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101.
A procedure for the colorimetric assay of praziquantel has been developed. The method is based on the formation of charge-transfer
complexes with p-chloranil (I), dichloronitrophenol (II), 2,3-dichloro-5,6 dicyano-p-benzoquinone (III), 7,7,8,8-tetracyanoquinodimethane
(IV) and tetracyanoethylene (V) as π-acceptors to give highly coloured species. The coloured products are measured spectrophotometrically
at 550, 425, 460, 844 and 393 nm for I, II, III, IV and V, respectively. Optimization of the different reaction conditions
is described. The colour system obeyed Beer’s law in non-aqueous media in the concentration range 2.0–48 μg ml−1. It was stable for at least 4.0 h. The detection limit was found to be 0.6 μg ml−1. Applications of the procedure to the analysis of various pharmaceutical samples gave reproducible and accurate results.
Further, the validity of the procedure was confirmed by applying the standard addition technique. The total average recovery
was 100.2%.
Received June 10, 2000. Revision December 23, 2000. 相似文献
102.
The present investigation deals with the study of mechanical behavior of proton beam irradiated nitinol at room temperature. The specimens in austenitic phase were irradiated over periods of 15, 30, 45 and 60 min at room temperature using 2 MeV proton beam obtained from Pelletron accelerator. The stress-strain curves of both unirradiated and irradiated specimens were obtained using a universal testing machine at room temperature. The results of the experiment show that an intermediate rhombohedral (R) phase has been introduced between austenite and martensite phase, which resulted in the suppression of direct transformation from austenite to martensite (A-M). Stresses required to start R-phase (σRS) and martensitic phase (σMS) were observed to decrease with increase in exposure time. The hardness tests of samples before and after irradiation were also carried out using Vickers hardness tester. The comparison reveals that the hardness is higher in irradiated specimens than that of the unirradiated one. The increase in hardness is quite sharp in specimens irradiated for 15 min, which then increases linearly as the exposure time is increased up to 60 min. The generation of R-phase, variations in the transformation stresses σRS and σMS and increase in hardness of irradiated nitinol may be attributed to lattice disorder and associated changes in crystal structure induced by proton beam irradiation. 相似文献
103.
Maria BURGOS ;E Amin KAIDI ;Antonio Morales CAMPOY ;Antonio M. PERALTA ;Maribel RAMIREZ 《数学学报(英文版)》2008,24(2):185-200
We revise the notion of von Neumann regularity in JB^*-triples by finding a new characterisation in terms of the range of the quadratic operator Q(a). We introduce the quadratic conorm of an element a in a JB^*-triple as the minimum reduced modulus of the mapping Q(a). It is shown that the quadratic conorm of a coincides with the infimum of the squares of the points in the triple spectrum of a. It is established that a contractive bijection between JBW^*-triples is a triple isomorphism if, and only if, it preserves quadratic conorms. The continuity of the quadratic conorm and the generalized inverse are discussed. Some applications to C^*-algebras and von Neumann algebras are also studied. 相似文献
104.
Extensive continuum analyses are carried out to estimate the influence of matrix stiffness, a small length scale, and intertubular
radial displacements on free vibrations of an individual double-walled carbon nanotybe. The analyses are based on both local
and classical Euler–Bernoulli and Timoshenko elasticity theories with concentricity and nonconcentricity assumptions. The
effect of a small length scale is incorporated in the formulations. New intertubular resonant frequencies are calculated based
on these theories. Detailed results are demonstrated for the resonant frequencies as functions of matrix stiffness and the
small length scale. The results indicate that the internal radial displacement and the stiffness of the surrounding matrix
can greatly affect the resonant frequencies, especially at higher frequencies, and thus the latter does not keep the otherwise
concentric structure at ultrahigh frequencies. More over, at high frequencies and small aspect ratios, the effect of the small
length scale be comes more significant. 相似文献
105.
Herein, we propose a scheme for the realization of two-dimensional atomic localization in aλ-type three-level atomic medium such that the atom interacts with the two orthogonal standing-wave fields and a probe field. Because of the spatially dependent atom-field interaction, the information about the position of the atom can be obtained by monitoring the probe transmission spectra of the weak probe field for the first time. A single and double sharp localized peaks are observed in the one-wavelength domain. We have theoretically archived high-resolution and high-precision atomic localization within a region smaller thanλ/25×λ/25. The results may have potential applications in the field of nano-lithography and advance laser cooling technology. 相似文献
106.
We have theoretically investigated two-dimensional atom localization using the absorption spectra of birefringence beams of light in a single wavelength domain.The atom localization is controlled and modified through tunneling effect in a conductive chiral atomic medium with absorption spectra of birefringent beams.The significant localization peaks are investigated in the left and right circularly polarized beam.Single and double localized peaks are observed in different quadrants with minimum uncertainty and significant probability.The localized probability is modified by controlling birefringence and tunneling conditions.These results may be useful for the capability of optical microscopy and atom imaging. 相似文献
107.
The oxidative coupling reaction between hydroquinone or catechols and various sodium benzenesulfinates was investigated using the laccase from Trametes versicolor, in the presence of O2 in a phosphate buffer solution at room temperature to afford sulfonyl benzenediols in 75–95% yield. 相似文献
108.
Alaa S. Amin Ibrahim S. Ahmed Hassan A. Dessouki Hassan A. Mohamed 《Chemical Papers》2010,64(3):278-284
Simple and rapid spectrophotometric methods have been developed for the microdetermination of fluoxetine HCl. The proposed
methods are based on the formation of ion-pair complexes between fluoxetine and bromophenol blue (BPB), bromothymol blue (BTB),
bromocresol green (BCG), and bromocresol purple (BCP) which can be measured at optimum λmax. Optimization of reaction conditions was investigated. Beerșs law was obeyed in the concentration ranges of 0.5–8.0 μg mL−1, whereas optimum concentration as adopted from the Ringbom plots was 0.7–7.7 μg mL−1. The molar absorptivity, Sandell sensitivity, and detection limit were also calculated. The most optimal and sensitive method
was developed using BCG. The correlation coefficient was 0.9988 (n = 6) with a relative standard deviation of 1.25, for six determinations of 4.0 μg mL−1. The proposed methods were successfully applied to the determination of fluoxetine hydrochloride in its dosage forms and
in biological fluids (spiked plasma sample) using the standard addition technique. 相似文献
109.
A highly sensitive spectrophotometric method for palladium determination using piroxicam and tenoxicam as new chromogenic
reagents has been developed. In the presence of sodium lauryl sulfate (SLS), palladium reacts with piroxicam (PX) or tenoxicam
(TX) to form stable yellow orange complexes in an acetate buffer solution of pH 5.0 at 424 nm and 426 nm with molar absorptivity
of 7.16 × 104 L mol−1 cm−1 and 1.20 × 105 L mol−1 cm−1, respectively. Sandell sensitivity, detection, and quantitation limits were also calculated. Optimum conditions were evaluated
considering pH, reagent concentration, time, temperature, and surfactant concentration. The complex system conforms to Beer’s
law over the range of 0.07–1.28 μg mL−1 palladium. The stoichiometric ratio and stability constant were also evaluated. Tolerance limits of many cations and anions
were determined. Finally, the proposed method was applied successfully in the determination of palladium in jewellery, anode
mud, synthetic mixtures, catalysts, and alloy samples. 相似文献
110.
Vaughan PP Novotny P Haubrich N McDonald L Cochran M Serdula J Amin RW Jeffrey WH 《Photochemistry and photobiology》2010,86(6):1327-1333
Quinones are known producers of reactive oxygen species (ROS) that may be toxic in natural aquatic environments. In this study, the effects of parent quinones and their photodegradation products on bacterial growth were determined, and photochemical ROS formation rates were measured. Using (3)H-leucine incorporation to measure growth of the bacterium Pseudomonas aeruginosa and natural seawater bacterioplankton, growth inhibition was observed when samples were exposed to dichlone, chloranil and sodium anthraquinone-2-sulfonate (AQ2S). For seawater, compared with other quinones tested, dichlone showed the greatest toxicity in the dark, and AQ2S toxicity was greatest during simultaneous exposure to sunlight. Photodegraded chloranil and dichlone showed decreased toxicity compared with nonirradiated samples. For P. aeruginosa, AQ2S and its photodegradation products showed the greatest toxicity during simultaneous exposure to sunlight. Chloranil photodegradation products showed reduced toxicity compared with the parent compound during simultaneous exposure to sunlight. Dichlone was the only compound to show any toxicity to P. aeruginosa in the dark, and its photodegradation products were more toxic than the parent compound. Based on the results of dark and light controlled experiments measuring bacterial growth and estimated ROS production rates, ROS alone does not account for relative differences in toxicity between these quinones. 相似文献