全文获取类型
收费全文 | 65996篇 |
免费 | 9694篇 |
国内免费 | 7395篇 |
专业分类
化学 | 34650篇 |
晶体学 | 594篇 |
力学 | 2868篇 |
综合类 | 440篇 |
数学 | 5505篇 |
物理学 | 18109篇 |
无线电 | 20919篇 |
出版年
2024年 | 251篇 |
2023年 | 1545篇 |
2022年 | 1986篇 |
2021年 | 2548篇 |
2020年 | 2516篇 |
2019年 | 2264篇 |
2018年 | 1966篇 |
2017年 | 2046篇 |
2016年 | 2663篇 |
2015年 | 2981篇 |
2014年 | 3627篇 |
2013年 | 4581篇 |
2012年 | 5482篇 |
2011年 | 5346篇 |
2010年 | 4081篇 |
2009年 | 4036篇 |
2008年 | 4312篇 |
2007年 | 3897篇 |
2006年 | 3661篇 |
2005年 | 3171篇 |
2004年 | 2407篇 |
2003年 | 1919篇 |
2002年 | 1715篇 |
2001年 | 1474篇 |
2000年 | 1381篇 |
1999年 | 1424篇 |
1998年 | 1239篇 |
1997年 | 1085篇 |
1996年 | 1125篇 |
1995年 | 960篇 |
1994年 | 876篇 |
1993年 | 753篇 |
1992年 | 679篇 |
1991年 | 544篇 |
1990年 | 459篇 |
1989年 | 329篇 |
1988年 | 287篇 |
1987年 | 247篇 |
1986年 | 184篇 |
1985年 | 194篇 |
1984年 | 157篇 |
1983年 | 137篇 |
1982年 | 101篇 |
1981年 | 69篇 |
1980年 | 59篇 |
1979年 | 41篇 |
1978年 | 30篇 |
1976年 | 32篇 |
1975年 | 38篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Guangrui Chen Yuxing Yan Dr. Jie Wang Prof. Yong Sik Ok Guiyuan Zhong Prof. Bu Yuan Guan Prof. Yusuke Yamauchi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(44):19831-19836
Mesoporous core–shell nanostructures with controllable ultra-large open channels in their nanoshells are of great interest. However, soft template-directed cooperative assembly to mesoporous nanoshells with highly accessible pores larger than 30 nm, or even above 50 nm into macroporous range, remains a significant challenge. Herein we report a general approach for precisely tailored coating of hierarchically macro-/mesoporous polymer and carbon shells, possessing highly accessible radial channels with extremely wide pore size distribution from ca. 10 nm to ca. 200 nm, on diverse functional materials. This strategy creates opportunities to tailor the interfacial assembly of irregular mesostructured nanounits on core materials and generate various core–shell nanomaterials with controllable pore architectures. The obtained Fe,N-doped macro-/mesoporous carbon nanoshells show enhanced electrochemical performance for the oxygen reduction reaction in alkaline condition. 相似文献
52.
基于CVSD编码的无线语音系统方案的设计 总被引:2,自引:0,他引:2
简要介绍了连续可变斜率增量(CVSD)调制的原理。与目前应用较为广泛的其它语音编码方式相比较,CVSD拥有更优的数字特性。着重介绍了由CML公司研制开发的基于CVSD的语音编码芯片———CMX649的特点及相关的应用方式。CMX649能够成功地应用在广泛的语音编码系统中,尤其适合无线语音系统应用。在此基础上,给出了一种实用性很强的低成本、低功耗无线语音系统的设计与应用方案。该方案可提供清晰可靠的语音传输,可广泛应用于农村地区,具有广阔的市场空间。 相似文献
53.
54.
Djoumessi E.E. Marsan E. Caloz C. Chaker M. Wu K. 《Microwave and Wireless Components Letters, IEEE》2006,16(11):603-605
A tunable dual-band quadrature hybrid coupler for mobile GSM bands (900 and 1800MHz) is proposed and characterized. The structure is composed of four quarter-wavelength sections at a frequency located between the two operating frequencies and two pairs of open-ended stubs. Frequency tuning is achieved by modifying the electrical length of the open-ended stubs with varactor-diode capacitors. A dual-band tunability of 33% and 10% is obtained for the first and the second bands, respectively 相似文献
55.
Yang Aiying Wang Ziyu Zhang Zhaoyi Chen Zhangyuan Wu Deming 《电子科学学刊(英文版)》2003,20(6):461-466
A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG. 相似文献
56.
57.
The sunset diagram of λφ4 theory is evaluated numerically in cutoff scheme and a nonzero finite term(in accordance with dimensional regularization (DR) result) is found in contrast to published calculations. This findingdramatically reduces the critical couplings for symmetry breaking in the two-loop effective potential discussed in ourprevious work. 相似文献
58.
从美国有线电视产业应对竞争的策略和举措获得的启示 总被引:1,自引:0,他引:1
1前言
近年来出现了有关IP电视(网络电视)和移动电视(手机电视)属于电信增值业务,应当由电信企业主办、电信部门主管的大量论调,并已在社会上造成许多误解.由于其论据是外国情况、世界趋势就是这样,而且把这些信息网络传播视听节目的产业运营前景描绘得非常光明,笔者于是认真查考有关的外国情况,写了多篇综述(本刊2005年第2、第3、第5、第6、第8、第9、第14、第16及第22期),其中结合国情的评述,由于国内针对这些新事物的政策法规不明朗,论据尚有欠缺. 相似文献
59.
With the proliferation of mobile computing technologies, location based services have been identified as one of the most promising
target application. We classify mobile information service domains based on feature characteristics of the information sources
and different patterns of mobile information access. By carefully examining the service requirements, we identify the dynamic
data management problem that must be addressed for effective location based services in mobile environments. We then devise
a general architecture and cost model for servicing both location independent and location dependent data. Based on the architecture
and cost model, we propose a set of dynamic data management strategies that employs judicious caching, proactive server pushing
and neighborhood replication to reduce service cost and improve response time under changing user mobility and access patterns.
Detail behavior analysis helps us in precisely capturing when and how to apply these strategies. Simulation results suggest
that different strategies are effective for different types of data in response to different patterns of movement and information
access.
Shiow-yang Wu is an associate professor of the Department of Computer Science and Information Engineering at National Dong Hwa University,
Hualien, Taiwan, R.O.C. He received the BS and MS degrees in computer engineering from National Chiao Tung University, Hsinchu,
Taiwan, ROC, and the PhD degree in computer science from the University of Texas at Austin in 1984, 1986, and 1995, respectively.
His research interests include data/knowledge bases, mobile computing, distributed processing, intelligence information systems,
and electronic commerce.
Kun-Ta Wu was born in Taipei, Taiwan, R.O.C., in 1976. He received the B.S. degree in computer science from Soochow University, Taipei,
Taiwan, R.O.C., in 1999 and the M.S. degree in computer science and information engineering from National Dong Hwa University,
Hualien, Taiwan, R.O.C., in 2001.
Currently, he is an Assistant Researcher in the Domestic Division at Science and Technology Information Center, National Science
Council, R.O.C., as a member of Information Gathering and Analysis Group of National Information and Communication Security
Taskforce. His research interests include mobile computing, wireless network and information security. 相似文献
60.