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   125篇
  免费   4篇
化学   70篇
力学   19篇
数学   12篇
物理学   28篇
  2023年   1篇
  2022年   2篇
  2021年   11篇
  2020年   7篇
  2019年   4篇
  2018年   10篇
  2017年   4篇
  2016年   8篇
  2015年   4篇
  2014年   13篇
  2013年   8篇
  2012年   12篇
  2011年   10篇
  2010年   10篇
  2009年   7篇
  2008年   1篇
  2007年   6篇
  2006年   1篇
  2005年   1篇
  2004年   1篇
  2003年   2篇
  2002年   2篇
  2001年   1篇
  1998年   1篇
  1994年   1篇
  1986年   1篇
排序方式: 共有129条查询结果,搜索用时 15 毫秒
71.
Journal of the Iranian Chemical Society - The preparation and characterization of cobalt aluminate (CoAl2O4) magnetic nanoparticles and its application as a catalyst for the synthesis of a novel...  相似文献   
72.
In this note, single machine scheduling and minimizing absolute flow time deviation (TAFD) are considered. The relationship between this problem and the mean absolute deviation of job completion times about a common due date (MAD) is discussed. Based on the MAD problem optimal solutions of the TAFD problem are given. Furthermore, the generalization of the problem to the multiple machine case is discussed and an efficient algorithm for generating many optimal solutions of the problem, in the multi-machine case, is given.  相似文献   
73.
Metiamide is a class of medications called H2-receptor antagonist or H2 blockers. It decreases the amount of acid made in the stomach. It is commonly used in the treatment for peptic ulcer disease and gastroesophageal reflux disease. In this study, the metiamide tautomer stability, structural data, HOMO and LUMO (energies and shapes), ΔΕ HOMO–LUMO gaps, UV–visible data and graphs, dipole moments, Mulliken charges, and thermodynamic and kinetic stabilities in aqueous media as a biological solvent and some of the different media (vacuum, H2O, Et-OH and DMSO) were investigated for the tautomers of metiamide by the density functional theory DFT-B3LYP/6-31G* method. The results presented that the probability of the adaptability and compatibility of which tautomer (T1T6) are better than the other tautomers for interactions with the pattern and structural map of the H2-receptor. The diversities of the interaction points and mosaic patterns of the T3 and T4 tautomers in H2O media with the imaginary H2-receptor were investigated.  相似文献   
74.
75.
Optoacoustic tomography (PAT) is a two-dimensional medical imaging method that has the advantage of optical contrast and resolution of ultrasonic waves. The detection systems with a high sensitivity can be used for detecting small tumors, located deeply in human tissues, such as the breast. In this study, the sensitivity of existing ultrasonic detection systems has been compared experimentally with that by using thermoelastic waves as a broadband ultrasonic source. For the comparison, an optical stress transducer(OST), a polyvinylidene difluoride (PVDF) sheet and a calibrated PVDF needle hydrophone were used.To ensure all of the detection systems interrogated by the same ultrasonic field, a small optical instrument that fixed the generating laser head was constructed. The sensitivity was evaluated by measuring signalto-noise ratios (SNRs) and noise equivalent pressures (NEPs). The PVDF system, with a 4-kPa NEP has a 22 dB better performance than the OST. The OST showed nearly the same sensitivity as the hydrophone for detecting ultrasound waves at a 1-cm distance in water. PVDF detection system provides a useful tool for imaging of soft tissues because of its high sensitivity and broad detection range.  相似文献   
76.
77.
In this study, TiO2 nanoparticles have been obtained from low-grade ilmenite ore via two consecutive acid digestion and solvent extraction processes. The as-extracted TiO2 (Anatase phase) product was characterized using techniques such as XRD, XRF, FESEM, FTIR and BET surface area. Diluted sulfuric acid and D2EHPA (bis-(2-ethyl-hexyl) phosphoric acid) were used as digester agent and an extraction solvent, respectively. The effects of main parameters such as recycling capacities and D2EHPA concentration, as well as the extraction time and temperature on TiO2 extraction were investigated. The results demonstrated that the best performance and efficiency for titanium and total iron uptake were 99 and 3.8%, respectively, at the lowest concentration of D2EHPA.  相似文献   
78.
The vibrational behavior of electrostatically actuated microstructures subjected to nonlinear squeeze film damping and in-plane forces is investigated. First-Order Shear Deformation Theory is used to model dynamical system by means of finite element method, while finite difference method is applied to solve the nonlinear Reynolds equation of squeeze film damping simultaneously. Vibrational analysis of microplates is performed by solving eigenvalue problem, after validating the model by pull-in phenomenon and transient behavior. In addition, considering nonlinear squeeze film damping and step-input actuations, response frequencies of microplates are calculated. Effect of ambient pressure and in-plane forces on dynamic pull-in phenomenon is also studied. Results for simplified models are verified and are in good agreement with the published literature. This investigation can reveal nonlinear vibrational behavior of microstructures.  相似文献   
79.
In this paper describing functions inversion is used and the restoring force of a nonlinear element in a MDOF system is characterized. The describing functions can be obtained using linearized frequency response functions (FRFs). The response of the system to harmonic excitation forces at distinct frequencies close to the resonant frequency results in linearized FRFs. The nonlinear system can be approximated at each excitation frequency by an equivalent linear system. This approximation leads to calculation of the first-order describing functions. By having the experimental describing functions calculated and the system’s responses corresponding to the nonlinear element (measured or interpolated), nonlinear parameter identification can be performed. Two numerical and experimental case studies are provided to show the applicability of this method.  相似文献   
80.
Five new cavitands were prepared that have four pendant n-undecyl chains and "headgroups" connected by 2-carbon spacers. The headgroups were ~OCH(2)CONH-Ala-OCH(3), 1; ~OCH(2)CONH-Phe-OCH(3), 2; ~OCH(2)CONH-Ala-OH, 3; ~OCH(2)CONH-Phe-OH, 4; and ~OCH(2)CONHCH(2)CH(2)-thyminyl, 5. Pore formation by each cavitand was studied by use of the planar bilayer conductance experiment. All five compounds were found to form pores in asolectin bialyer membranes. Compounds 1-3 behaved in a generally similar fashion and exhibited open-close dynamics. Compounds 4 and 5 formed pores more rapidly, were more dynamic, and led more quickly to membrane rupture. Differences in the ion transport activity are rationalized in terms of structure and aggregate cavitand assemblies.  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