全文获取类型
收费全文 | 2050篇 |
免费 | 247篇 |
国内免费 | 351篇 |
专业分类
化学 | 2013篇 |
晶体学 | 75篇 |
力学 | 41篇 |
综合类 | 4篇 |
数学 | 11篇 |
物理学 | 504篇 |
出版年
2023年 | 21篇 |
2022年 | 24篇 |
2021年 | 51篇 |
2020年 | 77篇 |
2019年 | 55篇 |
2018年 | 33篇 |
2017年 | 69篇 |
2016年 | 94篇 |
2015年 | 82篇 |
2014年 | 78篇 |
2013年 | 244篇 |
2012年 | 74篇 |
2011年 | 86篇 |
2010年 | 104篇 |
2009年 | 103篇 |
2008年 | 116篇 |
2007年 | 146篇 |
2006年 | 149篇 |
2005年 | 147篇 |
2004年 | 127篇 |
2003年 | 113篇 |
2002年 | 103篇 |
2001年 | 61篇 |
2000年 | 60篇 |
1999年 | 51篇 |
1998年 | 44篇 |
1997年 | 33篇 |
1996年 | 47篇 |
1995年 | 58篇 |
1994年 | 46篇 |
1993年 | 48篇 |
1992年 | 29篇 |
1991年 | 17篇 |
1990年 | 17篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 4篇 |
排序方式: 共有2648条查询结果,搜索用时 15 毫秒
1.
《Mendeleev Communications》2022,32(4):537-539
The two novel conglomerates were obtained by crystallization of racemic (2'S,3aS,6aR)/(2'R,3aR,6aS) (glycoluril-1-yl)-3-methylbutanoic acid and (2'R,3aR,6aR)/(2'S,3aS,6aS) (4,6-dimethylglycoluril-1-yl)pentanoic acid synthesized by highly diastereoselective condensation of 4,5-dihydroxy- imidazolidin-2-ones with racemic ureido acids. The differences in the molecular geometry of synthesized racemates were studied by X-ray diffraction that showed them to crystallize as conglomerates in non-centrosymmetric space groups Pna21 and P212121, respectively 相似文献
2.
Poly(ε-caprolactone) (PCL) composites filled by multi-walled carbon nanotubes (MWCNTs) which was non-covalently modified by the combined surfactants of poly(sodium 4-styrenesulfonate) and cetyltrimethyl-ammonium bromide (PSS-CTAB) were fabricated via simple solution precipitation method. PCL/MWCNTs composites provided with the low procolation threshold (0.4?wt%) and high electrical conductivity due to good dispersion of MWCNTs. And the excellent mechanical properties and enhanced thermal stability were also obtained with the addition of modified MWCNTs. In addition, all PCL composites showed significantly enhanced crystallization with increasing the MWCNTs contents, which demonstrated that the MWCNT-induced crystallization of PCL could effectively regulate the properties of composites. In a word, introducing non-covalent functionalized MWCNTs in the polymer system was a promising way for developing excellent conductive composites. 相似文献
3.
采用施加压力的方法将聚苯硫醚熔体凝固,凝固后获得的聚苯硫醚样品经过降温和卸压后在常温常压下回收. X射线衍射和差示扫描量热分析表明:约20 ms时间的快速压缩过程可以抑制熔体结晶,制备出非晶态聚苯硫醚块材,样品的表面及中心都是非晶态.非晶态聚苯硫醚的玻璃化转变温度和晶化温度分别为318和362 K.常压下的退火实验表明,非晶态聚苯硫醚在425 K等温结晶的产物为正交相晶型.压致凝固法中熔体的凝固不是靠温度变化,而是靠压力变化,样品表面和内部处在一致的温度下同时受压凝固,避免了热传导对非晶尺寸的影响,因此非常有利于获得结构均匀的大尺寸非晶态材料. 相似文献
4.
Felix Krupp Wolfgang Frey Clemens Richert 《Angewandte Chemie (International ed. in English)》2020,59(37):15875-15879
The most reliable method to determine the absolute configuration of chiral molecules is X‐ray crystallography, but small molecules can be difficult to crystallize. We report rapid co‐crystallization of tetraaryladamantanes with small molecules as different as n‐decane to nicotine to produce crystals for X‐ray analysis and the assignment of absolute configuration when the molecules are chiral. A screen of 52 diverse compounds gave inclusion in co‐crystals for 88 % of all cases and a high‐resolution structure in 77 % of cases. Furthermore, starting from three milligrams of analyte, a combination of NMR spectroscopy and X‐ray crystallography produced a full structure in less than three days using an adamantane crystallization chaperone that encapsulates the analyte at room temperature. 相似文献
5.
Dr. Mingliang Li Dr. Xiaoge Wang Guozhi Wang Shizhao Ren Shuo Li Prof. Feng Wei Prof. Shouke Yan Prof. Xuefeng Guo Prof. Hailing Tu 《Chemphyschem》2020,21(2):181-186
Organic semiconductor (OSC) crystals have great potential to be applied in many fields, as they can be flexibly designed according to the demands and show an outstanding device performance. However, OSCs with the capacity of solid-state crystallization (SSC) are developing too slowly to meet demands in productions and applications, due to their difficulties in molecular design and synthesis, unclear mechanism and high dependence on experimental conditions. In this work, in order to solve the problems, we synthesized an organic semiconductor capable of SSC at room temperature by adjusting the relationship between conjugated groups and functional groups. The thermodynamic and kinetic properties have been studied to discover the model of film SSC. Moreover, it can be purposefully controlled to prepare the high-quality crystals, and their corresponding organic electronic devices were further fabricated and discussed. 相似文献
6.
Effects of β‐nucleating agent and crystallization conditions on the crystallization behavior and polymorphic composition of isotactic polypropylene/multi‐walled carbon nanotubes composites 下载免费PDF全文
Jian Kang Jinghan He Zhengfang Chen Feng Yang Jinyao Chen Ya Cao Ming Xiang 《先进技术聚合物》2015,26(1):32-40
In this study, the effects of crystallization conditions (cooling rate and end temperature of cooling) on crystallization behavior and polymorphic composition of isotactic polypropylene/multi‐walled carbon nanotubes (iPP/MWCNTs) composites nucleated with different concentrations of β‐nucleating agent (tradename TMB‐5) were investigated by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD) and scanning electronic microscopy (SEM). The results of DSC, WAXD and SEM revealed that the addition of MWCNTs and TMB‐5 evidently elevates crystallization temperatures and significantly decreases the crystal sizes of iPP. Because of the competition between α‐nucleation (provided by MWCNTs) and β‐nucleation (induced by TMB‐5), the β‐phase crystallization takes place only when 0.15 wt% and higher concentration of TMB‐5 is added. Non‐isothermal crystallization kinetics study showed that the crystallization activation energy ΔE of β‐nucleated iPP/MWCNTs composites is obviously higher than that of pure iPP, which slightly increases with the increase of TMB‐5 concentration, accompanying with the transition of its polymorphic crystallization behavior. The results of non‐isothermal crystallization and melting behavior suggested that the cooling rate and end temperature of cooling (Tend) are important factors in determining the proportion and thermal stability of β‐phase: Lower cooling rate favors the formation of less amount of β‐phase with higher thermal stability, while higher cooling rate encourages the formation of higher proportion of β‐phase with lower thermal stability. The Tend = 100°C can eliminate the β–α recrystallization during the subsequent heating and therefore enhance the thermal stability of the β‐phase. By properly selecting TMB‐5 concentration, cooling rate and Tend, high β‐phase proportion of 88.9% of the sample was obtained. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
7.
Konstantin V. Pochivalov Yaroslav V. Kudryavtsev Andrey V. Basko Tatyana N. Lebedeva Roman Y. Golovanov 《Journal of Macromolecular Science: Physics》2015,54(12):1427-1437
The full phase diagrams of low-density polyethylene (LDPE), high-density polyethylene (HDPE), and isotactic polypropylene (i-PP) mixtures with 1,2,4,5-tetrachlorobenzene (TeCB), including the solubility curve of TeCB in a solid polymer, were constructed by an optical method. The diagrams contain a eutectic point that corresponds to the situation when the crystallization of TeCB out of its solution in a polyolefin is accompanied by the crystallization of monomer units of the macromolecules. As a result, the polymer acquires a gel structure with crystallites as crosslinks and amorphous regions saturated with TeCB. It is demonstrated that the eutectic point position on the phase diagram can be used for ranking polymers with respect to their thermodynamic affinity to a solvent. For the studied systems, the affinity to TeCB was decreased in the order i-PP, HDPE, and LDPE. Direct experimental evidence was obtained that TeCB crystals can be dissolved in a solid polymer via a vapor phase mechanism, which leads to the polymer amorphization. 相似文献
8.
Minghua Min Yuyuan Shi Haiyou Ma Hongliang Huang Jiangao Shi Xiaoxue Chen 《Journal of Macromolecular Science: Physics》2015,54(4):411-423
The effects of addition of synthesized organic-suspension silver nanoparticles on the crystallization and thermal stability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were studied by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (XRD), UV-Vis absorption spectroscopy, polarized optical microscopy (POM), and thermal gravimetric analysis (TGA). The TEM images showed the average primary size of the as-synthesized silver nanoparticles, coated with a monolayer of the surfactants consisting of oleic acid and an alkylamine, was about 5 nm with narrow distribution, and that they were uniformly dispersed in n-heptane. PHBV/silver nanocomposites were prepared by melt mixing in an internal mixer and then injection molded into rectangle-shaped specimens by a labscale injection molding device. The coated silver nanoparticles showed a homogenuous dispersion in the PHBV matrix when the content of coated silver nanoparticles was about 1%. Both the DSC and POM data showed the efficient heterogeneous nucleation by the coated silver nanoparticles for facilitating PHBV crystallization. The thermal stability of the PHBV/silver nanocomposites improved with the increase in the content of the coated silver nanoparticles. 相似文献
9.
共轭高分子具有优异的光电性质和可加工性,被广泛用于有机光电器件的制备。共轭单元的存在使得此类高分子具有更刚性的主链结构。由于较强的分子间相互作用,共轭高分子容易在溶液中形成组装结构。共轭高分子的链构象、组装体结构、薄膜形貌和光电性能之间的联系研究成为了本领域的研究热点。然而,共轭高分子在可见光区存在较强的吸收效应,用传统的光散射技术对共轭高分子溶液的研究充满挑战。本文总结了近年来对于共轭高分子链刚性的研究,并从分子尺度上讨论了链结构与光学、电学性能间可能存在的关联;进一步阐述了共轭高分子溶液聚集的形成和演化,总结了溶液聚集与成膜过程中影响场效应迁移率的因素。试图在不同尺度上讨论共轭高分子的微观结构与宏观性能之间的关系。 相似文献
10.
A.L. Pirozerski O.I. Smirnova A.I. Nedbai O.L. Pirozerskaya N.A. Grunina V.M. Mikushev 《Physics letters. A》2019,383(30):125872
Melting and crystallization of n-decane embedded into porous glass with the mean pore size of about 6.4 nm were studied using acoustic and DSC methods. Smearing of the phase transitions, decrease of melting and freezing temperatures, pronounced hysteresis between melting and crystallization were revealed by both methods. In DSC measurements for the pore filling factors 70% and higher double peaks were observed upon cooling while only single peaks were present upon heating. Also a high reduction of the corresponding phase transition heats was revealed. Melting and freezing intervals determined by acoustic and DSC methods strongly differed from each other. A model which qualitatively explains the observed anomalies is proposed. It supposes the formation of liquid layers on the surface of the pores. 相似文献