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991.
We consider the problem where \(\Omega \) is either \(\mathbb {R}^{N}\) or a smooth domain in \(\mathbb {R} ^{N}\) with unbounded boundary, \(N\ge 3,\) \(V_{\infty }>0,\) \(V\in \mathcal {C} ^{0}(\mathbb {R}^{N}),\) \(\inf _{\mathbb {R}^{N}}V>-V_{\infty }\) and \(2<p<\frac{2N}{N-2}\). We assume V is periodic in the first m variables, and decays exponentially to zero in the remaining ones. We also assume that \(\Omega \) is periodic in the first m variables and has bounded complement in the other ones. Then, assuming that \(\Omega \) and V are invariant under some suitable group of symmetries on the last \(N-m\) coordinates of \(\mathbb {R}^{N}\), we establish existence and multiplicity of sign-changing solutions to this problem. We show that, under suitable assumptions, there is a combined effect of the number of periodic variables and the symmetries of the domain on the number of sign-changing solutions to this problem. This number is at least \(m+1\)
相似文献
$$\begin{aligned} -\Delta u+\left( V_{\infty }+V(x)\right) u=|u|^{p-2}u,\quad u\in H_{0} ^{1}(\Omega ), \end{aligned}$$
992.
Mirta L. Fascio Vernica J. Montesano Norma B. D'Accorso 《Journal of heterocyclic chemistry》1998,35(1):103-107
The synthesis of five 3-(1,2-O-isopropylidene-α-D-xylofuranosyl)-5-substituted-2-isoxazolines obtained by 1,3-dipolar cycloaddition are described, as well as the intermediate products from the synthetic route. The physical and spectroscopic characterization of these compounds are reported. 相似文献
993.
Mónica E. Quiroga Nora S. Fígoli Ulises A. Sedran 《Reaction Kinetics and Catalysis Letters》1998,63(1):75-80
MTBE synthesis has been studied over catalysts having different acidities: zeolites, fluorine-promoted SiO2−Al2O3 and sulfur-promoted ZrO2. Some catalysts perform similarly to acidic resins and a clear relationship between acidity and activity is not apparent. 相似文献
994.
Raul Figueroa Mnica García Isela Lavilla Carlos Bendicho 《Spectrochimica Acta Part B: Atomic Spectroscopy》2005,60(12):1556-1563
A method is described for the determination of selenium at the pg/mL level by electrothermal-atomic absorption spectrometry using in situ photogeneration of Se vapors, headspace sequestration onto an aqueous microdrop containing Pd(II) and subsequent injection in a graphite tube. Several organic acids (formic, oxalic, acetic, citric and ethylenediaminetetraacetic) have been tried for photoreduction of Se(IV) into volatile Se compounds under UV irradiation. Experimental variables such as UV irradiation time, organic acid concentration, Pd(II) concentration in the drop, sample and drop volumes, extraction time and pH were fully optimized. Low-molecular weight acids such as formic and acetic provided optimal photogeneration of volatile Se species at a 0.6 mol/L concentration. Citric and ethylenediaminetetraacetic acid allowed to use a concentration as low as 1 mmol/L, but extraction times were longer than for formic and acetic acids. Photogeneration of (CH3)2Se from Se(IV) in the presence of acetic acid provided a detection limit of 20 pg/mL, a preconcentration factor of nearly 285 and a precision, expressed as relative standard deviation, of 4%. Analytical performance seemed to depend not only on the photogeneration efficiency obtained with each acid but also on the stability of the vapors in the headspace. The method showed a high freedom from interferences caused by saline matrices, but interferences were observed for transition metals at a relatively low concentration. 相似文献
995.
A simple and rapid capillary electrophoresis method for low-molecular mass carboxylic acids measurement in coffee has been optimised and validated. Regarding separation conditions, phosphate concentration in the background electrolyte, surfactant type [cetyltrimethylammonium bromide (CTAB), tetradecyltri methylammonium bromide (TTAB) and hexadimethrine bromide (HDB)], percentages of organic modifier and pH were assayed. The best conditions were: 500 mM phosphate buffer at pH 6.25 with CTAB 0.5 mM. The separation was carried out with an uncoated fused-silica capillary (57 cm x 50 microm i.d.) which was operated at -10 kV potential. Detection was performed at 200 nm. In such conditions 17 short-chain organic acids: oxalic, formic, fumaric, mesaconic, succinic, maleic, malic, isocitric, citric, acetic, citraconic, glycolic, propionic, lactic, furanoic, pyroglutamic, quinic acids plus nitrate were separated, identified and measured. Validation parameters of the method allow us to consider it lineal, accurate and precise and, therefore, reliable for its employment in food composition studies or for quality control. Results in coffees with different industrial treatment allow the detection of important differences in the organic acid profile. 相似文献
996.
Paneque M Poveda ML Santos LL Salazar V Carmona E 《Chemical communications (Cambridge, England)》2004,(16):1838-1839
The in situ generated [Tp(Me2)Ir(C(6)H(5))(2)] fragment induces both aromatic and aliphatic C-H bond activation reactions, along with C-C bond formation, when heated with benzene and 1,2-dimethoxyethane. 相似文献
997.
Fernando Sartillo-Piscil Mónica VargasCecilia Anaya de Parrodi Leticia Quintero 《Tetrahedron letters》2003,44(20):3919-3921
We report the stereoselective synthesis of an optically pure spiroketal via an intramolecular tandem hydrogen abstraction reaction promoted by an alkoxy radical. Expanding the use of alkene radical cation under non-oxidizing conditions in the synthetic scenario. 相似文献
998.
López-García M Alfonso I Gotor V 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(12):3006-3014
The efficient chemoenzymatic synthesis of enantiopure 1,3-difunctionalized indane derivatives has been achieved. The corresponding cis and trans N-protected amino alcohols were successfully resolved by acetylation using lipase B, which is a biocatalyst isolated from Candida antarctica. All the possible isomers were obtained in very good chemical yields and ee values (>99 %). The utility of these compounds was subsequently shown by the preparation of orthogonally protected cis- and trans-indane-1,3-diamine using a Mitsunobu reaction. Both enantiomers of the trans isomer and a desymmetrized cis diastereomer were prepared in enantiopure form. Complete inversion of configuration during the Mitsunobu reaction was demonstrated by a combination of NMR techniques and molecular modeling. The utility and versatility of the strategy was also demonstrated by the selective deprotection of each nitrogen atom under mild reaction conditions. 相似文献
999.
Patricia I. Napolitano-Tabares Isaac Negrín-Santamaría Adrián Gutiérrez-Serpa Verónica Pino 《Current Opinion in Green and Sustainable Chemistry》2021
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1000.
A cyclic cis-nitroso dimer, 3,4-dibromo-3,5,5-trimethylpyrazoline 1,2-dioxide was oxidized directly to an open chain 1,3-dinitro compound by a peroxyacid but nitrosyl chloride displaced bromine, added, and oxidized the same compound to 3-chloro-4-nitro-3,5,5-trimethylpyrazoline 1,2-dioxide. 相似文献