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161.
《Mendeleev Communications》2021,31(5):696-697
R-Carvone on heating with Pb(OAc)4 in benzene gives (2RS)-2-hydroxy-2-[(1S)-4-methyl-5-oxocyclohex-3-en-1-yl)]-prop-1-yl bis(acetoxy)acetate. Alkaline hydrolysis of this compound affords the corresponding diol which under acidic catalysis is transformed into bis-hydroxy ether and 1,4-dioxane derivatives. 相似文献
162.
163.
Formation of Long,Multicenter π‐[TCNE]22− Dimers in Solution: Solvation and Stability Assessed through Molecular Dynamics Simulations
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Dr. Marçal Capdevila‐Cortada Dr. Jordi Ribas‐Arino Dr. Alain Chaumont Prof. Georges Wipff Prof. Juan J. Novoa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):17037-17046
Purely organic radical ions dimerize in solution at low temperature, forming long, multicenter bonds, despite the metastability of the isolated dimers. Here, we present the first computational study of these π‐dimers in solution, with explicit consideration of solvent molecules and finite temperature effects. By means of force‐field and ab initio molecular dynamics and free energy simulations, the structure and stability of π‐[TCNE]22? (TCNE=tetracyanoethylene) dimers in dichloromethane have been evaluated. Although the dimers dissociate at room temperature, they are stable at 175 K and their structure is similar to the one in the solid state, with a cofacial arrangement of the radicals at an interplanar separation of approximately 3.0 Å. The π‐[TCNE]22? dimers form dissociated ion pairs with the NBu4+ counterions, and their first solvation shell comprises approximately 20 CH2Cl2 molecules. Among them, the eight molecules distributed along the equatorial plane of the dimer play a key role in stabilizing the dimer through bridging C?H???N contacts. The calculated free energy of dimerization of TCNE . ? in solution at 175 K is ?5.5 kcal mol?1. These results provide the first quantitative model describing the pairing of radical ions in solution, and demonstrate the key role of solvation forces on the dimerization process. 相似文献
164.
Norihito Fukui Prof. Dr. Hideki Yorimitsu Prof. Dr. Atsuhiro Osuka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(51):18476-18483
A meso–meso‐linked diphenylamine‐fused porphyrin dimer and its methoxy‐substituted analogue were synthesized from a meso–meso‐linked porphyrin dimer by a reaction sequence involving Ir‐catalyzed β‐selective borylation, iodination, meso‐chlorination, and SNAr reactions with diarylamines followed by electron‐transfer‐mediated intramolecular double C?H/C?I coupling. While these dimers commonly display characteristic split Soret bands and small oxidation potentials, they produced different products upon oxidation with tris(4‐bromophenyl)aminium hexachloroantimonate. Namely, the diphenylamine‐fused porphyrin dimer was converted into a dicationic closed‐shell quinonoidal dimer, while the methoxy‐substituted dimer gave a meso–meso, β‐β doubly linked porphyrin dimer. 相似文献
165.
166.
We show that it is possible to derive the stationary coverage of an adsorption–desorption process of dimers with diffusional relaxation with a very simple ansatz for the stationary distribution of the process supplemented by a hypothesis of global balance. Our approach is compared to the exact result and we seek to understand its validity within an instance of the model. 相似文献
167.
I. V. Avilov É. I. Zen'kevich I. V. Filatov A. M. Shul'ga 《Journal of Applied Spectroscopy》2003,70(2):257-264
Quantum-chemical investigation of the electronic structure and properties of the excited states of porphyrin dimers, in which monomeric subunits are linked by the phenyl spacer, is performed by semiempirical methods. The molecular orbitals of the monomeric subunits are shown to interact with each other via molecular orbitals of the phenyl ring. Comparison of the experimental absorption data and quantum-chemical calculations of electronic absorption spectra for different conformations of Zn-tetraphenylporphyrin dimer is performed and the main conformation of the dimer in a solution at 295 K, in which the planes of tetrapyrrole macrocycles are located at an angle of about 60°, is substantiated. 相似文献
168.
Gorchein A 《Biomedical chromatography : BMC》2003,17(8):526-529
Reversed-phase TLC systems using ion-pairing reagents are described for the separation without prior derivatization of the porphyrins of rat Harderian gland. Porphyrins with R(f) values greater than protoporphyrin but smaller than coproporphyrin, representing harderoporphyrin, were labile to 1 m NaOH, which converted them to protoporphyrin, inconsistent with the established literature that harderoporphyrin is a tricarboxylic acid porphyrin. It was confirmed by HPLC/electrospray ionization MS that this 'harderoporphyrin' fraction consists of the recently characterized glycoconjugate, protoporphyrin-1-O-acyl beta-xyloside, with trace amounts of protoporphyrin-1-O-acyl beta-glucoside. 相似文献
169.
The photophysical characteristics and photochemical conversions of 5,10,15,20-tetrakis-(4-N-methylpyridyl)porphyrin in a highly polar solvent, formamide, are investigated. It has been established that no photochemical reactions occur on excitation in the visible spectral region, while UV excitation ( = 347 nm) causes photoreduction of porphyrin molecules followed by the formation of protonated products. The solvent molecules serve as a reducing agent. Photoreduction occurs in both air-saturated and deoxygenated solutions, but the nature of the products formed is different: chlorin molecules are formed in the air-saturated solutions and the successive photoconversion porphyrinphlorinporphometheneporphyrinogene occurs in the deoxygenated solutions. 相似文献
170.
Alexander Čeklovský Juraj Bujdák Adriana Czímerová Nobuo Iyi 《Central European Journal of Physics》2007,5(2):236-243
Tetracationic porphyrin dyes TMPyP and ZnPyP were intercalated into hydrophobized layered silicate films of three smectites.
The smectites represented the layered silicate specimens of high (Fluorohectorite, Corning; FHT), medium (Kunipia F montmorillonite;
KF) and low layer charge (Laponite, Laporte; LAP). The molecular orientations of the dye cations were studied by means of
linearly-polarized ultraviolet-visible (UV-VIS) spectroscopy. The spectral analysis and consequent calculations of tilting
angles of the transition moments at the wavelengths of Soret band transitions were in the range of 25°-35°. The determined
angles indicated molecular orientation of the dye cations being almost parallel to the surface of the silicates. Slightly
higher values (above 35°), determined for a FHT film, indicated either a slightly tilted orientation of the dye cations or
the change of molecular comformation after the intercalation of the dye.
Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia 相似文献