全文获取类型
收费全文 | 3888篇 |
免费 | 134篇 |
国内免费 | 23篇 |
专业分类
化学 | 3082篇 |
晶体学 | 39篇 |
力学 | 39篇 |
数学 | 249篇 |
物理学 | 636篇 |
出版年
2023年 | 21篇 |
2022年 | 17篇 |
2021年 | 34篇 |
2020年 | 57篇 |
2019年 | 58篇 |
2018年 | 36篇 |
2017年 | 32篇 |
2016年 | 76篇 |
2015年 | 66篇 |
2014年 | 125篇 |
2013年 | 234篇 |
2012年 | 192篇 |
2011年 | 233篇 |
2010年 | 160篇 |
2009年 | 145篇 |
2008年 | 230篇 |
2007年 | 222篇 |
2006年 | 227篇 |
2005年 | 232篇 |
2004年 | 212篇 |
2003年 | 184篇 |
2002年 | 172篇 |
2001年 | 74篇 |
2000年 | 67篇 |
1999年 | 38篇 |
1998年 | 48篇 |
1997年 | 41篇 |
1996年 | 42篇 |
1995年 | 20篇 |
1994年 | 50篇 |
1993年 | 32篇 |
1992年 | 47篇 |
1991年 | 28篇 |
1990年 | 22篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 25篇 |
1985年 | 48篇 |
1984年 | 56篇 |
1983年 | 32篇 |
1982年 | 46篇 |
1981年 | 51篇 |
1980年 | 32篇 |
1979年 | 35篇 |
1978年 | 25篇 |
1977年 | 34篇 |
1976年 | 27篇 |
1975年 | 19篇 |
1974年 | 23篇 |
排序方式: 共有4045条查询结果,搜索用时 234 毫秒
31.
32.
Tetrakis-acridinyl peptide 1 assuming a right-handed helical stacked conformation of the acridinyl units can bind to DNA duplex with a very high affinity of 10(8) (M-bp)(-1) even at a high salt concentration of 0.2 M NaCl, irrespective of the base composition. Peptide 1 gave rise to 1600-times enhancement of its fluorescence upon binding to an AT polymer due to the collapse of this stacked structure, but the fluorescence is not enhanced with a GC polymer, though the binding constants of 1 for both polymers were the same. 相似文献
33.
34.
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
35.
36.
Chowdhury Wasimul Q. Idehara Kenji Maeda Isamu Umeda Fusako Yagi Kiyohito Miura Yoshiharu Mizoguchi Tadashi 《Applied biochemistry and biotechnology》1996,57(1):361-366
Applied Biochemistry and Biotechnology - A marine photosynthetic bacterium,Rhodopseudomonas sp. strain W-1S, accumulated polyhydroxybutyrate (PHB) to 56% of the dry cell weight under microaerobic... 相似文献
37.
38.
Ohwada T Miura M Tanaka H Sakamoto S Yamaguchi K Ikeda H Inagaki S 《Journal of the American Chemical Society》2001,123(42):10164-10172
N-Nitrosamines can be considered as potential nitric oxide (NO)/nitrosonium ion (NO(+)) donors. However, the relation of the structures of N-nitrosamines, in particular of aliphatic N-nitrosamines, to the characteristics of release of NO or NO(+) remains unclear. Here we show that aliphatic N-nitrosoamines of 7-azabicyclo[2.2.1]heptanes can undergo heterolytic N-NO bond cleavage. On the basis of the observation of reduced rotational barriers of the N-NO bonds in solution and nitrogen-pyramidal structures of the N-nitroso group in the solid state, we postulate that N-NO bond cleavage of N-nitrosamines is enhanced by a reduction of the resonance in the N-NO group. Computational studies suggest that these structural features of the N-nitrosamines of 7-azabicyclo[2.2.1]heptane are derived from angle strain imposed on the CNC angles. 相似文献
39.
1,6-Enynes reacted with arylboronic acids in the presence of a catalytic amount of a rhodium(I) complex under mild conditions to give (Z)-1-(1-arylethylidene)-2-vinylcyclopentanes. The regioselective addition of an arylrhodium(I) species across the carbon-carbon triple bond triggered the cyclization process. Intramolecular carborhodation onto the pendent alkene in a 5-exo mode furnished a five-membered ring. Finally, the rhodium(I) methoxide generated by beta-methoxy elimination reacted with the arylboronic acid to promote the next catalytic cycle. 相似文献
40.
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