全文获取类型
收费全文 | 18381篇 |
免费 | 1701篇 |
国内免费 | 1029篇 |
专业分类
电工技术 | 559篇 |
技术理论 | 2篇 |
综合类 | 1736篇 |
化学工业 | 2278篇 |
金属工艺 | 525篇 |
机械仪表 | 426篇 |
建筑科学 | 5878篇 |
矿业工程 | 452篇 |
能源动力 | 341篇 |
轻工业 | 1657篇 |
水利工程 | 641篇 |
石油天然气 | 1074篇 |
武器工业 | 474篇 |
无线电 | 1059篇 |
一般工业技术 | 918篇 |
冶金工业 | 1049篇 |
原子能技术 | 133篇 |
自动化技术 | 1909篇 |
出版年
2024年 | 72篇 |
2023年 | 259篇 |
2022年 | 460篇 |
2021年 | 591篇 |
2020年 | 685篇 |
2019年 | 474篇 |
2018年 | 460篇 |
2017年 | 513篇 |
2016年 | 685篇 |
2015年 | 707篇 |
2014年 | 1208篇 |
2013年 | 1120篇 |
2012年 | 1336篇 |
2011年 | 1370篇 |
2010年 | 1102篇 |
2009年 | 1256篇 |
2008年 | 1068篇 |
2007年 | 1316篇 |
2006年 | 1198篇 |
2005年 | 1029篇 |
2004年 | 817篇 |
2003年 | 659篇 |
2002年 | 591篇 |
2001年 | 433篇 |
2000年 | 369篇 |
1999年 | 282篇 |
1998年 | 192篇 |
1997年 | 141篇 |
1996年 | 106篇 |
1995年 | 100篇 |
1994年 | 79篇 |
1993年 | 71篇 |
1992年 | 70篇 |
1991年 | 46篇 |
1990年 | 40篇 |
1989年 | 29篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 17篇 |
1985年 | 21篇 |
1984年 | 29篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1971年 | 4篇 |
1963年 | 3篇 |
1957年 | 4篇 |
1956年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Evidence suggests that transient visual information, such as animations, may be more challenging to learn than static visualizations. However, when a procedural-manipulative task is involved, our evolved embodied cognition seems to reverse this transitory challenge. Hence, for object manipulative tasks, instructional animations may be more suitable than statics. We investigated this argument further by comparing animations with statics using a Lego task shown to university students, by examining three potential moderators of effectiveness: (a) the environment of manipulation (virtual or physical), (b) the quality of visual information (focused or unfocused), and (c) the presence of hands (no hands or with hands). In Experiment 1 we found an advantage of animation over statics, and no differences among the environments. In Experiment 2, we again observed an animation advantage, a small advantage of focused static information compared to unfocused static information, and a positive effect of not showing the hands. 相似文献
3.
在取得土料场土料物理力学性质参数的情况下,遵循碾压试验基本原理、方法及参数组合,进行了现场碾压试验,通过试验成果的分析,得出了大坝碾压试验结论,为大坝土方填筑提供了技术依据。 相似文献
4.
6.
7.
ABSTRACT: Physical aging of amorphous anhydrous fructose at temperature 5 °C and at 22 °C was studied using differential scanning calorimetry (DSC). The dynamic glass transition temperature, Tg0 for unaged samples was 16 °C and 13.3 °C for heating rate of 10 °C/min and 1 °C/min, respectively. The fictive temperature, Tf0 for unaged samples calculated by Richardson and Savill method was 12 °C, which is close to the dynamic value obtained from the lower DSC heating rate. The fictive temperature Tf of the aged fructose glasses at temperatures both below and above the transition region was fitted well by a non-exponential decay function (Williams-Watts form). Aging above the transition region (22 °C) for 18 d increased both the dynamic glass transition temperature Tg and the fictive temperature Tf . However, aging below the transition region (5 °C) for 1 d increased the dynamic glass transition temperature Tg but decreased the fictive temperature Tf . 相似文献
8.
七号信令网管系统的数据库服务器采用惠普UNIX工作站及SYBASE数据库。由于采集的数据量增大,原先设计的数据库空间不能满足数据存储三个月的要求.因此采用一块外置硬盘对数据库空间进行扩展。详细地介绍了SYBASE数据库空间扩展的全过程。 相似文献
9.
Kathryn Kromroy Kathleen Ward Paul Castillo Jennifer Juzwik 《Landscape and urban planning》2007,80(4):375-385
Urbanization was associated with loss and transformation of the oak forest in the Twin Cities (Minneapolis and St. Paul) metropolitan area (TCMA) over a recent 7-year interval. Between 1991 and 1998, urbanization increased based on several indicators: population density, area of developed land, and area of impervious surface—total impervious area and area within three classes of increasing degree of imperviousness (protected, affected, and degraded). We quantified relationships between changes in urbanization and changes in several parameters describing the oak forest at the scale of ecological subsection. Increased total and affected impervious area were strongly correlated with decreased area of oak forest when changes of the urbanization indicators and oak were expressed as percentages of the subsection area. Relationships were reversed when changes were expressed as percentages of the 1991 values. Increased population density was strongly correlated with increased loss in numbers and increased isolation of oak patches, but weakly correlated with loss of oak forest area. This is the first study to quantify relationships between changes in urbanization and changes in a specific forest cover type. Our results demonstrate complexities of urbanization impacts on a metropolitan forest resource, and highlight the importance of selected variables, spatial and temporal scales, and expressions of change when quantifying these relationships. 相似文献
10.
Wilcox Sara; Evenson Kelly R.; Aragaki Aaron; Wassertheil-Smoller Sylvia; Mouton Charles P.; Loevinger Barbara Lee 《Canadian Metallurgical Quarterly》2003,22(5):513
This study examined whether widowhood was associated with physical and mental health, health behaviors, and health outcomes using a cross-sectional (N=72,247) and prospective (N=55,724) design in women aged 50-79 years participating in the Women's Health Initiative observational study (85.4% White). At baseline, married women reported better physical and mental health and generally better health behaviors than widowed women. Whereas women who remained married over the 3-year period showed stability in mental health, recent widows experienced marked impairments and longer term widows showed stability or slight improvements. Both groups of widows reported more unintentional weight loss over the 3-year period. Changes in physical health and health behaviors were inconsistent, with generally small effect sizes. Findings underscore the resilience of older women and their capacity to reestablish connections, but point to the need for services that strengthen social support among women who have difficulty during this transition. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献