全文获取类型
收费全文 | 19594篇 |
免费 | 2879篇 |
国内免费 | 2924篇 |
专业分类
化学 | 15373篇 |
晶体学 | 349篇 |
力学 | 1000篇 |
综合类 | 191篇 |
数学 | 1844篇 |
物理学 | 6640篇 |
出版年
2024年 | 28篇 |
2023年 | 376篇 |
2022年 | 511篇 |
2021年 | 780篇 |
2020年 | 840篇 |
2019年 | 900篇 |
2018年 | 707篇 |
2017年 | 728篇 |
2016年 | 920篇 |
2015年 | 917篇 |
2014年 | 1129篇 |
2013年 | 1506篇 |
2012年 | 1735篇 |
2011年 | 1749篇 |
2010年 | 1356篇 |
2009年 | 1220篇 |
2008年 | 1350篇 |
2007年 | 1131篇 |
2006年 | 1113篇 |
2005年 | 1012篇 |
2004年 | 852篇 |
2003年 | 712篇 |
2002年 | 740篇 |
2001年 | 618篇 |
2000年 | 430篇 |
1999年 | 361篇 |
1998年 | 258篇 |
1997年 | 178篇 |
1996年 | 200篇 |
1995年 | 156篇 |
1994年 | 143篇 |
1993年 | 139篇 |
1992年 | 107篇 |
1991年 | 120篇 |
1990年 | 66篇 |
1989年 | 55篇 |
1988年 | 45篇 |
1987年 | 38篇 |
1986年 | 36篇 |
1985年 | 32篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1971年 | 7篇 |
1970年 | 6篇 |
1959年 | 3篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
52.
YAN Xiaomin ZHAO Lin SHAO Jianhui TAN Xin SONG Zhengxiao School of Chemical Engineering Technology Tianjin University Tianjin China Slichem Liquid Material Co. Ltd. Shijiazhuang China 《Chinese Journal of Reactive Polymers》2004,(Z1)
1. INTRODUCTION Methionine, namely 2-amido-4-thiomethyl butyric acid with a structure of CH3SCH2CH2CHCOOH, is one of the essential amino acids and has two natural enantionmers, D and L-methionine. The mixture of L- and D-isomers can be used as analeptics or nutritive additives to maintain the equilibrium of amino acids of feed [1,2]. L-methionine can release active methyl and accelerate the synthesis of choline, which further speeds up the conversion of the lipid accumulated in liv… 相似文献
53.
Styrene (STY) is now produced industrially in fairly large quantities by the dehydrogenation of ethylbenzene (EB) using promoted iron oxide catalyst with superheated steam.In this case, small amount of carbon dioxide formed as a by-product was known to inhibit the catalytic activity of commercial catalyst. Recently, there have been some reports which carbon dioxide showed positive effects to promote catalytic activities on the reaction over several catalysts.In this study, we attempted to combine the dehydrogenation of EB to STY with the carbon dioxide shift-reaction. The combine reaction (EB + CO2 → STY + H2O + CO) can be considered as one of the ways of using CO2 resources and can yield simultaneously STY and Carbon oxide.Alumina oxide catalysts such as Al2O3, Na2O/Al2O3 and K2O/Al2O3 were prepared by the usual impregnation method with an aqueous solution of NaNO3 and KNO3, and then calcined at 650℃ for 5 h in a stream of air. The reaction condition is 600℃, flow of CO2 38ml/mon and space velocity (EB) 1.28h-1. 相似文献
54.
JianXinCAO YiFengWANG GuoFangLAI ShiDeLUO 《中国化学快报》2004,15(7):797-800
From the dried aerial part ofParepigynumfuningesis Tsiang et P. T. Li (Apocynaceae),a new cardiac glucoside, named parefuningoside (1) had been isolated. Its structure was determined by means of hydrolysis and spectral analysis. 相似文献
55.
56.
57.
58.
59.
A simple model has been developed to describe the Zeeman patterns of far-infrared laser magnetic resonance spectra of the monobromomethyl radical CH2Br observed at 447.3 and 671.1μm. A satisfactory agreement between the experimental spectra of the radical and their simulation with this simple model has been achieved. This approach can be used to gain further information about the structure and the spectrum of this interesting radical. 相似文献