全文获取类型
收费全文 | 5985篇 |
免费 | 271篇 |
国内免费 | 196篇 |
专业分类
化学 | 3368篇 |
晶体学 | 94篇 |
力学 | 82篇 |
综合类 | 1篇 |
数学 | 100篇 |
物理学 | 2807篇 |
出版年
2024年 | 5篇 |
2023年 | 13篇 |
2022年 | 41篇 |
2021年 | 56篇 |
2020年 | 86篇 |
2019年 | 84篇 |
2018年 | 67篇 |
2017年 | 84篇 |
2016年 | 134篇 |
2015年 | 139篇 |
2014年 | 126篇 |
2013年 | 535篇 |
2012年 | 152篇 |
2011年 | 248篇 |
2010年 | 161篇 |
2009年 | 268篇 |
2008年 | 373篇 |
2007年 | 423篇 |
2006年 | 402篇 |
2005年 | 316篇 |
2004年 | 320篇 |
2003年 | 267篇 |
2002年 | 345篇 |
2001年 | 232篇 |
2000年 | 289篇 |
1999年 | 231篇 |
1998年 | 214篇 |
1997年 | 123篇 |
1996年 | 93篇 |
1995年 | 111篇 |
1994年 | 94篇 |
1993年 | 79篇 |
1992年 | 68篇 |
1991年 | 23篇 |
1990年 | 26篇 |
1989年 | 27篇 |
1988年 | 20篇 |
1987年 | 30篇 |
1986年 | 23篇 |
1985年 | 26篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 19篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1973年 | 6篇 |
排序方式: 共有6452条查询结果,搜索用时 15 毫秒
131.
Intense parasitic nucleation has been observed at the surface of differential scanning calorimetry samples for various polymers, whereas their crystallization traces exhibit complex shapes. Revisited overall kinetics theories and computer simulation, taking into account small thickness of samples and transcrystallinity effects, allow to explain and reproduce experimental ‘double peaks’, currently observed with polyamide 6-6. The beginning of the transformation and the main peak are attributed to surface and bulk nucleations, respectively. As a consequence, any DSC experiment should be followed by a microscopic observation and more accurate models including thermal gradients and resistances should be developed for their interpretation. 相似文献
132.
Differential
scanning calorimetry (DSC) is a thermal analytical tool for preformulation
studies. Extrapolated melting temperature (TP)
and heat of fusion (ΔHf)
can be used as parameters for optimizing the DSC performance. Two model pharmaceuticals
acetaminophen and nicotinamide are used in this study. Using a factorial design
for the experimental model and matrix analysis the results, the effect of
sample mass, heating rate and the nitrogen flow rate were evaluated on the
ΔHf values
and TP values. Two
levels for each of the procedural variables were used as a balanced experimental
design with two sample sizes, two heating rates and two nitrogen flow rates.
It was found that the change in the heating rate caused significant changes
in the ΔHf
values but not the Tp
values for acetaminophen. However, no significant effect was found for the Tp value but ΔHf value was affected to a
certain extent for nicotinamide. 相似文献
133.
A. Coetzee M. E. Brown D. J. Eve C. A. Strydom 《Journal of Thermal Analysis and Calorimetry》1994,41(2-3):357-385
Both isothermal and programmed temperature experiments have been used to obtain kinetic parameters for the dehydrations and
the decompositions in nitrogen of the mixed metal oxalates: FeCu(ox)2·3H2O, CoCu(ox)2·3H2O and NiCu(ox)2·3.5H2O, [ox=C2O4]. Results are compared with those reported for the thermal decompositions of the individual metal oxalates, Cuox, Coox·2H2O, Niox·2H2O and Feox·2H2O. X-ray photoelectron spectroscopy (XPS) was also used to examinee the individual and the mixed oxalates.
Dehydrations of the mixed oxalates were mainly deceleratory processes with activation energies (80 to 90 kJ·mol−1), similar to those reported for the individual hydrated oxalates. Temperature ranges for dehydration were broadly similar
for all the hydrates studied here (130 to 180°C).
Decompositions of the mixed oxalates were all complex endothermic processes with no obvious resemblance to the exothermic
reaction of Cuox, or the reactions of physical mixtures of the corresponding individual oxalates.
The order of decreasing stability, as indicated by the temperature ranges giving comparable decomposition rates, was NiCu(ox)2>CoCu(ox)2>FeCu(ox)2, which also corresponds to the order of increasing covalency of the Cu−O bonds as shown by XPS.
In celebration of the 60th birthday of Dr. Andrew K. Galwey 相似文献
134.
Robert Liska 《Journal of polymer science. Part A, Polymer chemistry》2002,40(10):1504-1518
The synthesis of new water‐soluble photoinitiators (PIs) based on hydroxyalkylphenones, benzophenones, and thioxanthones with carbohydrate residues such as glucose, cellobiose, and 1‐amino‐1‐deoxy‐D ‐glucitol (glucamine) is described. In addition, selected initiators were reacted with methacryloyl chloride to obtain copolymerizable initiators with improved migration stability. Results from photo differential scanning calorimetry and gel‐content measurements in commercially available water‐thinnable and emulsion‐type resins as well as 2‐hydroxyethyl acrylate are included. Glucose‐modified PIs gave the best results with respect to compatibility with the resin, reactivity, and gel content. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1504–1518, 2002 相似文献
135.
G. G. G. Oliveira H. G. Ferraz J. S. R. Matos 《Journal of Thermal Analysis and Calorimetry》2005,79(2):267-270
Summary Taking into account the problems of desertification and agricultural practices able to provide income to the population at the semi-arid region of North-East Brazil, this work presents the results of the chemical and thermal characterization by TG and DSC of the seed derivatives of Cnidoscolus quercifolius , hereinafter called faveleira, aiming at the application of these materials as an alternative of food source for animals and for the human population at this region. The faveleira seed derivatives present thermodynamic properties similar to the ones of other foods utilized for human use, as well as an acceptable calorific value. According to TG and DSC results, was verified that the faveleira derivatives presents good thermal and oxidative stabilities. 相似文献
136.
137.
Joachim Angelkort Sander van Smaalen Prof. Dr. Sven Oliver Hauber Mark Niemeyer 《无机化学与普通化学杂志》2007,633(7):1031-1035
Single crystal X‐ray diffraction of Eu(SC36H49)2 has revealed a first order phase transition at a temperature of 119 K, that involves a reduction of the specific volume by 1 %. The transition corresponds to a doubling of the unit cell, as it is the result from reorientations of isopropyl groups that appear at peripheral sites of the organic ligands. It is argued that a denser packing is achieved at the expense of a less favourable conformation of one of the two crystallographically‐independent complexes in the low‐temperature phase. The Bond‐Valence method is used to show that interactions of equal strengths are present between europium and both sulphur atoms and both coordinating phenyl rings. 相似文献
138.
Cure kinetics of a cobalt catalysed dicyanate ester monomer in air and argon atmospheres from DSC data 总被引:1,自引:0,他引:1
A kinetic analysis of the cyclotrimerisation reaction of a dicyanate ester monomer catalysed by cobalt(II) acetylacetonate and nonylphenol in air and argon atmospheres has been carried out by differential scanning calorimetry (DSC). Dynamic and isothermal DSC scans as well as the glass transition temperature are the experimental data obtained. From isothermal scans a higher cyanate conversion in air than in argon was obtained. The cyanate conversions are satisfactorily described with a second-order kinetic equation in the kinetically controlled region, and by m-order (m<1) equation after vitrification is reached. Activation energies determined by different procedures agree among them, showing slightly higher values in argon than in air. 相似文献
139.
Gy. Marosi R. Lágner Gy. Bertalan P. Anna A. Tohl 《Journal of Thermal Analysis and Calorimetry》1996,47(4):1155-1161
Nucleating and transcrystallization behaviour of additives in engineering PP composites and the effect of modified interfacial structure is the subject of this series of papers. The first part concentrates on polypropylene/liquid crystalline polyester blends. Increased crystallisation temperature and degree of crystallinity of polypropylene is characteristic to the blends containing different amount of LCP additive. Transcrystallization process governs the formation of crystalline structure in these systems in course of isothermal crystallisation at 132C. The nucleating effect of LCP gives rise to more uniform crystalline structure in the polypropylene phase.The financial support of the OTKA 014194 is acknowledged with gratitude. 相似文献
140.
C. C. Seow C. H. Teo C. K. Vasanti Nair 《Journal of Thermal Analysis and Calorimetry》1996,47(5):1201-1212
Thermal characterization of gelatinized binary rice starch-water and ternary starch-sugar-water gels before and after aging was carried out using differential scanning calorimetry. The glass transition temperature of the maximally freeze-concentrated solution (Tg) in both fresh and aged gels was observed to decrease progressively with increasing sugar concentration. Aging of the gels generally shiftedTg to higher temperatures, but had little or no effect on the ice melting peak temperature (T
m). The presence of various sugars could either accelerate or retard starch (amylopectin) recrystallization, depending on the type and concentration of sugar, as well as on starch/water ratio. A hypothesis based on the dual antiplasticizing-plasticizing effects of sugars was postulated to explain the observed effects. Of the sugars studied, xylose and fructose appeared to display exceptional retardative and accelerative effects, respectively, on retrogradation.This study was funded by a Sixth Malaysia Plan R&D grant under the Intensification of Research Priority Areas (IRPA) Program of the Ministry of Science, Technology and Environment, Malaysia. We thank Dr. Harry Levine and Dr. Louise Slade for giving us the opportunity to contribute a paper to this special issue of JTA. 相似文献