全文获取类型
收费全文 | 41832篇 |
免费 | 5394篇 |
国内免费 | 4250篇 |
专业分类
化学 | 11390篇 |
晶体学 | 970篇 |
力学 | 9746篇 |
综合类 | 601篇 |
数学 | 15431篇 |
物理学 | 13338篇 |
出版年
2024年 | 89篇 |
2023年 | 443篇 |
2022年 | 782篇 |
2021年 | 948篇 |
2020年 | 1208篇 |
2019年 | 1067篇 |
2018年 | 1067篇 |
2017年 | 1477篇 |
2016年 | 1696篇 |
2015年 | 1299篇 |
2014年 | 2132篇 |
2013年 | 2992篇 |
2012年 | 2605篇 |
2011年 | 2922篇 |
2010年 | 2481篇 |
2009年 | 2769篇 |
2008年 | 2680篇 |
2007年 | 2655篇 |
2006年 | 2438篇 |
2005年 | 2256篇 |
2004年 | 1933篇 |
2003年 | 1753篇 |
2002年 | 1573篇 |
2001年 | 1327篇 |
2000年 | 1223篇 |
1999年 | 1100篇 |
1998年 | 1016篇 |
1997年 | 871篇 |
1996年 | 711篇 |
1995年 | 608篇 |
1994年 | 566篇 |
1993年 | 458篇 |
1992年 | 458篇 |
1991年 | 352篇 |
1990年 | 278篇 |
1989年 | 219篇 |
1988年 | 181篇 |
1987年 | 134篇 |
1986年 | 90篇 |
1985年 | 118篇 |
1984年 | 112篇 |
1983年 | 55篇 |
1982年 | 74篇 |
1981年 | 51篇 |
1980年 | 28篇 |
1979年 | 43篇 |
1978年 | 31篇 |
1977年 | 41篇 |
1976年 | 15篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
本文采用溶胶凝聚方法制备了超细氢氧化亚镍电极材料并通过在其中掺加适量碳纳米管的方法大大提高了电极的比容量并有效改善了电极材料的阻抗特性。掺有20%碳纳米管的氢氧化亚镍复合电极材料的单电极比容量可达到320 F·g-1。本文分别采用氢氧化亚镍/碳纳米管复合电极作为正极,活性炭作为负极,6 mol·L-1 KOH作为电解液制备了复合型电化学电容器。采用上述方法制备的复合型电容器工作电压达到1.6 V,电容器质量比容量达到60 F·g-1。复合型电容器能量密度达到20.11 Wh·kg-1,最大功率密度达到8.6 kW·kg-1,兼具高能量特性和优良的大电流放电特性。 相似文献
992.
993.
A new simple, selective and sensitive method for the determination of trace chlorine dioxide in water has been developed, based on the oxidation by chlorine dioxide to reduction the fluorescence of rhodamine dyes in ammonia-ammonium chloride buffer solution. Four rhodamine dyes systems such as rhodamine S, rhodamine G, rhodamine B and butyl-rhodamine B were tested. The rhodamine S system is the best, with a linear range of 0.0060-0.450 μg mL−1 and a detection limit of 0.0030 μg mL−1 ClO2. It was applied to the determination of chlorine dioxide in synthetic samples and real samples, with satisfactory results. This method has good selectivity, especially, other chlorine species such as chlorine, hypochlorite, chlorite and chlorate do not interfere the determination. The mechanism of fluorescence reduction was also considered. 相似文献
994.
995.
996.
OUH体系的结构和分析势能函数 总被引:3,自引:0,他引:3
采用密度泛涵B3LYP方法优化出了OUH分子的各种结构,确定了最稳定构型和离解能,以及它们的谐性力常数,并导出双原子分子UH,UO的Murrell-Sorbie势能函数及其光谱数据。采用多体项展式方法,导出OUH(X^4A')基态分子的分析势能函数,获得OUH(X^4A')体系的势能面,考察了这个势能函数的基本性质,正确地复现出OUH分子的平衡结构特征,结果表明:U+OH,O+UH,H+UO的反应均为无阈能的放热能反应。为进一步探讨OUH体系的反应动力学过程打下了基础。 相似文献
997.
Peter Scharfenberg 《Theoretical chemistry accounts》1985,67(3):235-243
Bromine parameters are proposed, matching well the standard values of first and second row atoms, as introduced by Pople et al. This is shown by comparisons of geometries, configurations, conformations, and dipole moments, obtained with different approaches. The new parameter set was found in a very simple and efficient way that may also be useful for other tasks, e.g. in non-empirical calculations. 相似文献
998.
《Arabian Journal of Chemistry》2022,15(12):104329
To reduce the amount of hazardous chemical bottle waste in the environment, we report the optimization research of silica extraction in chemical bottle waste into silica gel. Alkali fusion and sol–gel process were utilised to prepare silica gel effectively. The alkali fusion process was carried out by adding sodium hydroxide to produce sodium silicate. Afterwards, silica gel was prepared by the sol–gel method using hydrochloric acid. Box-Behnken Design (BBD) was applied to Optimisation factors the poptimiseactors affecting the silica recovery. The factors that optimised mass ratio, particle size, and temperature. The optimum recovery of silica gel was obtained by SiO2: NaOH mass ratio of 1:3, the particle size of 63–74 µm, and a temperature of 800 °C. The purity of silica gel optimum is 63.74% characterised using X-ray fluorescence. The structure of silica gel is the appearance of amorphous peaks at 2θ 20-30° characterised using an x-ray diffractogram. The silica gel surface was characterises using scanning electron microscopy-energy dispersive x-ray. It showed an irregular surface and characteristic showed that silica gel had a radius of 15.74 nm and a specific surface area of 297.08 m2. 相似文献
999.
298.15K下Li2B4O7-H2O体系水蒸汽分压及渗透系数的等压测定和离子相互作用模型 总被引:2,自引:0,他引:2
在已有研究含硼体系的文献中仅考虑了硼酸根B4O7^-2或B(OH)4^-和H3BO3的存在,而对Li2B4O7-H2O体系具有多种硼物种聚合平衡体系的热力学性质的研究尚未见报道.本文用等压法研究了Li2B4O7-H2O体系于298.15K下浓度由稀到过饱和溶液的平衡气相蒸汽压及渗透系数.考虑了水溶液中多种硼物种的存在,以Pitzer方程为基础,建立了可描述该含硼体系的离子相互作用模型。 相似文献
1000.
Heidar Raissi Effat Moshfeghi Abraham F. Jalbout Mohammad Saeid Hosseini Mustapha Fazli 《International journal of quantum chemistry》2007,107(9):1835-1845
The molecular structure and intramolecular hydrogen bond energy of 32 conformers of 4‐methylamino‐3‐penten‐2‐one were investigated at MP2 and B3LYP levels of theory using the standard 6–31G** basis set and AIM analyses. Furthermore, calculations for all the possible conformations of 4‐methylamino‐3‐penten‐2‐one in water solution were also carried out at B3LYP/6–31G** level of theory. The calculated geometrical parameters and conformational analyses in gas phase and water solution show that the ketoamine conformers of this compound are more stable than the other conformers (i.e., enolimine and ketoimine). This stability is mainly due to the formation of a strong N? H···O intramolecular hydrogen bond, which is assisted by π‐electrons resonance. Hydrogen bond energies for all conformers of 4‐methylamino‐3‐penten‐2‐one were obtained from the related rotamers method. The nature of intramolecular hydrogen bond existing within 4‐methylamino‐3‐penten‐2‐one has been investigated by means of the Bader theory of atoms in molecules, which is based on topological properties of the electron density. The results of these calculations support the results which obtained by related rotamers method. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献