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381.
LiNbO3 waveguides with Si overlays are emerging as a basic building block for a variety of integrated-optic components, including modulators, high-efficiency gratings, and narrowband WDM filters. However, the development and optimization of these devices are, in large part, hindered by the lack of understanding of the specifics of the Si-on-LiNbO3 structure which appear to differ dramatically from those of the Si and LiNbO3 waveguides, considered separately. In this work, we provide a specific insight into the waveguiding properties of vertically stacked Si-on-LiNbO3 waveguides. In particular, we present a detailed theoretical analysis of the effect of the Si film on the modal characteristics (propagation constant and field distribution) of the structure. The vectorial finite element method (VFEM) is used to numerically investigate a step-index and graded-index single-mode channel waveguide in LiNbO3, with a Si or Si/SiO2 multimode overlay. We show that for ~70% of all Si thicknesses, in the range from 0 to 1.6 μm, the highest order normal mode of the entire structure has more than 99.9% of the total energy confined in the LiNbO3 region, i.e., beneath the Si overlay. This fact is quite intriguing given the fact a planar Si layer of submicron thickness on bulk LiNbO3 is already multimoded. Furthermore, we show that the effective mode index of the structure is considerably modified compared to that of the LiNbO3 waveguide while the propagation loss is, on the other hand, practically unaffected (~0.3 dB/cm) even in the presence of the lossy Si film, as confirmed by our previous experimental results. Evidently, large modulation of the effective index and low-loss propagation provide an ideal combination of properties suitable for the fabrication of high-reflectance corrugated waveguide gratings, essential for a number of practical devices, in particular, WDM filters  相似文献   
382.
The potential energy constants and the mean amplitudes of vibration for NO2F and N2O4 were evaluated using the method of Green's function analysis. The rotational distortion constants and the Coriolis coupling constants were also evaluated for NO2F.  相似文献   
383.
384.
Summary The characteristic strong absorption infrared band near 720–725 cm–1 of an open chain methylene group of the type (CH2) n (n = 4 or more) has been used to estimate the number of n-paraffinic methylene groups in an average molecule of saturates, urea adductables and non-adductables of various gas-oil and vacuum gas oil fractions. The method was developed by computing the average absorptivity at 725 cm–1 of several pure n-paraffins (C14-C32). Although the interference due to the aromatic C — H band at 740 cm–1 disturbs the estimation of shorter chains, it is seen from the data on adductables and non-adductables that the estimation can be done in long chain paraffins even in the presence of aromatics.
Bestimmung von n-Paraffinstrukturen in Erdölfraktionen mit Hilfe der Infrarot-Spektroskopie
Zusammenfassung Die charakteristische starke IR-Absorptionsbande der paraffinischen Methylengruppe des Typs (CH2) n (n = 4 oder mehr) bei 720–725cm–1 wurde zur Bestimmung der Anzahl von Methylengruppen in einem durchschnittlichen Molekül von gesättigten Kohlenwasserstoffen, Harnstoffprodukten sowie Nicht-Addukten verschiedener Gasöl- und Vakuum-Gasöl-Fraktionen benutzt. Das Verfahren wurde durch Berechnung der durchschnittlichen Extinktion bei 725 cm–1 von mehreren reinen n-Paraffmen (C14-C32) entwickelt. Wenn auch die Bestimmung kürzerer Ketten durch die aromatische C — H-Bande bei 740 cm–1 gestört wird, so ergibt sich doch aus den Werten für Addukte und Nicht-Addukte, daß die Bestimmung bei langkettigen Paraffinen selbst in Gegenwart von Aromaten durchgeführt werden kann.
  相似文献   
385.
We establish uniqueness or comparison results for a class of Hamilton-Jacobi equations and give characterizations of maximal solutions of Hamilton-Jacobi equations. The results are applied to characterizing value functions of exit time problems in optimal control.  相似文献   
386.
EEG Based Biometric Framework for Automatic Identity Verification   总被引:1,自引:0,他引:1  
The energy of brain potentials evoked during processing of visual stimuli is considered as a new biometric. In particular, we propose several advances in the feature extraction and classification stages. This is achieved by performing spatial data/sensor fusion, whereby the component relevance is investigated by selecting maximum informative (EEG) electrodes (channels) selected by Davies–Bouldin index. For convenience and ease of cognitive processing, in the experiments, simple black and white drawings of common objects are used as visual stimuli. In the classification stage, the Elman neural network is employed to classify the generated EEG energy features. Simulations are conducted by using the hold-out classification strategy on an ensemble of 1,600 raw EEG signals, and 35 maximum informative channels achieved the maximum recognition rate of 98.56 ± 1.87%. Overall, this study indicates the enormous potential of the EEG biometrics, especially due to its robustness against fraud.
Danilo P. MandicEmail:
  相似文献   
387.
Diorganotin dichloride-phosphonic diamide complex, [Ph2SnCl2(tBuP(O)(NHiPr)2)2] (1), is prepared by the addition of two equivalents of tBuP(O)(NHiPr)2 to one equivalents of Ph2SnCl2 either in the presence or absence of triethylamine. Compound 1 is a rare example of an all-trans SnA2B2C2 complex that contains H-bonded six-membered rings which are made up of six different main group elements.  相似文献   
388.
Ortho‐carboxylate effects in Ullmann type nucleophilic substitution reactions were found to be much more pronounced as compared to those of other substituent and steric factors. In this study, we propose an ortho halogen assisted intramolecular oxidative addition‐reductive elimination mechanism that fits our experimental observations. Experimental data has been generated with halothiophenecarboxylic acids and halobenzoic acids by performing copper‐mediated nucleophilic substitution with scant referred sodium bisulphite as nucleophile under aqueous conditions. The novel mechanism was used to establish a new and improved process for preparation of monopotassium salts of 3‐sulphothiophene‐2‐carboxylic acid, 2‐sulphobenzoic acid, and 5‐sulphothiophene‐2‐carboxylic acid. These monopotassium salts are critical intermediates and building blocks in the preparation of several therapeutically valuable drugs. The differences in reactivity between the halogens, chlorine and bromine was utilized to prepare aryl ethers including 2‐acetyl‐3‐phenoxythiophene and 2‐acetyl‐3‐(m‐tolyloxy)thiophene that have not been reported in literature so far.  相似文献   
389.
Rainbow Connection Number and Radius   总被引:1,自引:0,他引:1  
The rainbow connection number, rc(G), of a connected graph G is the minimum number of colours needed to colour its edges, so that every pair of its vertices is connected by at least one path in which no two edges are coloured the same. In this note we show that for every bridgeless graph G with radius r, rc(G) ≤  r(r + 2). We demonstrate that this bound is the best possible for rc(G) as a function of r, not just for bridgeless graphs, but also for graphs of any stronger connectivity. It may be noted that for a general 1-connected graph G, rc(G) can be arbitrarily larger than its radius (K 1,n for instance). We further show that for every bridgeless graph G with radius r and chordality (size of a largest induced cycle) k, rc(G) ≤  rk. Hitherto, the only reported upper bound on the rainbow connection number of bridgeless graphs is 4n/5 ? 1, where n is order of the graph (Caro et al. in Electron J Comb 15(1):Research paper 57, 13, 2008). It is known that computing rc(G) is NP-Hard (Chakraborty and fischer in J Comb Optim 1–18, 2009). Here, we present a (r + 3)-factor approximation algorithm which runs in O(nm) time and a (d + 3)-factor approximation algorithm which runs in O(dm) time to rainbow colour any connected graph G on n vertices, with m edges, diameter d and radius r.  相似文献   
390.
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