全文获取类型
收费全文 | 9677篇 |
免费 | 1202篇 |
国内免费 | 783篇 |
专业分类
化学 | 5265篇 |
晶体学 | 37篇 |
力学 | 367篇 |
综合类 | 16篇 |
数学 | 808篇 |
物理学 | 2348篇 |
无线电 | 2821篇 |
出版年
2024年 | 14篇 |
2023年 | 223篇 |
2022年 | 195篇 |
2021年 | 371篇 |
2020年 | 354篇 |
2019年 | 310篇 |
2018年 | 270篇 |
2017年 | 231篇 |
2016年 | 358篇 |
2015年 | 365篇 |
2014年 | 479篇 |
2013年 | 608篇 |
2012年 | 783篇 |
2011年 | 778篇 |
2010年 | 550篇 |
2009年 | 499篇 |
2008年 | 610篇 |
2007年 | 544篇 |
2006年 | 535篇 |
2005年 | 448篇 |
2004年 | 304篇 |
2003年 | 306篇 |
2002年 | 226篇 |
2001年 | 229篇 |
2000年 | 225篇 |
1999年 | 236篇 |
1998年 | 173篇 |
1997年 | 150篇 |
1996年 | 185篇 |
1995年 | 173篇 |
1994年 | 116篇 |
1993年 | 99篇 |
1992年 | 93篇 |
1991年 | 77篇 |
1990年 | 100篇 |
1989年 | 72篇 |
1988年 | 49篇 |
1987年 | 42篇 |
1986年 | 30篇 |
1985年 | 25篇 |
1984年 | 17篇 |
1983年 | 24篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1979年 | 28篇 |
1978年 | 25篇 |
1977年 | 16篇 |
1975年 | 16篇 |
1974年 | 10篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
981.
热象无损检测技术应用 总被引:1,自引:1,他引:0
本文将热象无损检测技术应用于鉴定受测物结构和性质,并测出受测物中的缺陷,实验结果取得了较为满意的进展。 相似文献
982.
983.
984.
Smy T. Tan L. Chan K. Tait R.N. Broughton J.N. Dew S.K. Brett M.J. 《Electron Devices, IEEE Transactions on》1998,45(7):1414-1425
Modified sputtering techniques, such as long throw sputtering, collimation, and ionized sputtering, have been proposed to improve VLSI topography bottom coverage by narrowing the angular distribution of the sputter flux at the substrate and reducing subsequent flux shadowing at the bottom of topography. This paper first investigates a number of unique aspects involved in the simulation of long throw sputter systems. In particular, time importance of inhomogeneous film density and nonunity sticking coefficients are addressed. The second part of the paper presents a simulation study of long throw sputtering, providing a comparison to collimated and standard sputtering systems. The simulations are performed using the SIMSPUD/SIMBAD ballistic deposition tool. SIMSPUD is used to study film uniformity over a 300-mm wafer and to generate angular distributions at the center and edge of the wafer. The ability of SIMBAD to simulate directed sputtering systems is verified by direct comparison to Ti films deposited into oxide trenches. The importance of modeling the film microstructure is demonstrated by comparison between cross-sectional SEM's micrograph for evaporation and modeling results, such as long throw sputtering with a variety of substrate/target spacings, typical “standard” as well as “collimated” systems. SEM's of overhang structures and simulations are also presented to demonstrate nonunity sticking during the co-sputtering of TiW 相似文献
985.
H. S. Tan M. K. Han P. Y. Hu J. H. Zheng S. C. Ng H. Gong 《Applied Physics A: Materials Science & Processing》1994,59(3):245-251
An electron trap having an energy level of 0.14 eV from the conduction band edge was found in the bulk of copper-diffused VPE-grown n-GaAs0.6P0.4 by conventional DLTS measurements and by pulse-duration dependent capacitance amplitude measurements. The capture cross section at room temperature is about 1.0×10–21 cm2 and has a weak temperature dependence. These properties are attributed to a non-repulsive center having a capturing mechanism which involves multiphonon emission processes with hardly any lattice relaxation. Evolution of the spatial distributions of the traps with time under junction electric field were studied. The results suggest that the trap is positively charged and has a high diffusivity under electric field. The center can thus be identified as positively charged interstitial copper ion rather than some form of copper complexes. 相似文献
986.
987.
988.
Erjun Zhou Zhan'ao Tan Youjun He Chunhe Yang Yongfang Li 《Journal of polymer science. Part A, Polymer chemistry》2007,45(4):629-638
Two alternating poly[3‐(hex‐1‐enyl)thiophene‐co‐thiophene]s, Pa (with 77% trans‐isomer and 23% cis‐isomer) and Pb (with 100% trans‐isomer), were synthesized by the coupling of 2,5‐dibromo‐3‐hex‐1‐enyl‐thiophene to 2,5‐bis(tributylstannyl)thiophene via a Stille reaction and compared with poly(3‐hexylthiophene‐co‐thiophene) ( P1 ) to study the effect of changing the carbon(α)–carbon(β) single bond into a carbon–carbon double bond on the properties of the polymers. From P1 to Pb and to Pa , the ultraviolet–visible absorption peaks of the polymers were slightly redshifted, and their electrochemical bandgaps decreased by 0.05–0.1 eV. X‐ray diffraction analysis indicated that Pa had a better lamellar structure than Pb . The hole mobilities of the three polymers, determined with the space‐charge‐limited current model, were 5.23 × 10?6 ( P1 ), 2.34 × 10?4 ( Pb ), and 7.02 × 10?4 cm2/V s ( Pa ). The power conversion efficiencies (PCEs) of polymer solar cells based on the three polymers were 0.87 ( P1 ), 1.16 ( Pb ), and 1.70% ( Pa ). The increase in the hole mobility and PCE revealed the important effect of changing the carbon(α)–carbon(β) single bond into a carbon–carbon double bond on the properties of polythiophene derivatives containing 3‐alkylthiophene. The strategy used in this work enlarges the thinking to obtain novel, efficient donor polymers for optoelectronic applications. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 629–638, 2007 相似文献
989.
CAD技术在电子封装中的应用及其发展 总被引:1,自引:0,他引:1
现代电子信息技术的发展,推动电子产品向多功能、高性能、高可靠性、小型化、低成本的方向发展,微电子封装、IC设计和IC制造共同构成IC产业的三大支柱。计算机辅助设计(CAD)作为一种重要的技术手段在IC产业中发挥了巨大作用,已广泛应用于电子封装领域。本文结合各个时期电子封装的特点,介绍了封装CAD技术的发展历程,并简要分析了今后发展趋势。 相似文献
990.
从基本的气体动力学方程组出发分析了气流介质中由于放电、吸收激光等沉积能量所造成的热效应和气流的特性。对于典型的气流放电激光器条件,0.05≤M《0.2,气动方程有最简单的形式,很容易得到解析解,并可以用激光干涉法测量沉积能量和密度,温度和速度等气动参数沿流动方向的分布。 相似文献