全文获取类型
收费全文 | 741篇 |
免费 | 21篇 |
专业分类
电工技术 | 13篇 |
综合类 | 3篇 |
化学工业 | 113篇 |
金属工艺 | 18篇 |
机械仪表 | 11篇 |
建筑科学 | 33篇 |
矿业工程 | 1篇 |
能源动力 | 15篇 |
轻工业 | 103篇 |
水利工程 | 2篇 |
石油天然气 | 37篇 |
无线电 | 51篇 |
一般工业技术 | 75篇 |
冶金工业 | 200篇 |
原子能技术 | 6篇 |
自动化技术 | 81篇 |
出版年
2021年 | 13篇 |
2020年 | 6篇 |
2018年 | 11篇 |
2017年 | 8篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 16篇 |
2013年 | 46篇 |
2012年 | 24篇 |
2011年 | 25篇 |
2010年 | 24篇 |
2009年 | 22篇 |
2008年 | 22篇 |
2007年 | 30篇 |
2006年 | 19篇 |
2005年 | 22篇 |
2004年 | 25篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 18篇 |
2000年 | 6篇 |
1999年 | 10篇 |
1998年 | 35篇 |
1997年 | 30篇 |
1996年 | 18篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 15篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1977年 | 6篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1973年 | 9篇 |
1972年 | 7篇 |
1971年 | 8篇 |
1970年 | 5篇 |
1967年 | 5篇 |
排序方式: 共有762条查询结果,搜索用时 15 毫秒
41.
Conrad KJ Wright BD McKnight P McFall M Fontana A Rosenheck R 《Journal of applied measurement》2004,5(1):15-30
This study examined whether Rasch analysis could provide more information than true score theory (TST) in determining the usefulness of reverse-scored items in the Mississippi Scale for Posttraumatic Stress Disorder (M-PTSD). Subjects were 803 individuals in inpatient PTSD units at 10 VA sites. TST indicated that the M-PTSD performed well and could be improved slightly by deleting one item. Factor analysis using raw scores indicated that the reverse-scored items formed the second factor and had poor relationships with normally scored items. However, since item-total correlations supported their usefulness, they were kept. The subsequent Rasch analysis indicated that five of the seven worst fitting items were reverse-scored items. We concluded that using reversed items with disturbed patients can cause confusion that reduces reliability. Deleting them improved validity without loss of reliability. The study supports the use of Rasch analysis over TST in health research since it indicated ways to reduce respondent burden while maintaining reliability and improving validity. 相似文献
42.
James CD Spence AJ Dowell-Mesfin NM Hussain RJ Smith KL Craighead HG Isaacson MS Shain W Turner JN 《IEEE transactions on bio-medical engineering》2004,51(9):1640-1648
Neuronal cell networks have been reconstructed on planar microelectrode arrays (MEAs) from dissociated hippocampal pyramidal neurons. Microcontact printing (microCP) and a photoresist-liftoff method were used to selectively localize poly-L-lysine (PLL) on the surface of MEAs. Haptotaxis led to the organization of the neurons into networks localized adjacent to microelectrodes. Various grids of PLL with 2-25-microm-wide lines spaced by 50-200 microm with 15-25-microm nodes at intersection points were used to guide cell body attachment and neurite outgrowth. Bursting activity with spike amplitude attenuation was observed, and multichannel recordings detected instances of coincident firing activity. Finally, we present here an extracellular recording from a approximately 2 microm bundle of guided neurites. 相似文献
43.
The eutectic coarsening kinetics for 60Sn40Pb solder joints annealed at 50°C to 150° C was determined to be of the form
[`(D)]n - [`(D)]on = Ko exp( - Q/RT)t\bar D^n - \bar D_o^n = K_o \exp ( - Q/RT)t 相似文献
44.
Online services and applications extend the influencing opportunities of traditional word-of mouth (WOM). Unlike traditional word-of-mouth, the online environment allows for special features such as anonymity in user-generated content. Furthermore, the personality of online users affects their motivation when creating this content. The aim of this paper is to link specific online activities, i.e., the posting of product ratings and participation in discussions in online forums, with certain personality traits within an empirical study. The findings, based on an online survey with more than 16,900 completed questionnaires, indicate that opinion leaders in the online environment cannot be compared with traditional opinion leaders in terms of their articulation and personality structure. In regard to online activities with a high influencing potential, the results of moderated regression analyses show that persons with an introverted personality are more active as online opinion leaders due to the lack of social recognition they experience. The results have implications for how marketers should present incentive structures to address and integrate potential online opinion leaders, and how scholars should understand the role of opinion leaders in the online environment. 相似文献
45.
Conrad Nicole J.; Walsh Jennifer; Allen Jennifer M.; Tsang Christine D. 《Canadian Metallurgical Quarterly》2011,65(3):168
Caregivers around the world sing to their infants. Infants not only prefer to listen to infant-directed singing over adult-directed singing, but infant-directed singing also serves a function, communicating affective information to preverbal infants to aid in adjusting arousal levels. Pitch variation has previously been identified as one performance feature that may help to convey the message. Earlier research has indicated that infants' pitch preferences are context dependent, suggesting that infants are tuned in to the communicative intent of infant-directed singing. However, there are several other performance-based features present in infant-directed singing that may also contribute to the affective message. The current study examined the role of context on infants' tempo preferences in sung playsongs and lullabies. Using a head-turn preference procedure, we measured 24 preverbal infants' natural preferences for foreign language playsongs and lullabies as a function of tempo. Infants showed a preference for fast over slow tempo playsongs, but no such context dependent preference was found within lullabies. Results partially support the role of tempo as a communicative feature of infant directed singing. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
46.
Data in the literature on the effect of grain size from micrometers to nanometers on the flow stress, dislocation density,
apparent activation volume and strain rate sensitivity parameters for Cu are analyzed to determine the rate-controlling mechanism.
Accord occurs for the intersection of dislocations over the entire grain size range from 10 nm to 150 μm. The dislocation
density and its structure and the related Friedel factor are important parameters. 相似文献
47.
The influence of a nominal external electric field E=3 to 10 kV/cm on the sintering of iron powder compacts for 30 minutes at 1140 °C in a vacuum of ∼10−6 torr was investigated. It was found that the field reduced the porosity by as much as 29 to 73 pct compared to sintering
without a field, the magnitude depending on the procedure employed to measure the density of the specimen. Optical microscopy
revealed that the specimen electrosintered with E=10 kV/cm had a skin of ∼0.2 mm in thickness, where the porosity was significantly less than in the interior. This was also
the depth of carburization that was obtained upon carburizing the electrosintered specimens. It is proposed that the decrease
in porosity produced by the field results from a decrease in the chemical potential of vacancies at or just below the charged
external surface. Vacancy flux equations employed to calculate the porosity as a function of distance below the external surface
showed that the porosity becomes approximately zero at a distance of x
c=0.4 to 0.5 mm below the surface, which is in reasonable accord with the microscopy measurements. Similar values of x
c were obtained by assuming that the entire porosity decrease given by the density measurements occurred in a ring of thickness
of x
c below the external surface. The difference in the density measured by two Archimedes-principle procedures and microscopy
observations suggests that the cavities open to the external surface of the electrosintered specimens are smaller or narrower
than those for specimens sintered without a field. 相似文献
48.
Preston Kenzie L.; Umbricht Annie; Wong Conrad J.; Epstein David H. 《Canadian Metallurgical Quarterly》2001,69(4):643
Cocaine-using methadone-maintenance patients were randomized to standard contingency management (abstinence group, n?=?49) or to a contingency designed to increase contact with reinforcers (shaping group, n?=?46). For 8 weeks, both groups earned escalating-value vouchers based on thrice-weekly urinalyses: The abstinence group earned vouchers for cocaine-negative urines only; the shaping group earned vouchers for each urine specimen with a 25% or more decrease in cocaine metabolite (first 3 weeks) and then for negative urines only (last 5 weeks). Cocaine use was lower in the shaping group, but only in the last 5 weeks, when the response requirement was identical. Thus, the shaping contingency appeared to better prepare patients for abstinence. A 2nd phase of the study showed that abstinence induced by escalating-value vouchers can be maintained by a nonescalating schedule, suggesting that contingency management can be practical as a maintenance treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
49.
The influence of a continuous dc electric field applied orthogonal to the tensile direction on the flow stress, grain growth,
and cavitation during superplastic deformation (SPD) of ultrafine-grained 3Y-TZP at 1,450–1,600 °C was determined. The field
gave a significant reduction in the level of the stress-strain curve, and reduced grain growth and cavitation. The decrease
in flow stress by the field was attributed mainly to the retardation of grain growth. The decrease in cavitation correlated
with the retardation of grain growth and was attributed largely to the reduction in flow stress by the field. 相似文献
50.
|