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991.
Dr. María J. González Prof. Dr. Bernhard Breit 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(69):15746-15750
A new methodology to form C(sp3)−C(sp2) bonds by visible-light-driven intermolecular reductive ene–yne coupling has been successfully developed. The process relies on the ability of the Hantzsch ester to contribute in both SET and HAT processes through a unified cobalt and iridium catalytic system. This procedure avoids the use of stoichiometric amounts of reducing metallic reagents, which is translated into high functional-group tolerance and atom economy. 相似文献
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Pérez-Alonso A. Blanco I. J. Serrano J. M. González-González L. M. 《Fuzzy Optimization and Decision Making》2021,20(4):429-449
Fuzzy Optimization and Decision Making - Fuzzy association rules (FARs) are a recognized model to study existing relations among data, commonly stored in data repositories. In real-world... 相似文献
997.
Víctor González-Ruiz Yamisley González-Cuevas Sankaralingam Arunachalam M. Antonia Martín Ana I. Olives Pascual Ribelles M. Teresa Ramos J. Carlos Menéndez 《Journal of luminescence》2012,132(9):2468-2475
Luotonin A is an alkaloid structurally related to the natural anti-tumour agent camptothecin. The fluorescence behaviour of luotonin A and a series of six analogues is described in the present work. The influence of solvent polarity and pH on the native fluorescence properties of these alkaloids was studied, finding that in organic solvents or in aqueous solutions (pH 5.5–7.2) the neutral form of the luotonin derivatives emit in the region of 410–450 nm but, in both media, acidification to pH values below 3.0 causes a new emission band to appear at about 500 nm. An ESPT reaction occurs due to the protonation of the basic nitrogen atoms of the pentacyclic ring. Acid-base titrations of luotonin A and its derivatives in aqueous and acetonitrile media were carried out in order to determine their pKa? values which were around 2, showing these compounds to be very weak bases. In aqueous media, the absence of an iso-emissive point in the emission spectra suggests the existence of more than two species in the proton transfer equilibria. The basicity of the luotonin A derivatives is increased in organic media, and a good correlation between the pKa? values and the chemical structure was found. The protonation of luotonin A was also studied by 1H-NMR and 13C-NMR experiments, which proved the protonation of the nitrogen atoms at the positions 5 and 6 of the pentacyclic ring. The fluorescence quantum yields were determined in ethanol and in aqueous solutions under neutral and acidic conditions. The fluorescence quantum yields were higher in water for the case of the more polar compounds, and the opposite result was obtained for the more hydrophobic ones. The remarkable and interesting fluorescence properties of luotonin A prompted the development of its fluorimetric analytical quantitation, obtaining very good analytical features. 相似文献
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Justo Cabrera‐González Dr. Laura Cabana Dr. Belén Ballesteros Dr. Gerard Tobias Dr. Rosario Núñez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(15):5096-5101
An efficient process to produce boron cluster–graphene oxide nanohybrids that are highly dispersible in water and organic solvents is established for the first time. Dispersions of these nanohybrid materials in water were extraordinarily stable after one month. Characterization of hybrids after grafting of appropriate cobaltabisdicarbollide and closo‐dodecaborate derivatives onto the surface of graphene oxide (GO) was done by FT‐IR, XPS, and UV/Vis. Thermogravimetric analysis (TGA) clearly shows a higher thermal stability for the modified‐GO nanohybrids compared to the parent GO. Of particular note, elemental mapping by energy‐filtered transmission electron microscopy (EFTEM) reveals that a uniform decoration of the graphene oxide surface with the boron clusters is achieved under the reported conditions. Therefore, the resulting nanohybrid systems show exceptional physico‐chemical and thermal properties, paving the way for an enhanced processability and further expanding the range of application for graphene‐based materials. 相似文献
999.
M. Gadella M. A. García-Ferrero S. González-Martín F. H. Maldonado-Villamizar 《International Journal of Theoretical Physics》2014,53(5):1614-1627
The construction of Dirac delta type potentials has been achieved with the use of the theory of self adjoint extensions of non-self adjoint formally Hermitian (symmetric) operators. The application of this formalism to investigate the possible self adjoint extensions of the one dimensional kinematic operator $K=-\frac{d^{2}}{dx^{2}}$ on the infinite square well potential is quite illustrative and has been given elsewhere. This requires the definition and use of four independent real parameters, which relate the boundary values of the wave functions at the walls. By means of a different approach, that fixes matching conditions at the origin for the wave functions, it is possible to define a perturbation of the type aδ(x)+bδ′(x), thus depending on two parameters, on the infinite square well. The objective of this paper is to investigate whether these two approaches are compatible in the sense that perturbations like aδ(x)+bδ′(x) can be fixed and determined using the first approach. 相似文献
1000.
Marcos Couto Mauricio Cabrera Gustavo A. Echeverría Oscar E. Piro Mercedes González Hugo Cerecetto 《Molecular diversity》2014,18(2):285-294
In the course of our studies on 3 $H$ -1,2-dithiole-3-thione synthesis, a serendipitous reactivity with $\alpha $ -haloketones, in the presence of excess of potassium iodide, has been observed. Instead of the expected reaction of the nucleophile in a remote point of the molecule, we have obtained a product resulted from the electrophile character of the thiocarbonyl moiety on the 3-position of the 1,2-dithiole. In order to obtain an efficient protocol in terms of energy efficiency, this methodology was studied under conventional and microwave heating with similar or better results in the latter conditions. Simplicity and great efficiency in this one-step transformation are some of the advantages of this reaction. Moreover, the results can be explained according to the Pearson’s hard and soft acid base theory. 相似文献