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731.
Manganese(II) complexes of the general composition, Mn(L)2X2 (X = Cl or 1/2 SO4,L = semicarbazones and thiosemicarbazones of acetone, ethyl methyl ketone and 2-methyl cyclohexanone) have been prepared and
characterised by elemental analysis, magnetic moments, conductance measurements, IR, electronic and ESR spectral studies.
All the complexes are six-coordinate octahedral. 相似文献
732.
Xanthopoulos C. E. Tzavellas L. C. Haristos D. A. Katsoulos G. A. 《Structural chemistry》1994,5(3):147-154
A series of substituted 3-aroyldithiocarbazates has been synthesized and studied. The corresponding acid dissociation constants have been determined potentiometrically. Semiempirical PM3 molecular orbital calculations suggest the existence of several tautomeric forms of the compounds. Geometrical parameters, proton affinities, and static reactivity indices have been examined. Structural properties and protonation sites are well described by calculations. The strong correlations between the pK
a
values and the Hammett constants as well as the N(3) calculated proton affinities indicate that the N(3) atom is the most probable protonation site. The thermodynamics of the protonation process are mainly controlled by HOMO-LUMO rather than electrostatic interactions. According to PM3 results, 3-aroyldithiocarbazic acid should be quite stable in the gas phase, while a mechanism for its decomposition in solution is proposed. 相似文献
733.
S. F. Solodovnikov S. S. Yarovoi Yu. V. Mironov A. V. Vironets V. E. Fedorov 《Journal of Structural Chemistry》2004,45(5):865-873
New cluster compounds — rhenium and potassium thiohalides K3Re6S7Br7 (I) and K4Re6S8Cl6 (II) — have been synthesized. Their crystal structures have been determined by single crystal X-ray diffraction. The compounds are monoclinic; (I): space group P21/c, a = 9.32(1) Å, b = 13.528 Å, c = 12.413 Å, β = 110.21°, Z = 2, R = 0.038; (II): space group C2/m, a = 10.614 Å, b = 17.268 Å, c = 10.448 Å, β = 110.755°, Z = 2, R = 0.042. In both structures, the potassium ions are considerably distorted. The occupancies of the potassium sites are 0.17-0.34 (I) and 0. 01-0.26 (II), correlating well with the coordination numbers (c.n. 7-10 and 2-7 for I and II, respectively). In I, adjacent positions of potassium atoms are aggregated into discrete tetrahedral and angular clusters; in II, the individual (four-and six-membered) cyclic clusters of potassium sites are present along with bent chains of vertex-and edge-sharing tetrahedral “potassium clusters.” The shortest K-K distances in these “clusters” vary from 1.31 Å to 1.54 Å (I) and from 0.66 Å to 1.65 Å (II). The “instability” of the potassium site suggests that I and II are ion conductors.Original Russian Text Copyright © 2004 by S. F. Solodovnikov, S. S. Yarovoi, Yu. V. Mironov, A. V. Virovets, and V. E. Fedorov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 909–917, September–October, 2004. 相似文献
734.
Xueqin Wang Hao Wen Tianjing He Jian Zuo Cunyi Xu Fan-Chen Liu 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1997,53(14):2495-2504
Surface enhancement mechanism of Raman scattering from molecules adsorbed on silver oxide colloids is reported. Absorption spectra and Raman spectra of the cyanine dye D266 and pyridine molecules adsorbed on Ag2O colloids, and the influences of S2O32− and OH− on the SERS are studied respectively. The results indicate that ‘chemical' enhancement is dominant in Ag2O colloidal solution. Surface complexes of adsorbed molecules and small silver ion clusters Agn+ as the SERS active sites make an important contribution to surface enhanced Raman scattering (SERS). At these active sites, charge transfer between the adsorbed molecules and the small silver ion clusters is the main enhancement origin. The enhancement factor of D266 adsorbed on Ag2O colloids is theoretically estimated with the excited-state charge transfer model, which is roughly in accordance with the experiments. 相似文献
735.
A general approach to construct hybrid orbitals based on the projection of both the subspace of atomic orbitals and the subspace of hybrid orbitals is presented. It is shown that the projection must be associated with a chain of groups to ensure the independence of the method with respect to the selected coordinate system. The eigenfunction method to obtain symmetry projected functions turns out to be the natural projection technique to establish the present approach. The proposed method allows construction of hybrid orbitals in a systematic and general way, even in the hypothetical case where irreducible representations are contained more than once in the reduction of the space of hybrid orbitals. To illustrate our approach, a hybridization d2sp3 for octahedral molecules is discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
736.
A series of complexes of Co(II) and Ni(II) with 2-(R)-3-(X)-substituted quinazoline-(3H)-4-ones, where R = methyl/phenyl and
X = furalamino, uramino and thiouramino have been synthesised and characterised by analytical, conductivity, thermal and magnetic,
infrared and electronic spectral data. Based on analytical and conductivity studies the stoichiometries of the complexes have
been established. Conductivity data also show that all these complexes are non-electrolytes. Infrared spectral data indicate
that all the ligands manifest neutral bidentate with both the metal ions. Geometries for the complexes have been proposed
based on electronic spectral data. Various electronic spectral parameters have been calculated for all the complexes and relevant
conclusions have been drawn with respect to the nature of bonds present in them. 相似文献
737.
Two types of Co(III) tetraphenylporphyrins, Co(III)TPPX (I) and Co(III)(N)TPPX (II), where X = C1− or NO−2 and N = C5H5N or C6H5CH2C5H4N, are used as ionophores to prepare nitrite responsive polymeric membrane electrodes. The influence of the initial axial ligand (X− and N) on the operative ionophore mechanism of these metalloporphyrins within the solvent polymeric membranes is examined. Results from potentiometric and electrodialysis experiments suggest that in the presence of nitrite in the test sample and internal solution, both types of Co (III) porphyrins studied (I and II) act as neutral carriers and that the addition of lipophilic cationic sites (e.g., tridodecylmethylammonium ions (TDMA+)) to the organic membrane is essential to improve the selectivity and long term stability of sensors prepared with these species. Membranes formulated with (I) or (II) in the nitrite form along with TDMACl in plasticized PVC films exhibit the following selectivity sequence: SCN− > NO−2 ˜ C1O−4 > Sal− > NO−3 > Br− > C1−. Membrane electrodes with added lipophilic cationic sites are shown to exhibit rapid, fully reversible and Nernstian response towards nitrite ions in the concentration range of 10−1–10−5 M, with good long term stability. 相似文献
738.
Artem A. Barabanov Gennady D. Bukatov Vladimir A. Zakharov 《Journal of polymer science. Part A, Polymer chemistry》2008,46(19):6621-6629
The inhibition of ethylene polymerization with radioactive carbon monoxide (14CO) was used to obtain data on the number of active sites (CP) and propagation rate constant (kP) at ethylene polymerization in the temperature range of 35–70 °C over supported catalysts LFeCl2/Al2O3, LFeCl2/SiO2, and LFeCl2/MgCl2 (L: 2,6‐(2,6‐(Me)2C6H3N = CMe)2C5H3N) with activator Al(i‐Bu)3. The values of effective activation energy (Eeff), activation energy of propagation reaction (EP), and temperature coefficients of variation of the number of active sites (ECp = Eeff ? EP) were determined. The activation energies of propagation reaction for catalysts LFeCl2/Al2O3, LFeCl2/SiO2, and LFeCl2/MgCl2 were found to be quite similar (5.2–5.7 kcal/mol). The number of active sites diminished considerably as the polymerization temperature decreased, the ECp value being 5.2–6.2 kcal/mol for these catalysts at polymerization in the presence of hydrogen. The reactions of reversible transformations of active centers to the surface hydride species at polymerization in the presence and absence of hydrogen are proposed as the derivation of ECp. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6621–6629, 2008 相似文献
739.
Jing Guan Gang Yang Danhong Zhou Weiping Zhang Xianchun Liu Xiuwen Han Xinhe Bao 《Journal of molecular catalysis. A, Chemical》2009,300(1-2):41-47
Density Functional Theory (DFT) calculations were performed to optimize the Mo active sites in HBeta zeolite catalysts as well as to locate the reaction pathways to form the Mo-methylidene species. Two different Mo active sites, i.e., the oxidized MoVIO2 and its reduced form MoVO(OH), were developed and incorporated into HBeta zeolites by replacing a pair of Brønsted acidic sites. The Mo-methylidene species were found to be produced through two elementary reaction steps, and the Mo-oxametallacyclobutanes were identified as the intermediates. The activation barriers of the decompositions of the oxametallacyclobutane intermediates (Step 2) were estimated to be higher than those of the ethene addition on the Mo active sites (Step 1). The oxidation states of the Mo centers exerted marked influences on the stabilities of the intermediates as well as on the activation barriers and reaction heats of Steps 1 and 2, which were elucidated by the electronic properties of the Ob-ligands directly bonded to the Mo centers. Both free energy barriers and reaction heats have indicated that the whole processes of generating the Mo-methylidene species were preferred over the Mo(VI) rather than Mo(V) active site. Accordingly, the Mo(VI) active site was more efficient in catalyzing the formation of Mo-methylidene species in the heterogeneous Mo/HBeta catalytic systems. 相似文献
740.
A. Lassoued J. Deson C. Lalo P. Batamack A. Gédéon J. Fraissard 《Journal of fluorescence》2000,10(3):261-261
The interaction of quinoline with the surface of Nafion-H and Nafion-H (13 wt%)/silica gel composites, silica gel itself, HY zeolite, dealuminated or not, and two types of alumina is studied by laser-induced fluorescence. Strong Brønsted acid sites interact with quinoline to form the quinolinum, that ion being revealed by a band peaking at 390 nm. When Lewis acid sites are present, a complex formed between these sites and quinoline is observed. A dimeric species and the diffusion of the adsorbates on the surface of the Nafion-H polymer are discussed. 相似文献