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   264篇
  免费   10篇
化学   178篇
力学   10篇
数学   51篇
物理学   35篇
  2023年   2篇
  2022年   13篇
  2021年   12篇
  2020年   9篇
  2019年   11篇
  2018年   1篇
  2017年   6篇
  2016年   9篇
  2015年   5篇
  2014年   6篇
  2013年   19篇
  2012年   24篇
  2011年   22篇
  2010年   9篇
  2009年   10篇
  2008年   11篇
  2007年   11篇
  2006年   17篇
  2005年   14篇
  2004年   7篇
  2003年   7篇
  2002年   10篇
  2001年   2篇
  2000年   4篇
  1999年   3篇
  1998年   2篇
  1997年   1篇
  1996年   4篇
  1995年   1篇
  1993年   2篇
  1991年   1篇
  1989年   1篇
  1987年   2篇
  1985年   4篇
  1979年   2篇
  1978年   1篇
  1976年   2篇
  1975年   1篇
  1974年   1篇
  1967年   1篇
  1966年   2篇
  1965年   2篇
排序方式: 共有274条查询结果,搜索用时 46 毫秒
41.
Journal of Thermal Analysis and Calorimetry - This paper investigates a steady mixed convection in a lid-driven square cavity subjected to an inclined magnetic field and heated by corner heater...  相似文献   
42.
Science China Chemistry - Destructive quantum interference (DQI) provides a unique approach to controlling the leakage current in the OFF state of molecular devices. However, the DQI in...  相似文献   
43.
Journal of Solid State Electrochemistry - Remarkable selective analysis of biomolecules i.e., glucose and ascorbic acid on copper oxide facets was reported for the first time. The copper oxide...  相似文献   
44.
Densities, ρ, and speeds of sound, u, of systems formed by 1-heptanol, or 1-octanol, or 1-decanol and dibutylether have been measured at a temperature of (293.15, 298.15, and 303.15) K and atmospheric pressure using a vibrating tube densimeter and sound analyser Anton Paar model DSA-5000. The ρ and u values were used to calculate excess molar volumes, VE, and deviations from the ideal behaviour of the thermal expansion coefficient, Δαp and of the isentropic compressibilities, ΔκS. The available database on molar excess enthalpies, HE, and VE for (1-alkanol + linear monoether) systems was used to investigate interactional and structural effects in such mixtures. The enthalpy of the OH?O bonds is lower for methanol solutions, and for the remainder systems, it is practically independent of the mixture compounds. The VE variation with the chain length of the 1-alkanol points out the existence of structural effects for systems including longer 1-alkanols. The ERAS model is applied to the studied mixtures. ERAS represents quite accurately HE and VE data using parameters which consistently depend on the molecular structure.  相似文献   
45.
Diketo-1,3-dioxin-2-ones underwent retro-Diels-Alder reaction on heating in toluene at 110 degrees C to generate alpha,gamma,-triketo-ketenes. These were trapped with alcohols to provide 2,4,6-triketocarboxylates, which were smoothly aromatized by sequential reaction with potassium carbonate and methanolic hydrogen chloride to give resorcylate esters. The reaction was applied in the total synthesis of the marine antifungal agents 15G256beta (1), 15G256iota (2), and 15G256pi (3) and the mycotoxin S-(-)-zearalenone (4).  相似文献   
46.
The antiviral effects of the cationic acrylate polymer E100 on a panel of lipid-enveloped viruses and the interactions involved are studied. The treatment of several common viruses with E100 induced a dose-dependent inhibition of the infectivity of viruses below the detection limit of the assays employed. Similarly, the treatment of human sera infected with HIV or HCV reduced virus RNA plasma levels to undetectable values. This implies that Eudragit E100 can interact with enveloped viruses, even in the presence of proteins, through a mechanism that is not reversed by titration of the positively charged groups of the polymer, opening the possibility to remove viral particles with the polymer as it is eliminated.  相似文献   
47.
Detection of explosives on skin using ambient ionization mass spectrometry   总被引:3,自引:0,他引:3  
Single nanogram amounts of the explosives TNT, RDX, HMX, PETN and their mixtures were detected and identified in a few seconds on the surface of human skin without any sample preparation by desorption electrospray ionization (DESI) using a spray solution of methanol-water doped with sodium chloride to form the chloride adducts with RDX, HMX, and PETN while TNT was examined as the radical anion and tandem mass spectrometry was used to confirm the identifications.  相似文献   
48.
Here, it is shown that the “traditional approach” to variable bubble-point problems, using black-oil models, is not consistent, because it violates the “bubble-point conservation law.” In order to have a consistent approach, it is necessary to incorporate shocks—discussed in previous papers—in which the bubble-point is discontinuous. A “consistent approach” is applied to specific examples, and results compared with those of the “traditional” one. The conclusion that the “traditional approach” generally yields large errors for the production rates and other parameters of interest in the oil industry, is reached. © 1997 John Wiley & Sons, Inc.  相似文献   
49.
Accurate prediction of the macroscopic flow parameters needed to describe flow in porous media relies on a good knowledge of flow field distribution at a much smaller scale—in the pore spaces. The extent of the inertial effect in the pore spaces cannot be underestimated yet is often ignored in large-scale simulations of fluid flow. We present a multiscale method for solving Oseen’s approximation of incompressible flow in the pore spaces amid non-periodic grain patterns. The method is based on the multiscale finite element method [MsFEM Hou and Wu in J Comput Phys 134:169–189, 1997)] and is built in the vein of Crouzeix and Raviart elements (Crouzeix and Raviart in Math Model Numer Anal 7:33–75, 1973). Simulations of inertial flow in highly non-periodic settings are conducted and presented. Convergence studies in terms of numerical errors relative to the reference solution are given to demonstrate the accuracy of our method. The weakly enforced continuity across coarse element edges is shown to maintain accurate solutions in the vicinity of the grains without the need for any oversampling methods. The penalisation method is employed to allow a complicated grain pattern to be modelled using a simple Cartesian mesh. This work is a stepping stone towards solving the more complicated Navier–Stokes equations with a nonlinear inertial term.  相似文献   
50.

Abstract  

Pseudo-C-nucleosides have potential biological activity, and an efficient synthesis of new pseudo-C-nucleosides has been developed via the reaction of a β-formyl-α,β-unsaturated ester bearing a β-sugar moiety with hydrazines in neutral and acidic conditions. The preparation of the β-formyl-α,β-unsaturated ester was accomplished by oxidation of the secondary hydroxyl group of 3-O-benzyl-1,2-O-isopropylidene-α-d-glucofuranose, followed by elongation of its carbon chain with (ethoxycarbonylmethylene)triphenylphosphorane and oxidation of the hydroxymethyl group.  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