全文获取类型
收费全文 | 284篇 |
免费 | 80篇 |
国内免费 | 29篇 |
专业分类
化学 | 192篇 |
晶体学 | 2篇 |
力学 | 7篇 |
数学 | 26篇 |
物理学 | 166篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 23篇 |
2021年 | 11篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 13篇 |
2017年 | 17篇 |
2016年 | 24篇 |
2015年 | 21篇 |
2014年 | 20篇 |
2013年 | 33篇 |
2012年 | 36篇 |
2011年 | 33篇 |
2010年 | 28篇 |
2009年 | 24篇 |
2008年 | 17篇 |
2007年 | 8篇 |
2006年 | 7篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1989年 | 1篇 |
排序方式: 共有393条查询结果,搜索用时 15 毫秒
61.
Mo(Ⅵ)-5-溴水杨基荧光酮-CTMAB显色反应的研究及应用 总被引:7,自引:0,他引:7
研究了新的三元配合物体系Mo(Ⅵ)-溴水杨基荧光酮-CTMAB显色反应的条件,最大吸收波长λmax在528nm,试剂λmax在468nm,对比度为60nm,ε528=1.47*10^5L.mol^-1.cm^-1。该体系选择性好,方法简便、快速,用于测定水样中微量钼,结果满意。 相似文献
62.
Shao-Fang Xing Man Lin Yu-Rong Wang Tuo Chang Wei-Ye Cui 《Natural product research》2020,34(5):651-658
AbstractThree novel dammarane-type saponins, 2α,3β,12β,20(S),24(S)-pentahydroxydammar-25-ene-3-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl-20-O-β-D-glucopyranoside (1, namely gypenoside J1), 2α,3β,12β,20(S),25-pentahydroxydammar-23-ene-3-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl-20-O-β-D-glucopyranoside (2, namely gypenoside J2) and 2α,3β,12β,20(S)-tetrahydroxydammar-25-en-24-one-3-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl-20-O-β-D-xylopyranosyl-(1→6)-β-D-glucopyranoside (3, namely gypenoside J3) along with one known gypenoside (gypenoside LVII) were isolated from the aerial parts of G. pentaphyllum using various chromatographic methods. Their structures were elucidated on the basis of IR, 1D- (1H and 13C), 2D-NMR spectroscopy (HSQC, HMBC and COSY), and mass spectrometry (ESI-MS/MS). Their activity was tested using CCK-8 assay. These four compounds showed little anti-cancer activity with IC50 values more than 100?μM against four types of human cancer lines. The effects of them against H2O2-induced oxidative stress in human neuroblastoma SH-SY5Y cells were evaluated and they all showed potential neuroprotective effects with 3.64–18.16% higher cell viability than the H2O2-induced model group. 相似文献
63.
Shijia Feng Tuo Wang Bin Liu Congling Hu Lulu Li Zhi‐Jian Zhao Jinlong Gong 《Angewandte Chemie (International ed. in English)》2020,59(5):2044-2048
A facile photoetching approach is described that alleviates the negative effects from bulk defects by confining the oxygen vacancy (Ovac) at the surface of BiVO4 photoanode, by 10‐minute photoetching. This strategy could induce enriched Ovac at the surface of BiVO4, which avoids the formation of excessive bulk defects. A mechanism is proposed to explain the enhanced charge separation at the BiVO4 /electrolyte interface, which is supported by density functional theory (DFT) calculations. The optimized BiVO4 with enriched surface Ovac presents the highest photocurrent among undoped BiVO4 photoanodes. Upon loading FeOOH/NiOOH cocatalysts, photoetched BiVO4 photoanode reaches a considerable water oxidation photocurrent of 3.0 mA cm?2 at 0.6 V vs. reversible hydrogen electrode. An unbiased solar‐to‐hydrogen conversion efficiency of 3.5 % is realized by this BiVO4 photoanode and a Si photocathode under 1 sun illumination. 相似文献
64.
65.
采用原子力显微镜(AFM)对改性前后材料表面粘附生长的角膜基质细胞的亲和力、三维形貌和力学性能进行了分析。结果显示,改性后材料的细胞亲和力有较大改善,且材料表面细胞三维形态更加正常,铺展更为舒展,与材料的接触面积较大。细胞力学性能分析也发现改性后材料表面细胞具有更高的粘附力和杨氏模量,以及更低的硬度,说明未改性p(HEMA-MMA)材料具有明显的细胞毒性,这种毒性作用导致在其表面生长的细胞的细胞骨架遭到破坏,细胞健康状态明显不如改性后材料表面细胞。因此,改性后的Col/bFGF-p(HEMA-MMA)更适合作为人工角膜材料使用。 相似文献
66.
<正>"One-step"method for the synthesis of secondary aliphatic amine substituted nitrobenzaldehyde was developed.In the presence of Pd catalyst,halogenated nitrobenzaldehyde could be smoothly coupled with secondary aliphatic amine to give the target product in hexamethylphosphamide(HMPT) media without the protection of aldehyde groups. 相似文献
67.
Yang Luo Tuo Li Fang Yu Tal Kramer Ileana M. Cristea 《Journal of the American Society for Mass Spectrometry》2010,21(1):34-46
Current biological studies have been advanced by the continuous development of robust, accurate, and sensitive mass spectrometric
technologies. The MALDI LTQ Orbitrap is a new addition to the Orbitrap configurations, known for their high resolving power
and accuracy. This configuration provides features inherent to the MALDI source, such as reduced spectra complexity, forgiveness
to contaminants, and sample retention for follow-up analyses with targeted or hypothesis-driven questions. Here we investigate
its performance for characterizing the composition of isolated protein complexes. To facilitate the assessment, we selected
two well characterized complexes from Saccharomyces cerevisiae, Apl1 and Nup84. Manual and automatic MS and MS/MS analyses readily resolved their compositions, with increased confidence
of protein identification compared with our previous reports using MALDI QqTOF and MALDI IT. CID fragmentation of singly-charged
peptides provided sufficient information for conclusive identification of the isolated proteins. We then assessed the resolution,
accuracy, and sensitivity provided by this instrument in the context of analyzing the isolated protein assemblies. Our analysis
of complex mixtures of singly-charged ions up to m/z 4000 showed that (1) the resolving power, inversely proportional to the square root of m/z, had over four orders of magnitude dynamic range; (2) internal calibration led to improved accuracy, with an average absolute
mass error of 0. 5 ppm and a distribution centered at 0 ppm; and (3) subfemtomole sensitivity was achieved using both CHCA
and DHB matrices. Additionally, our analyses of a synthetic phosphorylated peptide in mixtures showed subfemtomole level of
detection using neutral loss scanning. 相似文献
68.
Junhua Luo Fei Tuo Xiangzhong Kong 《Journal of Radioanalytical and Nuclear Chemistry》2011,288(1):143-148
The cross sections for formation of metastable state of 178Hf (178m2Hf, 574.215 keV, 31 y) and 179Hf (179m2Hf, 362.55 keV, 25.05 d) through reactions induced by 14.8 ± 0.2 MeV neutrons on natural hafnium were measured for the first
time. The monoenergetic neutron beam was produced via the 3H(d, n)4He reaction on ZF-300-II Intense Neutron Generator at Lanzhou University. Induced gamma activities were measured by a gamma-ray
spectrometer with high-purity germanium (HPGe) detector. Measurements were corrected for gamma-ray attenuations, random coincidence
(pile-up), dead time and fluctuation of neutron flux. The neutron fluence were determined by the cross section of 93Nb(n, 2n)92mNb reaction. The neutron energy in the measurement were by the cross section ratios of 90Zr(n, 2n)89m+gZr and 93Nb(n, 2n)92mNb reactions. 相似文献
69.
70.
Ghazaleh Taherzadeh Yuedong Yang Tuo Zhang Alan Wee‐Chung Liew Yaoqi Zhou 《Journal of computational chemistry》2016,37(13):1223-1229
Protein–peptide interactions are essential for all cellular processes including DNA repair, replication, gene‐expression, and metabolism. As most protein – peptide interactions are uncharacterized, it is cost effective to investigate them computationally as the first step. All existing approaches for predicting protein – peptide binding sites, however, are based on protein structures despite the fact that the structures for most proteins are not yet solved. This article proposes the first machine‐learning method called SPRINT to make Sequence‐based prediction of Protein – peptide Residue‐level Interactions. SPRINT yields a robust and consistent performance for 10‐fold cross validations and independent test. The most important feature is evolution‐generated sequence profiles. For the test set (1056 binding and non‐binding residues), it yields a Matthews’ Correlation Coefficient of 0.326 with a sensitivity of 64% and a specificity of 68%. This sequence‐based technique shows comparable or more accurate than structure‐based methods for peptide‐binding site prediction. SPRINT is available as an online server at: http://sparks-lab.org/ . © 2016 Wiley Periodicals, Inc. 相似文献