全文获取类型
收费全文 | 333篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 290篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 20篇 |
物理学 | 30篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 10篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 21篇 |
2012年 | 26篇 |
2011年 | 21篇 |
2010年 | 21篇 |
2009年 | 12篇 |
2008年 | 23篇 |
2007年 | 20篇 |
2006年 | 18篇 |
2005年 | 17篇 |
2004年 | 12篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1889年 | 1篇 |
排序方式: 共有347条查询结果,搜索用时 31 毫秒
311.
N‐(trialkoxysilylalkyl) derivatives of 1,2,3,4‐tetrahydroquinoline, 1,2,3,4‐tetrahydroisoquinoline and 4,4‐dimethyl‐4‐sila‐1,2,3,4‐tetrahydroisoquinoline were prepared and characterized by elemental analysis, 1H, 13C and 29Si NMR spectroscopy. In vivo psychotropic properties and in vitro cytotoxic effects of 3‐[N‐(1,2,3,4‐tetrahydroisoquinolyl)]propyltriethoxysilane methiodide and 3‐[N‐(1,2,3,4‐tetrahydroisoquinolyl)]propylsilatrane are reported. Comparative study of 29Si shifts in newly synthesized compounds suggested donor–acceptor interaction between nitrogen and silicon atom, which increased electron density at Si nuclei, revealing a stronger increment of N → Si transannular bond in comparison with N → Si α‐effect. The molecular structure of 3‐[N‐(1,2,3,4‐tetrahydroisoquinolyl)]propylsilatrane features a penta‐coordinate silicon atom having CSiO3 pattern and Si…N intramolecular interaction. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
312.
Thomas Schüler Alla Nykytenko Andrea Csaki Robert Möller Wolfgang Fritzsche Jürgen Popp 《Analytical and bioanalytical chemistry》2009,395(4):1097-1105
The performance of DNA microarrays strongly depends on their surface properties. Furthermore, the immobilization method of
the capture molecules is of importance for the efficiency of the microarray in terms of sensitivity and specificity. This
work describes the immobilization of single-stranded capture oligonucleotides by UV cross-linking on silanated (amino and
epoxy) glass surfaces. Thereby we used amino (NH2) and poly thymine/poly cytosine modifications of the capture sequences as well as unmodified capture molecules. The results
were compared to UV cross-linking of the same DNA oligonucleotides on unmodified glass surfaces. Immobilization and hybridization
efficiency was demonstrated by fluorescence and enzyme-induced deposition of silver nanoparticles. We found out that single-stranded
DNA molecules do not require a special modification to immobilize them by UV cross-linking on epoxy- or amino-modified glass
surfaces. However, higher binding rates can be achieved when using amino-modified oligonucleotides on an epoxy surface. The
limit of detection for the used settings was 5 pM. 相似文献
313.
Francisca Zamora Khalid Hakkou Abdelilah Alla Romina Marín‐bernab María V. de Paz Antxon Martínez de Ilarduya Sebastin Muoz‐guerra Juan A. Galbis 《Journal of polymer science. Part A, Polymer chemistry》2008,46(15):5167-5179
The synthesis, characterization, and some properties of new copolyesters of poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) based on L ‐arabinitol and xylitol are described. These copolyesters were obtained by polycondensation reaction in the melt of mixtures of 1,4‐butanediol or ethylene glycol and 2,3,4‐tri‐O‐benzyl‐L ‐arabinitol or 2,3,4‐tri‐O‐benzyl‐xylitol with dimethyl terephthalate. Their weight‐average molecular weights ranged between 7000 and 55,000, with polydispersities ranging from 1.4 to 4.7. Copolymers containing 1,4‐butanediol could be analyzed by NMR, and were found to have a statistical microstructure. All these copolyesters were thermally stable, with degradation temperatures well above 300 °C. With increasing amounts of alditol in the copolyester, the melting temperature and crystallinity decreased in both series, and the glass transition temperature increased for the PBT series and decreased for the PET series. Only PBT‐derived copolyesters containing a maximum of 10% alditol units showed discrete scattering characteristic of crystalline material. No substantial differences in either structure or properties were observed between the L ‐arabinitol and xylitol copolyester series. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5167–5179, 2008 相似文献
314.
315.
Andrey A. Toropov Alla P. Toropova Luigi Cappellini Emilio Benfenati Enrico Davoli 《Molecular diversity》2018,22(2):397-403
Quantitative structure–property relationships for odor thresholds based on representation of the molecular structure by the simplified molecular input-line entry system were established using the CORAL software. The total set of compounds with numerical data on the so-called arithmetic odor thresholds (\(n=1259\)) was distributed into the training and validation sets, three times. The average statistical quality of these models is (1) for training set \(\tilde{n}=967\pm 20\;({\approx }\,80\%), {\mathop {{r}}\limits ^\frown }^{2}=0.62\pm 0.02\); and (2) for validation set \(\tilde{n}=290\pm 20\;({\approx }\,20\%), {\mathop {{r}}\limits ^\frown }^{2}=0.62\pm 0.04\). Thus, the predictive potential of this approach was confirmed for three different splits into training and validation sets. Domain of applicability and mechanistic interpretation of these models are defined from the probabilistic point of view. The suggested models are built up according to OECD principles. 相似文献
316.
Alina Amirova Tatyana Kirila Alexey Blokhin Alla Razina Andrey Tenkovtsev Alexander Filippov 《International Journal of Polymer Analysis and Characterization》2019,24(6):487-495
Star-shaped eight-arm poly(2-isopropyl-2-oxazoline)s with basic and acidic groups were synthesized using a “grafting from” approach. Molar masses were 13,700 and 14,900?g mol?1 for polybase and polyacid, respectively. The aqueous solutions of synthesized polymers and their mixture were investigated by the light scattering and turbidimetry methods within wide range of temperatures and pH values. It was shown that the studied polymers separately do not exhibit pH-sensitivity due to the low content of ionogenic groups. For the solutions of mixture, one phase transition was detected, the onset temperature T1 of which lies between the phase separation temperatures for polymers. The value of T1 for mixture decreases with increasing acidity of the medium. 相似文献
317.
New luminescent terbium complex for the determination of DNA 总被引:1,自引:0,他引:1
Yegorova A Karasyov A Duerkop A Ukrainets I Antonovich V 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(1-2):109-116
New terbium complexes of derivatives of 2-oxo-4-hydroxy-quinoline-3-carboxylic acid are reported, which are highly luminescent, water soluble and do not require luminescence enhancers. The triplet-state energy levels of the ligands, the relative quantum yields (QYs) and the excitation maxima of the respective terbium chelates were determined. The large luminescence enhancement of one of these complexes by nucleic acids was investigated and a mechanism of its interaction with DNA is proposed. The optimal conditions for determination of DNA are equal concentrations of Tb(3+) and ligand R(1) (C = 1 x 10(-6) M), pH 9.0. Under optimal conditions the luminescence intensity (RI) is proportional to the concentration of fish sperm DNA (fsDNA) or calf thymus DNA (ctDNA), respectively, within the range of 0.05-1.5 microg ml(-1). The detection limits were 10 ng ml(-1) for fsDNA and 12 ng ml(-1) for ctDNA. 相似文献
318.
319.
Natalya I. Dergousova Alexander Yu. Amerik Alla M. Volynskaya Lev D. Rumsh 《Applied biochemistry and biotechnology》1996,61(1-2):97-107
A new method for obtaining HIV-I protease was suggested. Fusion proteins composed of the N-terminal fragment of human γ-interferon
and HIV-I protease connected with (Asp)4Lys (protein I) or Asp-Pro (protein II) linkers were expressed inEscherichia coli cells. The fusion proteins were produced as insoluble inclusion bodies in the 20% yield of total cell protein. Protein I
was cleaved by enterokinase. The solubility of protein I was increased by treating with Nasulfite/Na-tetrathionate under denaturing
conditions.
Optimal conditions for efficient acidic hydrolysis of protein II at Asp-Pro bond were found. The hydrolysis products were
separated by reversed-phase FPLC. The amount of tryptophan and cysteine residues in the enzyme obtained was estimated. The
activity of HIV-I protease was determined using the chromogenic peptide AlaArgVal NleNphGluAlaNleNH2 and a high-mol-wt substrate consisting of β galactosidase and a fragment ofgag proteins, including pl7-p24 processing site. 相似文献
320.