全文获取类型
收费全文 | 305篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
化学 | 301篇 |
晶体学 | 3篇 |
力学 | 1篇 |
数学 | 9篇 |
物理学 | 15篇 |
出版年
2023年 | 3篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 11篇 |
2014年 | 9篇 |
2013年 | 17篇 |
2012年 | 26篇 |
2011年 | 30篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 35篇 |
2007年 | 13篇 |
2006年 | 29篇 |
2005年 | 22篇 |
2004年 | 15篇 |
2003年 | 15篇 |
2002年 | 10篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有329条查询结果,搜索用时 15 毫秒
1.
2.
By optimizing pump power ratio between 1st order backward pump and 2nd order forward pump on discrete Raman amplifier, we demonstrated over 2dB noise figure improvement without excessive non-linearity degradation. 相似文献
3.
Ryuhei Wakita Masanori Miyakoshi Yohji Nakatsuji Mitsuo Okahara 《Journal of inclusion phenomena and macrocyclic chemistry》1991,10(1):127-139
A series of noncyclic neutral ionophores has been synthesized by the reaction of oligoethylene glycol dihalides with 8-quinolinol. Complexation properties for alkali metal picrates were evaluated from solvent extraction and bulk liquid membrane transport experiments. Complexation profiles of the newly synthesized ionophores with a hexyl chain were similar to those of their homologues without the hexyl chain in the extraction experiments. Among them, the pentaethylene glycol derivatives showed the highest extraction efficiency and selectivity towards potassium ion. From the1H NMR spectra (400 MHz), the change in chemical shifts of the aromatic protons upon the addition of alkali metal thiocyanates suggested the existence of a stabilization effect which is caused by intramolecular stacking conformations between the quinoline rings during complexation. Aryl stacking interactions depend on the size of the cations and on the chain length of the oligoethylene glycol. The relationship between transport ability towards alkali metal cations and lipophilicity of these ionophores is also discussed. 相似文献
4.
TiO2(B) nanowires and TiO2 anatase nanowires were synthesized by the hydrothermal processing in 10 M NaOH aq. at 150 °C followed by the post-heat treatment at 300-800 °C. As-synthesized Na-free titanate nanowires (prepared by the hydrothermal treatment and repeated ion exchanging by HCl (aq.) were transformed into TiO2(B) structure with maintaining 1-D morphology at 300-500 °C, and further transformed into anatase structure at 600-800 °C with keeping 1-D shape. At 900 °C, they transformed into rod-shaped rutile grains. Microstructure of these 1-D TiO2 nanomaterials is reported. 相似文献
5.
Brown coals have a considerable number of acidic functional groups of which the main component is carboxyl groups, and the acidity has a wide distribution. In this paper, changes of the acidity distribution were examined by aqueous titration when brown coal was heat-treated to control its acidity distribution. For Loy Yang brown coal from Australia dried at 50 degrees C under vacuum (LY50), the acid dissociation constant, Ka, was distributed over a wide pKa range between 2 and 9. Then, using Gaussian functions, the acidity distribution was divided into four groups, which were characterized by average pKa values: average pKa value of 3.8 (hereafter referred to as Group A), 5.2 (Group B), 6.8 (Group C), and 8.3 (Group D). Among them, Groups A, B, and C were assigned to carboxyl groups. From the changes of the number of carboxyl groups when brown coal was heat-treated up to 400 degrees C, it was found that the way of decrease was different among these acidic groups. The decrease of the amount of carboxyl groups in Group C was significant, and at 325 degrees C most of them disappeared. On the other hand, the carboxyl groups in Group A remained even at a high temperature of 400 degrees C. We estimated approximately the structures around carboxyl groups for LY50 and their structural changes by heat treatment using the known pKa values for simple carboxylic acids and the pKa values calculated by the MOPAC program for complicated carboxylic acids. 相似文献
6.
Tricyclo[3.3.1.1]decanone azine ( adamantanone azine ) reacts with 4-substituted 1,2,4-triazoline-3,5-diones under elimination of diazo adamantane to give a 1,3-dipole ( “azomethinimine” ), which on treatment with dipolahophiles affords the [ 2 + 3] -cycloadducts. The reaction is compared with singlet oxygen oxidation. 相似文献
7.
M. Fujisawa T. Matsushita Y. Matsui K. Akasaka T. Kimura 《Journal of Thermal Analysis and Calorimetry》2004,77(1):225-231
The heat capacities of binary aqueous solutions of 1,2-ethanediol, 1,2-propanediol and 1,2-butanediol were measured at temperatures
ranging from 283.15 to 338.15 K by differential scanning calorimetry. The partial molar heat capacities at the infinite dilution
were then calculated for the respective alkanediols. For 1,2-ethanediol or 1,2-propanediol, the partial molar heat capacities
at the infinite dilution of increased with increasing temperature. In contrast, the partial molar heat capacities of 1,2-butanediol
at the infinite dilution decreased with increasing temperature.
Heat capacity changes by dissolution of the alkanediols were also determined. Heat capacity changes caused by the dissolution
of 1,2-ethanediol or 1,2-propanediol were increase with increasing temperature. On the other hand, heat capacity changes caused
by the dissolution of 1,2-butanediol are decrease with increasing temperature. Thus our results indicated that the structural
changes of water caused by the dissolution of 1,2-butanediol differed from that of the two other alkanediols.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Proton T1 measurement with the Fourier transform method combined with quenching of dipolar coupling through selective deuterium substitution is shown to be a useful method for elucidating intra- and intermolecular interactions in solution, with 2′,3′-isopropylideneadenosine as an example. Average distances between H-8 and ribose protons are determine in combination with carbon-13 T1 measurement. The method is compared with the nuclear Overhauser effect. 相似文献
9.
Cao B Wakahara T Tsuchiya T Kondo M Maeda Y Aminur Rahman GM Akasaka T Kobayashi K Nagase S Yamamoto K 《Journal of the American Chemical Society》2004,126(30):9164-9165
A new metallofullerene, La2@C78, has been synthesized by DC arc discharge method, isolated by high-performance liquid chromatography, and characterized by laser desorption time-of-flight mass spectrometry, UV-vis-NIR absorption, differential pulse voltammetry, 13C NMR spectroscopy, and theoretical calculations. The La2@C78/CS2 solution is dark violet and presents several characteristic absorption features at 647, 561, 533, and 386 nm, with an onset around 1000 nm. With respect to empty D3-C78, the capability of La2@C78 as an electron acceptor or donor is stronger. Addition of 1,1,2,2-tetrakis(2,4,6-trimethylphenyl)-1,2-disirane to La2@C78 photochemically, as well as thermally, affords bis- and mono-adducts. Theoretical studies and 13C NMR spectroscopic analysis of La2@C78 indicate that it possesses a D3h-C78 cage (78:5). 相似文献
10.
Large-scale separation of metallic and semiconducting single-walled carbon nanotubes 总被引:6,自引:0,他引:6
Maeda Y Kimura S Kanda M Hirashima Y Hasegawa T Wakahara T Lian Y Nakahodo T Tsuchiya T Akasaka T Lu J Zhang X Gao Z Yu Y Nagase S Kazaoui S Minami N Shimizu T Tokumoto H Saito R 《Journal of the American Chemical Society》2005,127(29):10287-10290
In the applications of single-walled carbon nanotubes (SWNTs), it is extremely important to separate semiconducting and metallic SWNTs. Although several methods have been reported for the separation, only low yields have been achieved at great expense. We show a separation method involving a dispersion-centrifugation process in a tetrahydrofuran solution of amine, which makes metallic SWNTs highly concentrated to 87% in a simple way. 相似文献