全文获取类型
收费全文 | 38301篇 |
免费 | 2667篇 |
国内免费 | 1044篇 |
专业分类
电工技术 | 4400篇 |
技术理论 | 1篇 |
综合类 | 2601篇 |
化学工业 | 3903篇 |
金属工艺 | 2964篇 |
机械仪表 | 3154篇 |
建筑科学 | 3075篇 |
矿业工程 | 1960篇 |
能源动力 | 2409篇 |
轻工业 | 1526篇 |
水利工程 | 781篇 |
石油天然气 | 1560篇 |
武器工业 | 945篇 |
无线电 | 2754篇 |
一般工业技术 | 2658篇 |
冶金工业 | 3979篇 |
原子能技术 | 728篇 |
自动化技术 | 2614篇 |
出版年
2024年 | 127篇 |
2023年 | 369篇 |
2022年 | 693篇 |
2021年 | 945篇 |
2020年 | 1044篇 |
2019年 | 655篇 |
2018年 | 516篇 |
2017年 | 811篇 |
2016年 | 1071篇 |
2015年 | 1163篇 |
2014年 | 2625篇 |
2013年 | 2054篇 |
2012年 | 3030篇 |
2011年 | 3167篇 |
2010年 | 2333篇 |
2009年 | 2280篇 |
2008年 | 1914篇 |
2007年 | 2625篇 |
2006年 | 2387篇 |
2005年 | 2005篇 |
2004年 | 1741篇 |
2003年 | 1619篇 |
2002年 | 1297篇 |
2001年 | 1096篇 |
2000年 | 1011篇 |
1999年 | 795篇 |
1998年 | 546篇 |
1997年 | 457篇 |
1996年 | 374篇 |
1995年 | 304篇 |
1994年 | 220篇 |
1993年 | 163篇 |
1992年 | 107篇 |
1991年 | 90篇 |
1990年 | 79篇 |
1989年 | 59篇 |
1988年 | 39篇 |
1987年 | 27篇 |
1986年 | 19篇 |
1985年 | 29篇 |
1984年 | 38篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1973年 | 2篇 |
1966年 | 2篇 |
1959年 | 3篇 |
1955年 | 2篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Very high resolution inverse synthetic aperture radar (ISAR) imaging of fast rotating targets is a complicated task. There may be insufficient pulses or may introduce migration through range cells (MTRC) during the coherent processing interval (CPI) when we use the conventional range Doppler (RD) ISAR technique. With compressed sensing (CS) technique, we can achieve the high-resolution ISAR imaging of a target with limited number of pulses. Sparse representation based method can achieve the super resolution ISAR imaging of a target with a short CPI, during which the target rotates only a small angle and the range migration of the scatterers is small. However, traditional CS-based ISAR imaging method generally faced with the problem of basis mismatch, which may degrade the ISAR image. To achieve the high resolution ISAR imaging of fast rotating targets, this paper proposed a pattern-coupled sparse Bayesian learning method for multiple measurement vectors, i.e. the PC-MSBL algorithm. A multi-channel pattern-coupled hierarchical Gaussian prior is proposed to model the pattern dependencies among neighboring range cells and correct the MTRC problem. The expectation-maximization (EM) algorithm is used to infer the maximum a posterior (MAP) estimate of the hyperparameters. Simulation results validate the effectiveness and superiority of the proposed algorithm. 相似文献
2.
山西某矿5308底抽巷在掘进过程中速度慢、效率低,直接影响工作面的瓦斯抽采,为了改善上述情形,对炮孔间距进行研究。通过使用ANSYS软件对不同炮孔间距下快速掘进效果的模拟分析,并经现场验证,得出了适应该矿的最佳炮孔间距。结果表明:炮孔间距为500 mm时,爆破产生裂隙发育范围和岩石损伤区域都最大,快速掘进的效果最好。 相似文献
3.
This paper presented the exergoeconomic evaluation of the developed desiccant-evaporative air-conditioning system. The developed system was evaluated based on the steady-state conditions at different regeneration and reference temperatures. The exergoeconomic evaluation method was implemented to the system components and the whole system to evaluate the exergy efficiency, exergy destruction ratios, cost rates, relative cost differences and exergoeconomic factors. The regeneration and reference temperatures affected the exergy efficiencies, exergy destruction ratios, cost rates, relative cost differences and exergoeconomic factors. The desiccant wheel, heating coil and evaporative cooler had a high cost rate (investment cost, operation and maintenance cost, and exergy destruction cost). The exit air fan, outdoor air fan and evaporative cooler had a high relative cost difference. The exit air fan, outdoor air fan and secondary heat exchanger had a high exergoeconomic factor. Replacement of the desiccant wheel with a higher dehumidification performance could decrease the high cost rate. A higher efficiency evaporative cooler and heating coil were needed. Cheaper air fans (outdoor air fans and exit air fans) were needed. 相似文献
4.
5.
Ben-Jye Chang 《Telecommunication Systems》2006,33(4):333-352
3G Wideband CDMA systems adopt the Orthogonal Variable Spreading Factor code tree as the channelization codes management for
achieving high data rate transmission in personal multimedia communications. It assigns a single channelization code for each
accepted connection. Nevertheless, it wastes the system capacity when the required rate is not powers of two of the basic
rate. One good solution is to assign multiple codes for each accepted connection but it causes two inevitable drawbacks: long
handoff delay and new call setup delay due to high complexity of processing with multiple channelization codes, and high cost
of using more number of rake combiners. Especially, long handoff delay may result in more call dropping probability and higher
Grade of Service, which will degrade significantly the utilization and revenue of the 3G cellular systems. Therefore, we propose
herein an adaptive efficient codes determination algorithm based on the Markov Decision Process analysis approach to reduce
the waste rate and reassignments significantly while providing fast handoff. Numerical results demonstrate that the proposed
approach yields several advantages, including the lowest GOS, the least waste rate, and the least number of reassignments.
Meanwhile, the optimal number of rake combiners is also analyzed in this paper.
This research was supported in part by the National Science Council of Taiwan, ROC, under contract NSC-93-2213-E-324-018. 相似文献
6.
房家贵 《石油化工设备技术》2006,27(1):1-5
文章介绍了近年来在催化裂化装置上应用的新设备、新技术,如BY型旋风分离器、BSX型旋分式三级旋风分离器、上下拱型三级旋风分离器、下拱型三级旋风分离器、SHS“自蔓延”技术、SWY外取热器、BWJ型喷嘴、自流浇注料、Actehem高耐磨衬里、弓形钢丝纤维、侧拉环锚固钉、分体可拆人孔等的结构特点及实际应用情况。 相似文献
7.
国产风机盘管空调系统常见问题分析 总被引:2,自引:1,他引:1
分析了国产风机盘管使用中常见的问题,指出机组因风量不足、冷量风量匹配不合理以及风机盘管某些设备故障,导致了风机盘管精度低、舒适性差、能耗高等一系列问题。指出应引起空调设计和运行维护人员的注意。 相似文献
8.
通过龙潭水电站对励磁装置可控硅元件实施过电压保护改进前后实际效果的分析,介绍了一种有效的过压保护方式. 相似文献
9.
叙述了二代近贴聚焦像增强器批量生产所用真空设备性能及特点,同时给出了管子工艺考核结果及管子纳秒时间响应特性。工艺考核结果表明,制管工艺可靠、性能稳定,管子批量生产合格率大于70%。 相似文献
10.
为了用有限的资金建设一个高标准、现代化的适合高校现代教育技术需要的数字化摄录编播系统,结合实际,详细介绍一种适合高校重大事件记录、课件制作及教学片拍摄、可以满足高校多种需求的数字化摄录编播设备的合理化配置。 相似文献