全文获取类型
收费全文 | 50459篇 |
免费 | 5311篇 |
国内免费 | 3575篇 |
专业分类
电工技术 | 1471篇 |
技术理论 | 5篇 |
综合类 | 3161篇 |
化学工业 | 17073篇 |
金属工艺 | 4208篇 |
机械仪表 | 921篇 |
建筑科学 | 1668篇 |
矿业工程 | 927篇 |
能源动力 | 6602篇 |
轻工业 | 3600篇 |
水利工程 | 823篇 |
石油天然气 | 4439篇 |
武器工业 | 369篇 |
无线电 | 2075篇 |
一般工业技术 | 5711篇 |
冶金工业 | 2401篇 |
原子能技术 | 1080篇 |
自动化技术 | 2811篇 |
出版年
2024年 | 242篇 |
2023年 | 1751篇 |
2022年 | 2479篇 |
2021年 | 2463篇 |
2020年 | 2386篇 |
2019年 | 2176篇 |
2018年 | 1878篇 |
2017年 | 2030篇 |
2016年 | 1900篇 |
2015年 | 1822篇 |
2014年 | 2663篇 |
2013年 | 3141篇 |
2012年 | 3191篇 |
2011年 | 3456篇 |
2010年 | 2574篇 |
2009年 | 2609篇 |
2008年 | 2284篇 |
2007年 | 2778篇 |
2006年 | 2519篇 |
2005年 | 2155篇 |
2004年 | 1925篇 |
2003年 | 1672篇 |
2002年 | 1487篇 |
2001年 | 1291篇 |
2000年 | 1101篇 |
1999年 | 940篇 |
1998年 | 737篇 |
1997年 | 609篇 |
1996年 | 559篇 |
1995年 | 466篇 |
1994年 | 447篇 |
1993年 | 309篇 |
1992年 | 232篇 |
1991年 | 183篇 |
1990年 | 186篇 |
1989年 | 130篇 |
1988年 | 108篇 |
1987年 | 87篇 |
1986年 | 57篇 |
1985年 | 57篇 |
1984年 | 63篇 |
1983年 | 30篇 |
1982年 | 25篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1964年 | 9篇 |
1957年 | 8篇 |
1955年 | 8篇 |
1951年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
《Journal of the European Ceramic Society》2020,40(8):3348-3353
Large transduction coefficient () is difficult to obtain in piezoelectric ceramics because these two parameters show opposite trends with compositional modifications. Herein, the Pb(Zr0.53Ti0.47)O3 ceramic powders were calcinated under different temperatures (A:830 °C, B:860 °C, and C:890 °C), and then mixed together according to different weight ratios (1A:1B:1C, 1A:2B:1C, 1A:2B:3C and 3A:2B:1C) for ceramics preparation. Both d33 and g33 are improved successfully, and the transduction coefficient with the weight ratio of 1A:2B:3C reaches up to 17,500 × 10−15 m2/N, which is 60 % higher than that with the powders calcinated under 830 °C, and at least twice those of commercial PZT-4, PZT-5A and PZT-8 ceramics. The improved transduction coefficient is owing to the enhanced piezoelectric constant and spontaneous polarization resulted from the increased grain size, relative density and the fraction of tetragonal phase. These results indicate that this is a simple but effective way to tailor the transduction coefficient in piezoelectric ceramics. 相似文献
2.
Many models of spoken word recognition posit the existence of lexical and sublexical representations, with excitatory and inhibitory mechanisms used to affect the activation levels of such representations. Bottom-up evidence provides excitatory input, and inhibition from phonetically similar representations leads to lexical competition. In such a system, long words should produce stronger lexical activation than short words, for 2 reasons: Long words provide more bottom-up evidence than short words, and short words are subject to greater inhibition due to the existence of more similar words. Four experiments provide evidence for this view. In addition, reaction-time-based partitioning of the data shows that long words generate greater activation that is available both earlier and for a longer time than is the case for short words. As a result, lexical influences on phoneme identification are extremely robust for long words but are quite fragile and condition-dependent for short words. Models of word recognition must consider words of all lengths to capture the true dynamics of lexical activation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
3.
基于进化算法的常减压装置模拟 总被引:1,自引:0,他引:1
提出了基于优选优生进化算法(Select—best and prepotency evolution algorithm,SPEA)的常减压装置模拟方法。以各塔的温度分布为目标,基于生产过程和分析数据,采用SPEA确定各塔板Murphree效率,从而精确描述各塔板平衡偏离程度。在实际应用中,获得具有良好精度的常减压装置模型。系统分析了SPEA算法的关键参数——优选领域大小与计算复杂性及寻优性能之间的关系,结果显示其取值为群体规模的10%最为合适。 相似文献
4.
醇解技术在制备皮革加脂剂方面的研究进展 总被引:1,自引:0,他引:1
本文介绍了醇解反应的动力学、影响醇解反应收率的因素以及醇解反应在合成加脂剂方面的应用。 相似文献
5.
6.
对上海高桥分公司2×10~4m~3/h(标准状态)制氢装置原设计的预转化催化剂还原流程进行了改进。先跳开预转化反应器,利用转化炉制取氢气,再用自产的高纯氢气代替重整氢,对预转化催化剂进行单独升温还原,避免了催化剂在还原初期因发生甲烷化反应而超温失活的问题,使催化剂具有更好的活性和稳定性。 相似文献
7.
8.
The scale along the coordinate axes in the equations of motion hitherto used for an H-maser (in relative units) is shown to depend on Q as the quality factor for an H-maser. This hinders both analysis of the operation of the H-maser and optimization of its parameters. The modified equations of motion proposed here do not have that shortcoming. We determine the atomic flux into the bulb that gives the H-maser the best metrological characteristics. 相似文献
9.
Biodegradation of monoaromatic hydrocarbons in aquifer columns amended with hydrogen peroxide and nitrate 总被引:1,自引:0,他引:1
The ability of indigenous microorganisms to degrade benzene, toluene, ethylbenzene and xylenes (BTEX) in laboratory scale flow-through aquifer columns was tested separately with hydrogen peroxide (110 mg/l) and nitrate (330 mg/l as NO3−) amendments to air-saturated influent nutrient solution. The continuous removal of individual components from all columns relative to the sterile controls provided evidence for biodegradation. In the presence of hydrogen peroxide, the indigeneous microorganisms degraded benzene and toluene (> 95%), meta- plus para-xylene (80%) and ortho-xylene (70%). Nitrate addition resulted in 90% removal of toluene and 25% removal of ortho-xylene. However, benzene, ethylbenzene, meta- and para-xylene concentrations were not significantly reduced after 42 days of operation. Following this experiment, low dissolved oxygen (< 1 mg/l) conditions were initiated with the nitrate-amended column influent in order to mimic contaminated groundwater conditions distal from a nutrient injection well. Toluene continued to be effectively degraded (> 90%), and more than 25% of the benzene, 40% of the ethylbenzene, 50% of the meta- plus para-xylenes and 60% of the ortho-xylene were removed after several months of operation. 相似文献
10.