全文获取类型
收费全文 | 9698篇 |
免费 | 1708篇 |
国内免费 | 1465篇 |
专业分类
化学 | 6005篇 |
晶体学 | 81篇 |
力学 | 384篇 |
综合类 | 83篇 |
数学 | 786篇 |
物理学 | 2508篇 |
无线电 | 3024篇 |
出版年
2024年 | 28篇 |
2023年 | 252篇 |
2022年 | 352篇 |
2021年 | 401篇 |
2020年 | 435篇 |
2019年 | 471篇 |
2018年 | 373篇 |
2017年 | 333篇 |
2016年 | 478篇 |
2015年 | 543篇 |
2014年 | 600篇 |
2013年 | 742篇 |
2012年 | 861篇 |
2011年 | 781篇 |
2010年 | 565篇 |
2009年 | 606篇 |
2008年 | 636篇 |
2007年 | 524篇 |
2006年 | 502篇 |
2005年 | 451篇 |
2004年 | 350篇 |
2003年 | 365篇 |
2002年 | 437篇 |
2001年 | 363篇 |
2000年 | 238篇 |
1999年 | 193篇 |
1998年 | 166篇 |
1997年 | 107篇 |
1996年 | 112篇 |
1995年 | 81篇 |
1994年 | 75篇 |
1993年 | 69篇 |
1992年 | 98篇 |
1991年 | 65篇 |
1990年 | 56篇 |
1989年 | 33篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 26篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
1959年 | 2篇 |
1957年 | 2篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
991.
使用低、高温两步法生长的高质量Ge薄膜作为缓冲层,在Si(001)衬底上采用分子束外延法生长出Ge0.975Sn0.025合金薄膜.X射线双晶衍射和卢瑟福背散射谱等测试结果表明,Ge0.975Sn0.025合金薄膜具有很好的晶体质量,并且没有发生Sn表面分凝.另外,Ge0.975Sn0.025合金薄膜在500 ℃下具有很好的热稳定性,有望在Si基光电器件中得到应用.
关键词:
GeSn
Ge
分子束外延
外延生长 相似文献
992.
设计了一种领结形中空表面等离子体波导.采用频域有限差分法,对这种波导所支持的基模的能流密度分布、有效折射率、传播长度和模式面积随几何结构参数和工作波长的依赖关系进行了分析.结果表明,沿纵向的能流主要分布在两个上下突起所形成的中间区域.通过调整几何参数及工作波长,可以调节模式的有效折射率、传播长度和模式面积.在工作波长确定的条件下,有效折射率随突起半径的增大呈减小趋势,而传播长度和模式面积则随着突起半径的增大呈增大趋势,四个角上的圆弧半径对波导的传输特性有微调作用,左右扇形区域的半径对波导的传输特性有较明显
关键词:
集成光学
光波导
表面等离子体波导 相似文献
993.
A Mach-Zehnder structure with modulation in one arm and dispersive time delay in the other is proposed to implement highly flexible single-bandpass chirped microwave photonic filters based on broadband optical sources. Both the amplitude response and the time delay slope can be fully reconfigured via control of the optical spectra and dispersion. The passband can also be widely tuned without changing the shape. A chirped filter with a bandwidth of ~4?GHz, a delay slope of ~-0.6?ns/GHz, and a tunability up to 40?GHz is demonstrated experimentally. 相似文献
994.
We propose a novel structure of a photonic RF phase shifter based on the vector-sum principle. The optical signal with quadrature double-sideband modulation passes through a dual-output Mach-Zehnder interferometer (MZI), and the two outputs are differentially detected. Two phase-quadrature RF terms are generated, and their amplitudes can be controlled in a triangularly complementary way by changing the phase of the MZI. A full tuning range of 0°-360° at 14?GHz is demonstrated experimentally accompanied by nearly constant RF amplitude. The validity of using our scheme in all-optical RF phase modulation is also verified. 相似文献
995.
Two kinds of nano TiO2-polyacrylate hybrid dispersions, TBM-w and TBM-e were synthesized by in-situ suspension polymerization and solution polymerization respectively, in order to fix the nano TiO2 on fabrics. The photocatalytic self-cleaning fabrics have received much attention in recent years for its water-saving and environment-protection advantages. However, the fixation of the photocatalyst on fabrics is still a key problem that inhibits industrialization of these eco-friendly fabrics. The cotton fabric was treated by the two hybrid dispersions. The photocatalytic self-cleaning property was characterized. Infrared spectroscopy, burning loss test and thermogravimetry showed that some copolymer chains entangled with the nano TiO2. Transmission electron microscope illustrated that there was a polymeric layer on the surface of nano TiO2. The average diameter of TBM-w was smaller than that of TBM-e based on size analysis. The photocatalytic decoloration of the grape syrup indicated that the fabric with TiO2-polymer hybrid had excellent self-cleaning property. 相似文献
996.
Development of long-life-cycle tablet ceramic adsorbent for geosmin removal from water solution 总被引:1,自引:0,他引:1
Rongzhi ChenQiang Xue Zhenya Zhang Norio SugiuraYingnan Yang Miao LiNan Chen Zhao Ying Zhongfang Lei 《Applied Surface Science》2011,257(6):2091-2096
In this study, the tablet ceramic adsorbent (TCA), a silica/iron(III) oxide composite material, has been developed for geosmin (GSM) removal from the water solution. The physicochemical characteristics of TCA were examined with XRD, SEM, EDX and BET analyses. The sorption characteristics of GSM on TCA were investigated in a batch system. Attempts have been made to understand the adsorption kinetics, the effect of initial GSM concentration, solution pH, and reaction time.The batch experiments equilibrium data were well fitted to the Lagergren kinetic equation, which indicate the first-order nature adsorption. Over 82% of the GSM was removed by the TCA within 600 min at an initial concentration of 200 ng/L with 20 g/L of TCA dose. The batch and regeneration study indicated that the TCA is a cost-effective GSM adsorbent with sufficient mechanical strength to retain its physical integrity after long-time adsorption, and high regeneration performance for long-life-cycle application. Almost no second contamination (toxic sludge or leached iron) was observed after adsorption, and the gas resultant of thermal regeneration is harmless to atmospheric environment. 相似文献
997.
Jihui Lang Xue Li Jinghai Yang Lili Yang Yongjun Zhang Yongsheng YanQiang Han Maobin Wei Ming Gao Xiaoyan Liu Rui Wang 《Applied Surface Science》2011,257(22):9574-9577
ZnO quantum-dot chains codoped with Eu3+ and Er3+ were synthesized by the chemical precipitation method and the codoping effects on the structures, morphologies and optical properties of the powders were briefly investigated. The X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) results indicated the Eu3+ and Er3+ were incorporated into the crystal lattice of ZnO host. Transmission electron microscope (TEM) measurements showed the sizes of the ZnO quantum dots decreased with the increase of Eu3+ and Er3+ doping concentration, and the quantum-dot chains were formed by codoping with Eu3+ and Er3+. The green emissions in the photoluminescence spectra were attributed to 4f-4f of Er3+ inner shell 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions, and the characteristic red emissions of Eu3+ ions were attributed to the 5D0 → 7F1 and 5D0 → 7F2 transitions, respectively. Moreover, the red emission of the Eu3+ ions gradually decreased with the Er3+ ions doping concentration increased, which may be due to the different energy storage centers in the powders. 相似文献
998.
Xiaoyan Zhou Zhaozhu Zhang Xuehu MenJin Yang Xianghui XuXiaotao Zhu Qunji Xue 《Applied Surface Science》2011,258(1):285-289
A superhydrophobic polyaniline (PANI) film has been fabricated by using a facile one-step spraying method. The PANI was synthesized via in situ doping polymerization in the presence of perfluorooctanoic acid (PFOA) as the dopant. The water contact angle of this superhydrophobic surface reaches to 156°. Both the surface chemical compositions and morphological structures were analyzed. A granular morphology of PANI with a moderate amount of nanofibers was obtained. Moreover, a rapid surface wettability transition between superhydrophobicity and superhydrophilicity can be observed when it is doped with PFOA and de-doped with base. The mechanism for this tunable wettability has been discussed in detail. 相似文献
999.
In this paper, we show that the leakage current properties of BiFeO3 (BFO) thin films have been greatly improved by Zr-doping. In contrast, the magnetic properties of Zr-doped BFO films are affected as a weak ferromagnetism. Beyond the double-exchange interactions arising from the creation of Fe2+, we propose another simple model considering the replacement of the magnetically active Fe3+, time to time, by a non-active Zr4+, which is expected to induce a local ferromagnetic coupling rather than an antiferromagnetic one. 相似文献
1000.
Friction and wear behaviors of graphite-like carbon (GLC) films in aqueous environment were investigated by a reciprocating sliding tribo-meter with ball-on-disc contact. Film structures and wear scars were studied by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and a non-contact 3D surface profiler. A comprehensive wear model of the GLC film in aqueous environment was established, and two feasible approaches to control critical factor to the corresponding wear failure were discussed. Results showed that wear loss of GLC films in aqueous environment was characterized by micro-plough and local delamination. Due to the significant material loss, local delamination of films was critical to wear failure of GLC film in aqueous environment if the film was not prepared properly. The initiation and propagation of micro-cracks within whole films closely related to the occurrence of the films delamination from the interface between interlayer and substrate. The increase of film density by adjusting the deposition condition would significantly reduce the film delamination from substrate, meanwhile, fabricating a proper interlayer between substrate and GLC films to prevent the penetration of water molecules into the interface between interlayer and substrate could effectively eliminate the delamination. 相似文献