全文获取类型
收费全文 | 379篇 |
免费 | 47篇 |
国内免费 | 37篇 |
专业分类
化学 | 89篇 |
晶体学 | 1篇 |
力学 | 181篇 |
综合类 | 11篇 |
数学 | 36篇 |
物理学 | 145篇 |
出版年
2023年 | 14篇 |
2022年 | 16篇 |
2021年 | 20篇 |
2020年 | 17篇 |
2019年 | 11篇 |
2018年 | 15篇 |
2017年 | 23篇 |
2016年 | 25篇 |
2015年 | 20篇 |
2014年 | 20篇 |
2013年 | 25篇 |
2012年 | 19篇 |
2011年 | 25篇 |
2010年 | 17篇 |
2009年 | 17篇 |
2008年 | 24篇 |
2007年 | 17篇 |
2006年 | 20篇 |
2005年 | 23篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 14篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有463条查询结果,搜索用时 187 毫秒
101.
Xuan Sun Long Chen Huijiao Yan Li Cui Hidayat Hussain Lei Xie Jie Liu Yujuan Jiang Zhaoqing Meng Guiyun Cao Jeonghill Park Daijie Wang 《Journal of separation science》2022,45(11):1856-1865
Paeonia lactiflora Pall., one of the most famous classical herbal medicine, has been used to treat diseases for over 1200 years. In this research, the functional ingredients were purified by online-switch two-dimensional high-speed counter-current chromatography combined with inner-recycling and continuous injection mode. The antioxidant activity was evaluated by investigating the 2,2′-azobis (2-amidinopropane) dihydrochloride-induced oxidant damage in vitro and confirmed through molecular docking. n-Butanol/ethyl acetate/water (2:3:5, v/v) solvent system was used for the first-dimensional separation and optimized the sample loading. Two pure compounds and a polyphenol-enriched fraction were separated. The polyphenol-enriched fraction was separated with a solvent system n-hexane/ethyl acetate/methanol/water (2:8:4:6, v/v) with continuous injection mode. Five compounds were successfully separated, including gallic acid ( 1 ), methyl gallate ( 2 ), albiflorin ( 3 ), paeoniflorin ( 4 ), and ethyl gallate ( 5 ). Their structures were identified by mass spectrometry and NMR spectroscopy. The results from the antioxidant effect showed that albiflorin had stronger antioxidant activity. Molecular docking results indicated that the affinity energy of the identified compounds ranged from -3.79 to -8.22 kcal/mol and albiflorin showed the lowest affinity energy. Overall, all those findings suggested that the strong antioxidant capacity of albiflorin can be potentially used for the treatment of diseases caused by oxidation. 相似文献
102.
103.
Chang Suk Kong Se Jin Choi Hyun Seok Lee 《Journal of Macromolecular Science: Physics》2016,55(2):201-210
Electrospinning is regarded as an effective method to generate nanoscale fibers. However, we believe that the mechanism of the formation of nanoscale fibers by Electrospinning has not yet been fully investigated. In this study, the jet behavior under various conditions was observed with a high-speed camera with short exposure periods. The behaviors of stable and unstable jets were compared. The effect of bending instability on the deposition pattern of jets was examined at different voltages and concentrations. In addition, the diameters of nanoscale fibers were analyzed as a function of sampling position. 相似文献
104.
S. V. Koshevaya M. Tecpoyotl-T E. A. Gutiérrez-D M. Hayakawa V. V. Grimalsky 《International Journal of Infrared and Millimeter Waves》1999,20(11):1925-1932
Theoretical and experimental analysis has been performed for surface oriented silicon plasma-based p,i,n structures used to control high power level, broadband devices. It is shown that these structures are very promising for their use as modulators in the millimeter and submillimeter wave range. 相似文献
105.
Llpophilic tea polyphenols (LTP) was prepared by esterification of green tea polyphenols (GTP) with hexadecanoyl chloride. A novel long-chaln acyl catechin was isolated and purified from LTP by high-speed countercurrent chromatography (HSCCC).Its molecular structure was elucidated as epigallocatechin-3-O-gallate-4‘-O-hexadecanate by elemental analysis, IR, MS and ^1H NMR spectra. 相似文献
106.
数字散斑法在局域剪切带三维变形研究中的应用 总被引:3,自引:0,他引:3
在适当的温度、应变率和预变形下,合金材料的拉伸试验中,将会出现伴随应力锯齿形跌落的雪崩式剪切变形带,即波特文-勒夏特利埃(Portevin-Le Chatelier,PLC)效应。利用高速数字摄像系统(分辨力1000 frames/s)并结合数字散斑干涉法(Digital speckle pattern interferometry,DSPI)和数字散斑相关法设计了一套光学变形测量系统,实现了拉伸试验中对试件表面三维变形的实时、精确测量。利用该光学系统对铝铜合金试件在拉伸试验中产生的跳跃传播的局域剪切带瞬态成核过程进行捕捉。通过结合数字散斑相关法得到的面内变形定量结果和数字散斑干涉法得到的表现离面变形的条纹图,再现了剪切变形带成核和传播瞬间的三维变形过程。 相似文献
107.
108.
I.?S.?KolesovEmail author R.?Androsch H.?-J.?Radusch 《Journal of Thermal Analysis and Calorimetry》2004,78(3):885-895
Non-isothermal crystallization and melting of metallocene-catalyzed polyethylene was analyzed using the power-compensating calorimetry as function of both cooling rate and branch-degree ranging from 1 to 300 K min–1, and from 0 to 72 hexyl-branches per 1000 carbon atoms, respectively. The onset crystallization temperature decreases linearly with increasing logarithm of cooling rate. The slope of this dependence increases with increasing branch-degree, which is explained by a stronger inhibition of the crystallization by the branches and the decreasing diffusion rate of molecules. The melting endotherms reveal a clear reduction of the crystallinity in the entire temperature range with increasing cooling rate.The authors gratefully acknowledge financial support by Deutsche Forschungsgemeinschaft (DFG). Samples of polyethylenes were kindly provided by Omya GmbH (Germany), or tailor-synthesized by Dr. S. Rudolph (Martin Luther University Halle-Wittenberg, Germany). Samples of adamantane and of liquid crystal M24 (4-cyano-4-octyloxybiphenyl) were kindly provided by Dr. S. Neuenfeld (Merck KGaA, Germany). Thanks are due to Dr. C. Gabriel (Friedrich Alexander University Erlangen-Nurnberg) for the molecular characterization of poly(ethylene-co-1-octene)s. 相似文献
109.
甲烷/空气预混气体火焰的传播特征 总被引:6,自引:0,他引:6
利用高速纹影摄像等技术探讨了密闭管道内不同当量比的甲烷/空气预混气体火焰的传播特征。结果表明,当甲烷含量接近当量值时,预混气体火焰传播中会发生火焰阵面由向未燃区弯曲到向已燃区弯曲的转折过程,逐渐由层流燃烧转变成湍流燃烧,并形成Tulip火焰结构;当甲烷含量偏离当量值一定程度时,预混火焰呈现出典型的层流燃烧特征,不会发生火焰阵面由向未燃区弯曲到向已燃区弯曲的转折过程。Tulip火焰结构形成于火焰传播速度迅速降低的区间里,且只有当减速阶段的最大加速度的绝对值大于某一数值时才能形成;Tulip火焰结构是预混火焰由层流燃烧向湍流燃烧转变的一个中间过程。 相似文献
110.
高速逆流色谱与硅胶柱色谱结合分离制备高纯度芦荟素异构体 总被引:6,自引:0,他引:6
芦荟素是芦荟叶中主要的蒽醌类成分,通常以芦荟素A和B两种非对映异构体形式并存,目前已成为许多芦荟产品质量控制指标之一。采用高速逆流色谱和硅胶柱色谱结合的方法,从老芦荟干粉中分离制备了高纯度的芦荟素A(纯度为98%)和芦荟素B(纯度为96%)样品,并采用快原子轰击质谱(FAB-MS)和核磁共振氢谱(1H NMR)以及GOESY(gradient-enhanced nuclear Overhauser effect spectroscopy)等方法对所得的两个芦荟素异构体的立体构象进行了确认。该法具有制备量大和分离效率高的特点。 相似文献