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91.
We report new transient stationary spherical waves generated by the time evolution of wave functions with angular momentum. In the study the 3D problem of the sudden release of a particle which initially was inside a spherical trap, the exact solution for the particle's time evolution is described by expected traveling incoming and outgoing spherical waves. However, unexpected transient stationary spherical waves are also present. The traveling waves have amplitudes describing diffraction in time, in a way similar to the optical diffraction by a single slit. In striking contrast with the similar 1D problem, the angular momentum generates unexpected transient stationary spherical waves which have their main contribution at points inside the sphere but only for very short times. 相似文献
92.
Arben Merkoçi Majlinda Vasjari Esteve Fàbregas Salvador Alegret 《Mikrochimica acta》2000,135(1-2):29-33
Two different approaches for the modification of glassy carbon electrodes using a mercury film and mercury-nafion are compared.
The mixture of mercury(II) chloride solution with a nafion solution diluted in ethanol is used to coat the polished glassy
carbon surface. The modified working electrodes are compared when measuring Pb and Cu in real seawater samples. An optimisation
of the parameters during the formation of the films was done to obtain well-defined stripping peaks. The type of inert supporting
electrolyte and the pH play an important role on the sensitivity of the measurement. Results for Pb and Cu determinations
show the advantages of Hg-nafion modification as an alternative method. These advantages include a shorter modification time,
the avoidance of Hg solutions during the formation of the Hg film and an improved sensitivity for Pb determination.
Received March 16, 1999. Revision April 24, 2000. 相似文献
93.
Sergio Madurga Josep Lluís Garcés Encarnació Companys Carlos Rey-Castro José Salvador Josep Galceran Eudald Vilaseca Jaume Puy Francesc Mas 《Theoretical chemistry accounts》2009,123(1-2):127-135
The influence of ion size and surface charge model in titrations of ionizable polyelectrolytes is studied by means of the Semi Grand Canonical Monte Carlo simulation method in the context of the primitive model. Three models describing a discrete distribution of charged functional groups on the polyelectrolyte and different values for the radius of the background electrolyte spanning from ionic to hydrated radii values were analyzed. The polyelectrolyte titrations were simulated by calculating the degree of ionization versus pH curves at two ionic strengths. The results allow us to quantify the impact of the sizes of the background salt ions and surface functional groups of the polyelectrolyte on the dissociation degree. This influence is explained in terms of the effectiveness of the screening of the charged surface sites. Finally, by comparison with the Non-Linear Poisson–Boltzmann model, the influence of ionic correlations and finite size of the solution ions is assessed. 相似文献
94.
M. Salvador J. Prauzner S. K?ber K. Meerholz 《Applied physics. B, Lasers and optics》2011,102(4):803-807
The effect of beam walk-off is known to reduce the overlap region of the writing beams in coherence domain holographic imaging. In photorefractive (PR) polymer devices this problem is particularly pronounced because of the restrictions that are imposed by the slanted recording geometry. Here, we demonstrate that by optically demagnifying the image bearing signal beam the field of view can be enhanced by a factor of 8. In addition, we found that the area ratio of the writing and readout beams determines both the PR performance and the depth resolution. In a second approach, we show that by changing the recording geometry from transmission to reflection the field of view can be almost fully recovered. 相似文献
95.
Gustavo Nicolodelli Cristina KurachiVanderlei Salvador Bagnato 《Applied Surface Science》2011,257(7):2419-2422
Femtosecond laser ablation of materials is turning to be an important tool for micromachining as well as for selective removal of biological tissues. In a great number of applications, laser ablation has to process through interfaces separating media of different properties. The investigation of the ablation behavior within materials and passing through interfaces is the main aim of this study. Especially, the analysis of the discontinuity in the ablation profile close to interfaces between distinct materials can reveal some of the phenomena involved in the formation of an ablated microcavity geometry. We have used a method that correlates the ablation cross sectional area with the local laser intensity. The effective intensity ablation properties were obtained from surface ablation data of distinct materials. The application of this method allows the prediction of the occurrence of a size discontinuity in the ablation geometry at the interface of distinct media, a fact which becomes important when planning applications in different media. 相似文献
96.
For a given convex body K in
\Bbb R3{\Bbb R}^3
with C
2 boundary, let P
c
n
be the circumscribed polytope of minimal volume with at most n edges, and let P
i
n
be the inscribed polytope of maximal volume with at most n edges. Besides presenting an asymptotic formula for the volume difference as n tends to infinity in both cases, we prove that the typical faces of P
c
n
and P
i
n
are asymptotically regular triangles and squares, respectively, in a suitable sense. 相似文献
97.
Christiane Werner Frederik Wegener Stephan Unger Salvador Nogués Pierrick Priault 《Rapid communications in mass spectrometry : RCM》2009,23(16):2428-2438
Recent advances in understanding the metabolic origin and the temporal dynamics in δ13C of dark‐respired CO2 (δ13Cres) have led to an increasing awareness of the importance of plant isotopic fractionation in respiratory processes. Pronounced dynamics in δ13Cres have been observed in a number of species and three main hypotheses have been proposed: first, diurnal changes in δ13C of respiratory substrates; second, post‐photosynthetic discrimination in respiratory pathways; and third, dynamic decarboxylation of enriched carbon pools during the post‐illumination respiration period. Since different functional groups exhibit distinct diurnal patterns in δ13Cres (ranging from 0 to 10‰ diurnal increase), we explored these hypotheses for different ecotypes and environmental (i.e. growth light) conditions. Mass balance calculations revealed that the effect of respiratory substrates on diurnal changes in δ13Cres was negligible in all investigated species. Further, rapid post‐illumination changes in δ13Cres (30 min), which increased from 2.6‰ to 5‰ over the course of the day, were examined by positional 13C‐labelling to quantify changes in pyruvate dehydrogenase (PDH) and Krebs cycle (KC) activity. We investigated the origin of these dynamics with Rayleigh mass balance calculations based on theoretical assumptions on fractionation processes. Neither the estimated changes of PDH and KC, nor decarboxylation of a malate pool entirely explained the observed pattern in δ13Cres. However, a Rayleigh fractionation of 12C‐discriminating enzymes and/or a rapid decline in the decarboxylation rate of an enriched substrate pool may explain the post‐illumination peak in δ13Cres. These results are highly relevant since δ13Cres is used in large‐scale carbon cycle studies. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
98.
99.
Laura Escuder‐Gilabert María Amparo Martínez‐Gómez Rosa María Villanueva‐Camañas Salvador Sagrado María José Medina‐Hernández 《Biomedical chromatography : BMC》2009,23(3):225-238
Stereoselectivity in protein binding can have a significant effect on the pharmacokinetic and pharmacodynamic properties of chiral drugs. The investigation of enantioselectivity of drugs in their binding with human plasma proteins and the identification of the molecular mechanisms involved in the stereodiscrimination by the proteins represent a great challenge for clinical pharmacology. In this review, the separation techniques used for enantioselective protein binding experiments are described and compared. An overview of studies on enantiomer–protein interactions, enantiomer–enantiomer interactions as well as chiral drug–drug interactions, including allosteric effects, is presented. The contribution of individual plasma proteins to the overall enantioselective binding and the animal species variability in drug–plasma protein binding stereoselectivity are reviewed. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
100.
Torres MF Sales PS de Rossi RH Fernández MA 《Langmuir : the ACS journal of surfaces and colloids》2010,26(23):17858-17866
The mixed system of a nonionic hydrocarbon surfactant, polyoxyethylene (23) lauryl ether (Brij-35), and a perfluorinated surfactant, perfluorononanoic acid, was investigated by a combination of methods. The critical micelle concentrations (cmc's) have been determined over a wide range of sample compositions by fluorescence and UV-visible spectrophotometry using pyrene and N-(4-nitrophenyl) perfluorononanamide, respectively, as molecular probes. The values of the cmc's obtained were considerably different with the two techniques employed. Measurements of the (19)F nuclear magnetic resonance chemical shift of the same mixtures showed two breaks in the plots of Δδ(f) versus molar fraction of the perfluorinated surfactant. Conductivity and surface tension measurements also showed two breaks. The behavior is attributed to the formation of mixed micelles that change their composition when the fraction of the fluorinated compound increases and some segregation of the fluorinated compound takes place at a high total surfactant concentration. 相似文献