全文获取类型
收费全文 | 4874篇 |
免费 | 582篇 |
国内免费 | 449篇 |
专业分类
电工技术 | 209篇 |
综合类 | 150篇 |
化学工业 | 1134篇 |
金属工艺 | 106篇 |
机械仪表 | 136篇 |
建筑科学 | 123篇 |
矿业工程 | 26篇 |
能源动力 | 419篇 |
轻工业 | 147篇 |
水利工程 | 82篇 |
石油天然气 | 42篇 |
武器工业 | 3篇 |
无线电 | 1121篇 |
一般工业技术 | 959篇 |
冶金工业 | 49篇 |
原子能技术 | 23篇 |
自动化技术 | 1176篇 |
出版年
2024年 | 19篇 |
2023年 | 219篇 |
2022年 | 135篇 |
2021年 | 235篇 |
2020年 | 261篇 |
2019年 | 185篇 |
2018年 | 170篇 |
2017年 | 208篇 |
2016年 | 195篇 |
2015年 | 207篇 |
2014年 | 286篇 |
2013年 | 315篇 |
2012年 | 370篇 |
2011年 | 396篇 |
2010年 | 322篇 |
2009年 | 356篇 |
2008年 | 298篇 |
2007年 | 426篇 |
2006年 | 398篇 |
2005年 | 162篇 |
2004年 | 94篇 |
2003年 | 67篇 |
2002年 | 77篇 |
2001年 | 74篇 |
2000年 | 49篇 |
1999年 | 55篇 |
1998年 | 28篇 |
1997年 | 18篇 |
1996年 | 20篇 |
1995年 | 27篇 |
1994年 | 24篇 |
1993年 | 22篇 |
1992年 | 19篇 |
1991年 | 9篇 |
1990年 | 24篇 |
1989年 | 21篇 |
1988年 | 24篇 |
1987年 | 37篇 |
1986年 | 27篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1981年 | 3篇 |
1979年 | 1篇 |
排序方式: 共有5905条查询结果,搜索用时 531 毫秒
151.
分别以氨基聚乙二醇(PEG-NH2)和氨基聚乙二醇单甲醚(M PEG-NH2)为大分子引发剂,制备了三嵌段(ABA)和两嵌段(AB)的聚L-丙氨酸-聚乙二醇嵌段共聚物;利用圆二色光谱(CD)研究了共聚物在溶液中的二级结构及其影响因素。结果表明,在水溶液中嵌段共聚物主链主要以α-螺旋构象存在;在一定范围内,α-螺旋含量随共聚物溶液浓度的增大而增大,随溶液离子强度的增大而降低;相同条件下,AB型共聚物在溶液中的α-螺旋含量比ABA型共聚物高。 相似文献
152.
153.
对比线阵CCD,CMOS图像传感器和InGaAs图像传感器的原理、特点和性能,提出了基于InGaAs图像传感器的光纤光栅传感解调技术,并设计了基于线阵InGaAs图像传感器的光纤光栅传感解调系统,而且通过计算机控制单独对应力和温度变化进行了测量实验,得到了理想的结果.基于线阵InGaAs图像传感器的解调系统不但测量精度和分辨率很高,而且基本上实现了光纤光栅传感的智能化,为光纤光栅传感的工业化奠定了基础,具有很好的应用前景. 相似文献
154.
The loading of multi-walled carbon nanotubes (MWNTs) and glucose oxidase (GOx) in the alternate layers of a glucose biosensor was first optimized based on a layer-by-layer construction on the surface of a graphite disk electrode. With the increasing of MWNTs/GOx layers, the response current to glucose was changed regularly and the response current reached a maximum value when the number of MWNTs/GOx layers was 6. Owing to a good electrical conductivity, strong adsorption and excellent bioconsistency of MWNTs, the (MWNTs/GOx)6 films-coated glucose biosensor had an excellent electrochemical properties. The response current of the (MWNTs/GOx)6 films-coated biosensor to 3 × 10− 2 M glucose was 1.63 μA while the response time was only 6.7 s. The linear range and the lowest detectable concentration of this biosensor was 5 × 10− 4∼1.5 × 10− 2 M and 0.9 × 10− 4 M, respectively. 相似文献
155.
A temperature-controlled, continuously and linearly tunable multiwavelength filter based on cascaded long period fiber gratings
has been realized. For the first time, a tunable wavelength range of 2.1 nm has been achieved with a temperature variation
of 62°C and a regression coefficient of 0.997. The experimental results are in good agreement with the theory. 相似文献
156.
High quality Tl2Ba2CaCu2O8 (Tl-2212) superconducting thin films are prepared on both sides of 2 in. LaAlO3(0 0 1) substrates by off-axis magnetron sputtering and post-annealing process. XRD measurements show that these films possess pure Tl-2212 phase with C-axis perpendicular to the substrate surface. The thickness unhomogeneity of the whole film on the 2 in. wafer is less than 5%. The superconducting transition temperatures Tcs of the films are around 105 K. At zero applied magnetic field, the critical current densities Jcs of the films on both sides of the wafer were measured to be above 2 × 106 A/cm2 at 77 K. The microwave surface resistance Rs of film was as low as 350 μΩ at 10 GHz and 77 K. In order to test the suitability of Tl-2212 thin films for passive microwave devices, 3-pole bandpass filters have been fabricated from double-sided Tl-2212 films on LaAlO3 substrates. 相似文献
157.
A model of a decision support system based on case-based reasoning for third-party logistics evaluation 总被引:1,自引:0,他引:1
The social demands for third‐party logistics (3PL) are further developing the model of supply chain management. The analysis of an effective approach for 3PL service supplier evaluation is given in terms of its direct relation to the operational efficiency and benefit of the service‐demanding enterprise as well as its supply chain management. An analysis of the traditional academic theoretical results and practical methods for 3PL supplier selection indicates the deficiencies of this approach. In this paper, a case‐based reasoning model framework is postulated for a 3PL evaluation and selection system. This work further expands upon the theoretical basis of this system and its reasoning process by discussing the advantages and practical value of this framework. 相似文献
158.
永磁无刷直流电机转矩波动的自抗扰控制 总被引:8,自引:3,他引:8
自抗扰控制器(ADRC)是在继承经典PID不依赖于对象模型优点的基础上,通过改进经典PID固有缺陷而形成的新型控制器,性能优良且算法简单。在分析永磁无刷直流电机转矩波动研究现状的基础上,根据其自身特点以及自抗扰控制器的设计原则,提出了基于自抗扰控制器的永磁无刷直流电机转矩波动抑制方法。将电机等效为由2个非线性系统构成的串联对象,设计了2个一阶自抗扰控制器实现对电机的内外环控制,即外环控制转速并给出内环转矩参照值,内环控制转矩以抑制转矩波动,其实质是改善馈电电流波形。内环转矩子系统采用3个相同的扩张状态观测器(ESO)对三相转矩分别进行观测,进而得到电磁转矩估计值及转矩子系统的实时作用值,据此构造以逆变器直流侧电压为控制输入的转矩子系统一阶自抗扰控制器。实验结果表明,该控制方案不仅能够明显抑制电机运行中的转矩波动,而且电机具有良好的动态响应性能,控制系统具有较强的适应性和鲁棒性。 相似文献
159.
Nonlinear system PID-type multi-step predictive control 总被引:1,自引:0,他引:1
A compound neural network was constructed during the process of identification and multi-step prediction. Under the PID-type long-range predictive cost function, the control signal was calculated based on gradient algorithm. The nonlinear controller‘ s structure was similar to the conventional PID controller. The parameters of this controller were tuned by using a local recurrent neural network on-line. The controller has a better effect than the conventional PID controller. Sinmlation study shows the effectiveness and good performance. 相似文献
160.