全文获取类型
收费全文 | 3157篇 |
免费 | 690篇 |
国内免费 | 767篇 |
专业分类
化学 | 3444篇 |
晶体学 | 57篇 |
力学 | 7篇 |
综合类 | 27篇 |
数学 | 6篇 |
物理学 | 1073篇 |
出版年
2024年 | 14篇 |
2023年 | 60篇 |
2022年 | 152篇 |
2021年 | 161篇 |
2020年 | 209篇 |
2019年 | 153篇 |
2018年 | 127篇 |
2017年 | 153篇 |
2016年 | 206篇 |
2015年 | 204篇 |
2014年 | 226篇 |
2013年 | 382篇 |
2012年 | 248篇 |
2011年 | 191篇 |
2010年 | 193篇 |
2009年 | 168篇 |
2008年 | 170篇 |
2007年 | 218篇 |
2006年 | 202篇 |
2005年 | 213篇 |
2004年 | 151篇 |
2003年 | 121篇 |
2002年 | 116篇 |
2001年 | 70篇 |
2000年 | 67篇 |
1999年 | 51篇 |
1998年 | 54篇 |
1997年 | 60篇 |
1996年 | 47篇 |
1995年 | 39篇 |
1994年 | 29篇 |
1993年 | 31篇 |
1992年 | 27篇 |
1991年 | 19篇 |
1990年 | 12篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有4614条查询结果,搜索用时 15 毫秒
991.
The effect of the nature and concentration of the acid component on the yield and ratio of the products of electrocatalytic
hydrogenation of citral was studied. The use of weak organic acids (e.g., AcOH) in amounts that are stoichiometric for hydrogenation of conjugated double bonds was shown to be advantageous.
For Communication 3 see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 480–483, March, 1997. 相似文献
992.
π-complexes of polystyrene with silver salts and their use as facilitated olefin transport membranes
Jong Hak Kim Jongok Won Yong Soo Kang 《Journal of Polymer Science.Polymer Physics》2004,42(12):2263-2269
π-Complexes of silver salts with polystyrene (PS) were prepared and tested in the separation of propylene/propane mixtures. After the incorporation of silver ions into the PS matrix, both the pure propylene gas permeance of the membrane and its olefin selectivity with respect to the propylene/propane mixtures were remarkably higher than those of the pure PS membrane, demonstrating facilitated propylene transport through the solid-state membrane. The remarkable separation performance of the PS/silver salt membranes was attributable to the unusually high solubility of the silver salts in the PS matrix, which was possibly due to the formation of π-complexes between the silver ion and aromatic CC bond of PS. The coordination properties and dissolution behavior of the silver salts in PS were investigated with Fourier transform infrared, Fourier transform Raman, and X-ray photoelectron spectroscopy. The values for the intersegmental d-spacing, determined by wide-angle X-ray scattering, also showed that significant transient crosslinks arose between the PS chains when the silver salts were added to the PS matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2263–2269, 2004 相似文献
993.
G. T. Vasilyuk 《Journal of Applied Spectroscopy》2003,70(1):1-6
The relationship between the optical properties of GRS-active substrates based on silver films and the parameters of their surface roughness have been studied by methods of mathematical statistics (correlation, regression, and factor analyses). The equations of nonlinear regression connecting these quantities were obtained. It is established that most correlatable are the maximum value of the optical density with the distance between islands and with the coefficient of their shape, and also its relation to the halfwidth of the optical density band of a silver film with the mentioned characteristics of the islands. 相似文献
994.
A new type of fibrous silver stearate (AgSt) was synthesized using double-jet method with KOH as pH regulator in water solution system. The structure, morphology and phase transiton behavior of the fibrous AgSt were characterized by FTIR, SEM, XRD and TG-DTA. SEM images showed that the diameter of the fibrous AgSt was about 150 nm and the length was 5~8 μm. XRD data indicated its layered structure and TG-DTA showed its high themal stability. In addition, the possible growth mechanism of the fibrous AgSt is also discussed. 相似文献
995.
微波法制备掺碳LiFePO4正极材料 总被引:7,自引:0,他引:7
Cathode material LiFePO4 of lithium-ion battery was synthesized by microwave heating. The “carbon-included” LiFePO4 with improved conductivity was synthesized by the addition of graphite. And the influence of microwave-heating time on structure, morphology and charge/discharge performance of the products was discussed. The results of XRD, SEM, XPS, CV and charge/discharge testing measurements showed that the LiFePO4 product after 9 min in microwave oven had more advantages than other products. 相似文献
996.
锂离子二次电池正极材料LiVPO4F的制备及其电化学性能的研究 总被引:3,自引:0,他引:3
A new cathode material, LiVPO4F, has been synthesized through two steps of solid-state reactions. In the first step, vanadium pentoxide, ammonium dihydrogen phosphate, and a high surface area carbon were pre-heated at 300 ℃ and reacted at 750 ℃ under an inert atmosphere to yield the trivalent vanadium phosphate VPO4. In the second step, the product LiVPO4F was synthesized by the reaction with VPO4 and LiF. The LiVPO4F was characterized by X-ray diffraction, scanning electron microscopy, cyclic voltammetry and charge/discharge testing measurements. The LiVPO4F is triclinic crystalline system. At 0.1 C rate, the first charge/discharge capacities were 150.1 mAh·g-1 and 132.6 mAh·g-1; At 0.2 C rate, the first charge/discharge capacities were 142.9 mAh·g-1 and 125.2 mAh·g-1. The LiVPO4F from this work has higher charge/discharge voltage 4.3 V and 4.1 V, respectively. 相似文献
997.
以天然来源的生物质百香果内膜为原料,采用热解炭化-KOH活化的方法制备出比表面积大、孔隙结构好的纳米片生物炭(BXG-AC),并通过扫描电子显微镜(SEM)、X射线光电子能谱(XPS)等方法对所制备催化剂进行了元素组成和微观形貌表征,采用循环伏安扫描(CV)和线性伏安扫描(LSV)对材料的电化学性能进行分析。结果表明,百香果内膜生物炭经过KOH活化后,在0.1 mol/L的磷酸缓冲液(PBS)中表现出良好的电催化活性。将所制备的催化剂应用于单室MFCs阴极时,对应的MFC最大功率密度达1153.3 mW/m2,略低于Pt/C的1214.3 mW/m2,且此MFC运行60 d后,其性能未见明显降低。表明BXG-AC催化剂具有显著的催化活性和稳定性,为开发高效MFC阴极催化剂提供了新途径。 相似文献
998.
Xing Xin Xuerui Tian Huixia Zhang Xueli He Xueliang Zhai 《Journal of Coordination Chemistry》2018,71(1):1-11
Ag-modified polyoxometalate [Na(H2O)]2[Ag(bpf)]3[PW12O40] (1) (bpf = 2,4-di(4-pyridyl)furan) was synthesized through a hydrothermal reaction. Single-crystal X-ray diffraction analysis revealed that 1 consists of a hybrid 3D MOF constructed from Keggin-type polyanionic [PW12O40]3- and cationic Ag-bpf units. Ligand bpf in 1 was in situ transferred from 1,3-bis(4-pyridyl)propane under the higher temperature and pressure of hydrothermal conditions. Catalytic performance of 1 as a heterogeneous catalyst for degradation of organic dye Rhodamine B (RhB) was investigated. Experimental results showed that hybrid 1 was especially active to catalytically degrade RhB under room temperature and natural light. RhB-containing solution (5.0 mg·L?1) could be quickly bleached in a short time, and the high removal efficiency (97%) could be reached in a mere 30 min. The degradation mechanism of RhB was discussed. 相似文献
999.
《Surface and interface analysis : SIA》2018,50(10):947-953
The archaeometallurgical analysis of ancient silver coins provides useful information regarding fabrication methodology, provenance, and trade route and explains large diversification in elementary composition, weight, and physical features. The present investigation deals with the chemical analysis and examination of the processing history of Indian punch‐marked silver coins dating to 400–200 bc . The chemical analysis was carried out by wavelength dispersive X‐ray fluorescence and X‐ray Diffraction (XRD). The microstructural examination was performed using field emission scanning electron microscope (FE‐SEM) and different phases were identified by Scanning Electron Microscopy coupled with Energy Dispersive X‐ray (SEM‐EDX) Spectroscopy. It was observed that all eight coins were manufactured with silver‐copper alloy. The ore used for obtaining silver was argentiferous galena, and cupellation was carried with perfection. The absence of slag inclusions as revealed by SEM examination indicated that coins (numbers 2, 4, 5, and 7) were cast from a molten state. The presence of Cu2O, CuO, and Ag2O on the surfaces of the coins was confirmed by XRD. The formed oxide layers provided protection and saved the coins from bulky corrosion products. The data reveal great divergence of coin surface from the composition of the core with the far better metallurgical process for refining of silver for this hoard. 相似文献
1000.