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   1746篇
  免费   64篇
  国内免费   15篇
电工技术   3篇
综合类   73篇
化学工业   72篇
金属工艺   10篇
机械仪表   19篇
建筑科学   169篇
矿业工程   1篇
轻工业   200篇
水利工程   1篇
石油天然气   1篇
武器工业   1篇
无线电   34篇
一般工业技术   161篇
冶金工业   949篇
原子能技术   2篇
自动化技术   129篇
  2024年   6篇
  2023年   26篇
  2022年   33篇
  2021年   55篇
  2020年   59篇
  2019年   33篇
  2018年   33篇
  2017年   37篇
  2016年   28篇
  2015年   30篇
  2014年   66篇
  2013年   80篇
  2012年   87篇
  2011年   135篇
  2010年   115篇
  2009年   111篇
  2008年   85篇
  2007年   77篇
  2006年   99篇
  2005年   82篇
  2004年   110篇
  2003年   88篇
  2002年   73篇
  2001年   44篇
  2000年   6篇
  1999年   10篇
  1998年   11篇
  1993年   4篇
  1990年   7篇
  1989年   8篇
  1988年   9篇
  1987年   8篇
  1986年   5篇
  1984年   13篇
  1983年   5篇
  1981年   4篇
  1979年   5篇
  1966年   7篇
  1965年   6篇
  1964年   21篇
  1963年   6篇
  1962年   3篇
  1961年   14篇
  1960年   7篇
  1959年   5篇
  1958年   5篇
  1957年   6篇
  1956年   4篇
  1955年   14篇
  1954年   4篇
排序方式: 共有1825条查询结果,搜索用时 31 毫秒
11.
The indoor air quality (IAQ) was investigated in sixty-four primary school buildings in five Central European countries (Czech Republic, Hungary, Italy, Poland, and Slovenia). The concentration of volatile organic compounds, aldehydes, PM2.5 mass, carbon dioxide, radon, as well as physical parameters were investigated during the heating period of 2017/2018. Significant differences were identified for the majority of the investigated IAQ parameters across the countries. The median indoor/outdoor ratios varied considerably. A comprehensive evaluation of IAQ in terms of potential health effects and comfort perception was performed. Hazard quotient values were below the threshold value of 1 with one exception. In contrast, 31% of the school buildings were characterized by hazard index values higher than 1. The maximum cumulative ratio approach highlighted that the concern for non-carcinogenic health effects was either low or the health risk was driven by more substances. The median excess lifetime cancer risk values exceeded the acceptable value of 1 × 10−6 in the case of radon and formaldehyde. PM2.5 mass concentration values exceeded the 24 h and annual guideline values set by the World Health Organization in 56 and 85% of the cases, respectively. About 80% of the schools could not manage to comply with the recommended concentration value for carbon dioxide (1000 ppm).  相似文献   
12.
ABSTRACT

Families are increasingly choosing to raise children in the growing number of private, high-rise apartment complexes developed in Australian capital cities. However, most of these developments have been designed for the childless and there are concerns as to how supportive these settings are for young children. This paper explores parents’ experiences of the environment surrounding their high-rise dwellings in an inner-city municipality of Melbourne, Australia using the participatory method, Photovoice. Ten parents photographed elements of their dwellings and environments that had positive or negative impacts on raising young children. Findings indicate that environments surrounding parents’ high-rise dwellings were used on a daily basis, often due to limited space within apartment complexes. However, aspects of this environment were challenging, requiring mutual accommodation between families and their immediate settings. This has implications for policy to ensure the neighbourhoods surrounding high-rise developments in inner-city areas are more child friendly.  相似文献   
13.
This study aims to explore the ways of involving children with autism in participatory product design processes. Due to the impaired skills of children with autism, a key aspect of the process is to gain an understanding of the nature of the disorder and how these children interact with their social and material surroundings as well as their daily life problems. Considering this, a case study was conducted with children with autism, their parents and teachers, and also industrial design students in a public special education centre in ?zmir, Turkey. The design task was to reconsider the conventional trampoline design with respect to the needs of the sample group and the special education centre as well as the benefits it provides. The task was based on the patterns of behaviours, actions and movement. Observations, interviews and questionnaires were carried out, as well as collaborative meetings and discussion meetings. Through the case study, the findings provided insights into conducting a participatory process with children with autism, the roles of the participants, and the interaction and communication among them. Furthermore, participants’ attitude towards participatory design, the potential benefits of the design process, and innovations to benefit children with autism were explained.  相似文献   
14.
To better understand the magnitude of arsenic contamination in groundwater and its effects on human beings, a detailed study was carried out in Jalangi, one of the 85 arsenic affected blocks in West Bengal, India. Jalangi block is approximately 122 km2 in size and has a population of 215538. Of the 1916 water samples analyzed (about 31% of the total hand tubewells) from the Jalangi block, 77.8% were found to have arsenic above 10 microg l(-1) [the World Health Organization (WHO)-recommended level of arsenic in drinking water], 51% had arsenic above 50 microg l(-1) (the Indian standard of permissible limit of arsenic in drinking water) and 17% had arsenic at above 300 microg l(-1) (the concentration predicting overt arsenical skin lesions). From our preliminary medical screening, 1488 of the 7221 people examined in the 44 villages of Jalangi block exhibit definite arsenical skin lesions. An estimation of probable population that may suffer from arsenical skin lesions and cancer in the Jalangi block has been evaluated comparing along with international data. A total of 1600 biologic samples including hair, nail and urine have been analyzed from the affected villages of Jalangi block and on an average 88% of the biologic samples contain arsenic above the normal level. Thus, a vast population of the block may have arsenic body burden. Cases of Bowen's disease and cancer have been identified among adults who also show arsenical skin lesions and children in this block are also seriously affected. Obstetric examinations were also carried out in this block.  相似文献   
15.
This communication presents results of our 2-year survey on groundwater arsenic contamination in three districts Ballia, Varanasi and Gazipur of Uttar Pradesh (UP) in the upper and middle Ganga plain, India. Analyses of 4,780 tubewell water samples revealed that arsenic concentrations in 46.5% exceeded 10 microg/L, in 26.7%, 50 microg/L and in 10% 300 microg/L limits. Arsenic concentrations up to 3,192 microg//L were observed. The age of tubewells (n=1,881) ranged from less than a year to 32 years, with an average of 6.5 years. Our study shows that older tubewells had a greater chance of contamination. Depth of tubewells (n=3,810) varied from 6 to 60.5 m with a mean of 25.75 m. A detailed study in three administrative units within Ballia district, i.e. block, Gram Panchayet, and village was carried out to assess the magnitude of the contamination. Before our survey the affected villagers were not aware that they were suffering from arsenical toxicity through contaminated drinking water. A preliminary clinical examination in 11 affected villages (10 from Ballia and 1 from Gazipur district) revealed typical arsenical skin lesions ranging from melanosis, keratosis to Bowens (suspected). Out of 989 villagers (691 adults, and 298 children) screened, 137 (19.8%) of the adults and 17 (5.7%) of the children were diagnosed to have typical arsenical skin lesions. Arsenical neuropathy and adverse obstetric outcome were also observed, indicating severity of exposure. The range of arsenic concentrations in hair, nail and urine was 137-10,900, 764-19,700 microg/kg, and 23-4,030 microg/L, respectively. The urine, hair and nail concentrations of arsenic correlated significantly (r=0.76, 0.61, and 0.55, respectively) with drinking water arsenic concentrations. The similarity to previous studies on arsenic contamination in West Bengal, Bihar and Bangladesh indicates that people from a significant part of the surveyed areas in UP are suffering and this will spread unless drives to raise awareness of arsenic toxicity are undertaken and an arsenic safe water supply is immediately introduced.  相似文献   
16.
This paper explores who uses woodlands near their homes, why they visit, what benefits they believe they obtain and what makes the difference between them choosing to visit or not. In the research, supported by the Forestry Commission, a multi-method, user-led approach was used, based on focus groups, questionnaire surveys and on-site observation in relation to five different communities in the central belt of Scotland. The conclusions demonstrate the overriding importance of childhood woodland visits as predictors of adult patterns of use. Proximity of woodlands is important for regular woodland users and freedom from rubbish is the physical quality people care most about. The physical qualities that make a difference as to whether people visit woodlands or not include directional signs, good information boards, variety of trees and tidiness of appearance. Perceptions of woodlands differ according to age and sex but are predominantly positive across all groups sampled: most people feel at peace in a woodland.  相似文献   
17.
ABSTRACT

Sickle cell disease (SCD) is one of the common inherited blood disorders in humans and has been associated with decreased dietary intake which results in poor nutritional status and impaired growth. Nutrition is one of the most important but often forgotten aspect of care of patients with chronic disorders and there have been emerging concern in literature on increased nutritional needs of SCD patients. This paper sought to review the available literature on the roles of individual nutrients in the pathophysiology and management of SCD among children. Children with SCD have been shown to exhibit suboptimal status with respect to both macronutrients and micronutrients. Thus, nutrition could play an important role in the management of SCD. However, there is paucity of evidence coming from trials with large sample sizes to support the suggestion that supplementation with various nutrients that have been considered in this review will be helpful.  相似文献   
18.
This case study uncovers a turning point in the production of play space in Amsterdam. Whereas over the first half of the twentieth century the creation of play spaces used to be the primary responsibility of the Amsterdam civil society, this situation started to change after the Second World War. Between 1947 and 1970, the Amsterdam Urban Planning Department created over 700 public play spaces. These spaces were little niches in the urban public domain, specifically designed and constructed to enable city children's play. This remarkable change from a predominantly private to a public intervention, is explained through a rapid increase of the number of children (the post-war baby-boom), the existence of the General Extension Plan (AUP) with its detailed age specific approach and the fruitful collaboration between powerful urban planners and politically dominant socialist politicians.  相似文献   
19.
The concentration of lead in the scalp hair of 257 school children within the age range of 6–12, living in the Manzini region in Swaziland, was measured using a graphite furnace atomic absorption spectrometer. Mean lead concentration ranged between 7.75–9.19 μ.g/g, and 4.95–5.95 μg/g for the urban and rural schools, respectively. The mean lead concentrations in the hair for urban school children were significantly higher than those of the rural school children. The rapid industrialization within the city centre with increasing number of vehicles using leaded petrol may be a contributing factor to the observed levels. Although the mean lead concentration was higher in girls (7.59 μg/g) than in boys (6.62 μg/g), this difference was not statistically significant.  相似文献   
20.
Problem: Rates of walking and bicycling to school have declined sharply in recent decades, and federal and state governments have committed funds to reverse these trends. To increase rates of walking and biking to school will require understanding why many parents choose to drive their children to school and how well existing programs, like Safe Routes to School, work.

Purpose: We aimed to understand why many parents choose to drive their children even short distances to school, and what implications this has for programs to increase walking and biking to school.

Methods: We used data from a telephone survey to explore why parents drive their children to school.

Results and conclusions: We found that 75% of parents driving their children less than 2 miles to school said they did this for convenience and to save time. Nearly half of parents driving their children less than 2 miles did not allow their child to walk to school without adult supervision. Accompanying a child on a walk to school greatly increases the time the household devotes to such a trip. Few Safe Routes to School programs effectively address issues of parental convenience and time constraints.

Takeaway for practice: Safe Routes to School programs should take parental convenience and time constraints into account by providing ways children can walk to school supervised by someone other than the parent, such as by using walking school buses. To be effective, such programs need institutional support. Schools should take a multimodal approach to pupil transportation.

Research support: This research was funded by the Active Living Research program of the Robert Wood Johnson Foundation and the U.S. and California Departments of Transportation through the University of California Transportation Center.  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