthalpies of transfer shows excellent agreement between
experimental and calculated values over the entire range of solvent compositions. The analyses show that tetrapropylammonium
bromide, Pr4NBr, and tetrapentylammonium bromide, Pen4NBr, are preferentially solvated by water; in contrast tetrabutylammonium bromide, Bu4NBr, is preferentially solvated by DMF. The solvation of tetramethylammonium bromide, Me4NBr, and cesium bromide, CsBr, is random. The extent to which the tetraalkylammonium bromides disrupt solvent–solvent bonds
increases systematically in going from Me4NBr to Pen4NBr. 相似文献
84.
All-cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C3H5)]2 efficiently catalyzes the Sonogashira reaction of propiolaldehyde diethyl acetal with a variety of aryl bromides and chlorides. A minor electronic effect of the substituents of the aryl bromide was observed. Similar reaction rates were observed in the presence of activated aryl bromides such as 4-trifluoromethylbromobenzene and deactivated aryl bromides such as bromoanisole. Turnover numbers up to 95,000 can be obtained for this reaction. Even aryl chlorides and heteroarylbromides or chlorides have been successfully alkynylated with this catalyst. Moreover, a wide variety of substituents on the aryl halide such as fluoro, trifluoromethyl, acetyl, benzoyl, formyl, nitro, dimethylamino or nitrile are tolerated. 相似文献
85.
Pedro Oliver Dunstan 《Thermochimica Acta》2004,409(1):19-24
The compounds [MBr2(pyNO)n] (where M: Mn, Fe, Co, Ni, Cu or Zn; pyNO is pyridine N-oxide and n=2, 3 or 6) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and pyNo in methanol were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (ΔrHθ), the standard enthalpies of formation (ΔfHθ), the standard enthalpies of decomposition (ΔDHθ), the lattice standard enthalpies (ΔMHθ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (ΔrHθ(g)). The mean bond dissociation enthalpies of the M(II)-oxygen bonds () have been estimated. 相似文献
86.
The apparent molar volumes, Vφ of tetramethylammonium, tetraethylammonium, tetrabutylammonium, butyltriethylammonium, dibutyldiethylammonium, and tributylethylammonium
bromides have been measured at 298.15K in the concentration range from 0.01 to 0.04mol⋅kg−1. The concentration dependence of Vφ is given using the Redlich and Meyer relation. The apparent molar volume at infinite dilution, V∘_φ, and the empirical constant, BV, have been calculated. The CH2-group contribution has been obtained by the additivity rule. The results were interpreted in terms of solute–solvent interactions. 相似文献
87.
Kinetics of the reactions of propyl, propargyl and allyl bromides with anilines has been studied in methanol and dipolardmf. All reactions were found to be of second order. The values of the Bronsted slope (0–4) suggested that bond formation occurs
to a considerable extent in the transition state. Electron-donating substituents increased the rate, while electron-withdrawing
groups decreased the rate. The magnitudes of the negative values (≈1) indicate that the reaction rate depends on the availability
of electron-density on the nitrogen atom, which implies bond formation, suggesting that all the reactions are SN2 in nature, forming a loose transition state. Isokinetic temperature values calculated from the three methods for the reaction
of allyl bromide-anilines suggested that the reaction series indmf is entropy controlled while in a methanol medium hydrogen bonding is responsible for the solute-solvent interactions. 相似文献
88.
Yue-Qing Zheng Horst Borrmann Yuri Grin Karl Peters Hans Georg von Schnering 《无机化学与普通化学杂志》1999,625(12):2115-2119
The reaction of W6Br12 with AgBr in evacuated silica tubes (temperature gradient 925 K/915 K) yielded brownish black octahedra of Ag[W6Br14] ( I ) and yellowish green platelets of Ag2[W6Br14] ( II ) both in the low temperature zone. ( I ) crystallizes cubically (Pn3 (no. 201); a = 13.355 Å, Z = 4) and ( II ) monoclinically (P21/c (no. 14); a = 9.384 Å, b = 15.383 Å, c = 9.522 Å, β = 117.34°, Z = 2). Both crystal structures contain isolated cluster anions, namely [(W6Bri8)Bra6]1– and [(W6Bri8)Bra6])]2–, respectively, with the mean distances and angles: ( I ) d(W–W) = 2.648 Å, d(W–Bri) = 2.617 Å, d(W–Bra) = 2.575 Å, d(Bri…Bri) = 3.700 Å, d(Bri…Bra) = 3.692 Å, ∠W–Bri–W = 60.78°. ( II ) d(W–W) = 2.633 Å, d(W–Bri) = 2.624 Å, d(W–Bra) = 2.613 Å, d(Bri…Bri) = 3.710 Å, d(Bri…Bra) = 3.707 Å, ∠W–Bri–W = 60.23°. The Ag+ cations are trigonal antiprismatically coordinated in ( I ) with d(Ag–Br) = 2.855 Å, but distorted trigonally planar in ( II ) with d(Ag–Br) = 2.588–2.672 Å. The structural details of hitherto known compounds with [W6Br14] anions will be discussed. 相似文献
89.
Specific conductivities of a homologous series of n-alkyl trimethylammonium bromides (C8,C10,C12 and C14TABs) in the presence of poly(l-aspartate) in glycine buffer at pH 3.2 and 25 ∘C have been measured over a range of C
n
TAB concentrations. From the conductivity changes, the number of surfactant molecules absorbed onto the polymer, the Gibbs
free energies of adsorption and the equilibrium constants have been calculated. A statistical thermodynamics analysis was
used to obtain the Gibbs free energies of adsorption. The results obtained using both methods are compared and analysed.
Received: 15 December 1999 Revised form: 29 February 2000 Accepted: 3 March 2000 相似文献
90.
The extensive thermal emission spectrum attributed to the diatomic bromides of calcium, strontium and barium has been observed
in the visible region at temperatures about 2200–2400° C, using a vacuum graphite furnace. Many new bands,viz., 141 in CaBr, 53 in SrBr and 68 in BaBr, have been recorded and classified. The vibrational constants agree with those determined
by earlier workers and involved the ground state in each case. The transition C→X apears in each molecule and consists of
two equally intense systems,viz., C1→X and C2→X. The general spectroscopic features of the C→X systems of the bromides of the II A sub group of the periodic table have
been compared. They exhibit a close structural similarity and furnish a good example of homologous spectra. The system C→X
in all these molecules arises from a C2
π−X2
Σ
+ transition where the2
π state appears to be intermediate between Hund’s cases (a) and (b). 相似文献