全文获取类型
收费全文 | 25610篇 |
免费 | 2174篇 |
国内免费 | 881篇 |
专业分类
电工技术 | 1389篇 |
技术理论 | 1篇 |
综合类 | 1413篇 |
化学工业 | 4600篇 |
金属工艺 | 1344篇 |
机械仪表 | 1346篇 |
建筑科学 | 1901篇 |
矿业工程 | 585篇 |
能源动力 | 899篇 |
轻工业 | 1729篇 |
水利工程 | 355篇 |
石油天然气 | 1366篇 |
武器工业 | 125篇 |
无线电 | 3190篇 |
一般工业技术 | 3298篇 |
冶金工业 | 1453篇 |
原子能技术 | 320篇 |
自动化技术 | 3351篇 |
出版年
2024年 | 112篇 |
2023年 | 462篇 |
2022年 | 795篇 |
2021年 | 1121篇 |
2020年 | 758篇 |
2019年 | 718篇 |
2018年 | 717篇 |
2017年 | 834篇 |
2016年 | 776篇 |
2015年 | 943篇 |
2014年 | 1262篇 |
2013年 | 1603篇 |
2012年 | 1585篇 |
2011年 | 1743篇 |
2010年 | 1420篇 |
2009年 | 1453篇 |
2008年 | 1351篇 |
2007年 | 1254篇 |
2006年 | 1368篇 |
2005年 | 1174篇 |
2004年 | 847篇 |
2003年 | 765篇 |
2002年 | 766篇 |
2001年 | 545篇 |
2000年 | 523篇 |
1999年 | 610篇 |
1998年 | 580篇 |
1997年 | 473篇 |
1996年 | 452篇 |
1995年 | 354篇 |
1994年 | 286篇 |
1993年 | 194篇 |
1992年 | 175篇 |
1991年 | 118篇 |
1990年 | 92篇 |
1989年 | 73篇 |
1988年 | 88篇 |
1987年 | 48篇 |
1986年 | 44篇 |
1985年 | 25篇 |
1984年 | 33篇 |
1983年 | 19篇 |
1982年 | 28篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 15篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1975年 | 4篇 |
1965年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
本文主要根据电子整机的发展要求,从集成化、高性能和高可靠等三方面分析国外模似IC的发展,进而说明模拟IC总的发展趋势及其表现。最后指出,模拟IC正面临一个新的变革时期。 相似文献
92.
Weikai Su Wei Hong ZhengHau Zhu YunYi Wang 《Journal of Infrared, Millimeter and Terahertz Waves》1992,13(12):1925-1941
In this paper, the scattering parameters of a waveguide cross junction loaded with a metallic post in the center are analyzed for the first time by using the Method of Lines. The homogeneous boundary condition of the third kind and curved boundary are introduced in the formulation. Numerical results are in good agreement with the experimental data. The scattering parameters at Ka-band and W-band of the cross junctions loaded with metallic posts of different radii are presented. It is shown from the numerical results that loaded with metallic posts is an effective means for adjusting the network parameters of the waveguide cross junction to satisfy some special requirements in the design of millimeter wave components. 相似文献
93.
GaN buffer and main layers were grown by the conventional hydride vapor phase epitaxy technique using GaCl3 consecutively. The deposited buffer layers were investigated by atomic force microscopy and X-ray analysis. To examine the behavior of the buffer layers at main layer growth temperature, heat treatment was conducted at 900°C. Based on the results of the buffer layer study, GaN thick films were grown at 1050°C. Optimum deposition conditions of buffer layer from the buffer and main layer studies generally coincided. On the φ scanning pattern, the GaN films grown on (0001) Al2 O3 were single-crystalline. Band-edge emission dominated photoluminescence was observed at room temperature. 相似文献
94.
本文从智能网的基本概念入手,论述了利用 ZXJ10程控交换系统为发展智能网业务提供支持功能的技术策略以及分阶段实现的过程,并对各个阶段能够实现的业务作了简要介绍。 相似文献
95.
The basic structural units of the genome are nucleotides. A single nucleotide polymorphism (SNP) is a mutation at a single nucleotide position. This paper discusses several major problems in SNP data analysis and review some existing solutions in this work. Generally speaking, a rich set of SNP analysis problems are cast in the signal processing framework. Our objective is to offer a state-of-the art review on this topic from a signal processing viewpoint so that researchers in the signal processing field can grasp the important domain knowledge to overcome the barrier between the two fields 相似文献
96.
In this paper, a novel generalization of subspace-based blind channel identification methods in cyclic prefix (CP) systems is proposed. For the generalization, a new system parameter called repetition index is introduced whose value is unity for previously reported special cases. By choosing a repetition index larger than unity, the number of received blocks needed for blind identification is significantly reduced compared to all previously reported methods. This feature makes the method more realistic especially in wireless environments where the channel state is usually fast-varying. Given the number of received blocks available, the minimum value of repetition index is derived. Theoretical limit allows the proposed method to perform blind identification using only three received blocks in absence of noise. In practice, the number of received blocks needed to yield a satisfactory bit-error-rate (BER) performance is usually on the order of half the block size. Simulation results not only demonstrate the capability of the algorithm to perform blind identification using fewer received blocks, but also show that in some cases system performance can be improved by choosing a repetition index larger than needed. Simulation of the proposed method over time-varying channels clearly demonstrates the improvement over previously reported methods. 相似文献
97.
横流均匀环境中三维线源型正负浮力射流特性研究 总被引:2,自引:2,他引:0
本文利用混合有限分析法及交错网格。对横流均匀环境中三维线源型正负浮力射流及负浮力射流的特性进行研究,分析了不同工况下流速,温度和湍动能在断面上的分布及影响射流轨迹线的因素,讨论了轨迹线上温度的变化及浮力射流的贴壁现象。对三维长线源型负浮力射流,分析了流速比,喷口弗汝德数对负浮力射流的影响。 相似文献
98.
无线信道中的电波传播 总被引:2,自引:0,他引:2
分析了信号在无线信道中传输时所经受的两种衰落,介绍了主要的无线传播模型,在此基础上提出了对抗衰落的措施。 相似文献
99.
Penalty interference of nonlinear propagation impairments and polarisation mode dispersion (PMD) caused signal distortions is experimentally investigated 相似文献
100.
定向井井眼轨道预测方法研究及其应用 总被引:2,自引:0,他引:2
对定向井片眼轨道进行预测是实现井眼轨道定量控制的关键.本文提出了井眼轨道预测控制的力-位移模型.在此基础上,建立了描述侧向切削问题的多元幂积模式,推导了预测井斜、方位及其变化率的基本预测公式,形成了井眼轨道预测控制系统,并进一步研制了适于井场快速预测的自适应信号跟踪顶测软件,针对IBM-PC微机,开发了定向井井眼控制预测软件包DTCPS.多例预测实践表明,使用该软件包预测井眼轨道,精度较高,相符程度较好. 相似文献