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排序方式: 共有450条查询结果,搜索用时 15 毫秒
71.
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V.-X. Tran 《Engineering Fracture Mechanics》2010,77(9):1417-1438
In this paper, three-dimensional finite element analyses for spot welds with ideal geometry in lap-shear specimens of different materials and thicknesses were first conducted. The computational results indicate that the stress intensity factor and J integral solutions based on the finite element analyses agree well with the analytical solutions and that the analytical solutions can be used with a reasonable accuracy. Three-dimensional finite element analyses based on the micrographs of an aluminum 6111 resistance spot weld, an aluminum 5754 spot friction weld, and a dissimilar Al/Fe spot friction weld were also conducted. The computational results indicate that the stress intensity factor and J integral solutions based on the finite element analyses for the aluminum 6111 resistance spot weld and aluminum 5754 spot friction weld with complex geometry are in good agreement with the analytical solutions for the equivalent spot welds with ideal geometry. However, the stress intensity factor and J integral solutions based on the finite element analysis for the Al/Fe spot friction weld with complex geometry are completely different from the analytical solutions for the equivalent spot weld with ideal geometry. Different three-dimensional finite element analyses based on the meshes that represent different features of the complex geometry of the Al/Fe spot friction weld were then conducted. The computational results indicate that the stress intensity factor and J integral solutions for the Al/Fe spot friction weld based on the finite element analysis agree reasonably well with the analytical solutions for the equivalent spot weld with consideration of gap and bend. The computational and analytical results suggest that the stress intensity factor and J integral solutions based on the finite element analysis and the analytical solutions with consideration of gap and bend may be used to correlate with the fatigue crack growth patterns of Al/Fe spot friction welds observed in experiments. 相似文献
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Pedestrian–vehicle conflicts are considered as a common safety problem at signalized intersections. The threat to pedestrian safety is mainly related to the interaction with turning vehicles, especially left-turners (left-hand traffic system). This study aims to analyze the lag/gap acceptance behavior of left-turners considering pedestrian movement at signalized crosswalks. Furthermore, the severity of pedestrian–vehicle conflicts is addressed by analyzing vehicle speeds at the conflict points. User behavior at several signalized intersections in Japan is observed by using video cameras. It is assumed that pedestrian movements have their origin at either the near-side (the side of the exiting vehicular traffic) or far-side of the crosswalk. Accepted/rejected lags and gaps are extracted, classified depending on the direction of pedestrian movement, and modeled by using Cumulative Weibull distribution function. The results show that drivers tend to accept shorter lags/gaps between near-side pedestrians compared to far side pedestrians. Furthermore, drivers tend to accept short lags while being conservative about short gaps. Simultaneously vehicles clear the conflict area with significantly higher speeds when accepting lags with single pedestrians. This indicates that the conflicts that occur at low pedestrian demand levels are more severe compared to those at high demand levels. 相似文献
75.
Ali Iranmanesh Yaser Alizadeh Bahman Taherkhani 《International journal of molecular sciences》2008,9(2):131-144
In this paper we give a GAP program for computing the Szeged and the PI indices of any graph. Also we compute the Szeged and PI indices of VC5C7 [ p,q] and HC5C7 [ p,q] nanotubes by this program. 相似文献
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Muhammad Kashif Iqbal Khan Maarten A.I. SchutyserKarin Schroën Remko Boom 《Journal of food engineering》2012,108(3):410-416
There is a continuous need for thinner edible coatings with excellent barrier properties, and this requires new application methods. Electrospraying is known to yield fine droplets of size down to 20 μm, giving the potential of very thin and even coatings. A single electrospraying nozzle was used to characterise droplet formation and investigate the formation of thin films on well-defined surfaces. The experimental droplet size was successfully described as a function of operational parameters and liquid properties using scaling relations. The influence of operating parameters as nozzle height and electrostatic potential were evaluated as well.Thin film deposition was experimentally investigated for sunflower oil electro-sprayed on a highly conductive (aluminium) and insulating target surface (Parafilm). For both aluminium foil and Parafilm the droplet deposition was found to be random. For aluminium foil, being a conductive target, this was expected as repellence between droplets on the surface and new droplets is low, due to charge leakage to the ground. For Parafilm, droplet repellence appeared so large that droplets deposited on larger empty spots or were even pushed away from the surface. To evaluate the film formation performance, Monte Carlo simulations were carried out, and it was found that the method is a useful tool to characterise droplet deposition and film formation characteristics. 相似文献
78.
Christopher H. Braithwaite Jiri Pachman Jiri Majzlik David M. Williamson 《Propellants, Explosives, Pyrotechnics》2012,37(5):614-620
A series of gap‐test experiments were conducted in accordance with the EMTAP Test 22a guidelines to characterize the stress output from a donor charge of ROWANEX 3601. Forty eight successful gap‐tests were conducted at the University of Pardubice in addition to two supporting plate impact experiments performed at the Cavendish Laboratory, University of Cambridge. The experiments indicated that there are two principal release mechanisms, which produce the observed reduction in stress with increasing gap distance. The first is attenuation of the input wave, something which is expected during explosive loading due to the triangular nature of the loading pulse. The second is an interaction between the input wave and lateral release waves from the edges of the test sample at the measurement station. Attenuation of the input wave due to visco‐elastic loss in the PMMA “gap” used is likely to be less significant than these other two release mechanisms. The data generated by this investigation forms a robust dataset that gives an accurate calibration for ROWANEX 3601 for users of the EMTAP 22a test procedure. In addition the data represent an excellent “set problem” for those developing and wishing to validate, computational models of similar physical phenomena. 相似文献
79.
G. Ghidini N. GalbiatiC. Scozzari A. SebastianiR. Piagge A. Del VittoP. Comite M. AlessandriP. Tessariol I. BaldiE. Moltrasio E. Mascellino 《Microelectronic Engineering》2011,88(7):1182-1185
The aim of this work is to investigate the physical mechanisms behind the write/erase and retention performances of band gap engineering (BE) layers used as tunnel oxide in charge trap memory stack. The investigation of the BE layers alone will be completed with the analyses of its integration within a TANOS (TaN/Alumina/Nitride/Oxide/Silicon) stack, pointing out the correlation between electrical performance and reliability limits.Good write/erase/retention performances can be achieved with BE tunnel oxide by using silicon nitride layer integrated in SiO2-Si3N4-SiO2 stack, as long as all different mechanisms are taken into account in optimizing stack composition: hole injection which improves erase efficiency, charge trapping and de-trapping from the thin silicon nitride which causes program instabilities and initial charge loss which does not significantly impact long term retention. All these phenomena make very crucial the BE tunnel process control and difficult its use for multi-level application. 相似文献
80.