全文获取类型
收费全文 | 49108篇 |
免费 | 6638篇 |
国内免费 | 4768篇 |
专业分类
化学 | 25776篇 |
晶体学 | 358篇 |
力学 | 2231篇 |
综合类 | 241篇 |
数学 | 4289篇 |
物理学 | 13570篇 |
无线电 | 14049篇 |
出版年
2024年 | 169篇 |
2023年 | 1148篇 |
2022年 | 1366篇 |
2021年 | 1814篇 |
2020年 | 1788篇 |
2019年 | 1605篇 |
2018年 | 1382篇 |
2017年 | 1333篇 |
2016年 | 1884篇 |
2015年 | 2042篇 |
2014年 | 2483篇 |
2013年 | 3187篇 |
2012年 | 3949篇 |
2011年 | 3868篇 |
2010年 | 2799篇 |
2009年 | 2762篇 |
2008年 | 2987篇 |
2007年 | 2656篇 |
2006年 | 2576篇 |
2005年 | 2256篇 |
2004年 | 1747篇 |
2003年 | 1392篇 |
2002年 | 1248篇 |
2001年 | 1071篇 |
2000年 | 1044篇 |
1999年 | 1176篇 |
1998年 | 1034篇 |
1997年 | 934篇 |
1996年 | 991篇 |
1995年 | 863篇 |
1994年 | 782篇 |
1993年 | 679篇 |
1992年 | 625篇 |
1991年 | 492篇 |
1990年 | 415篇 |
1989年 | 300篇 |
1988年 | 267篇 |
1987年 | 235篇 |
1986年 | 166篇 |
1985年 | 183篇 |
1984年 | 152篇 |
1983年 | 132篇 |
1982年 | 99篇 |
1981年 | 66篇 |
1980年 | 58篇 |
1979年 | 38篇 |
1978年 | 30篇 |
1976年 | 31篇 |
1975年 | 36篇 |
1974年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
利用引进的制造技术和设备,制作出了 APT(STLRI)—1.78型系列化光纤连接器。 相似文献
105.
We investigate the origin of ultraviolet (UV) emission from Mg0.12 Zn0.88 O alloy thin films with a wurtzite structure fabricated on c-plane Al2O3 substrates by plasma assisted molecular beam epitaxy. At room temperature, the absorption edge and UV emission band of the Mg0.12Zn0.88O film shift to high-energy side compared with ZnO films. Temperature dependence of the photoluminescence spectra shows that the UV emission is composed of free exciton and neutral donor bound exciton emissions. Two-step dissociation processes of the UV emission are observed with the increasing temperature. The thermal quenching mechanism is attributed to the dissociation of the free exciton from the neutral donor bound exciton in the low temperature region and the dissociation of free electron and hole from the free exciton in the high temperature region. 相似文献
106.
A new electroactive polynuclear inorganic compound of rare earth metal, gadolinium hexacyanoferrate (GdHCF), was prepared and characterized using the techniques of FTIR spectroscopy, thermogravimetric analysis (TG), UV-Vis spectrometry, X-ray photoelectron spectroscopy (XPS), ICP atomic emission spectroscopy, and EDX. The results of ICP atomic emission spectroscopy, EDX, and TGA indicated that the prepared GdHCF sample had a stoichiometry of NaGdFe(CN)6·12H2O (when GdHCF was prepared in NaCl solution). The FTIR spectrum of GdHCF showed that there were two types of water molecules in the structure of GdHCF: one was the interstitial water (5 H2O), which resulted from the association of water due to H-bonding, and the other was water coordinated with Gd (7 H2O). The results obtained using XPS showed that the oxidation state of Fe and Gd in the GdHCF sample was +2 and +3, respectively. GdHCF was immobilized on the surface of spectroscopically pure graphite (SG) electrode forming the GdHCF/SG electrode, and the solid-state electrochemistry of the resultant electrode was studied using cyclic voltammetry. The cyclic voltammetric results indicated that the GdHCF/SG electrode exhibited a pair of well-defined and stable redox peaks with the formal potential of E0′=(197±3) mV. The effects of the concentration of the supporting electrolyte on the electrochemical characteristics of GdHCF were studied, and the results showed that the value of E0′ increased linearly with the activity of the cationic ion of the supporting electrolyte (lgaNa+), with a slope of 54.1 mV, which may become a novel method for determining the activity of Na+ in solution. Further experimental results indicated that GdHCF had electrocatalytic activities toward the oxidation of dopamine (DA) and ascorbic acid (AA), and the electrocatalytic current increased linearly with the concentration of DA (or AA) in the range of 1.0–10.0 mmol·L?1 (for DA) or 0.5–20.0 mmol·L?1 (for AA). 相似文献
107.
随着电容测量技术的迅速发展,电容传感器在非电量测量和自动检测中得到广泛应用,但它在使用过程中也存在一些问题,针对在使用电容传感器过程中存在的几个问题,从电容传感器的原理和工作过程两个方面进行了讨论,并提出行之有效的处理方法。 相似文献
108.
Wu Jigang Srikanthan T. Schroder H. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2005,13(8):976-979
This paper proposes an efficient techniques to reconfigure a two-dimensional degradable very large scale integration/wafer scale integration (VLSI/WSI) array under the row and column routing constraints, which has been shown to be NP-complete. The proposed VLSI/WSI array consists of identical processing elements such as processors or memory cells embedded in a 6-port switch lattice in the form of a rectangular grid. It has been shown that the proposed VLSI structure with 6-port switches eliminates the need to incorporate internal bypass within processing elements and leads to notable increase in the harvest when compared with the one using 4-port switches. A new greedy rerouting algorithm and compensation approaches are also proposed to maximize harvest through reconfiguration. Experimental results show that the proposed VLSI array with 6-port switches consistently outperforms the most efficient alternative proposed in literature, toward maximizing the harvest in the presence of fault processing elements. 相似文献
109.
Wei-Cheng Lin Tsung-Chien Wu Yi-Hung Tsai Long-Jei Du Ya-Chin King 《Electron Devices, IEEE Transactions on》2005,52(7):1478-1483
Circuit reliability of class-E and class-A power amplifiers is investigated based on a newly developed degradation subcircuit model. Measured degradation characteristics on the fabricated circuits agree well with the simulation predictions. Using this model, we have found that the class-E amplifier degrades faster than a class-A amplifier, due to a much higher stress level during switching. With a drastic decrease of PAE, a shorter lifetime is expected for a class-E amplifier. 相似文献
110.
An experimental study of an optical burst switching network based on wavelength-selective optical switches 总被引:1,自引:0,他引:1
Li Xinwan Chen Jianping Wu Guiling Wang Hui Ye Ailun 《Communications Magazine, IEEE》2005,43(5):S3-10
In this article we report the system structure and test results of an experimental optical burst switching network with three edge router's and one core node. Wavelength-selective switches developed for this system and their characteristics are depicted. The implementation and performance of our new scheme for the just-in-time protocol are described. We also report experimental results of FTP and VOD services on this system. Some parameters, including traffic rate, average burst data length, and assembly time, are studied. 相似文献