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991.
Djairo G. de Figueiredo João Marcos do Ó Bernhard Ruf 《Journal of Fixed Point Theory and Applications》2008,4(1):77-96
We establish a priori bounds for positive solutions of semilinear elliptic systems of the form
where Ω is a bounded and smooth domain in . We obtain results concerning such bounds when f and g depend exponentially on u and v. Based on these bounds, existence of positive solutions is proved.
Dedicated to Felix Browder on the occasion of his 80th birthday 相似文献
992.
993.
Silva EM Domingues P Tomé JP Faustino MA Neves MG Tomé AC Dauzonne D Silva AM Cavaleiro JA Ferrer-Correia AJ Domingues MR 《European journal of mass spectrometry (Chichester, England)》2008,14(1):49-59
Beta-nitroalkenyl meso-tetraphenylporphyrins [beta-TPPCHC(NO(2))R)], as free-bases and Zn(II) complexes, were studied by electrospray mass spectrometry (ESI-MS). Under this ionisation condition the [M + H](+) ions are formed. The fragmentation pattern of the resulting [M + H](+) ions were studied by electrospray tandem mass spectrometry (ESI-MS/MS). The ESI-MS/MS of beta- nitroalkenylporphyrins, either as free-bases or as Zn(II) complexes, show several interesting features, distinct from the typical behaviour of nitro compounds. For the studied compounds, common main fragmentation patterns are observed, namely characteristic losses of NO(2), HNO(2), 2OH, RNO(2), RCNO, RCNO(2), RCH(2)NO(2), C(6)H(5) plus NO(2) and the formation of the protonated macrocycle, [TPP + H](+) or [ZnTPP + H](+). However, depending on the presence or absence of the metal and the nature of the R substituent, important differences are observed on the relative abundances of the ions formed by the same fragmentation pathway. The presence of bromine in the alkenyl group leads to a peculiar behaviour, since the main fragmentation pattern corresponds to the combined elimination of the bromine atom with the typical nitro group fragments. When R = Br, the loss of the nitro group occurs in low relative abundance (11-16%). However, when R = CH(3), the relative abundance of the ion due to the loss of HNO(2) changes drastically from 100%, observed for the free-base porphyrin, to 29% in the case of the Zn(II) complex. These variations of the relative abundance of the fragment corresponding to the loss of the nitro moiety (typically considered as a diagnostic fragment) can induce to an erroneous interpretation of their MS/MS spectra. Some fragmentations are observed only for the free-base porphyrins, namely the loss of CH(NO(2)R and HNO(2) plus C(2)H(2), while the loss of OH, H(2)O, OH plus H(2)O and RCCH plus H(2)O is observed only for the complexes. Unusual and unexpected fragmentations are also observed, namely the losses of RCNO, RCNO(2) and HNO(2) plus C(2)H(2). This work demonstrates that valuable structural information about the beta-nitroalkenyl substituents linked to meso- tetraarylporphyrins can be achieved using MS/MS. These results can also be useful for the interpretation of the mass spectra of other nitroalkenyl substituted compounds. 相似文献
994.
Cailliez F Trzpit M Soulard M Demachy I Boutin A Patarin J Fuchs AH 《Physical chemistry chemical physics : PCCP》2008,10(32):4817-4826
We report a joint experimental and molecular simulation study of water intrusion in silicalite-1 and ferrerite zeolites. The main conclusion of this study is that water condensation takes place through a genuine first-order phase transition, provided that the interconnected pores structure is 3-dimensional. In the extreme confinement situation (ferrierite zeolite), condensation takes place through a continuous transition, which is explained by a shift of both the first-order transition line and the critical point with increasing confinement. The present findings are at odds with the common belief that conventional phase transitions cannot take place in microporous solids such as zeolites. The most important features of the intrusion/extrusion process can be understood in terms of equilibrium thermodynamics considerations. We believe that these findings are very general for hydrophobic solids, i.e. for both nonwetting as well as wetting water-solid interface systems. 相似文献
995.
Fenstad J 《Physical chemistry chemical physics : PCCP》2008,10(2):311-319
A new concept is presented for analysing the excess properties of mixing for asymmetric homogeneous mixtures. In its current form the concept is limited to binary mixtures, but applies to numerous classes of materials, and a wide selection of mixing properties. This paper demonstrates that this Log-symmetry concept is general enough to include (as special cases) several existing mixture models; specifically the Regular Solution Theory, van Laar equation, and the Rogalski-Malanowski expression. The above finding suggests log-symmetry is inherently fundamental, in a way that is (yet) not fully explored. In its most basic implementation (the Mirror Data Method) log-symmetric modelling requires merely one independent parameter. This paper employs high-precision experimental data to validate the concept. 相似文献
996.
997.
Molecular motions in amorphous ibuprofen as studied by broadband dielectric spectroscopy 总被引:1,自引:0,他引:1
Brás AR Noronha JP Antunes AM Cardoso MM Schönhals A Affouard F Dionísio M Correia NT 《The journal of physical chemistry. B》2008,112(35):11087-11099
The molecular mobility of amorphous ibuprofen has been investigated by broadband dielectric relaxation spectroscopy (DRS) covering a temperature range of more than 200 K. Four different relaxation processes, labeled as alpha, beta, gamma, and D, were detected and characterized, and a complete relaxation map was given for the first time. The gamma-process has activation energy E a = 31 kJ.mol (-1), typical for local mobility. The weak beta-relaxation, observed in the glassy state as well as in the supercooled state was identified as the genuine Johari-Goldstein process. The temperature dependence of the relaxation time of the alpha-process (dynamic glass transition) does not obey a single VFTH law. Instead two VFTH regimes are observed separated by a crossover temperature, T B = 265 K. From the low temperature VFTH regime, a T g (diel) (tau =100 s) = 226 K was estimated, and a fragility or steepness index m = 93, was calculated showing that ibuprofen is a fragile glass former. The D-process has a Debye-like relaxation function but the temperature dependence of relaxation time also follows the VFTH behavior, with a Vogel temperature and a pre-exponential factor which seem to indicate that its dynamics is governed by the alpha-process. It has similar features as the Debye-type process observed in a variety of associating liquids, related to hydrogen bonding dynamics. The strong tendency of ibuprofen to form hydrogen bonded aggregates such as dimers and trimers either cyclic or linear which seems to control in particular the molecular mobility of ibuprofen was confirmed by IR spectroscopy, electrospray ionization mass spectrometry, and MD simulations. 相似文献
998.
Brambilla R Pinto CF Miranda MS dos Santos JH 《Analytical and bioanalytical chemistry》2008,391(7):2673-2681
A series of octadecylsilane-modified silicas were prepared by sol-gel and grafting methods. Carbon contents and octadecyl
chain conformations were shown to depend on the preparative route. Grafting engenders a low carbon content and a liquid-like
chain conformation, while the sol-gel method affords a much higher carbon content and a crystalline conformation. The relationships
between the toluene adsorption of the hybrid silicas and their chain conformations, their carbon contents and their textural
characteristics are discussed. These sorbents, when used in combination with ultraviolet diffuse reflectance spectroscopy
(UV DRS), can be employed as a rapid screening method for detection of aromatic compounds in water and air environmental matrices.
Figure Octadecylsilane-modified silicas in the adsorption of toluene 相似文献
999.
Vanessa S. D. Gomes João C. C. Ferreira Renato E. Boto Paulo Almeida José R. Fernandes Maria João Sousa Lucinda V. Reis M. Sameiro T. Gonçalves 《Photochemistry and photobiology》2023,99(5):1282-1292
The antifungal performance and the possible use as fluorescent probes of a series of squarylium dyes derived from indolenine and benzo[e]indole previously synthesized was evaluated. Some photophysical properties were performed in ethanol and phosphate buffer, and the type of aggregates form in phosphate buffer was analyzed. Using the 1,3-diphenylisobenzofuran assay, a qualitative assessment of the capacity of dyes to produce singlet oxygen after irradiation was performed. Regarding the antifungal activity, this was studied through a broth microdilution assay using Saccharomyces cerevisiae PYCC 4072 as a biological model. The effect of irradiation of the dyes, with an appropriate light emitting diode system, on the antifungal activity was also evaluated, and it was verified that some of the dyes improve their activity after irradiation. Using fluorescence microscopy techniques, the colocalization of dyes in S. cerevisae cells was investigated and it was possible to verify that some of the squarylium dyes with a barbituric moiety in the four-membered central ring stained and accumulated preferentially in the mitochondrial web and perinuclear membrane of the cells. The possible use as a fluorescent probe for the detection of HSA was also evaluated for one of the dyes of the series, demonstrating a linear variation in the fluorescence intensity accompanied by the increase in the protein concentration. 相似文献
1000.
Dr. Maria João Álvaro-Martins José Garcés-Garcés Dr. Antoine Scalabre Dr. Peizhao Liu Prof. Fernando Fernández-Lázaro Prof. Ángela Sastre-Santos Dr. Dario M. Bassani Dr. Reiko Oda 《Chemphyschem》2023,24(3):e202200573
The synthesis and characterization of diketopyrrolopyrroles and perylenemonoimidodiesters linked to a substituted benzoic acid in the ortho, meta, and para positions, are reported. Grafting of these dyes on the surface of chiral silica nanohelices is used to probe how the morphology of the platform at the mesoscopic level affects the induction of chiroptical properties onto achiral molecular chromophores. The grafted structures are weakly (diketopyrrolopyrroles) or strongly (perylenemonoimidodiesters) emissive, exhibiting both locally-excited state emission and a broad, structureless emission assigned to excimers. The dissymmetry factors obtained using circular dichroism highlight optimized supramolecular organization between the chromophores for enhancing the chiroptical properties of the system. In the ortho- derivatives, poor organization due to steric hindrance is reflected in a low density of chromophores on walls of the silica-nanostructures (<0.1 vs. >0.3 and up to 0.6 molecules/nm2 for the ortho and meta or para derivatives, respectively) and lower gabs values than in the other derivatives (gabs<2×10−5 vs 6×10−5 for the ortho and para derivatives, respectively). The para derivatives presented a better organization and increased values of gabs. All grafted chromophores evidence varying degrees of excimer emission which was not found to directly correlate to their grafting density. 相似文献