全文获取类型
收费全文 | 67927篇 |
免费 | 6293篇 |
国内免费 | 3384篇 |
专业分类
电工技术 | 4041篇 |
技术理论 | 2篇 |
综合类 | 5941篇 |
化学工业 | 11427篇 |
金属工艺 | 3460篇 |
机械仪表 | 3842篇 |
建筑科学 | 4916篇 |
矿业工程 | 1552篇 |
能源动力 | 1757篇 |
轻工业 | 8108篇 |
水利工程 | 1330篇 |
石油天然气 | 2369篇 |
武器工业 | 594篇 |
无线电 | 7790篇 |
一般工业技术 | 7516篇 |
冶金工业 | 2758篇 |
原子能技术 | 689篇 |
自动化技术 | 9512篇 |
出版年
2024年 | 264篇 |
2023年 | 1028篇 |
2022年 | 2127篇 |
2021年 | 2773篇 |
2020年 | 2140篇 |
2019年 | 1756篇 |
2018年 | 1862篇 |
2017年 | 2036篇 |
2016年 | 1942篇 |
2015年 | 2715篇 |
2014年 | 3694篇 |
2013年 | 4305篇 |
2012年 | 4921篇 |
2011年 | 5444篇 |
2010年 | 4921篇 |
2009年 | 4719篇 |
2008年 | 4809篇 |
2007年 | 4387篇 |
2006年 | 4042篇 |
2005年 | 3325篇 |
2004年 | 2409篇 |
2003年 | 1933篇 |
2002年 | 1977篇 |
2001年 | 1651篇 |
2000年 | 1368篇 |
1999年 | 1045篇 |
1998年 | 844篇 |
1997年 | 616篇 |
1996年 | 586篇 |
1995年 | 456篇 |
1994年 | 298篇 |
1993年 | 249篇 |
1992年 | 172篇 |
1991年 | 143篇 |
1990年 | 108篇 |
1989年 | 92篇 |
1988年 | 95篇 |
1987年 | 57篇 |
1986年 | 40篇 |
1985年 | 37篇 |
1984年 | 26篇 |
1983年 | 27篇 |
1982年 | 21篇 |
1981年 | 15篇 |
1980年 | 30篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 14篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
72.
73.
Polyaryloxydiphenylsilanes were prepared from phosphorus‐containing diols and diphenydichlorolsilane through solution polymerization. With a stoichiometric imbalance in feed monomers, the resulting polymers exhibited moderate melting points and good processing properties. The polymers prepared showed initial decomposition temperatures above 340 °C, excellent thermal stability, high char yields at 850 °C and very high limited oxygen index values of 56–59. The polymers' char yields and their (P + Si) contents showed linear relationships. © 2003 Society of Chemical Industry 相似文献
74.
75.
对己二腈工业反应器提出了两釜串联带回流的模型,通过模拟计算得出模型的级间返混系数 f=6的结论。该模型能较好地预测工业反应器中物料组分浓度变化和气、液两相的流动特性;指出了现工业反应器的鼓泡中和段体积偏小是造成己二酸浓度偏高的关键;提出了可以通过增加串连一个鼓泡预反应段的改造方案,能有效地降低己二酸的浓度,从7%降至4%左右,从而能较好地减缓腐蚀和结焦。 相似文献
76.
W. Lim C. K. Wang 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,370(2-3):568-572
The one-dimensional (1D) position-sensitive superheated-liquid-droplet dosimeter (SLDD) has been fabricated and tested in the laboratory. The 1D SLDD is fabricated from a 9.525-mm OD, 6.35-mm ID, 20-cm long, Plexiglas-walled tube filled with a mixture of superheated-liquid Freon droplets and host medium glycerol. Washer-shaped piezoelectric acoustic transducers are positioned at both ends of the tube; they determine the number and positions of the acoustic events when the superheated-liquid droplets evaporate upon neutron irradiation. The SLDD is irradiated with the 137Cs and 60Co γ-sources, as well as 252Cf neutron source to test for its radiation response and spatial resolution. The SLDD based on the Freon-134a superheated-liquid droplets operating at 20°C and 1 atm is found to be ideal for measuring absorbed neutron dose. This study also proves that the positions of the radiation-induced nucleation acoustic events can be linearly determined from the differences in the transmission times received by the acoustic transducers on the 1D SLDD. The spatial resolution of the neutron depth-dose is 1 mm due the finite response time (1 μs) of the piezoelectric acoustic transducers. 相似文献
77.
Ying Tan 《The Journal of VLSI Signal Processing》2002,32(1-2):45-54
In this paper, we propose a new approach for signal detection in wireless digital communications based on the neural network with transient chaos and time-varying gain (NNTCTG), and give a concrete model of the signal detector after appropriate transformations and mappings. It is well known that the problem of the maximum likelihood signal detection can be described as a complex optimization problem that has so many local optima that conventional Hopfield-type neural networks fail to solve. By refraining from the serious local optima problem of Hopfield-type neural networks, the NNTCTG makes use of the time-varying parameters of the recurrent neural network to control the evolving behavior of the network so that the network undergoes the transition from chaotic behavior to gradient convergence. It has richer and more flexible dynamics rather than conventional neural networks only with point attractors, so that it can be expected to have much ability to search for globally optimal or near-optimal solutions. After going through a transiently inverse-bifurcation process, the NNTCTG can approach the global optimum or the neighborhood of global optimum of our problem. Simulation experiments have been performed to show the effectiveness and validation of the proposed neural network based method for the signal detection in digital communications. 相似文献
78.
The effect of high oxide field stress is studied using capacitance-time (C-t) measurements of MOS capacitors. The stress results in parallel shifts of the C-t curve along the time axis. The flatband voltage shift ΔVFB obtained from the initial deep depletion capacitance C(t=0+) follows the same trend as that from the high-frequency C-V characteristics. However, the discrepancy between the two flatband voltages becomes larger as the stress increases due to the effect of interface charges on C-t characteristics. The flatband voltage difference is converted to interface trap density, showing a steady increase of interface trap density with stress, similar to that from low-frequency C-V measurements 相似文献
79.
LDD方法在提高电路工作电压中的应用研究 总被引:1,自引:0,他引:1
研究了利用轻掺杂漏结构来制作高电源电压器件的工艺方法。分析了LDD结构参数对器件击穿特性的影响,并结合实验结果对N^-区的注入剂量,长度及引入的串联电阻进行了优化设计。 相似文献
80.
存在未建模动态时,如何去除系统传递函数估计中噪声引起的偏差是系统辨识关心的重要问题。本文将我们已提出的BELS方法进行推广得出:当系统未建模动态可用-FIR模型描述时,应用本文的方法可得到系统传递函数的无偏辨识,而不需知道有关噪声和未建模动态概率分布函数的先验知识。 相似文献