全文获取类型
收费全文 | 170730篇 |
免费 | 15452篇 |
国内免费 | 8560篇 |
专业分类
电工技术 | 10988篇 |
技术理论 | 19篇 |
综合类 | 13729篇 |
化学工业 | 27310篇 |
金属工艺 | 9457篇 |
机械仪表 | 10417篇 |
建筑科学 | 13316篇 |
矿业工程 | 4592篇 |
能源动力 | 4725篇 |
轻工业 | 15763篇 |
水利工程 | 3363篇 |
石油天然气 | 8757篇 |
武器工业 | 1538篇 |
无线电 | 19058篇 |
一般工业技术 | 19055篇 |
冶金工业 | 7235篇 |
原子能技术 | 1808篇 |
自动化技术 | 23612篇 |
出版年
2024年 | 794篇 |
2023年 | 2856篇 |
2022年 | 5473篇 |
2021年 | 7238篇 |
2020年 | 5538篇 |
2019年 | 4357篇 |
2018年 | 4847篇 |
2017年 | 5458篇 |
2016年 | 4984篇 |
2015年 | 7018篇 |
2014年 | 8881篇 |
2013年 | 10253篇 |
2012年 | 11793篇 |
2011年 | 12889篇 |
2010年 | 11281篇 |
2009年 | 10659篇 |
2008年 | 10629篇 |
2007年 | 9924篇 |
2006年 | 9472篇 |
2005年 | 7780篇 |
2004年 | 5632篇 |
2003年 | 4849篇 |
2002年 | 4714篇 |
2001年 | 4075篇 |
2000年 | 3767篇 |
1999年 | 3796篇 |
1998年 | 3008篇 |
1997年 | 2385篇 |
1996年 | 2258篇 |
1995年 | 1805篇 |
1994年 | 1539篇 |
1993年 | 1071篇 |
1992年 | 860篇 |
1991年 | 628篇 |
1990年 | 501篇 |
1989年 | 444篇 |
1988年 | 307篇 |
1987年 | 229篇 |
1986年 | 167篇 |
1985年 | 111篇 |
1984年 | 78篇 |
1983年 | 63篇 |
1982年 | 75篇 |
1981年 | 57篇 |
1980年 | 65篇 |
1979年 | 22篇 |
1977年 | 10篇 |
1976年 | 15篇 |
1974年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
921.
922.
本文讨论一类非线性系统的全局鲁棒输出调节问题.假定被控非线性系统的系统输入方向未知,且产生参考或扰动信号的外部系统含未知参数,这为控制律的设计带来了挑战.文章使用自适应控制方法和内模原理,解决了一类相对阶为1的非线性输出反馈系统的输出调节问题,并将结果应用于处理Lorenz系统的渐近跟踪问题. 相似文献
923.
ABSTRACT In this research, the effect of particle size on the surface oxidation and flotation behavior of galena in the lime system was studied. Coarse (?0.074 + 0.038 mm), intermediate (?0.038 + 0.025 mm) and fine (?0.025 mm) galena particles were used in the experiment. The dissolution tests, flotation tests, and sorption tests were accomplished. Through further analysis by XPS, the effect of particle size and lime was observed. The decrease of mineral particle sizes increased the adsorption ratio of collector and the dissolution of galena, while the hydrophilic product OH?/Ca(OH)+ produced by dissolution occupied the dominant position, which led to the minerals hydrophilic. 相似文献
925.
A poly(ethylene terephthalate) (PET)/montmorillonite clay nanocomposite was synthesized via in situ polymerization. Microscopic studies revealed that in an isothermal crystallization process, some crystallites in the nanocomposite initially were rod‐shaped and later exhibited three‐dimensional growth. The crystallites in the nanocomposite were irregularly shaped, rather than spherulitic, being interlocked together without clear boundaries, and they were much smaller than those of neat PET. With Avrami analysis, the isothermal crystallization kinetic parameters (the Avrami exponent and constant) were obtained. The rate constants for the nanocomposite demonstrated that clay could greatly increase the crystallization rate of PET. The results for the Avrami exponent were consistent with the observation of the rodlike crystallites in the PET/clay nanocomposite during the initial stage. Wide‐angle X‐ray scattering and Fourier transform infrared studies showed that, in comparison with neat PET, the crystal lattice parameters and crystallinity of the nanocomposite did not change significantly, whereas more defects may have been present in the crystalline regions of the nanocomposite because of the presence of the clay. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1381–1388, 2004 相似文献
926.
基于梯度场的图像融合算法只适用于尺度差异不大于1∶4的多光谱图像与全色图像。针对尺度差异为1∶8的北京一号卫星多光谱图像及高分辨率全色图像的融合问题,提出一种结合小波变换的梯度场图像尺度渐进融合算法。利用小波变换方法将多光谱图像与高分辨率全色图像尺度差异倍数缩小,得到基于小波变换的初级融合,再进行基于梯度场的Poisson图像融合。实验结果表明,渐进融合图像与多光谱图像的平均颜色差异值为23.5,与高分辨率全色图像的平均梯度差异值为2.1,多尺度纹理特征值差异值分别为3.98、10.2、18.9,渐进融合图像与高分辨率全色图像的空间细节和纹理细节吻合程度更好。 相似文献
927.
ATO包裹硅酸锆的制备与应用 总被引:2,自引:0,他引:2
采用化学共沉淀技术制备了锑掺杂二氧化锡(ATO)包裹硅酸锆的导电粉体,对比了该导电粉体与ATO在防静电陶瓷中的应用效果。结果表明与掺纯ATO相比较,掺入ATO包裹硅酸锆的防静电陶瓷颜色比较浅,并且能明显减少氧化锡的用量,当陶瓷的表面电阻为107Ω/□量级时,用ATO包裹硅酸锆作为导电填料可以节省25%左右的ATO。 相似文献
928.
929.
Electrospinning technique has been recognized as an efficient method to manufacture nano-fiber. At present, research focuses on the structure and morphology of the fibers, a few investigations have been reported the mechanism of electrospinning. In our experiment, appropriate polymer EVOH (ethylene/vinyl alcohol copolymer) and different solvents were chosen, the energy change in the process of molecule orientation was analyzed by computer simulation, and the morphologies of the fiber were indicated by scanning electron microscope (SEM). Results indicate that: in the process of molecule orientation, some barriers should be overcome; the height of the barrier is determined by the relaxation times (τ) of the molecule. The relaxation times vary in different solutions, when the relaxation time is short, the orientation of molecule is easy, so jet instability will be fierce, and fibers with small diameter are obtained. 相似文献
930.
The swollen pore structure of a series of microporous isoporous resins (7.4–140 Å) are investigated with inverse GPC, n-alkylbenzenes and linear polystyrenes being used as probe molecules. The results indicated that, with the lowering of crosslinking degree of isoporous resins, the average pore diameter increased and the pore distribution curve broadened. All pore volume distribution obeyed a log-normal distribution. Based on the linear regression method, the experimental data were fitted to a monotonously declining exponential function and a normal distribution function by a computer, and some important structural parameters such as average pore diameter, pore volume distribution, specific surface area, etc. were obtained. The specific surface area of swollen gels were found much greater than those in the dry state measured by N2 adsorption. 相似文献