全文获取类型
收费全文 | 746篇 |
免费 | 65篇 |
国内免费 | 19篇 |
专业分类
化学 | 47篇 |
晶体学 | 2篇 |
力学 | 7篇 |
数学 | 38篇 |
物理学 | 98篇 |
无线电 | 638篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 32篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2017年 | 27篇 |
2016年 | 14篇 |
2015年 | 29篇 |
2014年 | 55篇 |
2013年 | 38篇 |
2012年 | 46篇 |
2011年 | 55篇 |
2010年 | 60篇 |
2009年 | 52篇 |
2008年 | 66篇 |
2007年 | 53篇 |
2006年 | 43篇 |
2005年 | 35篇 |
2004年 | 30篇 |
2003年 | 31篇 |
2002年 | 24篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1982年 | 2篇 |
1979年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有830条查询结果,搜索用时 265 毫秒
31.
高速差分过孔的仿真分析 总被引:1,自引:0,他引:1
高速差分信号传输中也存在着信号完整性问题。差分过孔在频率很高的时候会明显地影响差分信号的完整性,现介绍差分过孔的等效RLC模型,在HFSS中建立了差分过孔仿真模型并分析了过孔尤其过孔长度对信号完整性的影响。 相似文献
32.
PCB技术的革新与进步 总被引:2,自引:0,他引:2
文章概述了近几年来在PCB工业中生产技术的革新与进步情况,特别是直流电镀(镀层均匀性、填孔镀等)、表面涂(镀)覆(化学镀镍/钯浸金和直接浸金等)技术的革新与进步,推动了PCB工艺技术的发展。 相似文献
33.
34.
Image restoration is a fundamental problem in image processing. Blind image restoration has a great value in its practical application. However, it is not an easy problem to solve due to its complexity and difficulty. In this paper, we combine our robust algorithm for known blur operator with an alternating minimization implicit iterative scheme to deal with blind deconvolution problem, recover the image and identify the point spread function(PSF). The only assumption needed is satisfy the practical physical sense. Numerical experiments demonstrate that this minimization algorithm is efficient and robust over a wide range of PSF and have almost the same results compared with known PSF algorithm. 相似文献
35.
H. Hussain B. H. Tan C. S. Gudipati Y. Liu C. B. He T. P. Davis 《Journal of polymer science. Part A, Polymer chemistry》2008,46(16):5604-5615
Amphiphilic diblock copolymers of polystyrene (PS) and poly(N‐vinylpyrrolidone) (PNVP) were prepared by a combination of ATRP and MADIX. Well‐defined PS with bromine end group was synthesized by ATRP in bulk at 110 °C using (1‐bromoethyl) benzene as an initiator. The Br‐ end group was then converted to xanthate as verified by 1H NMR spectroscopy, elemental analysis, and UV‐spectroscopy. PS‐b‐PNVP copolymers were produced by MADIX of NVP in bulk at 60 °C using PS‐xanthate as a macro‐chain transfer agent and the kinetics of polymerization were investigated. The structures of PS‐b‐PNVP were characterized using GPC and 1H NMR. Amphiphilic PS‐b‐PNVP could form spherical micelles with PS cores and PNVP shells in aqueous solution as confirmed by 1H NMR and laser light scattering (LLS). The values of critical micelle concentration of PS‐b‐PNVP and the average aggregation number of PS‐b‐PNVP in the micelles were measured using pyrene as a probe and static LLS, respectively. The aggregation number increases concomitantly with temperature (10–50 °C), but the hydrodynamic radius of the micelles remains almost constant over the same temperature range, which may indicate shell dehydration at a higher temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5604–5615, 2008 相似文献
36.
We provide a global existence result for the time-continuous elastoplasticity problem using the energetic formulation. For
this, we show that the geometric nonlinearities arising from the multiplicative decomposition of the strain can be controlled
via polyconvexity and a priori stress bounds in terms of the energy density. While temporal oscillations are controlled via
energy dissipation, the spatial compactness is obtained via regularizing terms involving gradients of the internal variables.
Dedicated to Sir John Ball on the occasion of his 60th birthday. 相似文献
37.
高密度多重埋孔印制板的设计与制造 总被引:1,自引:0,他引:1
采用新材料及多重埋孔方式,研制出高密度及高可靠性印制电路板(PCB),其孔径,线宽/线间距以及厚径比分别为0.2mm,0.08mm/0.08mm和15:1,综合性能达到和超过国家军标GJB362的有关条款要求。 相似文献
38.
The compound NaAlF4 has been obtained in the form of thin fibrous crystals or fine colorless powder by condensation at 18 °C of vapors arising over chiolite Na5Al3F14 or NaCaAlF6, heated up to 800 °C. Thermal stability has been investigated by the methods of thermal analysis and high temperature X-ray diffraction. When heated in air, NaAlF4 is stable up to 390-400 °C, then there is an exothermal solid state decay into Na5Al3F14(s) and AlF3(s). At higher temperature Na5Al3F14(s) decays into Na3AlF6(s) and NaAlF4(g). The crystal structure (space group Cmcm, a=3.6124(1) Å, b=14.9469(7) Å, c=5.2617(3) Å, V=284.10 Å3) has been determined by X-ray powder diffraction method. In the crystal structure of NaAlF4 the octahedrons [AlF6] are joined through vertices and form corrugated layers, sodium ion layers being located between them. The distances between the atoms of Al-F are in the range 1.791-1.814 Å, and those for Na…F are in the range 2.297-2.439 Å. In spite of limited thermal stability of the crystal form, the compound NaAlF4 is the main component of the gas mixture over solid and molten salts in the ternary system NaF-AlF3-CaF2 and participates in chemical transformations between the phases at high temperature. 相似文献
39.
40.
This study examined imprint lithography with a two-step Ni stamp to solve the laser process problems and simultaneously form a blind via and layer pattern. The Ni stamp was fabricated by electroplating on a dry-etched Si mold, made from a SOI (silicon on insulator) wafer, and pattern replication. For the pattern transfer of the Ni stamp, hot embossing was performed on SU8-coated BT and Si wafer substrates. The residual layer was of a uniform thickness with an embossed shape of acceptable squareness. 相似文献