全文获取类型
收费全文 | 788篇 |
免费 | 39篇 |
国内免费 | 34篇 |
专业分类
电工技术 | 9篇 |
综合类 | 28篇 |
化学工业 | 83篇 |
金属工艺 | 16篇 |
机械仪表 | 30篇 |
建筑科学 | 16篇 |
矿业工程 | 3篇 |
能源动力 | 12篇 |
轻工业 | 69篇 |
水利工程 | 5篇 |
石油天然气 | 40篇 |
武器工业 | 3篇 |
无线电 | 96篇 |
一般工业技术 | 148篇 |
冶金工业 | 4篇 |
原子能技术 | 205篇 |
自动化技术 | 94篇 |
出版年
2024年 | 7篇 |
2023年 | 4篇 |
2022年 | 15篇 |
2021年 | 20篇 |
2020年 | 25篇 |
2019年 | 13篇 |
2018年 | 20篇 |
2017年 | 31篇 |
2016年 | 35篇 |
2015年 | 20篇 |
2014年 | 35篇 |
2013年 | 74篇 |
2012年 | 47篇 |
2011年 | 85篇 |
2010年 | 40篇 |
2009年 | 35篇 |
2008年 | 42篇 |
2007年 | 47篇 |
2006年 | 26篇 |
2005年 | 35篇 |
2004年 | 20篇 |
2003年 | 19篇 |
2002年 | 12篇 |
2001年 | 18篇 |
2000年 | 11篇 |
1999年 | 17篇 |
1998年 | 11篇 |
1997年 | 15篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 9篇 |
1991年 | 1篇 |
1990年 | 10篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有861条查询结果,搜索用时 15 毫秒
81.
Zhengqiang Pan Narayanaswamy Balakrishnan 《Reliability Engineering & System Safety》2011,96(8):949-957
Many highly reliable products usually have complex structure, with their reliability being evaluated by two or more performance characteristics. In certain physical situations, the degradation of these performance characteristics would be always positive and strictly increasing. In such a case, the gamma process is usually considered as a degradation process due to its independent and non-negative increments properties. In this paper, we suppose that a product has two dependent performance characteristics and that their degradation can be modeled by gamma processes. For such a bivariate degradation involving two performance characteristics, we propose to use a bivariate Birnbaum-Saunders distribution and its marginal distributions to approximate the reliability function. Inferential method for the corresponding model parameters is then developed. Finally, for an illustration of the proposed model and method, a numerical example about fatigue cracks is discussed and some computational results are presented. 相似文献
82.
Hossein Samimi 《International Journal of Communication Systems》2011,24(1):14-26
A new composite channel model is proposed for the performance analysis of shadowed fading channels. This model is represented as a mixture of generalized Gamma (GG) multipath fading and lognormal shadowing. GG distribution includes the Rayleigh, Nakagami, and Weibull as special cases; hence the presented model, which is referred to as GG‐L, is a generic model that covers many well‐known composite fading models, including the Rayleigh–lognormal (R‐L), Nakagami–lognormal (N‐L), and Weibull–lognormal (W‐L). The main drawback of the lognormal‐based composite models is that the composite probability density function (PDF) is not in closed form, thereby making the performance evaluation of communication links in these channels cumbersome. To bypass this problem, an approximation method is developed which makes it possible to derive a closed‐form, analytical expression for GG‐L composite distribution. The proposed method only needs the mean and the variance of the underlying lognormal distribution, and hence, bypasses the required complicated integration needed to calculate the PDF of the received signal envelope in GG‐L channel. Based on this method, the most statistical characteristics, such as cumulative density function (CDF) and moments of the GG‐L composite distribution, are derived and used for the performance analysis of a single receiver operating over GG‐L fading channel. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
83.
84.
The computation of outage probability in cellular radio system has been extensively studied. The Signal-to-Interference-plus-Noise
Ratio (SINR) distribution involves the sum of lognormal distributions due to dominant effect of shadowing in both the signal
and interference components. Since no closed-form expression can be found for the sum of lognormal distributions, many approximation
methods and bounds were proposed in the past. In this paper, Log Shifted Gamma (LSG) approximation is proposed to calculate
the sum of correlated lognormal random variables (RVs), hence the outage probability, accurately with a wide range of dB spreads,
number of interferers M, correlation coefficients r among interference components, and noise power N. Overall, LSG approximation
shows consistent accuracy due to its flexibility over the classical lognormal approximation, especially with small correlation
coefficients r and/or large dB spreads. 相似文献
85.
一种评价能谱测井质量的直观比值法 总被引:1,自引:1,他引:0
李桂荣 《勘探地球物理进展》2004,27(4):266-268
能谱测井反映地层沉积岩的自然放射性,通过对自然伽马能谱测井资料的地质分析,提取自然放射性铀相对比值和钍/铀比值,用于快速直观地对自然伽马能谱测井资料进行质量监控。目前这种方法在塔河油田奥陶系碳酸岩盐地层的能谱测井资料质量评价中取得了明显的效果。 相似文献
86.
Summary This paper is concerned with business mortality analysis in a Bayesian setting. We assume that a businessman startsN businesses at different points of time and at a certain epoch referred to as the ‘present’, the failure times of the failed
businesses and the survival times of the still surviving businesses are recorded. Bayesian prediction for business mortality
or survival up to a future time pointt
0 is made under the assumptions of a Weibull business survival distribution (WBSD) and the squared error loss function (SELF).
The results are extended to the situation where one of the observed times of business failure may possibly be an outlier. 相似文献
87.
G. A. Bohoris 《Quality and Reliability Engineering International》1994,10(2):105-115
This paper provides tabulated numerical values for the gamma function necessary for the analytical estimation of the mean and standard deviation of the Weibull distribution. The tables produced also include estimates of the Weibull coefficient of variation, a quantity very important for maintenance optimization calculations when Glasser's charts are employed. 相似文献
88.
γ能谱稳谱获取的研究 总被引:3,自引:0,他引:3
利用γ能谱光电峰的能量恒定和峰形不变的物理特性,提出一种以光电峰为基准的主动寻峰稳谱方法,以甄别阈为调整对象,直接作用于测量能窗的能量定位,保证能窗相对能量的稳定。 相似文献
89.
Summary De Finetti type theorems characterize models in terms of invariance. The idea is to take observables, postulate symmetry and
then represent the model as a mixture of standard parametric models. If additional conditions are specified, then the mixing
measure can be determined. Invariance under the action of special groups of orthogonal transformations may give results on
mixtures of parametric normal distributions (Diaconis, Eaton and Lauritzen, 1992). The additional conditions required to determine
the mixing measure in this case can be obtained using results in Diaconis and Ylvisaker (1979, 1985). From these results,
we obtain a predictivistic characterization of the multivariatet distribution. Furthermore, we state conditions under which then-dimensional law of sequences of random variables is a location mixture of multivariatet distributions. The results are extended to the case of sequences of orthogonally invariant random vectors. 相似文献
90.
Theodoros A. Tsiftsis 《International Journal of Communication Systems》2008,21(5):559-565
We present closed‐form bounds for the performance of wireless multihop communications systems with cooperative diversity over Nakagami‐m fading channels. The end‐to‐end signal‐to‐noise ratio is formulated and upper bounded by using the inequality between harmonic and geometric means of positive random variables. Closed‐form expression is derived for the moment‐generating function and is used to obtain lower bounds for the average error probability. Numerical results are compared with computer simulations showing the tightness of the proposed bounds. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献