全文获取类型
收费全文 | 4165篇 |
免费 | 664篇 |
国内免费 | 346篇 |
专业分类
化学 | 1626篇 |
晶体学 | 32篇 |
力学 | 510篇 |
综合类 | 24篇 |
数学 | 428篇 |
物理学 | 2555篇 |
出版年
2024年 | 4篇 |
2023年 | 30篇 |
2022年 | 65篇 |
2021年 | 80篇 |
2020年 | 95篇 |
2019年 | 108篇 |
2018年 | 93篇 |
2017年 | 104篇 |
2016年 | 140篇 |
2015年 | 136篇 |
2014年 | 251篇 |
2013年 | 336篇 |
2012年 | 257篇 |
2011年 | 309篇 |
2010年 | 220篇 |
2009年 | 279篇 |
2008年 | 304篇 |
2007年 | 291篇 |
2006年 | 232篇 |
2005年 | 231篇 |
2004年 | 248篇 |
2003年 | 197篇 |
2002年 | 151篇 |
2001年 | 140篇 |
2000年 | 114篇 |
1999年 | 107篇 |
1998年 | 115篇 |
1997年 | 94篇 |
1996年 | 65篇 |
1995年 | 66篇 |
1994年 | 49篇 |
1993年 | 58篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 2篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1973年 | 3篇 |
1957年 | 1篇 |
排序方式: 共有5175条查询结果,搜索用时 15 毫秒
51.
Stefano L. Paveri-Fontana C. V. M. van der Mee P. F. Zweifel 《Journal of statistical physics》1989,57(1-2):247-265
A BGK-type Boltzmann equation for a neutral gas is considered as a model for electron swarms, because the gas and the electron Boltzmann equation have a common diffusion approximation. Both full- and half-range theory are developed using orthogonality methods of solution. Preliminary comparisons with diffusion theory are presented. 相似文献
52.
表面包覆改性对纳米CeO2分散性的影响 总被引:1,自引:0,他引:1
了改善纳米CeO2在Zn-Al类共晶合金中的分散性,采用超声液相包覆法对纳米CeO2进行表面活性剂表面包覆改性,并用AES测定了包覆层的厚度,用TEM研究了CeO2的团聚状况,用TGA分析了有机物包覆层的炭化温度范围,最后用FE-SEM观察了CeO2在复合材料中的分散情况。结果表明,包覆在纳米CeO2表面的厚度约为20 nm的表面活性剂层提高了微粒的分散性,而且该包覆层在495℃时已经炭化。热力学计算的结果也表明,炭化层能与氧化膜反应,该反应提高了CeO2与基体间的润湿性,并使其均匀分布在基体合金中。 相似文献
53.
54.
Determination of Organophosphorus Pesticides in Soil by MMSPD-GC-NPD and Confirmation by GC-MS 总被引:1,自引:0,他引:1
A novel method, modified matrix solid-phase dispersion (MMSPD), has been developed for quantitative analysis of organophosphorus
pesticide residues in soil. It was based on matrix solid-phase dispersion (MSPD) and continuous liquid-solid extraction (continuous
LSE), using Florisil as sorbent and dichloromethane as the recycling solvent. Two soils with different texture and physicochemical
properties were studied to validate the method. The effect of residence time of pesticides in soil was also studied. MMSPD
was compared with MSPD and continuous LSE respectively. Determination was carried out by gas chromatography with nitrogen-phosphorus
detection (GC-NPD). The method gave recoveries ranging from 72–105% with relative standard deviations (RSDs) lower than 15%
for the pesticides studied. The limits of detection (LODs) ranged from 0.1 to 0.6 ng g−1. Two pesticide residues have been detected in real soil samples from Fujian, China, using MMSPD. The pesticides were confirmed
by gas chromatography-mass spectrometry (GC-MS) in a selected-ion monitoring (SIM) mode.
Revised: 4 and 9 April 2006 相似文献
55.
J. Howard Rytting Danny R. McHan Takeru Higuchi David J. W. Grant 《Journal of solution chemistry》1986,15(8):693-703
Henry's law constants have been determined for -butyrolactone (BL), ethyl acetate (EA), and 2-methyl-3-pentanol (MEP) in mixtures of iso-octane (ISO) and toluene (TOL), for BL, EA, TOL, and ISO in cinnamaldehyde (CIN) and for TOL and ISO in each other and in BL. From these data and published vapor pressures, the activity coefficients at infinite dilution and the standard molar Gibbs free energy of transfer, G
2
0
of the solutes from dilute solution in ISO to dilute solution in each solvent medium have been calculated. The different behavior patterns of BL and EA are attributed to differences in their abilities to exist in different conformations possessing different dipole moments. For polar solutes, G
2
0
decreases with increasing polarizability of the solvent and with increasing dipole moment of the solute, suggesting increased contributions from dipole-induced dipole (Debye) interactions. The sigmoidal plot of G
2
0
against the change in pair potential energy calculated from the classical expressions suggests that G
2
0
seriously underestimates the strength of the Debye interactions in comparison with the London interactions. 相似文献
56.
本文评述了表面热电离质谱(TIMS),特别是负离子质谱(NTI-MS)对非金属和具有高电离电位的金属元素的同位素测定的进展,引用文献34篇。 相似文献
57.
58.
The disadvantages of Normally White Twisted Nematic Liquid Crystal Display (NW-TN-LCD) were discussed. The reason that the negative birefringent polyimide thin filmswere used to compensate NW-TN-LCD to decrease off-axis leakage, improve contrast ratiosand enlarge viewing angles was explained in this paper. A certain polyimide thin film wastaken as an example to show compensation effect on NW-TN-LCD. 相似文献
59.
The formation of negative hydrogen ions in a conventional hollow cathode discharge has been investigated. A mixture of Ne and H2 proved to be more advantageous compared to pure hydrogen. The study has been performed by solving the electron Boltzmann equation, coupled with a system of balance equations for neon and hydrogen neutral and charged particles. The vibrational distribution function of hydrogen has been calculated. Our calculations show unusually high population of vibrationally excited hydrogen molecules in a Ne–H2 mixture, which explains the high density of negative hydrogen ions under optimal conditions (total gas pressure of few Torr, hydrogen number mole fraction of 1–10% and discharge current of 10–100 mA). Line intensities originating from highly excited neon states vs. hydrogen pressure have been calculated and a comparison with existing experimental results has been made. 相似文献
60.
用气相流动吸附法制备复合载体,用浸渍法制备WO3/(TiO2-S iO2)催化剂.应用LRS和TPR技术研究WO3在复合载体TIO2-S iO2表面的分散状态,发现TiO2在S iO2表面的分散可增强WO3与载体之间的相互作用,提高WO3在载体表面的分散阈值.另外TPR实验证明,TiO2的存在不仅大大改善WO3的分散状态,而且使WO3在TiO2-S iO2的还原温度升高,WO3与载体之间的作用增强.负载于经TiO2调变的S iO2上的催化剂其HDS、HYD、BHD活性高于负载于单纯S iO2上的催化剂的活性. 相似文献