全文获取类型
收费全文 | 147篇 |
免费 | 27篇 |
国内免费 | 6篇 |
专业分类
化学 | 83篇 |
晶体学 | 1篇 |
力学 | 13篇 |
综合类 | 2篇 |
数学 | 12篇 |
物理学 | 69篇 |
出版年
2023年 | 9篇 |
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 8篇 |
2019年 | 10篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 4篇 |
2014年 | 9篇 |
2013年 | 5篇 |
2012年 | 11篇 |
2011年 | 11篇 |
2010年 | 7篇 |
2009年 | 4篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1987年 | 1篇 |
排序方式: 共有180条查询结果,搜索用时 15 毫秒
51.
本文采用氧化水解制样及流动注射在线萃取火焰原子吸收光谱法,测定明胶中微量Fe和Cu,解决了水解法制样测定结果偏低和不能直接测定低含量样品的问题。本方法测定Fe和Cu的灵敏度分别提高了14.5倍和17.6倍,分析速度达36次/h,Fe和Cu的回收率分别在90.8-110.5%和87.5~107.0%之间,测定精密度分别为4.53%和4.26%。 相似文献
52.
Determination of trace lead by hydride generation-inductively coupled plasma-mass spectrometry 总被引:1,自引:0,他引:1
A newly developed hydride generation-inductively coupled plasma-mass spectrometry (HG-ICP-MS) system was employed to determine trace amounts of lead in geological and biological samples. Laboratory-made single-stage and double-stage gas-liquid separators (GLSs) were investigated in order to replace the consumable membrane-GLS. Possible reasons were given why double-stage GLSs were superior over the single-stage ones according to the factors such as GLS volume and configuration, carrier gas inlet mode and flow rate. Interferences in liquid and vapor phase from concomitant ions and their products were investigated employing different flow mani-folds. Memory effects contributed to the blank values, but could be reduced employing a special wash protocol. Internal and external standardization were combined to improve the accuracy of the method, with bismuth as the internal standard according to its similarity with lead in the HG-ICP-MS system. Compared with ICP-MS and hydride generation-atomic fluorescence spectrometry (HG-AFS) methods, the system performance of HG-ICP-MS was characterized with improved detection limit to 0.002 ng/ml and acceptable short- and long-term stabilities. The linear dynamic range of this method was up to 50 ng/ml lead. Three Chinese national certified reference materials: poplar leaves, human hair and copper ore, were analyzed for method validation, and the results agreed well with the certified values. At last, the method was also employed to determine wide range of lead concentrations in lightweight limestone and nervous tissue samples from infants of albino rats with recoveries between 95 and 105% (n=10). 相似文献
53.
Lee S Bowman BR Ueno Y Wang S Verdine GL 《Journal of the American Chemical Society》2008,130(35):11570-11571
The predominant product of aberrant DNA methylation is the genotoxic lesion N7-methyl-2'-deoxyguanosine (m7dG). M7dG is recognized and excised by lesion-specific DNA glycosylases, namely AlkA in E. coli and Aag in humans. Structural studies of m7dG recognition and catalysis by these enzymes have been hampered due to a lack of efficient means by which to incorporate the chemically labile m7dG moiety site-specifically into DNA on a preparative scale. Here we report a solution to this problem. We stabilized the lesion toward acid-catalyzed and glycosylase-catalyzed depurination by 2'-fluorination and toward base-catalyzed degradation using mild, nonaqueous conditions in the DNA deprotection reaction. Duplex DNA containing 2'-fluoro-m7dG (Fm7dG) cocrystallized with AlkA as a host-guest complex in which the lesion-containing segment of DNA was nearly devoid of protein contacts, thus enabling the first direct visualization of the N7-methylguanine lesion nucleobase in DNA. The structure reveals that the base-pairing mode of Fm7dG:C is nearly identical to that of G:C, and Fm7dG does not induce any apparent structural disturbance of the duplex structure. These observations suggest that AlkA and Aag must perform a structurally invasive interrogation of DNA in order to detect the presence of intrahelical m7dG lesions. 相似文献
54.
Mengqi Zhang Dr. Chenghao Bi Yuexing Xia Dr. Xuejiao Sun Xingyu Wang Aqiang Liu Shuyu Tian Prof. Xinfeng Liu Prof. Nora H. de Leeuw Prof. Jianjun Tian 《Angewandte Chemie (International ed. in English)》2023,62(12):e202300149
Perovskite colloidal quantum wells (QWs) are promising to realize narrow deep-blue emission, but the poor optical performance and stability suppress their practical application. Here, we creatively propose a water-driven synthesis strategy to obtain size-homogenized and strongly confined deep-blue CsPbBr3 QWs, corresponding to three monolayers, which emit at the deep-blue wavelength of 456 nm. The water controls the orientation and distribution of the ligands on the surface of the nanocrystals, thus inducing orientated growth through the Ostwald ripening process by phagocytizing unstable nanocrystals to form well-crystallized QWs. These QWs present remarkable stability and high photoluminescence quantum yield of 94 %. Furthermore, we have prepared light-emitting diodes based on the QWs via the all-solution fabrication strategy, achieving an external quantum efficiency of 1 % and luminance of 2946 cd m−2, demonstrating state-of-the-art brightness for perovskite QW-based LEDs. 相似文献
55.
56.
In this paper, a semi-implicit finite element method is presented for the coupled Cahn–Hilliard and Navier–Stokes equations with the generalized Navier boundary condition for the moving contact line problems. In our method, the system is solved in a decoupled way. For the Cahn–Hilliard equations, a convex splitting scheme is used along with a P1-P1 finite element discretization. The scheme is unconditionally stable. A linearized semi-implicit P2-P0 mixed finite element method is employed to solve the Navier–Stokes equations. With our method, the generalized Navier boundary condition is extended to handle the moving contact line problems with complex boundary in a very natural way. The efficiency and capacity of the present method are well demonstrated with several numerical examples. 相似文献
57.
In this paper, the resonance frequency equation and expression of displacement amplitude magnifications of a full-wave barber ultrasonic horn are obtained. By discussing the relationships between the displacement amplitude magnifications and the geometrical dimensions, the optimized design of the horn for the largest magnification is proposed, which is helpful to improve the radiation power and the transfer efficiency of the acoustic energy of the ultrasonic oscillatory system. Based on the optimized design of the horn, we introduced a barbell ultrasonic transducer operated in the longitudinal full-wave vibrational model and obtained the resonance frequency equations. For comparison, the resonance frequencies of the full-wave barbell horn and the full-wave barbell transducer are also analyzed by finite element method (FEM). It is shown that the values obtained by theoretical analysis and FEM are in good agreement with experimental observations. We hope that the research of this paper is helpful for the use of the barbell horn and transducer in the applications such as ultrasonic liquid processing. 相似文献
58.
59.
The proventriculus is a specialized part of the foregut in the alimentary canal in some insects, varying greatly in its structure across different insect groups. The ultramorphology of the proventriculus in Mecoptera was investigated in eight species of Panorpidae and one of the Bittacidae using light microscopy and scanning electron microscopy. The proventriculus consists of the outer circular muscles, the inner longitudinal muscles, an epithelium, and a sclerotized intima with dense acanthae. The proventricular acanthae could be divided into three categories: the anterior acanthae (AA), the main acanthae (MA), and the posterior acanthae (PA). In Panorpidae the AA are rounded in cross section and could be subdivided into two subtypes, the long AA with a polytomy apiculus and the short AA with a V-shaped or spine-like apiculus. The MA, covering the majority of the proventricular inner surface, are dense, uniform, and hollow rectangular structures in cross section with forked apiculi. Each hollow base of the MA was first found to be inserted with a cone-shaped process of the corresponding epithelial cell. The PA are very thin, with a spine-like apiculus. In Bittacidae the proventriculus is specialized by a ring of cuticular thickening within its anterior orifice, and the AA are shaped like a ring of thin spines. Six cardiac valves were observed in Panorpidae and ten in Bittacidae. The functions of the various types of acanthae in digestion and extra-oral digestion and their significance in insect systematics are briefly discussed. 相似文献
60.
Lin S 《Ultrasonics》2006,44(Z1):e545-e548
The high power air-coupled compound ultrasonic transducer in flexural vibration is studied. The transducer consists of a sandwich longitudinal piezoelectric transducer and a circular thin plate in flexural vibration. The resonance frequency equation and the equivalent circuit of a circular radiator with clamped boundary condition are derived. The resonance frequency equation and the equivalent circuit of the compound transducer are also obtained. The radiated acoustic field of the circular thin plate radiator is analyzed and the directional pattern is calculated. It can be seen that when the vibrational order of the circular thin plate in flexural vibration is increased, the radiated acoustic field becomes complex. 相似文献