全文获取类型
收费全文 | 7921篇 |
免费 | 397篇 |
国内免费 | 242篇 |
专业分类
电工技术 | 228篇 |
技术理论 | 1篇 |
综合类 | 516篇 |
化学工业 | 808篇 |
金属工艺 | 70篇 |
机械仪表 | 125篇 |
建筑科学 | 1777篇 |
矿业工程 | 484篇 |
能源动力 | 429篇 |
轻工业 | 388篇 |
水利工程 | 762篇 |
石油天然气 | 116篇 |
武器工业 | 14篇 |
无线电 | 221篇 |
一般工业技术 | 273篇 |
冶金工业 | 849篇 |
原子能技术 | 16篇 |
自动化技术 | 1483篇 |
出版年
2024年 | 11篇 |
2023年 | 63篇 |
2022年 | 109篇 |
2021年 | 167篇 |
2020年 | 194篇 |
2019年 | 148篇 |
2018年 | 149篇 |
2017年 | 173篇 |
2016年 | 277篇 |
2015年 | 276篇 |
2014年 | 417篇 |
2013年 | 472篇 |
2012年 | 461篇 |
2011年 | 651篇 |
2010年 | 504篇 |
2009年 | 540篇 |
2008年 | 502篇 |
2007年 | 563篇 |
2006年 | 491篇 |
2005年 | 393篇 |
2004年 | 383篇 |
2003年 | 333篇 |
2002年 | 267篇 |
2001年 | 210篇 |
2000年 | 138篇 |
1999年 | 117篇 |
1998年 | 88篇 |
1997年 | 71篇 |
1996年 | 65篇 |
1995年 | 48篇 |
1994年 | 43篇 |
1993年 | 31篇 |
1992年 | 31篇 |
1991年 | 18篇 |
1990年 | 30篇 |
1989年 | 16篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 20篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1964年 | 3篇 |
1961年 | 2篇 |
排序方式: 共有8560条查询结果,搜索用时 140 毫秒
41.
面向表面组装工艺技术的PCB焊盘设计 总被引:1,自引:1,他引:0
尽管电子设计类软件已相当先进和方便,而且更新速度也很快,但是仍然无法满足各个层次的设计人员的需求,特别是适合各种元素封装形式的焊盘设计库并不能让设计和制造者满意,为了在此方面对PCB设计有所帮助,从印制电路板焊盘的设计方法入手,针对表面组装工艺技术特点,分析了PCB焊盘对PCA可靠性的影响因素,并根据相关的质量要求提出了较为简便的设计方案。 相似文献
42.
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
43.
本文描述了醋酸纤维素-纤维素大孔增强超滤膜的结构特征一分离性能之间的关系。详细论述了膜材料含量和粘连剂含量及其分子量对膜结构和性能的影响。论述了不同配方铸膜液的膜,其孔径,水通量和截留率随操作压力的变化规律。实验证明这种高强度的CAC膜经多次重复使用后,其结构性能保持完好。 相似文献
44.
45.
46.
47.
稠油热采注汽管道由于长期在高温、高压下运行,极易发生各种损伤,如腐蚀、裂纹、材料退化等,极易造成管道承压能力降低,发生失效事故。如何检测出潜在危险性缺陷,判断注汽管道能否继续使用,是保证注汽管道安全运行的关键问题。探讨了高温压力管道在线检测技术发展现状及其应用范围。 相似文献
48.
49.
Bray James H.; Adams Gerald J.; Getz J. Greg; McQueen Amy 《Canadian Metallurgical Quarterly》2003,71(3):553
The study used latent growth modeling to investigate longitudinal relationships between individuation, peer alcohol use, and adolescent alcohol use among African American, Mexican American, and non-Hispanic White adolescents (N=6,048) from 7th, 8th, and 9th grades over a 3-year period. Initial levels of peer alcohol use were significantly related to changes in adolescents' alcohol use, whereas initial adolescent alcohol use also significantly related to changes in peers' alcohol use, suggesting a bidirectional relationship. Higher levels of intergenerational individuation were related to smaller increases in adolescent alcohol use and higher levels of separation were related to larger increases in youth drinking. The findings were similar across ethnic groups. Implications for development of prevention and intervention programs are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
50.
As cropland and pasture have replaced forest and cerrado in Brazilian Amazônia, concern has mounted over the effects of changing the biogeochemical and hydrological properties of one of the world's great storehouses of biomass and biodiversity. Although much recent effort has focused on the location, effects, and causes of deforestation and cerrado conversion, much less is known about the basin-wide spatial distribution and density of the land use following conversion for crops or pasture.In this paper, we use census and satellite records to develop maps of the distribution and abundance of major agricultural land uses across 4.5×108 ha of Brazilian Amazônia in 1980 and 1995. Results indicate an overall expansion of 7.0×106 ha in total agricultural area in Brazilian Amazônia between 1980 and 1995. The net change during this period is estimated for three different land-use types: croplands (an increase of 0.8×106 ha), natural pastures (a decrease of 8.4×106 ha), and planted pastures (an increase of 14.7×106 ha). These estimates, the first spatially explicit quantifications of agricultural land-use activities in 1980 and 1995 across Brazilian Amazônia, are shown to be consistent with the results of applying a land use change and secondary regrowth model to published deforestation rates for the period.The resulting time slices, presented for each land-use category at 5-min (∼9 km) spatial resolution, allow for the quantification of land-use changes in this region for biogeochemical, demographic and economic models. Several foci of agricultural change existed within Brazilian Amazônia during this period: in the state of Pará, cropland was lost and planted pasture increased markedly; in Mato Grosso, both cropland and planted pasture increased; in Rondônia, planted pasture replacing forest was the primary route to agricultural expansion. 相似文献