首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2263篇
  免费   2篇
  国内免费   1篇
化学工业   11篇
金属工艺   1篇
机械仪表   6篇
矿业工程   1篇
轻工业   1篇
无线电   5篇
一般工业技术   2篇
冶金工业   2237篇
自动化技术   2篇
  2023年   1篇
  2022年   1篇
  2017年   2篇
  2012年   3篇
  2011年   2篇
  2008年   1篇
  2007年   2篇
  2006年   2篇
  2003年   5篇
  2001年   1篇
  2000年   2篇
  1999年   70篇
  1998年   736篇
  1997年   371篇
  1996年   267篇
  1995年   131篇
  1994年   112篇
  1993年   120篇
  1992年   19篇
  1991年   28篇
  1990年   18篇
  1989年   21篇
  1988年   19篇
  1987年   21篇
  1986年   15篇
  1985年   16篇
  1983年   3篇
  1982年   11篇
  1981年   12篇
  1980年   17篇
  1979年   1篇
  1978年   3篇
  1977年   67篇
  1976年   160篇
  1975年   3篇
  1964年   1篇
  1955年   2篇
排序方式: 共有2266条查询结果,搜索用时 13 毫秒
61.
62.
63.
Multicriteria choice of the optimal fixture configuration from a set of competing options is considered. An approach is developed for automated formulation of those options on the basis of a library of functional elements and the system of functional elements of modular reusable fixtures.  相似文献   
64.
65.
We focused on contextual patterns in the portrayals of television violence. Patterns are constructed by comparing contextual cues at one level of the television show, such as the macrolevel of the entire program, with the contextual cues at a more microlevel, such as the violent interaction. When the two sets of cues match on characteristics such as harm to victims and punishment to perpetrators, there is a consistent pattern of context across levels. To the extent that there is consistency in contextual cues across narrative levels, viewers' interpretations are likely to be reinforced. To the extent that there is inconsistency in cues across narrative levels, viewers, especially children, can become confused. We found more evidence of consistency than inconsistency across levels, but a high degree of that consistency reinforces the interpretation that violence is frequently unpunished and socially acceptable.  相似文献   
66.
Differences between the left and right eye's views of the world carry information about three-dimensional scene structure and about the position of the eyes in the head. The contemporary Bayesian approach to perception implies that human performance in using this source of eye-position information can be analysed most usefully by comparison with the performance of a statistically optimal observer. Here we argue that the comparison observer should also be statistically robust, and we find that this requirement leads to qualitatively new behaviours. For example, when presented with a class of stereoscopic stimuli containing inconsistent information about eccentricity of gaze, estimates of this gaze parameter recorded from one robust ideal observer bifurcate at a critical value of stimulus inconsistency. We report an experiment in which human observers also show this phenomenon and we use the experimentally determined critical value to estimate the vertical acuity of the visual system. The Bayesian analysis also provides a highly reliable and biologically plausible algorithm that can recover eye positions even before the classic stereo-correspondence problem is solved, that is, before deciding which features in the left and right images are to be matched.  相似文献   
67.
CONTEXT: One or both commercial tuberculin skin test reagents (Aplisol and Tubersol) may have a high rate of false-positive reactions. OBJECTIVE: To compare the reaction size and specificity of skin testing with Aplisol, Tubersol, and the standard purified protein derivative (PPD-S1). DESIGN: Double-blind trial, conducted between May 14, 1997, and October28, 1997, in which each individual received 4 tuberculin skin reagents at sites assigned at random. SETTING: Health departments and universities in 6 US cities. PARTICIPANTS: A total of 1555 persons at low risk of latent tuberculosis infection. INTERVENTION: Simultaneous skin tests with Aplisol, Tubersol, PPD-S1, and either a second PPD-S1 or PPD-S2 (a proposed new standard). MAIN OUTCOME MEASURE: Reaction size at each injection site measured by 2 investigators blinded to type of reagent. RESULTS: Aplisol produced slightly larger reactions than Tubersol, but this difference did not significantly change skin test interpretation. The mean +/- SD reaction sizes were 3.4+/-4.2 mm with Aplisol, 2.1+/-3.2 mm with Tubersol, and 2.5+/-3.6 mm with PPD-S1. Assuming that all participants were uninfected and using a 10-mm cutoff, the specificities of the tests were high: Aplisol, 98.2%; Tubersol, 99.2%; and PPD-S1, 98.9%. Significant variability was not detected in interobserver, host, and lot-to-lot reagent comparisons. CONCLUSION: Using a cutoff of at least 10 mm, testing with 3 different PPD reagents resulted in similar numbers of uninfected persons being correctly classified.  相似文献   
68.
OBJECTIVE: In attempting to explain the familial predisposition to panic disorder, most studies have focused on the heritability of physiologic characteristics (e.g., CO2 sensitivity). A heretofore unexplored possibility is that a psychological characteristic that predisposes to panic-anxiety sensitivity-might be inherited. In this study, the authors examined the heritability of anxiety sensitivity through use of a twin group. METHOD: Scores on the Anxiety Sensitivity Index were examined in a group of 179 monozygotic and 158 dizygotic twin pairs. Biometrical model fitting was conducted through use of standard statistical methods. RESULTS: Broad heritability estimate of the Anxiety Sensitivity Index as a unifactorial construct was 45%. Additive genetic effects and unique environmental effects emerged as the primary influences on anxiety sensitivity. There was no evidence of genetic discontinuity between normal and extreme scores on the Anxiety Sensitivity Index. CONCLUSIONS: This study suggests that one psychological risk factor for the development of panic disorder-anxiety sensitivity-may have a heritable component. As such, anxiety sensitivity should be considered in future research on the heritability of panic disorder.  相似文献   
69.
70.
A previously undescribed cause of abnormal uterine bleeding is presented. Nine of 310 women evaluated by sonohysterography for abnormal bleeding demonstrated an 8 to 17 mm gap in the anterior lower uterine segment myometrium at the site of prior cesarean deliveries. All women were premenopausal and had a history of 2 to 12 days of postmenstrual spotting. Presumably a lack of coordinated muscular contractions occurs around the cesarean scar, allowing the defect to collect menstrual debris. Subsequently, the debris leaches out through the cervix for several days after the majority of menstrual flow has ceased.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号