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111.
Background: Environmental contaminants, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other structurally related ‘environmental hormones’, exert their harmful biological effects through the Ah receptor signaling pathway. Several naturally occurring substances also bind to this receptor, but its natural role is still obscure. Tryptophan derivatives of the indolo[3,2-b]carbazole type, earlier suggested by us to be endogenous ligands for the receptor, should be a powerful tool in understanding receptor function. We therefore: set out to determine their identity.Results: The two tryptophan-derived Ah receptor ligands have been chemically analyzed and characterized by means of mass spectrometry, 1H NMR and 13C NMR. UV, infra-red and fluorescence spectra were also recorded. All data are in accordance with the two compounds being closely related indolo[3,2-b]carbazole derivatives. Evidence is presented that compound A (MW = 312) is the symmetrical 6,12-diformylindolo[3,2-b]carbazole, and compound B (MW = 284) is the monosubstituted 6-formylindolo[3,2-b]carbazole.Conclusions: The elucidation of the structures of the two high affinity Ah receptor ligands 6,12-diformylindolo[3,2-b]carbazole and 6-formylindolo[3,2-b]carbazole provides the necessary basis for further mechanistic studies of this important group of compounds, and will help in determining the natural role of the Ah receptor. 相似文献
112.
固体石蜡作粘合剂的纯碳糊电极的电化学活化及其应用于色氨酸的测定 总被引:6,自引:2,他引:6
研究了以固体石蜡作粘合剂的纯碳糊电极的电化学活主用于色氨酸直接测定的方法。活化后的电极对色氨酸的吸附能力大大增加,在HAc-NaC溶液中,于+0.3V富集后,于=1.01V出峰,用线扫伏安法测定时,二次微分溶电流,与色氨酸浓度在8-10μg/L范围内成线性;检测限可达2μg/L;2倍的酪氨酸和其它氨基酸不干扰,用于氨基酸酸芭物样品和合成血清样品中色氨酸的测定,相对标准偏差小于2%。 相似文献
113.
Yan Xiang Jiangju Si Qi Zhang Yang Liu Hong Guo 《Journal of polymer science. Part A, Polymer chemistry》2009,47(3):925-934
A novel series of artificial glycoprotein, peptide‐chitosan copolymers with secondary structural side chain have been synthesized by ring‐opening polymerization of L ‐tryptophan N‐carboxyanhydride under homogeneous conditions. Their chemical structures and polymerization degree (DP) were characterized by IR, 13C NMR, and XRD spectra. Distinctly secondary protein structure has been found in the poly‐L ‐tryptophan side chains of copolymers and with the lengthening of side chain (i.e., the increase of DP at the same time), its conformations could transfer from β‐sheet to α‐helix. The content of α‐helix reaches about 41% when DP of polytryptophan is 22. The solubility of graft copolymers in polar solvent strongly depends on the length of poly‐L ‐tryptophan side chains. Unique fluorescence emission at 360 nm has been observed in the glycopolymers and the intensity shows the positive‐correlation with the increasing of DP of polytryptophan. Importantly, the fluorescence effect can be quenched easily by the coordination with copper ions which provides the possibility on the biosensor design. In comparison with chitosan, glycopolymers also present impressively enhanced compressive strength and elastic modules when it is blended with epoxy E 44 to form epoxy‐copolymer hybrid resin. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 925–934, 2009 相似文献
114.
A high‐performance liquid chromatography (HPLC) method for assay of d ‐Lys6–GnRH contained in a microemulsion‐type formulation is described. The peptide is extracted from the microemulsion matrix and quantified using a two‐step gradient method. Separation from microemulsion compounds and potential peptide oxidation products was achieved on a Jupiter C18 column at 40°C, using a gradient of 10–35% CH3CN for peptide elution. The correlation of peak intensity measured at 220 nm and peptide concentration was linear over the range 2.5–60 µg/mL with a correlation coefficient of 0.9997 and a y‐intercept not significantly different from zero (p > 0.05). Intraday and interday variability of the assay was less than 5% for multiple injections of samples containing 7.5, 30 and 60 µg/mL. The lower limit of quantitation was calculated to be 0.38 µg/mL, and the lower limit of detection was 0.13 µg/mL. The assay was applied to samples that were stressed under physiological conditions (37°C, pH 7.4) over 4 days. Three degradation peaks were well resolved from the parent peptide, demonstrating the selectivity of the assay. Off‐line MALDI TOF mass spectrometry was applied to identify these degradation species as oxidation products of the peptide. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
115.
L. Patron G. Marinescu D. Culita L. Diamandescu O. Carp 《Journal of Thermal Analysis and Calorimetry》2008,91(2):627-632
The thermal stability of two amino acid-(tyrosine and tryptophan) coated magnetite and their corresponding precursors, [Fe2IIIFeII(Tyr)8]·9H2O and [Fe2IIIFeII(Trp)2(OH)4](NO3)2·8H2O (where tyrosine=Tyr and tryptophan=Trp), was analyzed in comparison with free amino acids. The complexes present a lower
thermal stability relative to the free ligand, due to the catalytic effect introduced by the iron cation and the presence
of NO3− groups. The presence of NO3− group determines also a different degradation’s stoichiometry of the amino acid anion comparative with the one expressed
by the free ligand molecule. The amino acid bonded to magnetite decomposes in two steps, its presence inducing an increasing
of γ-Fe2O3→Fe2O3 conversion temperature. 相似文献
116.
117.
荧光光谱法研究槲皮素与氨基酸的相互作用 总被引:1,自引:0,他引:1
采用荧光光谱法研究荧光活性物质槲皮素(Qct)与色氨酸(Try)、酪氨酸(Tyr)和苯丙氨酸(Phe)的相互作用.在pH 7.4的磷酸缓冲溶液(PBS)中,测得不同温度下的反应平衡常数(K)和结合摩尔比(n)及结合的热力学常数.槲皮素与游离的氨基酸间有较强的结合作用,且是自发进行.并由所得热力学常数确定了结合的作用力类型. 相似文献
118.
119.
Smaniotto A Comai S Bertazzo A Costa CV Allegri G Seraglia R Traldi P 《Journal of mass spectrometry : JMS》2006,41(7):921-930
The activity of tyrosinase and peroxidase + H2O2 in promoting melanogenesis from tryptophan (Trp) and 7-hydroxytryptophan (7-HTP) has been investigated. The reaction samples have been drawn at different reaction times and analysed by MALDI mass spectrometry. The data obtained showed that tryptophan undergoes, under tyrosinase and peroxidase action, an oligomerization process mainly due to the reaction of anthranilic acid (AA) and Trp. However, analysing the UV and fluorescence data, it is seen that the oligomers cannot belong to the melanin pattern, but their possible role in melanogenesis is not to be excluded. Once it reacts with the two enzymes, 7-hydroxytryptophan leads to dark brown products, indicating its possible role in melanin production. In contrast to what was observed in the case of 5-hydroxytryptophan, for which oligomers were constituted by 5-hydroxytryptophan (5-HTP) and 5-hydroxytryptamine (5-HT) units, the MALDI data indicate a sharply different behaviour for 7-HTP. In fact, in the case of 5-hydroxytryptophan, oligomerization takes place through the formation of 5-hydroxytryptamine and the oligomerization products are due to mixed 5-HTP-5-HT oligomers. In the case of 7-hydroxytryptophan, the formation of 7-hydroxytryptamine (7-HT) is also observed, but it does not seem to play any role; the only oligomerization products formed are due to the reaction of 7-hydroxytryptophan and AA. The data so obtained indicate that 7-hydroxytryptophan acts like an effective melanin precursor in the presence of both tyrosinase and peroxidase + H2O2. 相似文献
120.
Sample preparation is an important issue in analytical chemistry, and is often a bottleneck in chemical analysis. So, the major incentive for the recent research has been to attain faster, simpler, less expensive, and more environmentally friendly sample preparation methods. The use of auxiliary energies, such as heat, ultrasound, and microwave, is one of the strategies that have been employed in sample preparation to reach the above purposes. Application of electrical driving force is the current state-of-the-art, which presents new possibilities for simplifying and shortening the sample preparation process as well as enhancing its selectivity. The electrical driving force has scarcely been utilized in comparison with other auxiliary energies. In this review, the different roles of electrical driving force (as a powerful auxiliary energy) in various extraction techniques, including liquid-, solid-, and membrane-based methods, have been taken into consideration. Also, the references have been made available, relevant to the developments in separation techniques and Lab-on-a-Chip (LOC) systems. All aspects of electrical driving force in extraction and separation methods are too specific to be treated in this contribution. However, the main aim of this review is to provide a brief knowledge about the different fields of analytical chemistry, with an emphasis on the latest efforts put into the electrically assisted membrane-based sample preparation systems. The advantages and disadvantages of these approaches as well as the new achievements in these areas have been discussed, which might be helpful for further progress in the future. 相似文献