全文获取类型
收费全文 | 30678篇 |
免费 | 2649篇 |
国内免费 | 946篇 |
专业分类
电工技术 | 1304篇 |
综合类 | 1047篇 |
化学工业 | 5827篇 |
金属工艺 | 1794篇 |
机械仪表 | 2067篇 |
建筑科学 | 1399篇 |
矿业工程 | 617篇 |
能源动力 | 1140篇 |
轻工业 | 2360篇 |
水利工程 | 346篇 |
石油天然气 | 976篇 |
武器工业 | 116篇 |
无线电 | 4341篇 |
一般工业技术 | 5509篇 |
冶金工业 | 1820篇 |
原子能技术 | 261篇 |
自动化技术 | 3349篇 |
出版年
2024年 | 118篇 |
2023年 | 577篇 |
2022年 | 946篇 |
2021年 | 1410篇 |
2020年 | 1027篇 |
2019年 | 889篇 |
2018年 | 1095篇 |
2017年 | 1085篇 |
2016年 | 1172篇 |
2015年 | 1240篇 |
2014年 | 1538篇 |
2013年 | 1942篇 |
2012年 | 2037篇 |
2011年 | 2394篇 |
2010年 | 1914篇 |
2009年 | 1864篇 |
2008年 | 1651篇 |
2007年 | 1380篇 |
2006年 | 1284篇 |
2005年 | 1110篇 |
2004年 | 904篇 |
2003年 | 839篇 |
2002年 | 751篇 |
2001年 | 643篇 |
2000年 | 610篇 |
1999年 | 602篇 |
1998年 | 689篇 |
1997年 | 490篇 |
1996年 | 436篇 |
1995年 | 322篇 |
1994年 | 278篇 |
1993年 | 186篇 |
1992年 | 153篇 |
1991年 | 101篇 |
1990年 | 98篇 |
1989年 | 91篇 |
1988年 | 60篇 |
1987年 | 45篇 |
1986年 | 49篇 |
1985年 | 29篇 |
1984年 | 29篇 |
1983年 | 21篇 |
1982年 | 15篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 14篇 |
1976年 | 22篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Magnesium (Mg) and its alloys have broad application prospects in the fields such as biomedical materials and automobile manufacturing. A micro-alloyed Mg-2.0Nd-0.2Sr (wt.%) magnesium alloy is designed and obtained through semicontinuous casting. The evolution of microstructures and tensile properties are investigated with different heat treatments and extrusion treatments. The grain sizes decrease significantly after extrusion, thus changing the fracture mode during the tensile testing process. The ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of the properly processed extrusion alloy (referred to as MNS-E2) reach to 247 MPa, 228 MPa and 24%, respectively. The dramatical improvement of mechanical properties results from the refined grains and interactions between dislocations and precipitates. Some nanoparticle bands blocking the slippage and movement of dislocations are also found in the MNS-E2 alloy. The above causes combined result in an integrated effect of grain boundary strengthening, dislocation strengthening, precipitation strengthening and nanoparticle band strengthening. The contribution of strengthening mechanisms of MNS-E2 alloy consists of grain boundary with around 96 MPa, dislocations with around 3.4 MPa, precipitation strengthening with around 45 MPa and the nanoparticle band with around 18 MPa, respectively. 相似文献
992.
993.
To evaluate the dynamic behaviours of bridges, many researchers have analysed interactions between vehicles and bridges with numerical methods instead of field loading tests. However, conventional numerical methods take too much time and cost to evaluate the impact factor of bridges in design and maintenance practice. The objective of this study was to propose improved design criteria by using impact factors based on natural frequency rather than span length of railway bridges using dynamic field load-carrying capacity test database. The improved design criteria use a different methodology than that outlined in the International Union of Railway specifications Code. Statistical regressions are applied to more easily estimate the natural frequency of a bridge with a span length of 20?m or longer with steel plate girder or truss superstructures. Calculated impact factors were compared to impact factors obtained from field measurements. Results indicated that the improved method could provide a very reliable estimation for actual impact factors. Since the suggested impact factor criteria are conservative, the proposed method can be used in design and management stages to consider dynamic effects of railway bridges in a more intuitive manner. 相似文献
994.
Qiusheng Li Yuncheng He Yinghou He Kang Zhou Xuliang Han 《Structure and Infrastructure Engineering》2019,15(1):54-71
This article presents the observations of the atmospheric boundary layer (ABL) and wind effects on a 600 m high skyscraper during a landfall typhoon. Wind structure and characteristics throughout the entire ABL are presented and discussed based on records from a Doppler radar wind profiler and near-ground measurements at several meteorological stations. Wind speed profiles with the feature of low-level jets and radial-distance and exposure dependences of gradient height are stressed. Afterwards, wind-induced pressures on building surfaces of the skyscraper are investigated with highlights on non-Gaussian probability distributions of negative pressures and vortex shedding occurred alternately at two sides of the building. The structural responses measured by both accelerometers and strain gauges are analyzed subsequently. Modal parameters of the skyscraper and their dependence on response amplitude are presented and discussed. This study aims to provide useful information for the wind-resistant design of skyscrapers in tropic cyclone-prone regions. 相似文献
995.
本文采用座滴法在真空下系统研究了硼含量对TiZrNiCu/Ti60润湿性的影响,且在940°C保温10分钟条件下实现了与的钎焊。通过SEM、XRD以及剪切实验研究了界面显微组织及剪切力学性能。添加B元素可以与Ti原位合成TiBw,从而细化界面的显微组织。当B含量为0.3 wt %时,TiBw-TC4 /TiZrNiCu-B/Ti60接头的最大剪切强度为177 MPa,比无B含量的接头强度高65%。然而,过量的B含量使TiZrNiCu-B在Ti60合金基体上产生大量的TiBw,导致润湿性恶化,在钎焊接头形成微孔和未焊合区域,从而使剪切强度下降。 相似文献
996.
997.
998.
999.
1000.
国际选煤大会是全球煤炭界的重要会议,是国际选煤界最具权威性、最具影响力的专业盛会。目前,已有16个国家成为国际选煤大会组织的成员,中国于1972年加入国际选煤大会组织。2006年10月17日到19日召开的第15届国际选煤大会由中国煤炭工业协会和中国国际贸易促进委员会煤炭行业分会(商会)共同举办,主题为“煤炭洗选产业的发展和环保”。中国煤炭工业协会会长、中国工程院院士范维唐致欢迎辞,中国煤炭工业协会第一副会长、煤炭贸促会会长濮洪九主持了开幕式并参加了闭幕式。国家科技部、国有资产监督管理委员会和国家发展改革委员会的有关领导参加了会议,并做重要讲话。 相似文献