全文获取类型
收费全文 | 997篇 |
免费 | 51篇 |
国内免费 | 19篇 |
专业分类
化学 | 33篇 |
力学 | 20篇 |
综合类 | 7篇 |
数学 | 313篇 |
物理学 | 234篇 |
无线电 | 460篇 |
出版年
2023年 | 7篇 |
2022年 | 17篇 |
2021年 | 13篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 18篇 |
2017年 | 15篇 |
2016年 | 30篇 |
2015年 | 25篇 |
2014年 | 49篇 |
2013年 | 105篇 |
2012年 | 65篇 |
2011年 | 70篇 |
2010年 | 59篇 |
2009年 | 56篇 |
2008年 | 71篇 |
2007年 | 69篇 |
2006年 | 59篇 |
2005年 | 45篇 |
2004年 | 44篇 |
2003年 | 49篇 |
2002年 | 32篇 |
2001年 | 17篇 |
2000年 | 22篇 |
1999年 | 23篇 |
1998年 | 12篇 |
1997年 | 17篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有1067条查询结果,搜索用时 265 毫秒
1.
2.
3.
The focus of this paper lies in the practical aspects of voice over IP communication. VoIP configurations in the H.323 standard will be presented briefly. Following that, the fundamental protocol procedure of H.323 communication will be briefly explained. A further part of the paper will address the subject QoS (quality of service), and present the common measurement methods used in QoS. Results gained from experiments conducted in a VoIP environment will then follow. The investigations concentrate primarily on the load behavior of voice packets in relation to important parameters of this service. The results obtained are presented and evaluated in diagrams. The paper concludes with a summary. 相似文献
4.
可变抽样区间的非参数控制图 总被引:1,自引:1,他引:0
最近几年一些学者研究了可变抽样区间的质量控制图。Amin等提出了可变抽样区间(VSI)的非参数控制图———符号 (Sign)统计量图〔1〕。本文在此基础上研究位置VSI符号控制图的制定方法 ,并设计离散VSI符号控制图。符号控制图的优点是对非正态总体亦可应用 ,并且不需要过程方差的信息。本文将所设计的VSI符号控制图同固定抽样区间 (FSI)的常规图作比较 ,并举实例说明符号控制图的应用 相似文献
5.
Omer Ozturk Steven N. MacEachern 《Annals of the Institute of Statistical Mathematics》2004,56(4):701-720
We develop a method of randomizing units to treatments that relies on subjective judgement or on possible coarse modeling
to produce restrictions on the randomization. The procedure thus fits within the general framework of ranked set sampling.
However, instead of selecting a single unit from each set for full measurement, all units within a set are used. The units
within a set are assigned to different treatments. Such an assignment translates the positive dependence among units within
a set into a reduction in variation of contrasting features of the treatments.
A test for treatment versus control comparison, with controlled familywise error rate, is developed along with the associated
confidence intervals. The new procedure is shown to be superior to corresponding procedures based on completely randomized
or ranked set sample designs. The superiority appears both in asymptotic relative efficiency and in power for finite sample
sizes. Importantly, this test does not rely on perfect rankings; rather, the information in the data on the quality of rankings
is exploited to maintain the level of the test when rankings are imperfect. The asymptotic relative efficiency of the test
is not affected by estimation of the quality of rankings, and the finite sample performance is only mildly affected. 相似文献
6.
Riikka Susitaival Ilmari Juva Markus Peuhkuri Samuli Aalto 《Telecommunication Systems》2006,33(1-3):67-88
In this paper we analyze measurements gathered from a 2.5~Gbps link in the Finnish university network (Funet) in 2004. The
traffic is broken down into origin-destination (OD) pair components based on source and destination IP address. We study the
traffic characteristics of these components, and identify four typical representative OD pairs. For these pairs we investigate
the validity of a moving IID Gaussian model. We find that the statistical properties of these OD pairs differ significantly
from each other, with only some of them close to Gaussian. The OD pairs are also found to have some cross-correlation between
each other, contradicting an often made assumption about OD pair independence. Furthermore, the existence of a mean-variance
relation between the OD pairs is studied. We find that there is a relation between mean and variance, but for some periods
of time it is rather weak. 相似文献
7.
基于回归方法的移动通信话务量预测 总被引:2,自引:0,他引:2
针对移动通信话务量与市场用户和相应资费政策相关的特点,采用回归预测方法,建立了基于市场用户数及每用户收入的话务量预测模型,并对模型进行了经济学意义上的检验。根据此模型,对话务量进行了初步的预测分析。 相似文献
8.
谱任意的符号模式矩阵 总被引:1,自引:0,他引:1
一个n阶符号模式矩阵A称为是谱任意的,如果对任意的实系数n次首1多项式r(x),在A的定性矩阵类Q(A)中至少存在一个实矩阵B,使得B的特征多项式是r(x),文中证明了当n为奇数时n阶谱任意符号模式矩阵是存在的。 相似文献
9.
Koji Yamada Noboru Miura Chihiro Hamaguchi Norihiko Kamata 《Solid-state electronics》1989,32(12):1113-1117
Hot carrier magnetophonon resonances of n-type Si, short channel InP and p-type InSb were investigated in pulsed high magnetic fields up to 40 T. Using a recently developed high resolution technique in pulsed high fields, many new features of the hot carrier-phonon interactions in high magnetic fields were found. 相似文献
10.
We study the four-directional traffic flow on a two-dimensional lattice. In the case of discrete densities, we assume equal number of vehicles in each lane. Except for the minimum density, the gridlock emerges swiftly. Two kinds of gridlock have been observed. The global gridlock dominates the system when the density is twice the minimum value. At higher densities, the system is pervaded by local gridlocks. We also analyze the time evolution of average speed. In the case of continuous densities, the vehicle numbers vary from lane to lane. The global gridlock is then destroyed by the fluctuations; while the local gridlock can still be observed. 相似文献