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   112篇
  免费   0篇
化学   44篇
晶体学   3篇
力学   1篇
数学   3篇
物理学   61篇
  2022年   1篇
  2020年   2篇
  2017年   2篇
  2016年   1篇
  2015年   3篇
  2013年   1篇
  2012年   1篇
  2011年   8篇
  2010年   1篇
  2009年   1篇
  2008年   2篇
  2007年   5篇
  2006年   11篇
  2005年   2篇
  2004年   8篇
  2003年   6篇
  2002年   4篇
  2001年   7篇
  2000年   3篇
  1999年   4篇
  1996年   1篇
  1995年   5篇
  1994年   2篇
  1993年   5篇
  1992年   1篇
  1991年   3篇
  1990年   3篇
  1989年   2篇
  1988年   1篇
  1987年   3篇
  1986年   1篇
  1984年   3篇
  1982年   2篇
  1977年   1篇
  1975年   3篇
  1974年   2篇
  1973年   1篇
排序方式: 共有112条查询结果,搜索用时 15 毫秒
11.
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection.  相似文献   
12.
This paper describes an electrochemical biosensor for free cholesterol monitoring. The sensor is a multienzymatic electrodic system in which horseradish peroxidase and cholesterol oxidase are simultaneously immobilized within a polymeric film, on the surface of a pyrolitic graphite electrode. From voltammetric and amperometric (flow-injection) data obtained, the efficiency, reproducibility and stability of the system are discussed. Results obtained, of interest for basic and applied biochemistry, represent a first step for construction of a mediator-free biosensor with potentialities for a successful application in the biosensor area.  相似文献   
13.
14.
15.
A new method is proposed here for measuring the optical constants of solids. The method is based on measuring the change of the derivative of reflectance with the angle of incidence Θ of p-polarized light for different Θ around the pseudo-Brewster angle. The accuracy of the method has been checked by determining the optical constants of some transparent and opaque materials. The method seems very sensitive to the presence of thin oxide layers and it is also expected to be useful in determining oxide thicknesses.  相似文献   
16.
Summary By means of a new experimental technique based on a non-steady-state method,i.e. on the propagation properties of thermal waves, we have measured the thermal diffusivityD of a copper wire by changing properly its boundary conditions in order to ascertain whether the values ofD were independent of the surface heat losses. Temperature oscillations at the fixed frequency of 0.0121 Hz were excited at one end of the specimen which was in nitrogen atmosphere at different pressures ranging from ∼10−2 mTorr to 220 mTorr. The temperatures of the far end of the specimen and the walls of the container had the same constant value of 0°C, while the temperature gradient between the average value of the oscillating temperatures and this constant temperature was changed from 2°C to 12°C for each pressure by adjusting the heater power. By operating in this way it was possible to change either the heat losses due to conduction and convection or those due to radiation. The major cause of error came from the uncertainty in the measurements of the phase shift between the thermal oscillations detected at the two fixed points of the specimen which introduces in the evaluation ofD an error of about 2%. The experimental values obtained for the thermal diffusivity in these different boundary conditions were in any case comprised within this uncertainty sinceD=(1.17±0.02) cm2s−1, in good agreement with the literature. The results so far obtained show that the experimental method has the great advantage of giving the thermal diffusivity and, therefore, the thermal conductivity of a solid without the necessity of taking particular care in insulating the specimen.
Riassunto Utilizzando una tecnica sperimentale che consente di determinare in fili metallici sia la diffusività termicaD sia il coefficienteμ di perdita superficiale mediante la misura diretta del ritardo di fase e dell'attenuazione di un'onda termica tra due punti fissi del campione, ci si è proposti di analizzare alcuni risultati ottenuti recentemente in un campione di rame, variando opportuamente le condizioni al contorno. In particolare, ci si è voluti assicurare che la diffusività termica non risultasse dipendente dal valore del coefficiente di perdita superficiale. Le misure sono state eseguite alla frequenza fissa di 0.0121 Hz in atmosfera di azoto, a pressioni diverse comprese tra ∼10−2 mTorr e 220 mTorr. L'estremità lontana del campione e le pareti del contenitore erano tenuti costantemente alla stessa temperatura (0°C), mentre il gradiente termico era sistematicamente variato tra 2°C e 12°C, in corrispondenza di ciascuna pressione. Operando in questo modo, si potevano variare opportunamente sia la conduzione sia l'irraggiamento del calore dalla superficie laterale del campione nel mezzo circostante. In queste misure, la causa predominante di errore viene dalla misura dello sfasamento delle due onde, che introduce nella valutazione diD un'incertezza del 2%. I valori sperimentali ottenuti nelle diverse condizioni prima ricordate risultano, in ogni caso, compresi entro i limiti di questa incertezza, poichéD=(1.17±0.02) cm2/s, in ottimo accordo con i dati della letteratura. Questo risultato dimostra pertanto che la diffusività termica, determinata con questo metodo dinamico, risulta effettivamente indipendente dalla quantità di calore transmesso dal campione nel mezzo circostante, consentendo pertanto piú agevoli determinazioni della conducibilità termica dei solidi, noti la densità ed il calore specifico.

Резюме С помощью новой экспериментальной техники, основанной на нестационарном методе, т.е. на свойствах распространения тепловых волн, мы измеряем коэффициент температуропроводностиD медного провода, посредством измения граничных условий, чтобы выяснить независимость величинD от поверхностных потерь тепла. Температурные осцилляции при фиксированной частоте 0.0121 Гц возбуждаются на одном конце образца, который помеЩен в атмосферу азота при различных давлениях в области от ∼10−2 мтор до 220 мтор. Температуры другого конца образца и стенок контейнера являются постояннюми 0°C, тогда как градиент температуры между средним значением осциллирующей темпертурой и этой постоянной температурой изменяется от 2°C до 12°C для каждого значения давления, за счет регулировки мощности нагревателя. Этот метод позволяет изменять тепловые потери, обусловленные либо проводимостью и конвекцией, либо излучением. Основная причина ошибок проистекает из неопределенности в измерениях фазового сдвига между тепловыми осцилляциями, заререгистрированными в двух фиксированных точках образца. Ошибка при измерении составляет около 2%. Экспериментальные значения, полученные для коэффициента температуропроводности при различных граничных условиях,D=(1.17±0.02) см−2с−1, хорошо согласуются с данными в литературе. Полученные результаты показывают, что предложенный экспериментальный метод обладает большим преимуществом при определении температуропроводности и, следовательно, теплопроводности твердых тел, не уделяя особого внимания изоляции образца.


To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.

This research was supported by the Consiglio Nazionale delle Ricerche, Rome (Italy).

Some preliminary results were presented at the ?LXVII Congresso della Società Italiana di Fisica?, Pisa, October 1981.  相似文献   
17.
    
The 2(H)-pyran-2-one bearing electron-donating tert-butylcarbamate (BocNH-) group at the 5- position is a “chameleon” diene and undergoes efficient Diels–Alder cycloadditions with alkene dienophiles with both electron-rich and electron-deficient substituents. Cycloadditions afford the 5-substituted bicyclic lactone cycloadducts regardless of the electronic nature of the dienophile. However, cycloadditions with electronically matched electron-deficient dienophiles proceed faster than those with electronically mismatched electron-rich dienophiles.  相似文献   
18.
Crack free, dense and transparent CdTiO3 thin films have been prepared by sol-gel technique using titanium butoxide and cadmium acetate. The formation of the CdTiO3 phase started from 500°C annealing temperature onwards. The complete orthorhombic structure of CdTiO3 was formed on Silicon (100) substrate at an annealing temperature of 600°C for 5 h. As the annealing temperature increased from 600 to 700°C, we have observed the cadmium silicate phase at the interface of Si and CdTiO3 phase. Structural, morphological and elemental evolution of these CdTiO3 thin films produced by sol-gel synthesis were characterised by grazing incidence X-ray diffraction (GIXRD), tapping mode atomic force microscopy (TMAFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) respectively.  相似文献   
19.
Density-functional all-electrons calculations within local-density approximation show that the two isoelectronic polymers poly(para-phenylene) and poly(para-borazylene) weakly interact with zigzag single-walled carbon nanotubes. The analysis of the electronic properties of the joint systems, both with the polymer inside and outside the nanotubes, reveals a physisorption process with small changes in band structures and densities of states with respect to the constituents. We evaluate the potential barrier arising between polymers and nanotubes. Finally, we remark a generic selectivity of poly(para-phenylene) with respect to the electronic behavior of nanotubes, leading to a change in the density of states of metallic tubules.  相似文献   
20.
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