全文获取类型
收费全文 | 8284篇 |
免费 | 407篇 |
专业分类
公路运输 | 2562篇 |
综合类 | 2471篇 |
水路运输 | 2052篇 |
铁路运输 | 1352篇 |
综合运输 | 254篇 |
出版年
2024年 | 14篇 |
2023年 | 43篇 |
2022年 | 206篇 |
2021年 | 349篇 |
2020年 | 259篇 |
2019年 | 123篇 |
2018年 | 145篇 |
2017年 | 147篇 |
2016年 | 146篇 |
2015年 | 262篇 |
2014年 | 378篇 |
2013年 | 457篇 |
2012年 | 581篇 |
2011年 | 618篇 |
2010年 | 658篇 |
2009年 | 649篇 |
2008年 | 649篇 |
2007年 | 701篇 |
2006年 | 699篇 |
2005年 | 538篇 |
2004年 | 242篇 |
2003年 | 186篇 |
2002年 | 142篇 |
2001年 | 167篇 |
2000年 | 114篇 |
1999年 | 48篇 |
1998年 | 40篇 |
1997年 | 24篇 |
1996年 | 35篇 |
1995年 | 19篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有8691条查询结果,搜索用时 0 毫秒
131.
132.
133.
134.
135.
HLA仿真作为新一代分布仿真体系结构,对仿真界产生了深刻影响。但是由于HLA与其它中间件技术没有建立广泛的联系,使得HLA的可重用性仅仅局限在HLA范围内,同时HLA的开发也具有很大的复杂性。在深入研究HLA仿真框架的基础上,提出了一种基于CORBA构件模型(CCM)构件的HLA仿真开发方法,该方法利用CCM构件技术来实现各联邦成员的具体功能。该方法提高了软件重用率和仿真开发效率,并优化了HLA仿真系统的软件层次结构。验证中该方法成功运用于舰船作战系统联邦的指控系统联邦成员仿真。结果表明该方法确实可行。 相似文献
136.
初始缺陷对耐压圆柱壳结构极限承载力的影响 总被引:2,自引:0,他引:2
为了考察初始缺陷、材料等因素对耐压圆柱壳结构极限承载力的影响,本文利用ANSYS有限元软件构造模型对耐压圆柱壳结构进行模拟.研究了缺陷幅值在一定范围内变化时,初始缺陷对耐压圆柱壳极限承载力的影响,并将有限元计算结果与理论计算结果进行比较,讨论了材料的改变对极限承载力的影响.初始缺陷幅值不会改变耐压圆柱壳结构的失稳模态,且对结构极限承载力的影响有限,但材料的改进对提高结构极限承载力的效果显著. 相似文献
137.
结合哈大铁路客运专线DK651+972涵洞施工的实例,论述了根据实际水文地质条件确定降水方案,对以往经验参数进行修改,以达到降水目的及确保工程顺利进行。 相似文献
138.
139.
Chorng-Shern Horng Chih-An Huh Kuo-Hang Chen Pin-Ru Huang Kan-Hsi Hsiung Hui-Ling Lin 《Journal of Marine Systems》2009,76(4):468
Kaohsiung City and its neighborhood in the southwestern coastal plain of Taiwan have suffered serious air pollution since the region became the largest center for heavy-industry on the island. In order to unravel the air pollution history of the region, four 210Pb- and 137Cs-dated sediment box cores recovered in 2006 from offshore of this area were chosen for magnetic and petrographic analyses. The data were used to distinguish changes in concentration, composition and grain size of magnetic particles in the sediments due to inputs of anthropogenic magnetic spherules. Sedimentation rates have been reasonably constant for the last one hundred years, except at the core tops which were affected by a turbidite layer induced by a typhoon in 2005. Down-core profiles of mass-specific magnetic susceptibility (χ) and saturation isothermal remanent magnetization (SIRM) are similar among the cores, and reflect similar trends to magnetic spherule counts. This reveals that χ and SIRM of modern marine sediments can be used as air pollution indicators for nearby industrialized upwind areas. The studied record indicates that industrialization of the area was gradual during 1950–1980 and boomed afterward, resulting in a high production of airborne magnetic spherules, which is consistent with evidence for poor air quality at that time. Optical and scanning electron microscopic (SEM) surveys of magnetic extracts indicate that the magnetic spherules have grain sizes ranging from a few micrometers up to 50 μm and consist mainly of iron oxides with variable Si, Al, and Ca contents. X-ray diffraction analysis on magnetic extracts from different depths in the cores further indicates that magnetite and pyrrhotite, which are derived from terrigenous detritus, form the magnetic constituents of the sediments before the area was industrialized. In contrast, during the industrial boom, anthropogenic magnetite and hematite spherules became the dominant magnetic particles in the sediments. Down-core profiles of hard isothermal remanent magnetization (HIRM) below the turbidite layer also reveal similar trends to the corresponding magnetic spherule counts, which indicate that the concentration of hematite in the sediments is also closely related to the extent of air pollution. In addition, relatively low values of χARM/χ, which are indicative of coarse magnetic grains, started to occur when large magnetite spherules became significant during the industrialized period. The air pollution history elucidated from our sediment core data not only reflects the development of Kaohsiung from a small village to a highly industrialized metropolitan area in the 20th century, but it is also consistent with the most recent air pollution trends revealed by real time air quality measurements of PM10. Our results demonstrate the usefulness of magnetic parameters for delineating the air pollution history of coastal marine sediments down-wind of nearby industrialized regions. 相似文献
140.