全文获取类型
收费全文 | 211篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 3篇 |
综合类 | 2篇 |
化学工业 | 21篇 |
金属工艺 | 5篇 |
机械仪表 | 4篇 |
建筑科学 | 9篇 |
能源动力 | 7篇 |
轻工业 | 11篇 |
水利工程 | 3篇 |
石油天然气 | 1篇 |
无线电 | 73篇 |
一般工业技术 | 22篇 |
冶金工业 | 37篇 |
自动化技术 | 22篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 5篇 |
2013年 | 11篇 |
2012年 | 8篇 |
2011年 | 6篇 |
2010年 | 6篇 |
2009年 | 10篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 9篇 |
2005年 | 7篇 |
2004年 | 11篇 |
2003年 | 10篇 |
2002年 | 11篇 |
2001年 | 1篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 19篇 |
1997年 | 10篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1965年 | 1篇 |
1943年 | 1篇 |
排序方式: 共有220条查询结果,搜索用时 15 毫秒
71.
Pinto P.C. Giorgetti A. Win M.Z. Chiani M. 《Selected Areas in Communications, IEEE Journal on》2009,27(7):1268-1282
With the increasing proliferation of different communication devices sharing the same spectrum, it is critical to understand the impact of interference in heterogeneous wireless networks. In this paper, we put forth a mathematical model for coexistence in networks composed of both narrowband (NB) and ultrawideband (UWB) wireless nodes, based on fundamental tools from stochastic geometry. Our model considers that the interferers are spatially scattered according to a Poisson field, and are operating asynchronously in a wireless environment. We first determine the statistical distribution of the aggregate interference for both cases of NB and UWB emitters. We then provide error probability expressions for two dual configurations: 1) a NB victim link subject to the aggregate UWB interference, and 2) a UWB victim link subject to the aggregate NB interference. The results show that while the impact of a single interferer on a link is often negligible due to restrictions on the transmitted power, the aggregate effect of multiple interferers may cause significant degradation. Therefore, aggregate interference must be considered to ensure coexistence in heterogeneous networks. The proposed analytical framework shows good agreement with physical-level simulations of the system. 相似文献
72.
MIMO systems with antenna selection 总被引:3,自引:0,他引:3
Multiple-input-multiple-output (MIMO) wireless systems are those that have multiple antenna elements at both the transmitter and receiver. They were first investigated by computer simulations in the 1980s. Since that time, interest in MIMO systems has exploded. They are now being used for third-generation cellular systems (W-CDMA) and are discussed for future high-performance modes of the highly successful IEEE 802.11 standard for wireless local area networks. MIMO-related topics also occupy a considerable part of today's academic communications research. The multiple antennas in MIMO systems can be exploited in two different ways. One is the creation of a highly effective antenna diversity system; the other is the use of the multiple antennas for the transmission of several parallel data streams to increase the capacity of the system. This article presented an overview of MIMO systems with antenna selection. The transmitter, the receiver, or both use only the signals from a subset of the available antennas. This allows considerable reductions in the hardware expense. 相似文献
73.
Honglei Zhang Dennis L. Goeckel Shuangqing Wei Moe Z. Win 《The Journal of VLSI Signal Processing》2006,43(1):7-23
Impulsive ultra-wideband (UWB) radio provides many promising features for wireless communications in a dense multipath environment.
However, these features are largely the result of the enormous effective processing gain, which can make acquisition difficult
at the receiver. In this paper, a recently developed theory of minimum complexity sequential detection is applied to the hybrid
acquisition problem. As in previous hybrid schemes, a number of potential timing phases are checked as a group; however, a
phase is disregarded as soon as it appears unlikely rather than waiting for a “winner” to be chosen from the group. Another
phase then replaces the disregarded one. Analysis and simulation results indicate that the proposed scheme can improve average
acquisition times for highly spread systems operating over either additive white Gaussian noise (AWGN) or multipath fading
channels.
This paper is based in part upon work supported by the Army Research Office under Contract DAAD10-01-1-0477 and employed equipment
obtained under National Science Foundation Grant EIA-0080119. 相似文献
74.
Bit-error probability for optimum combining of binary signals in the presence of interference and noise 总被引:1,自引:0,他引:1
Mallik R.K. Win M.Z. Chiani M. Zanella A. 《Wireless Communications, IEEE Transactions on》2004,3(2):395-407
We derive an exact bit-error probability (BEP) expression for coherent detection of binary signals with optimum combining in wireless systems in the presence of multiple cochannel interferers and thermal noise. A flat Rayleigh fading environment with space diversity, uncorrelated equal-power interferers, and additive white Gaussian noise is considered. The approach is to use the chain rule of conditional expectation together with the joint probability density function (pdf) of the eigenvalues of the interference correlation matrix. This joint pdf is related to the Vandermonde determinant. Let N/sub A/ denote the number of antennas and N/sub I/ the number of interferers. We consider both the cases of an overloaded system, in which N/sub I//spl ges/N/sub A/, and an underloaded system, in which N/sub I/相似文献
75.
Channel capacity of adaptive transmission with maximal ratio combining in correlated Rayleigh fading
Mallik R.K. Win M.Z. Shao J.W. Alouini M.-S. Goldsmith A.J. 《Wireless Communications, IEEE Transactions on》2004,3(4):1124-1133
We derive closed-form expressions for the single-user capacity of maximal ratio combining diversity systems taking into account the effect of correlation between the different branches. We consider a Rayleigh fading channel with two kinds of correlation: 1) equal branch signal-to-noise ratios (SNRs) and the same correlation between any pair of branches and 2) unequal branch SNRs and arbitrary correlation between branches such that the eigenvalues of the branch covariance matrix are all distinct. Three adaptive transmission schemes are analyzed: 1) optimal simultaneous power and rate adaptation; 2) optimal rate adaptation with constant transmit power; and 3) channel inversion with fixed rate. 相似文献
76.
We analyze the performance for the noncoherent reception of M-ary orthogonal frequency shift keying with postdetection equal gain combining over a correlated fading channel. Two kinds of correlated fading statistics are considered: (1) Nakagami fading in which the diversity branches can have unequal signal-to-noise ratios (SNRs) as well as different m-parameters and (2) Rician fading in which the diversity branches can have unequal SNRs. Using the characteristic function of the combiner output SNR, closed-form expressions for the symbol error probability are obtained 相似文献
77.
Khor HL Ng KW Htay AS Schantz JT Teoh SH Hutmacher DW 《Journal of materials science. Materials in medicine》2003,14(2):113-120
Solvent-cast sheets of polycaprolactone were biaxially stretched to produce 10–15 m thick films. PCL films were found to have a tensile strength of 55 MPa which is about two and a half times stronger than native skin. One of our previous studies using non-coated PCL membranes showed that only 36% of the membrane surface was covered with keratinocytes after 9 days of culture. The present study examined the effects of coating the surface of PCL membranes with fibrin on the proliferation of keratinocytes. Qualitative analysis revealed that the cells attached and proliferated better on coated PCL films. Keratinocytes exhibited healthy cobblestone morphology and proliferated as continuous monolayers over a period of 16 days. The results indicated that fibrin coated PCL films would support the attachment and proliferation of human keratinocytes and have the potential to be applied as a matrix material for tissue engineering an epidermal equivalent. 相似文献
78.
SA Plotkin TJ Wiktor H Koprowski EI Rosanoff H Tint 《Canadian Metallurgical Quarterly》1976,103(1):75-80
The records of 340 patients treated surgically over the 20 year period 1950 through 1969 at this clinic for primary epidermoid carcinoma of the anterior two-thirds of the tongue were reviewed to evaluate the effectiveness of elective versus therapeutic radical neck dissection in their treatment. There has been a change in the clinical presentation of this disease, with more people presenting at an earlier stage, with a smaller primary lesion and fewer cervical node metastases. The over-all survival rate has shown a marked improvement to 69 per cent at five years. The proportion of women afflicted has increased. The status of the cervical nodes is a major prognostic factor, the determining five year survival rate being reduced from 78 to 26 per cent if the nodes are metastatically involved. It cannot be directly proved that removal of occult metastasis to the neck by elective radical neck dissection before nodes are clinically detectable leads to a better survival rate partly because the two groups being compared are selected and not randomly assigned. However, the marked tendency for carcinoma of the tongue to metastasize regionally at some time in its course, the significant error in clinical evaluation of the neck, the significant conversion of clinically negative nodes to positive in patients not treated with radical neck dissection, the poor prognosis after treatment of conversion from clinically negative into positive and the fact that more than half of the deaths are due to uncontrolled disease of the neck alone, make us strongly favor the principle of elective radical neck dissection to enhance the survival time in the group of patients without clinical evidence of nodal involvement. With current surgical expertise, the mortality and morbidity rates of simultaneous radical neck dissection are low, and the potential benefit of the procedure outweighs its potential risks. Obviously, elective radical neck dissection, if beneficial, would most likely be so in patients with the highest likelihood of having occult metastasis. 相似文献
79.
We derive analytical expressions for the symbol error probability (SEP) for a hybrid selection/maximal-ratio combining (H-S/MRC) diversity system in multipath-fading wireless environments. With H-S/MRC, L out of N diversity branches are selected and combined using maximal-ratio combining (MRC). We consider coherent detection of M-ary phase-shift keying (MPSK) and quadrature amplitude modulation (MQAM) using H-S/MRC for the case of independent Rayleigh fading with equal signal-to-noise ratio averaged over the fading. The proposed problem is made analytically tractable by transforming the ordered physical diversity branches, which are correlated, into independent and identically distributed (i.i.d.) “virtual branches,” which results in a simple derivation of the SEP for arbitrary L and N. We further obtain a canonical structure for the SEP of H-S/MRC as a weighted sum of the elementary SEPs, which are the SEPs using MRC with i.i.d. diversity branches in Rayleigh fading, or equivalently the SEPs of the nondiversity (single-branch) system in Nakagami fading, whose closed-form expressions are well-known. We present numerical examples illustrating that H-S/MRC, even with L≪N, can achieve a performance close to that of N-branch MRC 相似文献
80.