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   56篇
  免费   0篇
化学   41篇
力学   1篇
数学   4篇
物理学   10篇
  2023年   1篇
  2022年   2篇
  2021年   4篇
  2020年   2篇
  2019年   2篇
  2017年   1篇
  2015年   1篇
  2013年   3篇
  2012年   6篇
  2011年   5篇
  2010年   3篇
  2009年   1篇
  2007年   4篇
  2006年   1篇
  2005年   5篇
  2004年   3篇
  2002年   1篇
  2000年   1篇
  1999年   3篇
  1998年   1篇
  1996年   1篇
  1995年   1篇
  1992年   1篇
  1990年   1篇
  1986年   1篇
  1981年   1篇
排序方式: 共有56条查询结果,搜索用时 31 毫秒
1.
Summary We discuss a null experiment to search for the fifth force at ranges around 10 km. It is proposed to use a three-axis gravity gradiometer to measure the trace of the Earth gravity tensor from a freely falling elevator dropped by a balloon. The main error sources are considered to some extent. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.  相似文献   
2.
A new HPLC method with fluorescence detection using pyridinium hydrobromide perbromide as a post-column derivatising agent has been developed to determine aflatoxin M1 in milk and cheese. The detection limits were 1 ng/kg for milk and 5 ng/kg for cheese. The calibration curve was linear from 0.001 to 0.1 ng injected. The method includes a preliminary C18-SPE clean-up and the average recoveries of Aflatoxin M1 from milk and cheese, spiked at levels of 25-75 ng/kg and 100-300 ng/kg, respectively, were 90 and 76%; the precision (RSDr) ranged from 1.7 to 2.6% for milk and from 3.5 to 6.5% for cheese. The method is rapid, easily automatable and therefore useful for accurate and precise screening of aflatoxin M1 in milk and cheese.  相似文献   
3.
The cationic ring‐opening polymerization of 3,3‐bis(hydroxymethyl)oxetane (BHMO) and the copolymerization of BHMO with 3‐ethyl‐3‐(hydroxymethyl)oxetane (EOX) were studied. Medium molecular weight polymers (number‐average molecular weight ≈ 2 × 103) were obtained in bulk polymerization. Poly[3,3‐bis(hydroxymethyl)oxetane], as highly insoluble, was only characterized by gel permeation chromatography and NMR methods in the esterified form. Copolymers of BHMO and EOX that were slightly soluble in organic solvents were characterized in more detail. In a copolymerization from a 1:1 mixture, the comonomers were consumed at equal rates. Matrix‐assisted laser desorption/ionization time‐of‐flight analysis confirmed that a random 1:1 copolymer was formed. 13C NMR analysis indicated that in contrast to previously described homopolymers of EOX in which the degree of branching was limited, the homopolymers of BHMO were highly branched. This pattern was preserved in the copolymers; EOX units were predominantly linear, whereas BHMO units were predominantly branched. The copolymerization of BHMO with EOX provides, therefore, a route to multihydroxyl branched‐polyethers with various degrees of branching containing ? OH groups exclusively as ≡C? CH2? OH units. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1991–2002, 2002  相似文献   
4.
Taste plays an important role in processes such as food choices, nutrition status and health. Salivary proteins contribute to taste sensitivity. Taste reduction has been associated with obesity. Gender influences the obesity predisposition and the genetic ability to perceive the bitterness of 6-n-propylthiouracil (PROP), oral marker for food preferences and consumption. We investigated variations in the profile of salivary proteome, analyzed by HPLC-ESI-MS, between sixty-one normal weight subjects (NW) and fifty-seven subjects with obesity (OB), based on gender and PROP sensitivity. Results showed variations of taste-related salivary proteins between NW and OB, which were differently associated with gender and PROP sensitivity. High levels of Ps-1, II-2 and IB-1 proteins belonging to basic proline rich proteins (bPRPs) and PRP-1 protein belonging to acid proline rich proteins (aPRPs) were found in OB males, who showed a lower body mass index (BMI) than OB females. High levels of Ps-1 protein and Cystatin SN (Cyst SN) were found in OB non-tasters, who had lower BMI than OB super-tasters. These new insights on the role of salivary proteins as a factor driving the specific weight gain of OB females and super-tasters, suggest the use of specific proteins as a strategic tool modifying taste responses related to eating behavior.  相似文献   
5.
The international seafood trade is based on food safety, quality, sustainability, and traceability. Mussels are bio-accumulative sessile organisms that need regular control to guarantee their safe consumption. However, no well-established and validated methods exist to trace mussel origin, even if several attempts have been made over the years. Recently, an inorganic multi-elemental fingerprint coupled to multivariate statistics has increasingly been applied in food quality control. The mussel shell can be an excellent reservoir of foreign inorganic chemical species, allowing recording long-term environmental changes. The present work investigates the multi-elemental composition of mussel shells, including Al, Cu, Cr, Zn, Mn, Cd, Co, U, Ba, Ni, Pb, Mg, Sr, and Ca, determined by inductively-coupled plasma mass-spectrometry in Mytilus galloprovincialis collected along the Central Adriatic Coast (Marche Region, Italy) at 25 different sampling sites (18 farms and 7 natural banks) located in seven areas. The experimental data, coupled with chemometric approaches (principal components analysis and linear discriminant analysis), were used to create a statistical model able to discriminate samples as a function of their production site. The LDA model is suitable for achieving a correct assignment of >90% of individuals sampled to their respective harvesting locations and for being applied to counteract fraud.  相似文献   
6.
Curcumin, the dietary polyphenol isolated from Curcuma longa (turmeric), is commonly used as an herb and spice worldwide. Because of its bio-pharmacological effects curcumin is also called “spice of life”, in fact it is recognized that curcumin possesses important proprieties such as anti-oxidant, anti-inflammatory, anti-microbial, antiproliferative, anti-tumoral, and anti-aging. Neurodegenerative diseases such as Alzheimer’s Diseases, Parkinson’s Diseases, and Multiple Sclerosis are a group of diseases characterized by a progressive loss of brain structure and function due to neuronal death; at present there is no effective treatment to cure these diseases. The protective effect of curcumin against some neurodegenerative diseases has been proven by in vivo and in vitro studies. The current review highlights the latest findings on the neuroprotective effects of curcumin, its bioavailability, its mechanism of action and its possible application for the prevention or treatment of neurodegenerative disorders.  相似文献   
7.
A straightforward strategy for the synthesis and functionalization of polyurethanes (PUs) via the use of alkyne‐functionalized polytetrahydrofuran (PTHF) diols is described. The alkyne groups have been introduced into the PTHF chains by the cationic ring‐opening copolymerization of tetrahydrofuran and glycidyl propargyl ether. These PTHF prepolymers were combined with 1,4‐butanediol and hexamethylene diisocyanate for the synthesis of linear PUs with latent functionalization sites. The polyether segments of the PUs have then been coupled with several types of functionalized azides by the copper‐catalyzed azide‐alkyne “click” chemistry, for example with phosphonium containing azides for their antibacterial properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011  相似文献   
8.
Summary The experimental techniques developed to build a sensitive gravitational wave antenna can find application in many different fields of research. In the present paper we discuss briefly two experiments that we are developing in the Istituto Fisica Spazio Interplanetario of C.N.R. More precisely, a noncryogenic gravity gradiometer to be flown on the subsatellite of the TSS and a cryogenic force sensor which will be used to verify some recent results on the interaction of neutrino with matter are described. To speed up publication the proofs were not sent to the authors and were superivised by the Scientific Committee.  相似文献   
9.
The cationic copolymerization of ε‐caprolactone with ethylene oxide (EO) under the conditions of activated monomer polymerization, that is, with a low‐molecular‐weight diol as an initiator and BF3 etherate as a catalyst, was studied. To ensure the uniform composition of the resulting copolymers (telechelic oligodiols), the copolymerization was conducted with incremental feeding of the EO comonomer, which was more reactive in the cationic process. 1H NMR analysis of samples isolated at different stages of the copolymerization indicated that the average composition of the copolymer was indeed nearly constant over the course of the copolymerization. Matrix‐assisted laser desorption/ionization time‐of‐flight spectra of the products revealed, however, that for the same degree of polymerization, macromolecules containing different numbers of EO units were present. The observed distribution was compared with the distribution simulated under the assumption that the probability of incorporating a given unit depended only on the feed composition (nearly constant during the copolymerization). With this assumption, a good agreement between the observed and simulated spectra was obtained. This indicated that, even when the optimum conditions for the formation of a uniform copolymer were created, the individual macromolecules differed in composition because of the statistical character of the copolymerization. The results of differential scanning calorimetry analysis were compatible with such a conclusion; two melting peaks appeared on differential scanning calorimetry curves when a sample was heated immediately after fast cooling, and this may indicate the presence of different types of crystallites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3788–3796, 2005  相似文献   
10.
Multifunctional initiators for atom transfer radical polymerization (ATRP) are prepared by converting ditrimethylolpropane with four hydroxyl groups, dipentaerythritol with six hydroxyl groups, and poly(3‐ethyl‐3‐hydroxymethyl‐oxetane) with ~11 hydroxyl groups to the corresponding 2‐bromoisobutyrates or 2‐bromopropionates as obtained by reaction with acid bromides. Star polystyrene (PS) is produced by using these macroinitiators and neat styrene in a controlled manner by ATRP at 110 °C, employing the catalytic system CuBr and bipyridine. Mn up to 51,000 associated with narrow molecular weight distributions (PDI < 1.1) are obtained with conversions up to 32%. Hydrolysis of the star‐PS leads to linear chains having the expected Mn values. The star‐PS polymers based on dipentaerythritol degrade thermally in nitrogen in a two‐step process in which the first low‐temperature step involves scission of the ester linkages and the second step corresponds to the normal PS degradation. Star poly(methyl acrylates) with various cores are likewise prepared in a controlled manner by ATRP of methyl acrylate in bulk and in solution at 60–80 °C with the 1,1,4,7,7‐pentamethyldiethylene triamine ligand. Under these conditions, higher conversions were possible still maintaining low PDI signaling controlled star growth. Multiarm stars of poly(n‐butyl acrylate) and poly(n‐hexyl acrylate) with controlled characteristics have also been prepared. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3748–3759, 2005  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