全文获取类型
收费全文 | 676篇 |
免费 | 186篇 |
国内免费 | 86篇 |
专业分类
化学 | 289篇 |
晶体学 | 109篇 |
力学 | 99篇 |
综合类 | 8篇 |
数学 | 7篇 |
物理学 | 436篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 18篇 |
2021年 | 22篇 |
2020年 | 14篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 33篇 |
2016年 | 32篇 |
2015年 | 17篇 |
2014年 | 33篇 |
2013年 | 90篇 |
2012年 | 65篇 |
2011年 | 60篇 |
2010年 | 50篇 |
2009年 | 67篇 |
2008年 | 36篇 |
2007年 | 40篇 |
2006年 | 40篇 |
2005年 | 33篇 |
2004年 | 32篇 |
2003年 | 31篇 |
2002年 | 26篇 |
2001年 | 19篇 |
2000年 | 29篇 |
1999年 | 19篇 |
1998年 | 14篇 |
1997年 | 28篇 |
1996年 | 8篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有948条查询结果,搜索用时 0 毫秒
1.
玻璃陶瓷材料中Tm3+离子红外到蓝色上转换发光 总被引:4,自引:0,他引:4
系统研究了PbF2+GeO2+WO3ⅩⅣTmF3玻璃陶瓷材料中,在近红外光(1.06μm)激发下,Tm3+离子的发光特性.实验中观测到Tm3+离子的两组峰值位置分别在20920cm-1和22173cm-1的蓝色上转换发光,并证实这两组上转换发光分别与吸收三个和四个光子有关,同时建立了上转换发光的模型.为了选择最佳掺杂浓度,详细地测量了Tm3+离子峰值为20920cm-1的蓝色上转换发光强度与TmF3浓度的关系. 相似文献
2.
Total-reflection X-ray fluorescence spectrometry has been compared with Instrumental Neutron Activation Analysis in order to test its potential application to the study of archaeological ceramics in the archaeometric field. Two direct solid non-chemical sample preparation procedures have been checked: solid sedimentation and solid chemical homogenization. For sedimentation procedure, total-reflection X-ray fluorescence allows the analysis of the elemental composition with respect to the size fraction but not the average evaluation of the composition. For solid chemical homogenization procedure, total-reflection X-ray fluorescence provides precise (from 0.8% to 27% of coefficient of variation) and accurate results (from 91% to 110% of recovery) for 15 elements (Cr, Hf, Ni, Rb, Al, Ba, Ca, K, Mn, Ti, V, Cu, Ga, Y and Fe) with an easy sample preparation process of the solid clay and without previous chemical treatment. The influence of the particle sizes has been checked by total-reflection X-ray fluorescence sample angle scans and anomalous behaviors have been found for three additional detected elements: As, Sr and Zn, which can be attributed to interference effects of the mineral grain sizes of their associated chemical phases in the total-reflection X-ray fluorescence interference region. The solid chemical homogenization procedure produces data useful for archaeological interpretation, which is briefly illustrated by a case-study. Finally, the decantation procedure data can be also useful for size chemical speciation and, consequently, for alternative environmental total-reflection X-ray fluorescence applications. 相似文献
3.
氟氧化物陶瓷的多谱线上转换发光 总被引:1,自引:0,他引:1
以氧化硅、氟化铅为基质制备了Er3 :Yb3 共掺杂氟氧化物陶瓷 ,X 射线分析表明陶瓷中存在着 β PbF2 晶相 ,沉积在其中的稀土离子由于具有很低的无辐射跃迁几率而显示出良好的上转换性能。Er3 ,Yb3 离子之间存在的多种能量传递通道 ,导致稀土离子十分丰富的上转换谱线的出现。 相似文献
4.
V. Nastro D. Vuono M. Guzzo G. Niceforo I. Bruno P. De
Luca 《Journal of Thermal Analysis and Calorimetry》2006,84(1):181-184
The aim of this paper is to characterize some raw
materials used for ceramics material production. Five samples of clay have
been analyzed. It has been carried out a patterned sampling in a quarry in
Rosarno (South Italy).
Chemical-physical
properties on clay samples are determined. Test pieces have been prepared
and physical properties after firing are determined by DSC thermal analysis,
XRD analysis and X-ray fluorescence. It is important to note the high amount
of Fe2O3. The mixture principally
contains quartz, illite and oligoclase. It has been observed the colour and
the shape after firing: predominant colour is red. In this case the clay has
been used in mixtures covered with glazes. The colour of internal clay is
hidden by opaque of glazes. The analysed raw materials can be used in a slip
for single fired red tiles. The A2sp clay produces best ceramics at 1000°C. 相似文献
5.
6.
V. Balek H. Hamerská L. Montanaro A. Negro 《Journal of Thermal Analysis and Calorimetry》1992,38(4):567-573
The results of the investigations of thermal behaviour of Li2ZrO3, prepared in the amorphous state by means of sol-gel technique are demonstrated. The thermal treatment was carried out in air under constant heating rate of 5 deg·min–1 and cooling rate of 2.5 deg·min–1. The methods of DTA, TG, Emanation Thermal Analysis (ETA) and dilatometry were used, for characterization of the thermal behaviour in dynamic conditions. The X-ray diffraction patterns were used for characterization of the phase changes observed by TA Methods.
Zusammenfassung Ergebnisse aus Untersuchungen des thermischen Verhaltens von Li2ZrO3, hergestellt mittels einer Sol-Gel-Technik im amorphen Zustand werden dargelegt. Die thermische Behandlung wurde in Luft bei einer konstanten Aufheizgeschwindigkeit von 5 Grad·min–1 und einer Abkühlgeschwindigkeit von 2,5Grad·min–1 durchgeführt. Zur Beschreibung des thermischen Verhaltens unter dynamischen Verhältnissen wurden DTA, TG, Emanationsthermoanalyse und Dilatometrie angewendet. Zur näheren Charakterisierung der bei TG beobachteten Phasenumwandlungen wurde Röntgendiffraktion verwendet.相似文献
7.
Englert BC Scholz S Leech PJ Srinivasarao M Bunz UH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(3):995-1000
We describe the synthesis of two cyclobutadiene(cyclopentadienyl)cobalt-containing poly(p-phenylene ethynylene)s (PPEs) and their use as precursors for stable ceramic surface coatings. Organometallic PPEs were shaped into hexagonally ordered assemblies by using the breath-figure method. Such breath figures can be washed away with an appropriate solvent. Upon pyrolysis at 500 degrees C under either nitrogen or air, the bubble arrays persist as ceramics and are insoluble in organic solvents or water. The formed pyrolyzed bubble arrays were analyzed by optical and scanning electron microscopy, as well as energy dispersive X-ray microanalysis (EDX). The composition of the ceramic materials is discussed based on EDX and IR data. 相似文献
8.
The SHS route is based on the well-known thermite reaction, in which a strongly exothermic reaction can sustain itself and propagate in the form of a combustion wave until the reactants have been completely consumed. The successful application of the method to the synthesis of superconducting ceramics of stoichiometry RBa2Cu3Oy (R=Y, Er, Yb) is reported. The 123 phase was obtained when pellets of R2O3, BaO2 and Cu metal in the correct proportions were dropped into a heater held at 800°C in an oxygen atmosphere and left there for only 10 minutes. Thermal methods (DSC and DTA) are excellent techniques with which to investigate the dependence of the reaction on heating rate, atmosphere and starting composition. 相似文献
9.
V. A. Drebushchak L. N. Mylnikova T. N. Drebushchak V. V. Boldyrev 《Journal of Thermal Analysis and Calorimetry》2005,82(3):617-626
Summary Ancient ceramic samples (single fragments and different parts of pots, unbroken and repaired; total about 180 samples) dated
from the transitional period of late Bronze to early Iron Age (VIII-VI centuries BC) and early Iron Age (VII-IV centuries
BC) were investigated by thermal analysis, X-ray powder diffraction, petrography, and scanning electron microscopy equipped
with the energy-dispersive X-ray analyzer. In addition to that, to identify the clay sources for the ceramic manufacturing,
about 15 samples of clays and soils found near archeological digs and taken from the mineralogical museum were investigated.
We found out that the calcite content of ceramics is a very informative parameter for the identification of the clay source
for the pottery manufactured at low technological level (low-temperature firing). 相似文献
10.
AES depth profiles on ceramic powders (untreated/hydrolyzed/oxidized/ (Al, Y)2O3 coated Si3N4, [BaO, SiO2] coated Al2O3) are feasible on thin, homogeneous layers or m sized agglomerations prepared on an Au foil. By means of the depth profiles one can qualitatively characterize the coating around the particles. Factor analysis of the depth profiles on the differently treated Si3N4 powders suggests the existence of an Si2N2O phase on the oxidized sample.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday 相似文献