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   736篇
  免费   46篇
  国内免费   2篇
电工技术   7篇
化学工业   210篇
金属工艺   8篇
机械仪表   11篇
建筑科学   63篇
矿业工程   2篇
能源动力   13篇
轻工业   157篇
水利工程   15篇
石油天然气   2篇
无线电   20篇
一般工业技术   105篇
冶金工业   71篇
原子能技术   2篇
自动化技术   98篇
  2024年   1篇
  2023年   12篇
  2022年   33篇
  2021年   47篇
  2020年   22篇
  2019年   29篇
  2018年   26篇
  2017年   20篇
  2016年   24篇
  2015年   24篇
  2014年   36篇
  2013年   66篇
  2012年   39篇
  2011年   62篇
  2010年   46篇
  2009年   50篇
  2008年   30篇
  2007年   37篇
  2006年   32篇
  2005年   17篇
  2004年   16篇
  2003年   20篇
  2002年   14篇
  2001年   14篇
  2000年   9篇
  1999年   6篇
  1998年   8篇
  1997年   7篇
  1996年   8篇
  1995年   1篇
  1994年   3篇
  1993年   6篇
  1992年   6篇
  1991年   1篇
  1989年   3篇
  1987年   1篇
  1981年   1篇
  1973年   1篇
  1957年   1篇
  1926年   1篇
  1924年   2篇
  1922年   2篇
排序方式: 共有784条查询结果,搜索用时 781 毫秒
41.
Optimal loading and operating conditions for a new, superior immobilization of amano lipase from Pseudomonas fluorescens on woolen cloth were determined. The optimal enzyme loading was 46.8 mg g dry cloth−1 with activity of 200 U. A batch reactor was used to characterize process conditions important to industrial application of the wool immobilized lipase. The optimal pH for immobilized lipase in tributyrin hydrolysis was 7, slightly lower than that of free lipase (pH 8). The optimal temperature for both free and immobilized lipase was 45 °C. The immobilized lipase was more stable to reuse than some other lipase immobilizations, maintaining 85% of its activity after 6 long term runs and 75.8% of the original activity after storage of 40 weeks at 4 °C. The thermal stability of lipase was improved by 2.4 times after immobilization. The thermal deactivation rate of immobilized lipase followed the Arrhenius law with Ed = 199 kJ mol−1. The Michaelis–Menten constant (Km) of the lipase increased from 1.63 mM to 4.48 mM after immobilization. The immobilized lipase was also successfully applied for tributyrin hydrolysis in a novel enzyme process intensification technology – the spinning cloth disc reactor (SCDR): conversion increased by around 13% under similar conditions compared to a conventional batch stirred tank reactor. The SCDR is therefore key to exploiting the advantages of the wool immobilized lipase developed in this work.  相似文献   
42.
A polymerizable gemini surfactant was used to adsolubilize styrene and phenylethanol, representing less and more polar organic solutes, respectively, in order to evaluate the impact of admicellar polymerization on the adsolubilization process. Adsolubilization was also evaluated using a polymerizable monomeric surfactant and conventional surfactant for comparison purposes. The main results were that: (1) polymerized and unpolymerized admicelles showed similar adsolubilization potential—validating the use of polymerized admicelles without sacrificing adsolubilization, and (2) gemini surfactants showed adsolubilization capacities equal to or higher than conventional surfactants.  相似文献   
43.
The carabid fauna of 28 derelict sites in the West Midlands (England) were sampled over the course of one growing season (April-October, 1999). The study aimed to investigate the relationship between carabid assemblages and five measures of landscape structure pertinent to derelict habitat. At each site measurements of landscape features pertinent to derelict habitat were made: (i) the proximity of habitat corridors; (ii) the density of surrounding derelict land; (iii) the distance between the site and the rural fringe; and (iv) the size of the site. Concurrent surveys of the soil characteristics, vegetation type, and land use history were conducted. The data were analysed using a combination of ordination (DCA, RDA), variance partitioning (using pRDA) and binary linear regression. The results suggest that: 1. There is very little evidence that the carabid assemblages of derelict sites were affected by landscape structure, with assemblages instead being principally related to within-site habitat variables, such as site age (since last disturbance), substrate type and vegetation community. 2. No evidence was found to support the hypothesis that sites away from railway corridors are impoverished in their carabid fauna than sites on corridors. 3. There are some suggestions from this study that rarer and non-flying specialist species may be affected by isolation, taking longer to reach sites. We infer from this that older sites with retarded succession, and sites in higher densities of surrounding derelict land may eventually become more species rich and that these sites may be important for maintaining populations of rarer and flightless species. 4. Conservation efforts to maintain populations of these species should focus principally on habitat quality issues, such as maintaining early successional habitats that have a diversity of seed producing annuals and perennial plants and enhancing substrate variability rather than landscape issues.  相似文献   
44.
There is an urgent need for new drugs for the treatment of tropical parasitic diseases such as human African trypanosomiasis, which is caused by Trypanosoma brucei. The enzyme trypanothione reductase (TryR) is a potential drug target within these organisms. Herein we report the screening of a 62 000 compound library against T. brucei TryR. Further work was undertaken to optimise potency and selectivity of two novel‐compound series arising from the enzymatic and whole parasite screens and mammalian cell counterscreens. Both of these series, containing either a quinoline or pyrimidinopyrazine scaffold, yielded low micromolar inhibitors of the enzyme and growth of the parasite. The challenges of inhibiting TryR with druglike molecules is discussed.  相似文献   
45.
The impact of waste disposal on marsh soils was assessed in topsoil samples collected at eight randomly selected points in the salt marsh in Ramallosa (Pontevedra, Spain) at 4-month intervals for 2 years. Polluted soil samples were characterized in physico-chemical terms and their heavy metal contents determined by comparison with control, unpolluted samples. The results revealed a marked effect of waste discharges on the soils in the area, which have low contents in heavy metals under normal environmental conditions. In fact, the studied soils were found to contain substantial amounts of total and DTPA-extractable Cd, Cu, Pb and Zn. Based on the relationship of the redox potential with the DTPA-extractable Cd, Cu, Pb, and Zn contents of the soils, strongly reductive conditions raised the total contents in these elements by effect of their remaining in the soils as precipitated sulphides. Such contents, however, decreased as oxidative conditions gradually prevailed. The contents in DTPA-extractable metals increased with increasing Eh through the release of the metals in ionic form to the soil solution under oxidative conditions. The contents in heavy metals concentrating in the polluted soils were several times higher than those in the control soils (viz. 2 vs. 6 for Cd, 4 vs. 6 for Cu, 4 vs. 20 for Pb, and 2 vs. 15 for Zn, all in mg kg−1). This can be expected to influence the amounts of available heavy metals present in the soils, and hence the environmental quality of the area, in the near future. Based on its geoaccumulation index (Class ≥3 for Cd and Cu, and 1–4 for Pb and Zn), the Ramallosa marsh is highly polluted with Cd and moderately to highly polluted with Cu, Pb and Zn. The enrichment factors obtained confirm that the salt marsh is highly polluted (especially with Cd) as the primary result of anthropic activity.  相似文献   
46.
In this study, the authors examined parent-adolescent cortisol associations in 45 families with adolescent children (24 girls; M age = 15.78 years, SD = 1.44 years). Family members’ salivary cortisol levels were measured seven times a day on 2 typical weekdays. Family members provided reports of demographic and health variables, and adolescents rated parent-child relationship characteristics. After accounting for the effects of time of day and relevant demographic and health control variables on cortisol levels, hierarchical linear models indicated the presence of significant covariation over time in mother-adolescent cortisol (i.e., physiological synchrony). Furthermore, moderating tests revealed that mother-adolescent cortisol synchrony was strengthened among dyads characterized by mothers and adolescents spending more time together, and in families rated higher on levels of parent-youth shared activities and parental monitoring or supervision. Analysis of momentary characteristics indicated that maternal presence at the time of cortisol sampling lowered adolescent cortisol levels but did not account for mother-adolescent cortisol synchrony. Within-family physiological synchrony was amplified in momentary contexts of elevated maternal negative affect and elevated adolescent negative affect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
47.
48.
Film music has powerful aesthetic effects on the perception and understanding of screen content, but does it also influence viewers' sense of connection with movie characters thereby creating antecedents for an experience of empathy? Participants viewed clips showing characters' neutral or ambiguous reaction to an event, person, or object. Viewers rated character likability and their certainty about characters' thoughts in three conditions: thriller music, melodrama music, and no music. The effect of music conditions differed significantly from the no music condition. Compared to melodramatic music, thriller music significantly lowered likability and certainty about characters' thoughts. During subsequent cued recall of screen content, thriller music increased anger attributions and lowered sadness attributions, while melodramatic music increased love attributions and lowered fear attributions. The study provides evidence that film music can influence character likability and the certainty of knowing the character's thoughts, which are antecedents of empathetic concern and emphatic accuracy. Thus film music may be regarded as modulating antecedents of empathic concern and empathic accuracy. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
49.
The ideas of children about the environmental impact of vehicle emissions have been explored using a precoded questionnaire. The children were from British National Curriculum Years 7 (age 11/12 years), 9 (age 13/14) and 11 (age 15/16). Even in the oldest group only about half of the children appreciated the advantages of smaller, well‐maintained cars; this could have practical implication if not corrected in the adult population. Children seemed well aware of the environmental problems, smog, Acid Rain and Global Warming, to which vehicle emissions contribute, but these are part of an over‐generalised model which children employ in which cars are envisaged as contributing to other problems such as Ozone Layer depletion. We suggest that the use of the generic term ‘pollution’ to describe a wide range of environmental insults and the use of the word ‘environment’ in a non‐defined way might hinder children's differentiation of the different causes of separate environmental problems. The gaps in children's knowledge of the different components of vehicle emissions may reflect and exacerbate this difficulty. Ironically, children have a regard for the environmental and an interest in cars, and a combination of these enthusiasms may provide an opportunity for environmental education and curriculum science teaching.  相似文献   
50.
Reports an error in "Does Barbie make girls want to be thin? The effect of experimental exposure to images of dolls on the body image of 5- to 8-year-old girls" by Helga Dittmar, Emma Halliwell and Suzanne Ive (Developmental Psychology, 2006 Mar, Vol 42[2], 283-292). A substantive error occurs in the Body shape dissatisfaction section on page 287. The sentence describing the calculation of body shape dissatisfaction scores from girls' responses to the Child Figure Rating Scale should instead read as follows: "A body shape dissatisfaction score was computed by subtracting the girl's actual from her ideal body size." (The following abstract of the original article appeared in record 2006-03514-007.) The ubiquitous Barbie doll was examined in the present study as a possible cause for young girls' body dissatisfaction. A total of 162 girls, from age 5 to age 8, were exposed to images of either Barbie dolls, Emme dolls (U.S. size 16), or no dolls (baseline control) and then completed assessments of body image. Girls exposed to Barbie reported lower body esteem and greater desire for a thinner body shape than girls in the other exposure conditions. However, this immediate negative impact of Barbie doll was no longer evident in the oldest girls. These findings imply that, even if dolls cease to function as aspirational role models for older girls, early exposure to dolls epitomizing an unrealistically thin body ideal may damage girls' body image, which would contribute to an increased risk of disordered eating and weight cycling. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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