全文获取类型
收费全文 | 24176篇 |
免费 | 4541篇 |
国内免费 | 3195篇 |
专业分类
电工技术 | 4652篇 |
综合类 | 2791篇 |
化学工业 | 1578篇 |
金属工艺 | 406篇 |
机械仪表 | 1790篇 |
建筑科学 | 498篇 |
矿业工程 | 239篇 |
能源动力 | 414篇 |
轻工业 | 836篇 |
水利工程 | 225篇 |
石油天然气 | 515篇 |
武器工业 | 412篇 |
无线电 | 5029篇 |
一般工业技术 | 2697篇 |
冶金工业 | 288篇 |
原子能技术 | 317篇 |
自动化技术 | 9225篇 |
出版年
2024年 | 196篇 |
2023年 | 604篇 |
2022年 | 874篇 |
2021年 | 928篇 |
2020年 | 1111篇 |
2019年 | 1028篇 |
2018年 | 964篇 |
2017年 | 1148篇 |
2016年 | 1247篇 |
2015年 | 1321篇 |
2014年 | 1680篇 |
2013年 | 1945篇 |
2012年 | 1897篇 |
2011年 | 2109篇 |
2010年 | 1488篇 |
2009年 | 1529篇 |
2008年 | 1563篇 |
2007年 | 1609篇 |
2006年 | 1399篇 |
2005年 | 1140篇 |
2004年 | 1003篇 |
2003年 | 844篇 |
2002年 | 614篇 |
2001年 | 562篇 |
2000年 | 523篇 |
1999年 | 400篇 |
1998年 | 349篇 |
1997年 | 333篇 |
1996年 | 285篇 |
1995年 | 214篇 |
1994年 | 169篇 |
1993年 | 159篇 |
1992年 | 139篇 |
1991年 | 120篇 |
1990年 | 92篇 |
1989年 | 63篇 |
1988年 | 46篇 |
1987年 | 27篇 |
1986年 | 20篇 |
1985年 | 26篇 |
1984年 | 38篇 |
1983年 | 25篇 |
1982年 | 33篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1960年 | 3篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
This paper finds the appropriate pi-coefficients for a parameter estimation adaptive system and uses them to analyze the stability of two estimation algorithms. The estimation error dynamics of the system are modeled by a linear time-invariant subsystem and a nonlinear time-varying update law in a feedback loop. Then the so-called max-p problems are formulated and solved to obtain the pi-coefficients for the linear subsystem and nonlinear update low. For the investigated system, the quantitative results show that the least-squares update algorithm has larger stability range than that of the gradient algorithm, and the σ-modification scheme gives larger stability ranges for both algorithms. 相似文献
63.
正交频分多址(OFDM:orthogonal frequency division multiplexing)技术由于其在多径环境下克服码间干扰的固有特点,在移动通信中已得到广泛地应用。利用阵列天线上行链路信号到达角估计实时信息,计算OFDM系统下行链路阵列天线权重,将阵列天线应用于下行链路中,最后给出系统误码率性能的计算机仿真结果。 相似文献
64.
非理想信道下Colpitts混沌电路的自适应同步研究 总被引:1,自引:0,他引:1
本文研究了Colpitts混沌电路在非理想信道条件下的自适应同步问题。引入自适应控制器对输入到响应部分(response system)的衰变混沌信号进行预处理,来补偿衰落信道对于同步性能的影响。给出了系统的数学模型,对恒定信道衰变和时变信道衰变两种非理想信道条件下的混沌ColpiRs电路的自适应同步进行了数值仿真研究。仿真结果表明,对于恒定或慢变化的时变信道衰变,自适应控制器可以有效的提高Colpitts电路响应部分和驱动部分(Drive system)的同步性能。 相似文献
65.
基于多信道预约可冲突避免的多址接入协议 总被引:3,自引:0,他引:3
本文为多跳分布多无线网络提出了一套灵活而有效的自适应获取冲突避免(AACA)的多址接入协议。在该协议中,各节点竞争公共信道,利用RTS/CTS对话形式来预约各业务信道,成功预约后的分组传输不会受到其他节点的干扰。它使用任意确定数目信道,以异步方式工作,并且使得各节点利用半双工无线电台就可以灵活、简便地实现资源预约。分析和比较结果说明,所提出的多信道预约协议可以有效地解决隐藏终端、暴露终端以及侵入终端的问题。 相似文献
66.
References: 《中国炼油与石油化工》2007,(3):35-42
The proton nuclear magnetic resonance spectroscopy (1H-NMR), the synchronous fluorescence spectrometry (SFS) and the ruthenium ions catalyzed oxidation (RICO) method were used to determine the chemical structure of polyaromatic nucleus in Oman residue fractions. The results of 1H-NMR analyses showed that the average numbers of aromatic rings in the aromatics, resins and asphaltenes units were 3.2, 5.6 and 8.2, respectively. SFS was used to investigate the distribution of aromatic rings in residue fractions, the main distribution range of aromatic rings in aromatics, resins and asphaltenes were 3 4 rings, 3--5 rings and more than 5 rings, respectively. The aromatic network in residue fractions was oxidized to produce numerous carboxylic acids. The types and content of benzenepolycarboxylic acids, such as phthalic acid, benzenetricarboxylic acids, benzenetetracarboxylic acids, benzenepentacarboxylic acid and benzenehexacarboxylic acid disclosed the condensed types of aromatic nuclei in the core. The biphenyl fraction (BIPH), the cata-condensed fraction (CATA), the peri-condensed fraction (PERI) and the condensed index (BCI) were calculated based on the benzenepolycarboxylic acids formed. The results implied that there was less biphenyl type structures in all residue fractions. The aromatics fraction was almost composed of the cata-condensed type system, and the asphaltenes fraction was wholly composed of the peri-condensed type system, while in the resins fraction co-existed the two types, herein the peri-con- densed type was predominant over the cata-condensed type. Based on the analytical results obtained in the study, the components --aromatics, resins and asphaltenes -- were given the likely structural models. 相似文献
67.
Koji Yamada Noboru Miura Chihiro Hamaguchi Norihiko Kamata 《Solid-state electronics》1989,32(12):1113-1117
Hot carrier magnetophonon resonances of n-type Si, short channel InP and p-type InSb were investigated in pulsed high magnetic fields up to 40 T. Using a recently developed high resolution technique in pulsed high fields, many new features of the hot carrier-phonon interactions in high magnetic fields were found. 相似文献
68.
L. V. El’nikova 《Journal of Superconductivity and Novel Magnetism》2007,20(2):197-199
We describe the lyotropic liquid crystalline phase transitions in the lipid mixture dipalmitoil-PC/dilauroy-PC/cholesterol
by 3D spin-1 lattice model. The formation of nanoscale domains with the characteristic size about 300 nm was studied in experiments
on confocal fluorescence microscopy (CFM) (G. V. Feigenson and J. T. Buboltz, Biophys. J.
80, 2775 (2001)). The structure parameters of the lamellar vesicle in dipalmitoil-PC-rich phase, corresponding to these regions,
are verified by numerical Monte Carlo simulations on the lattice. We point its superconductivity analogy properties at the
region of phase stability for composition-dependent nanoscopic region. 相似文献
69.
This paper proposes a low complexity joint space-time multiuser detection algorithm for asynchronous DS/CDMA antenna array systems. The proposed multiuser detector is composed of an adaptive antenna array, used as a linear beamformer, and a sliding window decorrelator. A QPSK modulation scheme is used in order to increase bandwidth efficiency. Numerical results are given in terms of Bit Error Rate (BER) under the assumption of a frequency-selective Rayleigh slow fading channel. In particular, the proposed receiver is shown to be near-far resistant, even in worst fading cases, and to exploit completely array introduction while maintaining acceptable computational complexity. The proposed architecture avoids linear filter realization of the decorrelator, which is impractical in the case of a large number of users, and operates with relatively short data frames instead of the complete information sequence. Finally, this receiver is very flexible to changes in timing configuration. 相似文献
70.