全文获取类型
收费全文 | 3229篇 |
免费 | 166篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 20篇 |
综合类 | 2篇 |
化学工业 | 702篇 |
金属工艺 | 71篇 |
机械仪表 | 73篇 |
建筑科学 | 173篇 |
矿业工程 | 6篇 |
能源动力 | 105篇 |
轻工业 | 165篇 |
水利工程 | 43篇 |
石油天然气 | 28篇 |
无线电 | 245篇 |
一般工业技术 | 709篇 |
冶金工业 | 545篇 |
原子能技术 | 15篇 |
自动化技术 | 496篇 |
出版年
2023年 | 40篇 |
2022年 | 64篇 |
2021年 | 104篇 |
2020年 | 77篇 |
2019年 | 87篇 |
2018年 | 89篇 |
2017年 | 79篇 |
2016年 | 90篇 |
2015年 | 80篇 |
2014年 | 116篇 |
2013年 | 211篇 |
2012年 | 177篇 |
2011年 | 240篇 |
2010年 | 158篇 |
2009年 | 144篇 |
2008年 | 168篇 |
2007年 | 152篇 |
2006年 | 125篇 |
2005年 | 93篇 |
2004年 | 81篇 |
2003年 | 88篇 |
2002年 | 64篇 |
2001年 | 46篇 |
2000年 | 48篇 |
1999年 | 33篇 |
1998年 | 44篇 |
1997年 | 51篇 |
1996年 | 39篇 |
1995年 | 25篇 |
1994年 | 40篇 |
1993年 | 30篇 |
1992年 | 31篇 |
1991年 | 22篇 |
1990年 | 30篇 |
1989年 | 31篇 |
1988年 | 29篇 |
1987年 | 37篇 |
1986年 | 15篇 |
1985年 | 21篇 |
1984年 | 23篇 |
1983年 | 25篇 |
1982年 | 26篇 |
1981年 | 15篇 |
1980年 | 16篇 |
1979年 | 24篇 |
1978年 | 24篇 |
1977年 | 17篇 |
1976年 | 16篇 |
1975年 | 17篇 |
1973年 | 13篇 |
排序方式: 共有3398条查询结果,搜索用时 15 毫秒
1.
2.
3.
The 2011 AASHTO Roadside Design Guide (RDG) contains perhaps the most widely used procedure for choosing an appropriate length of need (LON) for roadside barriers. However, this procedure has several limitations. The procedure uses a highly simplified model of vehicle departure, and the procedure does not allow designers to specify an explicit level of protection. A new procedure for choosing LON that addresses these limitations is presented in this paper. This new procedure is based on recent, real-world road departure trajectories and uses this departure data in a more realistic way. The new procedure also allows LON to be specified for a precisely known level of protection – a level which can be based on number of crashes, injury outcomes or even estimated crash cost – while still remaining straightforward and quick to use like the 2011 RDG procedure. 相似文献
4.
The proliferation of both online and bricks and mortar outlet stores underscores the observation that secondary markets are readily accessible to retailers of short-life-cycle products. These secondary markets provide recourse channels for retailers to sell excess inventory of out-of-favor items at reduced prices when overstocking occurs in a primary market. We study the problem of determining when a retailer should terminate its primary selling season by selling remaining inventory on a secondary market. The retailer has a single opportunity to procure prior to a primary selling season consisting of multiple periods. Demand in each period is random, but correlated. At the end of each period, any remaining inventory incurs a holding cost. Then, based upon the current level of inventory and the cumulative demand-to-date, the retailer decides either to terminate the primary selling season by selling all or part of the remaining inventory on a secondary market, or to extend the current primary selling season by another period. We develop structural properties of the optimal policy for determining when to terminate the primary selling season, and we develop corresponding implications for procurement. 相似文献
5.
Myers Nicholas D.; Payment Craig A.; Feltz Deborah L. 《Canadian Metallurgical Quarterly》2004,8(3):182
This study examined reciprocal relationships between collective efficacy and team performance over a season of competition in women's intercollegiate ice hockey within weekends where the opponent was constant for 2 games. Collective efficacy beliefs within 12 teams were assessed prior to both games for at least 7 weekends. Team performance indexes produced an overall measure of performance for each game. The average influence of Saturday collective efficacy on Saturday performance was moderate and positive after controlling for Friday performance. The average influence of Friday performance on Saturday collective efficacy was small and positive after removing the influence of Friday collective efficacy from Friday performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
6.
Nicholas Biery Marc De Graef Jack Beuth Rafel Raban Andrew Elliott Tresa M. Pollock Curt Austin 《Metallurgical and Materials Transactions A》2002,33(10):3127-3136
Tensile experiments have been performed on specimens of four different investment-cast TiAl-based alloys with variations in
casting conditions. The average ductilities obtained in these experiments vary between approximately 0.8 to 2.0 pct plastic
strain to failure in tension. By using the three-parameter form of the Weibull relation, with the 0.2 pct offset yield strength
as the minimum failure strength, the resulting variability in the data can be quantified and is found to be similar for those
alloys with similar microstructural scale (grain size). Large variations in lamellar volume fraction, segregation, and phase
distribution have a minor influence on property variability, compared to changes in the scale of the grain structure caused
by either variations in cooling rate during casting or the addition of grain refiners. 相似文献
7.
Many engineering students enter and exit general chemistry courses with little appreciation of chemistry's relevance to other fields. At WPI many of these students go on to take introductory materials science and arrive with poor attitudes about chemistry and little retention of key concepts, but then become more engaged as they discover connections to engineering applications. Consequently, instructors in chemistry and mechanical engineering collaborated to augment general chemistry laboratories with explicit “bridges” to material properties and applications. Evaluation results showed that while students' attitudes toward chemistry were unaffected by bridging, particular aspects of the students' lab experience were enhanced to a statistically significant degree. Similar cross‐disciplinary collaborations might be considered elsewhere as a means of helping students find meaning and integrate subject matter, in a manner that is more feasible than large‐scale course or curriculum restructuring. 相似文献
8.
9.
This study used a pretest-posttest preexperimental design to examine the effect of a 10-week behavioral medicine support group intervention in a sample of persons with HIV. Using Solomon's psychoneuroimmunologic framework, the 10-week behavioral medicine program focused on the mind/body interaction, the relaxation response, coping with illness, hardiness, and nutrition. Pearson correlation coefficients and t tests were performed on the pre- and postintervention measures of hardiness, social support, immune function, and perceived health status. Results of the study indicated that hardiness (preintervention) and CD4 counts (pre- and postintervention) were significantly correlated with health status; however, CD4 counts decreased over the course of the behavioral medicine program. Implications for nursing and recommendations for further research are discussed. 相似文献
10.