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11.
Operator dependence of 3-D ultrasound-based computational fluid dynamics for the carotid bifurcation 总被引:2,自引:0,他引:2
Glor FP Ariff B Hughes AD Verdonck PR Thom SA Barratt DC Xu XY 《IEEE transactions on medical imaging》2005,24(4):451-456
The association between vascular wall shear stress (WSS) and the local development of atherosclerotic plaque makes estimation of in vivo WSS of considerable interest. Three-dimensional ultrasound (3DUS) combined with computational fluid dynamics (CFD) provides a potentially valuable tool for acquiring subject-specific WSS, but the interoperator and intraoperator variability associated with WSS calculations using this method is not known. Here, the accuracy, reproducibility and operator dependence of 3DUS-based computational fluid dynamics were examined through a phantom and in vivo studies. A carotid phantom was scanned and reconstructed by two operators. In the in vivo study, four operators scanned a healthy subject a total of 11 times, and their scan data were processed by three individuals. The study showed that with some basic training, operators could acquire accurate carotid geometry for flow reconstructions. The variability of measured cross-sectional area and predicted shear stress was 8.17% and 0.193 N/m/sup 2/ respectively for the in vivo study. It was shown that the variability of the examined parameters was more dependent on the scan operators than the image processing operator. The range of variability of geometrical and flow parameters reported here can be used as a reference for future in vivo studies using the 3DUS-based CFD approach. 相似文献
12.
13.
We study an index calculus algorithm to solve the discrete logarithm problem (DLP) in degree 0 class groups of non-hyperelliptic
curves of genus 3 over finite fields. We present a heuristic analysis of the algorithm which indicates that the DLP in degree 0
class groups of non-hyperelliptic curves of genus 3 can be solved in an expected time of
. This heuristic result relies on one heuristic assumption which is studied experimentally.
We also present experimental data which show that a variant of the algorithm is faster than the Rho method even for small
group sizes, and we address practical limitations of the algorithm. 相似文献
14.
Daniel Coillot François O. Méar Renaud Podor Lionel Montagne 《Advanced functional materials》2010,20(24):4371-4374
A new process that enables glassy materials to self‐repair from mechanical damage is presented in this paper. Contrary to intrinsic self‐healing, which involves overheating to enable crack healing by glass softening, this process is based on an extrinsic effect produced by vanadium boride (VB) particles dispersed within the glass matrix. Self‐repair is obtained through the oxidation of VB particles, and thus without the need to increase the operating temperature. The VB healing agent is selected for its capacity to oxidize at a lower temperature than the softening point of the glass. Thermogravimetric analyses indeed show that VB oxidation is rapid and occurs below the glass transition temperature. Solid‐state nuclear magnetic resonance spectroscopy indicates that VB is oxidized into V2O5 and B2O3, which enable the local formation of glass. The autonomic self‐healing effect is demonstrated by an in situ experiment visualized using an environmental scanning electron microscope. It is shown that a crack could be healed by the VB oxidation products. 相似文献
15.
Wireless Networks - Most existing connectivity-based localization algorithms require high node density which is unavailable in many large-scale sparse mobile networks. By analyzing large datasets... 相似文献
16.
A theoretical analysis of the predicted performance and field distributions for semiconductor junction circulators is based on Bosma's Green's function approach which involves a summation of infinite series in the mathematical derivation. The effects are considered of taking a different number of terms in the series, looking at three different circulators centred at 120 GHz. The narrowband semiconductor circulators show a similar effect to the ferrite junction circulator because the field distributions inside the semiconductor discs can be approximated by only considering the dominant modes. However, there is no dominant mode in the broadband circulator and the higher order modes play an important role in the operation of this circulator. In order to obtain a precise representation of the circulation effects inside both narrowband and broadband circulators, at least up to the 6th term, or 18 terms in all, are required to be added in the summation of Green's functions. 相似文献
17.
This paper investigates the morphology changes that occur with the oxidation of a ti-tanium silicide—polysilicon system. These
changes were studied as a function of poly-silicon doping and silicide formation parameters. Emphasis was placed on transmission
electron microscopy studies of the samples by planar and cross sectional techniques. Various surface analysis methods have
also been used to characterize the films. This study helps to define the possible use and shortcomings of a self aligned titanium
silicide insulator. The results show that varying quality insulators result, dependent largely on the initial conditions of
the titanium silicide. After oxidation the Auger and TEM anal-ysis show that in all cases some form of silicon dioxide was
created, but typically a considerable amount of titanium oxide was also present. For instance, it was apparent that more titanium
oxide formed on the samples RTA’ed for 1 min at 700° C than the 5 min at 800° C and considerably more on the arsenic doped
sample than the boron doped. The silicide also had morphology changes as the result of the oxidation. There was a phase change
from the C49 to C54 phase for the 1 min at 700° C samples as would be expected at the time and temperature of the oxidation.
There also was a sig-nificant amount of agglomeration and epitaxial growth observed. Further work is re-quired to completely
characterize these phenomena. 相似文献
18.
Implementing polarization shift keying over satellite – system design and measurement results 下载免费PDF全文
Lionel Arend Ray Sperber Michel Marso Jens Krause 《International Journal of Satellite Communications and Networking》2016,34(2):211-229
Polarization shift keying (PolSK) is a digital modulation technique using the state of polarization of an electromagnetic wave as the signalling quantity. PolSK comes from fibre communications, where the channel offers two orthogonal states of polarization. This article develops on the idea to adapt this technology to satellite communications, where similar channel conditions exist. For this purpose, a digital PolSK modem was implemented on a programmable logic board. A proposal for constellation design as well as thoughts on synchronization of PolSK over satellite is presented. The modem was used to demonstrate a 16‐state Polarization Shift Keying link over a commercial satellite in Ku band. Measurements have been conducted in a back‐to‐back setup on intermediate frequency and on a Ku band transponder simulator to assess the impact of path‐length differences, carrier recovery and non‐linearity. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
19.
Angéline Poulon-Quintin Cyril Faure Lionel Teulé-Gay Jean-Pierre Manaud 《Thin solid films》2010,519(5):1600-1605
Thermo chemical computing validates the stability of different nitrides against Co, Mo, and methane up to 1150 K, showing the highest chemical stability against carburization for ZrN and TaN under static conditions.Single zirconium and tantalum nitrides layers have been sputtered onto WC-Co substrates as diffusion barriers and buffer layers under specific reactive sputtering conditions. To improve the nuclei density of diamond during CVD processing, a thin Mo extra layer has been added (< 500 nm). In this study, two bilayer systems have been tested: TaN-Mo and ZrN-Mo. Nano crystalline diamond has been grown under negative biased substrates.After diamond deposition, a massive carburization of molybdenum and tantalum nitride is observable whereas zirconium nitride is not. Nevertheless, a small amount of cobalt has migrated through the ZrN layer. The better efficiency of the ZrN layer to prevent diffusion of the Co element, leads to expect an increased adhesion of diamond on ZrN-Mo bilayer coating. A TEM study is done to improve understanding of phenomena occurring at the interfaces during process. 相似文献
20.
Chasen Ranger Vahid Tari Susan Farjami Matthew J. Merwin Lionel Germain Anthony Rollett 《Metallurgical and Materials Transactions A》2018,49(10):4521-4535
Texture and grain size distribution of the austenite phase at high temperature have distinct effects on the subsequent transformed microstructure and mechanical properties of steel alloys at room temperature. Measurement of austenite at high temperature is not, however, a trivial task especially if orientation maps are desired. Therefore, a technique for determining austenite texture and grain size that was present at high temperature is highly desirable. In this work, we review several pipe samples intended for use as well casing with large variations in toughness and martensitic microstructures at room temperature. Microstructural analysis of the martensite structures could not easily explain these differences due to how martensite forms from austenite. An algorithm was developed to reconstruct the parent austenite at high temperature from martensite microstructure at room temperature. This technique successfully reconstructed orientation maps for the prior austenite in these samples, demonstrating differences in texture, grain orientation spread, and austenite grain size that could account for the differences in mechanical properties. 相似文献