全文获取类型
收费全文 | 60715篇 |
免费 | 12702篇 |
国内免费 | 20986篇 |
专业分类
化学 | 44532篇 |
晶体学 | 2656篇 |
力学 | 4644篇 |
综合类 | 2247篇 |
数学 | 10033篇 |
物理学 | 30291篇 |
出版年
2024年 | 139篇 |
2023年 | 737篇 |
2022年 | 2215篇 |
2021年 | 2293篇 |
2020年 | 2310篇 |
2019年 | 2223篇 |
2018年 | 2069篇 |
2017年 | 2919篇 |
2016年 | 2243篇 |
2015年 | 3289篇 |
2014年 | 3960篇 |
2013年 | 5030篇 |
2012年 | 5212篇 |
2011年 | 5585篇 |
2010年 | 5376篇 |
2009年 | 5623篇 |
2008年 | 6150篇 |
2007年 | 5487篇 |
2006年 | 5391篇 |
2005年 | 4442篇 |
2004年 | 3404篇 |
2003年 | 2483篇 |
2002年 | 2417篇 |
2001年 | 2467篇 |
2000年 | 2580篇 |
1999年 | 1543篇 |
1998年 | 806篇 |
1997年 | 614篇 |
1996年 | 577篇 |
1995年 | 530篇 |
1994年 | 546篇 |
1993年 | 516篇 |
1992年 | 508篇 |
1991年 | 323篇 |
1990年 | 304篇 |
1989年 | 327篇 |
1988年 | 290篇 |
1987年 | 239篇 |
1986年 | 226篇 |
1985年 | 158篇 |
1984年 | 154篇 |
1983年 | 132篇 |
1982年 | 101篇 |
1981年 | 80篇 |
1980年 | 73篇 |
1979年 | 88篇 |
1978年 | 24篇 |
1977年 | 20篇 |
1965年 | 35篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
MgFe2O4-Fe2O3纳米粉体的软化学合成及电磁学特性 总被引:1,自引:0,他引:1
Nano-MgFe2O4-Fe2O3 magnetic powders were synthesized by citrate gel under microwave irradiation. The structure,particle size distribution,electromagnetic characteristics of nano-MgFe2O4-Fe2O3 were characterized by using TG-DTA, X-ray, electronic microscope, nano-size measurement and electromagnetism measurement apparatus。The results show that the product is a mixture of MgFe2O4 and Fe2O3 with average size of 44 nm, tanδ for the product is 0.265 and 0.610 at frequency of 1.0 GHz and 1.8 GHz respectively. 相似文献
993.
The Fourier transform far infrared spectra of oxalate hydrates of whole rare-earth series except Pm and Sc are investigated in the range of 100-400 cm~(-1). The assignment of vibrational frequencies is made on the basis of normal coordinate analysis using our NORVIB program. The model used for the hghter elements of the lanthanide series (La to Eu) is based on the crystal structure of Nd_2(C_2O_4)_3. 10H_2O, in which each lanthanide ion is surrounded by nine O atoms, six from three oxalate ions and three from Water molecules.The model adopted for the heavier elements of the lanthanide series (Gd to Lu) and Ytterbium is based on the crystal structure of Yb_2(C_2O_4)_3· 6H_2O, in which each ion is surrounded by eight atoms, six from three oxalate ions and two from water molecules. The variation of the metal-ligand frequencies and force constants with the atomic numbers of lanthanides is plotted and discussed. 相似文献
994.
Hu H Qiao M Xie F Fan K Lei H Tan D Bao X Lin H Zong B Zhang X 《The journal of physical chemistry. B》2005,109(11):5186-5192
The desulfurization of thiophene on Raney Ni and rapidly quenched skeletal Ni (RQ Ni) has been studied in ultrahigh vacuum (UHV) by X-ray photoelectron spectroscopy (XPS). The Raney Ni or RQ Ni can be approximated as a hydrogen-preadsorbed polycrystalline Ni-alumina composite. It is found that thiophene molecularly adsorbs on Raney Ni or RQ Ni at 103 K. At 173 K, thiophene on alumina is desorbed, while thiophene in direct contact with the metallic Ni in Raney Ni undergoes C-S bond scission, leading to carbonaceous species most probably in the metallocycle-like configuration and atomic sulfur. On RQ Ni, the temperature for thiophene dissociation is about 100 K higher than that on Raney Ni. The lower reactivity of RQ Ni toward thiophene is tentatively attributed to lattice expansion of Ni crystallites in RQ Ni due to rapid quenching. The existence of alumina and hydrogen may block the further cracking of the metallocycle-like species on Raney Ni and RQ Ni at higher temperatures, which has been the dominant reaction pathway on Ni single crystals. By 473 K, the C 1s peak has disappeared, leaving nickel sulfide on the surface. 相似文献
995.
SynthesesandCharacterizationsof(η~5-C_5H_5)MoFeCo(CO)_8(μ_3-S)and(η~5-C_5H_5)_2Mo_2Fe(CO)_7(μ_3-S):X-rayCrystalStructureof(η~5-C_5H_... 相似文献
996.
This paper has analysed the major characteristics of long-term variation, of summermonsoon climate in South Asia since 1888. An abrupt enhancement of summer monsoon inthe 1920s and its synchronism with the global rapid warming have been detected by theMann-Kendall Rank Statistic test. Based on diagnostic analysis on the atmospheric circulationover the monsoon region and the thermal conditions of both ocean and land during theperiod of abrupt change, it is found that the warming over land was stronger and earlierthan that over the ocean, which would enhance the land-sea thermal contrast and thereforebe favorable to the development of monsoon low and the disturbance in the monsoon flow.This may be a direct factor for the abrupt enhancement of summer monsoon. 相似文献
997.
STUDIES OF ELECTRON SPIN RESONANCE ON BILIRUBIN FREE RADICALS 总被引:1,自引:0,他引:1
The nature of ESR signals derived from bilirubin-Ⅸα has been studied by focusing onthe samples treated with free radical generating and inhibiting systems, i.e. X-XOD, Fe/EDTA, SOD, mannitol/ascorbate, CO, KCN, etc. In all the cases, the stable signals comprisethose originated from semiquinone radical (g = 2.0012) and superoxide free radical (g_∥=2.041, g_⊥= 2.0040). The superoxide is shown binding with certain metal ions chelated bybilirubin. The free radical scavengers are able to destroy these radicals. The kinetic curveof the regeneration of bilirubin radicals has been determined and the reaction follows azero order mechanism. It is likely that both the physiological and toxic actions of bilirubinare related to the characters of its free radicals. Bilirubin is discussed as "active oxygensink" in mammalians. 相似文献
998.
999.
1000.
为了研究白血病骨髓移植病人全血微量元素铜的变化及其意义 ,用原子吸收光谱法检测了正常对照组与白血病骨髓移植患者预处理前及移植后骨髓空虚期全血微量元素铜的含量。结果表明 ,正常对照组全血铜浓度与白血病骨髓移植患者预处理前全血铜浓度差异无显著性 (P >0 0 5 ) ,而与骨髓空虚期全血铜浓度有显著性差异 (P <0 0 5 ) ,说明白血病缓解后血铜接近正常对照组水平 ,而白血病骨髓移植患者预处理后骨髓空虚期全血铜含量高于正常对照组 ,说明预处理影响微量元素铜的代谢 ,本文就其影响机理进行了研究 相似文献