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501.
502.
V. A. Shagun L. M. Sinegovskaya D. -S. D. Toryashinova A. G. Mal'kina L. Brandsma B. A. Trofimov 《Russian Chemical Bulletin》2000,49(10):1691-1695
The possibility of proton attack on various centers in pyrrolo[2,1-b]thiazole (1) has been evaluated. The results of semiempirical (MNDO, AM1, and PM3) andab initio (6-31G*) calculations were compared. The MNDO and 6-31G* methods give “chemically proper” and qualitatively coincident results. Analysis of the intramolecular (geometric and electronic)
reorganization of molecule1, depending on the protonation center, has been carried out. The most probable attack centers, depending on the mechanism
of electrophilic reaction, have been recognized. The energy parameters of intramolecular prototropic rearrangements in cation1 and the “blocking” factor value of methyl groups reducting the corresponding complex stability have been evaluated. It has
been established that the relative stability of the protonated forms does not change on going to pyrrolo[2,1-b]selenium- and telluriumazoles, but the range of variations is considerably narrowed in the series S>Se>Te.
Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1707–1711, October, 2000. 相似文献
503.
Hong Xue Haixiang Gao Jean'ne M. Shreeve 《Journal of polymer science. Part A, Polymer chemistry》2008,46(7):2414-2421
Energetic polymers salts from 1‐vinyl‐1,2,4‐triazole derivatives have been synthesized via free radical polymerization of 1‐vinyl‐1,2,4‐triazolium monomer salts or by protonation of poly(1‐vinyl‐1,2,4‐triazole) with inorganic or organic acids. Standard enthalpies of formation of the new monomer salts were calculated using the computationally feasible DFT(B3LYP) and MP2 methods in conjunction with an empirical approach based on densities of salts. Compared with the monomer salts, the polymer salts have good thermal properties with high densities > 1.5 g cm?3. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2414–2421, 2008 相似文献
504.
The formation constants of the species formed in the systems H+ + dimethyltin(IV) + 5′‐IMP and 5′‐UMP, H+ + 5′‐IMP and H+ + 5′‐UMP have been determined in aqueous solution in the pH range 1.5–9.5 at constant temperature (25 °C) and constant ionic strength (0.1 mol dm−3 NaClO4), using spectrophotometric and potentiometric techniques. 1H and 31P NMR investigations in aqueous solution confirmed the species formation. The precipitated complexes of IMP and UMP by Me2Sn(IV)2+ at low pH values were characterized by elemental analysis and FTIR spectroscopy methods, the bonding sites of the ligands were determined and ruled out purine and pyrimidine moieties (N‐7 and N‐1 in IMP and N‐3 in UMP, respectively) while a bidentated coordination of the phosphate group is concluded in both cases. Finally, the experiments revealed the existence of complexes with trigonal bipyramidal structures that is in agreement with similar systems resulted previously. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
505.
Saravanan Gowrisankar 《Tetrahedron letters》2008,49(43):6241-6244
We prepared various 1,5-dicarbonyl and related compounds from Baylis-Hillman adducts by using a Pd-mediated decarboxylative protonation protocol. 相似文献
506.
507.
用密度泛函(DFT)(B3LYP) 方法,在6-31G(d,p)基组水平上优化了两种质子化的硝酸甲酯异构体几何构型和能量,研究了异构体与H2O、CH3OH等分子之间的氢键的相互作用,提出了氢键超分子复合物的两种平面结构。研究发现在酯位质子化异构体的相对稳定性高于在硝氧位质子化的异构体。但当异构体在液相中与ROH类分子发生分子间相互作用后这一顺序发生了反转,说明了该体系中的分子间相互作用对异构体较强的影响。 相似文献
508.
Zhong Huang Yohei Ishida Tetsu Yonezawa 《Angewandte Chemie (International ed. in English)》2019,58(38):13411-13415
The synthesis of high‐purity and high‐yield Au25 clusters protected by the basic pyridyl ethanethiol (HSCH2CH2Py, 4‐PyET and 2‐PyET) is presented. Single‐crystal X‐ray diffraction of the [Au25(4‐PyET)18]??Na+ clusters has revealed a structure similar to that known for the phenyl ethanethiolate analogue, but with pyridyl‐N coordination to Na+, a more relaxed ligand shell, and a profoundly layered arrangement in the solid state. Because of the pendant Py moiety, the [Au25(PyET)18]? clusters are endowed with unique (de)protonation equilibria, which has been characterized in detail by UV/Vis absorption and 1H NMR spectroscopy. [Au25(PyET)18]? clusters showed an unexpectedly H+‐dependent solubility that is tunable in aqueous and organic solvents. The successful synthesis of the basic Py‐terminated thiolate‐protected Au25 clusters paves the way to realize a new family of metalloid clusters possessing basic properties. 相似文献
509.
Multiple approaches reveal the strong effects of a positive charge introduced by protonation or ionization on the conformation of o-heteroaromatic ethers and amides. The ethers and amides containing an ortho-N heteroatom are syn-preferring while those containing an ortho-O or ortho-S heteroatom are mostly anti-preferring. However, for all the monocyclic o-heteroaromatic ethers and amides, the protonated ones are all anti-preferring while the ionized ones are all syn-preferring. Interestingly, although both the protonation and ionization introduce a positive charge, they have such different effects on molecular conformation, very informative for understanding the origin of conformational preferences. Detailed analysis shows that the population of the introduced positive charge dictates the conformational preferences via electrostatic and orbital interactions. Compared to ortho-heteroatoms, meta-heteroatoms have weaker effect on conformational preference. Achieved by complete inductive method, the regularity of conformational preferences and switching provides easy ways to modulate conformers (by pH or redox), and makes this kind of ether or amide bond a conformational hinge applicable to design of functional molecules (drugs and materials) and modulation of molecular biological processes. 相似文献
510.
Effect of Surface Protonation on Device Performance and Dye Stability of Dye-sensitized TiO2 Solar Cell
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A flat thin TiO2 film was employed as the photo-electrode of a dye sensitized solar cell (DSSC), on which only a geometrical mono-layer of dye was attached. The effect of sur-face protonation by HCl chemical treatment on the performance of DSSCs was studied. The results showed that the short-circuit current Jsc increased significantly upon the HCl treatment, while the open-circuit voltage Voc decreased slightly. Compared to the untreated DSSC, the Jsc and energy conversion efficiency was increased by 31% and 25%, respectively, for the 1 mol/L HCl treated cell. TiO2 surface protonation improved electronic coupling between the chemisorbed dye and the TiO2 surface, resulting in an enhanced electron in-jection. The decreased open-circuit voltage after TiO2 surface protonation was mainly due to the TiO2 conduction band edge downshift and was partially caused by increased electron recombination with the electrolyte. In situ Raman degradation study showed that the dye stability was improved after the TiO2 surface protonation. The increased dye stability was contributed by the increased electron injection and electron back reaction with the electrolyte under the open-circuit condition. 相似文献