全文获取类型
收费全文 | 20452篇 |
免费 | 2340篇 |
国内免费 | 483篇 |
专业分类
化学 | 1383篇 |
晶体学 | 14篇 |
力学 | 486篇 |
综合类 | 268篇 |
数学 | 4525篇 |
物理学 | 2450篇 |
无线电 | 14149篇 |
出版年
2024年 | 55篇 |
2023年 | 213篇 |
2022年 | 431篇 |
2021年 | 663篇 |
2020年 | 603篇 |
2019年 | 468篇 |
2018年 | 456篇 |
2017年 | 755篇 |
2016年 | 870篇 |
2015年 | 902篇 |
2014年 | 1565篇 |
2013年 | 1618篇 |
2012年 | 1436篇 |
2011年 | 1505篇 |
2010年 | 1028篇 |
2009年 | 1065篇 |
2008年 | 1276篇 |
2007年 | 1346篇 |
2006年 | 1076篇 |
2005年 | 993篇 |
2004年 | 844篇 |
2003年 | 696篇 |
2002年 | 526篇 |
2001年 | 470篇 |
2000年 | 375篇 |
1999年 | 308篇 |
1998年 | 274篇 |
1997年 | 204篇 |
1996年 | 205篇 |
1995年 | 192篇 |
1994年 | 129篇 |
1993年 | 117篇 |
1992年 | 95篇 |
1991年 | 69篇 |
1990年 | 61篇 |
1989年 | 39篇 |
1988年 | 34篇 |
1987年 | 41篇 |
1986年 | 27篇 |
1985年 | 54篇 |
1984年 | 39篇 |
1983年 | 22篇 |
1982年 | 27篇 |
1981年 | 25篇 |
1980年 | 17篇 |
1979年 | 22篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
61.
随着图像系统的广泛应用,对图像的稳定要求也越来越高。图像的运动和不稳定是常见的,往往是由于载体的运动引起的,为了达到图像稳定的目的,就需要对其运动进行描述,然后采用相应的算法进行补偿。给出了运动对图像清晰度的影响及像偏移的估算,并对数字电子图像稳定系统进行了简单阐述。 相似文献
62.
63.
An admissible minimax estimator of a bounded scale-parameter in a subclass of the exponential family under scale-invariant squared-error loss 总被引:3,自引:0,他引:3
Mohammad Jafari Jozani Nader Nematollahi Khalil Shafie 《Statistics & probability letters》2002,60(4):437-444
A subclass of the scale-parameter exponential family is considered and for the rth power of the scale parameter, which is lower bounded, an admissible minimax estimator under scale-invariant squared-error loss is presented. Also, an admissible minimax estimator of a lower-bounded parameter in the family of transformed chi-square distributions is given. These estimators are the pointwise limits of a sequence of Bayes estimators. Some examples are given. 相似文献
64.
65.
66.
Statistical Inference with Fractional Brownian Motion 总被引:3,自引:1,他引:2
Kukush Alexander Mishura Yulia Valkeila Esko 《Statistical Inference for Stochastic Processes》2005,8(1):71-93
We give a test between two complex hypothesis; namely we test whether a fractional Brownian motion (fBm) has a linear trend against a certain non-linear trend. We study some related questions, like goodness-of-fit test and volatility estimation in these models. 相似文献
67.
Jeannette H. C. Woerner 《商业与工业应用随机模型》2005,21(1):27-44
In the framework of stochastic volatility models we examine estimators for the integrated volatility based on the pth power variation (i.e. the sum of pth absolute powers of the log‐returns). We derive consistency and distributional results for the estimators given high‐frequency data, especially taking into account what kind of process we may add to our model without affecting the estimate of the integrated volatility. This may on the one hand be interpreted as a possible flexibility in modelling, for example adding jumps or even leaving the framework of semimartingales by adding a fractional Brownian motion, or on the other hand as robustness against model misspecification. We will discuss possible choices of p under different model assumptions and irregularly spaced data. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
68.
The usual tool for modelling bond ratings migration is a discrete, time‐homogeneous Markov chain. Such model assumes that all bonds are homogeneous with respect to their movement behaviour among rating categories and that the movement behaviour does not change over time. However, among recognized sources of heterogeneity in ratings migration is age of a bond (time elapsed since issuance). It has been observed that young bonds have a lower propensity to change ratings, and thus to default, than more seasoned bonds. The aim of this paper is to introduce a continuous, time‐non‐homogeneous model for bond ratings migration, which also incorporates a simple form of population heterogeneity. The specific form of heterogeneity postulated by the proposed model appears to be suitable for modelling the effect of age of a bond on its propensity to change ratings. This model, called a mover–stayer model, is an extension of a Markov chain. This paper derives the maximum likelihood estimators for the parameters of a continuous time mover–stayer model based on a sample of independent continuously monitored histories of the process, and develops the likelihood ratio statistic for discriminating between the Markov chain and the mover–stayer model. The methods are illustrated using a sample of rating histories of young corporate issuers. For these issuers the default probabilities predicted by the Markov chain and mover–stayer models are different. In particular for 1–4 years old bonds the mover–stayer model estimates substantially lower default probabilities from rating C than a Markov chain. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
69.
数据通信网综合网管的设计分析 总被引:3,自引:0,他引:3
结合TMN电信管理网的体系结构.对数据通信网综合网管的结构和功能进行了分析。 相似文献
70.
根据某雷达系统对测量信号的快速传输要求,提出采用滑动帧的处理方法并在FPGA中实现,克服了传统帧处理难以满足快速传输要求的不足。阐述了滑动帧结构的构造思想,详述了滑动帧结构的特点及具体功能模块的实现。根据实际应用需求构造了滑动帧结构处理器,试验和应用结果表明设计可行有效,能充分满足实时数据传输的要求。 相似文献