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   127篇
  免费   10篇
化学   110篇
力学   1篇
数学   11篇
物理学   15篇
  2023年   1篇
  2022年   6篇
  2021年   5篇
  2020年   8篇
  2019年   11篇
  2018年   5篇
  2017年   7篇
  2016年   10篇
  2015年   5篇
  2014年   8篇
  2013年   14篇
  2012年   4篇
  2011年   9篇
  2010年   6篇
  2009年   4篇
  2008年   3篇
  2007年   7篇
  2006年   1篇
  2005年   5篇
  2004年   1篇
  2003年   4篇
  2002年   1篇
  2000年   1篇
  1995年   1篇
  1992年   1篇
  1990年   1篇
  1988年   1篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1977年   1篇
  1975年   1篇
  1967年   1篇
排序方式: 共有137条查询结果,搜索用时 515 毫秒
51.
Quantum dots (QDs) with a nanoscale size range have attracted significant attention in various areas of nanotechnology due to their unique properties. Different strategies for the synthesis of QD nanoparticles are reported in which various factors, such as size, impurities, shape, and crystallinity, affect the QDs fundamental properties. Consequently, to obtain QDs with appropriate physical properties, it is required to select a synthesis method which allows enough control over the surface chemistry of QDs through fine‐tuning of the synthesis parameters. Moreover, QDs nanocrystals are recently used in multidisciplinary research integrated with biological interfaces. The state‐of‐the‐art methods for synthesizing QDs and bioconjugation strategies to provide insight into various applications of these nanomaterials are discussed herein.  相似文献   
52.
We present the preliminary results of our code OPAQS(opacity calculation using quantum statistical model) that is based on the self consistent Hartree-Fock-Slater model for the average atom. The code is capable of performing robust calculations of average charge state, frequency-dependent and mean opacities. The accuracy of the atomic model is verified by comparing the calculations of average charge state with various published results. The monochromatic opacities for iron computed at different sets of temperatures and densities are compared with LEDCOP. The Rosseland and Planck opacities for iron and aluminum are validated with some state-of-the-art codes. The results are in good agreement with the published data.  相似文献   
53.
Due to the definition of second-order stochastic dominance (SSD) in terms of utility theory, portfolio optimization with SSD constraints is of major practical interest. We contribute to the field in two ways: first, we present a self-contained theory with some new results and new proofs of known results; second, we perform a set of tests for computational efficiency. We provide new and simple arguments for the formulation of SSD constraints in a mathematical programming framework. For many individuals, an SSD constraint may seem too severe wherefore various relaxations (ASSD), have been proposed. We introduce yet another relaxation, directional SSD, where a candidate portfolio is admissible if a step from the benchmark in the direction of the candidate yields a dominating portfolio. Optimal step size depends on individual preferences reflected by the objective function. We compare computational efficiency of seven approaches for SD constrained portfolio problems, including SSD and ASSD constrained cases.  相似文献   
54.
55.
Five new di‐ and triglycosides, irigenin 7‐[Oβ‐D ‐glucopyranosyl‐(1→6)‐β‐D ‐glucopyranoside] ( 1 ), 6‐hydroxygenistein 4′‐[Oβ‐D ‐glucopyranosyl‐(1→6)‐β‐D ‐glucopyranoside] ( 2 ), nigricin 4′‐[Oβ‐D ‐glucopyanosyl‐(1→6)‐β‐D ‐glucopyranoside] ( 3 ), nigricin 4′‐[Oβ‐D ‐glucopyanosyl‐(1→2)‐O‐[α‐L ‐rhamnopyranosyl‐(1→6)]‐β‐D ‐glucopyranoside] ( 4 ), and 7‐{4′‐{[2″‐O‐(4′′′′‐acetyl‐2′′′′‐methoxyphenyl)‐β‐D ‐glucopyranosyl]oxy}‐3′‐(β‐D ‐glucopyranosyloxy)phenyl]‐9‐methoxy‐8H‐1,3‐dioxolo[4,5‐g]‐[1 benzopyran‐8‐one‐] ( 5 ), along with a known compound, nigricin 4′‐(β‐D ‐glucopyranoside) ( 6 ), were isolated from the rhizomes of Iris germanica. The structures of these compounds were established by spectroscopic methods, including 2D NMR spectroscopic techniques.  相似文献   
56.
A series of cis-platinum ethynyl complexes with the general formula cis-[Pt(dppe)(C[triple bond]CR)2](dppe = 1,2-bis(diphenylphosphino)ethane; R = C6H4-p-NO2 1, C6H4-p-CH3 2, C6H4-p-C[triple bond]CH 3 and C6H4-p-C6H4-p-C[triple bond]CH 4) have been prepared by the coupling reaction of cis-[Pt(dppe)Cl2] with two equivalents of the appropriate alkyne. The new complexes have been fully characterized by spectroscopic techniques, and the cis square planar arrangement at the platinum centre has been confirmed by single-crystal X-ray diffraction studies of complexes 1, 2 and 4. The absorption spectra of the complexes 1-4 are dominated by a pi-->pi* band that contains some platinum (n + 1) p orbital character. The position of the band is dependent on the electron donating or withdrawing properties of the ethynyl substituents, R. Complex 1 displays a triplet emission in the green, at room temperature, while complexes 2-4, display singlet emissions in the blue. Again, the difference can be attributed to the nature of the R substituents.  相似文献   
57.
Pandanus odorifer (Forssk.) Kuntze is an economically important aromatic plant. The essential oil from male flowers is widely used in aromatherapy, cosmetics and as food flavouring agent. Phenylethyl methyl ether (PEME), the major constituent of essential oil, gives the chief characteristic fragrance to the oil. In the present study, 180 samples from 12 different regions were collected and hydrodistilled for essential oil isolation. The oil was then subjected to GC and GC-MS analysis to find out the percentage of the constituents. The results revealed PEME as the major constituent ranging from 58.03 to 81.86% and terpinen-4-ol, the second major constituent ranging from 7.81 to 21.46%. Soil nitrogen was found to be the most influential factor for oil yield and PEME content. The flowers containing high essential oil yield and PEME content could be used as elite chemotypes with enough potential for large-scale commercial cultivation to meet the demand of kewda industries.  相似文献   
58.
Journal of Radioanalytical and Nuclear Chemistry - Many efforts have been made to introduce an appropriate radiopharmaceutical as a theranostic agent for metastatic castration-resistant prostate...  相似文献   
59.
Journal of Statistical Physics - We study the dynamics of a macroscopic superconducting qubit coupled to two independent non-stationary reservoirs by using time-dependent perturbation theory. We...  相似文献   
60.
Although protein biomarkers have a great potential as biomarkers for diagnosis of diseases, they are seldom used in hospitals. There are many reasons for this, for instance, the difficulties to (i) find a biomarker for which the concentration in body fluids clearly differs between patients and healthy subjects, (ii) attain purification of the biomarker close to 100%, which is required for production of conventional protein antibodies as well as artificial gel antibodies for selective capture of a biomarker, (iii) design a standard curve for rapid and accurate determination of the concentration of the biomarker in the body fluid because of adsorption of the biomarker onto vials, pipettes, etc., (iv) determine accurately the sample volume delivered by a pipette, (v) avoid polymerization of the biomarker upon storage and to decide whether it is in the form not only of monomers, but also of dimers, trimers, etc., in the native state, (vi) determine the degree of possible glycosylation and amidation of the biomarker and (vii) decide whether glycosylation and amidation positively or negatively affects the possibility to use the protein as a biomarker. In this article, we discuss in quantitative terms the difficulties (iii–vii) and how to overcome them, which also may help to overcome the difficulty (ii), which in turn minimizes difficulty (i).  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