全文获取类型
收费全文 | 892篇 |
免费 | 36篇 |
国内免费 | 5篇 |
专业分类
化学 | 685篇 |
晶体学 | 34篇 |
力学 | 17篇 |
数学 | 42篇 |
物理学 | 155篇 |
出版年
2024年 | 4篇 |
2023年 | 3篇 |
2022年 | 10篇 |
2021年 | 16篇 |
2020年 | 11篇 |
2019年 | 16篇 |
2018年 | 24篇 |
2017年 | 14篇 |
2016年 | 16篇 |
2015年 | 28篇 |
2014年 | 21篇 |
2013年 | 63篇 |
2012年 | 51篇 |
2011年 | 48篇 |
2010年 | 29篇 |
2009年 | 38篇 |
2008年 | 54篇 |
2007年 | 57篇 |
2006年 | 42篇 |
2005年 | 40篇 |
2004年 | 35篇 |
2003年 | 28篇 |
2002年 | 45篇 |
2001年 | 23篇 |
2000年 | 21篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 13篇 |
1983年 | 13篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1969年 | 2篇 |
排序方式: 共有933条查询结果,搜索用时 15 毫秒
11.
Methods for concentrating dilute fluids using adsorption followed by partial thermal regeneration were studied using the simulation package ADSIM. The systems studied were NaCl in liquid water on Amberlite XD-2 resin and benzene vapor in nitrogen on activated carbon. Cycles studied included counter-current regeneration with pure hot fluid, co-current regeneration with pure hot fluid, a new process called Hot Feed Addition (HFA) consisting of co-current regeneration with pure hot fluid followed by hot feed, and cycling zone adsorption (co-current alternating hot and cold feeds with no pure regeneration fluid). The optimum system depends upon the conditions of the system and the value function chosen to evaluate the systems. For example, for benzene in nitrogen with hot regeneration gas at 467.4 K, cycling zone adsorption used no carrier gas, had the most concentrated benzene stream and a very pure nitrogen product, but the energy use was greater than the other processes. For liquid systems counter-current operation could produce the purest product, but regenerant requirements were high. With slightly lower purity requirements HFA reduced solvent usage and increased the concentration of the concentrated waste stream. For the liquid system all processes used approximately 3% or less of the energy that would be required for evaporation. 相似文献
12.
Mariappan PeriasamyN. KishoreBabu Keela Natarajan Jayakumar 《Tetrahedron letters》2003,44(50):8939-8941
The reactions of arylacetic acid esters with tertiary arylamines in the presence of TiCl4 give α-arylated products in 65-90% yields, as well as 10-20% yields of the corresponding benzidines. 相似文献
13.
Jayakumar G. Gilbert Anthony W. Addison Mallayan Palaniandavar Raymond J. Butcher 《Journal of heterocyclic chemistry》2002,39(2):399-404
Procedures are given for the preparation of new linear bidentate, tetradentate and tripodal heptadentate ligands incorporating benzimidazole, benzothiazole and pyridyl groups. The compounds were characterized by their nmr, uv and mass spectra. The crystal and molecular structure is reported for a chiral benzothiazole derived from camphoric acid. 相似文献
14.
Extraction of promethium(III), uranium(VI), plutonium(IV), americium(III), zirconium(IV), ruthenium(III), iron(III) and palladium(II) has been carried out with a mixture of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and tributyl phosphate (TBP) in dodecane. The effects of nitric acid, TBP and CMPO concentrations on the extraction of these metal ions have been studied. The nature of the species of the above metal ions extracted into the organic phase has been suggested. 相似文献
15.
The infrared spectra, transmittance and polarized reflectance, of KNaSO4 and K3Na(SO4)2 are reported. Group theoretical analysis was carried out and a vibrational assignment proposed on basis of C3v and D3d symmetries. Factor group and site effects are discussed. 相似文献
16.
The infrared spectra, transmittance, and polarized reflectance of Cs3CoCl5 are reported. The group theoretical analysis was executed and a vibrational assignment proposed on the basis of D4h symmetry. Factor group and site effects are discussed. 相似文献
17.
18.
19.
Raschig rings used as a safety mechanism, to avoid critical reactions in solutions containing radioactive materials, are usually made of borosilicate glass. Since boron is the active neutron absorbing ingredient, it is important to determine the boron content in the Raschig rings at any given time. A method has been developed to determine rapidly the boron content of borosilicate glasses. Ion exchange and potentiometric measurement are used to determine boron as the tetrafluoroborate ion. The precision of the method is ±2.0 mV. The average difference between values of a wet chemical analysis and those of the potentiometric method is 7.7%. 相似文献
20.