全文获取类型
收费全文 | 110710篇 |
免费 | 10111篇 |
国内免费 | 8225篇 |
专业分类
化学 | 32635篇 |
晶体学 | 342篇 |
力学 | 7183篇 |
综合类 | 1560篇 |
数学 | 30122篇 |
物理学 | 26552篇 |
无线电 | 30652篇 |
出版年
2024年 | 200篇 |
2023年 | 1089篇 |
2022年 | 1857篇 |
2021年 | 2342篇 |
2020年 | 2525篇 |
2019年 | 2445篇 |
2018年 | 2172篇 |
2017年 | 2868篇 |
2016年 | 3369篇 |
2015年 | 3465篇 |
2014年 | 5310篇 |
2013年 | 6994篇 |
2012年 | 5817篇 |
2011年 | 6110篇 |
2010年 | 5118篇 |
2009年 | 6318篇 |
2008年 | 6822篇 |
2007年 | 7195篇 |
2006年 | 6575篇 |
2005年 | 5639篇 |
2004年 | 5061篇 |
2003年 | 4925篇 |
2002年 | 4216篇 |
2001年 | 3520篇 |
2000年 | 3342篇 |
1999年 | 2913篇 |
1998年 | 2636篇 |
1997年 | 2205篇 |
1996年 | 2039篇 |
1995年 | 1805篇 |
1994年 | 1575篇 |
1993年 | 1371篇 |
1992年 | 1316篇 |
1991年 | 1026篇 |
1990年 | 857篇 |
1989年 | 726篇 |
1988年 | 642篇 |
1987年 | 493篇 |
1986年 | 402篇 |
1985年 | 494篇 |
1984年 | 473篇 |
1983年 | 242篇 |
1982年 | 395篇 |
1981年 | 426篇 |
1980年 | 320篇 |
1979年 | 326篇 |
1978年 | 237篇 |
1977年 | 218篇 |
1976年 | 166篇 |
1974年 | 120篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
121.
This paper presents a low‐cost RF parameter estimation technique using a new RF built‐in self‐test (BIST) circuit and efficient DC measurement for 4.5 to 5.5 GHz low noise amplifiers (LNAs). The BIST circuit measures gain, noise figure, input impedance, and input return loss for an LNA. The BIST circuit is designed using 0.18 μm SiGe technology. The test technique utilizes input impedance matching and output DC voltage measurements. The technique is simple and inexpensive. 相似文献
122.
123.
SHI Yan-rui CAO Pei-xia Shijiazhuang Post Telecommunication Technical College Shijiazhuang P.R. China. 《中国邮电高校学报(英文版)》2004,11(Z1)
1 Introduction ExpressMailService (EMS )wasopenedupbyChinaPostintheearly 80stomeettheneedsofeco nomicdevelopment.It sthemostcompetitiveoneofthepostservices.There recivilaviation ,Chinarail wayandotherprivateexpressdeliverycompaniesdomesticallyandUPS ,TNT ,DHLandTEDEXcompetingwithEMSintheinternationalmarket.OneofthemostpowerfulcompeteweaponofthesecompaniesisthelowerpricethanEMS[1 ] .BecauseofthefiercecompetitionEMSdeclinedfromthemo nopolistindomesticandinternationalmarketoftheear… 相似文献
124.
Recent years have witnessed a rapid growth of interest in the study of the dynamic behavior of replenishment rules of bullwhip effect. We prove that bullwhip effect and butterfly effect share a same the self-oscillation amplifying mechanism that is the ordering decisions the supplier self-oscillation amplify the perturbations brought by the errors in the processing of retailers' demand information. This results as an explicit self-similar structure of the sensitivity of the system to the initial values duty to the nonlinear mechanism. In this paper, the causes process of the bullwhip effect is described as the internal nonlinear mechanism and study on the complexity of bullwhip effect for order-up-to policy under demand signal processing. The methodology is based on fractal and chaotic theory and allows important insights to be gained about the complexity behavior of bullwhip effect. 相似文献
125.
子空间方法盲多用户检测技术分析与探索 总被引:1,自引:0,他引:1
着重分析了基于子空间跟踪的盲线性多用户检测算法 ,并对其内部算法模块进行了仿真比较 ,最后对算法性能改善方法提出了自己的新思路 相似文献
126.
多传感器目标的模糊识别 总被引:5,自引:0,他引:5
根据模糊理论,采用信息融合技术和模糊识别技术,讨论了在多类传感器网内进行多目标模糊识别的一般原理和方法。 相似文献
127.
128.
基于直升机目标旋转部件的调制模型,本文针对防空雷达提出了分析直升机信号特征的一种新方法——WVD法,并对直升机目标旋转部件调制回波信号在不同噪声情况下加以仿真分析,结果表明:用WVD分析雷达回波中直升机信号特征是一种非常有效的方法。 相似文献
129.
As we approach 100 nm technology the interconnect issues are becoming one of the main concerns in the testing of gigahertz system-on-chips. Voltage distortion (noise) and delay violations (skew) contribute to the signal integrity loss and ultimately functional error, performance degradation and reliability problems. In this paper, we first define a model for integrity faults on the high-speed interconnects. Then, we present a BIST-based test methodology that includes two special cells to detect and measure noise and skew occurring on the interconnects of the gigahertz system-on-chips. Using an inexpensive test architecture the integrity information accumulated by these special cells can be scanned out for final test and reliability analysis. 相似文献
130.
In this paper, we study the existence of the uniformly minimum risk equivariant (UMRE) estimators of parameters in a class
of normal linear models, which include the normal variance components model, the growth curve model, the extended growth curve
model, and the seemingly unrelated regression equations model, and so on. The necessary and sufficient conditions are given
for the existence of UMRE estimators of the estimable linear functions of regression coefficients, the covariance matrixV and (trV)α, where α > 0 is known, in the models under an affine group of transformations for quadratic losses and matrix losses, respectively.
Under the (extended) growth curve model and the seemingly unrelated regression equations model, the conclusions given in literature
for estimating regression coefficients can be derived by applying the general results in this paper, and the sufficient conditions
for non-existence of UMRE estimators ofV and tr(V) are expanded to be necessary and sufficient conditions. In addition, the necessary and sufficient conditions that there
exist UMRE estimators of parameters in the variance components model are obtained for the first time. 相似文献