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771.
772.
773.
M. C. Gutiérrez A. Gómez-Hens D. Pérez-Bendito 《Fresenius' Journal of Analytical Chemistry》1989,334(4):344-348
Summary A kinetic study of the colour reactions between butylated hydroxyanisole (BHA) and Gibbs and Ehrlich reagents carried out with a stopped-flow system is reported. Kinetic methods for the determination of BHA were developed with both reagents. The parameters used were the initial rate and the signal amplitude. The use of a diode-array photodetector allowed the application of an amplification method with a decreased detection limit. The different kinetic methods developed were satisfactorily applied to the determination of BHA in different commercial oil samples. Analytical recovery data are also reported.
Photometrische Stopped-Flow Bestimmung von butyliertem Hydroxyanisol相似文献
774.
It is shown that the Bochner-Riesz operator on of negative order is of restricted weak type in the critical points and , where , for in the two-dimensional case and , for if .
775.
O. Descalzi J. Cisternas P. Gutiérrez H. R. Brand 《The European physical journal. Special topics》2007,146(1):63-70
We discuss the results of the interaction of
counter-propagating pulses for two coupled complex cubic-quintic
Ginzburg–Landau equations as they arise near the onset of a weakly
inverted Hopf bifurcation. As a result of the interaction of the
pulses we find in 1D for periodic boundary conditions
(corresponding to an annular geometry) many different possible
outcomes. These are summarized in two phase diagrams using the
approach velocity, v, and the real part of the cubic
cross-coupling, cr, of the counter-propagating waves as
variables while keeping all other parameters fixed. The novel
phase diagram in the limit v ↦0, cr ↦0 turns out to be
particularly rich and includes bound pairs of 2 π holes as
well as zigzag bound pairs of pulses. 相似文献
776.
We introduce a codomain to represent semiorders, total preorders and interval orders by means of a single map. We characterize the semiorders that are representable in the extended real line. 相似文献
777.
We study the expected value of support functions of random polytopes in a certain direction, where the random polytope is given by independent random vectors uniformly distributed in an isotropic convex body. All results are obtained using probabilistic estimates in terms of Orlicz norms that were not used in this connection before. 相似文献
778.
Stefano Ercoli Jos Parada Luis Bustamante Isidro Hermosín-Gutirrez Boris Contreras Pablo Cornejo Antonieta Ruiz 《Molecules (Basel, Switzerland)》2021,26(2)
The effect of cooking on the concentrations of phenolic compounds and antioxidant activities in 33 colored-fleshed potatoes genotypes was evaluated. The phenolic profiles, concentrations, and antioxidant activity were evaluated with a liquid chromatography diode array detector coupled to a mass spectrometer with an electrospray ionization interface (HPLC-DAD-ESI-MS/MS). Eleven anthocyanins were detected; in the case of red-fleshed genotypes, these were mainly acyl-glycosides derivatives of pelargonidin, whereas, in purple-fleshed genotypes, acyl-glycosides derivatives of petunidin were the most important. In the case of the purple-fleshed genotypes, the most important compound was petunidin-3-coumaroylrutinoside-5-glucoside. Concentrations of total anthocyanins varied between 1.21 g kg−1 in fresh and 1.05 g kg−1 in cooked potato and the decreases due to cooking ranged between 3% and 59%. The genotypes that showed the highest levels of total phenols also presented the highest levels of antioxidant activity. These results are of relevance because they suggest anthocyanins are important contributors to the antioxidant activity of these potato genotypes, which is significant even after the drastic process of cooking. 相似文献
779.
Torpocco V Chávez H Estévez-Braun A Ravelo AG 《Chemical & pharmaceutical bulletin》2007,55(5):812-814
Two new dammarane triterpenes have been isolated from the stem bark exudates of Maytenus macrocarpa. Their structures were determined by extensive 1D and 2D NMR spectroscopic studies as 24(Z)-3-oxodammara-20(21),24-dien-27-oic acid (1) and octa-nor-13-hydroxydammara-1-en-3,17-dione (2). These compounds were tested for antitumoral activity. 相似文献
780.
Ballester L Gutiérrez A Perpiñán MF Sánchez AE Fonari M Gdaniec M 《Inorganic chemistry》2007,46(10):3946-3955
The hexaazamacrocycle 1,4,7,10,13,16-hexaazacyclooctadecane, [18]ane-N6, forms mono- and dinuclear derivatives with copper chloride depending on the reaction stoichiometries and times. The mononuclear derivative, [Cu([18]ane-N6)]Cl2.H2O, presents the macrocycle wrapped around the metal atom in a distorted octahedral coordinative environment, while the dinuclear derivative, [Cu2([18]ane-N6)Cl2]Cl2.4H2O, is formed by a central Cu2Cl2 core surrounded by an almost planar macrocycle. The crystal structure of both derivatives is stabilized by a network of hydrogen bonds involving the amine macrocyclic groups, the chloride anions, and the crystallization water molecules. The copper atoms in the dinuclear derivative show a strong antiferromagnetic coupling, as expected for the crystal structure parameters. A mononuclear nickel derivative has also been obtained from nickel nitrate by following the same synthetic procedure. These compounds react with TCNQ salts with formation of two types of derivatives, [M([18]ane-N6)](TCNQ)2 and [M([18]ane-N6)](TCNQ)4, depending on the use of radical-anionic or mixed-valence TCNQ salts in the reaction. The crystal structures of the nickel derivatives show that the former derivatives are built up by macrocyclic metal cations surrounded by dimeric dianions (TCNQ)22-, either isolated or stacked along the crystal. The derivative with four TCNQ units/formula consists of alternated chains of metallomacrocyclic cations and stacked TCNQ anions. The crystal parameters suggest that every TCNQ holds approximately 0.5 electrons and overlaps with a neighboring unit to form dimeric monoanions, (TCNQ)2-. 相似文献