全文获取类型
收费全文 | 1488篇 |
免费 | 161篇 |
国内免费 | 151篇 |
专业分类
化学 | 1033篇 |
晶体学 | 8篇 |
力学 | 84篇 |
综合类 | 18篇 |
数学 | 229篇 |
物理学 | 428篇 |
出版年
2024年 | 1篇 |
2023年 | 34篇 |
2022年 | 31篇 |
2021年 | 42篇 |
2020年 | 42篇 |
2019年 | 55篇 |
2018年 | 46篇 |
2017年 | 28篇 |
2016年 | 64篇 |
2015年 | 65篇 |
2014年 | 73篇 |
2013年 | 87篇 |
2012年 | 112篇 |
2011年 | 140篇 |
2010年 | 98篇 |
2009年 | 103篇 |
2008年 | 103篇 |
2007年 | 90篇 |
2006年 | 99篇 |
2005年 | 55篇 |
2004年 | 56篇 |
2003年 | 45篇 |
2002年 | 30篇 |
2001年 | 23篇 |
2000年 | 33篇 |
1999年 | 40篇 |
1998年 | 22篇 |
1997年 | 30篇 |
1996年 | 18篇 |
1995年 | 15篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 15篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有1800条查询结果,搜索用时 15 毫秒
41.
A novel cellulose-based polyampholyte derivative, carboxylethyl quaternized cellulose (CEQC), was homogeneously synthesized by introducing positively charged quaternary ammonium groups and negatively charged carboxyl groups to the backbone of cellulose. The structure and dilute solution properties of CEQCs were characterized with elemental analysis, FTIR, NMR, viscometer, light scattering and zeta-potential measurement. The nitrogen content and total degree of substituent of acylamino and carboxyl groups increased with an increase of the molar ratio of acrylamide to the anhydroglucose unit of quaternized cellulose (QC). The salt-resistance of CEQC was improved remarkably by introducing opposite charged carboxyl to the QC chains. The intrinsic viscosity of the prepared polyampholytes was found to be very sensitive to the pH of the solutions. CEQC-1, the sample with relative low content of carboxyl groups, behaved as a classical cationic polyelectrolyte. However, CEQC-2 and CEQC-3, the samples with higher content of carboxyl groups, displayed typical polyampholyte behavior, and the isoelectric points (IEP) were determined to be 5.0 and 3.8 respectively. This work provided a facile method for the synthesis of novel cellulose-based polyampholytes with different IEP. 相似文献
42.
Lei Wang Ruiquan Liu Cong Lv Junjun Ou Feng Liu Shangzhong Liu Min Wang Jiangchun Zhong 《Tetrahedron: Asymmetry》2013,24(4):173-177
Six optically active α-hydroxyl-β,γ-unsaturated acid esters 1a to 1f were synthesised, and they are significant moieties of the cerebrosides. The chiral intermediate alkynol 4 prepared by catalytic asymmetric addition had 99% ee, and which was converted into the target compounds 1a to 1f with high enantiomeric purity. 相似文献
43.
Jiping Huo Hongyun Wang Pei Hu Pingya Li Jinping Liu Ji Jiang 《Biomedical chromatography : BMC》2013,27(12):1701-1707
A specific, sensitive and rapid method based on high performance liquid chromatography coupled to tandem mass spectrometry (HPLC‐MS/MS) was developed for the determination of pseudo‐ginsenoside GQ in human plasma. Liquid–liquid extraction was used to isolate the analyte from biological matrix followed by injection of the extracts onto a C8 column with isocratic elution. Detection was carried out on a triple quadrupole tandem mass spectrometer (API‐4000 system) in multiple reaction monitoring mode using negative electrospray ionization. The mobile phase consisted of methanol–10 mm ammonium acetate (90:10, v/v) and the flow rate was 0.3 mL/min. The method was validated over the concentration range of 5.0–5000.0 ng/mL for plasma. Inter‐ and intra‐day precisions (relative standard deviation) were all within 15% and the accuracy (relative error) was ≤9.4%. The lower limit of quantitation was 5.0 ng/mL. The pseudo‐ginsenoside GQ was stable after 8 h at room temperature, 24 h at autosampler and three freeze–thaw cycles (from ?30 to 25 °C). The method was successfully applied to the pharmacokinetic study of pseudo‐ginsenoside GQ in healthy Chinese volunteers. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
44.
Combining the experimental research with the simulation calculation, the error evaluation for Zernike polynomials fitting (ZPF) based phase compensation of digital holographic microscopy (DHM) is performed. The obtained results show that the reconstructed phase with high precision can be obtained by ZPF phase compensation algorithm. Moreover, the phase error for ZPF based phase compensation algorithm increases with both the variation of object height and object transverse area, the larger variation of object height, the larger of phase error, and the larger of object transverse area, the faster increase of RMS phase error. To decrease the error of ZPF phase compensation algorithm, it is required to ensure one of the variations of object height and object transverse area to be a small value. Importantly, the proposed method supplies a useful tool for the error evaluation of phase compensation algorithm. 相似文献
45.
Advances in wide bandgap SiC for optoelectronics 总被引:1,自引:0,他引:1
Haiyan Ou Yiyu Ou Aikaterini Argyraki Saskia Schimmel Michl Kaiser Peter Wellmann Margareta K. Linnarsson Valdas Jokubavicius Jianwu Sun Rickard Liljedahl Mikael Syväjärvi 《The European Physical Journal B - Condensed Matter and Complex Systems》2014,87(3):1-16
Silicon carbide (SiC) has played a key role in power electronics thanks to its unique physical properties like wide bandgap, high breakdown field, etc. During the past decade, SiC is also becoming more and more active in optoelectronics thanks to the progress in materials growth and nanofabrication. This paper will review the advances in fluorescent SiC for white light-emitting diodes, covering the poly-crystalline doped SiC source material growth, single crystalline epitaxy growth of fluorescent SiC, and nanofabrication of SiC to enhance the extraction efficiency for fluorescent SiC based white LEDs. 相似文献
46.
Yanxin Chen Honbing Tang Jinping Liu Hui He 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(1):41-47
Development of the petroleum industry has resulted in increasing production of oil sludge, the disposal of which risks introducing
hazardous elements into the environment. In the frames of these studies the presence of the toxic metals arsenic, chromium
and zinc in oil sludge and the leachability of those toxins. Samples were obtained from a refinery plant in Sg Udang, Melaka
and from the Miri Crude Oil Terminal, Sarawak, both in Malaysia. k
0-Instrumental Neutron Activation Analysis was used to measure mass fractions of elements. The samples were packed and irradiated
in a TRIGA Mark II reactor. Mass fraction of arsenic in the oil sludge samples were found to be higher than the EPA pollutant
mass fraction limit; mass fractions of chromium and zinc were below of this limit. Samples were also tested for leachability,
which was found to be contributed to by controlled diffusion. Slow leachability of arsenic was found to be higher than the
EPA limit in these oil sludge samples, influenced by such factors as redox condition. It was found however, that the most
leachable of these elements in all samples from both sites was zinc, followed by arsenic and chromium, indicating that zinc
may present a more serious threat of environmental contamination than the other two. 相似文献
47.
Magnetic Co3O4 nanoparticles were prepared by using microporous regenerated cellulose films as sacrificial scaffolds. The cellulose macromolecules
and the porous structure of the films made them used as spatially confined reacting sites where Co(OH)2 nanoparticles could be synthesized in situ. When the cellulose matrix was removed by sintering at 500 °C, Co3O4 nanoparticles were obtained. XRD and XPS indicated that the prepared nanoparticles were pure Co3O4 without any impurity. TEM and SEM images revealed that the particle size of the nanoparticles was smaller than 100 nm. The
nanoparticles had weak ferromagnetic properties at 25 °C. Furthermore, the pronounced quantum confinement effects of the synthesized
nanoparticles have been observed, the optical bandgap energies determined were about 1.92 ~ 2.12 and 2.74 ~ 2.76 eV for O2− → Co3+ and O2− → Co2+ charge-transfer processes, respectively. Furthermore, the resulted Co3O4 nanoparticles behaved stable electrochemical performance with promising applications in the electrode for lithium ion battery. 相似文献
48.
Nanocomposite cellulose films with obvious magnetic anisotropy have been prepared by in situ synthesis of plate-like Fe2O3 nanoparticles in the cellulose matrix. The influence of the concentrations of FeCl2 and FeCl3 solutions on the morphology and particle size of the synthesized Fe2O3 nanoparticles as well as on the properties of the composite films has been investigated. The Fe2O3 nanoparticles synthesized in the cellulose matrix was γ-Fe2O3, and its morphology was plate-like with size about 48 nm and thickness about 9 nm, which was totally different from those
reported works. The concentration of FeCl2 and FeCl3 solution has little influence on the particle size and morphology of the Fe2O3 nanoparticles, while the content of Fe2O3 nanoparticles increased with the increase of the concentration of the precursor solution, indicating that porous structured
cellulose matrix could modulate the growth of inorganic nanoparticles. The unique morphology of the Fe2O3 nanoparticles endowed the composite films with obvious magnetic anisotropy, which would expand the applications of the cellulose
based nanomaterials. 相似文献
49.
Dr. Weihui Ou Dr. Binbin Zhou Junda Shen Dr. Tsz Wing Lo Prof. Dangyuan Lei Dr. Shengliang Li Jing Zhong Prof. Yang Yang Li Prof. Jian Lu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(17):6856-6859
Hot carriers (HCs) and thermal effects, stemming from plasmon decays, are crucial for most plasmonic applications. However, quantifying these two effects remains extremely challenging due to the experimental difficulty in accurately measuring the temperature at reaction sites. Herein, we provide a novel strategy to disentangle HCs from photothermal effects based on the different traits of heat dissipation (long range) and HCs transport (short range), and quantitatively uncover the dominant and potential-dependent role of photothermal effect by investigating the rapid- and slow-response currents in plasmon-mediated electrochemistry at nanostructured Ag electrode. Furthermore, the plasmoelectric surface potential is found to contribute to the rapid-response currents, which is absent in the previous studies. 相似文献
50.
Yiyi Ou Dr. Weijie Zhou Dr. Zece Zhu Dr. Fengkai Ma Dr. Rongfu Zhou Fang Su Dr. Lirong Zheng Prof. Li Ma Prof. Hongbin Liang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(52):24018-24024
Optical multiplexing based on luminescent materials with tunable color/lifetime has potential applications in information storage and security. However, the available tunable luminescent materials reported so far still suffer from several drawbacks of low efficiency or poor stability, thus restraining their further applications. Herein, we demonstrate a strategy to develop efficient and stable lanthanide coordination polymers (LCPs) with tunable luminescence as a new option for optical multiplexing. Their multicolor emission from green to red and naked-eye-sensitive green emission with tunable lifetime (from ca. 300 to ca. 600 μs) can be controlled by host differential sensitization and energy transfer between lanthanide ions. The quantum efficiencies of developed samples range from around 20 % to 46 % and the luminescence intensity/lifetime appear quite stable in polar solvents up to ten weeks. Furthermore, with the aid of inkjet printing and concepts of luminescence lifetime imaging and time-gated imaging, we illustrate their promising applications of information storage and security in spatial and temporal domains. 相似文献