全文获取类型
收费全文 | 42461篇 |
免费 | 5143篇 |
国内免费 | 3376篇 |
专业分类
电工技术 | 4930篇 |
技术理论 | 2篇 |
综合类 | 4605篇 |
化学工业 | 3345篇 |
金属工艺 | 3183篇 |
机械仪表 | 2985篇 |
建筑科学 | 2865篇 |
矿业工程 | 1726篇 |
能源动力 | 1829篇 |
轻工业 | 1265篇 |
水利工程 | 1313篇 |
石油天然气 | 5400篇 |
武器工业 | 658篇 |
无线电 | 5514篇 |
一般工业技术 | 4887篇 |
冶金工业 | 1546篇 |
原子能技术 | 872篇 |
自动化技术 | 4055篇 |
出版年
2024年 | 213篇 |
2023年 | 661篇 |
2022年 | 1158篇 |
2021年 | 1347篇 |
2020年 | 1382篇 |
2019年 | 1211篇 |
2018年 | 1090篇 |
2017年 | 1558篇 |
2016年 | 1623篇 |
2015年 | 1728篇 |
2014年 | 2406篇 |
2013年 | 2440篇 |
2012年 | 3078篇 |
2011年 | 3351篇 |
2010年 | 2485篇 |
2009年 | 2519篇 |
2008年 | 2269篇 |
2007年 | 2846篇 |
2006年 | 2702篇 |
2005年 | 2288篇 |
2004年 | 1952篇 |
2003年 | 1778篇 |
2002年 | 1395篇 |
2001年 | 1153篇 |
2000年 | 1122篇 |
1999年 | 957篇 |
1998年 | 748篇 |
1997年 | 673篇 |
1996年 | 584篇 |
1995年 | 465篇 |
1994年 | 415篇 |
1993年 | 275篇 |
1992年 | 212篇 |
1991年 | 171篇 |
1990年 | 171篇 |
1989年 | 167篇 |
1988年 | 104篇 |
1987年 | 48篇 |
1986年 | 35篇 |
1985年 | 24篇 |
1984年 | 31篇 |
1983年 | 13篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1959年 | 12篇 |
1958年 | 6篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
刘有菊 《辽东学院学报(自然科学版)》2012,19(2):122-125
采用波前相因子判断法并考虑到光栅孔径的影响来分析多缝的衍射。得出多缝衍射的波前函数、像面上多缝衍射振幅和光强公式,并模拟出像面衍射振幅分布和光强分布,最后得出中央主极大的半角宽度。结果表明该研究为多缝衍射分析提供了一种新的分析方法。 相似文献
962.
在分析异步电动机瞬态激励数学模型的基础上,提出电流瞬态响应二次测量结果相叠加获得转子位置信息的技术.该技术利用电压源逆变器产生的驱动信号作为激励信号,通过检测PWM逆变器馈电时电机绕组电流瞬态变化来辨识静止状态到较高速时的电机转子信息.采用仿真手段分析逆变器死区时间及电子元件压降的影响,并给出了相应的补偿方式,边界条件为:电机理想对称,逆变器为理想状态.仿真研究表明:由于死区时间t0的影响,电流瞬态响应发生变化,导致工作点漂移.针对3kW/380V/50Hz异步电机进行了实验,实测结果验证了该方法实现无传感器磁场定向控制转子位置检测的可行性和优越性. 相似文献
963.
磁化水改善混凝土抗渗性能试验研究 总被引:2,自引:0,他引:2
利用磁化水拌制强度等级分别为C20,C25,C30和C35混凝土,对23组试件进行抗渗性能试验,旨在研究混凝土的抗渗性能与水的磁化程度之间的变化关系.借助混凝土抗渗试验仪对比在相同强度条件下,磁化水拌制的混凝土与普通水拌制的混凝土抗渗性能的差异,并采用定量方法分析试验数据对选择的试验参数确定其最佳磁化强度和最佳水流速度,从而为进一步探索和推广磁化水拌制混凝土技术提供理论依据. 相似文献
964.
惯导产品输出脉冲信号存在干扰信号,为减少其对惯导产品性能的影响,文中设计了一种基于FPGA的脉冲信号数字滤波器,并对滤波后脉冲信号以5ms为计数单元进行无缝计数,计数结果可由串行总线上传至上位机进行显示和处理.通过该方法测量的惯导产品输出脉冲信号频率最高可达13MHz,其中可对频率范围为50kHz~12.5MHz的干扰信号进行滤除,满足惯导产品性能测试要求. 相似文献
965.
966.
967.
This paper presents an automatic scanning and visualizing system for ultrasound field of a planar piston transducer. This system consists of a water tank with wedge absorber, stepper motors driver, system controller, a planar piston transducer, a needle-type hydrophone and data processing software. Our software realizes the processing and displaying of ultrasonic data, which are acquired by adjusting accurately positions of the hydrophone and transducer that are driven by stepper motors. And the ultrasonic field is represented by employing 1D, 2D or 3D graphs of data, respectively. Experimental results show that this auto-scanning and visualizing system provides a more spatial structure of ultrasonic field and reveals a more characteristic of ultrasonic beam radiated by the planar piston transducer. 相似文献
968.
In this paper, we proposed a new method using long digital straight segments (LDSSs) for fingerprint recognition based on such a discovery that LDSSs in fingerprints can accurately characterize the global structure of fingerprints. Different from the estimation of orientation using the slope of the straight segments, the length of LDSSs provides a measure for stability of the estimated orientation. In addition, each digital straight segment can be represented by four parameters: x-coordinate, y-coordinate, slope and length. As a result, only about 600 bytes are needed to store all the parameters of LDSSs of a fingerprint, as is much less than the storage orientation field needs. Finally, the LDSSs can well capture the structural information of local regions. Consequently, LDSSs are more feasible to apply to the matching process than orientation fields. The experiments conducted on fingerprint databases FVC2002 DB3a and DB4a show that our method is effective. 相似文献
969.
《Ergonomics》2012,55(5):663-670
The aim of this study was to compare estimation of energy expenditure (EE) in working environments, either from accelerometry or from an individual oxygen consumption/heart rate ([Vdot]O2/HR) regression curve. The study participants were 46 volunteer workers aged 27±6 years old. A significant correlation between EE predicted by the [Vdot]O2/HR curve and the accelerometer was observed (r=0.78, p <0.01). However, more disparities were observed between the two methods when the mean job intensity was not within 16% and 23% higher than resting HR. The accelerometer overestimated by a mean of 34.4% the prediction by [Vdot]O2/HR regression if the intensity of the task was lower than a total of 1000 kcal/shift and underestimated the prediction by a mean of –24.9% if EE estimation of the work shift was higher than a total of 1500 kcal/shift. Despite a high correlation between both methods in the whole group, EE evaluated by accelerometry does not correspond to EE predicted by the [Vdot]O2/HR regression curves when evaluated individually. 相似文献
970.
《Behaviour & Information Technology》2012,31(6):457-473
User involvement has been shown to be beneficial in the development of useful and usable systems. The trend of software development becoming a product-oriented activity creates challenges to user involvement. Field studies appear a promising approach, but the analysis of the gathered user needs has been shown to be demanding. This study presents, on the basis of seven case studies, an early user-involvement process showing how user needs can be analysed and how the input to product development can be identified. In addition, the process is evaluated in two industrial cases with interviews and a questionnaire. The results show that the process supports effective early user involvement; the resulted requirements were evaluated as being more successful and their quality as better than average in a company. However, the case studies show that user involvement not only provides useful information about users' needs but also increases the understanding of users' values. 相似文献