全文获取类型
收费全文 | 140637篇 |
免费 | 34508篇 |
国内免费 | 28782篇 |
专业分类
化学 | 74493篇 |
晶体学 | 1399篇 |
力学 | 7604篇 |
综合类 | 271篇 |
数学 | 14207篇 |
物理学 | 64219篇 |
无线电 | 41734篇 |
出版年
2024年 | 807篇 |
2023年 | 2547篇 |
2022年 | 2698篇 |
2021年 | 3165篇 |
2020年 | 3542篇 |
2019年 | 4648篇 |
2018年 | 4198篇 |
2017年 | 4864篇 |
2016年 | 6114篇 |
2015年 | 6839篇 |
2014年 | 7058篇 |
2013年 | 9424篇 |
2012年 | 10683篇 |
2011年 | 11440篇 |
2010年 | 13085篇 |
2009年 | 12831篇 |
2008年 | 7079篇 |
2007年 | 6262篇 |
2006年 | 5915篇 |
2005年 | 5588篇 |
2004年 | 5870篇 |
2003年 | 4828篇 |
2002年 | 4603篇 |
2001年 | 4487篇 |
2000年 | 3646篇 |
1999年 | 3794篇 |
1998年 | 3257篇 |
1997年 | 3002篇 |
1996年 | 3392篇 |
1995年 | 3568篇 |
1994年 | 3486篇 |
1993年 | 3469篇 |
1992年 | 3069篇 |
1991年 | 2690篇 |
1990年 | 2183篇 |
1989年 | 2230篇 |
1988年 | 2057篇 |
1987年 | 1310篇 |
1986年 | 1362篇 |
1985年 | 998篇 |
1984年 | 1081篇 |
1982年 | 953篇 |
1981年 | 784篇 |
1980年 | 814篇 |
1979年 | 554篇 |
1978年 | 560篇 |
1977年 | 660篇 |
1976年 | 1072篇 |
1973年 | 464篇 |
1972年 | 555篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
91.
92.
C. Lavoie F. M. d Heurle C. Detavernier C. Cabral Jr. 《Microelectronic Engineering》2003,70(2-4):144-157
In this paper, we review some of the advantages and disadvantages of nickel silicide as a material for the electrical contacts to the source, drain and gate of current and future CMOS devices. We first present some of the limitations imposed on the current cobalt silicide process because of the constant scaling, of the introduction of new substrate geometries (i.e. thin silicon on insulator) and of the modifications to the substrate material (i.e. SiGe). We then discuss the advantages of NiSi and for each of the CoSi2 limitations, we point out why Ni is believed to be superior from the point of view of material properties, miscibility of phases and formation mechanisms. Discussion follows on the expected limitations of NiSi and some of the possible solutions to palliate these limitations. 相似文献
93.
94.
The possibility of realizing SASE Free Election Laser in x-ray waveband with EM-wave wiggler is studied in this paper. SASE effect including saturation length, saturation power and nonlinear process is explored through a 3-D simulation code. A utilization of seed light from laser plasma x-ray is also analyzed, which demonstrates the feature of shortening the interaction length for saturation. The results show that sizeable output power of x-ray laser would be generated with a middle energy electron beam. 相似文献
95.
96.
Due to the demand for real time wavelet processors in applications such as video compression [1], Internet communications compression [2], object recognition [3], and numerical analysis, many architectures for the Discrete Wavelet Transform (DWT) systems have been proposed. This paper surveys the different approaches to designing DWT architectures. The types of architectures depend on whether the application is 1-D, 2-D, or 3-D, as well as the style of architecture: systolic, semi-systolic, folded, digit-serial, etc. This paper presents an overview and evaluation of the architectures based on the criteria of latency, control, area, memory, and number of multipliers and adders. This paper will give the reader an indication of the advantages and disadvantages of each design. 相似文献
97.
Padavattan Govindaswamy Patrick J. Carroll Yurij A. Mozharivskyj Mohan Rao Kollipara 《Journal of Chemical Sciences》2006,118(4):319-326
The reaction of [{(η5-C5Me5)M(μ-Cl)Cl}2] {where M = Rh (1), Ir (2)} with functionalized phosphine viz., diphenyl-2-pyridylphosphine (PPh2Py) in dichloromethane solvent yield neutral ϰ1-P-coordinated rhodium and iridium complexes [(η5-C5Me5)RhCl2(κ1-P-PPh2Py)]3 and [(η5-C5Me5) IrCl2(ϰ1-P-PPh2Py)]4. Reaction of complexes 1 and 2 with the ligand PPh2Py in methanol under reflux give bis-substituted complexes such as [(η5-C5Me5)RhCl(ϰ1-P-PPh2Py)2]+
5 and [(η5-C5Me5)IrCl(ϰ1-P-PPh2Py)2]+
6, whereas stirring in methanol at room temperature gives P-, N-chelating complexes of the type [(η5-C5Me5)RhCl(ϰ2-P-N-PPh2Py)]+ 7 and [(η5-C5Me5)IrCl(ϰ2-P-N-PPh2Py)]+
8. Neutral ϰ1-P-coordinated complexes [(η5-C5Me5)RhCl2(ϰ1-P-PPh2Py)]3 and [(η5-C5Me5)IrCl2(ϰ1-P-PPh2Py)]4 easily undergo conversion to the cationic P-, N-chelating complexes [(η5-C5Me5)RhCl(ϰ2-P-N-PPh2Py)]+
7 and [(η5-C5Me5) IrCl(ϰ2-P, N-PPh2Py)]+
8 on stirring in methanol at room temperature. These complexes are characterized by FT-IR and FT-NMR spectroscopy as well as
analytical methods. The molecular structures of the representative complexes [(η5-C5Me5)RhCl2(ϰ1-P-PPh2Py)]3, [(η5-C5Me5)IrCl2(ϰ1-P-PPh2Py)]4 and hexafluorophosphate salt of complex [(η5-C5Me5)IrCl(ϰ2-P-PPh2Py)2]+
6 are established by single-crystal X-ray diffraction methods 相似文献
98.
99.
Chun-Yuan Chen Shiou-Ying Cheng Wen-Hui Chiou Hung-Ming Chuang Wen-Chau Liu 《Electron Device Letters, IEEE》2003,24(3):126-128
A novel InP/InGaAs tunneling emitter bipolar transistor (TEBT) is fabricated and demonstrated. The studied device exhibits a very small collector-emitter offset voltage of 40 mV and an extremely wide operation regime. The operation region is larger than 11 decades in magnitude of collector current (10/sup -12/ to 10/sup -1/A). A current gain of 3 is obtained even if the device is operated at an ultralow collector current of 3.9 /spl times/ 10/sup -12/A (1.56 /spl times/ 10/sup -7/A/cm/sup 2/). Furthermore, the common-emitter breakdown voltage of the studied device is higher than 2 V. Consequently, the studied device shows a promise for low supply voltage, and low-power consumption circuit applications. 相似文献
100.
详细分析了终端对话音业务和新业务的影响。在分析终端对话音业务的影响时从用户和终端两方面进行了阐述,指明为了进一步提高用户敷和砖络的使用率,运营商在进行话音营销对应逐渐将工作重点适当转向农村市场。也从对个人和行业用户的影响两方面阐明了终端对新业务的影响。 相似文献