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71.
72.
Jiawang Zhou Ljiljana Stojanovi Andrey A. Berezin Tommaso Battisti Abigail Gill Benson M. Kariuki Davide Bonifazi Rachel Crespo-Otero Michael R. Wasielewski Yi-Lin Wu 《Chemical science》2021,12(2):767
Development of purely organic materials displaying room-temperature phosphorescence (RTP) will expand the toolbox of inorganic phosphors for imaging, sensing or display applications. While molecular solids were found to suppress non-radiative energy dissipation and make the RTP process kinetically favourable, such an effect should be enhanced by the presence of multivalent directional non-covalent interactions. Here we report phosphorescence of a series of fast triplet-forming tetraethyl naphthalene-1,4,5,8-tetracarboxylates. Various numbers of bromo substituents were introduced to modulate intermolecular halogen-bonding interactions. Bright RTP with quantum yields up to 20% was observed when the molecule is surrounded by a Br⋯O halogen-bonded network. Spectroscopic and computational analyses revealed that judicious heavy-atom positioning suppresses non-radiative relaxation and enhances intersystem crossing at the same time. The latter effect was found to be facilitated by the orbital angular momentum change, in addition to the conventional heavy-atom effect. Our results suggest the potential of multivalent non-covalent interactions for excited-state conformation and electronic control.The number and position of halogen substituents in purely organic π–π* chromophores critically affect the efficiency of phosphorescence. 相似文献
73.
Salvatore Abate Yun Gyong Ahn Tobias Kind Tommaso R. I. Cataldi Oliver Fiehn 《Rapid communications in mass spectrometry : RCM》2010,24(8):1172-1180
Many metabolomic applications use gas chromatography/mass spectrometry (GC/MS) under standard 70 eV electron ionization (EI) parameters. However, the abundance of molecular ions is often extremely low, impeding the calculation of elemental compositions for the identification of unknown compounds. On changing the beam‐steering voltage of the ion source, the relative abundances of molecular ions at 70 eV EI were increased up to ten‐fold for alkanes, fatty acid methyl esters and trimethylsilylated metabolites, concomitant with 2‐fold absolute increases in ion intensities. We have compared the abundance, mass accuracy and isotope ratio accuracy of molecular species in EI with those in chemical ionization (CI) with methane as reagent gas under high‐mass tuning. Thirty‐three peaks of a diverse set of trimethylsilylated metabolites were analyzed in triplicate, resulting in 342 ion species ([M+H]+, [M–CH3]+ for CI and [M]+ . , [M–CH3]+ . for EI). On average, CI yielded 8‐fold more intense molecular species than EI. Using internal recalibration, average mass errors of 1.8 ± 1.6 mm/z units and isotope ratio errors of 2.3 ± 2.0% (A+1/A ratio) and 1.7 ± 1.8% (A+2/A ratio) were obtained. When constraining lists of calculated elemental compositions by chemical and heuristic rules using the Seven Golden Rules algorithm and PubChem queries, the correct formula was retrieved as top hit in 60% of the cases and within the top‐3 hits in 80% of the cases. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
74.
M.V. Bartuccelli J.H.B. Deane G. Gentile F. Schilder 《Nonlinear Analysis: Real World Applications》2010,11(5):3344-3362
In this paper we consider a resonant injection-locked frequency divider which is of interest in electronics, and we investigate the frequency locking phenomenon when varying the amplitude and frequency of the injected signal. We study both analytically and numerically the structure of the Arnol’d tongues in the frequency–amplitude plane. In particular, we provide exact analytical formulae for the widths of the tongues, which correspond to the plateaux of the devil’s staircase picture. The results account for numerical and experimental findings presented in the literature for special driving terms and, additionally, extend the analysis to a more general setting. 相似文献
75.
76.
77.
m moments and of degree . For such theories the entropy principle is still valid only, if the non equilibrium field variables and their derivatives
are sufficiently small with respect to the required approximation order. In this paper we prove through simple examples of
stationary problems that the entropy principle fails in general, if all the non-equilibrium variables are of the same order
of magnitude. This is due to the fact that there exist some derivatives of non equilibrium variables (critical derivatives) that are not small along all the solutions. This property can be used to fix the non controllable boundary data in such
a manner that the critical derivatives are kept small for the solution that we may choose. Thus, for the stationary unidimensional
case we propose the requirement that the critical derivatives vanish on the boundary, eventually with some successive derivatives. This is a sufficient condition for the validity of the
entropy principle at least in a neighborhood of the boundary and makes it possible to assign the non controllable data in
a simple manner when the number of moments is greater than 13. We have tested this procedure in several cases of theories, showing that the criterion implies continuity with respect to the change of the moment number and to the truncation
order. In particular for the planar unidimensional heat conduction problem we have obtained a behavior for the temperature
that is always the same as the one predicted by the classical Fourier law. This result is in evident contrast with the minimax
principle expectation. However we have qualitative differences between the temperature behavior described by Extended Thermodynamics
and the one by Fourier-Navier-Stokes theory for heat conduction in radial symmetry.
Received June 25, 2001 / Published online February 28, 2002 相似文献
78.
We consider a system of N balance laws compatible with an entropy principle and convex entropy density. Using the special symmetric form induced by
the main field, we define the concept of principal subsystem associated with the system. We prove that the 2
N
−2 principal subsystems are also symmetric hyperbolic and satisfy a subentropy law. Moreover we can verify that for each principal subsystem the maximum (minimum) characteristic velocity is not larger (smaller)
than the maximum (minimum) characteristic velocity of the full system. These are the subcharacteristic conditions. We present
some simple examples in the case of the Euler fluid. Then in the case of dissipative hyperbolic systems we consider an equilibrium
principal subsystem and we discuss the consequences in the setting of extended thermodynamics. Finally in the moments approach
to the Boltzmann equation we prove, as a consequence of the previous result, that the maximum characteristic velocity evaluated
at the equilibrium state does not decrease when the number of moments increases.
(Accepted October 6, 1995) 相似文献
79.
80.
Muniz-Miranda M Del Rosso T Giorgetti E Margheri G Ghini G Cicchi S 《Analytical and bioanalytical chemistry》2011,400(2):361-367
We investigated the chemisorption of self-assembled monolayers of sulfur-functionalized 4-amino-7-nitrobenzofurazan on gold
and silver nanoisland films (NIFs) by means of surface-enhanced fluorescence (SEF) and surface-enhanced Raman scattering (SERS).
The ligand is a push–pull molecule, where an intramolecular charge transfer occurs between an electron-donor and an electron-acceptor
group, thus exhibiting nonlinear optical properties that are related to both SERS and SEF effects. The presence of different
heteroatoms in the molecule ensures the possibility of chemical interaction with both silver and gold substrates. The SERS
spectra suggest that furazan is bound to silver via lone pairs of the nitrogen atoms, whereas the ligand is linked to gold
via a sulfur atom. Silver NIFs provide more efficient enhancement of both fluorescence and Raman scattering in comparison
with gold NIFs. The present SEF and SERS investigation could provide useful information for foreseeing changes in the nonlinear
responses of this push–pull molecule. 相似文献