全文获取类型
收费全文 | 424篇 |
免费 | 17篇 |
专业分类
化学 | 288篇 |
晶体学 | 3篇 |
力学 | 3篇 |
数学 | 33篇 |
物理学 | 114篇 |
出版年
2023年 | 4篇 |
2021年 | 4篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 6篇 |
2013年 | 19篇 |
2012年 | 13篇 |
2011年 | 21篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 26篇 |
2007年 | 22篇 |
2006年 | 26篇 |
2005年 | 23篇 |
2004年 | 14篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1984年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1971年 | 2篇 |
1969年 | 4篇 |
1968年 | 3篇 |
1966年 | 4篇 |
1932年 | 4篇 |
1923年 | 2篇 |
1920年 | 2篇 |
排序方式: 共有441条查询结果,搜索用时 15 毫秒
1.
Cluster ions have been recognized as a superb primary species in time of flight secondary ion mass spectroscopy (ToF-SIMS) compared with monatomic primary ions, as they significantly enhance the secondary ion yields from bulk samples. Self-assembled monolayers provide an important system for studying the fundamental mechanism involved in the yield enhancement.We used a gold cluster ion source to analyze a new type of self-assembled monolayer: a fluorocarbon-grafted polyethylene terephthalate. In addition to the structure details, which helped to understand the grafting mechanism, ToF-SIMS analysis revealed that fluorocarbon secondary ion yield enhancements by cluster ions were due to the enhanced sputter efficiency. A larger information depth may also be expected from the enhancement. Both mathematical definitions of damage cross-section and disappearance cross-section were revisited under a new context. Another cross-section parameter, sputter cross-section, was introduced to differentiate the beam induced sputter process from damage process. 相似文献
2.
3.
Kelley BD Booth J Tannatt M Wub QL Ladner R Yuc J Potter D Ley A 《Journal of chromatography. A》2004,1038(1-2):121-130
Polypeptides for use in affinity chromatography of factor VIII were identified using phage display technology. Phage libraries were designed to express polypeptide fusions containing five to seven residues flanked by two cysteines that form a disulfide bond. Individual bacteriophage were selected for the ability of these polypeptides to bind factor VIII, and then release the protein under mild elution conditions. Strong consensus sequences were observed that appear to be necessary for this reversible interaction. Chemically synthesized ligands identified by this screening were immobilized onto a chromatographic support and used for affinity purification of factor VIII from a complex feedstream. A chromatographic step was developed that provided a 10000-fold reduction in host cell proteins and DNA, while providing exceptional product recovery. 相似文献
4.
[structure: see text] Derivatives of the highly fluorescent and DNA-binding dye thiazole orange (TO) are described that feature appended peptides. Functionalization of TO can be achieved at either of the endocyclic nitrogens, and the photophysical properties and DNA-binding modes are sensitive to the position of the tethered peptide. A series of TO-peptide conjugates are described, demonstrating the utility of a solid-phase synthesis approach to their preparation and illustrating how the photophysical and DNA-binding properties of the compounds are influenced by chemical structure. 相似文献
5.
Toward a microchip-based solid-phase extraction method for isolation of nucleic acids 总被引:7,自引:0,他引:7
Wolfe KA Breadmore MC Ferrance JP Power ME Conroy JF Norris PM Landers JP 《Electrophoresis》2002,23(5):727-733
A silica-based solid-phase extraction system suitable for incorporation into a microchip platform (nu-total analytical system; nu-TAS) would find utility in a variety of genetic analysis protocols, including DNA sequencing. The extraction procedure utilized is based on adsorption of the DNA onto bare silica. The procedure involves three steps: (i) DNA adsorption in the presence of a chaotropic salt, (ii) removal of contaminants with an alcohol/water solution, and (iii) elution of the adsorbed DNA in a small volume of buffer suitable for polymerase chain reaction (PCR) amplification. Multiple approaches for incorporation of this protocol into a microchip were examined with regard to extraction efficiency, reproducibility, stability, and the potential to provide PCR-amplifiable DNA. These included packing microchannels with silica beads only, generating a continuous silica network via sol-gel chemistry, and combinations of these. The optimal approach was found to involve immobilizing silica beads packed into the channel using a sol-gel network. This method allowed for successful extraction and elution of nanogram quantities of DNA in less than 25 min, with the DNA obtained in the elution buffer fraction. Evaluation of the eluted DNA indicated that it was of suitable quality for subsequent amplification by PCR. 相似文献
6.
Carol A. Loeschorn Charles J. Kelley Robert N. Hanson Michael A. Davis 《Tetrahedron letters》1984,25(32):3387-3390
The addition of methyl Grignard to diethyl acetamido(cyanoselenobenzyl)malonates 3 and 4 at ?78° followed by hydrolysis yields the 3-(4-and 3-methylselenophenyl)alanines 1 and 2. 相似文献
7.
Acyclovir was synthesized in five steps from 7-formamido-5-methylthiofurazano[3,4-d]pyrimidine 2 . Alkylation of 2 with 2-(benzoyloxy)ethoxymethyl chloride, followed by reductive cleavage of the furazan ring gave 9-[[2-(benzoyloxy)ethoxy]methyl]-2-(methylthio)adenine 5 . Hydrolysis of the 6-amino group of 5 , followed by amination of 7 with ammonia gave 9-[(2-hydroxyethoxy)methyl]guanine ( 1 , acyclovir). 相似文献
8.
[reaction: see text] A practical synthesis of the potent class I alpha-mannosidase inhibitor kifunensine (1) beginning from the inexpensive and readily available starting material L-ascorbic acid (15) is described. The protected amino-alcohol ((2R,3R,4R,5R)-5-amino-2,3:4,6-diisopropylidenedioxyhexanol, 11) served as a key intermediate from which several N-1 substituted kifunensine analogues (including N-methyl, N-cyclohexyl, and N-bis(hydroxymethyl)methyl) and 2-desoxakifunensine analogues (including N-H and N-methyl) were prepared and screened for inhibition of human endoplasmic reticulum alpha-mannosidase I (ER Man I) and mouse Golgi alpha-mannosidase IA (Golgi Man IA). In addition, several pseudodisaccharide kifunensine analogues in which a mannose residue was tethered to N-1 of kifunensine via a two-, three-, or four-carbon linker and an affinity-bound kifunensine analogue were also prepared and evaluated for biological activity. While the synthesized N-1 kifunesine analogues were found to be less potent inhibitors of Class I alpha-mannosidases than kifuensine itself, the bis(hydroxymethyl)methylkifunensine analogue 6 was shown to selectively inhibit ER Man I over Golgi Man IA. 相似文献
9.
Product state distributions from low energy He+N2 and N+2He collisions are presented. These data, obtained from collision-produced emission spectra, show severe deviations from Franck-Condon behavior which cannot be solely the result of molecular distortion arising from electrodynamic effects. A model based on consideration of the short-range interaction between the collision partners is proposed. 相似文献
10.