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   152篇
  免费   4篇
  国内免费   2篇
化学   107篇
晶体学   2篇
力学   2篇
数学   35篇
物理学   12篇
  2024年   1篇
  2023年   2篇
  2022年   13篇
  2021年   12篇
  2020年   3篇
  2019年   7篇
  2018年   5篇
  2017年   2篇
  2016年   5篇
  2015年   4篇
  2014年   9篇
  2013年   15篇
  2012年   15篇
  2011年   10篇
  2010年   7篇
  2009年   8篇
  2008年   5篇
  2007年   3篇
  2006年   4篇
  2004年   2篇
  2003年   4篇
  2002年   1篇
  2000年   3篇
  1998年   1篇
  1997年   2篇
  1996年   2篇
  1995年   3篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1990年   3篇
  1988年   1篇
  1982年   1篇
  1979年   1篇
排序方式: 共有158条查询结果,搜索用时 15 毫秒
81.
Journal of Solid State Electrochemistry - Metal sulfide and oxides have drawn interest as economical substitutes to noble metal catalysts due to their ability for oxygen evolution reaction (OER)...  相似文献   
82.
Honey is a well-known natural sweetener and is rich in natural antioxidants that prevent the occurrence of oxidative stress, which is responsible for many human diseases. Some of the biochemical compounds in honey that contribute to this property are vitamins and phenolic compounds such as phenolic acids and flavonoids. However, the extent to which these molecules contribute towards the antioxidant capacity in vitro is inconsistently reported, especially with the different analytical methods used, as well as other extrinsic factors that influence these molecules’ availability. Therefore, by reviewing recently published works correlating the vitamin, total phenolic, and flavonoid content in honey with its antioxidant activities in vitro, this paper will establish a relationship between these parameters. Based on the literature, vitamins do not contribute to honey’s antioxidant capacity; however, the content of phenolic acids and flavonoids has an impact on honey’s antioxidant activity.  相似文献   
83.
Dynamic light scattering (DLS) measurements have been performed at 30 degrees C to see the effects of additives on the microstructure of gemini alkanediyl-alpha,omega-bis(dimethylcetylammonium bromide) surfactants, (Br-, n-C16H33N+Me2-(CH2)s-Me2- N+n-C16H33, Br-, 16-s-16, where s = 4, 5, 6). In pure aqueous solutions, the hydrodynamic diameter, Dh, was found to increase rapidly with geminis in comparison to their monomeric counterpart cetyltrimethylammonium bromide (n-C16H33N+Me3, Br-, CTAB) on increasing surfactant concentration. The additives considered in the present study are n-alcohols (C4-C6OH) and n-hexylamine (C6NH2) on the micellar growth of 0.03 M 16-4-16 in the presence and absence of 0.001 M KBr. The presence of 0.001 M KBr or organic additives at lower concentrations singly or jointly has little effect on the micellar size. As the chain length of the additive increases, the size increases with the increase of additive concentration, the magnitude being substantial in the presence of 0.001 M KBr. However, for equal chain length additives (C6OH, C6NH2), the effect was greater for C6OH. In case of C6NH2, the value of Dh reaches to almost constancy when the concentration of the additive was increased. Increased effectiveness of additives in the presence of added salt (KBr) is discussed in light of electrostatic and hydrophobic forces operating in the solution, which are always responsible for growth processes.  相似文献   
84.
85.
A strain of Bacillus amyloliquefaciens KUB29 was identified by 16S ribosomal RNA sequencing (Genbank: MF772779.1). Production of thermostable protease, amylase and lipase were done by the isolated strain. The produced enzymes were partially purified by ammonium precipitation followed by dialysis process. Protease and lipase enzymes are effectively used in bio-oil extraction from proteinaceous sample followed by transesterification to produce methyl ester. Amylase enzyme is widely used in food and laundry industry. The produced enzymes are active at thermophilic condition of 55 °C. Use of these enzymes in biofuel production process will make the process cleaner and greener.  相似文献   
86.
The surface excitation effect is investigated by using the quantum mechanical frame work of complex self-energy of electrons which interact with a bounded semi-infinite medium. In the self-energy formalism, differential inverse inelastic mean free path (DIIMFP) has contributions from bulk and surface plasmons. Monte Carlo simulation of the interaction of electrons with a solid medium and surface has been performed. The surface excitation parameter (SEP) is then obtained from the simulated reflection electron energy loss spectroscopy (REELS) spectra. The calculated SEP results by Monte Carlo simulation are compared with the previous calculations of total surface excitation probability, which was estimated by a numerical integration of surface term of DIIMFP. The contribution merely due to surface excitations towards REELS spectra is extracted by subtracting the two Monte Carlo simulated REELS spectra that based on the two models of electron inelastic scattering, i.e. a full surface model (SM) and a pure bulk model (BM). The surface excitations found to be significant at low energy losses and diminish at higher energy losses whereas the bulk plasmon contributions show opposite behavior and are negligible at lower energy losses. The average number of surface excitations is then evaluated by the computation of ratio of the integrated surface contribution to the elastic peak. The calculated results for Ag are found to be reasonably in agreement with our previous results for total probability of surface excitations and other reported experimental data for SEP. Surface correction factor (SCF) is calculated using SEP for several metals and is compared with the reported ratio of SCF with Ni sample as reference.  相似文献   
87.
Generally, the bioconversion of lignocellulolytics into a new biomolecule is carried out through two or more steps. The current study used one-step bioprocessing of date palm fronds (DPF) into citric acid as a natural product, using a pioneer strain of Trichoderma harzianum (PWN6) that has been selected from six tested isolates based on the highest organic acid (OA) productivity (195.41 µmol/g), with the lowest amount of the released glucose. Trichoderma sp. PWN6 was morphologically and molecularly identified, and the GenBank accession number was MW78912.1. Both definitive screening design (DSD) and artificial neural network (ANN) were applied, for the first time, for modeling the bioconversion process of DPF. Although both models are capable of making accurate predictions, the ANN model outperforms the DSD model in terms of OA production, as ANN is characterized by a higher value of R2 (0.963) and validation R2 (0.967), and lower values of the RMSE (13.44), MDA (11.06), and SSE (9749.5). Citric acid was the only identified OA as was confirmed by GC-MS and UPLC, with a total of 1.5%. In conclusion, DPF together with T. harzianum PWN6 is considered an excellent new combination for citric acid biosynthesis, after modeling with artificial intelligence procedure.  相似文献   
88.
We generalize the main result of an earlier paper by the authors (Exponentiation in power series fields, Proc. Amer. Math. Soc. 125 (1997), 3177-3183) concerning the convex embeddings of a chain in a lexicographic power . For a fixed non-empty chain , we derive necessary and sufficient conditions for the existence of non-empty solutions to each of the lexicographic functorial equations

, (\Delta ^{\Gam... ...Gamma \mbox{ and } (\Delta ^{\Gamma})^{<0} \simeq \Gamma\;.\end{displaymath}">

  相似文献   

89.
We describe the valuation theoretic properties of the Hardy fields associated to models of , where T is the theory of a polynomially bounded o-minimal expansion of the reals and is the real exponential function. We deduce that has levels with parameters and is exponentially bounded. We establish a maximality property of , the Hardy field of the expansion by the restricted analytic functions and power functions. Received: 10 July 2000 ; in final form: 15 April 2002/Published online: 24 February 2003 RID="*" ID="*" This paper was written while both authors were partially supported by a Canadian NSERC research grant.  相似文献   
90.
Herein, we report the B(C6F5)3-catalyzed E-selective isomerization of alkenes. The transition-metal-free method is applicable across a diverse array of readily accessible substrates, giving access to a broad range of synthetically useful products containing versatile stereodefined internal alkenes. The reaction mechanism was investigated by using synthetic and computational methods.  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