全文获取类型
收费全文 | 1145篇 |
免费 | 36篇 |
国内免费 | 3篇 |
专业分类
化学 | 852篇 |
晶体学 | 8篇 |
力学 | 7篇 |
数学 | 105篇 |
物理学 | 212篇 |
出版年
2022年 | 20篇 |
2021年 | 18篇 |
2020年 | 20篇 |
2019年 | 15篇 |
2018年 | 11篇 |
2017年 | 7篇 |
2016年 | 28篇 |
2015年 | 16篇 |
2014年 | 26篇 |
2013年 | 53篇 |
2012年 | 55篇 |
2011年 | 68篇 |
2010年 | 29篇 |
2009年 | 35篇 |
2008年 | 66篇 |
2007年 | 68篇 |
2006年 | 42篇 |
2005年 | 63篇 |
2004年 | 45篇 |
2003年 | 71篇 |
2002年 | 52篇 |
2001年 | 13篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 10篇 |
1997年 | 14篇 |
1996年 | 19篇 |
1995年 | 9篇 |
1994年 | 16篇 |
1993年 | 8篇 |
1992年 | 19篇 |
1991年 | 9篇 |
1990年 | 16篇 |
1989年 | 8篇 |
1988年 | 14篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 23篇 |
1984年 | 25篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 15篇 |
1978年 | 16篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有1184条查询结果,搜索用时 15 毫秒
21.
Miyuki Narita Junya Itoh Tohru Kikuchi Fumio Hamada 《Journal of inclusion phenomena and macrocyclic chemistry》2002,42(1-2):107-114
-Cyclodextrin dimer linked with ethylenediamine at the upper rim of the cyclodextrin has been synthesized and then modified with two dansyl moieties inthe presence of N,N'-dicyclohexylcarbodiimide. The sensing ability and bindingproperty of the title compound were investigated for steroids and terpenoids. Thefluorescence intensity of this dimer was decreased when a host–guest complex was formed. The value I/I0, where I0 and I are fluorescence intensitiesin the absence and presence of a guest and I is I0- I, was used as a parameter of sensitivity. This host exhibited a much higher sensitivity and selective molecular recognition ability for bile acids such as ursodeoxycholic acid andchenodeoxycholic acid and terpenoids such as (-)-borneol than the dansyl-modifiedcyclodextrins reported previously including -cyclodextrin dimer. The behaviors of the appended moieties of the host during the formation of host–guest complexes were studied using induced circular dichroism (ICD) and fluorescence spectra. The ICD intensityof this dimer was decreased on accommodation of a guest and this spectral pattern of the title dimer was opposite to that of bis dansyl-modified -cyclodextrin monomer. Theguest-induced variations in the fluorescence and ICD intensities suggest that this dimer formed a 1 : 1 host–guest complex and the appended moieties act as a hydrophobic cap. 相似文献
22.
A superconducting sample (Nd0.1Y0.9Ba2Cu3O7-δ) has been tried as a catalyst for H2O2 decomposition. All parameters affecting the reaction rate (concentration of H2O2, weight of catalyst, temperature and pH) were studied and the optimum conditions were evaluated. A mixture of the superconducting
cuprate with [Cu2(TS)(OH)(OAc)] using different percentages of the sample has been prepared and tried kinetically under the same mentioned
conditions. An attempt was made to increase the activity of the complex. The data show that the cuprate sample alone was found
to be almost inactive when compared with that of the mixture. The catalytic mechanism in the absence and presence of the complex
was suggested. 相似文献
23.
Fujitani T Nakamura I Kobayashi Y Takahashi A Haneda M Hamada H 《The journal of physical chemistry. B》2005,109(37):17603-17607
Adsorption and reactions of NO on clean and CO-precovered Ir(111) were investigated by means of X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HR-EELS), infrared reflection absorption spectroscopy (IRAS), and temperature-programmed desorption (TPD). Two NO adsorption states, indicative of fcc-hollow sites and atop sites, were present on the Ir(111) surface at saturation coverage. NO adsorbed on hollow sites dissociated to Na and Oa at temperatures above 283 K. The dissociated Na desorbed to form N2 by recombination of Na at 574 K and by a disproportionation reaction between atop-NO and Na at 471 K. Preadsorbed CO inhibited the adsorption of NO on atop sites, whereas adsorption on hollow sites was not affected by the coexistence of CO. The adsorbed CO reacted with dissociated Oa and desorbed as CO2 at 574 K. 相似文献
24.
Miyuki Narita Fumio Hamada Mayumi Sato Iwao Suzuki Tetsuo Osa 《Journal of inclusion phenomena and macrocyclic chemistry》1999,34(4):421-430
Flexible hosts, 6A,6B-; 6A,6C-; 6A,6D-; and 6A,6E-bis dansylglycine-modified -cyclodextrins (-1, -2, -3, and -4, respectively) have been synthesized as a sensing molecule for organic guests including terpenoids and bile acids. These host compounds show a pure monomer fluorescence whose intensity is decreased or enhanced upon addition of guest species. The value I/I0, where I and I0 are fluorescence intensities in the presence and absence of a guest and I is I0- I, was used as a parameter of sensitivity. These hosts exhibit highly sensitive and selective molecular recognition ability, particularly, for lithochoic acid, chenodeoxycholic acid, and ursodeoxycholic acid. The behaviors of the appended moieties of these hosts when host–guest complexation occurs are studied by induced circular dichroism (ICD) spectra and fluorescence spectral change on accommodation of a guest. The ICD pattern of these hosts alone or on accommodation of a guest is very similar, indicating that the behavior of the appended moieties are very similar. The guest-induced variations in the fluorescence or ICD intensity suggest that the appended moieties act as a hydrophobic cap that enables the cyclodextrin to form 1 : 1 host–guest complexes. 相似文献
25.
Kurosaki H Yasuzawa H Yamaguchi Y Jin W Arakawa Y Goto M 《Organic & biomolecular chemistry》2003,1(1):17-20
A fluorescent probe for the detection of a metallo-beta-lactamase (IMP-1), N-[2-(5-dimethylaminonaphthalen-1-ylsulfonylamino)ethyl]-3- mercaptopropionamide (Dansyl-C2SH), 1, was designed based on combining the inhibitory function of mercaptocarboxylate and a fluorophore. The binding of 1 to IMP-1 was investigated by fluorescence spectroscopy. Compound 1 can act as fluorescent probe for detecting IMP-1 selectively. 相似文献
26.
Four new cycloartane glycosides from Aquilegia vulgaris 总被引:2,自引:0,他引:2
Four new cycloartane glycosides, named aquilegiosides G-J, were isolated from the dried aerial parts of Aquilegia vulgaris. Their structures were determined by spectroscopic analysis and chemical evidence. 相似文献
27.
New fan-shaped ionic liquids forming columnar liquid crystalline phases have been prepared to obtain one-dimensional ion-transporting materials. The ionic liquids consist of two incompatible parts: an imidazolium-based ionic part as an ion-conducting part and tris(alkyloxy)phenyl parts as insulating parts. Two compounds having octyl and dodecyl chains have been synthesized. Self-assembly of these materials leads to the formation of thermotropic hexagonal columnar liquid crystalline states at room temperature. Anisotropic one-dimensional ionic conductivities have been successfully measured by the cells having comb-shaped gold electrodes. The self-organized columns have been aligned macroscopically in two directions by shearing perpendicular and parallel to the electrodes. The ionic conductivities parallel to the column axis are higher than those perpendicular to the axis. The incorporation of lithium salts in these columnar materials leads to the enhancement of the ionic conductivities and their anisotropy. These materials would be useful for anisotropic transportation of ions at the nanometer level. 相似文献
28.
The molecular assembly of thiacalix[6]arene was formed by π-π stacking and π-DMF interactions between thiacalix[6]arene and adjoining thiacalix[6]arene and between thiacalix[6]arene and DMF, respectively. The X-ray crystal analysis also revealed that hydroxyl groups of thiacalix[6]arene adopted novel two sets of hydrogen bond with two DMF and intramolecular hydrogen bond between phenolic units, which cause to make 1,2,3-alternate configuration structure of thiacalix[6]arene. 相似文献
29.
The degradation of unsaturated polyesters crosslinked with styrene was performed in sub-critical water (SCW) in the absence and presence of organic additives. The unsaturated polyesters were de-crosslinked by hydrolysis of ester chains to form polystyrene derivatives on SCW treatment at 300 °C. With an increase in treating time, carboxylic acid groups in the polystyrene derivatives were turned into carboxylic anhydride groups in SCW. The de-crosslinking rate was much enhanced on SCW treatment in the presence of hydroxy compounds with a long alkyl chain and alkylamines, while carboxylic acids, benzenesulfonate salts, and quaternary ammonium salts were ineffective even though they had a long alkyl chain. The degree of de-crosslinking was reduced in the presence of diamines and amino acids because re-crosslinking at both ends of the additive molecules proceeded. 相似文献
30.
The performance of a 160 keV slant hole collimator (160 keV SH) was compared with that of a 140 keV high resolution collimator (140 keV HR) for SPECT imaging of the head using 99mTc. The minimum radius of revolution was reduced from about 23 cm to 13 cm using 160 keV SH. Relative sensitivity of the 160 keV SH was 108% of that of the 140 keV HR. Compared with SPECT using 140 keV HR, 160 keV SH SPECT yielded approximately a 15% increase in resolution. The 160 keV SH SPECT images of phantom were superior in resolution and contrast to that of 140 keV HR SPECT. We concluded that high quality SPECT images of the head can be obtained from rotating gamma cameras equipped with slant hole collimators. 相似文献