全文获取类型
收费全文 | 2276篇 |
免费 | 258篇 |
国内免费 | 159篇 |
专业分类
电工技术 | 147篇 |
综合类 | 238篇 |
化学工业 | 218篇 |
金属工艺 | 113篇 |
机械仪表 | 226篇 |
建筑科学 | 322篇 |
矿业工程 | 80篇 |
能源动力 | 116篇 |
轻工业 | 13篇 |
水利工程 | 50篇 |
石油天然气 | 217篇 |
武器工业 | 42篇 |
无线电 | 268篇 |
一般工业技术 | 263篇 |
冶金工业 | 83篇 |
原子能技术 | 87篇 |
自动化技术 | 210篇 |
出版年
2024年 | 16篇 |
2023年 | 27篇 |
2022年 | 75篇 |
2021年 | 89篇 |
2020年 | 86篇 |
2019年 | 58篇 |
2018年 | 44篇 |
2017年 | 90篇 |
2016年 | 97篇 |
2015年 | 98篇 |
2014年 | 159篇 |
2013年 | 159篇 |
2012年 | 197篇 |
2011年 | 178篇 |
2010年 | 130篇 |
2009年 | 124篇 |
2008年 | 106篇 |
2007年 | 136篇 |
2006年 | 140篇 |
2005年 | 106篇 |
2004年 | 84篇 |
2003年 | 81篇 |
2002年 | 64篇 |
2001年 | 59篇 |
2000年 | 57篇 |
1999年 | 34篇 |
1998年 | 29篇 |
1997年 | 33篇 |
1996年 | 22篇 |
1995年 | 25篇 |
1994年 | 30篇 |
1993年 | 19篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1959年 | 3篇 |
1951年 | 1篇 |
排序方式: 共有2693条查询结果,搜索用时 0 毫秒
1.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015. 相似文献
2.
3.
N Kayansayan 《International Journal of Refrigeration》1996,19(3):197-207
The paper describes an effectiveness-NTU design method of bayonet-tube evaporators and condensers. Including the effect of the wall superheat on the shell-side film coefficient, and using an energy balance on the tube, differential equations for the steady-state fluid temperatures are formulated. Because of the nonlinear nature of the governing equations, the fourth-order Runge-Kutta method is employed to the solution of the finite difference equations. The results are iterated with the combination of integration techniques. An upper bound to the numerical error being ±5% the fluid temperature distribution as well as the exchanger effectiveness are determined, and presented as a function of the Hurd number, the number of heat transfer units and the flow arrangement. For flow entering through the inner tube, the temperature distribution displays the occurrence of a minimum at a point other than the tube-tip of the exchanger. In an extension of the analysis, an effort is made to illustrate the deviation of the results obtained by uniform film coefficient from the present study, and the differences are outlined. 相似文献
4.
5.
6.
It is shown that the purely growing electrostatic rippling mode can couple with the shear Alfven wave to give rise to an oscillatory electromagnetic instability in tokamak edge regions. This mechanism can be one of the causes of electromagnetic fluctuations observed near plasma edges. This instability can occur only in the very low temperature regions where resistivity fluctuations can become important due to large electron-ion collision frequency. 相似文献
7.
8.
9.
In this paper an extension of the method of the Fourier series expansion to the fire analysis of composite beams is presented. In particular the extension concerns the introduction of the temperature dependent interaction of all the components: steel beams, concrete slab and steel connectors. These last are considered of finite stiffness, and a proper account is given to the combined effect of thermal degradation of the properties, and stress amplification caused by the differential thermal expansion across the interface.The proposed method compares very well with some experimental fire tests of simply supported and framed composite beams. Due to its relative simplicity and speed, it can be used for design purposes in evaluating the critical temperature in terms of critical deflection. Finally we recall that the method is capable of dealing with every type of fastening distribution, such as discontinuous or variable length. 相似文献
10.
K.K. Padmanabhan 《Tribology International》1992,25(5)
Metallic mating surfaces in structural joints offer a good source of frictional energy dissipation resulting in a damped dynamic structural response. This paper reports the results of experiments where the energy dissipation per cycle occurring at a preloaded flat metallic annular interface subjected to cyclic tangential forces is measured. The effects of certain pertinent joint variables on this frictional energy dissipation are investigated by the application of Response Surface Methodology. A central composite rotatable design was utilized for developing empirical expressions for energy loss. The methodology presented suggests a useful technique for tribological research. 相似文献