全文获取类型
收费全文 | 42447篇 |
免费 | 3958篇 |
国内免费 | 1844篇 |
专业分类
电工技术 | 2847篇 |
技术理论 | 2篇 |
综合类 | 2709篇 |
化学工业 | 7184篇 |
金属工艺 | 2575篇 |
机械仪表 | 2734篇 |
建筑科学 | 3264篇 |
矿业工程 | 1222篇 |
能源动力 | 1177篇 |
轻工业 | 2907篇 |
水利工程 | 769篇 |
石油天然气 | 2432篇 |
武器工业 | 353篇 |
无线电 | 4983篇 |
一般工业技术 | 5363篇 |
冶金工业 | 1988篇 |
原子能技术 | 523篇 |
自动化技术 | 5217篇 |
出版年
2024年 | 187篇 |
2023年 | 762篇 |
2022年 | 1430篇 |
2021年 | 1847篇 |
2020年 | 1431篇 |
2019年 | 1208篇 |
2018年 | 1354篇 |
2017年 | 1498篇 |
2016年 | 1270篇 |
2015年 | 1743篇 |
2014年 | 2187篇 |
2013年 | 2518篇 |
2012年 | 2663篇 |
2011年 | 2850篇 |
2010年 | 2445篇 |
2009年 | 2442篇 |
2008年 | 2429篇 |
2007年 | 2198篇 |
2006年 | 2220篇 |
2005年 | 1877篇 |
2004年 | 1223篇 |
2003年 | 1167篇 |
2002年 | 1157篇 |
2001年 | 1017篇 |
2000年 | 1031篇 |
1999年 | 1132篇 |
1998年 | 910篇 |
1997年 | 790篇 |
1996年 | 658篇 |
1995年 | 598篇 |
1994年 | 437篇 |
1993年 | 353篇 |
1992年 | 302篇 |
1991年 | 199篇 |
1990年 | 173篇 |
1989年 | 158篇 |
1988年 | 104篇 |
1987年 | 65篇 |
1986年 | 44篇 |
1985年 | 36篇 |
1984年 | 25篇 |
1983年 | 21篇 |
1982年 | 28篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The effects of yttrium and cerium on microstructures and properties of Nb-Si system composites were investigated by scanning electron microscopy( SEM), energy dispersive spectrum(EDS), X-ray diffraction(XRD) and high temperature oxidation experiments.It is found that the coarse primary silicide phase became finer and more homogeneous with Y and Ce addition.The results of high temperature oxidation experiments show that the oxidation rates of NbSi system composites with an appropriate amount of Y and Ce decrease compared with those of alloys without Y or Ce addition, and oxidation products mainly distribute along the phase boundaries between the Nb solid solution and silicide. 相似文献
92.
基于DSP的电力数据采集平台的设计与研究 总被引:1,自引:0,他引:1
介绍了一种用于电力系统的数据采集系统.该系统采用数字信号处理器(DSP)和复杂可编程逻辑器件(CPLD)作为核心芯片,给出了主要部分的电路及其原理、功能,系统中使用CPLD实现基本逻辑,使系统有足够的冗余和灵活性,具有可靠性高、可升级等优点. 相似文献
93.
94.
Analyzing the performance and fairness of BitTorrent-like networks using a general fluid model 总被引:2,自引:0,他引:2
In this paper, a general fluid model is developed to study the performance and fairness of BitTorrent-like networks. The fluid model incorporates two important features previously isolated from system performance models, user settings with multiple groups and inter-group data exchange induced by the choking algorithm. Our numerical results point out some key parameters of performance, such as the staying time of seeders. Generally, selfish behavior does not receive equal performance degradation, and in some scenarios users have strong incentives of free-riding. We also find content delivery can be greatly deterred when malicious free-riders are overwhelming. 相似文献
95.
The continuous reduction of chip size driven by the market demand has a significant impact on circuit design and assembly process of IC packages. Shrinking chip size and increasing I/O counts require finer bond pad pitch and bond pad size for circuitry layout. As a result, serious wire deflection during transfer molding process could make adjacent wires short, and this issue becomes more critical as a smaller wire diameter has to be applied for the finer pitch wire bonded IC devices.This paper presents a new encapsulation process development for 50 μm fine pitch plastic ball grid array package. Since reduced wire diameter decreases the bending strength of bonded wires significantly, wire deflection during molding process becomes quite serious and critical. Experiments on conventional transfer molding were conducted to evaluate wire span threshold with 23.0 μm diameter gold wire. The results show that the wire span threshold is about 4.1 mm, which is much shorter than the wire span threshold of over 5.0 mm for wire with 25.4 μm diameter. Finite element analysis shows there is a significant difference in the wire deflection between 23.0 μm gold wire and 25.4 μm gold wire diameter under the same action of mold flow. A novel encapsulation method is introduced using non-sweep solution. The wire span could be extended to over 5.0 mm with wire sweep less than 1%. Reliability tests conducted showed that all the units passed 1000 temperature cycles (−55 to 125 °C) with JEDEC moisture sensitivity level 2a (60 °C/60% relative humidity for 120 h) and 3 times reflow (peak temperature at 220–225 °C). It is believed that this solution could efficiently overcome the risk of wire short issues and improve the yield of ultra fine pitch wire bonds in high-volume production. 相似文献
96.
在Reissner厚板理论中,利用分离变量法得到挠度函数W(x,y)和应力函数ψ(x,y)的解。在这些解中.选择一些三角级数和多项式作为该问题的挠度函数W(x,y)和应力函数ψ(x,y),从而得到了两相邻边固定另两边任意支承矩形厚板弯曲问题的精确解.这里不需要繁琐地叠加. 相似文献
97.
98.
川东地区井下套管损坏的原因分析及对策 总被引:4,自引:0,他引:4
本文就近年来在钻井施工中遇到的4口井发套管损坏的问题进行了原因分析,提出了防止井下套管损坏对策。 相似文献
99.
橡塑共混热塑性弹性体的形态结构与性能 总被引:2,自引:0,他引:2
综述了影响共混热塑性弹性体的形态结构与性能的主要因素。 相似文献
100.
A clinical case control study to identify prognostic factors present at hospital admission associated with early sequelae and fatal outcome of acute Japanese encephalitis (JE) was carried out in Gusi county, Henan Province, central China from June to September 1991. A total of 70 patients with laboratory-confirmed acute JE were studied, of whom 3 cases died and 33 cases had neurological or psychiatric sequelae at the end of three months follow-up. The results showed that acute JE at younger age, with higher body temperature, high white cell count in CSF, and deep coma present at hospital admission were markers for unfavorable outcomes (sequelae or fatal). A history of the vaccination was not correlated with the early sequelae and fatal outcome of the disease. The paper suggests that early diagnosis and treatment and universal JE vaccination for all susceptible populations are keys for decreasing incidence of sequelae and fatal outcome of acute JE. 相似文献