全文获取类型
收费全文 | 518篇 |
免费 | 28篇 |
国内免费 | 7篇 |
专业分类
化学 | 402篇 |
晶体学 | 7篇 |
力学 | 37篇 |
数学 | 30篇 |
物理学 | 77篇 |
出版年
2023年 | 2篇 |
2022年 | 9篇 |
2021年 | 14篇 |
2020年 | 11篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 15篇 |
2014年 | 16篇 |
2013年 | 24篇 |
2012年 | 43篇 |
2011年 | 37篇 |
2010年 | 33篇 |
2009年 | 28篇 |
2008年 | 32篇 |
2007年 | 27篇 |
2006年 | 34篇 |
2005年 | 40篇 |
2004年 | 30篇 |
2003年 | 23篇 |
2002年 | 20篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 2篇 |
排序方式: 共有553条查询结果,搜索用时 484 毫秒
121.
Reaction of (S)-2-(tert-butyldiphenylsilyloxy)-5-(mesyloxy)pentanal with hydroxylamine in allyl alcohol brought about simultaneous 1,3-dipolar cycloaddition of the resulting nitrone to allyl alcohol to give three diastereoisomeric adducts, from which (+)-febrifugine and (+)-isofebrifugine, potent antimalarial alkaloids, were synthesized. 相似文献
122.
Six aliphatic sulfates, kairomones released from a crustacean Daphnia pulex induce morphological changes of phytoplankton Scenedesmus gutwinskii at ppb (10−9 g/mL) concentrations. 相似文献
123.
The ultrafast optical response in a quasi-one-dimensional halogen-bridged mixed-valence complex [Pd(en)2] [PdCl2(en)2] (ClO4)4 (en = ethylenediamine) has been investigated by the use of a femtosecond absorption spectrum, calculated from a pump—probe reflection spectrum at room temperature by the Kramers—Kronig relations. The time dependence of the transient photoinduced absorption around 1.7 eV and the bleaching from 1.9 to 2.5 eV were calculated for three decay components. They are free excitons with a lifetime of about 800 fs, self-trapped excitons with a lifetime of about 3 ps, and polaron pairs which relax within a 100 ps time period. 相似文献
124.
125.
A highly stable Q-switched laser incorporating a mechanically exfoliated tungsten sulphoselenide (WSSe) thin sheet saturable absorber (SA) is proposed and demonstrated. The SA assembly, formed by sandwiching a thin WSSe sheet between two fiber ferrules within the erbium-doped fiber laser, is used to effectively modulate the laser cavity losses. The WSSe-based SA has a saturation intensity of ~0.006 MW∕cm~2 and a modulation depth of 7.8%, giving an optimum Q-switched laser output with a maximum repetition rate of 61.81 kHz and a minimum pulse width of 2.6 μs. The laser's highest output power of 0.45 mW and highest pulse energy of 7.31 nJ are achieved at the maximum pump power of 280.5 mW. The tunability of the cavity's output at the maximum pump power is analyzed with a C-band tunable bandpass filter, giving a broad tunable range of ~40 nm, from 1530 nm to 1570 nm. The output performance of the tunable Q-switched laser correlates well with the gain spectrum of erbium-doped fibers, with the shift in the gain profile as a result of the saturated SA. 相似文献
126.
Dong Choon Hyun Unyong Jeong Du Yeol Ryu 《Journal of Polymer Science.Polymer Physics》2007,45(19):2729-2738
The thermodynamic shape and position of a polymer drop sandwiched between two polymer melt plates were predicted by simulating the change of the interfacial energy according to various shapes and position of the drop. The calculation results were in a precise coincidence with the experimental results exhibiting lens, spreading, and encapsulation. The simple formula and easy concept of the calculation can be useful to predict the morphology of immiscible ternary blends with the information of the interfacial tensions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2729–2738, 2007 相似文献
127.
Choon Ki Ahn 《International Journal of Theoretical Physics》2009,48(12):3498-3509
This paper investigates the adaptive anti-synchronization problem for time-delayed chaotic neural networks with unknown parameters.
Based on Lyapunov-Krasovskii stability theory and linear matrix inequality (LMI) approach, the adaptive anti-synchronization
controller is designed and an analytic expression of the controller with its adaptive laws of unknown parameters is shown.
The proposed controller can be obtained by solving the LMI problem. An illustrative example is given to demonstrate the effectiveness
of the proposed method. 相似文献
128.
Xianbin Liu Laisheng LiYu Du Zhen GuoTeng Teng Ong Yuan ChenSiu Choon Ng Yanhui Yang 《Journal of chromatography. A》2009,1216(45):7767-7773
A modified synthesis approach for spherical large pore-diameter SBA-15 mesoporous silica (SLP-SBA-15) with particle size range of 0.5–1 μm was being reported. It was worth mentioning that in this improved methodology, the use of cetyltrimethylammonium bromide (CTAB) as co-template significantly reduced the self-assembly time from 24 h to 45 min. Moreover, under reflux condition, the reaction time could be further shortened by reducing the aging time from 48 h to 6 h. The resultant SLP-SBA-15 was thereafter successfully functionalized and packed into an ultra-high-performance liquid chromatography (UHPLC) column for the separation of aromatic compounds. A variety of characterizations demonstrated that the silica products exhibited a well-ordered 2d hexagonal mesostructure with well-formed spherical morphology. pore-diameter can be enlarged up to 8.2 nm without affecting the structural order. The SLP-SBA-15 samples showed excellent thermal and hydrothermal stabilities. The octadecyltriethoxysilane functionalized SLP-SBA-15 (SLP-C18-SBA-15) was demonstrated to be an effective stationary phase in UHPLC application because the column exhibited significantly reduced column pressure (2800 psi) at a flow rate of 0.4 ml/min. Accordingly, it would afford greater flexibility for tuning of the flow rate to meet the fast separation requirement. 相似文献
129.
Ozturk Ozum Farouk Fathima Manaal Ooi Luyi Law Christine Shing Wei Muhammed Muhammed Tilahun Aki-Yalcin Esin Yeong Keng Yoon 《Molecular diversity》2022,26(5):2863-2876
Molecular Diversity - Selectively inhibiting butyrylcholinesterase (BChE) is hypothesized to help in the management of Alzheimer’s disease (AD). Several studies have determined a correlation... 相似文献
130.