全文获取类型
收费全文 | 8636篇 |
免费 | 271篇 |
国内免费 | 156篇 |
专业分类
电工技术 | 184篇 |
综合类 | 2683篇 |
化学工业 | 439篇 |
金属工艺 | 130篇 |
机械仪表 | 182篇 |
建筑科学 | 925篇 |
矿业工程 | 178篇 |
能源动力 | 75篇 |
轻工业 | 193篇 |
水利工程 | 465篇 |
石油天然气 | 210篇 |
武器工业 | 13篇 |
无线电 | 273篇 |
一般工业技术 | 224篇 |
冶金工业 | 1926篇 |
原子能技术 | 12篇 |
自动化技术 | 951篇 |
出版年
2023年 | 38篇 |
2022年 | 89篇 |
2021年 | 161篇 |
2020年 | 135篇 |
2019年 | 98篇 |
2018年 | 81篇 |
2017年 | 129篇 |
2016年 | 185篇 |
2015年 | 191篇 |
2014年 | 533篇 |
2013年 | 402篇 |
2012年 | 568篇 |
2011年 | 660篇 |
2010年 | 585篇 |
2009年 | 620篇 |
2008年 | 524篇 |
2007年 | 592篇 |
2006年 | 502篇 |
2005年 | 439篇 |
2004年 | 453篇 |
2003年 | 407篇 |
2002年 | 333篇 |
2001年 | 244篇 |
2000年 | 138篇 |
1999年 | 104篇 |
1998年 | 52篇 |
1997年 | 52篇 |
1996年 | 26篇 |
1995年 | 29篇 |
1994年 | 31篇 |
1993年 | 18篇 |
1989年 | 22篇 |
1988年 | 25篇 |
1987年 | 22篇 |
1986年 | 22篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1975年 | 14篇 |
1965年 | 25篇 |
1964年 | 32篇 |
1963年 | 25篇 |
1962年 | 21篇 |
1961年 | 29篇 |
1960年 | 23篇 |
1959年 | 28篇 |
1958年 | 32篇 |
1957年 | 26篇 |
1956年 | 31篇 |
1955年 | 41篇 |
1954年 | 26篇 |
排序方式: 共有9063条查询结果,搜索用时 15 毫秒
21.
80年代黄河中游来沙量减少,主要原因是降雨量减少和降雨强度减小,流域综合治理也起到了减沙作用。据分析,降雨因素减沙约占总减沙量的70%,流域综合治理减沙约占30%。 相似文献
22.
This article clarifies several research issues raised in a recent article by Krieshok, Arnold, Kuperman, and Schmitz concerned with repertory grid methodology. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
23.
Hishinuma Earl S.; Else 'Iwalani R. N.; Chang Janice Y.; Goebert Deborah A.; Nishimura Stephanie T.; Choi-Misailidis Soojean; Andrade Naleen N. 《Canadian Metallurgical Quarterly》2006,21(3):286
School psychologists are generally not provided with the knowledge and skills to address both educational and psychosocial issues of Asian American and Pacific Islander students. The present study is the first of its kind in examining 36 independent (i.e., demographic, social, cultural, psychological) variables in association with four school outcomes (i.e., grade point average, absences, suspensions, and school infractions) with a large sample of Caucasian, Filipino, Native Hawaiian, Japanese, mixed/non-Hawaiian, and "other" Hawai'i high school students (N = 2,833). Given the relatively unique sample in question and the sheer number of variables, an exploratory approach was utilized with the goal of determining the most robust independent variables, with the unique inclusion of Hawaiian cultural identification. A cross-validation technique was used, whereby stepwise regressions were performed for each of two cross-validation samples; only common variables were retained in a final stepwise model for each of the four school outcomes. The results indicated that, remarkably, substance use accounted for the most variance (i.e., 8.4% -16.1 %) in the four school measures. Further analyses detailed the relationship, including the finding that smoking cigarettes regularly, accounted for the most variance compared to the other five substance use items. Further research and implications of the findings are discussed, including the need for prevention and intervention programs that incorporate substance use as a component, both within and outside of school environments. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
24.
Lopez Frederick G.; Fons-Scheyd Alia; Morúa Wendy; Chaliman Rebecca 《Canadian Metallurgical Quarterly》2006,53(4):543
This study examined the nature and impact of dyadic perfectionism over a 3-month interval within a sample of 116 college students who were currently involved in an intimate heterosexual relationship. Dyadic perfectionism scores were stable and correlated as expected with scores on concurrent measures of adult attachment orientations and relationship satisfaction. Logistic regression analyses revealed that, controlling for initial commitment status and adult attachment orientations, Time 1 dyadic perfectionism scores significantly and uniquely predicted relationship continuity 3 months later. Lastly, controlling for social desirability, relationship commitment status, and Time 1 adult attachment orientation scores, Time 1 dyadic perfectionism scores also uniquely predicted Time 2 relationship distress. Findings provide additional evidence that dyadic perfectionism is a risk factor for relationship dysfunction. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
25.
Students (N = 167) from the 4th, 8th, and 11th grades sorted meals, listed on individual cards, according to whether they would or would not eat them. Students were told to either consider eating the meals at home or at school. Forty-two different meals were selected from a pool of unique meals created by students in a previous study. The meals differed in head component, the presence or absence of vegetables, and the number of different foodstuffs. On average, approximately half of the meals were deemed acceptable, but older students accepted more meals than younger ones, boys accepted more meals than girls, and meals to be consumed at home were accepted more than those to be consumed at school. In addition, students tended to accept meals comprised of a small number of foodstuffs that did not contain vegetables. The also chose more meat-based meals over those containing fish or soup. These results suggest that students have rather unique food preferences that do not correspond well with nutritional standards. In order to address this problem we recommended that students be given more good choices in the school cafeteria through the introduction of a two-meal system and salad bars. 相似文献
26.
Krieshok Thomas S.; Arnold John J.; Kuperman Bernard D.; Schmitz Nancy K. 《Canadian Metallurgical Quarterly》1988,35(2):211
We respond to Cochran's critique of our 1986 study, which was in part a replication of Cochran's original grid methodology for the study of career values. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
27.
The author explored the mathematics efficacy beliefs of 270 South Asian (Indo Canadian) immigrant and Anglo Canadian nonimmigrant Grade 7 students. Self-efficacy beliefs strongly predicted mathematics performance for both cultural groups, but there were differences between the 2 groups in the sources of self-efficacy, the predictiveness of the secondary motivation variables, and the vertical dimensions of individualism and collectivism. It is argued that the Indo Canadian students are more vertical or hierarchical than the Anglo Canadian students and that comparison with others strongly influences their motivation beliefs and the formation of their efficacy beliefs. Self-efficacy in some cultures may be more other-oriented than is typically seen in Western cultures. A caution against generalizing about Asian populations is given, and implications for school settings are explored. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
28.
Differentiation of the construct of emotional intelligence was investigated in young and middle-aged adults, on the basis of hypotheses generated from differential emotions theory, discrete emotions functionalist theory, and empirical literature on age-related changes in affective complexity and differentiation of abilities. Both age groups were characterized by the same set of comparably related dimensions. However, midlife adults reported significantly greater use of optimism as a mood-regulation strategy than was reported by young adults. This study considers implications of possible structural continuity in emotional intelligence in conjunction with mean increases in the use of optimism as a strategy for managing affect. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
29.
Peer-assisted learning interventions with elementary school students: A meta-analytic review. 总被引:1,自引:0,他引:1
Rohrbeck Cynthia A.; Ginsburg-Block Marika D.; Fantuzzo John W.; Miller Traci R. 《Canadian Metallurgical Quarterly》2003,95(2):240
A meta-analytic review of group comparison design studies evaluating peer-assisted learning (PAL) interventions with elementary school students produced positive effect sizes (ESs) indicating increases in achievement (unweighted mean ES = 0.59, SD = 0.90; weighted ES, d = 0.33, p 相似文献
30.
浅谈绿色生态住宅小区的给排水设计 总被引:5,自引:0,他引:5
介绍了设计绿色生态住宅小区的水环境系统各个子系统时应满足的水质、水量和应遵循的设计规范。提出了对节水设施、器具和绿色管材的选用原则 相似文献