全文获取类型
收费全文 | 12347篇 |
免费 | 1744篇 |
国内免费 | 813篇 |
专业分类
电工技术 | 389篇 |
综合类 | 1118篇 |
化学工业 | 4270篇 |
金属工艺 | 550篇 |
机械仪表 | 482篇 |
建筑科学 | 643篇 |
矿业工程 | 214篇 |
能源动力 | 351篇 |
轻工业 | 1403篇 |
水利工程 | 247篇 |
石油天然气 | 1132篇 |
武器工业 | 147篇 |
无线电 | 806篇 |
一般工业技术 | 1734篇 |
冶金工业 | 344篇 |
原子能技术 | 108篇 |
自动化技术 | 966篇 |
出版年
2024年 | 36篇 |
2023年 | 204篇 |
2022年 | 293篇 |
2021年 | 364篇 |
2020年 | 425篇 |
2019年 | 437篇 |
2018年 | 381篇 |
2017年 | 470篇 |
2016年 | 704篇 |
2015年 | 750篇 |
2014年 | 848篇 |
2013年 | 947篇 |
2012年 | 886篇 |
2011年 | 1014篇 |
2010年 | 652篇 |
2009年 | 741篇 |
2008年 | 629篇 |
2007年 | 790篇 |
2006年 | 701篇 |
2005年 | 635篇 |
2004年 | 467篇 |
2003年 | 397篇 |
2002年 | 337篇 |
2001年 | 287篇 |
2000年 | 278篇 |
1999年 | 174篇 |
1998年 | 158篇 |
1997年 | 143篇 |
1996年 | 128篇 |
1995年 | 113篇 |
1994年 | 103篇 |
1993年 | 62篇 |
1992年 | 74篇 |
1991年 | 46篇 |
1990年 | 39篇 |
1989年 | 33篇 |
1988年 | 19篇 |
1987年 | 27篇 |
1986年 | 12篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1964年 | 4篇 |
1958年 | 2篇 |
1956年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 347 毫秒
61.
通过改变激光器的相对激发,观察到了氩离子激光器振荡频率的演变特性。用模竞争效应对实验现象进行了理论解释。 相似文献
62.
A new method for characterization of stratified thermal energy stores (TES) that integrates both the first law and the second law concerns is presented here. The first law concern is incorporated into a quantity called energy response factor and the second law concern into an entropy generation ratio. A product of these two quantities is at the heart of the TES efficiency definitions. This approach removes the overemphasis of the existing methods either on the first or the second law of thermodynamics which often biases the characterization results. The information about the evolution of the temperature field of the system in time is the prerequisite of the new method. It may be obtained from experiments or from suitable numerical simulations. The current method can be easily integrated into computational fluid dynamic (CFD) simulations and thus facilitate CFD-based design analysis. As an example of such CFD-integrated analysis, a large-scale hot water seasonal heat store is numerically studied to identify the effects of aspect ratio, containment shape, internal structures, and containment size on their efficiency. The results suggest the effectiveness of the new method in deriving useful design insights. 相似文献
63.
主要是以氧化镓为原料,通过气相沉积法,制备出GaN纳米线和纳米带.通过X-射线衍射(XRD),扫面电镜(SEM)和高分辨透射电镜(HRTEM)等测试手段对其形貌进行了表征和分析.研究了实验过程中工艺条件的改变对所制备GaN纳米结构形貌特征的影响.对两种GaN纳米材料的拉曼散射光谱进行了分析. 相似文献
64.
本文用不热形变栅状直丝化学气相沉积(CVD)法生长金刚石膜,在Si及WC-Co硬质合金衬底上金刚石膜晶面显露规律随衬底温度和甲烷浓度而异,经适当表面处理及选择合适的工艺条件,当生长初期衬底上就呈现出良好晶形的沉积膜,衬底与膜之间的粘结力能得到提高。Raman谱分析表明此膜仅具有特征金刚石1332cm ̄(-1)峰,通过SEM观察揭示出盒刚石膜可在表面、侧面及棱上生长,并与衬底有良好的联结。 相似文献
65.
A new surface characterization technique: RIMAPS (Rotated Image with Maximum Average Power Spectrum)
This work introduces a new imaging technique, Rotated Image with Maximum Average Power Spectrum (RIMAPS), for use in determining orientation and characteristics of surface topography. It consists of computing the maximum value of the averaged power spectrum, given by one step of the two‐dimensional Fourier transform, for each angle of rotation of a digitized image. The basic measurement science of this technique is described and different cases are studied. The characterization of simple geometrical figures explains the meaning of peaks and their angular positions given by RIMAPS analysis. A known surface pattern made on a sample of pure copper, mechanically ground, is used to study reproducibility, dependence on image quality and topography scale relative to pixel size and magnification. Samples of pure zinc, mechanically ground and chemically etched, were used to show the main features of RIMAPS analysis when characterizing a more complicated pattern on a real surface. All the studies performed under different conditions for observation and acquisition of images give strong evidence of the stability and robustness of RIMAPS as a technique for the characterization of topography. 相似文献
66.
本文重点讨论了在平稳m相依噪声中弱随机信号的最佳无记忆Robust检测问题;并且以渐近功效函数为测度准则得到了最大最小无记忆非线性Robust检测器。 相似文献
67.
Sandra Aparecida de Assis Pedro Fernandes Bruno Sommer Ferreira Joaquim MS Cabral Olga Maria Mascarenhas Faria Oliveira 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2004,79(3):277-280
A partially purified extract of pectinmethylesterase (PME) from acerola fruit was immobilized on various supports: glass, celite, chrysotile, agarose, concanavalin A Sepharose 4B, egg shell, polyacrylamide and gelatin. In addition, reticulation with glutaraldehyde was assessed, as well as the use of gelatin in the presence of celite, glass and silica. The highest immobilization yields were obtained when the pectinmethylesterase was immobilized in concanavalin A Sepharose 4B (81.7%) and in gelatin‐water (78.0%). Copyright © 2004 Society of Chemical Industry 相似文献
68.
卫星编队飞行中的队形设计研究 总被引:6,自引:1,他引:5
目前关于卫星编队飞行的研究有显著的增加。多颗从属卫星(从星)在近距离内与主卫星(主星)组成特定的队形以完成相应的任务,是卫星编队飞行的特点及潜在优势。卫星在编队飞行时,其队形定义为以各颗卫星质心为顶点所构成的几何形状,而队形设计则是根据队形的几何形状求出各卫星的轨道根数(其中主星的轨道根数可以根据任务的要求事先确定)。基于相对轨道根数法,根据卫星相对运动方程,提出了“自然队形”的概念及队形设计的一般方法,并给出了具体的例子。 相似文献
69.
Experimental data for the densities, dynamic viscosities, sound speeds, and relative permittivities and for three binary systems of methyl methacrylate (MMA)+di-ethers (ethyl, isopropyl, and butyl) at 298.15 and 308.15 K and at atmospheric pressure are reported. The mixture viscosities are correlated by Grunberg–Nissan, McAllister, and Auslander equations over the complete composition range. The sound speeds for the mixtures are also calculated by using free length and collision factor theories, and Nomoto and Junjie equations. From the measured primary properties, deviation functions such as deviations in viscosities, sound speeds, relative permittivities, molar polarizations, excess isentropic compressibilities, and molar electrical susceptibilities were calculated, and the compositional dependence of each of the functions was expressed with a Redlich–Kister type equation. The variation of the Kirkwood correlation factor was determined over the complete composition range. 相似文献
70.