全文获取类型
收费全文 | 175篇 |
免费 | 5篇 |
国内免费 | 4篇 |
专业分类
化学 | 76篇 |
数学 | 1篇 |
物理学 | 6篇 |
综合类 | 101篇 |
出版年
2023年 | 2篇 |
2022年 | 19篇 |
2021年 | 18篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2012年 | 7篇 |
2011年 | 6篇 |
2010年 | 6篇 |
2009年 | 11篇 |
2008年 | 16篇 |
2007年 | 7篇 |
2006年 | 11篇 |
2005年 | 14篇 |
2004年 | 11篇 |
2003年 | 1篇 |
2002年 | 8篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有184条查询结果,搜索用时 46 毫秒
141.
Gaetano Cammilleri Andrea Pulvirenti Antonella Costa Stefania Graci Rosaria Collura Maria Drussilla Buscemi 《Natural product research》2020,34(1):158-161
AbstractA total of 1104 fish samples from markets of Sicily were analysed for the detection and species identification of Anisakidae nematodes. The preliminary analysis of the fish samples showed the presence of 2459 larvae. All the fish species revealed different prevalence of infestation, with a maximum of 100% for Lepidopus caudatus and a minimum of 4.5% in Sardina pilchardus. The 80% of the larvae examined by PCR-RFLP analysis belonged to Anisakis pegreffii species. The seasonal infestation trend of Anisakis was evaluated in all the fish sample examined. The results of the seasonal infestation trend showed a marked connection with the ecological aspects of the fish species examined. As far as we know, this work report for the first time important ecological aspects of Lepidopus caudatus specimens of South Mediterranean. This work could be useful to plan a seasonal fishing strategy aimed at reducing the health risks related to Anisakis. 相似文献
142.
MEI Yan-jun SHAO Da WANG Yu-hong YANG Zhong-kang YANG Wen-qing GAO Yue-song HE Shang-ming ZHENG Yi LI Ai-guo SUN Li-guang 《光谱学与光谱分析》2018,38(5):1640-1647
对采自中国南海的5个砗磲(1个现代砗磲、4个化石砗磲)进行了两种高分辨率Sr/Ca比值分析。电感耦合等离子体发射光谱法(ICP-OES)得到的Sr/Ca比值呈现出年周期变化,且与海表面温度呈现负相关关系,这表明Sr/Ca可作为良好的SST替代性指标。ICP-OES是测试砗磲壳体Sr/Ca常用的方法,但大量的样品需要钻样及预处理,相当耗时。而同步辐射X射线荧光分析(SR-XRF)可以克服这些缺点,它只需要前期的样品制备,并允许固态样品原位无损快速分析,具有高空间分辨率(微米级)、高灵敏度和多元素分析的特点。在本研究中,我们用SR-XRF方法测试砗磲样品化学元素的可行性。据查阅,目前尚未有类似的相关研究文献。本文实验结果显示SR-XRF 数据能够揭示元素含量及其比值变化。且SR-XRF测得的砗磲Sr/Ca比值与ICP-OES分析方法测得的Sr/Ca通过相关统计分析发现其显著性水平p值(5个砗磲样品的p值均<0.05)非常显著,表明高分辨率SR-XRF测得的砗磲Sr/Ca比值在一定程度上代替ICP-OES分析方法的可能性非常大。SR-XRF方法在砗磲重建古气候领域有很大的应用前景。 相似文献
143.
Wei‐Guang Shan You‐Min Ying Hai‐Ning Yu Wen‐Hong Liu Zha‐Jun Zhan 《Helvetica chimica acta》2010,93(4):772-776
Cultivation of the fungus Penicillium spp. HS‐3, an endophytic fungus from the stems of Huperzia serrata, led to the isolation of a new diketopiperazine alkaloid, named as tryhistatin ( 1 ), together with three known ones, 2 – 4 , all of which share a similar backbone. The structure of 1 was established by detailed interpretation of the 1D‐ and 2D‐NMR spectra, and HR‐ESI‐MS data. Furthermore, 1D‐ and 2D‐NMR experiments were employed to elucidate the structure of 2 which was deduced previously only on the basis of the LC/MS method. In this article, we confirmed the correctness of the previously reported structure and made a complete assignment of the NMR signals of 2 for the first time. 相似文献
144.
Fabrication of a novel capacitive immunosensor based on grafted ethylene diamine and self-assembled gold nanoparticle monolayer on glassy carbon electrode for the detection of Salmonella spp. is described for the first time. In the present study, the Salmonella spp. monoclonal antibodies (denoted as McAbs) was immobilized on gold nanoparticles. Interaction of McAbs and Salmonella spp. was detected directly using the electrochemical impedance spectroscopy (EIS) technique. The experimental results showed that the concentration of antigen was measured through the relative change in capacitance in the corresponding specific binding of Salmonella spp. and McAbs. Under the optimized conditions, the relative changes in capacitance were proportional to the logarithmic values of Salmonella spp. concentrations in the range of 1.0 × 102 to 1.0 × 105 CFU mL−1 (r = 0.991) with the detection limit of 1.0 × 102 CFU mL−1. The stability of proposed immunosensor could be estimated by determining the relative change in capacitance, which remained almost the same in two months and decreased gradually to 85.3% of initial value after four months’ storage. The used immunosensor could be regenerated repeatedly by immersing in glycine-HCl buffer solution (pH 2.8). Finally, the proposed immunosensor was successfully used for the detection of Salmonella spp. in lab-processed commercial pork samples. 相似文献
145.
Bulbus Fritillariae (BF), referred to the bulbs of several Fritillaria species (Liliaceae), is a commonly used antitussive and expectorant herb in traditional Chinese medicine (TCM). Due to the complexity of BF botanical origin in the herbal markets, it is urgently needed to develop a reliable method for species identification. Previous studies based on morphological and histological as well as molecular biological techniques have respective limitations. For the purpose of finding a possible discriminant method among Fritillaria species, 27 steroidal alkaloids in 17 Fritillaria species and 12 BF-containing compound formulas were identified and characterized by a high-performance liquid chromatography with mass spectrometry (HPLC-MS) method. The estimated relative composition of steroidal alkaloids was used to carry out a chemotaxonomical study on Fritillaria species by means of hierarchial cluster analysis. In addition, the characteristic occurring patterns of the examined bases were compared in an effort to distinguish the botanical origin of BF-containing compound formulas. The results demonstrated that the qualitative and quantitative differences in steroidal alkaloids were useful not only for chemotaxonomy in some medicinal Fritillaria species but also for species identification in compound formulas. The described method has important implications in quality control of BF-containing TCM preparations, allowing for the prevention of BF confusion, and also revealing the possible presence of adulteration. 相似文献
146.
相思树聚戊糖含量近红外光谱分析模型的建立及修正 总被引:4,自引:0,他引:4
建立适应不同产地相思树化学组分含量的近红外光谱分析模型对预测木材化学组分含量具有重要的意义。用常规化学法测量了取自广西78个和福建33个相思树样品的聚戊糖含量,并结合近红外光谱数据用偏最小二乘法建立了广西相思树聚戊糖含量的近红外光谱模型。校正模型的决定系数R2cv为0.947,内部交叉验证均方差RMSECV为0.464,验证模型Rv2al为0.925,RMSEP为0.455。为了扩大模型的适用范围,用福建不同数量样品对该模型进行修正。结果表明:在广西模型的基础上加入一个有代表性的福建样品就能大大降低直接用广西模型预测福建样品的误差。加入3个有代表性的福建样品后能够得到较好的模型。用该模型预测未参加建模的福建样品,预测模型的Rv2al为0.904,RMSEP为0.759。用4组(每组3个样)不同的福建样品修正广西模型,用固定的20个未参与修正广西模型的样品来验证,预测误差略有不同,表明样品的选择在一定程度上影响着修正模型的质量。 相似文献
147.
《Analytical letters》2012,45(16):2487-2495
A reversed-phase high-performance liquid chromatographic (HPLC) method was developed and validated for the determination of aucubin in Plantago lanceolata. The analyses were carried out on Zorbax SB-C18 column with an aqueous phosphoric acid and acetonitrile gradient. The correlation coefficient of calibration curve showed good linearity (r > 0.9995), with average recoveries between 96.7 and 104.5%. The developed method was applied for quantification in P. atrata, P. bellardii, P. coronopus, P. holosteum, P. reniformis, and P. schwarzenbergiana. The aucubin content in plant extracts was compared by HPLC, HPTLC, and LC-ESI-MS techniques and no significant differences between the conducted methods were observed. 相似文献
148.
Musarat Amina Perwez Alam Samerah A. Al-Hwaity Nada S. Al-Rashidi 《Natural product research》2018,32(7):804-809
We report isolation of a new sesquiterpene (compound 2: plectranol A) along with three known compounds (1: maaliol, 3: penduletin and 4: chrysosplenol D) from the aerial parts of Plectranthus cylindraceus Hoechst. Ex. Benth ethyl acetate extract (PCEAE). Their structures were established by UV, IR, NMR (1H & 13C), HRESIMS and HSQC methods. The MTT cell proliferation assay of the compounds and the extract performed on human breast, skin and cervical cancer cell lines showed high toxicity, and their IC50 (μg/mL) values were determined. The validated HPTLC analyses of maaliol and PCEAE (method I) and, penduletin, chrysosplenol D and PCEAE (method II) furnished sharp and compact peaks. The estimated high contents (μg/mg) of maaliol (17.06), penduletin (39.36) and chrysosplenol D (31.66) in PCEAE approved the plant’s cytotoxic property. Since, P. cylindraceus contains a variety of cytotoxic terpenoids and flavonoids; our data warrant its further phytochemical and biological characterisation towards developing promising anti-cancer drugs. 相似文献
149.
Marguérite Kamdem Simo Mireille Dongmo Nguepi Modeste Lambert Sameza Rufin Kouipou Toghueo Fabrice Boyom Fekam 《Natural product research》2018,32(17):2092-2095
The free-radical scavenging activity of ethanolic and methanolic extracts of leaves, stems and roots of Annona muricata, Monodora tenuifolia, Uvaria comperei, Uvaria muricata and Xylopia africana was evaluated using DPPH and ORAC assays. Further, phytochemical analysis, total phenolic and total flavonoid contents were also determined. Moreover, the antifungal activity of extracts was studied. The findings indicated that A. muricata and U. comperei extracts own antiradical activities and moderate antifungal properties. 相似文献
150.
本文根据酯酶、过氧化物酶同工酶的酶带数、Rf,累积值,以及籽粒糊化温度级别,对亚洲栽培稻7个生态型的56个品种进行了WordMethod离差平方和聚类分析,结果表明:56个品种可分为2类8群:I类中以Aman,Tjere,Bulu生态型品种为Ⅱ类中以Boro,Gundil,Aus生态型品种为主.Aman,Bulu,Boro,Gundil因遗传分化程度较低,分布相对集中,基本上形成了以各生态型品种为主导的群,Aus,Tjere,Upland生态型品种几乎散布于各个群中.根据类群的划分及生态型在类群中所占的品种数,可以推测:同一类的Aman,Tjere与Bulu,Aus,Boro和Gundil间的亲缘关系相对接近. 相似文献