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   137篇
  免费   8篇
化学   80篇
晶体学   2篇
力学   11篇
数学   16篇
物理学   36篇
  2021年   6篇
  2020年   5篇
  2019年   4篇
  2018年   4篇
  2017年   4篇
  2016年   9篇
  2015年   5篇
  2014年   1篇
  2013年   11篇
  2012年   6篇
  2011年   11篇
  2010年   5篇
  2009年   6篇
  2008年   4篇
  2007年   12篇
  2006年   8篇
  2005年   6篇
  2004年   5篇
  2003年   3篇
  2002年   6篇
  2001年   3篇
  2000年   5篇
  1999年   2篇
  1998年   3篇
  1997年   4篇
  1996年   1篇
  1995年   1篇
  1994年   1篇
  1992年   1篇
  1990年   2篇
  1987年   1篇
排序方式: 共有145条查询结果,搜索用时 15 毫秒
21.
The crystal structure of the title compound, C2H10N2O2+·2Cl, is built up from one 2‐hydroxy­ethyl­hydrazinium(2+) cation and two Cl anions. The mol­ecular structure is stabilized by O—H⋯Cl and N—H⋯Cl hydrogen bonds. The crystal structure is stabilized by one N—H⋯O and three N—H⋯Cl inter­actions, and the three‐dimensional network of hydrogen bonds stabilizes the crystal packing. All five hydrazinium H atoms are involved in hydrogen bonds to Cl anions. The Cl⋯H contact distances range from 2.122 (15) to 2.809 (14) Å.  相似文献   
22.
Organic acids, sugars, phenolic compositions and antioxidant capacities of orange juice and orange wine obtained from the cv. Kozan of Turkey were determined. High-performance liquid chromatographic methods were used to identify and quantify of these compounds. Three organic acids (citric, malic and ascorbic acids) and three sugars (sucrose, glucose and fructose) were determined. The major organic acid was found as citric acid. With regard to sugars, sucrose was present in the largest amounts for orange juice and wine. A total of 13 phenolic compounds were identified and quantified in orange juice and wine, including hydroxybenzoic acids (2), hydroxycinnamic acids (5), and flavanones (6). Hesperidin, narirutin and ferulic acid were the most abundant phenolic compounds in orange juice and wine. Antioxidant activities of orange juice and wine were measured using the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, and the antioxidant capacity of orange juice was found to be higher than that of orange wine.  相似文献   
23.
Quantitative analyses in secondary ion mass spectrometry (SIMS) become possible only if ionization processes are controlled. The Storing Matter technique has been developed to circumvent this so‐called matrix effect, primarily for inorganic samples, but has also been extended to organic samples. For the latter, it has been applied to polystyrene in order to investigate the extent of damage in the polymer, its fragmentation during the sputter deposition process and the effect of the deposition process on the spectra taken by Time‐of‐Flight SIMS (ToF‐SIMS). In this work, a multi‐technique approach, which employs the Storing Matter technique for deposition and ToF‐SIMS and X‐ray photoelectron spectroscopy for characterization, is used to enhance the control of the deposition process, including the thickness of the deposit, the alteration of the source film and the influence of polymer composition on the Storing Matter process. Poly (methyl methacrylate) (PMMA) is used for this work. More detailed information about the sticking of polymer fragments on the metal collector is obtained by density functional theory calculations. This work allows for the conclusion that a part of the fragments deposited on the collector surface diffuses on the latter, reacts and recombines to form larger fragments. The behaviour observed for PMMA is similar to polystyrene, showing that oxygen has no major influence on the processes occurring during the sputter deposition process. Additionally, we have developed a new methodology using 2D ToF‐SIMS images of the deposit to monitor the deposit thickness and to identify surface contaminations. The latter are not only located at the position of the deposit but all over the collector surface. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
24.
Undoped ZnO film and ZnO films, which are co-doped with F and In (FIZO) at different concentrations, were synthesized by sol–gel technique and the effects of co-doping of F and In on structural and optical properties of ZnO thin films were investigated. The concentration ratio of [F]/[Zn] was altered from 0.25 to 1.75 with 0.50 step at.% mole and [In]/[Zn] was altered from 0.25 to 1.00 with 0.25 step at.% mole. X-ray diffraction analysis indicates that the films have polycrystalline nature and the (0 0 2) preferred orientation is the stronger peak. No extra phases involving zinc, fluorine and indium compounds were observed even at high F and In content. The grain size of undoped ZnO and FIZO thin films varied between 15 and 20 nm with a small fluctuation. From the SEM images, although the undoped ZnO had a smooth and particle-shaped surface, FIZO films had nanofiber-networks shapes over the surface with average size of 500 nm. The surface morphologies and crystallite sizes for the F and In doped films were slightly different from than those of undoped film. From the optical study, a slight shrinkage of band gap was backwardly observed from 3.36 to 3.25 eV with the increasing of F and In content.  相似文献   
25.
Unsteady plunging (heaving) of a wing in the form of a flat plate can give rise to pronounced axial flow in the small-scale leading-edge vortex, during its initial stage of formation. Opposing axial flows along the vortex interact at the plane of symmetry giving rise to large-scale patterns of streamwise-oriented vorticity, which can dominate the tip vortices over part of the oscillation cycle.  相似文献   
26.
The molecular structure of the title compound, C11H9NOS, has three planar moieties, two of which are rings, namely the hydroxy­phenyl and the thio­phene, with an angle of 20.76 (10)° between them. The crystal structure is stabilized by an O—H?N hydrogen bond and by C—H?O intermolecular interactions. The C?O intermolecular contact distance is 3.443 (2) Å.  相似文献   
27.
We discuss the properties of oscillators whose spectrum is given by a generalized Fibonacci sequence. The properties include: invariance under the unitary quantum group, generalized angular momentum, coherent states and difference calculus, relativistic interpretation.  相似文献   
28.
The determination of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) in food and beverages sold in Turkey was carried out using liquid chromatography–tandem mass spectrometry (LC-MS/MS). A total of 123 samples of selected food and beverages such as fish, meat, offal, egg, cracker, chips, cake, chocolate, vegetable, milk and juice were examined. The highest PFOA concentrations were determined in cow meat (5.15 ng g?1), cow kidney (5.65 ng g?1), cow spleen (5.06 ng g?1) and chicken liver (5.02 ng g?1). The highest PFOS levels were found in horse mackerel (52.43 ng g?1), pike-perch (45.87 ng g?1), sardine (42.83 ng g?1) and black cod (41.33 ng g?1). Fish was found to be major source of the PFOS intake, while meat and offal were found to be major sources of the PFOA intake.  相似文献   
29.
The total attenuation cross sections in elements Ti, Fe, Ni and Zn for K and K group of liens of element 22Z92 by using tranmission method. K X-rays of seconder excitor were counted by a Ge(Li) detector with resolution 190 eV at 5.9 keV. The experimentally mesured attentuation cross sections have ben found in a good agreement with the theoretical values of Stom, Israel and Hubbell, Seltzer.  相似文献   
30.
A simple and direct method has been used to obtain fairly accurate total atomic attenuation, total atomic photoelectric and total scattering cross sections by measuring the transmission factor and K X-ray fluorescence spectrum induced by 60 keV -rays for Gd, Tb, Dy and Er by employing a Si(Li) detector system in a 2 geometry set-up. All the parameters are compared with their corresponding theoretical values and a good agreement between them is obtained.  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