全文获取类型
收费全文 | 33973篇 |
免费 | 3867篇 |
国内免费 | 2276篇 |
专业分类
电工技术 | 8353篇 |
综合类 | 3725篇 |
化学工业 | 1876篇 |
金属工艺 | 2064篇 |
机械仪表 | 2476篇 |
建筑科学 | 2485篇 |
矿业工程 | 914篇 |
能源动力 | 1263篇 |
轻工业 | 776篇 |
水利工程 | 1199篇 |
石油天然气 | 1096篇 |
武器工业 | 254篇 |
无线电 | 3468篇 |
一般工业技术 | 3900篇 |
冶金工业 | 1281篇 |
原子能技术 | 391篇 |
自动化技术 | 4595篇 |
出版年
2024年 | 129篇 |
2023年 | 411篇 |
2022年 | 669篇 |
2021年 | 902篇 |
2020年 | 1037篇 |
2019年 | 825篇 |
2018年 | 791篇 |
2017年 | 954篇 |
2016年 | 1009篇 |
2015年 | 1218篇 |
2014年 | 2055篇 |
2013年 | 2038篇 |
2012年 | 2562篇 |
2011年 | 2625篇 |
2010年 | 2015篇 |
2009年 | 2103篇 |
2008年 | 2056篇 |
2007年 | 2283篇 |
2006年 | 2076篇 |
2005年 | 1808篇 |
2004年 | 1501篇 |
2003年 | 1424篇 |
2002年 | 1147篇 |
2001年 | 1084篇 |
2000年 | 908篇 |
1999年 | 849篇 |
1998年 | 630篇 |
1997年 | 562篇 |
1996年 | 504篇 |
1995年 | 395篇 |
1994年 | 294篇 |
1993年 | 239篇 |
1992年 | 235篇 |
1991年 | 182篇 |
1990年 | 151篇 |
1989年 | 146篇 |
1988年 | 101篇 |
1987年 | 44篇 |
1986年 | 37篇 |
1985年 | 26篇 |
1984年 | 23篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1963年 | 2篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Calcining of the mixture of BaCO3 and TiO2 with a ratio 1:4 at different temperatures was carried out to synthesize BaTi4O9 powders. Phase evolution of the samples was studied using the differential thermal analysis (DTA) and X-ray diffractometry
(XRD). Both techniques confirmed that the formation of BaTi4O9 started around 1000 °C. The XRD peaks showed that BaTi4O9 was most pronounced at 1250 °C. X-ray line broadening methods were employed to study the variation of particle size and microstrain
of the BaTi4O9 powders. The Voigt function in a single line and the pseudo-Voigt function in the variance methods were used in our case.
We found that both functions resulted in the same trends, i.e., the particle size increased with the temperature with the
biggest size of 180 and 160 nm, whilst the microstrain yielded the opposite trend with the lowest values of 6.2 × 10–3 and 1.1 × 10–3. The scanning electron microscopy (SEM) study revealed the size of the large particles formed, due to agglomeration, to be
about 0.5–1.9 μm. Furthermore, it was shown that irregular shapes of BaTi4O9 powders necked to each other appeared at 1000 °C and grew into ellipse and rod shapes at 1250 °C.
Electronic Publication 相似文献
72.
基于误码率与Q值的对应关系,本文介绍一种Q值在线检测方法,模块设计采用DSP技术,并讨论了该模块在光纤工业专用网(FIN)中的应用。 相似文献
73.
74.
正交曲线坐标下三维代数应力通量模型 总被引:7,自引:1,他引:6
针对弯曲及不规则明渠的水动力及物质输运特性,本文建立了曲线坐标系下的三维代数应力通量数学模型,对平面上弯曲及不规则复杂边界情形,采用Poisson方程进行正交曲线坐标变换,各向异性的湍流代数应力通量模型被引用于本文的模拟计算中,以体现复杂边界条件引起的水动力及物质输运特性的变化。通过180度强弯曲明渠水槽及贵溪电厂不规则边界河段物理模型试验两个实例计算表明,实测值与计算吻合良好,效果令人满意。 相似文献
75.
本文介绍利用Super Frame软件进行色彩浓淡设计的原理、方法和步骤。据此原理和方法,使用C语言设计开发出了应用实例——折线浓淡分布曲线。 相似文献
76.
The corrosion of low carbon steel in natural sea-water is characterized by the formation and growth of compact and thick layers composed of oxides, insoluble salts and organic materials. These layers are the result of corrosion processes induced by local environmental conditions, water oxygen supply; ionic species; bacteria and organic matter. The exchange of various species (ions, molecules, gas) between sea-water and the rust layers or the metal depends both on the kinetics of the Faradaic reactions of the entities with either the oxides or the metal, as well as on their transport properties through the different strata of the rust layers. In this work, an impedance study was carried out using the 4-electrodes cell arrangement with corrosion products picked up on steel sheet piling immersed for 25 years and analyzed as free standing membranes. This new approach is a good way to reach the specific transport and transfer properties of the oxide without being blurred by the metal influence. The physical model developed in this work was based on a transmission line, and accurately described the experimental diagrams. The electronic resistivity of the oxide layer, its porosity, the mean pore size and the reaction kinetics parameters could be determined from the fittings. 相似文献
77.
Akitoshi Iwata Shinji Ichikawa Mutuwo Tomita Shinji Doki Shigeru Okuma 《Electrical Engineering in Japan》2006,155(3):62-69
This paper presents a novel on‐line parameter identification method for sensorless control of Synchronous Reluctance Motors (SynRMs). Although conventional sensorless control methods based on mathematical models usually need some complex measurements of motor parameters in advance, the proposed identification method does not require them and can be realized on‐line. The proposed method identifies motor parameters under sensorless control, so rotor position and velocity cannot be used to identify these parameters. However, the proposed method does not need rotor position and velocity, and identified parameters are not affected by these estimation errors. The sensorless control using identified motor parameters is realized, and the effectiveness of the proposed method is verified by experimental results. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 62–69, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20258 相似文献
78.
An effective system control method is presented for applying a three‐phase current‐source PWM converter with a deadbeat controller to active power filters (APFs). In the shunt‐type configuration, the APF is controlled such that the current drawn by the APF from the utility is equal to the current harmonics and reactive current required for the load. To attain the time‐optimal response of the APF supply current, a two‐dimensional deadbeat control scheme is applied to APF current control. Furthermore, in order to cancel both the delay in the two‐dimensional deadbeat control scheme and the delay in DSP control strategy, an Adaptive Line Enhancer (ALE) is introduced in order to predict the desired value three sampling periods ahead. ALE has another function of bringing robustness to the deadbeat control system. Due to the ALE, settling time is made short in a transient state. On the other hand, total harmonic distortion (THD) of source currents can be minimized compared to the case where ideal identification of the controlled system can be made. The experimental results obtained from the DSP‐based APF are also reported. The compensating ability of this APF is very high in accuracy and responsiveness although the modulation frequency is rather low. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 50–61, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20014 相似文献
79.
本文对网上成绩考核系统进行了总体设计.其中,设计了校园网的网络结构模型、网上成绩考核系统的模块结构及其数据库和数据表. 相似文献
80.
介绍了一种专为时分复用系统设计的时院分配计算算法。这种算法中主要用到的技术是从一个话务矩阵的各行选出一个区别代表的系统方法。对于任何话务矩阵,这种算法的分配效率都能达到100%,所产生的模式矩阵个数最多为n2-2n+2个(对于n×n矩阵)。 相似文献