全文获取类型
收费全文 | 11880篇 |
免费 | 1649篇 |
国内免费 | 668篇 |
专业分类
电工技术 | 1560篇 |
综合类 | 1046篇 |
化学工业 | 400篇 |
金属工艺 | 3409篇 |
机械仪表 | 1238篇 |
建筑科学 | 734篇 |
矿业工程 | 818篇 |
能源动力 | 343篇 |
轻工业 | 181篇 |
水利工程 | 230篇 |
石油天然气 | 597篇 |
武器工业 | 119篇 |
无线电 | 341篇 |
一般工业技术 | 1074篇 |
冶金工业 | 972篇 |
原子能技术 | 186篇 |
自动化技术 | 949篇 |
出版年
2024年 | 32篇 |
2023年 | 132篇 |
2022年 | 273篇 |
2021年 | 305篇 |
2020年 | 337篇 |
2019年 | 303篇 |
2018年 | 263篇 |
2017年 | 394篇 |
2016年 | 466篇 |
2015年 | 426篇 |
2014年 | 692篇 |
2013年 | 662篇 |
2012年 | 820篇 |
2011年 | 912篇 |
2010年 | 713篇 |
2009年 | 746篇 |
2008年 | 589篇 |
2007年 | 896篇 |
2006年 | 834篇 |
2005年 | 625篇 |
2004年 | 590篇 |
2003年 | 551篇 |
2002年 | 469篇 |
2001年 | 413篇 |
2000年 | 307篇 |
1999年 | 276篇 |
1998年 | 221篇 |
1997年 | 209篇 |
1996年 | 157篇 |
1995年 | 131篇 |
1994年 | 105篇 |
1993年 | 77篇 |
1992年 | 52篇 |
1991年 | 47篇 |
1990年 | 41篇 |
1989年 | 44篇 |
1988年 | 20篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1984年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1964年 | 4篇 |
1962年 | 2篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1958年 | 3篇 |
1956年 | 4篇 |
1955年 | 3篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
在介绍推进波作用下底泥起动特点的基础上,将上层水体作为粘性流体,底泥作为粘弹性体,推导了推进波作用下泥床面剪应力的表达式,并根据试验结果,给出了推进波作用下底泥起动时的床面剪应力与底泥流变参数的关系。 相似文献
52.
Although the gas metal arc welding (GMAW) process is widely used for joining metals, its planning is still a cumbersome task. The planning procedure involves many complex interrelationships among the process variables and depends heavily on empirical knowledge. Therefore, a solution method that allows a convenient way to represent the domain knowledge and evaluate the process variable relationships is needed. Further, the lack of a strong domain theory to quantify these interrelationships is a deficiency in the planning of the GMAW process. This paper presents a solution method that overcomes this deficiency and introduces a convenient knowledge representation scheme. The solution method considers the planning procedure to be a constraint satisfaction problem (CSP). The AC-4 algorithm is used to obtain arc consistency among nodes in the constraint network and the PC-4 algorithm is applied to obtain path consistency in the network. A modified version of the AC-4 algorithm is developed to reduce the search space and correspondingly reduce the computation time. An example is presented to demonstrate the capability of the method and its potential to reduce lead time. 相似文献
53.
大型储罐底板焊接及变形控制是保证储罐整体施工质量的关键环节,采用碎丝填充的焊接方法可以防止变形,同时可以有效地避免应力集中,提高施工质量。文章介绍了碎丝埋弧焊的原理、工艺参数和焊接方法。实践证明,填充碎丝不仅是一种减小底板焊接变形的手段,同时可以充分利用焊接热能,节约焊接时间和焊剂用量,经济效益好,是一种值得推广的技术。 相似文献
54.
55.
56.
Before 12 months of age, infants have difficulties coordinating and sequencing their movements to retrieve an object concealed in a box. This study examined (a) whether young infants can discover effective retrieval solutions and consolidate movement coordination earlier if exposed regularly to such a task and (b) whether different environments, indexed by box transparency, would impact the rate of learning and time of discovery of these solutions. Infants (N=12) were presented with an object retrieval task every week from 6 1/2 months of age until they were able to retrieve the toy from the box using coordinated two-handed patterns for 3 weeks. To reach that criterion, infants tested with an opaque box took 2 1/2 months and infants tested with a semitransparent box took 1 1/2 months. Both groups outperformed age-matched controls who received a one-time exposure to the task. Repeated exposure to the task and vision of the toy significantly enhanced this process of solution discovery. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
57.
Fluorescence microscopy techniques have become important tools in mitosis research. The well-known disadvantages of fluorescence microscopy, rapid bleaching, phototoxicity and out-of-focus contributions blurring the in-focus image are obstacles which still need to be overcome. Confocal fluorescence microscopy has the potential to improve our capabilities of analyzing cells, because of its excellent depth-discrimination and image processing power. We have been using a confocal fluorescence microscope for the study of the mechanism of poleward chromosome movement, and report here (1) a cell preparation technique, which allows labeling of fixation sensitive spindle antigens with acceptable microtubule preservation; (2) the use of image processing methods to represent the spatial distribution of various labeled elements in pseudocolour; (3) a novel immunoelectron microscopic labeling method for microtubules, which allows the visualization of their distribution in semithin sections at low magnification; and (4) a first attempt to study microtubule dynamics with a confocal fluorescence microscope in living cells, microinjected with rhodamine labeled tubulin. Our experience indicates that confocal fluorescence microscopy provides real advantages for the study of spatial colocalization of antigens in the mitotic spindle. It does not, however, overcome the basic limits of resolution of the light microscope. Therefore, it has been necessary to use an electron microscopic method. Our preliminary results with living cells show that it is possible to visualize the entire microtubule network in stereo, but that the sensitivity of the instrument is still too low to perform dynamic time studies. It will be worthwhile to further develop this new type of optical instrumentation and explore its usefulness on both fixed and living cells. 相似文献
58.
本文给出了一种椭圆弧长的作图求解方法,即由作图求得椭圆弧长的近似值。通过对100个椭圆弧长的求解结果表明,由此方法求得的椭圆弧长的误差甚小,从而在相当高的精度范围内,提供了一种工程中适用并且简单易行的求解椭圆弧长的方法。 相似文献
59.
60.