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121.
Luminescence spectrum and its temperature dependence have been investigated for hexagonal YMnO3 crystal which is ferroelectric below TC=914 K and becomes simultaneously antiferromagnetic below TN=74 K. The luminescence spectrum is as broad as two-magnon Raman scattering spectrum. The luminescence intensity is comparable to the latter at room temperature and it increases rapidly as the temperature decreases. These characteristics are discussed based upon other optical responses and theoretical results. 相似文献
122.
Dielectric measurements, differential thermal analyses, and density measurements are reported on concentrated solutions of polyvinylchloride in tetrahydrofuran. The relaxation processes observed between 80 and 400°K have been classified into four types. From the analysis of experimental data, the primary process at the highest temperature and the process at the lowest temperature are assigned, respectively, to segmental motion of the polymer and motion of the solvent. Activation plots for the primary process conform to the Vogel–Tamman equation. The dielectric glass-transition temperature T'g (defined as the temperature at which the dielectric relaxation time is 100 sec) determined with this equation agrees well with the glass-transition temperature Tg from thermal analysis. Therefore, Tg can be represented by an expression of the form The parameters of the Vogel–Tamman equation A and B are nearly independent of concentration, whereas To depends strongly on concentration. The dipole moment per monomeric unit calculated from the experimental data changes with concentration and exhibits steep increments around 30% and 90% by weight. The width of the distribution of the relaxation time also increases with the concentration. The results were compared with those for the system polystyrene–toluene studies in the same way. 相似文献
123.
124.
Kobayashi S Mori K Wakabayashi T Yasuda S Hanada K 《The Journal of organic chemistry》2001,66(16):5580-5584
A convergent total synthesis of khafrefungin, a novel inhibitor of fungal sphingolipid syntheses isolated from the fermentation culture MF6020, has been developed. Alkenylboronic acid 5 and alkenyliodide 6, key fragments for the total synthesis, were prepared from the corresponding achiral aldehydes using tin(II)-catalyzed and Zr(IV)-catalyzed asymmetric aldol reactions, respectively. The Suzuki coupling reaction of these two fragments was successfully performed to give 17 in good yield. Through the total synthesis, epimerization of the C4 position having a rather highly acidic proton did not occur, indicating that khafrefungin was under strict conformational constraints to prevent the epimerization process. This characteristic stability of khafrefungin has also been discussed using semiempirical calculation and synthesis. Finally, khafrefungin derivatives have also been synthesized, and their antifungal activities have been measured to obtain information on the structure--activity relationships. 相似文献
125.
Tetsuji Kametani Hiroo Matsumoto Toshio Honda Mitsuo Nagai Keiichiro Fukumoto 《Tetrahedron》1981,37(15):2555-2560
A stereoselective synthesis of des-A-ring steroids and has been achieved by an intramolecular cycloaddition of 3-isopropenyl-5-(4-methoxybenzocyclobutenyl) pentan-2-one-2-ethylene ketal and 1-(4-methoxy-benzocyclobutenyl)-4-methylpent-4-en-3-ol , respectively. 相似文献
126.
A method is described for simultaneous determination of 14 lanthanides and yttrium in monazites and xenotimes by inductively-coupled plasma atomic emission spectrometry. The ore samples were decomposed by heating with nitric acid/perchloric acid or hydrofluoric/nitric/perchloric acids, or sulfuric acid, or by fusion with sodium carbonate. Among these methods, treatment of the samples with sulfuric acid, by evaporation to dryness followed by dissolution of the residue with hydrochloric acid is recommended; it provided complete decomposition for the five monazites and xenotimes examined. The accuracy and precision of the results were significantly influenced by spectral interferences of the rare earth elements themselves; correction methods and factors are given. The chondrite-normalized rare-earth patterns were examined to characterize the monazite and xenotime samples. 相似文献
127.
Tetsuji Kametani Ryuko Nitadori Hirohumi Terasawa Keiichi Takahashi Masataka Ihara Keiichiro Fukumoto 《Tetrahedron》1977,33(9):1069-1071
Atheroline (3) an oxoaporphine alkaloid, has been synthesised by photolysis of 8 bromo 1-(3-hydroxy-4-methoxybenzoyl)-6,7-dimethoxyisoquinoline (13) in the presence of sodium hydroxide. 相似文献
128.
Keisuke Kitamura Miharu Takenaka Sachiyo Yoshida Mariko Ito Yuriko Nakamura Keiichiro Hozumi 《Analytica chimica acta》1991
The dissociation constants (pKa) for sparingly soluble phenothiazines (promazine, chlorpromazine, trifluoropromazine) in water were measured by second-derivative spectrophotometry. The intense background signals in the absorption spectra due to the turbidity caused by the precipitation of insoluble free base of the phenothiazine derivatives were eliminated in the second-derivative spectra, and the solubilities of the phenothiazine derivatives could be easily determined from the peak-to-trough lengths (D values) of the second-derivative signals. The pKa values were calculated from the pH dependence of the D values. The pKa values obtained agreed well with reported values and the standard deviations for 6–10 determinations were ? 0.02. The solubilities of the free bases of the phenothiazines were also determined. 相似文献
129.
Masataka Ihara Keiichiro Fukumoto 《Angewandte Chemie (International ed. in English)》1993,32(7):1010-1022
The one-pot intramolecular double Michael reaction of compounds having two different α, β-unsaturated carbonyl groups to form polycyclic compounds can be carried out by three different methods: in the first the substrate is treated with lithium hexamethyldisilazide, in the second with chlorotrimethylsilane, triethylamine, and zinc chloride at an elevated temperature, and in the third with tert-butyldimethylsilyl trifluoromethanesulfonate and triethylamine. The reaction proceeds with complete regioselectivity and high stereoselectivity following a stepwise mechanism. Spiro-fused bicyclo[2.2.2]octane derivatives can be constructed with high stereoselectivity by the intromolecular double Michael reaction by using the first method. Enantiomerically pure atisine and the enantiomer of atisirene were synthesized stereoselectively by application of this methodology. The syntheses of steroids and angular triquinane-type sesquiterpenoids were possible with the second method. Heterocyclic compounds with a bridgehead nitrogen atom were obtained by the reaction of α, β-unsaturated amides following the second and third methods. The asymmetric synthesis of tylophorine with diastereofacial control was achieved by the intramolecular reaction according to the third method. The sulfur-mediated intramolecular double Michael reaction utilizing the third method produced trans-hydroindane derivatives. Furthermore, the intramolecular Michael-aldol reaction can be employed in synthesizing polycyclic systems with cyclobutane units by treatment with tert-butyldimethylsilyl trifluoromethanesulfonate in the presence of triethylamine. The intermolecular double Michael reaction and related reactions will also be described. 相似文献
130.
Nakamura M Mori Y Okuyama K Tanikawa K Yasuda S Hanada K Kobayashi S 《Organic & biomolecular chemistry》2003,1(19):3362-3376
Large-scale synthesis, design, and structure-activity relationships of khafrefungin are reported. Khafrefungin is an antifungal agent that inhibits inositol phosphorylceramide (IPC) synthase, an enzyme involved in fungal sphingolipid biosynthesis. Unlike other inhibitors that inhibit the corresponding enzyme in fungi and mammals to the same extent, khafrefungin does not impair sphingolipid synthesis in mammals. We have developed an efficient method for large-scale synthesis of khafrefungin, and various khafrefungin derivatives were synthesized based on this method. While most of the khafrefungin derivatives lost antifungal activity, a lactone-type derivative had almost the same activity as khafrefungin. We also designed and synthesized derivatives which contain a five- or six-membered ring at the central part of the structure based on NOE experiments of khafrefungin. A macrocyclic khafrefungin derivative was also synthesized, but the antifungal activity was lost. These results suggest that the structure of khafrefungin might be strictly recognized in fungi. 相似文献