全文获取类型
收费全文 | 1020篇 |
免费 | 35篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 17篇 |
综合类 | 1篇 |
化学工业 | 137篇 |
金属工艺 | 27篇 |
机械仪表 | 23篇 |
建筑科学 | 36篇 |
矿业工程 | 8篇 |
能源动力 | 15篇 |
轻工业 | 114篇 |
水利工程 | 10篇 |
无线电 | 54篇 |
一般工业技术 | 144篇 |
冶金工业 | 335篇 |
原子能技术 | 8篇 |
自动化技术 | 128篇 |
出版年
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 31篇 |
2020年 | 21篇 |
2019年 | 13篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 29篇 |
2015年 | 20篇 |
2014年 | 35篇 |
2013年 | 50篇 |
2012年 | 39篇 |
2011年 | 47篇 |
2010年 | 20篇 |
2009年 | 38篇 |
2008年 | 54篇 |
2007年 | 51篇 |
2006年 | 31篇 |
2005年 | 28篇 |
2004年 | 25篇 |
2003年 | 22篇 |
2002年 | 17篇 |
2001年 | 23篇 |
2000年 | 25篇 |
1999年 | 23篇 |
1998年 | 54篇 |
1997年 | 46篇 |
1996年 | 25篇 |
1995年 | 27篇 |
1994年 | 14篇 |
1993年 | 21篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1972年 | 5篇 |
排序方式: 共有1057条查询结果,搜索用时 31 毫秒
11.
12.
M. J. Caton J. W. Jones H. Mayer S. Stanzl-Tschegg J. E. Allison 《Metallurgical and Materials Transactions A》2003,34(1):33-41
An investigation of the fatigue properties of cast W319-T7, an Al-Si-Cu alloy used in automotive engine components, was conducted
using ultrasonic testing equipment with operating frequencies of 20 kHz. The stress-life (S-N) behavior at room temperature
was determined for three solidification conditions of this alloy, where stresses for fatigue lives ranging from 105 to 109 cycles were determined. The results are compared to fatigue data acquired using servohydraulic equipment operating at 40
Hz. No influence of loading frequency has been observed. A discrete endurance limit is indicated for each of the three solidification
conditions of W319-T7. The scientific and practical implications of this result are discussed. A material model presented
previously is modified by introducing a crack growth threshold condition in order to predict the observed endurance limits.
The model is shown to effectively predict the influence of solidification time on the fatigue properties of W319-T7. 相似文献
13.
Faith Myles S.; Fontaine Kevin R.; Baskin Monica L.; Allison David B. 《Canadian Metallurgical Quarterly》2007,133(2):205
The authors reviewed the evidential basis of three environmental approaches to reducing population obesity: What are the effects of (a) taxing or subsidizing foods, (b) manipulating the ease of food access, and (c) restricting access to certain foods? A narrative review evaluated evidence using National Heart, Lung, and Blood Institute criteria. There was strong evidence that subsidization influences food purchases, but not necessarily food consumption or body weight. Ease of food access may influence food purchases, and possibly food intake and body weight. Data on restriction were lacking. More studies are needed to justify that altering these macro-environmental variables will necessarily reduce population obesity. A proposed conceptual model posits that the steps through environmental interventions may exert intended and unintended influences on body weight and obesity prevalence. Contemplated policy changes should weigh scientific evidence with social judgments and values concerning changes to the environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
14.
A method of reacquiring a previous phase lock-point using the pulsed phase-locked loop (PPLL) ultrasonic system in situations where the measurement is interrupted such as by removing and recoupling the transducer is developed. Operation of the PPLL is mathematically analyzed in the time domain rather than in the conventional frequency domain, providing a method of characterizing multiple lock-points. The general lock-point reacquisition method that follows from the model relies on measurement over a frequency range that spans several lock-points and is demonstrated to work well for interrupted measurements on threaded fasteners. The method is analyzed for sensitivity to signal noise, and an equation is derived, expressing the number of lock-points over which to measure for successful lock-point reacquisition as a function of signal noise level. Experimental verification on a glass block shows that theoretical values obtained with this model are in good agreement with measurements. Automation of the method presented has been demonstrated, showing that it offers a practical, objective approach to making interrupted load measurements, thereby greatly widening the range of applications of the PPLL 相似文献
15.
16.
Randomized trial of breast self-examination in Shanghai: methodology and preliminary results 总被引:3,自引:0,他引:3
DB Thomas DL Gao SG Self CJ Allison Y Tao J Mahloch R Ray Q Qin R Presley P Porter 《Canadian Metallurgical Quarterly》1997,89(5):355-365
BACKGROUND: The efficacy of breast self-examination in helping to reduce mortality from breast cancer has not been rigorously demonstrated. PURPOSE: To assess efficacy, a large, randomized trial was initiated in Shanghai, China. METHODS: From October 1989 to October 1991, 267040 current and retired female employees associated with 520 factories in the Shanghai Textile Industry Bureau were randomly assigned on the basis of factory to either a self-examination instruction group (133375 women) or a control group (133665 women). The women were born within the period from 1925 through 1958. Women in the instruction group were given intensive training in breast self-examination, including the use of silicone breast models and personalized instruction, plus two subsequent reinforcement sessions and multiple reminders to practice the technique. Women in the control group were asked to attend training sessions on the prevention of low back pain. All women have been followed for the development of breast diseases and for death from breast cancer. RESULTS: A high level of participation during the first 4-5 years of the trial was documented among women in the instruction group. Randomly sampled women in this group demonstrated greater proficiency in detecting lumps in breast models than did randomly sampled women in the control group. Approximately equal numbers of breast cancers were detected in the two groups (331 in the instruction group and 322 in the control group) through 1994, which is the last year for which case-finding efforts have been completed. The breast cancers detected in the instruction group were not diagnosed at an appreciably earlier stage or smaller size than those in the control group. More benign breast lesions were detected in the instruction group than in the control group (1457 versus 623, respectively), suggesting a higher index of suspicion for women who received training. Cumulative breast cancer mortality rates through 5 years from entry into the study were nearly equivalent for the two groups. CONCLUSIONS: Breast self-examination has not led to a reduction in mortality from breast cancer in this study cohort in the first several years since the trial began. A shift toward the diagnosis of disease at a less advanced stage in women given instruction has also not been demonstrated. Longer follow-up of participants in this trial is required before final assessment can be made of the efficacy of breast self-examination. IMPLICATIONS: At this time, there is insufficient evidence to recommend for or against the teaching of breast self-examination. 相似文献
17.
18.
RA Reinhardt MP Masada GK Johnson LM DuBois GJ Seymour AC Allison 《Canadian Metallurgical Quarterly》1993,20(7):514-519
Interleukin (IL)-1 alpha and beta are cytokines which can mediate inflammatory, bone resorbing, and reparative effects in the periodontium, but few longitudinal data exist exploring their role following periodontal therapy. This study examined gingival crevicular fluid (GCF) concentrations of IL-1 alpha and IL-1 beta at sites with shallow sulci (SS) or inflamed moderate/advanced pockets (M/AP) before and 6 months after treatment with closed scaling/root planing (SC/RP) or papillary flap debridement (PFD), all in the same subject (n = 14 patients). No significant differences were noted in IL-1 alpha or beta concentrations (determined with two-site enzyme-linked immunosorbent assays) between SS and M/AP sites at baseline. While both therapies improved clinical parameters of periodontal disease, IL-1 alpha concentration increased significantly (p < 0.05) in M/AP-PFD sites 6 months after treatment, but were unchanged in other groups. IL-1 beta concentrations were numerically lower after therapy, except for a significant increase (p < 0.05) in M/AP-PFD sites. These data suggest that surgical wound healing in an inflamed, plaque-infected site (M/AP-PFD) results in prolonged production of IL-1, which may be a reflection of the extent of tissue trauma and delayed wound healing. In spite of increased IL-1 levels, these sites demonstrated significant short-term improvement in clinical attachment level (+ 1.8 mm, p < or = 0.001) postoperatively. 相似文献
19.
G. M. Vyletel J. E. Allison D. C. Van Aken 《Metallurgical and Materials Transactions A》1995,26(12):3143-3154
The low-cycle and high-cycle fatigue behavior and cyclic response of naturally aged and overaged 2219/TiC/15p and unreinforced
2219 Al were investigated using plastic strain-controlled and stress-controlled testing. In addition, the influence of grain
size on the particle-reinforced materials was examined. In both reinforced and unreinforced materials, the naturally aged
conditions were cyclically unstable, exhibiting an initial hardening behavior followed by an extended region of cyclic stability
and ultimately a softening region. The overaged reinforced material was cyclically stable for the plastic strains examined,
while the overaged unreinforced material exhibited cyclic hardening at plastic strains greater than 2.5 × 10−4. Decreasing grain size of particle-reinforced materials modestly increased the cyclic flow stress of both naturally aged
and overaged materials. Reinforced and unreinforced materials exhibited similar fatigue life behaviors; however, the reinforced
and unreinforced naturally aged materials had superior fatigue lives in comparison to the overaged materials. Grain size had
no effect on the fatigue life behavior of the particle-reinforced materials. The fatigue lives were strongly influenced by
the presence of clusters of TiC particles and exogenous Al3Ti intermetallics.
formerly Research Assistant with the Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI
48109
This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the
1994 TMS/ASM Spring meeting, held February 28–March 3, 1994 in San Francisco, California, under the auspices of the Joint
TMS-SMD/ASM-MSD Composite Materials Committee. 相似文献
20.
Einstein Gilles O.; McDaniel Mark A.; Richardson Sarah L.; Guynn Melissa J.; Cunfer Allison R. 《Canadian Metallurgical Quarterly》1995,21(4):996
Past research has frequently failed to find age differences in prospective memory. This article tested the possibility that age differences would be more likely to emerge on a prospective memory task that was high in self-initiated retrieval. In the 1st experiment, participants were asked to perform an action every 10 min (a time-based task presumed to be high in self-initiated retrieval); in the 2nd experiment, participants were asked to perform an action whenever a particular word was presented (an event-based task presumed to be relatively low in self-initiated retrieval). Age differences were found with the time-based task but not with the event-based task. This pattern of age differences was again found in a 3rd experiment in which a new experimental procedure was used and the nature of the prospective memory task was directly varied. Generally, the results suggest that self-initiated retrieval processes are an important component of age-related differences across both retrospective and prospective memory tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献