全文获取类型
收费全文 | 21175篇 |
免费 | 3576篇 |
国内免费 | 1630篇 |
专业分类
化学 | 2791篇 |
晶体学 | 50篇 |
力学 | 372篇 |
综合类 | 174篇 |
数学 | 2578篇 |
物理学 | 5656篇 |
无线电 | 14760篇 |
出版年
2024年 | 73篇 |
2023年 | 258篇 |
2022年 | 385篇 |
2021年 | 605篇 |
2020年 | 647篇 |
2019年 | 517篇 |
2018年 | 498篇 |
2017年 | 771篇 |
2016年 | 924篇 |
2015年 | 942篇 |
2014年 | 1592篇 |
2013年 | 1906篇 |
2012年 | 1707篇 |
2011年 | 1867篇 |
2010年 | 1378篇 |
2009年 | 1327篇 |
2008年 | 1441篇 |
2007年 | 1530篇 |
2006年 | 1338篇 |
2005年 | 1106篇 |
2004年 | 943篇 |
2003年 | 836篇 |
2002年 | 632篇 |
2001年 | 536篇 |
2000年 | 500篇 |
1999年 | 376篇 |
1998年 | 275篇 |
1997年 | 286篇 |
1996年 | 235篇 |
1995年 | 177篇 |
1994年 | 132篇 |
1993年 | 125篇 |
1992年 | 122篇 |
1991年 | 76篇 |
1990年 | 65篇 |
1989年 | 48篇 |
1988年 | 57篇 |
1987年 | 22篇 |
1986年 | 15篇 |
1985年 | 25篇 |
1984年 | 11篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
数字调幅制式是当前国际上较先进的调制技术,DX系列全固态数字调幅中波发射机的电声指标和工业效率都是很先进的,过去的DX大功率机采用风冷方式,本文介绍了最新水冷DX-600发射机的设备情况和技术特点。 相似文献
83.
Hans C. Fogedby 《Journal of statistical physics》1992,69(1-2):411-425
We elaborate in some detail on a new phase space approach to complexity, due to Y.-C. Zhang. We show in particular that the connection between maximal complexity and power law noise or correlations can be derived from a simple variational principle. For a 1D signal we find 1/f noise, in accordance with Zhang. 相似文献
84.
描述了一种延长EPR波谱仪中速调管使用寿命的方法.根据这种方法,只要正确地调谐微波桥的工作状态和适当地调整功率电平器的功率校正电平.即使对于已经严重老化的速调管仍然可以继续使用一段时间,维持仪器的正常运行. 相似文献
85.
王福臣 《固体电子学研究与进展》1992,(4)
对WC76型S频段大功率振荡用砷化镓场效应晶体管的微波性能作了介绍。文中给出了测试振荡器的设计。测试结果表明,WC76型振荡管在s频段的微波性能良好,振荡频率在3GHz左右时,输出功率可达3.5w,直流—射频转换效率可达44%,而且在2~4GHz的整个S频段均能满意地工作。 相似文献
86.
87.
Marcus T. Schmitz Bashir M. Al-Hashimi Petru Eles 《Design Automation for Embedded Systems》2002,6(4):401-424
In this paper, we introduce the LOPOCOS (Low Power Co-synthesis) system, a prototype CAD tool for system level co-design. LOPOCOS targets the design of energy-efficient embedded systems implemented as heterogeneous distributed architectures. In particular, it is designed to solve the specific problems involved in architectures that include dynamic voltage scalable (DVS) processors. The aim of this paper is to demonstrate how LOPOCOS can support the system designer in identifying energy-efficient hardware/software implementations for the desired embedded systems. Hence, highlighting the necessary optimization steps during design space exploration for DVS enable architectures. The optimization steps carried out in LOPOCOS involve component allocation and task/communication mapping as well as scheduling and dynamic voltage scaling. LOPOCOS has the following key features, which contribute to this energy efficiency. During the voltage scaling valuable power profile information of task execution is taken into account, hence, the accuracy of the energy estimation is improved. A combined optimization for scheduling and communication mapping based on genetic algorithm, optimizes simultaneously execution order and communication mapping towards the utilization of the DVS processors and timing behaviour. Furthermore, a separation of task and communication mapping allows a more effective implementation of both task and communication mapping optimizationsteps. Extensive experiments are conducted to demonstrate the efficiency of LOPOCOS. We report up to 38% higher energy reductions compared to previous co-synthesis techniques for DVS systems. The investigations include a real-life example of an optical flow detection algorithm. 相似文献
88.
Two types of optical current transducers (OCTs) have a bulk Faraday sensor inserted into the gap of an iron core and a porcelain
insulator with optical fiber. The sensor consists of Bi12SiO20 (BSO) single crystal, a polarizer, and an analyzer. The OCTs satisfied the target performance requirement for fault location
and metering and demonstrated maintained performance at some power utilities in Japan and the US. We have developed a fault
location system that immediately detects the fault current with the OCTs, there by locating the fault section. The OCT can
easily replace the existing support insulators for the disconnecting switch without any modifications to structure height
or bus-bar. For metering requiring 0.3% class accuracy, use of a BSO with right optical rotatory power combined with BSO with
left optical rotatory power results in a Faraday sensor with improved temperature characteristics. The OCT demonstrated 0.3%
class accuracy for metering described in the current transformer Specifications of IEEE C57–13, 1993. 相似文献
89.
This paper proposes a floating-point genetic algorithm (FPGA) to solve the unit commitment problem (UCP). Based on the characteristics of typical load demand, a floating-point chromosome representation and an encoding–decoding scheme are designed to reduce the complexities in handling the minimum up/down time limits. Strategic parameters of the FPGA are characterized in detail, i.e., the evaluation function and its constraints, population size, operation styles of selection, crossover operation and probability, mutation operation and probability. A dynamic combination scheme of genetic operators is formulated to explore and exploit the FPGA in the non-convex solution space and multimodal objective function. Experiment results show that the FPGA is a more effective technique among the various styles of genetic algorithms, which can be applied to the practical scheduling tasks in utility power systems. 相似文献
90.
首先对OFDM的发展以及应用做了简要的介绍,然后讨论了当前OFDM研究过程中的两个关键技术问题,最后展望了OFDM的未来发展。 相似文献