全文获取类型
收费全文 | 80325篇 |
免费 | 17826篇 |
国内免费 | 6900篇 |
专业分类
化学 | 60107篇 |
晶体学 | 740篇 |
力学 | 2396篇 |
综合类 | 406篇 |
数学 | 5821篇 |
物理学 | 13724篇 |
无线电 | 21857篇 |
出版年
2024年 | 98篇 |
2023年 | 820篇 |
2022年 | 1006篇 |
2021年 | 1630篇 |
2020年 | 3078篇 |
2019年 | 4355篇 |
2018年 | 2609篇 |
2017年 | 2272篇 |
2016年 | 5441篇 |
2015年 | 5872篇 |
2014年 | 6283篇 |
2013年 | 7427篇 |
2012年 | 6605篇 |
2011年 | 5911篇 |
2010年 | 5841篇 |
2009年 | 5919篇 |
2008年 | 5590篇 |
2007年 | 4831篇 |
2006年 | 4307篇 |
2005年 | 4047篇 |
2004年 | 3268篇 |
2003年 | 2867篇 |
2002年 | 3611篇 |
2001年 | 2718篇 |
2000年 | 2405篇 |
1999年 | 1363篇 |
1998年 | 746篇 |
1997年 | 608篇 |
1996年 | 599篇 |
1995年 | 484篇 |
1994年 | 424篇 |
1993年 | 323篇 |
1992年 | 284篇 |
1991年 | 256篇 |
1990年 | 221篇 |
1989年 | 175篇 |
1988年 | 154篇 |
1987年 | 113篇 |
1986年 | 85篇 |
1985年 | 82篇 |
1984年 | 46篇 |
1983年 | 49篇 |
1982年 | 40篇 |
1981年 | 29篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1978年 | 23篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Hyun‐Cheol Kim Charalampos Z. Patrikakis Nikos Minogiannis Pantelis N. Karamolegkos Alex Lambiris Kyuheon Kim 《ETRI Journal》2006,28(4):411-424
This paper presents a multimedia streaming platform for efficiently transmitting MPEG‐4 content over IP networks. The platform includes an MPEG‐4 compliant streaming server and client, supporting object‐based representation of multimedia scenes, interactivity, and advanced encoding profiles defined by the ISO standard. For scalability purposes, we employ an application‐layer multicast scheme for media transmission using overlay networks. The overlay network, governed by the central entity of the network distribution manager, is dynamically deployed according to a set of pre‐defined criteria. The overlay network supports both broadcast delivery and video‐on‐demand content. The multimedia streaming platform is standards‐compliant and utilizes widespread multimedia protocols such as MPEG‐4, real‐time transport protocol, real‐time transport control protocol, and real‐time streaming protocol. The design of the overlay network was architected with the goal of transparency to both the streaming server and the client. As a result, many commercial implementations that use industry‐standard protocols can be plugged into the architecture relatively painlessly and can enjoy the benefits of the platform. 相似文献
92.
93.
贴片机脱机编程的快捷方法 总被引:7,自引:4,他引:3
SMT生产线中的大多数加工设备均为数控设备。它们编程所需要的大多数特征数据均可从CAD设计系统中得到。文章介绍了如何从CAD设计系统中导出X、Y坐标数据,并转换成贴片数据的方法和思路,以期引起更多的同行加入到这方面的研究中。 相似文献
94.
工作流技术及其应用研究 总被引:6,自引:0,他引:6
文章介绍了工作流技术及其发展历史,对工作流的系统模型进行了详细分析,探讨了工作流技术在企业管理信息系统中的实际应用。 相似文献
95.
论文提出利用用户提供的个性化信息来随机产生关联大素数,保证了素数选取的随机化、个性化,提高了RSA算法的安全性。 相似文献
96.
容错技术广泛应用于各个行业来保证系统的冗余和可靠性。文章在分析比较当前的双机容错系统的性能优缺点后,提出了一种全新的基于“层”模式的双机容错系统解决方案。按照这种模式,可以从链路层到应用层构建一个通用的系统级的双机容错系统。文章对其实现的关键技术进行了阐述。 相似文献
97.
B.‐J. Fang Y.‐J. Shan H.‐Q. Xu H.‐S. Luo Z.‐W. Yin 《Advanced functional materials》2004,14(2):169-173
Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZNT91/9) single crystals were grown by two methods: from solution using PbO as a self‐fluxing agent (SC method) and directly from the melt without fluxing (MC method). In both growth methods, an allomeric Pb[(Mg1/3‐Nb2/3)0.69Ti0.31]O3 (PMNT69/31) single crystal was used as a seed. X‐ray diffraction patterns of ground crystals showed that phase‐pure perovskite PZNT91/9 single crystals were successfully fabricated by the above two methods. The composition of the crystals obtained by both the SC and MC methods was analyzed using X‐ray fluorescence, which confirmed that the crystal composition is close to the nominal value, although volatilization of PbO and segregation during crystal growth are inevitable. The MC PZNT91/9 crystals exhibit excellent piezoelectric properties, with the piezoelectric constant, d33, in the range of 1800–2200 pC N–1. This value is comparable to that of the SC crystals. However, the MC crystals show an abnormal dielectric behavior. In contrast with the SC crystals, in the MC crystals a much broader dielectric peak appears in the dielectric response curves, accompanied by a much lower peak temperature of around 105 °C. Furthermore, frequency dispersion is apparent over a much wider temperature range (even more apparent than in pure relaxors), where a large, i.e., about 70 °C, full width at half maximum (FWHM) for the dielectric peaks is observed in the dielectric response. It is speculated that such an unusual phenomenon correlates with defects, microinhomogeneities, and polar regions in the as‐grown MC crystals. The origins of this abnormality have not been interpreted in detail until now. However, optical observation of the domain structure confirms that both the SC and MC crystals possess complex structural states. 相似文献
98.
Yong Zhang Yuanlong Mo Xiaolan Zhou Jianqing Li 《Journal of Infrared, Millimeter and Terahertz Waves》2003,24(12):2085-2094
Recently disk-loaded waveguide has been widely used in high-power traveling wave tubes (HPTWT). It has been shown in many experiments that the interaction efficiency and output power can be increased greatly by injecting plasma into the vacuum microwave device. Using field analysis, the dispersion characteristics and the interaction impedance of the disk-loaded waveguide filled with plasma are analyzed in a strong longitudinal magnetic field. In conclusion, the frequency of the TM01 mode increases as the density of the plasma increases. It also can be found when the plasma density increases to a large scale, the TM01 mode of the disk-loaded waveguide overlaps the TG mode, these two modes couple each other and form the new hybrid modes. 相似文献
99.
100.
MANET(Mobile Ad hoc Network)中没有一个永久的中心机构,其网络拓扑结构不断变化,所以必须有一种能够对网络主机地址动态自配置和管理的协议。给出了在MANET中动态地址自配置与管理的方法,不同方案的特点及适应情况,最后对目前Ad hoc网络地址配置研究进行总结和展望。 相似文献