全文获取类型
收费全文 | 615篇 |
免费 | 103篇 |
国内免费 | 82篇 |
专业分类
化学 | 232篇 |
晶体学 | 4篇 |
力学 | 9篇 |
综合类 | 10篇 |
数学 | 70篇 |
物理学 | 162篇 |
无线电 | 313篇 |
出版年
2023年 | 8篇 |
2022年 | 32篇 |
2021年 | 20篇 |
2020年 | 12篇 |
2019年 | 28篇 |
2018年 | 27篇 |
2017年 | 14篇 |
2016年 | 12篇 |
2015年 | 11篇 |
2014年 | 26篇 |
2013年 | 62篇 |
2012年 | 51篇 |
2011年 | 76篇 |
2010年 | 31篇 |
2009年 | 38篇 |
2008年 | 50篇 |
2007年 | 62篇 |
2006年 | 75篇 |
2005年 | 34篇 |
2004年 | 26篇 |
2003年 | 20篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 8篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有800条查询结果,搜索用时 687 毫秒
81.
采用确定性分析方法,研究TDLTE与TD-SCDMA及GSM系统之间干扰共存问题,通过分析计算出各种干扰情况下系统之间需要的隔离损耗,并就工程实施中经常使用的几种解决干扰问题的方法进行分析。 相似文献
82.
83.
84.
在进行TD-SCDMA网络建设时,利用现网资源和用户资源,实现网络以及用户体验的平滑过渡。2G/3G互操作主要解决混合组网过程中碰到的网络驻留、小区选择、小区重选、切换以及用户接入控制和转网策略等问题。 相似文献
85.
移动WiMAX已成为3G标准之一,研究和吸收移动WiMAX的先进技术,促进现有3G技术的发展具有十分重要的意义。在深入分析移动WiMAX的基本概念和物理层参数的基础上,详细计算出其在不同调制方式和编码速率下的理论数据传输速率和频带利用率,并和WCDMA HSDPA进行了对比分析。 相似文献
86.
Shi Mingtao 《信息通信技术》2009,(4):29-33
The UMTS auction in 2000 brought approximately 100 billion DM (Deutsche Mark) for the German National Treasury. T-Mobile (D1-Netz), Vodafone (D2-Netz), E-Plus (E1-Netz) and 02 (E2-Netz) have gradually evolved from GSM to full-fledged UMTS operators over the past years. The conglomerate of China Telecom was split twice. China acceded to WTO and promulgated the FITE Provisions. MIIT (Ministry of Industry and Information Technology) became the regulator and China Netcom was incorporated into China Unicorn in 2008. Most recently the layout of 3G future has been reconfirmed by MIIT. Voice service has remained the main source of income in both countries and operators have continued to focus on voice quality and network availability in their respective 2G networks. Because value-added and higher-speed data applications have been gaining market attention, 2.5G and 3G infrastructure has increasingly become the focal network strategy for the operators since the beginning of the new century. Germany has rolled out WCDMA/UMTS services on a large scale in the consumer market, while China has adopted all three 3G standards (TD-SCDMA, WCDMA/UMTS, CDMA2000), which shall gradually capture a wider 3G subscriber base. The summary shows that the development of the cellular technology and market in Germany and China can be discussed in three distinct historical periods. The conclusion suggests that the case of the cellular technology appears to be consistent with and applicable to a number of arguments widely disputed in economics and management related to technology and innovation, such as dominant design, technology waves/ S-Curve, disruptive technologies, Technology Adoption Life Cycle. 相似文献
87.
Abstract Measurements of electron paramagnetic resonance, infrared and electrical properties were carried out for the K2SO4—Na2SO4 mixed system before and after γ-irradiation. EPR measurements revealed the presence of a quartet of lines characterized by an isotropic g-value of 2.0034. These lines are mainly attributed to the formation of a SO? 3 center which results from the interaction of γ-rays with the sulfate ion. A decrease in the absorption intensity of the Infrared radiation was observed after γ-irradiation due to radiation damage in the sulfate group. The electrical conductivity, σ, was measured for the K2SO4—Na2SO4 system before and after γ-irradiation in the temperature range from 30 up to 430°C. A considerable decrease in the conductivity value accompanied by an increase in the activation energy was observed after γ-irradiation. The energy of formation of Frenkel defects was estimated to be 2.94eV. The current-voltage characteristics were measured at different temperatures in order to estimate the type of conduction in the samples. Isothermal annealing kinetics was investigated at different temperatures before and after γ-irradiation. The electrical conductivity decreases with increasing time of annealing and the annealing process is dominated by a unique rate process. 相似文献
88.
Péter Simon 《Applicable analysis》2013,92(3-4):383-395
An analogue of the so—called Sunouchi operator with respect to the Walsh—Kaczmarz system will be investigated. We show the boundedness of this operator if we take it as a map from the dyadic Hardy space H p to L p for all 0<p≤1.. For the proof we consider a multiplier operator and prove its (H p H p)—boundedness for 0<p≤1. Since the multiplier is obviously bounded from L 2 to L 2, a theorem on interpolation of operators can be applied to show that our multiplier is of weak type (1,1) and of type (q q) for all 1<q<∞. The same statements follow also for the Sunouchi operator. 相似文献
89.
Radford M. Neal 《Journal of computational and graphical statistics》2013,22(2):249-265
Abstract This article reviews Markov chain methods for sampling from the posterior distribution of a Dirichlet process mixture model and presents two new classes of methods. One new approach is to make Metropolis—Hastings updates of the indicators specifying which mixture component is associated with each observation, perhaps supplemented with a partial form of Gibbs sampling. The other new approach extends Gibbs sampling for these indicators by using a set of auxiliary parameters. These methods are simple to implement and are more efficient than previous ways of handling general Dirichlet process mixture models with non-conjugate priors. 相似文献
90.