全文获取类型
收费全文 | 26197篇 |
免费 | 3961篇 |
国内免费 | 1822篇 |
专业分类
电工技术 | 17331篇 |
综合类 | 1788篇 |
化学工业 | 814篇 |
金属工艺 | 580篇 |
机械仪表 | 964篇 |
建筑科学 | 417篇 |
矿业工程 | 432篇 |
能源动力 | 1037篇 |
轻工业 | 212篇 |
水利工程 | 366篇 |
石油天然气 | 165篇 |
武器工业 | 93篇 |
无线电 | 4398篇 |
一般工业技术 | 1031篇 |
冶金工业 | 569篇 |
原子能技术 | 343篇 |
自动化技术 | 1440篇 |
出版年
2024年 | 70篇 |
2023年 | 383篇 |
2022年 | 677篇 |
2021年 | 816篇 |
2020年 | 954篇 |
2019年 | 749篇 |
2018年 | 750篇 |
2017年 | 1113篇 |
2016年 | 1147篇 |
2015年 | 1386篇 |
2014年 | 1863篇 |
2013年 | 1608篇 |
2012年 | 2254篇 |
2011年 | 2394篇 |
2010年 | 1672篇 |
2009年 | 1797篇 |
2008年 | 1748篇 |
2007年 | 1979篇 |
2006年 | 1753篇 |
2005年 | 1320篇 |
2004年 | 991篇 |
2003年 | 873篇 |
2002年 | 707篇 |
2001年 | 663篇 |
2000年 | 541篇 |
1999年 | 394篇 |
1998年 | 244篇 |
1997年 | 207篇 |
1996年 | 193篇 |
1995年 | 144篇 |
1994年 | 146篇 |
1993年 | 120篇 |
1992年 | 81篇 |
1991年 | 60篇 |
1990年 | 52篇 |
1989年 | 39篇 |
1988年 | 30篇 |
1987年 | 17篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Influence of ion bombardment on the properties and microstructure of unbalanced magnetron deposited niobium coatings 总被引:3,自引:0,他引:3
The effect of the ion bombardment to unbalanced magnetron deposited, approximately 1.5 and 4.5 μm thick, Nb coatings have been investigated as the bias voltage was varied from UB=−75 to −150 V. Increasing bias voltage increased the hardness of the coating from 4.5 to 8.0 GPa. This was associated with residual stress and Ar incorporation into the Nb lattice. Strong {110} texture developed in the samples deposited at low bias voltages, while beyond UB=−100 V a {111} texture became dominant. However, strong {111} texture was observed only with the thicker 3Nb coatings. Secondary electron microscopy investigation of the coating topography showed fewer defects in the thicker coatings. All coatings exhibited good corrosion resistance, with the thicker coatings clearly outperforming the thinner ones. Excessive bias voltages (UB=−150 V) was found to lead to poor adhesion and loss of corrosion resistance. 相似文献
52.
53.
楼滨乔 《核电子学与探测技术》1993,(4)
本文对最基本的HCMOS器件(反相器和与非门)作了γ辐射损伤实验。通过器件性能变化,分析了γ辐射对电路的作用。 相似文献
54.
Theory of a novel voltage-sustaining layer for power devices 总被引:3,自引:0,他引:3
The theory of a novel voltage-sustaining layer for power devices, called a Composite Buffer layer (CB-layer for short) is proposed. The CB-layer can be implemented in several ways, one particular implementation is used here, which consists of alternating n- and p-type regions, that are parallel to the direction of the applied electric field. In the off-state, the fields induced by the depletion charges of both region types compensate each other to allowing the doping in both n-regions and p-regions to be very high without causing a reduction of the breakdown voltage. In the onstate the heavy doping ensures the voltage drop is very low and that the saturation current density high. A simple relationship between the specific on-resistance and Ron and the sustaining voltage VB can be shown to be Ron=2.53 × 10−7bVB1.23 ωcm2, where the breadth b (in μm) of each region is much smaller than the thickness W. The design method of the CB-layer is discussed in some detail. The simulation results are shown to be in perfect agreement with the theory. The structure has application to a wide variety of different power devices. An RMOST structure has been used to demonstrate the benefits of the technique in the paper, for which excellent performance is demonstrated. 相似文献
55.
Xu You-heng Dong Li-yun Huang Dong-qun Fudan University Shanghai P. R. China 《水动力学研究与进展(B辑)》1998,(3)
In this paper,the oscillation amplitude of the free end of a group of threecylinders are studied.The three cylinders are erected at the vertices of an equilateral trian-gle,and three arrangements are made in this study.One of the three cylinders is served asa working cylinder which is mounted by a flexible cantilever and two accelerometers areattached on the free end in two directions.The results of the three-cylinder arrangementare compared with those of two cylinders in tandem/side-by-side arrangement in the samecondition.The experimental results show that the rear cylinder of a group of three cylin-ders is affected more seriously than that of the corresponding two cylinders in the contrastarrangement.The main direction of oscillation is changed.The transversal oscillation isstronger than the longitudinal oscillation in the three-cylinder arrangement.On the con-trary,the transversal oscillation is much weaker than the longitudinal oscillation in two-cylinder arrangement.The largest transversal oscillat 相似文献
56.
Takashi Yamazaki Yoichi Takino Ryosuke Matsuoka Susumu Ito 《Electrical Engineering in Japan》1993,113(8):26-36
According to the recent analysis results of temporary ac overvoltage in the ac system connected with a frequency converter station, large-magnitude over-voltages were confirmed to occur under some special system conditions. Most of the station insulators currently used cannot withstand such overvoltages according to an evaluation based on the data obtained earlier. The necessity of tests to be done to evaluate such performance more accurately was recognized. Both power frequency and switching impulse overvoltage flashover tests were made on contaminated insulators by the method well simulating the natural wetting condition. Switching impulse flashover voltage with the waveshape having a long wavefront time of 2 ms can be well correlated with the flashover voltage characteristics of temporary ac overvoltage. Higher flashover voltage characteristics were obtained by a clean fog test method compared with those obtained by equivalent fog test method. 相似文献
57.
用于高压电容器的SrTiO3基陶瓷 总被引:3,自引:0,他引:3
报道SrTiO3基陶瓷的制备方法和介电性质,给出了用此种陶瓷制成的高压电容器的试验结果,并对它位进行了讨论。 相似文献
58.
59.
60.
以镁法海绵钛生产工艺中大型无隔板镁电解槽的实际节能情况为例,探讨了在镁电解生产中的非生产耗电、生产耗电、漏电等因素造成的能量浪费,阐述了生产中粗镁直流电耗、电流效率、工作电压3者之间的关系,指出了影响电解槽工作电压的有关因素及降低电解槽工作电压的途径。 相似文献