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   586篇
  免费   14篇
  国内免费   3篇
化学   421篇
晶体学   5篇
力学   14篇
数学   59篇
物理学   104篇
  2022年   9篇
  2021年   23篇
  2020年   9篇
  2019年   6篇
  2018年   8篇
  2017年   3篇
  2016年   11篇
  2015年   7篇
  2014年   13篇
  2013年   27篇
  2012年   34篇
  2011年   32篇
  2010年   13篇
  2009年   23篇
  2008年   43篇
  2007年   37篇
  2006年   44篇
  2005年   30篇
  2004年   31篇
  2003年   21篇
  2002年   18篇
  2001年   9篇
  2000年   3篇
  1999年   6篇
  1998年   4篇
  1997年   9篇
  1996年   12篇
  1995年   5篇
  1994年   7篇
  1992年   3篇
  1991年   4篇
  1990年   6篇
  1989年   4篇
  1988年   10篇
  1987年   9篇
  1985年   6篇
  1984年   9篇
  1983年   4篇
  1982年   6篇
  1981年   4篇
  1980年   2篇
  1978年   6篇
  1977年   3篇
  1976年   2篇
  1975年   2篇
  1974年   4篇
  1973年   3篇
  1972年   3篇
  1970年   2篇
  1888年   4篇
排序方式: 共有603条查询结果,搜索用时 11 毫秒
81.
An apertureless near-field scanning optical microscope (ANSOM) that utilizes the enhanced field around a gold nanosphere, which is attached to the end of an atomic force microscope (AFM) tip, is used to image the local dielectric constant of the patterned metallic surfaces and local electric field around plasmonic nanosphere samples. A colloidal gold nanosphere (approximately 50 nm diameter) is linked to the extremity of the conventional etched-silicon probe. The scattering of laser radiation (633 or 532 nm) is modulated by the oscillating nanosphere-functionalized silicon tip, and the scattered radiation is detected. The approach curve (scattering intensity as a function of the tip-sample distance), the polarization dependence (scattering intensity as a function of the excitation polarization direction), and ANSOM image contrast confirm that the spherical nanosphere attached to the silicon tip acts as a point dipole that interacts with the sample surface via a dipole-dipole coupling, in which the dipole created by the field at the tip interacts with its own image dipole in the sample. The image obtained with the nanoparticle functionalized tip provides a dielectric map of the sample surface with a spatial resolution better than 80 nm. In addition, we show that the functionalized tip is capable of imaging the local electric field distribution above the plasmonic nanosphere samples. Overall, the result shows that high-resolution ANSOM is possible without the aid of the lightning-rod effect. With an improved tip-fabrication method, we believe that the method can provide a versatile high-resolution chemical imaging that is not available from usual forms of ANSOM.  相似文献   
82.
We describe the first example of immunoanalysis performed within an ionic liquid with minimal deleterious effect; our results bode well for the development of second-generation biosensors, particularly in applications involving poorly water soluble analytes including pesticides, phospholipids, and illicit drugs.  相似文献   
83.
An intriguing and novel charge-transfer complex between dimethyldihydrophenazine and diethylviologen has been crystallized from an ionic liquid at room temperature, resulting in an interesting stacking motif of interrupted D***A***D type triads: efficient formation of the complex is seen within an ionic liquid and acetone, with the complex absorbing strongly across nearly the entire visible-NIR spectral region.  相似文献   
84.
S. Bivona  R. Burlon  D. Gurrera  C. Leone 《Physica A》2008,387(23):5910-5915
We present an algorithm that allows us to analyze the cross-correlation of wind velocity measured in different locations; this algorithm is applied to 29 recording stations in Sicily. The results show that such correlations present a significant and persistent ultrametric structure that is influenced by the geographical neighborhood as well as by the presence of mountain and the sea. The algorithm presented, that is also able to reveal weak correlations, can be used as a starting point for the development of multivariate models of wind.  相似文献   
85.
Prunus mahaleb L. fruit has long been used in the production of traditional liqueurs. The fruit also displayed scavenging and reducing activity, in vitro. The present study focused on unravelling peripheral and central protective effects, antimicrobial but also anti-COVID-19 properties exerted by the water extract of P. mahaleb. Anti-inflammatory effects were studied in isolated mouse colons exposed to lipopolysaccharide. Neuroprotection, measured as a blunting effect on hydrogen-peroxide-induced dopamine turnover, was investigated in hypothalamic HypoE22 cells. Antimicrobial effects were tested against different Gram+ and Gram- bacterial strains. Whereas anti-COVID-19 activity was studied in lung adenocarcinoma H1299 cells, where the gene expression of ACE2 and TMPRSS2 was measured after extract treatment. The bacteriostatic effects induced on Gram+ and Gram- strains, together with the inhibition of COX-2, TNFα, HIF1α, and VEGFA in the colon, suggest the potential of P. mahaleb water extract in contrasting the clinical symptoms related to ulcerative colitis. The inhibition of the hydrogen peroxide-induced DOPAC/DA ratio indicates promising neuroprotective effects. Finally, the downregulation of the gene expression of ACE2 and TMPRSS2 in H1299 cells, suggests the potential to inhibit SARS-CoV-2 virus entry in the human host. Overall, the results support the valorization of the local cultivation of P. mahaleb.  相似文献   
86.
87.
88.
Proton nuclear magnetic resonance (1H NMR) experiments have been performed to measure the spin-lattice, T1, and spin-spin, T2, relaxation times of the three functional groups in water/methanol mixtures at different methanol molar fractions (XMeOH=0, 0.04, 0.1, 0.24, 0.5, 1) as a function of temperature in the range 205 K相似文献   
89.
The fluorescent dye thioflavin T (ThT) is commonly used for in situ amyloid fibril detection. In this work, we focused on the spectroscopic properties and chemical stability of ThT in aqueous solution as a function of pH, temperature, and dye concentration. A reversible hydroxylation process occurs in alkaline solutions, which was characterized using a combination of UV-vis absorption spectroscopy, proton NMR, and density functional theory (DFT). On the basis of these studies, we propose a chemical structure for the hydroxylated form. Finally, by means of fluorescence spectroscopy, ThT hydroxylation effects on in situ amyloid detection have been investigated, providing new insights on the efficiency of the ThT assay for quantitative fibril evaluation at basic pH.  相似文献   
90.
The synthesis of new D-seco-C-nor-taxane derivatives in which the D-ring has been deleted and the C-ring has been transformed into a new pentatomic ring, i.e., the polyfunctionalized tetrahydrofuranosyl and cyclopentenyl or cyclopentyl ring, was performed starting from baccatin III derivatives. The synthetic strategy adopted took advantage of the oxetane ring opening and disconnection of the C4-C5 bond, followed by an intramolecular condensation. The formation of furanosyl or cyclopentyl rings is strictly dependent on the presence of unprotected or protected oxygen at C-7 in the starting material. The reactions proceeded with good diastereoselectivity with control of the stereochemistry of one or two stereocenters.  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