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   5410篇
  免费   387篇
  国内免费   3篇
电工技术   26篇
综合类   7篇
化学工业   1473篇
金属工艺   56篇
机械仪表   47篇
建筑科学   241篇
矿业工程   82篇
能源动力   81篇
轻工业   960篇
水利工程   49篇
石油天然气   25篇
武器工业   1篇
无线电   334篇
一般工业技术   864篇
冶金工业   879篇
原子能技术   37篇
自动化技术   638篇
  2023年   48篇
  2022年   143篇
  2021年   212篇
  2020年   116篇
  2019年   103篇
  2018年   127篇
  2017年   185篇
  2016年   215篇
  2015年   194篇
  2014年   223篇
  2013年   353篇
  2012年   304篇
  2011年   347篇
  2010年   288篇
  2009年   250篇
  2008年   290篇
  2007年   296篇
  2006年   235篇
  2005年   183篇
  2004年   167篇
  2003年   149篇
  2002年   138篇
  2001年   100篇
  2000年   74篇
  1999年   89篇
  1998年   115篇
  1997年   110篇
  1996年   70篇
  1995年   56篇
  1994年   69篇
  1993年   71篇
  1992年   54篇
  1991年   31篇
  1990年   38篇
  1989年   29篇
  1988年   35篇
  1987年   34篇
  1986年   23篇
  1985年   28篇
  1984年   18篇
  1983年   28篇
  1982年   18篇
  1981年   12篇
  1980年   21篇
  1979年   16篇
  1978年   8篇
  1977年   14篇
  1976年   9篇
  1975年   10篇
  1974年   9篇
排序方式: 共有5800条查询结果,搜索用时 15 毫秒
101.
At the year end of 2011 Belgium formed a government, after a world record breaking period of 541 days of negotiations. We have gathered and analysed 68,000 related on-line news articles published in 2011 in Flemish newspapers. These articles were analysed by a custom-built expert system. The results of our text mining analyses show interesting differences in media coverage and votes for several political parties and politicians. With opinion mining, we are able to automatically detect the sentiment of each article, thereby allowing to visualise how the tone of reporting evolved throughout the year, on a party, politician and newspaper level. Our suggested framework introduces a generic text mining approach to analyse media coverage on political issues, including a set of methodological guidelines, evaluation metrics, as well as open source opinion mining tools. Since all analyses are based on automated text mining algorithms, an objective overview of the manner of reporting is provided. The analysis shows peaks of positive and negative sentiments during key moments in the negotiation process.  相似文献   
102.
Questions S. L. Bem's (see record 1983-21087-001) definition of a gender schema and argues that male and female sex-typed individuals do not have equivalent gender schemata. The high-androgynous individuals are the only ones for whom both masculinity and femininity are equally available and who might be properly termed "gender schematic." (6 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
103.
Sewage sludge ash (SSA) is a waste material obtained from the incineration of wastewater sludge. The physical, chemical and mineralogical characteristics of SSA, and the evaluation of its use in cement-based materials, are presented in this paper. Results show that SSA is composed of irregular grains having a high specific surface area and thus leading to a significantly high water demand. A fraction of the ash is rapidly soluble (sulfates, aluminum and silica) and can create new-formed products in presence of lime. SSA induces short delays of cement hydration, probably due to both minor elements of the ash and dilution effect. Compressive strengths of mortars containing 25% and 50% of SSA are always lower than those of reference mortars but it is shown that SSA has a long-term positive effect which might be related to a slight pozzolanic activity. The amount of elements leached from SSA mortars is slightly higher than from the reference mortar without residue but it remains of the same order of magnitude. An extensive literature review was performed in order to compare the residue used in this study with others included in the same category. This analysis highlighted the principal characteristics that must be taken into account to use SSA correctly in cement-based materials.  相似文献   
104.
Lecontite, (NH4)Na(SO4).2H2O, was synthesised at room temperature in high purity compared to earlier work with a minor impurity of mascagnite, (NH4)2SO4. Rietveld refinement of the XRD results confirmed the crystal structure and unit cell dimensions as published earlier. Raman and Infrared spectroscopy, in conjunction with factor group analysis, resulted in a complex pattern of overlapping sulphate, NH and OH modes. The NH modes υ1 was observed around 2880 cm−1, υ2 around 1700 cm−1 overlapping with water OH-bending modes, υ3 around 3300 cm−1 overlapping with water OH-stretching modes around 3023, 3185 and 3422 cm−1, and υ4 around 1432, 1447 and 1462 cm−1. The sulphate group in the crystal structure displays a decrease in symmetry from Td as evidenced by the activation of the ν1 mode at 982 cm−1 and the ν2 mode around 452 cm−1 in the Infrared spectrum. The υ3 mode shows clear splitting in the infrared spectra with a strong band at 1064 cm−1 accompanied by two shoulders at 1107 and 1139 cm−1. The Raman spectra show three weak bands at 1068, 1109 and 1135 cm−1 with a shoulder at 1155 cm−1. Similar splitting was observed for the υ4 mode around 611 and 632 cm−1 in the Infrared and Raman spectra, respectively.  相似文献   
105.
Children's vulnerability to jealousy surrounding their best friends was explored in 2 studies. Study 1 involved 94 adolescents who reported on their friendship jealousy on a newly created measure. Results indicated that the jealousy measure had sound psychometric properties and produced individual differences that were robust over time and free from socially desirable responding. As expected, girls and adolescents with low self-worth reported the greatest friendship jealousy. Study 2 involved 399 young adolescents and extended the measurement of self-report jealousy to a broader age range. In addition, Study 2 included assessments of jealousy provided by friends and other peers. Self- and peer-reported jealousy were only modestly associated and had somewhat distinct correlates. Structural modeling revealed that young adolescents' reputation for friendship jealousy was linked to behaving aggressively and to broader peer adjustment difficulties. Both self- and peer-reported jealousy contributed to loneliness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
106.
Early Head Start, a federal program begun in 1995 for low-income pregnant women and families with infants and toddlers, was evaluated through a randomized trial of 3,001 families in 17 programs. Interviews with primary caregivers, child assessments, and observations of parent-child interactions were completed when children were 3 years old. Caregivers were diverse in race-ethnicity, language, and other characteristics. Regression-adjusted impact analyses showed that 3-year-old program children performed better than did control children in cognitive and language development, displayed higher emotional engagement of the parent and sustained attention with play objects, and were lower in aggressive behavior. Compared with controls, Early Head Start parents were more emotionally supportive, provided more language and learning stimulation, read to their children more, and spanked less. The strongest and most numerous impacts were for programs that offered a mix of home-visiting and center-based services and that fully implemented the performance standards early. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
107.
为了给医生利用医学图象进行诊断和分析心血管疾病提供一个有效的工具和途径,利用计算机视觉中的正则化方法,结合心脏和心血管动态特征的临床知识,对两种医学动态图象(超声心动图和心血管造影图)进行了定量的运动分析,并完成了一套应用软件.实验结果证明,该方法明显优于以往的图象分析方法。  相似文献   
108.
109.
This article provides an overview of the factors that may contribute to the effective term of protection for a pharmaceutical product in the USA––by patent and by FDA market exclusivities, identifies public and commercial sources for collecting relevant patent term and exclusivity data, and provides a strategy for ensuring that the effective term of protection has been calculated accurately.  相似文献   
110.
The authors examined the role of family factors and the course of schizophrenia by carrying out additional assessments and analyses in 2 previously published studies of Mexican American and Anglo American patients and families. The authors found partial support for an attributional model of relapse for families who are low in emotional overinvolvement. Attributions of control, criticism, and warmth together marginally predicted relapse. The data also indicated that for Mexican Americans, family warmth is a significant protective factor, whereas for Anglo Americans, family criticism is a significant risk factor. These findings suggest that the sociocultural context shapes the pathways by which family processes are related to the course of illness. Moreover, the warmth findings suggest that families may contribute to preventing relapse. (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