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1.
The fragmentation patterns of 24 substituted phenyltrifluoromethanesulfonates has been determined by exact mass and metastable transition measurements. The influence of the ring substituent(s) on the abundance of the [ArO]+ ions has been investigated at low energies and a new standard parameter for plotting against Hammett's ó constants is proposed. The direct loss of CF3SO3 from the molecular ion of 3,5-(diisopropyl)-phenyl-, 3,5-(dicyclopropyl)phenyl- and 3,5-di(α-methylcyclopropyl)-phenyl-methanesulfonate, and further observations on the fragmentation processes of these compounds are consistent with M.O. calculations on the ‘through bond’ stabilization of the [Ar]+ σ state by meta electron donor substituents. 相似文献
2.
Olivia Vidoni Stefan Neumeier Nathalie Bardou Jean-Luc Pelouard Günter Schmid 《Journal of Cluster Science》2003,14(3):325-336
The elaboration of closed-packed monolayers of Au55(PPh3)12Cl6 clusters on oxidized and non-oxidized GaAs surfaces is reported. The first part of this work describes the use of silanethiol modified GaAs oxide surfaces to trap 18 nm gold colloids and Au55(PPh3)12Cl6 clusters. The surfaces characterized by AFM measurements present high-quality coverage on a quite long range for both metallic species. The second part is devoted to the elaboration of Au55(PPh3)12Cl6 cluster monolayers on non-oxidized p-type GaAs substrates, functionalized with dithiol molecules. AFM measurements demonstrate the presence of closed-packed two-dimensional arrangements of Au55 clusters. 相似文献
3.
Groundstate absorption, fluorescence, excited-state absorption, and stimulated emission of Pr:YA1O3 were measured in dependence on the polarization. The results reflect the anisotropy of the host lattice. Especially the polarized spectra of the stimulated emission fit very well with the laser data of this material. Seven cw laser transitions in the visible spectral range obtained so far in Pr:YA1O3 with argon-ion laser pumping were identified in the spectra of the stimulated emission. In addition, two infrared cw laser transitions were realized. The best results were achieved for the3
P
03
F
4 laser transition at 746.9 nm with a maximum slope efficiency of 24.6%, a maximum output power of 49.6 mW, and a laser threshold of 25 mW. 相似文献
4.
Jean-Luc Derocque 《Journal of mass spectrometry : JMS》1975,10(2):81-88
In the particular case where a specific ion [c]+· is generated with different internal energy, the variation of Z(E) = [(f)+]/[(c)+·] vs energy of the electron beam is discussed in relation to the P(Ei) and k(Ei) functions which describe the decay process [c]+· → [f]+. Qualitative application to seven isomeric hydrocarbons suggests that, among these isomers, two pairs might rearrange to a common intermediate before fragmentation occurs. It is found that in such cases the curves Z = f(E) for a given fragmentation are not superimposable but parallel, as suggested by theoretical considerations. 相似文献
5.
Jean-Claude Fiaud Bernard Denner Jean-Luc Malleron 《Journal of organometallic chemistry》1985,291(3):393-402
Various mono- and di-substituted cyclopentadienes have been prepared by palladium-catalyzed alkylation of allylic esters with cyclopentadienide and t-butyl-cyclopentadienide anions. The same procedure has been applied to the preparation of substituted indenes. 相似文献
6.
A simple equation has been derived relating the temperature dependence of activity functions with excess enthalpies and excess heat capacities. Using experimentally determined parameters at 298.15°K, it is possible to predict osmotic coefficients and mean activity coefficients of alkali halides in water up to 1 m from 273°K to about 350°K. In general, the predicted functions agree with the measured values within the uncertainty of the activity data. An equation is also given for the pressure dependence of the excess free energies, but it was not possible to check the limitation of this equation due to lack of activity data at various pressures.To whom correspondence should be addressed. 相似文献
7.
Jean-Luc Decout Alain Lablache-Combier Claude Loucheux 《Journal of polymer science. Part A, Polymer chemistry》1980,18(7):2371-2390
Vinylpyridine-N-oxide units were introduced in polymeric chains in order to study their photocrosslinking. Copolymers of styrene and 4-vinylpyridine-N-oxide were especially synthesized and studied. The methods used for characterization of photocrosslinked films were a “photoresist test” or the measurement of the insolubility and of the swelling ratio. The Cleavage of the N-oxide bond was responsible for the photocrosslinking. The competitive formation of carbonyl compounds took place and decreased the rate of photocrosslinking. This last reaction is favored by triplet-state quenchers. The photosensitivity of the copolymers was determined as a function of the wavelength of the radiation used. When the photocrosslinking proceeded, a film of the copolymeric material became transparent in the 280–320-nm range. Thick films could therefore be completely photocrosslinked when irradiated in this range of wavelength. 相似文献
8.
Hans Fritz Rolf Gleiter Michel Nastasi Jean-Luc Schuppiser Jacques Streith 《Helvetica chimica acta》1978,61(8):2887-2898
3-Substituted 1-iminopyridinium ylides 1 undergo photo-induced ring enlargement to 1H-1,2-diazepines. With strongly electron-withdrawing substituents the ring expansion process is regiospecific and leads exclusively to 4-substituted 1 H-1, 2-diazepines. Weak electron-donating substituents, like a methyl group and halogen atoms, do not have any directing effect since both 4- and 6-substituted 1 H -1,2-diazepines are obtained. With strong electron-donating substituents no diazepines are formed; instead one observes photo-induced isomerization to the 2-aminopyridine derivatives, the process being non-regiospecific. Regiospecific photo-induced ring expansion processes are explained in terms of a simple HMO model. 相似文献
9.
This paper studies the focusing of high-frequency solutions of semilinear hyperbolic equations. In previous papers, we studied two opposite phenomena. First, the focusing of nonlinear waves can force the solutions to blow up, even before reaching the caustics. Second, for strongly dissipative equations, nonlinear oscillations can be completely absorbed when they reach the caustic set. In this paper, we study the intermediate case of equations with globally Lipschitz nonlinearities. The nonlinear oscillations persist after crossing the caustic set. The solutions are described using oscillatory integrals, which are associated with Lagrangian manifolds in the cotangent bundle. The equations of nonlinear geometric optics lift to these manifolds. In contrast to the linear case, the transport equations for amplitudes living above the same points of spacetime are coupled. © 1996 John Wiley & Sons, Inc. 相似文献
10.
We proceed with our study of increasing self-described sequences F, beginning with 1 and defined by a functional equation
In [1] we exhibited the simple solution f (t)=Ct, for some (0,1), of the associated functional-differential equation
and we proved that provided <2/(2+d()), where
we have the asymtotic equivalence F(m)~ Cm.In the present paper we show that this last result is optimal, in the sense that the self-described sequence defined by |F–1(m)|=F(m)2, that is
for which the boundary case =2/(2+d())(=1/2) holds, does not satisfy F(m) ~ Cm. We also show that the m-th term F(m) of a sequence F for which the boundary case holds is nevertheless of asymptotic order m.Then we investigate the behaviour of self-described sequences F when lies beyond the boundary case. In [1] we established the estimates
when is the unique fixed point of a certain associated function. We were only able to prove in general that the latter holds when does not lie beyond the boundary case, however. In the present paper we prove that whenever
is the unique fixed point of this function, and in addition we obtain estimates more precise than (*). This applies for instance to the sequence defined by
that is
相似文献