全文获取类型
收费全文 | 125791篇 |
免费 | 7228篇 |
国内免费 | 3547篇 |
专业分类
电工技术 | 6229篇 |
技术理论 | 7篇 |
综合类 | 11042篇 |
化学工业 | 9170篇 |
金属工艺 | 5283篇 |
机械仪表 | 14169篇 |
建筑科学 | 28636篇 |
矿业工程 | 3919篇 |
能源动力 | 2960篇 |
轻工业 | 4973篇 |
水利工程 | 3660篇 |
石油天然气 | 4182篇 |
武器工业 | 1448篇 |
无线电 | 7623篇 |
一般工业技术 | 13008篇 |
冶金工业 | 2887篇 |
原子能技术 | 660篇 |
自动化技术 | 16710篇 |
出版年
2024年 | 317篇 |
2023年 | 1190篇 |
2022年 | 1949篇 |
2021年 | 2632篇 |
2020年 | 2822篇 |
2019年 | 2165篇 |
2018年 | 2141篇 |
2017年 | 2696篇 |
2016年 | 3141篇 |
2015年 | 3418篇 |
2014年 | 9021篇 |
2013年 | 7089篇 |
2012年 | 8906篇 |
2011年 | 9558篇 |
2010年 | 8115篇 |
2009年 | 8413篇 |
2008年 | 7542篇 |
2007年 | 9055篇 |
2006年 | 7590篇 |
2005年 | 6687篇 |
2004年 | 5401篇 |
2003年 | 5096篇 |
2002年 | 4059篇 |
2001年 | 3406篇 |
2000年 | 2783篇 |
1999年 | 2171篇 |
1998年 | 1807篇 |
1997年 | 1508篇 |
1996年 | 1268篇 |
1995年 | 992篇 |
1994年 | 798篇 |
1993年 | 562篇 |
1992年 | 440篇 |
1991年 | 371篇 |
1990年 | 239篇 |
1989年 | 238篇 |
1988年 | 185篇 |
1987年 | 137篇 |
1986年 | 81篇 |
1985年 | 93篇 |
1984年 | 122篇 |
1983年 | 81篇 |
1982年 | 93篇 |
1981年 | 31篇 |
1980年 | 35篇 |
1979年 | 27篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1959年 | 11篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
本文阐述了折流杆换热器CAD系统的开发方法,包括:把大量线图、数表进行数据程序化,利用ADSRX技术、PDB界面设计技术和参数化图形设计技术对折流杆换热器的一百多种类型、三万多种规格的零部件进行了设计,将数据信息采用数据文件和数据库的方式进行了集成和管理,从而实现折流杆换热器工艺、机械、零部件子系统的集成。 相似文献
992.
Flow characteristics in the entrance of plate-fin heat exchanger have been investigated by means of particle image velocimetry (PIV). The flow field was measured using the two-frame cross-correlation technique. Streamline and velocity contour graphs at different cross-sections were obtained in the experiment. The experimental results indicate that flow maldistribution in the conventional header is very serious, while the improved header configuration with punched baffle can effectively improve the uniformity. The flow maldistribution parameter in plate-fin heat exchanger has been reduced from 1.21 to 0.21, and the ratio of the maximum velocity to the minimum is reduced from 23.2 to 1.8 by installing the punched baffle. The results suggest room for the optimum design of plate-fin heat exchanger. 相似文献
993.
消能锥形阀是一种用于中、高水头下的消能控流阀门,其内部结构设计的好坏直接影响着控流效果。为探究消能锥形阀在不同开度下,过流流量及内部流场的变化情况。进行了模型试验与CFD数值模拟计算,试验中发现开度从100%关至85%时出现了流量反而上升、进口压力下降的情况。利用CFD数值模拟的方法对内部流场进行了可视化研究。研究结果表明,在全开状态下锥形阀内部存在以下问题:过强的局部高速高压区域、低速流动死区范围过大、涡流区过度影响高速过流部分。并对锥形阀进行了一定的结构改进,优化了其内部流场情况。 相似文献
994.
995.
Musculoskeletal pain is commonly reported by police officers. A potential cause of officer discomfort is a mismatch between vehicle seats and the method used for carrying appointments. Twenty-five police officers rated their discomfort while seated in: (1) a standard police vehicle seat, and (2) a vehicle seat custom-designed for police use. Discomfort was recorded in both seats while wearing police appointments on: (1) a traditional appointments belt, and (2) a load-bearing vest/belt combination (LBV). Sitting in the standard vehicle seat and carrying appointments on a traditional appointments belt were both associated with significantly elevated discomfort. Four vehicle seat features were most implicated as contributing to discomfort: back rest bolster prominence; lumbar region support; seat cushion width; and seat cushion bolster depth. Authorising the carriage of appointments using a LBV is a lower cost solution with potential to reduce officer discomfort. Furthermore, the introduction of custom-designed vehicle seats should be considered. 相似文献
996.
Ahmet Kolus Philippe-Antoine Dubé Daniel Imbeau Richard Labib Denise Dubeau 《Applied ergonomics》2014
In new approaches based on adaptive neuro-fuzzy systems (ANFIS) and analytical method, heart rate (HR) measurements were used to estimate oxygen consumption (VO2). Thirty-five participants performed Meyer and Flenghi's step-test (eight of which performed regeneration release work), during which heart rate and oxygen consumption were measured. Two individualized models and a General ANFIS model that does not require individual calibration were developed. Results indicated the superior precision achieved with individualized ANFIS modelling (RMSE = 1.0 and 2.8 ml/kg min in laboratory and field, respectively). The analytical model outperformed the traditional linear calibration and Flex-HR methods with field data. The General ANFIS model's estimates of VO2 were not significantly different from actual field VO2 measurements (RMSE = 3.5 ml/kg min). With its ease of use and low implementation cost, the General ANFIS model shows potential to replace any of the traditional individualized methods for VO2 estimation from HR data collected in the field. 相似文献
997.
This paper addresses the problem of designing controllers that are robust to a great uncertainty in a time constant of the plant. Plants must be represented by minimum phase rational transfer functions of an arbitrary order. The design specifications are: (1) a phase margin for the nominal plant, (2) a gain crossover frequency for the nominal plant, (3) zero steady state error to step commands, and (4) a constant phase margin for all the possible values of the time constant (T): 0<T<∞. We propose a theorem that defines the structure of the set of controllers that fulfil these specifications and show that it is necessary for these robust controllers to include a fractional-order PI term. Examples are developed for both stable and unstable plants, and the results are compared with a standard PI controller and a robust controller designed using the QFT methodology. 相似文献
998.
999.
溪源泄洪洞出口位于闽江之上,为分析泄洪洞出口处的设计水位,采用设计流量和水位流量关系推求法及实测水位资料推求法两种方法对工程设计水位进行计算,经过合理性分析,工程所在地近年水位变化剧烈,采用设计流量和水位流量关系推求法更符合现状情况,为工程建设提供可靠的设计成果。 相似文献
1000.
介绍 4 0 0 kt/ a硫酸系统电除雾器总体结构及工艺设计参数 ,投入运行后 ,除雾效率低 ,介绍对存在问题的分析及解决过程 ,并介绍 2点成功经验 相似文献