全文获取类型
收费全文 | 5527篇 |
免费 | 457篇 |
国内免费 | 112篇 |
专业分类
电工技术 | 244篇 |
综合类 | 202篇 |
化学工业 | 947篇 |
金属工艺 | 196篇 |
机械仪表 | 181篇 |
建筑科学 | 345篇 |
矿业工程 | 53篇 |
能源动力 | 301篇 |
轻工业 | 453篇 |
水利工程 | 96篇 |
石油天然气 | 176篇 |
武器工业 | 4篇 |
无线电 | 636篇 |
一般工业技术 | 810篇 |
冶金工业 | 378篇 |
原子能技术 | 20篇 |
自动化技术 | 1054篇 |
出版年
2024年 | 17篇 |
2023年 | 93篇 |
2022年 | 167篇 |
2021年 | 219篇 |
2020年 | 172篇 |
2019年 | 172篇 |
2018年 | 216篇 |
2017年 | 200篇 |
2016年 | 235篇 |
2015年 | 213篇 |
2014年 | 229篇 |
2013年 | 425篇 |
2012年 | 328篇 |
2011年 | 417篇 |
2010年 | 340篇 |
2009年 | 337篇 |
2008年 | 279篇 |
2007年 | 236篇 |
2006年 | 234篇 |
2005年 | 187篇 |
2004年 | 126篇 |
2003年 | 145篇 |
2002年 | 193篇 |
2001年 | 140篇 |
2000年 | 103篇 |
1999年 | 60篇 |
1998年 | 88篇 |
1997年 | 67篇 |
1996年 | 56篇 |
1995年 | 60篇 |
1994年 | 51篇 |
1993年 | 37篇 |
1992年 | 21篇 |
1991年 | 10篇 |
1990年 | 18篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 22篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1976年 | 15篇 |
1975年 | 7篇 |
排序方式: 共有6096条查询结果,搜索用时 15 毫秒
971.
972.
阴极开放式质子交换膜燃料电池实验性研究 总被引:1,自引:0,他引:1
文中围绕实验室自制的开放式阴极自增湿型质子交换膜燃料电池开展了大量相关实验,采用FLUKE Ti25红外温度成像仪测得了各种操作条件下电池表面温度分布图像。实验结果表明:在封闭式阳极(anode dead-end)操作条件下,液态水会在阳极逐渐积累而影响反应气的传质,造成电池输出性能的衰减。通过阳极排气可以使电池性能恢复。纵观电堆表面温度分布情况,总体呈现出沿氢气流道方向递增的趋势。且随着电流密度的增大,这种温度分布的不均匀性变得更加明显。在实验所测试的范围内,电堆的平均输出功率密度达到了583 mW/cm2。 相似文献
973.
A novel method using resistive pulse sensors for electrokinetic surface charge measurements of nanoparticles is presented. This method involves recording the particle blockade rate while the pressure applied across a pore sensor is varied. This applied pressure acts in a direction which opposes transport due to the combination of electro-osmosis, electrophoresis, and inherent pressure. The blockade rate reaches a minimum when the velocity of nanoparticles in the vicinity of the pore approaches zero, and the forces on typical nanoparticles are in equilibrium. The pressure applied at this minimum rate can be used to calculate the zeta potential of the nanoparticles. The efficacy of this variable pressure method was demonstrated for a range of carboxylated 200 nm polystyrene nanoparticles with different surface charge densities. Results were of the same order as phase analysis light scattering (PALS) measurements. Unlike PALS results, the sequence of increasing zeta potential for different particle types agreed with conductometric titration. 相似文献
974.
In this paper, we report on the effect of chemical vapor etching-based porous silicon (PS) on the performance of multicrystalline silicon solar cells performed via deep n+/p junction-type structures. Chemical vapor etching of silicon leads to the formation of porous silicon (PS) nanostructures that dramatically decrease the surface reflectivity from 30% to about 8%, and increase the minority carrier diffusion lengths from 90 μm to 170 μm. As a result, the short-circuit current density was improved by more than 20% and the fill factor (FF) by about a 10%. An enhancement of the photovoltaic conversion energy efficiency of the solar cells from 7% to 10% was observed. This low-cost PS formation process can be applied in the photovoltaic cell technology as a standard procedure. 相似文献
975.
In a typical thermal energy storage system, a heat transfer fluid is usually used to deposit/extract heat when it flows through a packed bed of solid thermal storage material. A one-dimensional model of the heat transfer and energy storage/extraction for a packed-bed thermal storage system has been developed previously by the authors. The model treats the transient heat conduction in the thermal storage material by using the lumped capacitance method, which is not valid when the Biot number is large. The current work presents an effective heat transfer coefficient between the solid and fluid for large Biot numbers. With the corrected heat transfer coefficient, the lumped capacitance method can be applied to model the thermal storage in a wide range of Biot numbers. Four typical structures for the solid thermal storage material are considered. Formulas for the effective heat transfer coefficient (and effective Biot number) are presented. To verify the prediction by the lumped capacitance method using the effective heat transfer coefficient, we compare the results to the corresponding analytical solutions. The results are in very good agreement. The effective heat transfer coefficient extended the validity of the lumped capacitance method to large Biot numbers, which is of significance to the analysis of thermal energy storage systems. 相似文献
976.
977.
The [N(CH3)4][N(C2H5)4]ZnCl4 compound was prepared and characterized by electrical technique. The temperature dependence of the dielectric permittivity shows that this compound is ferroelectric below T = 268 K. The two semi-circles observed in the complex impedance identify the presence of the grain interior and grain boundary contributions to the electrical response in the material. The equivalent circuit is modeled by a combination series of two parallel RP–CPE circuits. The frequency dependent conductivity is interpreted in term of Jonscher's law. The modulus plots can be characterized by the empirical Kohlrausch–Williams–Watts (K.W.W.) function: ?(t) = exp [(−t/τ)β]. The temperature dependence of the alternative current conductivity (σp), direct current conductivity (σdc) and the relaxation frequency (fp) confirm the presence of the ferroelectric–paraelectric phase transition. 相似文献
978.
979.
Loomis J King B Burkhead T Xu P Bessler N Terentjev E Panchapakesan B 《Nanotechnology》2012,23(4):045501
This paper reports large light-induced reversible and elastic responses of graphene nanoplatelet (GNP) polymer composites. Homogeneous mixtures of GNP/polydimethylsiloxane (PDMS) composites (0.1-5 wt%) were prepared and their infrared (IR) mechanical responses studied with increasing pre-strains. Using IR illumination, a photomechanically induced change in stress of four orders of magnitude as compared to pristine PDMS polymer was measured. The actuation responses of the graphene polymer composites depended on the applied pre-strains. At low levels of pre-strain (3-9%) the actuators showed reversible expansion while at high levels (15-40%) the actuators exhibited reversible contraction. The GNP/PDMS composites exhibited higher actuation stresses compared to other forms of nanostructured carbon/PDMS composites, including carbon nanotubes (CNTs), for the same fabrication method. An extraordinary optical-to-mechanical energy conversion factor (η(M)) of 7-9 MPa W(-1) for GNP-based polymer composite actuators is reported. 相似文献
980.
B. S. Ben B. A. Ben Ch. Ratnam S. H. Yang 《International Journal of Mechanics and Materials in Design》2012,8(4):297-309
We present an ultrasonic-based Lamb wave propagation method for identifying and measuring the damage location in a material as a basis for structural health monitoring (SHM). Lamb waves can propagate in a structure via mode conversion and reflection from the surfaces of the structure, and can lead to interference patterns as a resulting wave vector propagates along the structure. We determined the experimental and analytical effects of various parameters on the sensitivity of damage detection. A methodology is proposed for estimating and measuring the location of damage in test specimens. An experimental setup is used for generating Ao? Lamb waves by calibrating ultrasonic pulse generation for optimal values of parameters. Materials with different damage levels are tested in their undamaged and damaged conditions, and the effects of the parameters on the generated waves in test specimens are observed experimentally. 相似文献