全文获取类型
收费全文 | 880篇 |
免费 | 71篇 |
国内免费 | 108篇 |
专业分类
化学 | 518篇 |
晶体学 | 8篇 |
力学 | 104篇 |
数学 | 72篇 |
物理学 | 357篇 |
出版年
2023年 | 60篇 |
2022年 | 27篇 |
2021年 | 37篇 |
2020年 | 56篇 |
2019年 | 40篇 |
2018年 | 25篇 |
2017年 | 52篇 |
2016年 | 36篇 |
2015年 | 53篇 |
2014年 | 60篇 |
2013年 | 53篇 |
2012年 | 74篇 |
2011年 | 43篇 |
2010年 | 36篇 |
2009年 | 50篇 |
2008年 | 25篇 |
2007年 | 47篇 |
2006年 | 42篇 |
2005年 | 25篇 |
2004年 | 14篇 |
2003年 | 23篇 |
2002年 | 18篇 |
2001年 | 26篇 |
2000年 | 15篇 |
1999年 | 17篇 |
1998年 | 19篇 |
1997年 | 13篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 2篇 |
1976年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1059条查询结果,搜索用时 31 毫秒
101.
102.
M. Nikl A. Yoshikawa K. Kamada K. Nejezchleb C.R. Stanek J.A. Mares K. Blazek 《Progress in Crystal Growth and Characterization of Materials》2013,59(2):47-72
A review of research and development of Lu3Al5O12 (LuAG)-based single crystal scintillators is presented. Crystals of this type have been prepared by the micro-pulling down method at the initial stage of material screening and by Czochralski or Bridgman methods to obtain higher quality and larger size single crystals afterward. Several different activators, namely Ce3+, Pr3+, Yb3+ and Sc3+ have been reported in the literature and such doped LuAG single crystals have been extensively studied to understand a number of issues, including: the scintillation mechanism, underlying energy transfer and trapping processes including the nature and role of material defects involved in the scintillation process and their relation to manufacturing technology. Significant improvements in the understanding of aluminum garnet scintillators lead to the discovery of multicomponent garnet single crystal scintillators in 2011, which are described. These materials gave rise to new class of ultraefficient complex oxide scintillators, the light yield of which considerably exceeds the values achieved for the best Ce-doped orthosilicate scintillators. 相似文献
103.
The rheological behaviors of polypropylene (PP)/poly(1-butene) (PB) blends with homo-polypropylene (PP1) or impact polypropylene (PP2), a poly(propylene-co-ethylene) as the PP component were studied. With increasing of PB resin content for both PP/PB blends, the blends showed higher G'(ω), G''(ω) and η*(ω) at low frequencies but lower values at high frequencies which implied that the processability was improved. A two-phase morphology was observed through the various rheological responses, including G'(ω)-ω terminal region curves, Cole-Cole plots and the weighted relaxation spectra with the PB contents up to 40?wt%. With the same PB content, the rheological parameters of the PP2/PB blends were quite different from those of the PP1/PB, which can be attributed to the stronger interaction between PB chains and the ethylene-co-propylene copolymer in PP2. The impact strength of the PP2/PB blends was improved dramatically over that of the PP1/PB. The more significant toughening effect for the PP2/PB blends can be attributed to the special responses of its rheological behaviors. 相似文献
104.
《Chemical physics letters》2002,350(5-6):664-669
A simplified arc discharge apparatus was used for growing carbon nanotubes, required only water (solution) in a glass container with no need for vacuum, water-cooled chamber. Carbon nanotubes with highest purity (20%) and highest yield (7 mg/min) were obtained when using salt solution as the medium. Resonance Raman spectrum of multi-walled carbon nanotubes (MWNTs) presented in as-grown materials was measured and RBM peaks originating from very thin core nanotubes were observed. The results show that high-quality MWNTs can be effectively prepared in water-arcing process. 相似文献
105.
《Vibrational Spectroscopy》2002,28(1):167-175
We investigated the hormonal influences on cervical cells using infrared microspectroscopy and found that there were observable spectral changes occurring throughout the cycle. The main differences were seen in the glycogen region (1200–1000 cm−1) and the greatest cyclical variation was observed in spectra of ectocervical cells of women not taking any form of oral contraception. Ectocervical cells from women taking monophasic contraception and endocervical cells from both groups did not display the same degree of variation. Principal component analysis revealed that, although there is cyclical variation, these cells are normal and discrimination between histologically normal and abnormal (high-grade dysplasia) cells was maintained. 相似文献
106.
107.
《Tetrahedron letters》2019,60(28):1825-1829
Pyrroloquinoline alkaloids are well known bioactive metabolites commonly found from latrunculiid sponges. Two new pyrroloquinoline alkaloids, 6-bromodamirone B (1) and makaluvamine W (2), were isolated from the Tongan sponge Strongylodesma tongaensis. Makaluvamine W (2) contains an oxazole moiety, which is rare in this large group of natural products, and is the first example of a pyrroloquinoline with nitrogen substitution at C-8. Both 1 and 2 lacked activity against a human promyelocytic leukemia cell line (HL-60), supporting the premise that an intact iminoquinone moiety plays a key role in the cytotoxicity of this compound class. The chemotaxonomic impact of these makaluvamine-type compounds is also discussed. 相似文献
108.
109.
In the emerging field of nanoscience, tubular structures have been attracting remarkable interest due to their well-defined geometry, high specific area, and exceptional physical and chemical properties. Among them, oriented ZnO tubular arrays are regarded as promising candidates for various applications such as optoelectronics, solar cells, sensors, field emission, piezoelectrics, and catalysis. Although template-directed and selective dissolution synthesizing strategies are commonly used to prepare ZnO nanotubes, repeatability and large scale preparation are still challenging. In this study, ZnO nanotube arrays were controllably prepared by tuning the hydrothermal parameters, without the use of any additives. The mechanism underlying the self-conversion of ZnO nanorods to nanotubes was comprehensively studied based on the surface energy theory. It has been proved that the metastable top surface of the ZnO nanorods dissolves preferentially to reach a stable state during the hydrothermal growth. The specific surface energy of different crystal faces of ZnO nanorods was calculated using molecular dynamics simulation. The top surface of the ZnO nanorod, the Zn-terminated [0001] face, demonstrated much higher surface free energy than did the lateral faces, which indicated that the self-dissolution of top face (002) is energetically favorable. The self-conversion behavior of ZnO nanorod arrays with different diameters was specifically investigated by adjusting the initial precursor concentration, density of the crystal seed layers, and growth time. The dissolution-crystallization equilibrium concentration, determined by crystal surface energy, was found to be a key factor for the formation of the tubular structure. Notably, the critical equilibrium conditions for the self-conversion of ZnO nanorods to nanotubes, including zinc ion concentration and pH, have been identified by studying parameters corresponding to the dissolution-crystallization equilibrium for the metastable top surface of the ZnO nanorods. The preparation of the ZnO nanotube arrays was successfully accelerated and simplified via two-step procedure: (1) preparation of ZnO nanorod arrays and (2) self-conversion of ZnO nanorods to nanotubes. The preparation method based on the self-conversion mechanism from rods to tubes for polar oxides is simpler and more easily controllable as compared to the reported methods involving variety of additives. Because of the advantages of adaptability to a wide range of substrates, excellent conducting properties, and filling ability, the prepared ZnO nanotube array films were used in encapsulating phase-change materials. The encapsulated phase-change material exhibited excellent heat storage/release properties and heat conductivities. This indicates the potential application of precision devices for temperature control. 相似文献
110.
《中国化学快报》2019,30(10):1843-1848
Stokes shift is an important feature of fluorescence, which reveals the energy loss between the excitation and the emission. For most fluorescent materials(e.g., organic dyes and proteins), the large overlap between the absorption and emission spectra endow them a small Stokes shift that induced reabsorption by fluorophore itself. Although the self-absorption can be effectively reduced due to the emergence of fluorescent nanomaterials, fluorescence attenuation is still observed in aggregated or concentrated nanocrystals, causing reduced sensitivity of biosensors. Therefore, increasing the Stokes shift can effectively improve the performance of nano-agents based biosensing. In this critical review, through understanding the Stokes shift from the viewpoint of self-absorption, the influence of Stokes shift on fluorescence properties are discussed. Based on the principle of changing the Stokes shift of fluorescent nanomaterials, we described the methods for constructing various optically large Stokes shift-based nanomaterials, and the application of these nanocrystals in biosensing is especially concerned in this review. 相似文献