全文获取类型
收费全文 | 14627篇 |
免费 | 1822篇 |
国内免费 | 1441篇 |
学科分类
工业技术 | 17890篇 |
出版年
2024年 | 60篇 |
2023年 | 447篇 |
2022年 | 554篇 |
2021年 | 751篇 |
2020年 | 709篇 |
2019年 | 498篇 |
2018年 | 407篇 |
2017年 | 444篇 |
2016年 | 448篇 |
2015年 | 478篇 |
2014年 | 679篇 |
2013年 | 846篇 |
2012年 | 855篇 |
2011年 | 886篇 |
2010年 | 757篇 |
2009年 | 837篇 |
2008年 | 840篇 |
2007年 | 1092篇 |
2006年 | 992篇 |
2005年 | 854篇 |
2004年 | 776篇 |
2003年 | 618篇 |
2002年 | 496篇 |
2001年 | 484篇 |
2000年 | 357篇 |
1999年 | 325篇 |
1998年 | 235篇 |
1997年 | 169篇 |
1996年 | 156篇 |
1995年 | 131篇 |
1994年 | 132篇 |
1993年 | 92篇 |
1992年 | 69篇 |
1991年 | 59篇 |
1990年 | 54篇 |
1989年 | 42篇 |
1988年 | 38篇 |
1987年 | 25篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1966年 | 12篇 |
1965年 | 9篇 |
1964年 | 13篇 |
1960年 | 7篇 |
1957年 | 8篇 |
1955年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
齿科微晶玻璃的腐蚀机理及溶胶-凝胶防腐蚀涂层研究 总被引:4,自引:0,他引:4
利用体外试验方法以及SEM/EDAX、ICP、FTIR等分析技术,对氟硅碱钙石(fluorcanasite,K2Na4Ca5Si12O30F4)齿科微晶玻璃的腐蚀机理,以及溶胶-凝胶Al2O3,、TiO2及ZrO2涂层改善微晶玻璃抗侵蚀的效果进行了比较分析.研究表明,口腔溶液对该齿科微晶玻璃的侵蚀源于溶液中的H3O 离子与微晶玻璃表面的Na 及K 发生迅速的离子交换,从而形成结构疏松的表面富SiO2层,其Si-O网络进而被H2O分子所断开,使SiO2以可溶性硅胶形式溶解于溶液中.此反应导致大量的表面结构缺陷,从而降低了材料的强度和使用寿命。浸泡25天后微晶玻璃表面最终的反应产物是一层低结晶度的颗粒状碳酸羟基磷灰石Cal0(PO4)6(2OH-,CO3^2-).溶胶-凝胶A12O3涂层具有显著的改善齿科微晶玻璃抗唾液腐蚀的作用。 相似文献
82.
粒子群优化算法及其应用 总被引:20,自引:0,他引:20
粒子群优化(PSO)算法是一种新颖的演化算法,它属于一类随机全局优化技术,PSO算法通过粒子间的相互作用在复杂搜索空间中发现最优区域。PSO的优势在于简单而又功能强大。介绍了基本的PSO算法、研究现状及其应用,并讨论将来可能的研究内容。 相似文献
83.
84.
Christine Di Massimo Paul A. Lant Aidan Saunders Gary A. Montague Ming T. Tham A. Julian Morris 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,53(3):265-277
The last decade has seen the development of a number of approaches for estimating those variables which are difficult to measure on-line in industrial process situations. Whilst a range of techniques is available, a common element is the use of process knowledge in the form of a system model. In the case of bioprocess systems, although a large range of models has been presented in the literature, their use in estimation schemes on an industrial scale has been limited. A number of reasons can be identified for their low level of utilisation. Of particular significance is the uncertainty which exists in quantifying system performance and the process-model mismatch which inevitably results. The level of ‘pre-defined model’ uncertainty, together with the knowledge gained during the course of the fermentation, serves to dictate estimator structure. The paper considers a range of estimation strategies and contrasts, through industrial applications, their performance characteristics and utility. 相似文献
85.
从分析智能仪器产品设计与制造过程出发,依据产品可靠性研究中的样本数据,建立产品环境适应能力模型。结合工作条件变化模型,提出一套智能仪器产品在变化环境中可靠性评价的方法。 相似文献
86.
凌礼富 《武汉化工学院学报》1991,(4)
本文通过对SIMATIC S5—115U可编程控制器性能的简介,简述国外PC技术的现状和发展,并提出对PC国产化的看法. 相似文献
87.
88.
介绍了骑马岭水电站砂石加工系统的料源规划、系统规划设计、系统工艺流程及环保措施。该加工系统采用的典型的二段破碎工艺,对中小型水电站混凝土骨料生产系统的设计具有一定的参考价值。同时,该加工系统在废水处理水回收利用及细砂与石粉回收、防尘、降低噪声,以及固体废弃物处置等方面,均采取了相应的环保措施,以减少其对施工人员和周围环境的影响。 相似文献
89.
Multiple forms of a symbol-digit substitution task were used to provide a componential analysis of age differences in coding task performance. The results demonstrated age differences in feature encoding, memory, and visual search. A 2nd experiment was conducted with young adults to investigate a sensory deficit as a locus of age differences. The spatial contrast sensitivity deficit of older adults was simulated on forms by applying a digital filter. Persons in the age-simulated contrast condition performed worse than those in the normal contrast condition. The stimulus degradation effect was linked to visual search speed. The study illustrates the utility of componential analysis and offers direct support for the hypothesis that sensory deficits affect performance on tasks used to assess intelligence (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
90.
Dental amalgams are based on a broad spectrum of materials differing in their chemical composition, metallurgical treatment, and in the way the initial alloys powders are prepared. In addition to their chemical composition, amalgams based on various powders differ in both their microstructure and the amount of mercury needed for preparation. All these facts may affect electrochemical processes occurring during their interaction with oral fluids, and also mercury release. While verifying the effect of the technology used for the preparation of the high‐copper ternary alloy powder on the properties of resulting amalgams, this study aimed at the mechanism of their interaction with a model saliva solution as well as mercury release was included. Measurements were done in a model saliva solution using standard electrochemical methods and exposition measurements. The interaction of individual types of amalgams with artificial saliva did not reveal any significant differences. The free corrosion potential of all these amalgams in an aerated solution settled in the range of values in which tin oxidation, resulting in a layer of insoluble corrosion producsts, turned out to be the dominant anodic process. The rate of mercury release was the lowest for amalgams based on a gas‐atomized alloy. The highest rate of mercury release, and also its dependence on time, was exhibited by lathe‐cut powder based amalgam. In addition to different volume fraction of the Ag‐Hg phase and the level of its tin alloying, this different behaviour may be explained by differences in the rate at which a layer of tin corrosion products acting as a barrier to mercury release is formed. 相似文献