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1.
The times to gelation and to vitrification for the isothermal cure of an amine-cured epoxy (Epon 828/PACM-20) have been measured on macroscopic and molecular levels by dynamic mechanical spectrometry (torsional braid analysis and Rheometrics dynamic spectrometer), infrared spectroscopy, and gel fraction experiments. The relationships between the extents of conversion at gelation and at vitrification and the isothermal cure temperature form the basis of a theoretical model of the time–temperature–transformation (TTT) cure diagram, in which the times to gelation and to vitrification during isothermal cure versus temperature are predicted. The model demonstrates that the “S” shape of the vitrification curve depends on the reaction kinetics, as well as on the physical parameters of the system, i.e., the glass transition temperatures of the uncured resin (Tg0), the fully cured resin (Tg∞), and the gel (gelTg). The bulk viscosity of a reactive system prior to gelation and/or vitrification is also described. 相似文献
2.
Some dairy producers resist using bovine somatotropin (bST) beginning at 9 wk postpartum because of the concern that fertility is compromised. We conducted a trial with a total of 205 Holstein cows, 100 multiparous and 105 primiparous, to evaluate reproductive performance in two high producing herds in Arizona and southern California. Rolling herd averages for both herds for milk production exceeded 10,700 kg/yr. Data were collected for cows calving December 1996 through August 1997. The voluntary waiting period was 60 d postcalving, with cows randomly assigned to receive bST or no treatment (controls). In the 180-d interval after calving, 65.4% (68/104) of the control cows were diagnosed pregnant. With bST-treated cows, 48.5% (49/101) were pregnant in that same interval. A chi-square value from a linear model indicated that pregnancy outcome differed significantly between treatment groups. With a similar method of analysis, first-service conception rate was not significantly different between treatment groups. An extended voluntary wait and breeding interval is recommended for cows receiving bST, similar to suggestions from other published reports. 相似文献
3.
Participants from 5 groups with mean ages of 6, 8, 10, 22, and 72 yrs were tested on a series of speeded number discriminations: 1 vs 2, 3 vs 4, 6 vs 7, and 8 vs 9. The primary measure of interest (response time slope as a function of number size) decreased with age for numbers in the 1–4 range. However, a U-shaped age function emerged in the 6–9 range, with larger slopes for children and senior adults, and the smallest slopes for young adults. These data suggest that different processes are involved in enumerating small and large numbers of items. It is argued that subitizing, the process for small numbers, makes only minimal demands on spatial attention and thus shows developmental improvements without any decline in old age. In contrast, counting, the process for large numbers, requires sophisticated coordination of spatial attention, which has previously been shown first to improve and then decline over the life span. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
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A fundamental goal of visualization is to produce images of data that support visual analysis, exploration, and discovery of novel insights. An important consideration during visualization design is the role of human visual perception. How we "see" details in an image can directly impact a viewer's efficiency and effectiveness. This paper surveys research on attention and visual perception, with a specific focus on results that have direct relevance to visualization and visual analytics. We discuss theories of low-level visual perception, then show how these findings form a foundation for more recent work on visual memory and visual attention. We conclude with a brief overview of how knowledge of visual attention and visual memory is being applied in visualization and graphics. We also discuss how challenges in visualization are motivating research in psychophysics. 相似文献
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Five experiments demonstrate that when dots appear beside a briefly presented target object, and persist on view longer than the target, the flanked object is perceptually altered by the dots. Three methods are used to explore this object trimming effect. Experiments 1–3 assess participants’ conscious reports of trimmed digits, Experiment 4 uses repetition priming to explore the target representation, and Experiment 5 examines the perception of apparent motion in trimmed targets. Results of all three methods indicate that object trimming is influenced by mechanisms of perceptual grouping that operate on target representations prior to conscious access. Separate contributions from visual crowding and backward masking are also identified. These results imply that common-onset masking does not always result from the target being substituted by the mask, but that target and mask can sometimes maintain separate mental representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
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RH Enns 《Canadian Metallurgical Quarterly》1987,36(11):5441-5443
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This commentary elaborates on K. D. Arbuthnott, D. W. Arbuthnott, and L. Rossiter's (2001; see record 2001-00732-001) recommendations regarding the use of imagery in psychotherapy. The reflections focus primarily on occasions when imagery may be used to help clients reprocess and work through painful or traumatic memories. Highlighted are the values of (a) developing competence before using imagery, (b) attending to issues related to informed consent and ethics, (c) integrating the use of imagery within a comprehensive assessment, (d) establishing appropriate client expectations, (e) building on information derived from less directive methods, (f) being well versed with a variety of therapeutic tools, (g) paying attention to individual differences in clients' reactions to and use of imagery, and (h) responding appropriately if clients experience spontaneous memories of unknown origin. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
Three experiments, with 172 Ss (aged 6–24 yrs), examined the integration of shape information over successive glances. In Exps I and II, Ss classified line drawings subtending 1–26° visual angle as possible or impossible objects. Response times and errors increased as a function of figure size for all age groups. The decline in performance with figure size was greater for children than for adults. In Exp II, Ss also performed a classification task based on only 1 of the informative regions in each figure. Performance in the 2 tasks suggested that the ability to encode shape information from a single region of the figures did not change with age. In Exp III, a simultaneous condition, in which an intact figure was presented, was compared with sequential conditions in which blank intervals of 0–3 sec separated 2 views of different parts of the figure. All Ss classified the figures most quickly and accurately in the simultaneous condition, and children were more affected by longer delays between views than adults. It is concluded that these results point to age-related improvements in sequential integration of shape information, both when integration occurs through successive glimpses over space and when information is separated only in time. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献