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   991篇
  免费   103篇
电工技术   3篇
化学工业   216篇
金属工艺   9篇
机械仪表   10篇
建筑科学   54篇
矿业工程   1篇
能源动力   21篇
轻工业   141篇
水利工程   28篇
石油天然气   3篇
无线电   73篇
一般工业技术   174篇
冶金工业   245篇
原子能技术   3篇
自动化技术   113篇
  2024年   4篇
  2023年   22篇
  2022年   10篇
  2021年   51篇
  2020年   38篇
  2019年   38篇
  2018年   62篇
  2017年   42篇
  2016年   49篇
  2015年   31篇
  2014年   29篇
  2013年   40篇
  2012年   54篇
  2011年   85篇
  2010年   72篇
  2009年   43篇
  2008年   64篇
  2007年   51篇
  2006年   48篇
  2005年   35篇
  2004年   25篇
  2003年   27篇
  2002年   17篇
  2001年   11篇
  2000年   9篇
  1999年   13篇
  1998年   14篇
  1997年   7篇
  1996年   5篇
  1995年   4篇
  1994年   9篇
  1993年   4篇
  1992年   9篇
  1991年   3篇
  1990年   3篇
  1989年   3篇
  1985年   2篇
  1984年   2篇
  1983年   2篇
  1981年   2篇
  1980年   2篇
  1978年   2篇
  1977年   3篇
  1976年   3篇
  1935年   2篇
  1934年   10篇
  1933年   2篇
  1932年   2篇
  1926年   4篇
  1925年   11篇
排序方式: 共有1094条查询结果,搜索用时 93 毫秒
81.
82.
83.
84.
85.
In 1941, the Baltimore City Council passed a law, the Ordinance on the Hygiene of Housing, declaring that all property in the city should be ‘maintained in good repair by the owner or agent, and fit for human habitation’. The campaign of housing-code enforcement that followed, known as the Baltimore Plan, made the city famous. When historians write about American housing-reform efforts during the mid-20th century, they tend to focus on big-ticket federal policies; by contrast, the Baltimore Plan seems too small to be significant. But it is more than a curiosity. First in Baltimore and then across the country, the neat cause-and-effect it posited between good stewardship and good housing crowded out more challenging ways of thinking about the problem. Eventually, the Baltimore Plan turned into a policy tool that reinforced the interests of the real estate industry at the expense of poor people. In that regard, the Baltimore Plan laid the foundations for federal disinvestment in the provision of decent housing and the midcentury tragedy of urban renewal.  相似文献   
86.
87.
In offspring exposed in utero to a maternal diet high in fat (HF), we have previously demonstrated that despite similar birth weights, HF adult offspring at 6 months of age had significantly higher body weights, greater adiposity, and increased triacylglycerol (TAG) levels as compared to controls. We hypothesized that a maternal HF diet predisposes to offspring adiposity via a programmed increase in the synthesis of monounsaturated fatty acids in the liver and hence increased substrate availability for liver TAG synthesis. We further hypothesized that programmed changes in offspring liver fatty acid metabolism are associated with increased liver expression of the lipogenic enzyme stearoyl‐CoA desaturase‐1 (SCD‐1). Female rats were maintained on a HF diet rich in monounsaturated fatty acids (MUFA) prior to and throughout pregnancy and lactation. After birth, newborns were nursed by the same dam, and all offspring were weaned to control diet. Plasma and liver fatty acid compositions were determined using gas chromatography/mass spectrometry. Fatty acid C16 desaturation indices of palmitoleic/palmitic and (vaccenic + palmitoleic)/palmitic and the C18 desaturation index of oleic/stearic were calculated. Liver protein abundance of SCD‐1 was analyzed in newborns and adult offspring. Plasma and liver C16 desaturation indices were decreased in HF newborns, but increased in the adult offspring. Liver SCD‐1 expression was increased in the HF adult offspring. These data show that the maternal HF diet during pregnancy and lactation increases offspring liver SCD‐1 protein abundance and alters the liver C16 desaturase pathway.  相似文献   
88.
Planners, designers, environmentalists, concerned citizens, and government officials are interested in the management and preservation of small rare and unique ecological environments. Scholars have discovered that land-use and visual quality metrics often co-vary together and that various land-uses reside on a continuum scale from high respondent preference (biospheric land-uses) to low respondent preference (noospheric land-uses). This study assessed and documented the visual metrics for the Maxton Plains alvar/alvar grassland plant communities found on Drummond Island, Michigan, USA. These unique, small, and rare landscape types are not usually studied by large-scale visual quality mapping efforts which assess urban areas, woodlands, water, farmland, pastureland, and prairies. The visual metrics were assessed using two versions of predictive visual quality assessment models. Results from 60 field photographs reveal that the visual metrics assessment for the Maxton Plains alvars/alvar grasslands have a moderate visual preference, consistent visual quality scores: ranging from the low to middle 50s with the first equation and high 40s to low 50s with the second equation. Compared to many landscape and land-uses, these environments have scores that indicate a moderate visual preference and appreciation. Scores beyond±2.5 of the mean would indicate a significant (p≤0.05) perceivable drift from the existing conditions. The visual metrics provide a numerical framework for managing the spatial contents within and adjacent to the alvars. Landscape features such as buildings, invasive woodlands, agriculture, and pavement would all decrease the visual quality beyond the ± 2.5 score range.  相似文献   
89.
示波器是大多数电子工程师进行试验、信号评估、故障测试和规格检查过程中必不可少的设备。即使是在经济不景气的情况下,示波器市场也始终呈现出不断创新的态势。甚至可以说,这一创新趋势也正因为大环境的萧条显现的愈发明显。  相似文献   
90.
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