全文获取类型
收费全文 | 239篇 |
免费 | 17篇 |
专业分类
化学 | 195篇 |
力学 | 1篇 |
数学 | 11篇 |
物理学 | 49篇 |
出版年
2023年 | 1篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 4篇 |
2016年 | 20篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 14篇 |
2012年 | 22篇 |
2011年 | 18篇 |
2010年 | 7篇 |
2009年 | 14篇 |
2008年 | 18篇 |
2007年 | 21篇 |
2006年 | 18篇 |
2005年 | 16篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 16篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1989年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有256条查询结果,搜索用时 15 毫秒
71.
Margarita Guenther Gerald Gerlach Cathrin Corten Dirk Kuckling Martin Muller Zhangman Shi Joerg Sorber Karl-Friedrich Arndt 《Macromolecular Symposia》2007,254(1):314-321
Summary: A rapidly expanding field of on-line process monitoring and on-line control in biotechnology, food industry, pharmaceutical industry, process chemistry, environmental measuring technology, water treatment and sewage processing requires the development of new micro fabricated reliable chemical and biosensors that are specific for particular species and can attain the analytic information in a faster, simpler and cheaper manner. Using a functionalised polymer coating in sensors provides the possibility to detect, transmit and record the information regarding the concentration change or the presence of a specific analyte (a chemical or biological substance that needs to be measured) by producing a signal proportional to the concentration of the target analyte. However, the sensor response time and signal reproducibility are limited by the visco-elastical and hysteresis behaviour of the polymer material. We propose some methods improving the properties of the chemical sensors on the basis of thermo-shrinking N-isopropylacrylamide (NIPAAm) copolymer gels. 相似文献
72.
73.
Miyake Masato Takase Kazuya Narato Midori Khatipov Emir Schnackenberg Joerg Shirai Makoto Kurane Ryuichiro Asada Yasuo 《Applied biochemistry and biotechnology》2000,84(1-9):991-1002
Genetic characterization and enhancement of polyhydroxybutyrate (PHB) accumulation in cyanobacteria were investigated for
efficient PHB production from CO2. The genome DNAs in the PHB-accumulating strains Synechococcus sp. MA19 and Spirulina platensis NIES46 retained the highly homologous region to phaC of Synechocystis PCC6803, whereas low homology was detected in the nonaccumulating strains Synechococcus sp. PCC7942 and Anabaenacylindrica NIES19. Synechococcus sp. MA19, which accumulates PHB up to 30% of dry cell weight from CO2 as the sole carbon source, was mutated by insertion of transposon Tn5 to enhance the PHB accumulation. Genetic and physiological
analysis of the mutant indicated that decreased phosphotransacetylase activity could trigger an increase of acetyl coenzyme
A leading to enhancement of PHB accumulation. PHB synthase in Synechococcus sp. MA19 was probably attached to thylakoid membrane since PHB granules were associated with pigments. A genetically engineered
cyanobacteria retaining soluble PHB synthase from Ralstonia eutropha accumulated pigment-free PHB granules, which is an advantage for the purification of PHB. 相似文献
74.
Cell organization, proliferation, and differentiation are impacted by diverse cues present in the cellular microenvironment. As a result, the surface of a material plays an important role in cellular function. Synthetic surfaces may be augmented by physical as well as chemical means. In particular, patterning and interfacial gradients may be utilized to mitigate the cellular response. Patterning is advantageous as it affords control over a range of feature sizes from several nanometers to millimeters. Gradients exist in vivo, for instance in stem cell niches, and the ability to create interfacial gradients in vitro can provide valuable insights into the influence of a series of minute surface changes on a single sample. This review focuses on fabrication methods for generating micro‐ and nanoscale surface patterns as well as interfacial gradients, the impact of these surface modifications on the cellular response, and the advantages and challenges of these surfaces in in vitro applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys., 2013 相似文献
75.
Thomas Raidt Robin Hoeher Frank Katzenberg Joerg C. Tiller 《Macromolecular rapid communications》2015,36(8):744-749
In this work, syndiotactic polypropylene (sPP) as well as isotactic polypropylene (iPP) are cross‐linked to gain a shape memory effect. Both prepared PP networks exhibit maximum strains of 700%, stored strains of up to 680%, and recoveries of nearly 100%. While x‐iPP is stable for many cycles, x‐sPP ruptures after the first shape‐memory cycle. It is shown by wide‐angle X‐ray scattering (WAXS) experiments that cross‐linked iPP exhibits homoepitaxy in the temporary, stretched shape but in contrast to previous reports it contains a higher amount of daughter than mother crystals.
76.
Dr. Joerg H. Schrittwieser Dr. Bas Groenendaal Dr. Verena Resch Dr. Diego Ghislieri Dr. Silvia Wallner Eva‐Maria Fischereder Elisabeth Fuchs Barbara Grischek Dr. Johann H. Sattler Prof. Dr. Peter Macheroux Prof. Dr. Nicholas J. Turner Prof. Dr. Wolfgang Kroutil 《Angewandte Chemie (International ed. in English)》2014,53(14):3731-3734
Deracemization, that is, the transformation of a racemate into a single product enantiomer with theoretically 100 % conversion and 100 % ee, is an appealing but also challenging option for asymmetric synthesis. Herein a novel chemo‐enzymatic deracemization concept by a cascade is described: the pathway involves two enantioselective oxidation steps and one non‐stereoselective reduction step, enabling stereoinversion and a simultaneous kinetic resolution. The concept was exemplified for the transformation of rac‐benzylisoquinolines to optically pure (S)‐berbines. The racemic substrates were transformed to optically pure products (ee>97 %) with up to 98 % conversion and up to 88 % yield of isolated product. 相似文献
77.
Dr. Roland Frach Patrick Kibies Saraphina Böttcher Tim Pongratz Steven Strohfeldt Simon Kurrmann Dr. Joerg Koehler Martin Hofmann Prof. Dr. Werner Kremer Prof. Dr. Hans Robert Kalbitzer Prof. Dr. Oliver Reiser Prof. Dr. Dominik Horinek Prof. Dr. Stefan M. Kast 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(30):8900-8904
78.
The stability of low-density self-assembled monolayers of mercaptohexadecanoic acid on gold is studied under a variety of storage conditions--air at room temperature, argon at room temperature and 4 degrees C, and ethanol at room temperature. The structural monotony of the low-density monolayers was assessed by monitoring the alkyl chains of LDSAMs by grazing-angle Fourier transform infrared spectroscopy as a function of time. Independently of the storage conditions, both symmetric and asymmetric methylene stretches at 2923 and 2852 cm-1 decreased after 4 weeks to 2919 and 2849 cm-1, respectively. These data suggest an increased ordering of the alkyl chains that is distinctly different from that of conventional high-density monolayers of mercaptohexadecanoic acid included as a reference in this study. As a further extension of this observation, the electrochemical barrier properties of the low-density monolayers were assessed by electrochemical impedance spectroscopy and did not change significantly for any of the storage conditions over a period of 4 weeks. Moreover, X-ray photoelectron spectroscopy was used to assess the chemical changes in the low-density monolayers over time. The chemical composition was essentially unaltered for all storage conditions. Specifically, oxidation of the sulfur headgroup, a common cause of monolayer degradation, was excluded for all test conditions on the basis of XPS analysis. This study confirms excellent storage stability for low-density monolayers under commonly used storage conditions and bridges an important technological gap between these systems and conventional high-density systems. 相似文献
79.
Tissue refractometry using Hilbert phase microscopy 总被引:1,自引:0,他引:1
Lue N Bewersdorf J Lessard MD Badizadegan K Dasari RR Feld MS Popescu G 《Optics letters》2007,32(24):3522-3524
We present, for the first time to our knowledge, quantitative phase images associated with unstained 5 mum thick tissue slices of mouse brain, spleen, and liver. The refractive properties of the tissue are retrieved in terms of the average refractive index and its spatial variation. We find that the average refractive index varies significantly with tissue type, such that the brain is characterized by the lowest value and the liver by the highest. The spatial power spectra of the phase images reveal power law behavior with different exponents for each tissue type. This approach opens a new possibility for stain-free characterization of tissues, where the diagnostic power is provided by the intrinsic refractive properties of the biological structure. We present results obtained for liver tissue affected by a lysosomal storage disease and show that our technique can quantify structural changes during this disease development. 相似文献
80.
A series of N-alkyl-N,N-dimethyldeoxyammonium celluloses is synthesized by converting tosyl celluloses with DBA and DDA, respectively. Surface coatings with these water-insoluble derivatives contain well-defined densities of quaternary ammonium functions and nonactive hydrophobic and hydrophilic groups. It is shown that the antimicrobial activity of such surfaces against S. aureus requires a delicate balance between DDA, BDA, and hydrophobic groups. A mechanism is proposed that involves the selective adhesion of anionic phospholipids from the bacterial cell membrane. This so-called phospholipid sponge effect is supported by the fact that all coatings could be deactivated by treatment with SDS or negatively charged phospholipids, but not with neutral phospholipids. 相似文献