全文获取类型
收费全文 | 10354篇 |
免费 | 1547篇 |
国内免费 | 909篇 |
专业分类
化学 | 5709篇 |
晶体学 | 88篇 |
力学 | 492篇 |
综合类 | 36篇 |
数学 | 995篇 |
物理学 | 3051篇 |
无线电 | 2439篇 |
出版年
2024年 | 23篇 |
2023年 | 256篇 |
2022年 | 267篇 |
2021年 | 362篇 |
2020年 | 448篇 |
2019年 | 350篇 |
2018年 | 318篇 |
2017年 | 314篇 |
2016年 | 473篇 |
2015年 | 513篇 |
2014年 | 551篇 |
2013年 | 692篇 |
2012年 | 903篇 |
2011年 | 877篇 |
2010年 | 640篇 |
2009年 | 621篇 |
2008年 | 675篇 |
2007年 | 512篇 |
2006年 | 586篇 |
2005年 | 465篇 |
2004年 | 327篇 |
2003年 | 273篇 |
2002年 | 223篇 |
2001年 | 177篇 |
2000年 | 209篇 |
1999年 | 224篇 |
1998年 | 204篇 |
1997年 | 161篇 |
1996年 | 174篇 |
1995年 | 152篇 |
1994年 | 123篇 |
1993年 | 107篇 |
1992年 | 98篇 |
1991年 | 95篇 |
1990年 | 57篇 |
1989年 | 43篇 |
1988年 | 51篇 |
1987年 | 36篇 |
1986年 | 31篇 |
1985年 | 24篇 |
1984年 | 23篇 |
1983年 | 20篇 |
1982年 | 9篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1973年 | 8篇 |
1972年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
981.
The acid–base properties of nanoscopic water confined in the black soap films (BSFs), which were prepared from aqueous solutions of sodium dodecylsulphate (SDS) with the dye neutral red (NR) as a pH probe, were investigated using a combination of UV–vis and FTIR spectroscopy. For the SDS micellar solutions at pH 1.0–9.5 adjusted with HCl/NaOH solutions and at pH 9.4 with ammonium buffered solution, the aqueous core thicknesses in the corresponding BSFs ranged from 2.7 to 6.2 nm, and the nanoscopically confined water exhibits unusual buffer action resistant not only to acidic/alkaline solutions but also to standard buffer solution. In the heavily water-depleted confined zones, it is most likely that charge pairs in proton-transfer reactions could not be formed effectively and proton transfer was prohibited in the absence of sufficient solvating ability. Theoretical analyzes indicated that the buffer action of the nanoscopic water originated from the confinement effect of two charged surfaces of the BSFs. These results might inspire deeper understanding and further studies of biobuffering, enzyme superactivity, acid-catalyzed reactions, and Nafion fuel cell membranes. 相似文献
982.
低于1×10-6/℃的低压CMOS带隙基准电流源 总被引:1,自引:0,他引:1
提出了一种新颖的CMOS带隙基准电流源的二阶曲率补偿技术,通过增加一个运算跨导放大器(OTA),使带隙基准参考电路的电流特性与理论分析相符合,实现低温度系数(TC)的参考电流。该电路采用SMIC0.13μm标准CMOS工艺,可在1.2 V的电源电压下工作,有效面积为0.045 mm2。仿真结果表明,在-40~85℃温度范围内参考电流的温度系数为0.5×10-6/℃;当电源电压为1.1 V时,电路依然可以正常工作,电源电压调整率为1 mV/V。 相似文献
983.
984.
985.
Hong Yang Yeming Zhuang He Hu Xiaoxia Du Cuixia Zhang Xiangyang Shi Huixia Wu Shiping Yang 《Advanced functional materials》2010,20(11):1733-1741
Monodisperse silica‐coated manganese oxide nanoparticles (NPs) with a diameter of ~35 nm are synthesized and are aminated through silanization. The amine‐functionalized core–shell NPs enable the covalent conjugation of a fluorescent dye, Rhodamine B isothiocyanate (RBITC), and folate (FA) onto their surface. The formed Mn3O4@SiO2(RBITC)–FA core–shell nanocomposites are water‐dispersible, stable, and biocompatible when the Mn concentration is below 50 µg mL?1 as confirmed by a cytotoxicity assay. Relaxivity measurements show that the core–shell NPs have a T1 relaxivity (r1) of 0.50 mM ?1 s?1 on the 0.5 T scanner and 0.47 mM ?1 s?1 on the 3.0 T scanner, suggesting the possibility of using the particles as a T1 contrast agent. Combined flow cytometry, confocal microscopy, and magnetic resonance imaging studies show that the Mn3O4@SiO2(RBITC)–FA nanocomposites can specifically target cancer cells overexpressing FA receptors (FARs). Findings from this study suggest that the silica‐coated Mn3O4 core–shell NPs could be used as a platform for bimodal imaging (both magnetic resonance and fluorescence) in various biological systems. 相似文献
986.
硅片化学机械抛光(CMP)是机械作用与化学作用相结合的技术,硅片表面的化学反应层主要是由抛光液中磨料的机械作用去除,磨粒对硅片表面的摩擦和划擦对硅片表面材料的去除起着重要作用。磨粒在硅片表面上的划痕长度直接影响硅片表面的材料去除率。本文首先在实验结果的基础上分析了硅片CMP过程中磨粒的分布形式,然后根据运动学和接触力学理论,分析了硅片、磨粒及抛光垫三者之间的运动关系,根据磨粒在硅片表面上的运动轨迹长度,得出了材料去除率与抛光速度之间的关系,该分析结果与实验结果一致,研究结果可为进一步理解硅片CMP的材料去除机理提供理论指导。 相似文献
987.
We demonstrate a two-dimensional(2D) full-band ensemble Monte-Carlo simulator for heterostructures, which deals with carrier transport in two different semiconductor materials simultaneously as well as at the boundary by solving self-consistently the 2D Poisson and Boltzmann transport equations(BTE).The infrastructure of this simulator,including the energy bands obtained from the empirical pseudo potential method,various scattering mechanics employed,and the appropriate treatment of the carrier transport... 相似文献
988.
The Asymptotic Waveform Evaluation (AWE) technique is an extrapolation method that provides a reduced-order model of linear
system and has already been successfully used to analyze wideband electromagnetic scattering problems. As the number of unknowns
increases, the size of Method Of Moments (MOM) impedance matrix grows very rapidly, so it is a prohibitive task for the computation
of wideband Radar Cross Section (RCS) from electrically large object or multi-objects using the traditional AWE technique
that needs to solve directly matrix inversion. In this paper, an AWE technique based on the Characteristic Basis Function
(CBF) method, which can reduce the matrix size to a manageable size for direct matrix inversion, is proposed to analyze electromagnetic
scattering from multi-objects over a given frequency band. Numerical examples are presented to illustrate the computational
accuracy and efficiency of the proposed method. 相似文献
989.
基于TDM/TDMA的PON系统若不通过统一的管理控制会产生上行数据冲突,为解决上行数据冲突,测距技术是PON系统的关键技术。文章介绍了测距技术的原理和分类,详细分析了目前EPON和GPON系统所采用的测距原理、时延补偿机制及具体的实现过程。最后,提出PON系统测距中有关冲突避免算法还有待进一步的研究,需要继续跟踪研究。 相似文献
990.
This paper is concerned with the problem of robust l
2–l
∞ filter design for a class of uncertain switched time-delay systems based on a switched Lyapunov functional. The parametric
uncertainties are assumed to be time varying but norm bounded. The purpose is to design a switched filter such that, for all
admissible uncertainties, the resulting filtering error system is robustly stable and satisfies a prescribed l
2–l
∞ performance level. By introducing some extra matrices, a desired filter can be constructed by solving certain linear matrix
inequalities (LMIs). A numerical example is given to demonstrate the effectiveness of the proposed method. 相似文献