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21.
Summary Measured structure factors of liquid alkali metals are examined in the framework of screened pair potential theory. Information
on the main attractive well in the effective pair potential is obtained from the structural data by an approximate method
stemming from an optimized random-phase treatment of the indirect ion-ion attraction. The results are compared with a variety
of theoretical pair potentials in the cases of sodium and potassium, after a test of the method against computer simulation
data on a model for rubidium. Results for the other alkali metals are also given and discussed. The small-angle scattering
region is then examined in considerable detail, with special attention to the possibility of a linear term in a series expansion
of the structure factor at very small momentum transfer. Although sensitivity to both the bare electron-ion coupling and the
local field factor in the screening function is demonstrated and analysed, no linear term of the magnitude reported in recent
X-ray diffraction experiments is found in the present theoretical framework.
Riassunto Il lavoro discute i fattori di struttura misurati nei metalli alcalini liquidi nell'àmbito della teoria di potentiziali di coppia schermati. L'inversione dei dati strutturali permette di ottenere informazioni sulla buca attrattiva nel potenziale, che è confrontata con potenziali teorici dopo un controllo del metodo d'inversione su dati di simulazione. Si analizza quindi il comportamento del fattore di struttura a piccoli numeri d'onda, in relazione all'osservazione di un termine lineare nella figura di diffrazione di raggi X.
Резюме Измеренные структурные факторы жидких щелочных металлов исследуются в рамках теории экранированных парных потенциалов. Из структурных данных получается информация об основной яме притяжения в эффективном парном потенциале. Полученные результаты сравниваются с целым рядом теоретических парных потенциалов в случаях натрия и калия. Предложенный метод проверяется посредством компьютерного моделирования для рубидия. Также приводятся и обсуждаются результаты для других щело ных металлов. Подробно исследуется область малоуглового рассеяния, уделяя особое внимание возможности существования линейного члена в степенном разложении структурного фактора при очень малых передаваемых импульсах. Анализируется чувствительность предложенного подхода в связи с обнаружением линейного члена в экспериментах по дифракции рентгеновских лучей.相似文献
22.
塑料注射成型是加工热塑性塑料的一种主要方法。注射过程中,塑料在注射机料筒和模具中经历着复杂的运动和变化过程,直接影响到充模的过程,和塑料制品的微观、细观、宏观结构(取向、结晶、熔合均匀性等),从而影响到塑料制品的物理—机械性能。所以充模过程是注射成型的核心过程。 本文采用透明模实验装置,对多种模具型腔的注射充模流变过程进行了高速摄影研究。文中介绍了试验装置、光路系统,以及摄影结果,并采用影片运动数据分析处理系统,对园形模腔的充模流变过程进行了定量动态分析,研究了充模流变过程的运动规律。这对完善塑料注射成型工艺的基础理论,摆脱了目前生产中经验式和技艺式处理问题的工作方法,对减少模具设计和工艺参数确定过程中的盲目性具有重要的意义。 相似文献
23.
M. Affronte J.C. Lasjaunias A. Cornia 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):633-639
The effects of the internal guest substitution within hexa-iron molecular rings (Na:Fe6 and Li:Fe6) have been investigated
by means of low temperature specific heat (LTSH) measurements. By changing Na to Li as central metal ion, the Schottky anomaly
shifts towards lower temperatures. The data analysis is supported by the study of the LTSH of the non-magnetic Na:Ga6 compound
which has the same core structure as the iron rings. For the non-magnetic Na:Ga6, significant deviations from the simple Debye law were found and the use of conventional C
vs.
T fitting curves is critically discussed. The singlet-triplet energy gap ( K) and its zero-field splitting ( K) evaluated from the magnetic contribution of the Li:Fe6 LTSH are compared to values estimated by high field torque magnetometry.
Received 25 November 1999 相似文献
24.
The reaction mechanism of AsCl3 with H2 has been studied by using the method of BHandHLYP in Density Functional Theory (DFT) at the 6-311G** basis set. The transition state of each reaction is verified via the analysis of vibration mode and Intrinsic Reaction Coordinate (IRC). Meanwhile,single-point energy has been calculated at the QCISD(T)/6-311G** level,and the zero-point energy correction has been made to the total energy and reaction energy barrier. It shows that AsCl3 reacts with H2 to first result in AsHCl2 which may incline to self-decompose and finally afford the product As2,or continue to react with H2 to provide the product AsH3. The computing result demonstrates that the former is the main reaction channel. 相似文献
25.
HUANG Wei YUAN Cai Ansaldi Mireille Morelli Xavier Edward J. Meehan CHEN Li-Qing HUANG Ming-Dong 《结构化学》2007,26(5):594-598
TorI, a Tor system inhibitor acting through protein-protein interaction with the TorR response regulator, is an excisionase that interacts with the integrase and DNA during prophage excision. It has been crystallized by the vapor-diffusion method using polyethylene glycol 3350 as a precipitant at pH 8.5. The X-ray diffraction data sets from the TorI crystal was collected at a resolution of 2.1 , using a synchrotron source. The crystal belongs to primitive monoclinic lattice with cell parameters of 46.210 × 53.992 × 73.561 相似文献
26.
Theoretical Studies on the Reaction Mechanism of 1-Chloroethane with Hydroxyl Radical 总被引:1,自引:1,他引:0
WANG Bing-Xing WANG Li 《结构化学》2007,26(6):695-702
The reaction mechanism of 1-chloroethane with hydroxyl radical has been inves- tigated by using density functional theory (DFT) B3LYP/6-31G (d, p) method. All bond dissociation enthalpies were computed at the same theoretical level. It was found that hydrogen abstraction pathway is the most favorable. There are two hydrogen abstraction pathways with activation barriers of 0.630 and 4.988 kJ/mol, respectively, while chlorine abstraction pathway was not found. It was observed that activation energies have a more reasonable correlation with the reaction enthalpy changes (△Hr) than with bond dissociation enthalpies (BDE). 相似文献
27.
28.
Summary We have used a simple quasi-static model to study the microscopic behaviour of a Pb ion in the region of the solid-liquid
interface of aluminium. Calculations make use of anab initio potential, not used before in the literature. The potential field experienced by the Pb ion has a characteristic structure,
leading to anisotropic diffusion and segregation processes, depending on the orientation of the interface plane. This is qualitatively
related to experimental findings. 相似文献
29.
W. Boujelben A. Cheikh-Rouhou J.C. Joubert 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):419-423
Deficiency effects in the A site upon the structural, magnetic and electrical properties in the lacunar perovskite manganite
oxides Pr0.7Sr0.3-x
xMnO3 ( 0 ?
x
? 0.3) and Pr0.7-x
xSr0.3MnO3 ( 0 ?
x
? 0.23) have been investigated. This study focuses on the different parameters which govern the magnetic and electrical properties
in such samples. The powder X-ray diffraction patterns for all samples could be indexed either with a rhombohedral perovskite
structure and R
c space group for x
? 0.2 in strontium deficient samples and for x
? 0.1 for praseodymium deficient ones. For other values of x the samples could be indexed in the orthorhombic structure with Pbnm space group. Magnetic and electrical investigations
show that praseodymium and strontium vacancies do not have similar effects on the lacunar compounds. Magnetization measurements
versus temperature show that all our samples exhibit a magnetic transition when the temperature decreases. All the praseodymium
deficient samples exhibit a paramagnetic-ferromagnetic transition when the temperature decreases while the strontium deficient
ones exhibit this transition only for low x values. The magnetic transition temperature shifts to lower values as the strontium deficiency increases (from 265 K for
x
= 0 to 90 K for x
= 0.3) and to higher values with the praseodymium deficiency increase (from 265 K for x
= 0 to 315 for x
= 0.23). Resistivity measurements as a function of temperature show a semiconducting-metallic transition for all x values in the praseodymium lacunar samples and only for low x values ( 0 ?
x
? 0.1) in the strontium lacunar ones when the temperature decreases.
Received 12 April 2000 and Received in final form 8 January 2001 相似文献
30.
Girwar Singh Neeraj Kumar Ashok K. Yadav A. K. Mishra 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):621-630
( - )- cis -2(4-Methoxyphenyl)-3-hydroxy/methoxy-6,8-dichloro/6-chloro-2,3-dihydro-1,5-benzothiazepin-4[5H/5-chloroacetyl/5-(4'-methylpiperazino-1')acetyl]-ones have been synthesized by the condensation of 2-amino-3,5-dichloro/3-chloro benzenethiol with methyl-( - )- trans -3(4-methoxyphenyl)glycidate in xylene. Ribofuranosides viz ( - )- cis -2(4-methoxyphenyl)-3-methoxy-6,8-dichloro/6-chloro-2,3-dihydro-1,5-benzothiazepine-4-[5-(2',3',5'-tri- O -benzoyl- g -D-ribofuranosyl)-ones have been synthesized by the treatment of 3-methoxy derivatives of 1,5-benzothiazepines with sugar viz g -D-ribofuranose-1-acetate-2,3,5-tribenzoate in toluene at vacuo. Synthesized compounds have been characterized by elemental analysis, IR, 1 H NMR spectral studies and screened for their antimicrobial activity. 相似文献