全文获取类型
收费全文 | 2969篇 |
免费 | 525篇 |
国内免费 | 667篇 |
专业分类
化学 | 2686篇 |
晶体学 | 129篇 |
力学 | 46篇 |
综合类 | 24篇 |
数学 | 3篇 |
物理学 | 1273篇 |
出版年
2024年 | 6篇 |
2023年 | 60篇 |
2022年 | 55篇 |
2021年 | 80篇 |
2020年 | 147篇 |
2019年 | 110篇 |
2018年 | 145篇 |
2017年 | 159篇 |
2016年 | 180篇 |
2015年 | 144篇 |
2014年 | 172篇 |
2013年 | 284篇 |
2012年 | 351篇 |
2011年 | 248篇 |
2010年 | 168篇 |
2009年 | 206篇 |
2008年 | 160篇 |
2007年 | 213篇 |
2006年 | 189篇 |
2005年 | 130篇 |
2004年 | 130篇 |
2003年 | 88篇 |
2002年 | 108篇 |
2001年 | 90篇 |
2000年 | 79篇 |
1999年 | 73篇 |
1998年 | 57篇 |
1997年 | 53篇 |
1996年 | 59篇 |
1995年 | 51篇 |
1994年 | 33篇 |
1993年 | 26篇 |
1992年 | 26篇 |
1991年 | 13篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 6篇 |
1972年 | 1篇 |
排序方式: 共有4161条查询结果,搜索用时 15 毫秒
51.
A white substance was got by directly heating TiSi powder on Ti foil, under Ar+O
2 atmosphere. ED, EDX, SEM and HRTEM studies reveal that the white substance consists of amorphous SiO
2 nanowires of smooth surface and uniform diameter (40-90 nm). X-ray-induced luminescent emission experiment shows that two
broad peaks are at 430 and 570 nm. A one-dimensional growth mechanism, on the basis of the one-dimensional thermal flow during
nanowire formation, is discussed. 相似文献
52.
Hydrofluoric acid, added to seawater, can assist in the removal of chloride in the drying step by precipitating fluoride salts, thus suppressing the chloride interference effects induced on the atomization signals of Cu and Mn. By adding HF to seawater before the analysis, MgF2 and CaF2 are precipitated at the bottom of the sampling flask, without precipitating Cu and Mn, and are consequently not introduced into the graphite furnace. Because sodium salts are eliminated at the pretreatment step, the whole seawater matrix is eliminated before the atomization of Cu or Mn. Therefore, the analyzed volume of seawater can be increased by using the multi-injection procedure without degradation of the limit of detection and risks of spectral interferences. The limit of detection obtained for Cu and Mn are 0.05 and 0.01 μg L−1, respectively, for a 50 μL analyzed seawater volume. 相似文献
53.
54.
ZnO纳米线的电化学制备研究 总被引:10,自引:0,他引:10
High-quality ZnO nanowires have been synthesized at relatively low temperature via one-step electrochemical anodization technique. In this method, Zn sheet acted as the anode and Pb sheet served as the counter electrode, and the complex solution of HF-C2H5OH-H2O was used as electrolyte. ZnO nanowires were characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED) and X-ray Diffraction (XRD). The results show that the nanowires were wurtzite crystalline ZnO, and the ZnO nanowires with the diameters of 70 nm and 30~40 nm were obtained by adjusting preparation conditions, respectively. 相似文献
55.
《Surface and interface analysis : SIA》2004,36(4):339-346
Air‐formed oxide on a CuAl2 model alloy is shown to be free of copper species, with copper enriching in the alloy. With thickening of the oxide by anodizing, copper enriches further to a critical concentration at which its oxidation proceeds with incorporation of Cu(II) species into the film. Such species migrate more rapidly through the film than aluminium species. Incorporation of copper species is associated with generation of oxygen gas within the film and subsequent film rupture is due to release of the gas. Reduction of Cu(II) to Cu(I) species during XPS analysis is characterized and the accelerating role of charge neutralizing is highlighted. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
56.
The introduction of mesoporous nanosize zirconia to the catalyst for methanol synthesis dedicates the nanosized catalyst and mesoporous duplicated properties. The catalyst bears the larger surface area, larger mesoporous volume and more uniform diameter, more surface metal atoms and oxygen vacancies than the catalyst prepared with the conventional coprecipitation method. The modification of microstructure and electronic effect could result in the change of the reduced chemical state and decrease of reducuction temperature of copper, donating the higher activity and methanol selectivity to the catalyst. The results of methanol synthesis demonstrate that the Cu^+ is the optimum active site. Also, the interaction between the copper and zirconia shows the synergistic effect to fulfil the methanol synthesis. 相似文献
57.
E. U. Franck 《Journal of solution chemistry》1973,2(2-3):339-356
A survey is given of recent experimental results obtained from high-temperature, high-pressure investigations with water, aqueous solutions, and ionic fluids. Data on the static dielectric constant of water to 550°C and 5 kbar are given and discussed with respect to their relation to water structure. Infrared and Raman spectra of HDO in pure water have been obtained to 400°C and 4 kbar, which give information on hydrogen bonding. Xe–H2O and CO2–H2O mixtures were investigated in the infrared. Ni(II) and Cu(II) complexes were investigated by absorption spectroscopy in aqueous solutions of high chloride content to 350°C and 2–6 kbar. The gas-liquid critical point of ammonium chloride was found at 880°C and 1635 bars. This fluid appears to be predominantly ionic even in the critical region. The possibility of converting pure polar fluids such as ammonia and water into concentrated ionic solutions by self-ionization at very high pressures is mentioned.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank. 相似文献
58.
Donna C Arnold Olga Kazakova Guillaume Audoit Joseph M Tobin Jaideep S Kulkarni Sergey Nikitenko Michael A Morris Justin D Holmes 《Chemphyschem》2007,8(11):1694-1700
The synthesis of marokite CaMn(2)O(4) nanowires using a hydrothermal method is reported. Transmission electron microscopy and electron diffraction measurements show that the nanowires are polycrystalline in nature with diameters between 10 and 20 nm and lengths ranging from approximately 100 to 500 nm. Most interestingly, in contrast with the bulk material, magnetization measurements show that these nanowires exhibit ferromagnetic ordering with a Curie temperature (T(C)) of approximately 40 K. 相似文献
59.
STUDY OF Cu-Mu CATALYST FOR THE SYNTHESIS OF METHYL FORMATE AND METHANOL FROM SYNTHESIS GAS 下载免费PDF全文
将一种新型的CuMn催化剂用于由合成气合成甲酸甲酯和甲醇,该催化剂表现出良好的反应活性和甲酸甲酯选择性。考察了反应温度、合成气压力及催化剂制备方法等对合成甲酸甲酯和甲醇的反应活性及选择性的影响。在反应条件下,产物收率最高达60.10g/(L·h),产物甲酸甲酯的选择性很高。用BET、XRD及XPSAuger等测试方法对催化剂的比表面、晶相组成以及铜、锰在催化剂中的价态进行了表征,并探讨了催化剂失活的原因。 相似文献
60.