首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   99篇
  免费   2篇
  国内免费   1篇
化学   70篇
晶体学   1篇
数学   9篇
物理学   22篇
  2023年   1篇
  2022年   2篇
  2021年   1篇
  2020年   2篇
  2019年   1篇
  2018年   1篇
  2017年   2篇
  2016年   3篇
  2015年   2篇
  2014年   1篇
  2013年   6篇
  2012年   7篇
  2011年   11篇
  2010年   4篇
  2008年   1篇
  2007年   9篇
  2006年   7篇
  2005年   6篇
  2004年   5篇
  2003年   3篇
  2002年   1篇
  2001年   2篇
  1999年   1篇
  1995年   2篇
  1993年   1篇
  1992年   3篇
  1990年   1篇
  1989年   3篇
  1986年   1篇
  1985年   3篇
  1984年   2篇
  1980年   1篇
  1979年   1篇
  1977年   2篇
  1971年   2篇
  1968年   1篇
排序方式: 共有102条查询结果,搜索用时 31 毫秒
1.
The Voronoi diagram in a flow field is a tessellation of water surface into regions according to the nearest island in the sense of a “boat-sail distance”, which is a mathematical model of the shortest time for a boat to move from one point to another against the flow of water. The computation of the diagram is not easy, because the equi-distance curves have singularities. To overcome the difficulty, this paper derives a new system of equations that describes the motion of a particle along the shortest path starting at a given point on the boundary of an island, and thus gives a new variant of the marker-particle method. In the proposed method, each particle can be traced independently, and hence the computation can be done stably even though the equi-distance curves have singular points.  相似文献   
2.
Biologically important sites on intact porcine motilin (pMTL) were explored using its partial peptides. The partial peptides were synthesized using Fmoc (9-fluorenylmethyloxycarbonyl) solid phase methodology, and tested for the binding activity to motilin receptor and the smooth muscle contractile activity. The results were as follows: important residues for the contractile activity were found to be Phe1, Ile4, and Tyr7, and an open space existed beyond the N-terminus between motilin and its receptor. On the model of interaction between motilin and motilin receptor evolved from these results, the three points of interaction, due to Phe1, Ile4, and Tyr7, and the presence of an open space were expected. The motilin agonist and antagonist, designed on this model, will help the inquiry into motilin associated diseases.  相似文献   
3.
The microwave-assisted acid-digestion for the determination of metals in coal by ICP-AES was investigated, especially focusing on the necessity of adding HF. By testing five certified reference materials, BCR-180, BCR-040, NIST-1632b, NIST-1632c, and SARM-20, it was found that the two-stage digestion without HF (HNO3 + H2O2 was used) was very effective for the pretreatment of ICP-AES measurement. Both major metals (Al, Ca, Fe, and Mg) and minor or trace metals (Co, Cr, Cu, Mn, Ni, Pb, and Zn) in coal gave good recoveries for their certified or reference values. The possibility of ‘HF-memory effect’ was cancelled by the use of a set of vessels which had been never contacted with HF. Twenty-four Japanese standard coals (SS coals) were analyzed by the present method, and the concentrations of major metals measured by the present method provided very high accordance with those from the authentic JIS (Japanese Industrial Standard) method.  相似文献   
4.
A rapid method for the separation and purification of uridine diphosphate-glucuronosyltransferases (GT) was developed with the use of chromatofocusing on a high-performance liquid chromatograph. GT isoenzymes solubilized from hepatic microsomes of Wistar rats were separated on a Mono P column, a pre-packed column for chromatofocusing. Using 4-nitrophenol, testosterone and androsterone as substrates, four fractions with different GT activities were separated in a pH gradient from 9.5 to 7.0. Two isoenzymes, testosterone GT and androsterone GT were purified to apparent homogeneity. They were eluted at pH 8.9 and 8.0 and had subunit molecular weight values of 50000 and 52000, respectively. Approximately 10 mg of solubilized microsomal proteins was applied and the elution was completed within 2 h. Addition of N-nitrodiethylamine, an in vitro activator of GT activity, enhanced the GT activity toward 4-nitrophenol in the three fractions. This chromatographic analysis confirmed the absence of androsterone GT isoenzyme in LA Wistar rats, a mutant strain in terms of androsterone glucuronidation.  相似文献   
5.
Nonenzymatically glycated human serum albumin was incubated with ferric ion at 37 degrees C in 0.2 M phosphate buffer, pH 7.4, up to 30 days. In the incubation mixture, amino acids, tyrosine and phenylalanine, were detected, suggesting site specific cleavage of glycated human serum albumin.  相似文献   
6.
Syntheses of gem-difluorocyclopropyl ketones (3a–d) and their reactions with nucleophiles are described. Ring opening reactions of 3a,c and d with a methanolate and a thiolate anion took entirely different courses of bond scission of the cyclopropane ring.  相似文献   
7.
In this study, a fast and quantitative determination method for branched-chain amino acids (BCAAs), namely leucine, isoleucine, and valine, was developed using a pillar array column. A pillar array column with low-dispersion turns was fabricated on a 20?×?20-mm2 microchip using multistep ultraviolet photolithography and deep reactive ion etching. The BCAAs were fluorescently labeled with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), followed by reversed-phase separation on the pillar array column. The NBD derivatives of the three BCAAs and an internal standard (6-aminocaproic acid) were separated in 100 s. The calibration curves for the NBD-BCAAs had good linearity in the range of 0.4–20 μM, using an internal standard. The intra- and interday precisions were found to be in the ranges of 1.42–3.80 and 2.74–6.97 %, respectively. The accuracies for the NBD-BCAA were from 90.2 to 99.1 %. The method was used for the analysis of sports drink and human plasma samples. The concentrations of BCAAs determined by the developed method showed good agreements with those determined using a conventional high-performance liquid chromatography system. As BCAAs are important biomarkers of some diseases, these results showed that the developed method could be a potential diagnostic tool in clinical research.  相似文献   
8.
A detailed study of the Ni‐catalyzed [4+3+2] cycloaddition reaction between ethyl cyclopropylideneacetate and dienynes has been conducted, resulting in the development of a new method for the synthesis of compounds containing nine‐membered rings. We studied the reactivity of various dienynes, together with their substituent and conformational effects. The mechanism of the reaction was probed by examining the stoichiometric reactions of the Ni complexes and dienynes.  相似文献   
9.
10.
We have developed a novel synthetic method of phenylazomethine dendrons that uses 4,4'-methylenedianiline instead of 4,4'-diaminobenzophenone to synthesize the precursor of the phenylazomethine dendron and then oxidized the precursor to the next-generation dendron. For this method, the productivity of the dendrons has been significantly increased. Furthermore, as the synthesis of high-generation dendrons becomes easier, synthesis of DPA G5 was achieved. [structure--see text]  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号