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101.
Wojciech P. Ozimi
ski Jan Cz. Dobrowolski Aleksander P. Mazurek 《Journal of Molecular Structure》2004,680(1-3):107-115
DFT (B3LYP/6-311++G**, B3PW91/6-311++G**) Gibbs free energy and single point CCSD(T)/6-311++G**//DFT total energy calculations were performed to investigate stability and tautomerism of C5-substituted 1,2,4-triazoles. Three different tautomers are possible for the substituted 1,2,4-triazoles: N1–H, N2–H, and N4–H. Unlike for the 1,2,3-triazoles, where the most stable is the N2–H tautomer regardless of substituent applied, for the 1,2,4-triazoles, the electron donating substituents (–OH, –F, –CN, –NH2, and –Cl) and the C5-cation stablize the N2–H tautomer, whereas the electron withdrawing substituents (–CONH2, –COOH, –CHO, –BH2, and –CFO) and the C5-anion stablize the N1–H tautomer. Except for the C5-anion and C5-cation, the N4–H form is the least stable tautomer. The relative stability of the C5-substituted 1,2,4-triazole tautomers is strongly influenced by attractive and/or repulsive intramolecular interactions between substituent and electron donor or electron acceptor centres of the triazole ring. 相似文献
102.
At the dissolution of anhydrous bismuth(III) trifluoromethanesulfonate in N,N-dimethylthioformamide (DMTF) a deep red-orange complex, lambda(max) = 457 nm, is formed. Bismuth(III) is reduced by the solvent to a low-valent oxidation state stabilized by the sulfur-coordinating solvent DMTF. The obtained complex is weakly solvated seen by a low EXAFS amplitude and a slightly higher absorption energy of the L(III) edge than of the DMTF-solvated bismuth(III) ion. The EXAFS data reveal a dimeric bismuth complex solvated by a single DMTF molecule, which sulfur atom bridges the bismuth atoms. The Bi-S bond distance is 2.543(2) A, and the Bi...Bi distance is 3.929(7) A giving a Bi-S-Bi angle of 101.2(4) degrees. The very low number of coordinated solvent molecule shows that the lone electron pairs of the reduced bismuth ions are stereochemically active. Cyclic voltammetry investigations provide evidence that at least one bismuth atom in the dimer exists in an oxidation state lower than +III, seen by two peaks at approximately -0.36 and -0.57 V in the reduction half-cycle. The absence of EPR signals excludes the presence of bismuth(II) radicals. 相似文献
103.
Dominiak PM Filarowski A Hansen PE Woźniak K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(16):4758-4766
We have analyzed deuterium isotope effects on (13)C chemical shifts in a series of o-hydroxy Schiff bases by applying factor analysis. Two orthogonal factors were obtained that explain about 80 and 10 % of the variance of the data. The numerical values of these factors can be related to 1H NMR chemical shifts of the proton involved in the intramolecular bonds delta(XH) (X = O or N). Such a relation allows one to identify clusters of compounds with different tautomeric forms of hydrogen bonding. Application of a similar approach to solution 13C NMR chemical shifts produces three important factors, which have a different structure to factors describing isotope effects. This illustrates well the different nature of chemical shifts and isotope effects. The three factors explain about 54, 15, and 13 % of variance. They can be rationalized and are strongly related to the electronic properties and location of substituents. 相似文献
104.
Tat''yana V. Baukova Lyudmila G. Kuz''mina Natal''ya A. Oleinikova Dmitrii A. Lemenovskii Aleksander L. Blumenfel''d 《Journal of organometallic chemistry》1997,530(1-2):27-38
Two organogold derivatives of diphenylmethane and diphenylethane, Ph3PAu(o-C6H4)CH2(C6H4-o)AuPPh3 (1) and Ph3PAu(o-C6H4)(CH2)2(C6H4-o)AuPPh3 (2), have been synthesized by the reaction of ClAuPPh3 with Li(o-C6H4)CH2(C6H4-o)Li and Li(o-C6H4)(CH2)2(C6H4-o)Li respectively. The interaction of 1 with dppe results in the replacement of the two PPh3 groups to give a macrocyclic compound (3) that includes an Au Au bond. Compounds 1 and 2 react with one or two equivalents of [Ph3PAu]BF4 to form new types of cationic complex [CH2(C6H4-o)2(AuPPh3)3]BF4 (4), [CH2(C6H4-o)2(AuPPh3)4](BF4)2 (5), and [(CH2)2(C6H4-o)2(AuPPh3)4](BF4)2 (6). Complexes 1–6 have been characterized by X-ray diffraction studies, FAB MS, and IR as well as by 1H and 31P NMR spectroscopy. A complicated system of Au H-C agostic interactions, involving the bridging alkyl groups (—CH2— and CH2-CH2—) of diphenylmethane and diphenylethane ligands, has been found to occur in complexes 1–3 and 6. 相似文献
105.
A. Przepiera M. Jablonski M. Wisniewski 《Journal of Thermal Analysis and Calorimetry》1993,40(3):1341-1345
The reaction of ilmenite titanium raw materials with sulphuric acid has been studied in a non-isothermal-non-adiabatic type calorimeter. The influence of different starting conditions, temperature and ilmenite particle-size distribution on the thermo-kinetics of the reaction was investigated. A kinetic model is presented for this heterogeneous system for a specified ilmenite particle-size distribution and starting temperature. On the basis of this model and experimentally determined parameters it it possible to analyse by simulation the autothermic reaction of digestion of different titanium ores with sulphuric acid. 相似文献
106.
107.
Aleksander Rutkowski 《Order》1986,3(3):257-267
The purpose of this paper is the analysis and application of the concepts of a core (a pair of chains) and cutset in the fixed point theory for posets. The main results are:
- (Theorem 3) If P is chain-complete and (*), it contains a cutset S such that every nonempty subset of S has a join or a meet in P, then P has the fixed point property (FPP),
- (Theorem 5) If P or Q is chain-complete, Q satisfies (*) and both P and Q have the FPP, then P x Q has the FPP.
- (Theorem 6) Let P or Q be chain-complete and there exist p∈P and a finite sequence f 1, f 2, ..., f n of order-preserving mappings of P into P such that $$\left( {\forall x\varepsilon P} \right)x \leqslant f_1 \left( x \right) \geqslant f_2 \left( x \right) \leqslant \cdots \geqslant f_n \left( x \right) \leqslant p$$ If P and Q have the FPP then P x Q has the FPP.
- (Theorem 7) If T is an ordered set with the FPP and {P t :t∈T} is a disjoint family of ordered sets with the FPP then its ordered sum ∪{P t :t∈T} has the FPP.
108.
Ewa Andrzejewska Aleksander uk Ryszard Krzyminiewski Jerzy Pietrzak 《Journal of polymer science. Part A, Polymer chemistry》1987,25(12):3363-3371
The influence of the irradiation and polymerization atmosphere on polymer yield was observed. It was shown that in the initiation process oxygen presence is necessary. ESR studies of UV-and γ-irradiated 1,3,5-trithiane were done. The influence of the irradiation atmosphere on generated radicals and the influence of UV-action on radicals formed by γ-irradiation was also investigated. The possible initiation mechanism of cationic polymerization of 1,3,5-trithiane is discussed. A comparison of the 1,3,5-trithiane is polymerizations initiated chemically and by UV- or γ-irradiation is also given. 相似文献
109.
High-pressure mercury lamp irradiation of chiral alkyl glyoxylates [R(?)-menthyl,R(?)- andS(+)-2-octyl,R(?)-andS(+)-2, 2-dimethyl-3-butyl] with furan led to alkyl 2,7-dioxabicyclo-[3.2.0] hept-3-ene-6-car?ylates (13a–e) exhibiting low (2.5–7.3%) optical purity. Compounds13a–e were isomerized to alkyl 3-furylglycolates (14a–e) in good yield. ConfigurationS was assigned to levorotary methyl 3-furlymethoxyacetate. Two interpretations of the results of asymmetric synthesis were proposed. 相似文献
110.
Abstract Phase sensitive detection of fluorescence was used to directly record the initially excited and the solvent-relaxed emission spectra of N-acetyl-L-tryptophanamide in propylene glycol. Emission from the initially excited state was suppressed by adjusting the phase sensitive detector to be out of phase with the emission on the short wavelength side of the fluorescence spectrum. Then, the phase sensitive intensities revealed the emission spectrum of the solvent relaxed state. Similarly, the emission from the solvent relaxed state was suppressed by adjusting the detector to be out of phase with the emission on the long wavelength side of the spectrum, allowing the spectrum of the initially excited state to be directly recorded. Distinct emission spectra could be recorded when the solvent relaxation time was comparable to the fluorescence lifetime. At higher or lower temperatures, emission occurs predominantly from a single state, and suppression of the fluorescence signal at any arbitrary wavelength resulted in suppression of the entire emission. A simple theory is described which allows the spectral relaxation times to be estimated from the phase sensitive intensities. From this analysis we obtained an activation energy for spectral relaxation of 3 kcal/mol. This activation energy is smaller than that found for the temperature dependence of fluorescence depolarization, 7.8 kcal/mol. We attribute this difference to the smaller molecular motions required for spectral relaxation.
The method of phase sensitive detection of fluorescence shows excellent resolving power and sensitivity, and this method should facilitate measurement of spectral relaxation around tryptophan residues in proteins. 相似文献
The method of phase sensitive detection of fluorescence shows excellent resolving power and sensitivity, and this method should facilitate measurement of spectral relaxation around tryptophan residues in proteins. 相似文献