全文获取类型
收费全文 | 104313篇 |
免费 | 8570篇 |
国内免费 | 5325篇 |
专业分类
电工技术 | 5894篇 |
技术理论 | 3篇 |
综合类 | 9053篇 |
化学工业 | 16989篇 |
金属工艺 | 5825篇 |
机械仪表 | 6389篇 |
建筑科学 | 7441篇 |
矿业工程 | 2641篇 |
能源动力 | 2745篇 |
轻工业 | 8178篇 |
水利工程 | 1962篇 |
石油天然气 | 5280篇 |
武器工业 | 771篇 |
无线电 | 12384篇 |
一般工业技术 | 11516篇 |
冶金工业 | 4561篇 |
原子能技术 | 1398篇 |
自动化技术 | 15178篇 |
出版年
2024年 | 379篇 |
2023年 | 1312篇 |
2022年 | 2409篇 |
2021年 | 3407篇 |
2020年 | 2656篇 |
2019年 | 2305篇 |
2018年 | 2563篇 |
2017年 | 2905篇 |
2016年 | 2716篇 |
2015年 | 3706篇 |
2014年 | 4927篇 |
2013年 | 5997篇 |
2012年 | 6829篇 |
2011年 | 7437篇 |
2010年 | 6825篇 |
2009年 | 6591篇 |
2008年 | 6526篇 |
2007年 | 6221篇 |
2006年 | 6302篇 |
2005年 | 5400篇 |
2004年 | 4222篇 |
2003年 | 3747篇 |
2002年 | 4246篇 |
2001年 | 3687篇 |
2000年 | 2846篇 |
1999年 | 2437篇 |
1998年 | 1715篇 |
1997年 | 1473篇 |
1996年 | 1377篇 |
1995年 | 1163篇 |
1994年 | 903篇 |
1993年 | 672篇 |
1992年 | 523篇 |
1991年 | 396篇 |
1990年 | 318篇 |
1989年 | 234篇 |
1988年 | 214篇 |
1987年 | 143篇 |
1986年 | 82篇 |
1985年 | 76篇 |
1984年 | 59篇 |
1983年 | 49篇 |
1982年 | 49篇 |
1981年 | 33篇 |
1980年 | 29篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In this paper, a localized MEI method (L-MEI) is developed and combined with the domain decomposition method (DDM) for the simulation of scattering by a concave cylinder. In the L-MEI, the whole domain is decomposed into many subdomains. Different from the conventional MEI method, the MEI coefficients of the L-MEI method in each subdomain are only dependent on the localized metrons that are defined in the subdomain. The localization of metrons has the following advantages: (1) speeding up the calculation of MEI coefficients and saving memory, (2) making the MEI method available for concave structures, and (3) obtaining a band sparse matrix directly without any modification 相似文献
32.
基于数字信号处理器的直流电机控制系统 总被引:4,自引:0,他引:4
介绍了定点数字信号处理器(DSP)TMS320F240的一般性能及其在永磁无刷直流电机控制上的应用,给出了硬件设计方案、软件策略及输出结果。 相似文献
33.
34.
35.
Zhang Li Chun Jin Hai Yan Ye Hong Fei Gao Yu Zhi Ning Bao Jun Mo Bang Xian 《Electron Devices, IEEE Transactions on》2002,49(6):1075-1076
A polysilicon emitter RCA transistor (an ultra-thin interfacial oxide layer exists between polysilicon and silicon emitter) is presented which can operate at 77 K for the first time. An ultra-thin (1.5 nm) interfacial oxide layer is grown deliberately between polysilicon and silicon emitter using RCA oxidation and excellent device stability is obtained after rapid thermal annealing (RTA) treatment in nitrogen atmosphere. The RCA transistor exhibits good electrical performance at very low temperature for an emitter area of 3 × 8 μm2. The maximum toggle frequency of a 1:2 static divider is 1.2 GHz and 732 MHz at 300 K and 77 K, respectively 相似文献
36.
In this paper, the influence of viewing distance on subjective assessment of the impairment in video sequences is investigated. Subjective tests using the double-stimulus impairment scale variant II (DSIS II) method have been conducted at viewing distances of 5H (where H stands for the screen height) and 3H, respectively. Several statistical measures have been used to analyze the influence, including correlations and ANOVA (analysis of variance) tests. The results reveal that there is a very high correlation between the subjective scores, the variances are similar under the two viewing distances, the means of subjective data at these two viewing distances are the same, and there is no interaction between the viewing distance and the other two factors, i.e., the codec system and the source sequence. Throughout the tests, there is no evidence that a closer viewing distance such as 3H will vary the subjective test result statistically significantly. 相似文献
37.
This report deals with direct observations of microcrack linkage at the crack tip prior to macroscopic crack initiation. It is shown that this process is directly linked to the inclusion distribution in the material and can be considered in terms of an R curve to describe microcrack development. 相似文献
38.
Hong Jeong Jeong‐Ho Park 《International Journal of Adaptive Control and Signal Processing》2002,16(1):1-23
Tracking targets of interest is one of the major research areas in radar surveillance systems. We formulate the problem as incomplete data estimation and apply EM to the MAP estimate. The resulting filter has a recursive structure analogous to the Kalman filter. The advantage is that the measurement‐update deals with multiple measurements in parallel and the parameter‐update estimates the system parameters on the fly. Experiments tracking separate targets in parallel show that tracking maintenance ratio of the proposed system is better than that of NNF and RMS position error is smaller than that of PDAF. Also, the system parameters are correctly obtained even from incorrect initial values. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
39.
The reduction of calcium sulfate to produce calcium sulfide is a part of the cyclic process for converting sulfur dioxide
to elemental sulfur that is described in Part I. The kinetics of the hydrogen reduction of nickel-catalyzed calcium-sulfate
pellets were investigated using a thermogravimetric analysis (TGA) technique at reaction temperatures between 1023 and 1088
K and hydrogen partial pressures between 12.9 and 86.1 kPa. The reactivity of nickel-catalyzed calcium-sulfate pellets was
demonstrated by the conversion of 70 pct fresh nickel-catalyzed calcium sulfate to calcium sulfide in 20 minutes at 1073 K
under a hydrogen partial pressure of 86.1 kPa. Furthermore, the reactivity remained relatively intact after ten cycles of
reactions and regenerations. This observed characteristic of the pellets is important because the solids must be reusable
for repeated cycles to avoid generating secondary pollutants. The nucleation and growth rate expression was found to be useful
in describing the kinetics of the reaction, which had an activation energy of about 167 kJ/mol (∼40 kcal/mol) in all reaction
cycles except for the first regenerated samples that were lower at 146 kJ/mol (35 kcal/mol). The reaction order with respect
to hydrogen partial pressure was 0.22 in all cycles with the exception of the first regenerated sample for which it was 0.37. 相似文献
40.
Hong Wang Rong Zeng Xiuping Li 《Microwave Theory and Techniques》2005,53(2):564-570
In this paper, RF noise in 0.18-mum NMOSFETs concerning the contribution of carrier heating and hot carrier effect is characterized and analyzed in detail via a novel approach that modulates the channel carrier heating and number of hot carriers using body bias. We confirm qualitatively a negligible role of hot carrier effect on the channel noise in deep-submicrometer MOSFETs. For a device under reverse body bias (Vb), even though the increase in hot carrier population is clearly characterized by dc measurements, the device high-frequency noise is found to be irrelevant to the increase in the channel hot carriers. Experimental results show that the high-frequency noise is slightly reduced with the increase in |Vb|, and can be qualitatively explained by secondary effects such as the suppression of nonequilibrium channel noise and substrate induced noise. The reduction of NFmin and Rn with the increase in |Vb| may provide a possible methodology to finely adjust the device high-frequency noise performance for circuit design 相似文献