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排序方式: 共有461条查询结果,搜索用时 31 毫秒
71.
Mario Siewert Markus E. Gruner Alfred Hucht Heike C. Herper Antje Dannenberg Aparna Chakrabarti Navdeep Singh Raymundo Arróyave Peter Entel 《Advanced Engineering Materials》2012,14(8):530-546
The interplay of structural and magnetic properties of magnetic shape memory alloys is closely related to their composition. In this study the influence of the valence electron concentration on the tetragonal transformation in Ni2Mn1 + xZ1 ? x (Z = Ga, In, Sn, Sb) and Co2Ni1 + xGa1 ? x is investigated by means of ab initio calculations. While the type of magnetic interaction is different for the two series, the trends of the total energy changes under a tetragonal transformation are very similar. We find that tetragonal structures become energetically preferred with respect to the cubic one as the valence electron concentration e/a is increased regardless of the system under consideration. In particular, the energy difference between the austenite and martensite structures increases linearly with e/a, which is in part responsible for the linear increase of the matensite transformation temperature. The substitution of nickel by platinum increases even further the transformation temperature. 相似文献
72.
Michael Bäurer Heike Störmer Dagmar Gerthsen Michael J. Hoffmann 《Advanced Engineering Materials》2010,12(12):1230-1234
The macroscopic properties of most materials are strongly influenced by grain size. In ceramic materials the microstructure usually results from the sintering process. Understanding the basic mechanisms of grain growth on an atomic length scale in ceramics would be beneficial to tailor the microstructure for improved macroscopic performance of devices. A method is presented using grain growth experiments to select samples for closer examination of grain boundaries with transmission electron microscopy. The growth experiments are used to identify temperatures were changes at grain boundaries occur at high temperature. Subsequently samples of interest are investigated using transmission electron microscopy (TEM) methods. The correlation between TEM results and changes in grain growth behavior can be used to gain closer insight into the processes occurring during grain growth at an atomic length scale. Strontium titanate is used as model system to demonstrate the combination of growth experiments with TEM results. Normal grain growth shows two distinct drops in growth rate in the temperature range between 1 300 and 1 425 °C, independent of the A‐site to B‐site stoichiometry of the perovskite. In previous studies a high preference for grain boundary planes oriented parallel to the 100 direction of one of the adjacent grains was found in the high temperature regime. This study shows that the preference does not exist in the low temperature regime possibly explaining the change in grain growth rate. 相似文献
73.
Emmanuelle Dupont Heike Martensen George Yannis 《Accident; analysis and prevention》2010,42(2):645-653
This paper aims at addressing the interest and appropriateness of performing accident severity analyses that are limited to fatal accident data. Two methodological issues are specifically discussed, namely the accident-size factors (the number of vehicles in the accident and their level of occupancy) and the comparability of the baseline risk. It is argued that - although these two issues are generally at play in accident severity analyses - their effects on, e.g., the estimation of survival probability, are exacerbated if the analysis is limited to fatal accident data. As a solution, it is recommended to control for these effects by (1) including accident-size indicators in the model, (2) focusing on different sub-groups of road-users while specifying the type of opponent in the model, so as to ensure that comparable baseline risks are worked with. These recommendations are applied in order to investigate risk and protection factors of car occupants involved in fatal accidents using data from a recently set up European Fatal Accident Investigation database (Reed and Morris, 2009). The results confirm that the estimated survival probability is affected by accident-size factors and by type of opponent. The car occupants’ survival chances are negatively associated with their own age and that of their vehicle. The survival chances are also lower when seatbelt is not used. Front damage, as compared to other damaged car areas, appears to be associated with increased survival probability, but mostly in the case in which the accident opponent was another car. The interest of further investigating accident-size factors and opponent effects in fatal accidents is discussed. 相似文献
74.
Anett Spring Marc Lewerentz Torsten Bluhm Peter Heimann Christine Hennig Georg Kühner Hugo Kroiss Johannes G. Krom Heike Laqua Josef Maier Heike Riemann Jörg Schacht Andreas Werner Manfred Zilker 《Fusion Engineering and Design》2012,87(12):1954-1957
The set-up of experiment programs for the complex fusion device Wendelstein 7-X has to define a multitude of parameters which have to obey large number of rules arising from physics and technical constraints. Since this is hard to automate as long as the dependencies are not known sufficiently, the W7-X CoDaC team decided to implement an editor following a constructive approach: starting from an established experiment program the user is able to modify parts of it – thus complying the usual workflow of experimenters.Already the very first implementation has been deployed at the W7-X CoDaC prototype, the WEGA stellarator. Driven by agile programming principles the weighting of the requirements has been influenced by the editor usage in the daily experiment routine, thus ensuring client-oriented development steps and short release cycles. At present, a stable program editor implementation with graphical preview, immediate feedback on user actions and instantaneous warnings about incorrect settings is under continuous operation at the CoDaC prototype. It has potential to improve together with growing knowledge about the physical and technical constraints. The experiences gained give certainty that the editor is suitable for future use during the start-up phase and the first years of W7-X operation. 相似文献
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76.
Tomislav Hrkac Claudia Röhl Rainer Podschun Vladimir Zaporojtchenko Thomas Strunskus Heike Papavlassopoulos Dieter Garbe-Schönberg Franz Faupel 《Materials science & engineering. C, Materials for biological applications》2013,33(4):2367-2375
A silver containing coating used in the human body, e.g., on an implant should be both effectively antimicrobial and non-cytotoxic to human cells. It is generally believed that the biologic effect originates from silver ions released from the coating. Nanocomposites with well controlled Ag filling factor were prepared by co-sputtering, and the silver surface concentration and the silver release were determined by XPS and ICP-MS, respectively. Here we show that only a small therapeutic window exists for dissolved silver but the therapeutic window is largely increased at the surface. While the toxicity observed for mammalian cells in contact with the bioactive Ag/TiO2 nanocomposite surface and for silver ions in solution is rather similar the antimicrobial activity is drastically enhanced at the surface. A model is proposed to explain the strong increase of the antimicrobial activity at the surface. The present results not only question well-established tests for antimicrobial activity but they are also important for the design of antimicrobial coatings, e.g., for biomedical devices. 相似文献
77.
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79.
Schmidt Heike; McFarland John; Ahmed Mohamed; McDonald Colm; Elliott Mark A. 《Canadian Metallurgical Quarterly》2011,120(2):476
The authors investigated whether difficulties with temporal event coding, previously reported in patients with schizophrenia, are already present during first-episode psychosis (FEP). In this experiment, the subjective judgments of the simultaneity of visually presented stimuli were compared between 11 healthy controls, 9 patients with chronic schizophrenia (CSZ), and a sample of 11 FEP patients. Participants were asked to indicate whether 2 vertical bars appeared at the same time or at different times on a computer monitor. CSZ patients' thresholds were elevated, and the FEP sample showed higher thresholds relative to controls. Although preliminary, these findings indicate a generalized disturbance in event-structure coding at early stages of psychosis and question the specificity of its disturbance. Considering the proposed relationship between event-structure coding and the experience of time in general, this study recommends that future studies refocus on psychosis in general, rather than on schizophrenia as a particular case of abnormal temporal processing. In addition, it is suggested that the relevant psychopathology will be best determined by means of a comprehensive analysis of low-level temporal coding performance in different types of psychosis. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
80.
We report on the electrical characterization of one-sided p(+)-si/n-InAs nanowire heterojunction tunnel diodes to provide insight into the tunnel process occurring in this highly lattice mismatched material system. The lattice mismatch gives rise to dislocations at the interface as confirmed by electron microscopy. Despite this, a negative differential resistance with peak-to-valley current ratios of up to 2.4 at room temperature and with large current densities is observed, attesting to the very abrupt and high-quality interface. The presence of dislocations and other defects that increase the excess current is evident in the first and second derivative of the I-V characteristics as distinct peaks arising from trap-and phonon-assisted tunneling via the corresponding defect levels. We observe this assisted tunneling mainly in the forward direction and at low reverse bias but not at higher reverse biases because the band-to-band generation rates are peaked in the InAs, which is also confirmed by modeling. This indicates that most of the peaks are due to dislocations and defects in the immediate vicinity of the interface. Finally, we also demonstrate that these devices are very sensitive to electrical stress, in particular at room temperature, because of the extremely high electrical fields obtained at the abrupt junction even at low bias. The electrical stress induces additional defect levels in the band gap, which reduce the peak-to-valley current ratios. 相似文献