全文获取类型
收费全文 | 1488888篇 |
免费 | 26218篇 |
国内免费 | 6978篇 |
专业分类
电工技术 | 34409篇 |
综合类 | 6374篇 |
化学工业 | 271846篇 |
金属工艺 | 64178篇 |
机械仪表 | 42015篇 |
建筑科学 | 45901篇 |
矿业工程 | 11432篇 |
能源动力 | 50417篇 |
轻工业 | 110349篇 |
水利工程 | 14937篇 |
石油天然气 | 37681篇 |
武器工业 | 134篇 |
无线电 | 196285篇 |
一般工业技术 | 281053篇 |
冶金工业 | 151884篇 |
原子能技术 | 34042篇 |
自动化技术 | 169147篇 |
出版年
2021年 | 15847篇 |
2020年 | 11979篇 |
2019年 | 14730篇 |
2018年 | 15757篇 |
2017年 | 15029篇 |
2016年 | 21478篇 |
2015年 | 17519篇 |
2014年 | 28886篇 |
2013年 | 88230篇 |
2012年 | 34974篇 |
2011年 | 47334篇 |
2010年 | 42496篇 |
2009年 | 51018篇 |
2008年 | 44279篇 |
2007年 | 41377篇 |
2006年 | 44174篇 |
2005年 | 39031篇 |
2004年 | 41045篇 |
2003年 | 40930篇 |
2002年 | 40177篇 |
2001年 | 36657篇 |
2000年 | 35180篇 |
1999年 | 34014篇 |
1998年 | 40473篇 |
1997年 | 36834篇 |
1996年 | 33811篇 |
1995年 | 29892篇 |
1994年 | 28093篇 |
1993年 | 27977篇 |
1992年 | 26041篇 |
1991年 | 23083篇 |
1990年 | 23435篇 |
1989年 | 22577篇 |
1988年 | 21101篇 |
1987年 | 19305篇 |
1986年 | 18666篇 |
1985年 | 22020篇 |
1984年 | 22283篇 |
1983年 | 20251篇 |
1982年 | 19260篇 |
1981年 | 19349篇 |
1980年 | 17955篇 |
1979年 | 18477篇 |
1978年 | 17751篇 |
1977年 | 17474篇 |
1976年 | 18311篇 |
1975年 | 16034篇 |
1974年 | 15491篇 |
1973年 | 15581篇 |
1972年 | 13076篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
The early history of the IEEE Microwave Theory and Techniques Society (IEEE MTT-S) is summarized since its founding in 1952, and all administrative committee members and presidents are listed. Some of the more recent changes resulting from growth and multinational participation are described. Publications are discussed with editors listed for this Transactions, the IEEE Microwave and Wireless Components Letters, the IEEE Microwave Newsletter, and IEEE Microwave Magazine. The chronological evolution of the IEEE MTT-S's awards is presented, including a listing of all award winners. Distinguished lecturers and microwave symposia sites and chairpersons are also discussed. Early technology trends are described 相似文献
932.
933.
A robust classification procedure based on mixture classifiers and nonparametric weighted feature extraction 总被引:1,自引:0,他引:1
Bor-Chen Kuo Landgrebe D.A. 《Geoscience and Remote Sensing, IEEE Transactions on》2002,40(11):2486-2494
There are many factors to consider in carrying out a hyperspectral data classification. Perhaps chief among them are class training sample size, dimensionality, and distribution separability. The intent of this study is to design a classification procedure that is robust and maximally effective, but which provides the analyst with significant assists, thus simplifying the analyst's task. The result is a quadratic mixture classifier based on Mixed-LOOC2 regularized discriminant analysis and nonparametric weighted feature extraction. This procedure has the advantage of providing improved classification accuracy compared to typical previous methods but requires minimal need to consider the factors mentioned above. Experimental results demonstrating these properties are presented. 相似文献
934.
Portabella M. Stoffelen A. 《Geoscience and Remote Sensing, IEEE Transactions on》2002,40(12):2747-2759
Recent work has shown the important properties of the wind inversion residual or maximum-likelihood estimator (MLE) for quality Control (QC) of QuikSCAT Hierarchical Data Format (HDF) observations. Since March 2000, the QuikSCAT near-real-time (NRT) Binary Universal Format Representation (BUFR) product is available. As this product is used for numerical weather prediction (NWP) assimilation purposes, a QC procedure for the BUFR product is needed. We study the behavior of the MLE in order to determine whether the HDF QC procedure is appropriate for BUFR data. A comparison using real HDF and BUFR data reveals that the MLE distributions of HDF and BUFR differ and are actually poorly correlated. One important difference between BUFR and HDF is the amount of signal averaging prior to wind inversion. The averaging reduces the number of observations used in the wind retrieval for the BUFR product as compared to HDF. We show with a simple example that different MLE distributions are indeed expected due to this averaging. We also run a simulation in order to link theory and reality and better understand the behavior of the MLE. Despite the different MLE behavior in BUFR and HDF, the quality of the retrieved winds, as compared with the European Centre for Medium-Range Weather Forecasts winds, is very similar. We develop an MLE-based QC procedure for BUFR, similarly to the one in HDF, and we compare both. The skill of the QC in BUFR is again very similar to the one in HDF, showing that despite the different MLE behavior in both formats, the properties of the MLE as a QC indicator remain very similar. 相似文献
935.
Steinwandt R. Geiselmann W. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(11):2990-2991
An attack on the public key cryptosystem Polly Cracker is described, that reveals the complete secret key σ ∈ Fq n by means of n (nonadaptively) chosen "fake" ciphertexts 相似文献
936.
In antenna design there are some fundamental relationships based on reciprocity. The equivalence of antenna pattern in transmission and reception is well known. Less well known is the time-derivative relationship going from reception to transmission. These relationships are derived here and expressed in various useful forms. Electric and magnetic dipoles are given special consideration, and the combined form constructed as a terminated TEM transmission line (the BTW antenna) is discussed for its transmission and reception properties 相似文献
937.
Six months of data from the YSCAT94 experiment conducted at the CCIW WAVES research platform on Lake Ontario, Canada, are analyzed to evaluate a compound probability model. YSCAT was an ultrawideband small footprint (≈1 m) microwave scatterometer that operated at frequencies of 2-18 GHz, incidence angles from 0° to 60°, both h-pol and v-pol, and which tracked the wind using simultaneous weather measurements. The probability distribution function of the measured instantaneous backscattered amplitude (p(a)) is compared to theoretical distributions developed from-the composite model and a simple wave spectrum. Model parameters of the resulting Rayleigh/generalized lognormal distribution probability density function (pdf) (C, a1 , and a2) are derived directly from the data and are found to demonstrate relationships with wind speed, incidence angle, and radar frequency 相似文献
938.
Yuhua Cheng Chih-Hung Chen Matloubian M. Deen M.J. 《Electron Devices, IEEE Transactions on》2002,49(3):400-408
High-frequency (HF) AC and noise modeling of MOSFETs for radio frequency (RF) integrated circuit (IC) design is discussed. A subcircuit RF model incorporating the HF effects of parasitics is presented. This model is compared with the measured data for both y parameter and fT characteristics. Good model accuracy is achieved against measurements for a 0.25 μm RF CMOS technology. The HF noise predictivity of the model is also examined with measured data. Furthermore, a methodology to extract the channel thermal noise of MOSFETs from HF noise measurements is presented. By using the extracted channel thermal noise, any thermal noise models can be verified directly. Several noise models including the RF model discussed in this paper have been examined, and the results show that the RF model can predict the channel thermal noise better than the other models 相似文献
939.
Capacity-achieving sequences for the erasure channel 总被引:6,自引:0,他引:6
Oswald P. Shokrollahi A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(12):3017-3028
This paper starts a systematic study of capacity-achieving (c.a.) sequences of low-density parity-check codes for the erasure channel. We introduce a class A of analytic functions and develop a procedure to obtain degree distributions for the codes. We show various properties of this class which help us to construct new distributions from old ones. We then study certain types of capacity-achieving sequences and introduce new measures for their optimality. For instance, it turns out that the right-regular sequence is c.a. in a much stronger sense than, e.g., the Tornado sequence. This also explains why numerical optimization techniques tend to favor graphs with only one degree of check nodes. 相似文献
940.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication 相似文献