全文获取类型
收费全文 | 96011篇 |
免费 | 8346篇 |
国内免费 | 2384篇 |
专业分类
电工技术 | 3262篇 |
技术理论 | 6篇 |
综合类 | 11669篇 |
化学工业 | 17461篇 |
金属工艺 | 3581篇 |
机械仪表 | 5063篇 |
建筑科学 | 13457篇 |
矿业工程 | 2157篇 |
能源动力 | 1661篇 |
轻工业 | 7900篇 |
水利工程 | 1699篇 |
石油天然气 | 2210篇 |
武器工业 | 516篇 |
无线电 | 7327篇 |
一般工业技术 | 7888篇 |
冶金工业 | 5326篇 |
原子能技术 | 703篇 |
自动化技术 | 14855篇 |
出版年
2024年 | 368篇 |
2023年 | 1453篇 |
2022年 | 4161篇 |
2021年 | 4668篇 |
2020年 | 2561篇 |
2019年 | 2305篇 |
2018年 | 2402篇 |
2017年 | 3007篇 |
2016年 | 4528篇 |
2015年 | 5185篇 |
2014年 | 6973篇 |
2013年 | 6378篇 |
2012年 | 5957篇 |
2011年 | 5736篇 |
2010年 | 5028篇 |
2009年 | 4894篇 |
2008年 | 4306篇 |
2007年 | 5641篇 |
2006年 | 5812篇 |
2005年 | 4971篇 |
2004年 | 3671篇 |
2003年 | 3620篇 |
2002年 | 2878篇 |
2001年 | 1881篇 |
2000年 | 1736篇 |
1999年 | 1250篇 |
1998年 | 787篇 |
1997年 | 634篇 |
1996年 | 553篇 |
1995年 | 432篇 |
1994年 | 379篇 |
1993年 | 272篇 |
1992年 | 238篇 |
1991年 | 194篇 |
1990年 | 189篇 |
1989年 | 152篇 |
1988年 | 123篇 |
1987年 | 111篇 |
1986年 | 96篇 |
1985年 | 102篇 |
1984年 | 120篇 |
1983年 | 69篇 |
1982年 | 57篇 |
1981年 | 52篇 |
1980年 | 55篇 |
1966年 | 50篇 |
1964年 | 49篇 |
1962年 | 79篇 |
1957年 | 57篇 |
1955年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
介绍了一种基于高性能浮点DSP芯片TMS320C32、CPLD芯片XC95288和A/D采样芯片AD976组成的多路采集系统的工作原理以及设计方法。通过对第一路施加特殊的电压量,在CCS开发环境下读取采样缓冲区的值,并利用Matlab对采样数据进行了全波傅氏变换。此外,该系统已在继电保护中得到广泛应用,实践表明,该系统能较好地解决多路模拟量的采集,并确保了采样数据的安全可靠性。 相似文献
22.
Large lectures are the predominant way of teaching first-year students at universities in Norway. However, this forum for education is seldom discussed as a context for a formative feedback practice. The purpose of this sequential mixed methods study was to address whether and how a student-response system can open for a formative feedback practice in lectures and thereby support students' ability to monitor their own learning, as well as supply insight into how students engage with the feedback in their course work. The context for the study was large lectures (150–200 students) in a qualitative method course for first-year psychology students. Findings from the survey (n = 149) showed a positive correlation between the extent to which students report that they use clickers to monitor their own learning, and the extent to which they report that they used the feedback in their own course work. However, findings indicate that students valued the process of monitoring their own learning during the lectures to a greater extent than they actually used the feedback in their course work. Findings from interviews (n = 6) illustrated various ways students applied feedback in their course work. 相似文献
23.
Biological information is stored in DNA, RNA and protein sequences, which can be understood as genotypes that are translated into phenotypes. The properties of genotype–phenotype (GP) maps have been studied in great detail for RNA secondary structure. These include a highly biased distribution of genotypes per phenotype, negative correlation of genotypic robustness and evolvability, positive correlation of phenotypic robustness and evolvability, shape-space covering, and a roughly logarithmic scaling of phenotypic robustness with phenotypic frequency. More recently similar properties have been discovered in other GP maps, suggesting that they may be fundamental to biological GP maps, in general, rather than specific to the RNA secondary structure map. Here we propose that the above properties arise from the fundamental organization of biological information into ‘constrained'' and ‘unconstrained'' sequences, in the broadest possible sense. As ‘constrained'' we describe sequences that affect the phenotype more immediately, and are therefore more sensitive to mutations, such as, e.g. protein-coding DNA or the stems in RNA secondary structure. ‘Unconstrained'' sequences, on the other hand, can mutate more freely without affecting the phenotype, such as, e.g. intronic or intergenic DNA or the loops in RNA secondary structure. To test our hypothesis we consider a highly simplified GP map that has genotypes with ‘coding'' and ‘non-coding'' parts. We term this the Fibonacci GP map, as it is equivalent to the Fibonacci code in information theory. Despite its simplicity the Fibonacci GP map exhibits all the above properties of much more complex and biologically realistic GP maps. These properties are therefore likely to be fundamental to many biological GP maps. 相似文献
24.
25.
动态评价技术在塔河碳酸盐岩缝洞型油气藏中的应用 总被引:5,自引:2,他引:3
塔河油田奥陶系油气藏是大型碳酸盐岩溶洞型油气藏,其储渗空间主要为大小不同的溶洞、裂缝带、溶蚀孔隙等组成,该油气藏具有极强的非均质性,单纯用静态资料来认识这类油气藏是非常困难。文章提出利用生产动态资料和信息进行该类型油气藏研究的新思路,利用人工神经网络技术在处理非线性相关参数预测方面的优势,并以渗流理论为基础,结合试井成果,选用已知油井的产量、油嘴、油压、含水率、气油比、原油密度等6个开发动态参数作为样品输入数据,推导出影响油气藏开发的重要参数(地层系数)与生产信息的关系,建立了人工神经网络预测储层参数的结构模型。通过塔里木盆地塔河油气田实例研究,说明了利用动态信息评价油气藏技术在碳酸盐岩缝洞型油气藏储层预测和非均质性分析等方面具有较高的实用价值。 相似文献
26.
27.
随着计算机网络技术的发展,远程教学系统的结构发生了重大的变化,逐步由原来的客户机/服务器(C/S)结构转变为基于Internet的浏览器/服务器(B/S)结构。本文提出了基于CORBA技术的B/S结构系统模型。分析了其运行过程,并与传统的结构进行了比较,指明了其优越性。在本文的结尾。指出了使用这种技术的一个具体例子。 相似文献
28.
加氢反应器制造技术的新进展 总被引:2,自引:1,他引:1
王玉台 《石油化工设备技术》2006,27(5):8-9,13
随着加氢装置的大型化,对加氢反应器的设计、主体材质的选用及制造均提出了新的、更高的要求。文章较全面地介绍了国内外加氢反应器的设计准则、主体材质(抗氢钢)和制造技术等方面的新进展。 相似文献
29.
The strong tendency of organic nanoparticles to rapidly self‐assemble into highly aligned superlattices at room temperature when solution‐cast from dispersions or spray‐coated directly onto various substrates is described. The nanoparticle dispersions are stable for years. The novel precipitation process used is believed to result in molecular distances and alignments in the nanoparticles that are not normally possible. Functional organic light‐emitting diodes (OLEDs)—which have the same host–dopant emissive‐material composition—with process‐tunable electroluminescence have been built with these nanoparticles, indicating the presence of novel nanostructures. For example, only changing the conditions of the precipitation process changes the OLED emission from green light to yellow. 相似文献
30.