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91.
By means of ADE-FDTD method, this paper investigates the electromagnetic modelling of a rib-loaded waveguide composed of a
Nd3+ doped Silicon Rich Silicon Oxide active layer sandwiched between a SiO2 bottom cladding and a SiO2 rib. The Auxilliary Differential Equations are the rate equations which govern the levels populations. The Finite Difference
Time Domain (FDTD) scheme is used to solve the space and time dependent Maxwell equations which describe the electromagnetic
field in a copropagating scheme of both pumping (λ
pump
= 488 nm) and signal (λ
signal
= 1064 nm) waves. Such systems are characterized by extremely different specific times such as the period of electromagnetic
field ~ 10-15 s and the lifetimes of the electronic levels between ~ 10-10s and ~ 10-4 s. The time scaling method is used in addition to specific initial conditions in order to decrease the computational time.
We show maps of the Poynting vector along the propagation direction as a function of the silicon nanograin (Si-ng) concentrations.
A threshold value of 1024 Si-ng m-3 is extracted below which the pump wave can propagate so that a signal amplication is possible. 相似文献
92.
93.
In this article, the microstructure and photoluminescence (PL) properties of Nd-doped silicon-rich silicon oxide (SRSO) are
reported as a function of the annealing temperature and the Nd concentration. The thin films, which were grown on Si substrates
by reactive magnetron co-sputtering, contain the same Si excess as determined by Rutherford backscattering spectrometry. Fourier
transform infrared (FTIR) spectra show that a phase separation occurs during the annealing because of the condensation of
the Si excess resulting in the formation of silicon nanoparticles (Si-np) as detected by high-resolution transmission electron
microscopy and X-ray diffraction (XRD) measurements. Under non-resonant excitation at 488 nm, our Nd-doped SRSO films simultaneously
exhibited PL from Si-np and Nd3+ demonstrating the efficient energy transfer between Si-np and Nd3+ and the sensitizing effect of Si-np. Upon increasing the Nd concentration from 0.08 to 4.9 at.%, our samples revealed a progressive
quenching of the Nd3+ PL which can be correlated with the concomitant increase of disorder within the host matrix as shown by FTIR experiments.
Moreover, the presence of Nd-oxide nanocrystals in the highest Nd-doped sample was established by XRD. It is, therefore, suggested
that the Nd clustering, as well as disorder, are responsible for the concentration quenching of the PL of Nd3+. 相似文献
94.
Imène Lahouij Fabrice Dassenoy Ludvig de Knoop Jean-Michel Martin Béatrice Vacher 《Tribology Letters》2011,42(2):133-140
Inorganic fullerene-(IF)-like nanoparticles made of metal dichalcogenides (IF-MoS2, IF-WS2) have been known to be effective as anti-wear and friction modifier additives under boundary lubrication. The lubrication
mechanism of these nanoparticles has been widely investigated in the past and even if the exfoliation and third body transfer
of molecular sheets onto the asperities constitute the prevalent mechanism for the improved tribological behavior of IF nanoparticles,
it has also been suggested that a rolling friction process could also play a role for well crystallized and spherical particles.
In this study, in situ Transmission Electron Microscopy (TEM) observations of the behavior of single IF-MoS2 nanoparticles were conducted using a sample holder that combines TEM and Atomic Force Microscopy (AFM) which simultaneously
can apply normal and shear loads. It was shown that depending on the test conditions, either a rolling process or a sliding
of the fullerenes could be possible. These in situ TEM observations are the first carried out with IF nanoparticles. 相似文献
95.
Dehkordi VR Daou H Labeau F 《IEEE transactions on information technology in biomedicine》2011,15(6):831-838
In this paper, a method is proposed to compress multichannel electroencephalographic (EEG) signals in a scalable fashion. Correlation between EEG channels is exploited through clustering using a k-means method. Representative channels for each of the clusters are encoded individually while other channels are encoded differentially, i.e., with respect to their respective cluster representatives. The compression is performed using the embedded zero-tree wavelet encoding adapted to 1-D signals. Simulations show that the scalable features of the scheme lead to a flexible quality/rate tradeoff, without requiring detailed EEG signal modeling. 相似文献
96.
97.
98.
Mongin D Juvé V Maioli P Crut A Del Fatti N Vallée F Sánchez-Iglesias A Pastoriza-Santos I Liz-Marzán LM 《Nano letters》2011,11(7):3016-3021
The acoustic vibrations of metal nanoparticles encapsulated in a dielectric shell (Ag@SiO(2)) were investigated using a time-resolved femtosecond technique. The measured vibration periods significantly differ from those predicted for the bare metal cores and, depending on the relative core and shell sizes, were found to be either larger or smaller than them. These results show that the vibration of the whole core-shell particle is excited and detected. Moreover, vibrational periods are in excellent agreement with the predictions of a model based on continuum thermoelasticity. However, such agreement is obtained only if a good mechanical contact of the metal and dielectric parts of the core-shell particle is assumed, providing a unique way to probe this contact in multimaterial or hybrid nano-objects. 相似文献
99.
Multifractal functions are widely used to model irregular signals such as turbulence, data stream or road traffic. Here, we
consider multifractal functions defined as lacunar wavelet series observed in a white noise model. These random functions
are statistically characterized by two parameters. The first parameter governs the intensity of the wavelet coefficients while
the second one governs its sparsity. We construct estimators of these two parameters and discuss statistical properties of
this important model: the rate of the Fisher information and a testing procedure to check the multifractal feature of an observed
noisy signal.
相似文献
100.
G Fischer V Mutel G Trube P Malherbe JN Kew E Mohacsi MP Heitz JA Kemp 《Canadian Metallurgical Quarterly》1997,283(3):1285-1292
The interaction of Ro 25-6981 with N-methyl-D-aspartate (NMDA) receptors was characterized by a variety of different tests in vitro. Ro 25-6981 inhibited 3H-MK-801 binding to rat forebrain membranes in a biphasic manner with IC50 values of 0.003 microM and 149 microM for high- (about 60%) and low-affinity sites, respectively. NMDA receptor subtypes expressed in Xenopus oocytes were blocked with IC50 values of 0.009 microM and 52 microM for the subunit combinations NR1C & NR2B and NR1C & NR2A, respectively, which indicated a >5000-fold selectivity. Like ifenprodil, Ro 25-6981 blocked NMDA receptor subtypes in an activity-dependent manner. Ro 25-6981 protected cultured cortical neurons against glutamate toxicity (16 h exposure to 300 microM glutamate) and combined oxygen and glucose deprivation (60 min followed by 20 h recovery) with IC50 values of 0.4 microM and 0.04 microM, respectively. Ro 25-6981 was more potent than ifenprodil in all of these tests. It showed no protection against kainate toxicity (exposure to 500 microM for 20 h) and only weak activity in blocking Na+ and Ca++ channels, activated by exposure of cortical neurons to veratridine (10 microM) and potassium (50 mM), respectively. These findings demonstrate that Ro 25-6981 is a highly selective, activity-dependent blocker of NMDA receptors that contain the NR2B subunit. 相似文献