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221.
Hahn Susie Miller William M. Lichtenthaler Rudiger N. Prausnitz John M. 《Journal of solution chemistry》1985,14(2):129-137
A linear correlation was determined for oxygen- and nitrogen-containing solvents between the proton NMR shift of chloroform, dilute in a solvent, and the donor number (DN) of that solvent. Results are given for water and for 13 organic solvents. The best straight line is given by DN=7.4–16.6 (CHCl
3
) where (CHCl
3
) is the shift of pure chloroform relative to that of chloroform in dilute solution. Donor numbers of several solvents were estimated from the correlation. 相似文献
222.
Using the values of standard molar enthalpy of reaction for dimethylethyleneurea (dmeu),dimethylformamide (dmf), dimethylacetamide
(dma), tetramethylurea (tmu),hexamethylphosphoramide (hmpa) and pyridine (py) with the acids BF3, SbCl5, ZnCl2 and AsCl3, it is shown that, in terms of acid-base behaviour, ZnCl2 is closer to BF3, which differs from SbCl5. Furthermore, the equation −Δr
H
m(ZnCl2) = − [1.26⋅Δr
H
m(BF3)]−56.99 correlates with the standard molar enthalpy of reaction for the same set of molecules with ZnCl2 and BF3. A similar equation was obtained to estimate the enthalpy of reaction with AsCl3: −Δr
H
m(AsCl3) = − [4.12⋅Δr
H
m(BF3)]− 417.82. It is also shown that, for hmpa and tmu, sterical hindrance is a prominent factor that influences the coordination
chemistry of the acidic centres, whose deviation from the linearity can be considered as a measure for the steric contribution
to Δr
H
m.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
223.
Berruyer-Penaud F Bouchoux G Payen O Sablier M 《Journal of mass spectrometry : JMS》2004,39(6):613-620
The protonation energetics of lactic acid (LA) were experimentally determined by the kinetic method including the entropy effect. The values (proton affinity, PA(LA) = 817.4 +/- 4.3 kJ mol(-1); protonation entropy, DeltaS degrees (p)(LA) = -2 +/- 5 J K(-1) mol(-1); gas-phase basicity, GB(LA) = 784.5 +/- 4.5 kJ mol(-1)) agree satisfactorily with computed G2(MP2) expectations (PA(LA) = 811.8 kJ mol(-1); DeltaS degrees (p)(LA) = -7.1 J K(-1) mol(-1); GB(LA) = 777.4 kJ mol(-1)). The fragmentation behaviour of protonated lactic acid (LAH(+)) is dominated by carbon monoxide loss followed by elimination of a water molecule. Direct dehydration of LAH(+) is only a high-energy process hardly competitive with the CO loss. A complete mechanistic scheme, based on MP2/6-31G* calculations, is proposed; it involves isomerization of the various protonated forms of LA and the passage through the ion-neutral complex between the 2-hydroxypropyl acylium cation and a water molecule. 相似文献
224.
Acidity/basicity of mixed oxides of ZrO2−Y2O3 activated at various temperatures were determined by a titration method using Hammett indicators. The activity of these oxides
towards liquid phase oxidation of cyclohexanol are also reported. The activity data parallel the basicity of these oxides. 相似文献
225.
Li‐Kai Yan Zhong‐Min Su Ke Tan Min Zhang Lun‐Yu Qu Rong‐Shun Wang 《International journal of quantum chemistry》2005,105(1):37-42
The electronic properties of the anions mentioned in the title polyanions were calculated by means of Density Functional Theory (DFT). The redox properties and the basicity of the external oxygen sites of those polyanions were analyzed. The results show that the redox properties of Strandberg anions depend on the nature of heteroatom X. The organic group bonded to the heteroatom modifies the redox property of the cluster. The oxygen basicities of the polyanions were analyzed by virtue of molecular electrostatic potential (MEP). The MEP distribution suggests that the most basic centers are triple‐bridging oxygen atoms, one of which is shared with two metal atoms and one heteroatom X in [P2Mo5O23]6? and [As2Mo5O23]6?. In [(RP)2Mo5O21]4?, the triple‐bridging oxygen atoms and the double‐bridging oxygen atoms bonded to two Mo atoms identified as the most basic centers. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
226.
氧化铝负载钌基氨合成催化剂的制备条件及载体改性 总被引:16,自引:0,他引:16
利用等体积浸渍法制备了氧化铝负载钌基氨合成催化剂.考察了\r\n氢氧化铝的焙烧温度,催化剂的还原温度,助剂K、Ba和Sm的添加,以\r\n及用MgO和BaO改性氧化铝载体等对催化剂活性的影响.通过XRD,N2物\r\n理吸附和CO2化学吸附等方法表征了载体的物相结构、比表面积和表面\r\n碱性.研究结果表明,氧化铝表面碱性随着氢氧化铝焙烧温度的升高而\r\n增大是催化剂活性升高的主要原因,载体比表面积的降低对催化剂活性\r\n的影响相对较小.助剂K、Ba和Sm的加入显著地提高了催化剂的活性,\r\n同时助剂Ba和Sm还减弱了强吸附氢对氮吸附的抑制作用,明显提高了催\r\n化剂的高压活性.用MgO改性氧化铝载体降低了其比表面积,但是显著\r\n地提高了载体的表面碱性和催化剂的活性.BaO改性的氧化铝载体的比\r\n表面积、表面碱性及其负载的钌基催化剂的活性随着BaO含量的增加先\r\n升高后降低,当BaO摩尔含量为7.7%时,催化剂活性最高. 相似文献
227.
利用CO2-TPD技术考察了Ba-La2O3系催化剂的表面碱性,实验发现,催化剂表面仅有单一的强碱位或中碱位时,其催化性能均较差。只有表面的中碱位与强碱位以适当量共同存在的样品(6%Ba-La2O3),才能获得好的催化活性和C2选择性。此碱性特征可能有利于表面活性位的产生。同时利用XRD和XPS等技术分别对体相结构和表面氧物种进行了研究。结果表明,Ba-La2O3系催化剂表面存在O2^2-离子,但 相似文献
228.
229.
L. S. Kuznetsova A. R. Mustafina A. S. Michailov V. E. Kataev V. S. Reznik 《Journal of solution chemistry》2002,31(11):895-904
The acid–base behavior of the novel macrocycle, containing thiopyrimidine and uracil moieties 32-trimethyl-23,36-dioxo-15,19-dithio-2,9,13,20,24,31,34,35-octaazatatracyclo [28,3,110,14,120,24]hexatriacontaheptaen-1(34),10(35),11,13,21,30,32 (1) and the acyclic 1,6-bis[4-(N,N-dimethylamino)-6-methylpyrimidinile-2-thio]hexane (2) were studied by potentiometric, UV-Vis, 1H, NMR spectroscopic methods in water–dimethyl sulfoxide (methanol, 1,4-dioxane) solutions and at the interface between water and chloroform phases. The data obtained indicate, that thiopyrimidine nitrogens are the protonation sites of both 1 and 2. The protonation of 2 occurs in one step, while 1 is protonated stepwise in the pH range 9–2.5. The NMR data indicate that the intramolecular interaction between protonated pyrimidine and uracil moieties is the main reason for the stabilization of protonated forms of 1. The protonation constants of 1 were found to be different in various water–organic mixtures, which is in accord with the different 1H NMR spectra of 1 in various solvents. The protonation of 1 at the water–organic phase boundary is effected by the extraction of [1·2H]2+ into the aqueous phase, which can be regarded as a way of obtaining its water -soluble form. 相似文献
230.
有机物的气相碱性是指有机物分子在气相条件下与质子的亲合能力,通常用化合物的气相质子亲合能(PA)来表示,由于受到分子中不同取代基甚至不同空间构象的影响往往不同,因而很难测定。长期以来人们都是在溶液中测定有机物的碱性,高压质谱(HPMS)和离子回旋共振(ICR)等高新技术的发展和应用,使得人们在气相条件下测定分子本身固有的相对碱性成为可能。气相碱性比溶液中的碱性更能直接反映出化合物的分子结构特征,有利于有机化合物结构-性能/活性(QSPR/QSAR)关系的研究。 相似文献