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   140篇
  免费   7篇
  国内免费   2篇
化学   89篇
晶体学   1篇
力学   7篇
数学   24篇
物理学   28篇
  2023年   3篇
  2022年   1篇
  2021年   3篇
  2020年   1篇
  2019年   3篇
  2018年   3篇
  2017年   1篇
  2016年   2篇
  2015年   6篇
  2014年   5篇
  2013年   4篇
  2012年   14篇
  2011年   14篇
  2010年   5篇
  2009年   4篇
  2008年   10篇
  2007年   12篇
  2006年   8篇
  2005年   11篇
  2004年   5篇
  2003年   3篇
  2002年   5篇
  2001年   3篇
  2000年   2篇
  1998年   1篇
  1997年   1篇
  1996年   3篇
  1995年   1篇
  1994年   2篇
  1993年   3篇
  1991年   1篇
  1989年   1篇
  1988年   2篇
  1984年   1篇
  1983年   2篇
  1980年   1篇
  1977年   1篇
  1973年   1篇
排序方式: 共有149条查询结果,搜索用时 31 毫秒
31.
The decomposition of methylcyclohexane on H–NaY and PtH–NaY zeolites has been studied. It has been found that the presence or abscence of H2 affects not only the activity of these catalysts but also their selectivity to dehydrogenation and isomerization products.
H–NaY PtH–NaY. , H2 , .
  相似文献   
32.
33.
The main objective of the present experimental study is to analyse the turbulence properties in unsteady flows around bluff body wakes and to provide a database for improvement and validation of turbulence models, concerning the present class of non-equilibrium flows. The flow around a circular cylinder with a low aspect ratio () and a high blockage coefficient () is investigated. This confined environment is used in order to allow direct comparisons with realisable 3D Navier–Stokes computations avoiding ‘infinite’ conditions. The flow is investigated in the critical regime at Reynolds number 140,000. A cartography of the velocity fields in the near wake of the cylinder is obtained by PIV and Stereoscopic PIV techniques. Statistical means and phase-averaged quantities are determined. Furthermore, POD analysis is performed on the data set in order to extract coherent structures of the flow and to compare the results with those obtained by the conditional sampling technique. The Reynolds stresses, the strain-rate and vorticity fields as well as the turbulence production terms are determined.  相似文献   
34.
The diastereoisomeric 2-substituted 2-azabicyclo[2.2.1]hept-5-enes 2 – 4 were prepared by aza-Diels-Alder reaction of cyclopentadiene with the corresponding methaniminium ions. Their relative configurations were deduced using 1H, 1H-ROESY experiments, and their absolute configurations were assigned from the crystal structure of the aziridinium derivative (?)- 5 . The absolute configuration of (+)- 1 , i.e. (1R), was assigned by CD spectroscopy.  相似文献   
35.
The nonlinear absorption of new mesoionic compounds (MIC) was investigated using nanosecond laser pulses with wavelengths at 570, 605 and 618 nm. Nonlinear absorption cross-sections, σ2 ≈ 10−45 cm4 s/photon, larger than any recorded in the literature, were obtained due to the introduction of p-CF3-C6H4 electron-acceptor and p-CH3-C6H4 or p-CH(CH3)2-C6H4 electron-donor groups in the MIC ring. The large values of σ2, the ease of synthesis of these compounds and their marked stability, make them promising candidates for photonic applications.  相似文献   
36.
Activating the non‐symmetrical Bpin?Bdan diboron reagent with alkoxide leads to the formation of two possible adducts: MeO?→Bpin?Bdan or MeO?→Bdan?Bpin. Experimental and theoretical investigation confirms that the MeO?→Bpin interaction is preferred and thus selective formation of a C?Bdan bond upon reaction with an activated C?C bond.  相似文献   
37.
The effect of chenodeoxycholic acid as a coadsorbent on TiO 2 nanocrystalline solar cells incorporating phthalocyanine sensitizers was studied under various conditions. Adding chenodeoxycholic acid onto TiO 2 nanoparticles not only reduces the adsorption of phthalocyanine sensitizers but also prevents sensitizer aggregation, leading to different photovoltaic performance. The inspection of IPCE and absorption spectra showed that the load of phthalocyanine sensitizers is strongly dependent on the molar concentration of chenodeoxycholic acid coadsorbent. The open circuit voltage of the solar cells with chenodeoxycholic acid coadsorbent increases due to the enhanced electron lifetime in TiO 2 nanoparticles coupled with the band edge shift of TiO 2 to negative potentials.  相似文献   
38.
The most promising fluorescence based temperature sensing technique has been employed. The effect of variation of the temperature on the fluorescence intensity of the two bands, specially coming from the two closed levels to a common lower level in Sm3+ doped calibo glass monitored using 476.5nm line of Ar+ laser and inferred that the present system can be used as a temperature sensor.  相似文献   
39.
Understanding the adsorption of polymers onto particles is crucial for many technological and biomedical applications. Even though polymer adsorption on particles is a dynamic process, most experimental techniques can only study the adsorption indirectly, in equilibrium and on the ensemble level. New analysis methods are required to overcome these limitations. We investigated the use of single-particle electrophoresis to study the adsorption kinetics of cationic polymers onto anionic particles and compared the resulting data to a theoretical model. In this approach, the electrophoretic mobility of single polystyrene (PS) particles, exposed to different concentrations of poly(2-guanidinoethyl methacrylate), was measured as a function of time. The polymer adsorption leads to an electrophoretic mobility change of the PS particle over time, from the initial negative value to a positive value at equilibrium. By fitting the kinetics data to the Langmuir model, the adsorption rate, desorption rate and equilibrium constant were determined. Finally, the adsorption kinetics of several other polymers was investigated. This showed that the presented technique enables direct analysis and comparison of the kinetics of polymer adsorption on the single-particle level.  相似文献   
40.
Cid CC  Riu J  Maroto A  Rius FX 《The Analyst》2008,133(8):1005-1008
We report a field effect transistor (FET) based on a network of single-walled carbon nanotubes (SWCNTs) which can selectively detect human immunoglobulin G (HIgG). HIgG antibodies, which are strongly adsorbed onto the walls of the SWCNTs, are the basic elements of the recognition layer. The non-specific binding of proteins and the effects of other interferences are avoided by covering the non-adsorbed areas of the SWCNTs with Tween 20. The selectivity of the sensor has been tested against bovine serum albumin (BSA), the most abundant protein in plasma. HIgG in aqueous solution with concentrations from 1.25 mg L(-1) (8 nM) can be readily detected with response times of about 10 min. The SWCNT networks that form the basis of the sensor are easily grown by chemical vapour deposition. Silver screen-printed electrodes make the sensor quick to build. The sensitivity obtained with this sensor is similar to other FET devices based on SWCNTs built using much more complicated lithography processes. Moreover, the sensor is a reagentless device that does not need labels to detect HIgG.  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