全文获取类型
收费全文 | 17434篇 |
免费 | 1727篇 |
国内免费 | 937篇 |
专业分类
化学 | 17485篇 |
晶体学 | 347篇 |
力学 | 43篇 |
综合类 | 37篇 |
数学 | 9篇 |
物理学 | 2177篇 |
出版年
2024年 | 14篇 |
2023年 | 176篇 |
2022年 | 341篇 |
2021年 | 561篇 |
2020年 | 617篇 |
2019年 | 465篇 |
2018年 | 373篇 |
2017年 | 348篇 |
2016年 | 681篇 |
2015年 | 669篇 |
2014年 | 702篇 |
2013年 | 1458篇 |
2012年 | 884篇 |
2011年 | 787篇 |
2010年 | 853篇 |
2009年 | 861篇 |
2008年 | 869篇 |
2007年 | 936篇 |
2006年 | 880篇 |
2005年 | 830篇 |
2004年 | 854篇 |
2003年 | 765篇 |
2002年 | 1520篇 |
2001年 | 422篇 |
2000年 | 357篇 |
1999年 | 335篇 |
1998年 | 325篇 |
1997年 | 247篇 |
1996年 | 461篇 |
1995年 | 421篇 |
1994年 | 160篇 |
1993年 | 126篇 |
1992年 | 148篇 |
1991年 | 92篇 |
1990年 | 63篇 |
1989年 | 80篇 |
1988年 | 72篇 |
1987年 | 38篇 |
1986年 | 40篇 |
1985年 | 58篇 |
1984年 | 41篇 |
1983年 | 32篇 |
1982年 | 25篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 14篇 |
1975年 | 7篇 |
1973年 | 6篇 |
1966年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
972.
The olivine type LiMPO4 (M=Ni, Mn and Co) materials were synthesized by solution combustion technique using glycine as fuel. The structural characterizations were explored to confirm the phase formation of materials. The scanning electron microscope was used to identify the morphology of olivine materials. The local structure and chemical bonding between MO6 octahedral and (PO4)3- tetrahedral groups were probed by Raman spectroscopy. Grain and grain boundaries were contributed for ion relaxation and dc conduction in olivine materials. Two orders of enhancement in ionic conductivity was observed in these olivine materials than the reported value. Among all the explored olivine samples, LiMnPO4 showed highest enhancement in conductivity due to weak Li–O bonding and largest unit cell volume. 相似文献
973.
Nano-structured LiVPO4F/Ag composite cathode material has been successfully synthesized via a sol–gel route. The structural and physical properties, as well as the electrochemical performance of the material are compared with those of the pristine LiVPO4F. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal that Ag particles are uniformly dispersed on the surface of LiVPO4F without destroying the crystal structure of the bulk material. An analysis of the electrochemical measurements show that the Ag-modified LiVPO4F material exhibits high discharge capacity, good cycle performance (108.5 mAh g−1 after 50th cycles at 0.1 C, 93% of initial discharge capacity) and excellent rate behavior (81.8 mAh g−1 for initial discharge capacity at 5 C). The electrochemical impedance spectroscopy (EIS) results reveal that the adding of Ag decreases the charge-transfer resistance (Rct) of LiVPO4F cathode. This study demonstrates that Ag-coating is a promising way to improve the electrochemical performance of the pristine LiVPO4F for lithium-ion batteries cathode material. 相似文献
974.
Orientational order parameter S is evaluated in the nematic phase of six liquid crystal compounds, N-(p-n-propyl benzylidene)-p-n-alkoxy anilines, 3.Om and N-(p-n-propyloxy benzylidene)-p-n-alkoxy anilines, 3O.Om compounds with m = 6, 7 and 8, using different methods. The techniques employed are S from birefringence δn, Haller's approximation from (1?T/Tc) β, effective geometry parameter αg and Vuks’ scaling factor SC. The values of S obtained using the above methods are compared with one another and with the results on a number of liquid crystals; the liquid crystals favor isotropic Vuks’ method. 相似文献
975.
Mamta Chauhan 《Phase Transitions》2015,88(12):1193-1212
The structural, electronic, mechanical, phase transition, and thermo-physical properties of refractory carbides, viz. VC, NbC, and TaC have been computed in stable B1 and high pressure B2 phases by means of two different ab initio calculations using pseudo- and full-potential schemes. These materials have mixed covalent-, metallic-, and ionic-type bonding. The calculations of elastic constants show the mechanical stability of these materials in B1 phase only. The brittle nature and anisotropy is observed in these materials in B1 phase. Non-central forces are present in both the phases. Elastic wave velocities and Debye temperature have also been calculated. The present results on structural, phase transition, elastic, and other properties are in reasonably good agreement with the available experimental and theoretical data. The calculations in high pressure phase need experimental verification. 相似文献
976.
Werner Uhl 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4-5):743-748
Organogallium or-indium subhalides are easily available by the halogenation of the corresponding tetrahedral clusters E 4 [C(SiMe 3 ) 3 ] 4 . Three types of compounds are formed that retain the tetrahedral arrangement of In atoms or give chains with two or three Ga or In atoms connected by E─E bonds. These subhalides are suitable starting compounds for the synthesis of secondary products containing the elements in low oxidation states. Carboxylato derivatives or transition metal complexes were obtained on such a route. A persistent radical anion was formed on electron transfer to Ga 9 (CMe 3 ) 9 . 相似文献
977.
Il'yas S. Nizamov Alexey E. Popovich Elvira S. Batyeva Nail M. Azancheev Vladimir A. Al'fonsov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):167-178
Abstract The reactions of tetraphosphorus decasulfide and Lawesson's reagent with tetra-, tri- and dialkoxysilanes were studied. On the basis of these reactions, new S-silyl esters of phosphorus(V) thioacids have been prepared. The prepared compounds were identified by IR, 1H, and 31P NMR and mass spectra as well as elemental analyses. 相似文献
978.
M. El-borai M. F. Abdel-megeed 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):165-173
Abstract The mass spectral fragmentation of thiophenotropone, thiophenotropilidene derivatives and their iron and chromium tricarbonyl complexes are fully reported and discussed. The fragmentation patterns of the complexes are characterised by successive loss of three carbonyl groups. In general, the resulting ions after elimination of the metal behave in the same manner as the organic ligand. The iron complexes behave differently from their corresponding chromium complexes. The thiopheno[b]tropilidene iron tricarbonyl complex and its isomer thiopheno[c]tropilidene iron tricarbonyl complex could not be differentiated by mass spectrometry, such differentiation was achieved by proton magnetic resonance. 相似文献
979.
Christopher Hubrich Axel Schulz Harald Brand Alexander Villinger 《Phosphorus, sulfur, and silicon and the related elements》2013,188(9):2179-2196
The silyl ethers (siloxanes) Me4? xSi(OC6H5CN)x (x = 1–4) (1–4), O(Si(OC6H4CN) (Me)2)2 (5), and Me3Si–O–C6F4CN (6) have been synthesized by the reaction of the respective p-hydroxybenzonitriles and chlorosilanes in the presence of N,N,N′,N′-tetramethylethylenediamine (TMEDA) as hydrogen chloride acceptor. All compounds have been fully characterized by CHN-analysis, melting point, IR, Raman, mass spectroscopy, and 1H, 13C, 29Si NMR spectroscopy. Furthermore, the crystal structures of these compounds—with the exception of Me2Si(OC6H5CN)2, which is a liquid—were determined by X-ray diffractometry. 相似文献
980.