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   1058篇
  免费   57篇
  国内免费   1篇
电工技术   17篇
化学工业   118篇
金属工艺   5篇
机械仪表   8篇
建筑科学   28篇
矿业工程   2篇
能源动力   14篇
轻工业   220篇
水利工程   5篇
石油天然气   1篇
无线电   135篇
一般工业技术   163篇
冶金工业   336篇
原子能技术   8篇
自动化技术   56篇
  2023年   5篇
  2022年   16篇
  2021年   30篇
  2020年   27篇
  2019年   22篇
  2018年   18篇
  2017年   20篇
  2016年   23篇
  2015年   15篇
  2014年   24篇
  2013年   24篇
  2012年   31篇
  2011年   40篇
  2010年   33篇
  2009年   25篇
  2008年   39篇
  2007年   38篇
  2006年   41篇
  2005年   27篇
  2004年   26篇
  2003年   24篇
  2002年   16篇
  2001年   12篇
  2000年   19篇
  1999年   23篇
  1998年   100篇
  1997年   68篇
  1996年   58篇
  1995年   26篇
  1994年   26篇
  1993年   20篇
  1992年   21篇
  1991年   17篇
  1990年   11篇
  1989年   18篇
  1988年   14篇
  1987年   6篇
  1986年   8篇
  1985年   6篇
  1984年   8篇
  1983年   5篇
  1982年   5篇
  1981年   4篇
  1980年   9篇
  1979年   7篇
  1977年   8篇
  1976年   13篇
  1975年   5篇
  1974年   7篇
  1973年   4篇
排序方式: 共有1116条查询结果,搜索用时 15 毫秒
71.
Hunters have been a fundamental component of northern bobwhite quail conservation for most of the past century. Bobwhite quail hunters funded the first modern comprehensive life history study of a wild vertebrate in the 1920s to understand causes responsible for population declines. This investigation identified a causal link between frequent applications of prescribed fire and persistence of bobwhite quail populations in the Southeastern United States, and provided the foundation for contemporary fire ecology science. Since then, hunters in the Southeastern and Midwestern United States have funded numerous other bobwhite quail research and conservation efforts. Research and conservation efforts funded by quail hunters in Texas continue to be especially notable. Non-governmental organizations, and academia, as well as state and federal wildlife agencies have been the conduits for efforts to sustain bobwhite quail populations because predominant land uses no longer support bobwhite quail.  相似文献   
72.
This study aims at understanding the role of mixtures (mutual quality suppression) in the evaluation of impact of the human aging process on the perception of taste.

Heretofore, the effect of aging on taste has been directed at threshold and suprathreshold magnitudes of single chemicals (e.g., NaCl, sucrose, citric acid) in aqueous solution. Although absolute thresholds typically rise in advanced age (2 to 9 times, depending on the study), suprathreshold magnitude assessed by magnitude matching seems (except for bitter) to resist change in the way presbycusis spares suprathreshold loudness, fostering the impression that aging may handicap the aged little in the perception of food.

Asked, however, to discriminate the presence‐absence of the prescribed salt flavoring (nominally suprathreshold) in tomato soup, the young outperformed the middle‐aged who, in turn, outperformed the elderly. Moreover, NaCl thresholds in the presence of tomato measured several times higher than in water, but the difference between the young and the elderly continued to hold. Elevation of threshold to much higher levels by mixture suppression leaves the young‐elderly difference unchanged, implying that the elderly may fail to detect salt levels that really count in their diet.

To examine the relation between age and taste mixtures, we measured detection thresholds: (1) for NaCl in citric acid, from zero to strong; (2) for sucrose in citric acid, from zero to strong; and (3) for citric acid in sucrose, from zero to strong. Whether in water alone or in a weak or strong suppressor, the elderly subjects’ threshold was consistently 2 or 3 times higher than that of the young. Moreover, the way in which threshold for one quality rises with concentration of a suppressor is the same, except for constant upward displacement of the elderly peoples’ threshold. In general, both young and elderly confuse salty and sour (show large suppression at all concentrations of the suppressor) much more than they confuse sweet and sour (seen mainly at high concentrations of the suppressor). Study of other mixtures is planned.  相似文献   

73.
The effects of processing treatments (heat, sucrose addition) on the sensory quality of blackcurrant juices prepared from two genetically diverse cultivars (Ben Lomond and Ben Alder) were examined using sensory profiling. Sucrose level had the largest effect on the sensory profile, with heating and cultivar having smaller but still significant effects. Some interaction between sucrose level and heating of the juices was observed in the sensory profile. The results indicate that selection of preferred genotypes remains an important breeding objective in blackcurrant improvement programmes, since the sensory attributes associated with genotype persist, despite processing effects, in the extracted juice.  相似文献   
74.
Rodent fear conditioning models both excitatory learning and the pathogenesis of human anxiety, whereas extinction of conditional fear is a paradigm of inhibitory learning and the explicit model for behavior therapy. Many studies support a general learning rule for acquisition: Temporally spaced training is more effective than massed training. The authors asked whether this rule applies to extinction of conditional fear in mice. The authors find that both short- and long-term fear extinction are greater with temporally massed presentations of the conditional stimulus (CS). The data also indicate that once CS presentations are sufficiently massed to initiate, or "induce," extinction learning, further CS presentations are more effective when spaced. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
75.
76.
To measure tinnitus induced by sodium salicylate injections, 84 rats were used in a conditioned suppression paradigm. In Exp 1, Ss were trained with a conditioned stimulus/stimuli (CS) consisting of the offset of a continuous background noise. One group began salicylate injections before Pavlovian training, a 2nd group started injections after training, and a control group received daily saline injections. Resistance to extinction was profound when injections started before training but minimal when initiated after training, suggesting that salicylate-induced effects acquired differential conditioned value. In Exp 2, salicylate treatments were mimicked by substituting a 7 kHz tone in place of respective injections, resulting in effects equivalent to salicylate-induced behavior. A 3rd experiment included a 3 kHz CS, and again replicated the salicylate findings. In Exp 4, we decreased the motivational level, and the sequential relation between salicylate-induced effects and suppression training was retained. Findings support the demonstration of phantom auditory sensations in animals. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
77.
Investigated in 3 experiments the relationships between affect intensity and basal, evoked, and perceived cardiac arousal. Affect intensity was assessed using R. J. Larsen and E. Diener's (1987) Affect Intensity Measure (AIM). Cardiac arousal was evoked with exercise in the 1st study and with mental arithmetic in the 2nd and 3rd. Perceived cardiac arousal was measured under optimal conditions using a standard heartbeat discrimination procedure. Women as a group scored higher on the AIM. Affect intensity was unrelated to basal or evoked cardiac arousal and was negatively related to perceived cardiac arousal in all 3 studies. Data suggest that affect intensity, although unrelated to actual physiological arousal, is negatively related to the accuracy with which individuals perceive their own arousal. Results are discussed within the context of an expanded arousal-regulation model (J. Blascovich, 1990). (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
78.
Computer technologies, particularly electronic computer networks, can enhance nurses' abilities to initiate, facilitate, and sustain interpersonal contact with patients. Computer networks are electronic links between remote sites and as such provide a pathway for communication between nurses and patients. In an innovative project known as the ComputerLink, a team of nurses used an electronic network to provide information, communication, and decision support to homebound persons and their caregivers. This experiment allowed exploration of the unspoken language of nursing and provides direction for considering how nursing therapeutics can capitalize on the benefits of the electronic network.  相似文献   
79.
Poly(vinylalcohol) (PVA)-stabilized silver nanoparticles were prepared by a seeding method. Nanoparticles of varying morphology were obtained by controlled variation of the reaction conditions, and this method allowed the tailoring of the position of the surface plasmon resonance. The samples show two bands in the visible absorption spectrum: one in the 410-440-nm region and a second peak between 500 and 600 nm. This tunable surface plasmon resonance serves to increase the third-order optical nonlinearity (chi 3) of the nanoparticles (measured at 532 nm) by a factor of 16.  相似文献   
80.
FTIR measurements may be able to replace more laborious physical property determinations and thus serve as an efficient screening methodology in catalysis driven processes. This possibility was considered in evaluating alkane sulfonic acids catalyst performance to promote the cure of a melamine resin with acrylic polyols. The example chosen here is an evaluation of alkane sulfonic acid derivatives to measure catalytic efficiency of the cure reaction between hexamethoxymethylmelamine (HMMM) and an acrylicpolyol. The IR measurements provided information on the extent of reaction, via monitoring the disappearance of the OH stretching mode at 3472 cm−1 associated with the acrylic polyol. This method may also be used to provide detailed information on reaction kinetics and insight into the cure mechanism. As the reaction proceeds, the coating’s properties change and IR measurements can serve as a probe for these changes. 900 First Ave., King of Prussia, PA 19406.  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