全文获取类型
收费全文 | 1567篇 |
免费 | 33篇 |
国内免费 | 5篇 |
专业分类
化学 | 1128篇 |
晶体学 | 21篇 |
力学 | 17篇 |
数学 | 80篇 |
物理学 | 359篇 |
出版年
2021年 | 5篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2018年 | 5篇 |
2017年 | 11篇 |
2016年 | 21篇 |
2015年 | 25篇 |
2014年 | 37篇 |
2013年 | 69篇 |
2012年 | 66篇 |
2011年 | 77篇 |
2010年 | 38篇 |
2009年 | 51篇 |
2008年 | 89篇 |
2007年 | 116篇 |
2006年 | 85篇 |
2005年 | 97篇 |
2004年 | 70篇 |
2003年 | 65篇 |
2002年 | 46篇 |
2001年 | 44篇 |
2000年 | 40篇 |
1999年 | 29篇 |
1998年 | 13篇 |
1997年 | 22篇 |
1996年 | 14篇 |
1995年 | 18篇 |
1994年 | 27篇 |
1993年 | 13篇 |
1992年 | 23篇 |
1991年 | 25篇 |
1990年 | 20篇 |
1989年 | 12篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 16篇 |
1985年 | 30篇 |
1984年 | 27篇 |
1983年 | 15篇 |
1982年 | 22篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 20篇 |
1978年 | 16篇 |
1977年 | 19篇 |
1976年 | 10篇 |
1975年 | 14篇 |
1974年 | 10篇 |
1972年 | 7篇 |
1970年 | 6篇 |
排序方式: 共有1605条查询结果,搜索用时 15 毫秒
11.
12.
HPLC determination of (+)-pseudoephedrine and (-)-ephedrine in Japanese herbal medicines containing Ephedra herb using solid-phase extraction 总被引:2,自引:0,他引:2
Ichikawa M Udayama M Imamura K Shiraishi S Matsuura H 《Chemical & pharmaceutical bulletin》2003,51(6):635-639
We developed a rapid and simple HPLC method combined with solid-phase extraction (SPE) for quantitative analysis of (+)-pseudoephedrine (PEP) and (-)-ephedrine (EP) in Japanese herbal (Kampo) medicines such as Kakkon-to, Sho-seiryu-to, Goshaku-san and Bofu-tsusho-san. SPE was performed on TOYOPAK IC-SP M containing propylsulfonic groups. Determination of PEP and EP was carried out using ion-pair reversed-phase HPLC with sodium dodecyl sulfate. N-Benzyldiethylamine was used as an internal standard. The analytical procedure was validated with regard to specificity, linearity, accuracy, and precision. These data suggest that the analytical method developed in this study is useful for quantitative analysis of PEP and EP in various formulations of Kampo medicine containing Ephedra herb. 相似文献
13.
Takanori Suzuki Tomohiro Iwai Eisuke Ohta Hidetoshi Kawai Kenshu Fujiwara 《Tetrahedron letters》2007,48(20):3599-3603
Huge CD amplitude (A = +538) was attained by diastereomeric preference (50% de) for the title dication with two bis[4-(R)-sec-butoxyphenyl]methylium units in benzene at 23 °C. Intramolecular π-π stacking is the origin for effective transmission of point chirality to axial chirality to attain the chiroptical enhancement of 400-times. Thanks to the strong CD signaling, chiroptical changes upon electrolysis could be readily detected, thus realizing a new class of electrochiroptical response systems. Chiroptical properties could also be modified by solvent polarity. 相似文献
14.
Atsushi Ikeda Masaru Kawaguchi Yoshio Suzuki Tsukasa Hatano Munenori Numata Seiji Shinkai Akio Ohta Makoto Ohta 《Journal of inclusion phenomena and macrocyclic chemistry》2000,38(1-4):163-170
The calixarene-fullerene interaction,which causes only a slight change in the absorptionspectra, has been substantiated by calorimetricmeasurements: the H° values arecomparable with those obtained from the associationconstants estimated by a spectroscopic method. Furthermore, we determined the association constantbetween homooxacalix[3]arene and [60]fullerenederivatives with a porphyrin moiety by fluorescencespectra. 相似文献
15.
A chiral HWE reagent reacted with an alternative carbonyl group of meso-α-diketones of bicyclo[2.2.1] system to give non-racemic (Z)- and (E)-olefins, respectively. 相似文献
16.
17.
Fumoto M Hinou H Ohta T Ito T Yamada K Takimoto A Kondo H Shimizu H Inazu T Nakahara Y Nishimura S 《Journal of the American Chemical Society》2005,127(33):11804-11818
The chemoselective polymer blotting method allows for rapid and efficient synthesis of glycopeptides based on a "catch and release" strategy between solid-phase and water-soluble polymer supports. We have developed a heterobifunctional linker sensitive to glutamic acid specific protease (BLase). The general procedure consists of five steps, namely (i) the solid-phase synthesis of glycopeptide containing BLase sensitive linker, (ii) subsequent deprotections and the release of the glycopeptide from the resin, (iii) chemoselective blotting of the glycopeptide intermediates in the presence of water-soluble polymers with oxylamino functional groups, (iv) sugar elongations using glycosyltransferases, and (v) the release of target glycopeptides from the polymer platform by selective BLase promoted hydrolysis. The combined use of the solid-phase chemical syntheses of peptides and the enzymatic syntheses of carbohydrates on water-soluble polymers would greatly contribute to the production of complicated glycopeptide libraries, thereby enhancing applicative research. We report here a high-throughput synthetic system for the various types of MUC1 glycopeptides exhibiting a variety of sugar moieties. It is our belief that this concept will become part of the entrenched repertoire for the synthesis of biologically important glycopeptides on the basis of glycosyltransferase reactions in automated and combinatorial syntheses. 相似文献
18.
Electrothermal atomization of arsenic with a metal micro-tube atomizer has been studied. Thiourea and thionalide were found to give effective atomization of arsenic. A method involving extraction of the thionalide complex for determining traces of arsenic in water and soil is described. 相似文献
19.
Five paeonol glycosides, suffruticosides A, B, C, D, and E, and a monoterpene glucoside, galloyl-oxypaeoniflorin, were isolated from the glycosidic fraction of Chinese Moutan Cortex, the root cortex of Paeonia suffruticosa Andrews, together with paeonolide, apiopaeonoside, galloyl-paeoniflorin, oxypaeoniflorin, and paeoniflorin. The structures of five suffruticosides and galloyl-oxypaeoniflorin were elucidated on the basis of chemical and physicochemical evidence. Suffruticosides A, B, C, and D, galloyl-oxypaeoniflorin, and galloyl-paeoniflorin exhibited more potent radical scavenging effects than alpha-tocopherol. 相似文献
20.
A liquid chromatograph directly coupled with a quadrupole mass spectrometer through a vacuum nebulizing interface was applied to the analysis of various free fatty acids. Chemical ionization mass spectra of the C7? C22 free fatty acids were first examined using either methanol or benzene as the reagents. Then the practical compositional analysis of the fatty acids were performed with various biological samples such as bean oil, rape oil, palm oil and milk fat where most of the fatty acids are included as their triglycerides. 相似文献