全文获取类型
收费全文 | 4845篇 |
免费 | 751篇 |
国内免费 | 414篇 |
专业分类
化学 | 1314篇 |
晶体学 | 58篇 |
力学 | 441篇 |
综合类 | 33篇 |
数学 | 439篇 |
物理学 | 1980篇 |
无线电 | 1745篇 |
出版年
2024年 | 7篇 |
2023年 | 51篇 |
2022年 | 116篇 |
2021年 | 109篇 |
2020年 | 136篇 |
2019年 | 121篇 |
2018年 | 108篇 |
2017年 | 150篇 |
2016年 | 223篇 |
2015年 | 231篇 |
2014年 | 306篇 |
2013年 | 364篇 |
2012年 | 323篇 |
2011年 | 385篇 |
2010年 | 273篇 |
2009年 | 320篇 |
2008年 | 316篇 |
2007年 | 326篇 |
2006年 | 320篇 |
2005年 | 231篇 |
2004年 | 215篇 |
2003年 | 196篇 |
2002年 | 166篇 |
2001年 | 144篇 |
2000年 | 148篇 |
1999年 | 115篇 |
1998年 | 109篇 |
1997年 | 76篇 |
1996年 | 73篇 |
1995年 | 71篇 |
1994年 | 55篇 |
1993年 | 38篇 |
1992年 | 41篇 |
1991年 | 29篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有6010条查询结果,搜索用时 468 毫秒
161.
残影不良分析及改善对策研究 总被引:1,自引:1,他引:0
通过对大量残影不良样品进行分析,找到了残影不良产生的原因,并基于分析结果设计了改善残影的实验。通过分析发现:残影不良产生的原因是彩膜侧像素与黑矩阵之间的段差过大,在摩擦工程时段差过大区域形成了摩擦弱区,摩擦弱区内的液晶分子配向较弱,导致不良产生。为降低残影不良进行实验,结果显示:在彩膜侧加覆盖层可以有效降低残影不良的发生率,但不适用于量产;通过采用高预倾角的配向膜材料,同时控制配向膜工程到摩擦工程的时间,可使残影不良发生率由28.2%降低至0.2%,为企业的稳定高效生产奠定了基础。 相似文献
162.
晶圆背面减薄是集成电路后封装关键工艺,通过金刚石磨轮的磨削作用,对芯片背面的基体材料-硅材料去除一定的厚度,从而降低芯片厚度,改善芯片的散热效果,有利于后期的封装工艺。主要介绍了在晶圆减薄过程中的关键指标TTV 的影响因素,通过设备自动控制,进行工艺角度调整,能够减小晶圆TTV 值,从而提高晶圆磨削质量。 相似文献
163.
164.
入射余角是利用抛物方程模型研究地形条件下电波传播问题的重要参数,但该参数估计具有单次快拍、信号相干和实时性要求高的特点,传统的估计算法难以同时满足上述要求.针对上述问题,提出了基于单次快拍的空间平滑旋转不变性的信号参数估计(Estimating Signal Parameters via Rotational Invariance Techniques, ESPRIT)算法.直接采用单次数据的前后向空间平滑子阵构造centro-Hermitian伪协方差矩阵以实现信号解相干,应用酉变换将复数域的奇异值分解转换为实数域求解,利用ESPRIT算法代替多重信号分类算法估计入射余角.仿真结果表明:该算法能够实现电波传播入射余角的快速估计,准确反映地形起伏对入射余角的影响,与现有算法相比提高了实时性和估计精度. 相似文献
165.
Several hyperbranched polyimides (HBPIs) were applied in liquid crystal (LC) alignment layers and exhibited outstanding performance for LC alignment. The maximum pretilt angle was above 8°, and the minimum pretilt angle was 4.2°. The results of atomic force microscope measurement disclosed that a lot of grooves were aligned parallel to the rubbing direction and found that the grooves were not main factor for LC alignment. The LC alignment and pretilt angles are unambiguously associated with the intrinsic HBPI chemical structures. The results of thermal gravimetric analysis and ultraviolet–visible spectra showed that the HBPIs had good thermal stability and excellent transmittance. T5 and T10 were higher than 360°C and 400°C, respectively. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
166.
In order to ascertain the effect of a donor monomer, vinyl acetate (VAc), on the graft copolymerization of acceptor monomers, ethyl acrylate (EA) and butyl acrylate (BA), grafting of mixed vinyl monomers (EA + VAc) and (BA + VAc) was carried out on Himachali wool in aqueous medium using ceric ammonium nitrate (CAN) as a redox initiator. Graft copolymerization was carried out at different temperatures for various reaction periods. Percent grafting and percent efficiency were determined as functions of 1) concentration of mixed vinyl monomers, 2) concentration of CAN, 3) concentration of HNO3 4) temperature, and 5) reaction time. VAc, the donor monomer, was found to decrease percent grafting of EA and BA onto wool. 相似文献
167.
Charles E. Nwankire Gerard G. Donohoe Xin Zhang Jonathan Siegrist Martin Somers Dirk Kurzbuch Ruairi Monaghan Maria Kitsara Robert Burger Stephen Hearty Julie Murrell Christopher Martin Martha Rook Louise Barrett Stephen Daniels Colette McDonagh Richard O’Kennedy Jens Ducrée 《Analytica chimica acta》2013
In this paper we report a centrifugal microfluidic “lab-on-a-disc” system for at-line monitoring of human immunoglobulin G (hIgG) in a typical bioprocess environment. The novelty of this device is the combination of a heterogeneous sandwich immunoassay on a serial siphon-enabled microfluidic disc with automated sequential reagent delivery and surface-confined supercritical angle fluorescence (SAF)-based detection. The device, which is compact, easy-to-use and inexpensive, enables rapid detection of hIgG from a bioprocess sample. This was achieved with, an injection moulded SAF lens that was functionalized with aminopropyltriethoxysilane (APTES) using plasma enhanced chemical vapour deposition (PECVD) for the immobilization of protein A, and a hybrid integration with a microfluidic disc substrate. Advanced flow control, including the time-sequenced release of on-board liquid reagents, was implemented by serial siphoning with ancillary capillary stops. The concentration of surfactant in each assay reagent was optimized to ensure proper functioning of the siphon-based flow control. The entire automated microfluidic assay process is completed in less than 30 min. The developed prototype system was used to accurately measure industrial bioprocess samples that contained 10 mg mL−1 of hIgG. 相似文献
168.
Der‐Lii M. Tzou Lin‐Kai Ni Mei‐Man Chen Min‐Chuan Chiou Li‐Chou Chen Shan‐Te Hsu Kuo‐Lung Ku Chien‐Chung Cheng 《中国化学会会志》2013,60(9):1107-1112
Solid‐state Nuclear Magnetic Resonance (ss‐NMR) 13C single‐pulse excitation spectroscopy in combination with the magic‐angle spinning (MAS) technique was applied to a series of Phalaenopsis tissues, including the leaf, sheath, stem, and root, at different growth and spiking periods. Compared with{1H}/13C cross‐polarization MAS spectra, the 13C single‐pulse excitation MAS spectra displayed very distinct spectral patterns, recognizable as fingerprints of the tissues studied. 1Here, we demonstrate that solid‐state 13C single‐pulse excitation NMR spectroscopy provides a direct and robust analytical tool for studying the various tissues of Phalaenopsis in different growth and spiking induction periods. 相似文献
169.
Patrícia Santiago de Oliveira Patricio Iaci Miranda Pereira Natália Cristina Ferreira da Silva Eliane Ayres Fabiano Vargas Pereira Rodrigo Lambert Oréfice 《European Polymer Journal》2013
Polyurethane waterborne synthesis was performed using a two-step method, commonly referred to as a prepolymer method. Nanocomposites based on waterborne polyurethane and cellulose nanocrystals were prepared by the prepolymer method by altering the mode and step in which the nanofillers were incorporated during the polyurethane formation. The morphology, structural, thermal, and mechanical properties of the resulting nanocomposite films were evaluated by Fourier transform infrared spectroscopy (FTIR), small angle X-ray scattering (SAXS), scanning electron microscopy (SEM), and tensile tests. FTIR results indicated that the degree of interaction between the nanofillers and the WPU through hydrogen bonds could be controlled by the method of cellulose nanocrystal incorporation. Data obtained from SAXS experiments showed that the cellulose nanocrystals as well as the step of the reaction in which they are added influenced the morphology of the polyurethane. The reinforcing effect of CNCs on the nanocomposites depends on their morphology. 相似文献
170.
Firas Awaja Michael Gilbert Minoo Naebe Georgina Kelly Bronwyn Fox Russell Brynolf Paul J. Pigram 《Polymer Degradation and Stability》2013
Thermoplastic polyolefin panels were treated with a flame, flame & water, and accelerated thermo molecular adhesion process (ATmaP) treatment. XPS, contact angle and adhesion test (pull off) results were acquired over a one year period to determine the changes in the elemental composition, surface energy and adhesion strength respectively over time. All surface-treated thermoplastic polyolefin samples showed a sharp decline in adhesion strength up to an ageing period totalling 6 months. The decline in adhesion strength was correlated with a decline in the nitrogen-containing constituents and C–O functional groups at the surface and a decline in surface energy for the flame & water-treated sample. There was no significant change in adhesion strength for all samples for ageing periods greater than 6 months. ATmaP-treated thermoplastic polyolefin outperformed the other two surface treatments in adhesion strength tests due to ATmaP retaining nitrogen-based functional groups (mainly nitrogen oxides) over the year long study. This retention of functionality allowed for a slower ageing process for ATmaP-treated surfaces in comparison to the other surface treatments. 相似文献