全文获取类型
收费全文 | 254篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 190篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 43篇 |
物理学 | 27篇 |
出版年
2022年 | 15篇 |
2021年 | 9篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 10篇 |
2014年 | 7篇 |
2013年 | 16篇 |
2012年 | 17篇 |
2011年 | 15篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 20篇 |
2006年 | 13篇 |
2005年 | 13篇 |
2004年 | 12篇 |
2003年 | 9篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1975年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有265条查询结果,搜索用时 15 毫秒
251.
Antonio Junior Lepedda Gabriele Nieddu Silvia Rocchiccioli Pietro Fresu Pierina De Muro Marilena Formato 《Electrophoresis》2013,34(22-23):3227-3233
Bikunin is a plasma proteinase inhibitor often associated with inflammatory conditions. It has a half‐life of few minutes and it is rapidly excreted into urine as urinary trypsin inhibitor (UTI). UTI levels are usually low in healthy individuals but they can increase up to tenfold in both acute and chronic inflammatory diseases. This article describes a sensitive method for both direct UTI quantitation and structural characterization. UTI purification was performed by anion exchange micro‐chromatography followed by SDS‐PAGE. A calibration curve for protein quantitation was set up by using a purified UTI fraction. UTI identification and structural characterization was performed by Nano‐LC‐MS/MS analysis. The method was applied on urine samples from 9 patients with type 1 diabetes, 11 patients with type 2 diabetes, and 28 healthy controls, matched for age and sex with patients, evidencing higher UTI levels in both groups of patients with respect to controls (p < 0.001 and p = 0.001, respectively). Spearman's correlation tests highlighted no association between UTI levels and age in each group tested. Owing to the elevated sensitivity and specificity, the described method allows UTI quantitation from very low quantities of specimen. Furthermore, as UTI concentration is normalized for creatinine level, the analysis could be also performed on randomly collected urine samples. Finally, MS/MS analysis prospects the possibility of characterizing PTM sites potentially able to affect UTI localization, function, and pathophysiological activity. Preliminary results suggest that UTI levels could represent a useful marker of chronic inflammatory condition in type 1 and 2 diabetes. 相似文献
252.
Winfried Barth Michael Siegfried Kaiser Bettina Lommel Michael Maier Sascha Mickat Bernhard Schlitt Jutta Steiner Marilena Tomut Hartmut Vormann 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(2):1047-1053
For the proposed new heavy ion linac@GSI the installation of a carbon foil stripper section is under discussion. High duty factor as well as high current (but low duty factor) heavy ion beams were used for machine experiments. Long term tests were performed to check the carbon foil durability. Relevant beam parameters have been measured in three measurement campaigns. After beam testing stripper foils were analyzed with different offline methods. Additionally promising results of high current beam irradiation of rotating target wheels will be presented. In the transfer line to the SIS 18 the heavy ion beam is stripped to higher charge states in a thick carbon foil. The stripper foil is loaded with 3 % of the beam power. To avoid evaporation in a single beam pulse, the beam is rapidly swept over its width. Experiences collected during the last decade of foil stripper operation at GSI will be presented. 相似文献
253.
Andrea Bencini Antonio Bianchi Silvia Del Piero Claudia Giorgi Andrea Melchior Roberto Portanova Marilena Tolazzi Barbara Valtancoli 《Journal of solution chemistry》2008,37(4):503-517
The coordination features of a polyaza macrocycle, containing the diverse bipyridine unit 4,4′-(2,5,6,11,14-pentaaza[15]-[15](2,2′)-bipyridylophane
(L3), with Co(II) and Cd(II) have been studied in aqueous solution and in the aprotic solvent dimethylsulfoxide (DMSO). The study
was carried out at 298 K by means of potentiometric, spectrophotometric and calorimetric techniques. The formation of the
dinuclear species M2
L3 is observed for Co(II) both in water and in DMSO, whereas Cd(II) is able to form this type of dinuclear complex only in DMSO.
The FT-IR spectra of the mononuclear species ML3, formed in both solvents, provide evidence that the rigid structure of the polyaminic chain prevents metal ions from being
coordinated by all of the nitrogens of the macrocyclic cavity, in good agreement with the behavior suggested by the thermodynamic
parameters. The results are compared with those for the complexation of Co(II) and Cd(II) with similar polyazamacrocycles
containing a bipyridine unit directly inside the cavity. Semi-empirical calculations were also performed to obtain structural
information. 相似文献
254.
Zinellu A Sotgia S Usai MF Zinellu E Lepedda AJ Deiana L Formato M Carru C 《Analytical and bioanalytical chemistry》2008,391(8):2865-2868
We describe a new ultra-rapid capillary electrophoresis method with UV detection for analysis of the disaccharides obtained
after enzymatic depolymerization of plasma chondroitin sulfates. The free reducing groups of the released carbohydrate molecules
are derivatized with 2-aminoacridone by reductive amination in the presence of cyanoborohydride. The fluorotagged products
can be separated by short-end injection capillary electrophoresis in a capillary with an effective length of 10.2 cm. The
migration times of Δdi-0S and Δdi-4S were 0.95 and 1.81 min, respectively. We compared the proposed method with UV detection
to a reference CE-LIF assay by measuring plasma chondroitin sulfate in 94 subjects. The described assay for total plasma CS
measurement may, owing to the high throughput and the fast analytical times, be a good tool for routine studies both in research
and in clinical applications. 相似文献
255.
256.
dos Santos EO Meira M do Vale AE David JM de Queiróz LP David JP 《Natural product communications》2012,7(6):781-783
Two new ceramides were isolated from the bulbs of Lepidaploa cotoneaster (Willd. ex Spreng.) H. Rob. [Vernonia cotoneaster (Willd. ex Spreng.) Less.)], in addition to germanicol, beta-sitosterol, stigmasterol, 3-beta-O-beta-D-glucopyranosyl-sitosterol, lupeol, lupeoyl acetate and tiliroside. The structures of the new compounds were elucidated by spectral techniques (MS, 1H NMR, 13C NMR, HSQC, HMBC, DEPT, and TOCSY) and were compared with data reported in literature, and were established as 2S*,2'R*,3S*,4R*,11E)-N-[2'-hydroxyhenicosanoyl]-2-amino-nonadec-11-ene-1,3,4-triol (1) and (2S*,2'R*,3S*,4R*,8E)-N-[2'-hydroxytricosanoyl]-2-amino-nonadec-8-ene-1,3,4-triol (2). To establish the structure and to locate the double bond, the methyl ester of the fatty acid and dimethyl disulfide (DMDS) derivatives were prepared for both ceramides. 相似文献
257.
The reaction of the low-spin iron(III) complex [Fe(dmbpy)(CN)(4)](-) (1) with fully solvated cobalt(II) ions affords the cyanide-bridged heterobimetallic chain {[Fe(III)(dmbpy)(CN)(4)](2)Co(II)(H(2)O)(2)}(n) · 4nH(2)O (2), which exhibits intrachain ferromagnetic coupling and double slow relaxation of the magnetization. 相似文献
258.
Kajiwara T Katagiri K Hasegawa M Ishii A Ferbinteanu M Takaishi S Ito T Yamashita M Iki N 《Inorganic chemistry》2006,45(13):4880-4882
Dinuclear and cubane-shaped lanthanide cluster complexes containing EuIII)and TbIII were synthesized by step-by-step construction using p-tert-butylsulfonylcalix[4]arene as a cluster-forming ligand. The sulfonylcalixarene adopts a pinched-cone conformation in the dinuclear complexes and a cone conformation in the cubane complexes. Because the calixarene has a large pi-conjugate system expanding over the entire molecule, it behaves as a good antenna chromophore for UV and near-UV light, and a slight conformational change of the calixarene (from cone to pinched-cone and vice versa) has an effect on the energy levels of excited S1 and T1 states. As a result, selectivity is observed in the luminescent properties of dinuclear and cubane-shaped systems of EuIII and TbIII. 相似文献
259.
An efficient and simple method for the determination of furan in baby-food (vegetables and fruits) by solid phase micro-extraction-gas chromatography-mass spectrometry (SPME-GC-MS) was developed and validated. Experimental design was used to investigate the effects of temperature and time of extraction. The calculated regression model was used to find the experimental conditions providing the optimal SPME extraction yield. Validation was carried out in terms of limit of detection (LOD), limit of quantitation (LOQ), linearity, precision and trueness. LOD and LOQ values in the low ngkg(-1) were achieved, whereas linearity was established over two order of magnitude. Good precision was obtained both in terms of intra-day repeatability and between-day precision on two concentration levels (RSD% lower than 3.6%). Recovery values of 91.5+/-6.2% and of 96.1+/-1.3% (n=3) were calculated at 75 ngkg(-1) and 75 microgkg(-1) level. Finally, the applicability of the method to the determination of furan in a number of commercial and home-made baby-food samples was demonstrated. 相似文献
260.
Cristiana Lofrumento Marilena Ricci Luca Bachechi Denise De Feo Emilio Mario Castellucci 《Journal of Raman spectroscopy : JRS》2012,43(6):809-816
An extensive micro‐Raman spectroscopic study of prehistoric rock paintings found in Hararghe region, Ethiopia, was carried out, with the aim to evaluate the production skill of the local artist and the period of production of the discovered paintings. Attenuated Total Reflection Fourier Transform Infrared (ATR‐FTIR) Spectroscopy and Laser Induced Breakdown Spectroscopy (LIBS) were used as auxiliary techniques. Micro sampling were carried out on parts of red, white, black painting figures representing domestic and wild animals. The pigments used by artists were hematite for red color, calcite or gypsum for white color, and carbonaceous material for black coloration. A green pigment was also investigated; it resulted made of green earth. A consistent amount of Ca‐oxalate was found particularly on red samples as well as on the white ones. Former studies attributed oxalates origin to a biological substrate attack, whereas in the present case Ca‐oxalate is ascribed to the use of an organic stuff to spread properly the pigments on the substrate.Principal Component Analysis was performed on the hematite spectra; it evinced that the spectral features could be indicative of different sites and of the relative age.1These novel evaluations put into new perspective the knowledge about rock art pictorial technology of the Horn of Africa. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献