全文获取类型
收费全文 | 137752篇 |
免费 | 11437篇 |
国内免费 | 6456篇 |
专业分类
电工技术 | 8237篇 |
技术理论 | 10篇 |
综合类 | 9300篇 |
化学工业 | 22786篇 |
金属工艺 | 7431篇 |
机械仪表 | 8472篇 |
建筑科学 | 11622篇 |
矿业工程 | 3463篇 |
能源动力 | 4178篇 |
轻工业 | 8376篇 |
水利工程 | 2595篇 |
石油天然气 | 6799篇 |
武器工业 | 1026篇 |
无线电 | 16763篇 |
一般工业技术 | 16789篇 |
冶金工业 | 6805篇 |
原子能技术 | 1631篇 |
自动化技术 | 19362篇 |
出版年
2024年 | 610篇 |
2023年 | 2157篇 |
2022年 | 3877篇 |
2021年 | 5417篇 |
2020年 | 4025篇 |
2019年 | 3424篇 |
2018年 | 3830篇 |
2017年 | 4123篇 |
2016年 | 3740篇 |
2015年 | 5013篇 |
2014年 | 6656篇 |
2013年 | 7992篇 |
2012年 | 8671篇 |
2011年 | 9117篇 |
2010年 | 8430篇 |
2009年 | 7870篇 |
2008年 | 7532篇 |
2007年 | 7349篇 |
2006年 | 7277篇 |
2005年 | 6298篇 |
2004年 | 4791篇 |
2003年 | 4980篇 |
2002年 | 5328篇 |
2001年 | 4725篇 |
2000年 | 3733篇 |
1999年 | 3515篇 |
1998年 | 2907篇 |
1997年 | 2277篇 |
1996年 | 2077篇 |
1995年 | 1714篇 |
1994年 | 1406篇 |
1993年 | 1043篇 |
1992年 | 787篇 |
1991年 | 611篇 |
1990年 | 477篇 |
1989年 | 423篇 |
1988年 | 368篇 |
1987年 | 200篇 |
1986年 | 179篇 |
1985年 | 131篇 |
1984年 | 110篇 |
1983年 | 74篇 |
1982年 | 71篇 |
1981年 | 63篇 |
1980年 | 50篇 |
1979年 | 40篇 |
1977年 | 33篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1959年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
Kameyama H. Miyajima T. Zhi Ding 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(3):851-860
In multicarrier systems, when the order of a channel impulse response is larger than the length of the cyclic prefix (CP), there is a significant performance degradation due to interblock interference (IBI). This paper proposes a blind-channel shortening method in which the equalizer parameter vector is formed by the noise subspace of the received signal correlation matrix so that the output power is maximized. The proposed method can not only shorten the effective channel impulse response to within the CP length but also maximize the output signal-to-interference-and-noise ratio while eliminating the IBI. We point out that the performance depends on the choice of a decision delay and propose a simple method for determining the appropriate delay. We propose both a batch algorithm and an adaptive algorithm and show by simulation that they are superior to the conventional algorithms. 相似文献
74.
憎水性栀子蓝色素制备的研究 总被引:1,自引:0,他引:1
以浓盐酸为催化剂,采用乙酸酐酯化处理水溶性栀子蓝色素,制备了憎水性栀子蓝色素.探讨了栀子蓝色素与乙酸酐料液比、反应时间和反应温度等因素对憎水性栀子蓝色素色价的影响.结果表明:采用料液比1:20,在常温下反应4 h,为制备憎水性栀子蓝色素的最优条件.同时,通过红外光谱、可见吸收光谱及溶解性对栀子蓝色素的酯化改性进行了初步的探讨. 相似文献
75.
76.
Y.M. Wong W.P. Kang J.L. Davidson J.H. Huang D.V. Kerns 《Diamond and Related Materials》2008,17(4-5):552-555
A novel integrated vacuum field emission (VFE) differential amplifier (diff-amp) utilizing carbon nanotube (CNT) emitters has been developed. A dual-mask microfabrication process was employed to achieve a VFE diff-amp by integrating identical CNT VFE transistors with built-in split gates and integrated anodes. The identical pair of triode amplifiers was well-matched in their device characteristics. The measured ac small-signal characteristics of the diff-amp showed a common-mode-rejection ratio (CMRR) of ~ 320 (~ 50 dB). The proposed analytical model of the CMRR was verified to be in good agreement with the experimental data. The successful implementation of the CNT diff-amp demonstrates a new way to achieve temperature and radiation tolerant VFE integrated microelectronics. 相似文献
77.
Lei Liu Ying Kong Hong Xu Jin P. Li Jin X. Dong Zhi Lin 《Microporous and mesoporous materials》2008,115(3):624-628
A three-dimensional zinc phosphate compound with DFT topology, designated as ZnPO4-EU1, has been synthesized by an ionothermal approach from the system HF-ZnO–P2O5-choline chloride-imidazolidone. Ethylenediamine, derived from decomposition of the imidazolidone component of the deep-eutectic solvent (DES) itself, is delivered to the synthesis and serves as an appropriate template for ZnPO4-EU1. Experiments in which the synthesis conditions were varied showed that ZnPO4-EU1 may be prepared over a wide molar ratio of P/Zn = 0.55–13.0. Powder X-ray diffraction patterns have been obtained at intervals to track the crystallization process of this material. The experimental data show that Zn3(PO4)2 · 4H2O (a dense phase) was first isolated from the DES after reaction for 1 h. Subsequently, the pure phase of ZnPO4-EU1 was obtained with increasing crystallization time from 12 h to 72 h. The experimental results show that the nucleation and crystallization take place with relatively low levels of solvent degradation, demonstrating that zinc phosphate with a three-dimensional framework can be synthesized by in situ generation of an appropriate template using an unstable DES at high temperatures (150–200 °C). 相似文献
78.
79.
黄健宇 《机械工业标准化与质量》2005,(3):20-25
随着计算机及网络技术在现代企业生产经营管理中的广泛应用,特别是以网络为信息交流平台的企业CMIS、ERP和MRPII等管理系统的应用推广,使得企业生产经营的管理技术和理念相比传统管理的方式、方法也发生了根本性的变化。企业内外形成和交流的信息量成倍增加,组织生产经营信息逐步表现为操作流程规范化、信息应用集成化和信息环境复杂化的趋势,从而使得组织信息交流语言及接口的规范统一,标准化也日显重要。 相似文献
80.
A Low-Power CMOS Linear-in-Decibel Variable Gain Amplifier With Programmable Bandwidth and Stable Group Delay 总被引:1,自引:0,他引:1
Tsou S.-C. Li C.-F. Huang P.-C. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2006,53(12):1436-1440
This brief presents a new circuit architecture for linear-in-decibel, constant-bandwidth variable gain amplifier (VGA). To obtain high linearity under low-voltage operation, this VGA is a closed-loop structure. In loop amplifier design, two techniques are applied: first, the loop amplifier is given finite input impedance. This arrangement keeps the VGA bandwidth constant under different gain setting. Second, a current-buffered compensation is applied for loop stability. Compared to the Miller compensation, this method achieves wider bandwidth. The prototype chip using 0.18-mum CMOS technology demonstrates that -10- to 20-dB gain and 0.5- to 30-MHz bandwidth can be programmed independently. The group delay difference within 30-dB gain control range is smaller than 1%. The total circuit dissipates 1.35 mA from a 1.8-V supply 相似文献