全文获取类型
收费全文 | 29700篇 |
免费 | 2713篇 |
国内免费 | 1744篇 |
专业分类
电工技术 | 5439篇 |
综合类 | 2284篇 |
化学工业 | 3407篇 |
金属工艺 | 1662篇 |
机械仪表 | 1877篇 |
建筑科学 | 2756篇 |
矿业工程 | 1617篇 |
能源动力 | 1157篇 |
轻工业 | 1565篇 |
水利工程 | 2125篇 |
石油天然气 | 1899篇 |
武器工业 | 158篇 |
无线电 | 1657篇 |
一般工业技术 | 1940篇 |
冶金工业 | 1709篇 |
原子能技术 | 1070篇 |
自动化技术 | 1835篇 |
出版年
2024年 | 97篇 |
2023年 | 281篇 |
2022年 | 800篇 |
2021年 | 842篇 |
2020年 | 882篇 |
2019年 | 731篇 |
2018年 | 689篇 |
2017年 | 923篇 |
2016年 | 959篇 |
2015年 | 1078篇 |
2014年 | 1944篇 |
2013年 | 1903篇 |
2012年 | 2233篇 |
2011年 | 2230篇 |
2010年 | 1570篇 |
2009年 | 1616篇 |
2008年 | 1576篇 |
2007年 | 1878篇 |
2006年 | 1805篇 |
2005年 | 1489篇 |
2004年 | 1378篇 |
2003年 | 1213篇 |
2002年 | 1065篇 |
2001年 | 993篇 |
2000年 | 761篇 |
1999年 | 669篇 |
1998年 | 478篇 |
1997年 | 418篇 |
1996年 | 347篇 |
1995年 | 326篇 |
1994年 | 234篇 |
1993年 | 172篇 |
1992年 | 134篇 |
1991年 | 127篇 |
1990年 | 72篇 |
1989年 | 70篇 |
1988年 | 41篇 |
1987年 | 33篇 |
1986年 | 17篇 |
1985年 | 7篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1955年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
本总结了大庆长垣南部周期注水的做法和效果。实践证明,在低渗透,薄油层,单井低注低产的油田上实施周期注不仅能够改善油田开发状况,而且也为低注井的冬季管理提供了方便条件。 相似文献
92.
This paper reviews the characteristics of pulsating or cyclic flow of bulk solids during gravity discharge in bins and silos. The dynamic load phenomenon is often referred to as “silo quaking” and is influenced by various factors related to the type of flow pattern developed in the bin and the flow properties of the bulk material. Of particular relevance is the influence of ‘slip-stick’ during shear flow, and the velocity at critical sections in the silo during discharge. An overview of recent and current research on this subject is presented. 相似文献
93.
Core–shell type nanoparticles of poly(L ‐lactide)/poly(ethylene glycol) (LE) diblock copolymer were prepared by a dialysis technique. Their size was confirmed as 40–70 nm using photon correlation spectroscopy. The 1H‐NMR analysis confirmed the formation of core–shell type nanoparticles and drug loading. The particle size, drug loading, and drug release rate of the LE nanoparticles were slightly changed by the initial solvents that were used. The drug release behavior of LE core–shell type nanoparticles showed an initial burst during the first 12 h and then a sustained release until 100 h. The degradation behavior of LE block copolymer nanoparticles was divided into three phases: the initial rapid degradation phase, the stationary phase, and the rapid degradation phase until complete degradation. It was suggested that lidocaine release kinetics were predominantly governed by the diffusion mechanism in the initial burst phase and after that by both of the diffusion and degradation mechanisms. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2625–2634, 2002 相似文献
94.
补充型润滑油添加剂对改善和提高油品使用性能具有重要意义,有较大的发展应用潜力。本文对补充型添加剂及有关问题进行了分析和分析,认为补充型添加剂不是万能的,使用时须认真考虑与润滑油的协和性,要加强对它的质量监控。 相似文献
95.
作者研制成一种带光纤的电力变压器局放超声PZT传感器.文中分析了它的灵敏度与宽频带特性,介绍了原理、结构设计、实验数据及现场成功实例.理论与实验研究表明:具有这种高灵敏传感器的超声定位系统是确定电力变压器绝缘故障部位的一种方法. 相似文献
96.
通过某工程异形柱头混凝土置换实例,介绍了连续托梁分次置换技术的设计计算、施工方法和技术措施等。 相似文献
97.
98.
门式脚手架在已建高层建筑外装修中的应用 总被引:1,自引:0,他引:1
介绍门式脚手架在已建高层建筑外排栅中的整体搭设和应用实例。 相似文献
99.
户式中央空调发展方向的探讨 总被引:2,自引:1,他引:1
本文描述了我国户式中央空调的发展现状,分析了三种户式中央空调各自的特点,提出了把风管式机组作为我国户式中央空调的发展方向。 相似文献
100.
Floods cause environmental hazards and influence on socio‐economic activities. In this study, we evaluated the historic flood frequency at a confluence in the middle Yellow River, China. A non‐parametric, multivariate, empirical, orthogonal function matrix model, which consists of time correlation coefficients of flood discharge at different gauge stations and flood events was used for the analysis of flood frequency. The model addresses the characteristics of confluent floods such as frequency and the probability in multiple tributary rivers. Flood frequency analysis is often coupled with studies of hydrological routing processes that reduce the flood capacity of the rivers. Flood routing to the confluence were simulated using kinematic wave theory. Results of this flood frequency analysis showed that flooding frequency has intensified in the past 500 years, especially during the 19th century. Flooding in streams above the confluence was more frequent than in streams below the confluence. Over the last 2000 years, concurrent flooding in multiple tributary rivers accounted for 67.5% of the total flooding in the middle Yellow River. Simulation of flood routing processes shows that the decreased flooding capacity and elevated river bed of the shrunken main channel leads to an increased flood wave propagation time (24–52.3 h) in the study area after 1995. The model indicates that human activities, such as constructions of the Sanmenxia Dam, have changed flood routing boundary conditions and have contributed to the increased flood frequency at the confluence. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献