全文获取类型
收费全文 | 159575篇 |
免费 | 13235篇 |
国内免费 | 7281篇 |
专业分类
电工技术 | 8909篇 |
技术理论 | 12篇 |
综合类 | 10405篇 |
化学工业 | 26382篇 |
金属工艺 | 8549篇 |
机械仪表 | 9784篇 |
建筑科学 | 12014篇 |
矿业工程 | 4357篇 |
能源动力 | 4223篇 |
轻工业 | 11967篇 |
水利工程 | 2817篇 |
石油天然气 | 8124篇 |
武器工业 | 1150篇 |
无线电 | 19547篇 |
一般工业技术 | 19624篇 |
冶金工业 | 7806篇 |
原子能技术 | 1802篇 |
自动化技术 | 22619篇 |
出版年
2024年 | 693篇 |
2023年 | 2516篇 |
2022年 | 4386篇 |
2021年 | 5960篇 |
2020年 | 4532篇 |
2019年 | 3886篇 |
2018年 | 4456篇 |
2017年 | 4950篇 |
2016年 | 4457篇 |
2015年 | 5960篇 |
2014年 | 7523篇 |
2013年 | 9464篇 |
2012年 | 10217篇 |
2011年 | 11256篇 |
2010年 | 9961篇 |
2009年 | 9817篇 |
2008年 | 9664篇 |
2007年 | 9029篇 |
2006年 | 9014篇 |
2005年 | 7870篇 |
2004年 | 5451篇 |
2003年 | 4526篇 |
2002年 | 4136篇 |
2001年 | 3842篇 |
2000年 | 3675篇 |
1999年 | 3997篇 |
1998年 | 3280篇 |
1997年 | 2854篇 |
1996年 | 2543篇 |
1995年 | 2122篇 |
1994年 | 1714篇 |
1993年 | 1364篇 |
1992年 | 1064篇 |
1991年 | 828篇 |
1990年 | 660篇 |
1989年 | 552篇 |
1988年 | 426篇 |
1987年 | 328篇 |
1986年 | 232篇 |
1985年 | 188篇 |
1984年 | 119篇 |
1983年 | 92篇 |
1982年 | 104篇 |
1981年 | 59篇 |
1980年 | 53篇 |
1979年 | 43篇 |
1978年 | 34篇 |
1977年 | 35篇 |
1976年 | 53篇 |
1975年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Mixtures of Cr and Mo elemental powders, with the nominal compositions Cr25Mo75, Cr50Mo50, and Cr75Mo25, are processed by high-energy ball milling at ambient temperature. Milling is observed to force the mixing of the immiscible
bcc elements Cr and Mo into solid solutions. The lattice parameter of these solid solutions, measured by X-ray diffraction
(XRD), displays the expected positive deviation from Vegard’s law. These deviations are compared to the ones predicted by
Eshelby’s inclusion model for dilute alloys. The conventional Williamson-Hall approach is shown to fail to determine the grain
size in as-milled samples, probably due to the high density of dislocations. Annealing at 700 °C for 10 hours under argon
leads to a large reduction in structural defect density, without inducing any significant decomposition. The mixing measured
in Cr-Mo is discussed in the broader context of the mechanical mixing forced by ball milling in moderately immiscible systems. 相似文献
82.
83.
空时分集技术的最大优点在于在不增加带宽的情况下可以提高系统的可靠性,是目前移动通信的研究热点.常模算法是一种性能优良的码分多址(CDMA)盲多用户检测技术,能确保判决信号与实际传送信号之间的差错较小,误码率性能良好.文中提出将标准线性受限常模算法(LCCMA)与空时分组码(STBC)相结合,设计出一种收敛快、能够改善系统性能的基于2-空时分组码的多用户接收机. 相似文献
84.
85.
86.
Fang Wu Yaojiang Zhang Zaw Zaw Oo Erping Li 《Antennas and Propagation Magazine, IEEE》2005,47(4):110-118
The Multilevel Fast Multipole Method (FMM) is a well-established method and can be applied to solve electromagnetic (EM) scattering problems. Compared with other traditional methods, it requires less computational time and memory. However, constrained by a single processor's speed and memory limitations, the problem size that can be solved by serial implementation is still relatively small. For a million-unknown target, the computational time on a single processor is intolerable, and memory could be easily exhausted. Parallel-computing technology, which can utilize multiprocessors, provides an efficient way to solve electrically large-scale EM problems. This paper will focus on discussing the parallel methodologies applied to a multilevel FMM code, as well as demonstrating the computational efficiency of the parallel approach. 相似文献
87.
Microstructures of hundreds of micron thick poly(styrene-block-isoprene) copolymer films solution-cast in a cylindrical tube with the solvent evaporation controlled were investigated by transmission electron microscope (TEM), small angle X-ray scattering (SAXS) and optical microscope (OM). In a block copolymer with cylindrical polyisoprene microdomains, the orientation of the cylinders was varied along radial direction of the cylindrical tube. Highly aligned hexagonal arrays of in-plane polyisoprene cylinders were formed with their cylindrical axis parallel to the circumference of the tube in the regimes close to the wall edge. In contrast randomly ordered microdomains were observed at the center of the tube. We have also found that the orientation depends on the solvent evaporation rate and an intermediate rate (∼2.3 nL/s) provides the best orientation. In the case of a block copolymer with a bicontinuous double gyroid structure, we obtained a globally ordered microstructure where [111] crystallographic direction was parallel to the circumference of the tube. For both block copolymers, the area of highly ordered arrays of nanoscopic domains is over 1 mm2. Development of the orientation was explained by coupling two orthogonal fields: (1) The flow of a solution induced by strong capillary force at a meniscus between the cylindrical tube wall and the block copolymer solution and (2) the solvent evaporation. 相似文献
88.
双口RAM与常规RAM的最大区别是双口RAM具有两套独立的地址、数据和控制线,允许两个独立的CPU或控制器同时异步地访问存储单元,双口RAM由片内的仲裁逻辑来确定哪一侧的CPU可以访问内部RAM单元.IDT7132是2kB的标准双口RAM.文中重点介绍采用以自顶向下方法设计的基于CLD(复杂可编程逻辑器件)的大屏幕LED(发光二极管)显示系统中双口RAM的应用,并给出了系统设计方法及相关硬件电路.本设计中IDT7132双口RAM用来连接单片机信号处理模块和CPLD扫描模块. 相似文献
89.
CaiZhi WuYingjian YuWeisheng 《中国炼油与石油化工》2003,(1):43-46
Experimental use of multi-functional desulfurizing agent TS-01 for FCC gasoline in the FCC unit of SINOPEC Jiujiang Company shows that the multi-functional desulfurizing agent can effectively remove various kinds of sulfur in FCC gasoline and diesel fuel and fulfill passivation on heavy metals. 相似文献
90.
城市交通对城市的社会经济活动和生态资源环境具有双向作用,是城市功能中最活跃的因素.目前城市交通问题突出表现在交通阻塞和汽车尾气污染两个方面,已成为困扰着大中城市发展的主要问题.交通堵塞不仅给人们的生活和工作带来不便,而且增加了城市经济运行的时间成本,影响到城市功能的发挥和城市的健康发展,同时又进一步加剧了能源的消耗.可见城市交通问题是关系到城市可持续发展的关键问题之一. 相似文献