全文获取类型
收费全文 | 1201篇 |
免费 | 84篇 |
国内免费 | 199篇 |
专业分类
化学 | 976篇 |
晶体学 | 11篇 |
力学 | 65篇 |
综合类 | 19篇 |
数学 | 119篇 |
物理学 | 294篇 |
出版年
2023年 | 17篇 |
2022年 | 39篇 |
2021年 | 42篇 |
2020年 | 34篇 |
2019年 | 41篇 |
2018年 | 38篇 |
2017年 | 50篇 |
2016年 | 51篇 |
2015年 | 69篇 |
2014年 | 56篇 |
2013年 | 96篇 |
2012年 | 93篇 |
2011年 | 94篇 |
2010年 | 75篇 |
2009年 | 89篇 |
2008年 | 79篇 |
2007年 | 85篇 |
2006年 | 84篇 |
2005年 | 75篇 |
2004年 | 38篇 |
2003年 | 28篇 |
2002年 | 24篇 |
2001年 | 21篇 |
2000年 | 27篇 |
1999年 | 39篇 |
1998年 | 25篇 |
1997年 | 22篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有1484条查询结果,搜索用时 93 毫秒
151.
Quantum chemistry calculations have been performed using Gaussian03 program to compute optimized geometry, harmonic vibrational
frequency along with intensities in IR and Raman spectra at RHF/6-31++G** and B3LYP/6-31++G** levels for phenobarbitone (C12H12N2O3) in the ground state. The scaled harmonic vibrational frequencies have been compared with experimental FT-IR and FT-Raman
spectra. Theoretical vibrational spectra of the title compound were interpreted by means of potential energy distributions
(PEDs) using MOLVIB program. A detailed interpretation of the infrared spectra of the title compound is reported. On the basis
of the agreement between the calculated and observed results, the assignments of fundamental vibrational modes of phenobarbitone
were examined and some assignments were proposed. The theoretical spectrograms for FT-IR and FT-Raman spectra of the title
compound have been constructed. 相似文献
152.
Photocatalytic reduction of CO2 in methanol to methyl formate over CuO-TiO2 composite catalysts 总被引:3,自引:0,他引:3
Photocatalytic reduction of CO(2) on CuO-TiO(2) composite catalysts in the presence of methanol to prepare methyl formate had been investigated. Methanol was used as sacrificial reagent to react with the photo-generated holes in the valence band, and CO(2) was reduced by the electrons in the conduction band. CuO-TiO(2) was optimized for CuO loading, preparation method and calcination temperature. The catalyst of 1.0CuO-TiO(2), calcined at 450°C and CTAB as a dispersant showed the highest overall activity. The heterojunction between CuO and TiO(2) demonstrated with HRTEM played an important role in enhancing the photocatalytic activity. 相似文献
153.
Cheng X Jia H Long T Feng J Qin J Li Z 《Chemical communications (Cambridge, England)》2011,47(43):11978-11980
A new design strategy for the development of fluorescent turn-on chemodosimeters toward OCl(-) was proposed by the removal, but not the general inhibition, of the C=N isomerization. Accordingly, Flu-1 was prepared, which, as shown in the fluorescent picture, exhibited the off-on response for OCl(-), sensitively and selectively. 相似文献
154.
One pot production of 5-hydroxymethylfurfural with high yield from cellulose by a Brønsted-Lewis-surfactant-combined heteropolyacid catalyst 总被引:1,自引:0,他引:1
Zhao S Cheng M Li J Tian J Wang X 《Chemical communications (Cambridge, England)》2011,47(7):2176-2178
A Br?nsted-Lewis-surfactant-combined heteropolyacid (HPA) Cr[(DS)H(2)PW(12)O(40)](3) has been synthesized, and is used as a heterogeneous catalyst for the conversion of cellulose to 5-hydroxymethylfurfural in one pot within 2 h at 150 °C with 77.1% conversion and 52.7% yield. This micellar HPA catalyst shows stability and can be recycled by simple separation process. 相似文献
155.
156.
A number of nickel based materials are investigated as potential oxygen evolution catalysts under conditions close to those met in modern, high current density alkaline water electrolysers. Microelectrodes are used to avoid distortion of voltammetric data by IR drop even at the high current densities employed in such water electrolysers. High surface area nickel metal oxides prepared by cathodic deposition and mixed oxides prepared by thermal methods are considered. A mixed Ni/Fe oxide is the preferred electrocatalyst. The influence of hydroxide ion concentration and temperature on the voltammetry is defined. Preliminary stability tests in a zero gap cell with an OH(-) conducting membrane show no significant increase in overpotential during 10 days operation in 4 M NaOH electrolyte at a current density of 1 A cm(-2) at 333 K. 相似文献
157.
158.
用超声波分散处理Fe3O4粉末同稳定剂溶液的分散体系,使Fe3O4粉末能稳定地分散成细微粒子,同时增强了Fe3O4细微粒子同单体、引发剂的亲合性。苯乙烯—丙烯醛共聚物为高分子壳层,包裹Fe3O4得到了带醛基的磁性高分子复合微球。微球粒径可控制在50~200μm,微球中Fe3O4含量在0.4~1.5%之间,通过电导滴定法测定微球表面醛基含量在0.04~0.1mmoL·g-1范围内。着重考察了引发剂体系、稳定剂体系、分散介质等对微球粒径、表面醛基含量的影响。 相似文献
159.
Xiaohong Cao 《Journal of Mathematical Analysis and Applications》2006,323(1):267-274
Using a variant of the essential approximate point spectrum, we give the necessary and sufficient conditions for T for which the a-Browder's theorem or the a-Weyl's theorem holds. Also, the relation between hypercyclic operators (or supercyclic operators) and the operators which satisfy Weyl type theorem is discussed. 相似文献
160.