全文获取类型
收费全文 | 565篇 |
免费 | 45篇 |
国内免费 | 70篇 |
专业分类
化学 | 318篇 |
晶体学 | 3篇 |
力学 | 43篇 |
综合类 | 3篇 |
数学 | 43篇 |
物理学 | 78篇 |
综合类 | 192篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 18篇 |
2020年 | 14篇 |
2019年 | 9篇 |
2018年 | 20篇 |
2017年 | 9篇 |
2016年 | 23篇 |
2015年 | 16篇 |
2014年 | 26篇 |
2013年 | 27篇 |
2012年 | 47篇 |
2011年 | 34篇 |
2010年 | 34篇 |
2009年 | 28篇 |
2008年 | 41篇 |
2007年 | 44篇 |
2006年 | 24篇 |
2005年 | 24篇 |
2004年 | 22篇 |
2003年 | 24篇 |
2002年 | 23篇 |
2001年 | 22篇 |
2000年 | 21篇 |
1999年 | 18篇 |
1998年 | 18篇 |
1997年 | 9篇 |
1996年 | 21篇 |
1995年 | 15篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有680条查询结果,搜索用时 269 毫秒
81.
82.
Back Cover: Ultrasound‐Driven Secondary Self‐Assembly of Amphiphilic β‐Cyclodextrin Dimers (Chem. Eur. J. 13/2015)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
83.
84.
Facile preparation of ZrCO composite aerogel with high specific surface area and low thermal conductivity 总被引:2,自引:0,他引:2
Sheng Cui Hao Suo Feng Jing Shuwen Yu Jun Xue Xiaodong Shen Benlan Lin Shengjun Jiang Yu Liu 《Journal of Sol-Gel Science and Technology》2018,86(2):383-390
A novel ZrCO composite aerogel is synthesized using zirconium oxychloride and resorcinol–formaldehyde (RF) as precursors through the sol–gel route and carbothermal reduction process. The effects of different Zr/R molar ratios and calcination temperatures on the physical chemistry properties of ZrCO aerogels are investigated. The ZrCO composite aerogel consists of the C/ZrO2/ZrC ternary aerogel. The results show that with the increase of R/Zr molar ratios, the specific surface area and bulk density increase with calcination temperature up to 1300?°C, but decrease at even temperature (1500?°C). The specific surface area is as high as 637.4?m2/g for ZrCO composite aerogel (R:Zr?=?2:1), which was higher than ever reported. As the heat-treatment temperature increases to 1500?°C, the ZrC crystalline phase occurs and the t-ZrO2 phase still appears within the composite. The thermal conductivity of the carbon fiber mat-reinforced composite aerogel is as low as 0.057?W/m/K at room temperature (25?°C). 相似文献
85.
Diastereo‐ and Enantioselective Palladium‐Catalyzed Dearomative [3+2] Cycloaddition of 3‐Nitroindoles
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Diastereo‐ and enantioselective cycloaddition of 3‐nitroindoles with vinyl aziridine was realized under Pd‐catalysis using commercially available Walphos as the ligand, affording pyrroloindolines in high yields with high diastereo‐ and enantioselectivities. The reaction can be scaled up to a gram scale and the reaction products are easily converted to amino pyrroloindoline and other pyrroloindoline derivatives. 相似文献
86.
Wenna Zhou Zhenzhen Yuan Gang Li Jian Ouyang Yourui Suo 《Natural product research》2018,32(8):892-897
In this study, a valid method was established for the isolation and purification of flavone glycosides from Hippophae rhamnoides L. seed residues using high-speed counter-current chromatography in one step, with a solvent system of ethyl acetate-methanol-n-butyl alcohol-water (9:1:0.5:9, v/v/v/v). A total of 28.8 mg compound I and 57.3 mg compound II were obtained from 200 mg of flavone H-glycosides rich extract, with purities of 98.3 and 96.4%, respectively. The structures of two compounds were identified by MS and NMR. 3-O-β-D-Sophorosylkaempferol-7-O-{3-O-[2(E)-2,6-dimethyl-6-hydroxyocta-2,7-dienoyl]}-α-L-rhamnoside is compound I and compound II named hippophanone is a new compound were identified by MS and NMR. The method was efficient and convenient, which could be used for the preparative separation of flavone glycosides from H. rhamnoides L. seed residues. 相似文献
87.
应用广义函数的 Fourier积分变换导出一类反应扩散方程的基本解 ,在此基础上得到边界积分方程 ,消除了边界元计算中边界积分方程的区域积分项。 相似文献
88.
索洪敏 《贵州工业大学学报(自然科学版)》1998,27(4):10-13
本文证明在不动点理论、鞍点理论及多目标优化理论中均有重要应用的Ky Fan不等式组的解集是通有稳定的。 相似文献
89.
Cong Yu Zhengdong Guo Lifeng Yang Jiyu Cui Sen Chen Yawen Bo Xian Suo Qihan Gong Shang Zhang Prof. Xili Cui Shengbao He Prof. Huabin Xing 《Angewandte Chemie (International ed. in English)》2023,62(16):e202218027
Adsorptive separation is an energy-efficient alternative, but its advancement has been hindered by the challenge of industrially potential adsorbents development. Herein, a novel ultra-microporous metal-organic framework ZU-901 is designed that satisfies the basic criteria raised by ethylene/ethane (C2H4/C2H6) pressure swing adsorption (PSA). ZU-901 exhibits an “S” shaped C2H4 curve with high sorbent selection parameter (65) and could be mildly regenerated. Through green aqueous-phase synthesis, ZU-901 is easily scalable with 99 % yield, and it is stable in water, acid, basic solutions and cycling breakthrough experiments. Polymer-grade C2H4 (99.51 %) could be obtained via a simulating two-bed PSA process, and the corresponding energy consumption is only 1/10 of that of simulating cryogenic distillation. Our work has demonstrated the great potential of pore engineering in designing porous materials with desired adsorption and desorption behavior to implement an efficient PSA process. 相似文献
90.
Chenxu Ding Lingyun Wang Chunliang Tian Yulin Li Zhiwei Sun Honglun Wang Yourui Suo Jinmao You 《Chromatographia》2008,68(11-12):893-902
A novel labeling reagent 1-(2-naphthyl)-3-methyl-5-pyrazolone (NMP) coupling to liquid chromatography with electrospray ionization mass spectrometry for the detection of carbohydrates from the derivatized rape bee pollen samples is reported. Carbohydrates are derivatized to their bis-NMP-labeled derivatives. Derivatives showed an intense protonated molecular ion at m/z [M+H]+ in positive-ion detection mode. The mass-to-charge ratios of characteristic fragment ions at m/z 473.0 could be used for the accurately qualitative analysis of carbohydrates. This characteristic fragment ion is from the cleavage of C2–C3 bond in carbohydrate chain giving the specific fragment ions at m/z [MH-C m H2m+1O m -H2O]+ for pentose, hexose and glyceraldehydes and at m/z [MH-C m H2m-1O m+1-H2O]+ for alduronic acids such as galacturonic acid and glucuronic acid (m = n ? 2, n is carbon number of carbohydrate). No interferences for all aliphatic and aromatic aldehydes presented in natural environmental samples were observed due to the highly specific parent mass-to-charge ratio and the characteristic fragment ions. The method, in conjunction with a gradient elution, offered a baseline resolution of carbohydrate derivatives on a reversed-phase Hypersil ODS-2 column. The carbohydrates such as mannose, galacturonic acid, glucuronic acid, rhamnose, glucose, galactose, xylose, arabinose and fucose can successfully be detected. 相似文献