全文获取类型
收费全文 | 221383篇 |
免费 | 44759篇 |
国内免费 | 36369篇 |
专业分类
化学 | 116950篇 |
晶体学 | 2067篇 |
力学 | 10725篇 |
综合类 | 682篇 |
数学 | 21637篇 |
物理学 | 85605篇 |
无线电 | 64845篇 |
出版年
2024年 | 1213篇 |
2023年 | 4389篇 |
2022年 | 5412篇 |
2021年 | 6344篇 |
2020年 | 6673篇 |
2019年 | 7293篇 |
2018年 | 6901篇 |
2017年 | 7323篇 |
2016年 | 9616篇 |
2015年 | 10578篇 |
2014年 | 11682篇 |
2013年 | 15439篇 |
2012年 | 17175篇 |
2011年 | 18008篇 |
2010年 | 17978篇 |
2009年 | 17685篇 |
2008年 | 12063篇 |
2007年 | 10870篇 |
2006年 | 10301篇 |
2005年 | 9434篇 |
2004年 | 8649篇 |
2003年 | 7105篇 |
2002年 | 6563篇 |
2001年 | 6274篇 |
2000年 | 5277篇 |
1999年 | 5441篇 |
1998年 | 4641篇 |
1997年 | 4137篇 |
1996年 | 4490篇 |
1995年 | 4553篇 |
1994年 | 4374篇 |
1993年 | 4183篇 |
1992年 | 3697篇 |
1991年 | 3171篇 |
1990年 | 2609篇 |
1989年 | 2493篇 |
1988年 | 2257篇 |
1987年 | 1468篇 |
1986年 | 1543篇 |
1985年 | 1129篇 |
1984年 | 1180篇 |
1983年 | 532篇 |
1982年 | 1023篇 |
1981年 | 815篇 |
1980年 | 835篇 |
1979年 | 556篇 |
1978年 | 559篇 |
1977年 | 657篇 |
1976年 | 1066篇 |
1972年 | 547篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
912.
十几年前,NI提出“软件就是仪器”概念,引起了传统仪器产业的一场新革命。可是,现今各大测量仪器厂商仍力主创新传统仪器。那么,在这个盛行“做生意不简单,苦日子是常态”的现象之下,NI又是如何联手其系统联盟商和同行企业一步步角逐测量市场?也许,NI要成功,必须比对手更会执行,更了解客户! 相似文献
913.
编者按: 在仪器市场,大多数仪器制造商采用经销商代理产品来拓展市场,而经销商也通常是通过代理多个品牌的仪器来谋生存.那么,当这种渠道模式不可避免,而决定品牌的胜负关键又从"知名度"转移到"认同度"的时候,品牌厂商则要持续性学习与思考--如何保持与经销商之间唇齿相依的关系.因为,经销商已经成为另一类"媒体"! 相似文献
914.
915.
Q.-Y. Shao A.-D. Li J.-B. Cheng H.-Q. Ling D. Wu Z.-G. Liu N.-B. Ming C. Wang H.-W. Zhou B.-Y. Nguyen 《Applied Physics A: Materials Science & Processing》2005,81(6):1181-1185
LaAlO3 (LAO) gate dielectric films were deposited on Si substrates by low-pressure metalorganic chemical vapor deposition. The interfacial structure and composition distribution were investigated by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectroscopy (SIMS), and Auger-electron spectroscopy (AES). HRTEM confirms that there exists an interfacial layer between LAO and Si in most samples. AES, SIMS, and XPS analyses indicate that the interfacial layer is compositionally graded La–Al silicate and the Al element is severely deficient close to the Si surface. Electrical properties of LAO films were evaluated. No evident difference in electrical properties between samples with and without native SiO2 layers was observed. The electrical properties are discussed in terms of LAO growth mechanisms, in relation to the interfacial structure. PACS 73.40.Qv; 81.15.Gh; 77.55.+f; 68.35.-p 相似文献
916.
We present a semimonolithic frequency-doubler from 1080 to 540 nm with 80% doubling efficiency and up to 849-mW output power of green light. 相似文献
917.
Capacity has always been a major concern in wireless networks. This letter studies the impact of mobility on the overall system capacity in wireless cellular networks. In this letter, we present a simple system model which we developed to capture the inherent relationships among system capacity, new call blocking probability, handoff dropping probability, call terminating probability, and bandwidth utilization rate. We investigate the complex relationship between mobility and capacity‐related parameters. Through simulation, we demonstrate that mobility has a significant impact on capacity and is reversely proportional to the bandwidth reserved for handoff traffic. 相似文献
918.
919.
920.
An overview of ultra-wideband microwave imaging via space-time beamforming for early-stage breast-cancer detection 总被引:1,自引:0,他引:1
Xu Li Bond E.J. Van Veen B.D. Hagness S.C. 《Antennas and Propagation Magazine, IEEE》2005,47(1):19-34
Ultra-wideband (UWB) microwave imaging has recently been proposed for detecting small malignant breast tumors. In this article, we review the current research status of this approach. First, we introduce the concept of microwave imaging via space-time (MIST) beamforming and related signal-processing algorithms. The objective of these signal-processing techniques is to form a spatial image of scattered microwave energy, and to identify the presence and location of malignant lesions from their scattering signatures. Next, we present numerical studies based on finite-difference time-domain simulations to demonstrate the efficacy of MIST beamforming for detecting small malignant breast lesions in both prone and supine configurations. Finally, the experimental feasibility of UWB microwave imaging is demonstrated using an initial imaging prototype and multilayered breast phantoms. 相似文献