全文获取类型
收费全文 | 10415篇 |
免费 | 276篇 |
国内免费 | 32篇 |
专业分类
化学 | 7266篇 |
晶体学 | 23篇 |
力学 | 178篇 |
综合类 | 1篇 |
数学 | 2059篇 |
物理学 | 1196篇 |
出版年
2020年 | 74篇 |
2019年 | 86篇 |
2016年 | 183篇 |
2015年 | 173篇 |
2014年 | 231篇 |
2013年 | 403篇 |
2012年 | 266篇 |
2011年 | 259篇 |
2010年 | 228篇 |
2009年 | 214篇 |
2008年 | 291篇 |
2007年 | 271篇 |
2006年 | 295篇 |
2005年 | 277篇 |
2004年 | 251篇 |
2003年 | 259篇 |
2002年 | 268篇 |
2001年 | 189篇 |
2000年 | 172篇 |
1999年 | 116篇 |
1998年 | 113篇 |
1997年 | 135篇 |
1996年 | 136篇 |
1995年 | 119篇 |
1994年 | 126篇 |
1993年 | 147篇 |
1992年 | 144篇 |
1991年 | 121篇 |
1990年 | 131篇 |
1989年 | 136篇 |
1988年 | 139篇 |
1987年 | 141篇 |
1986年 | 120篇 |
1985年 | 229篇 |
1984年 | 199篇 |
1983年 | 126篇 |
1982年 | 171篇 |
1981年 | 157篇 |
1980年 | 200篇 |
1979年 | 196篇 |
1978年 | 198篇 |
1977年 | 230篇 |
1976年 | 188篇 |
1975年 | 170篇 |
1974年 | 136篇 |
1973年 | 186篇 |
1972年 | 97篇 |
1971年 | 91篇 |
1970年 | 73篇 |
1933年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Antonin Tuynman Hans E. Schoemaker Ron Wever 《Monatshefte für Chemie / Chemical Monthly》2000,131(6):687-695
Summary. Horseradish peroxidase (HRP), myeloperoxidase (MPO), and manganese peroxidase (MnP) have been shown to catalyze the asymmetric
sulfoxidation of thioanisole. When H2O2 was added stepwise to MPO, a maximal yield of 78% was obtained at pH 5 (ee 23%), whereas an optimum in the enantiomeric excess (32%, (R)-sulfoxide) was found at pH 6 (60% yield). For MnP a yield of 18% and a high enantiomeric excess of 91% of the (S)-sulfoxide were obtained at pH 5 and a yield of 36% and an ee of 87% at pH 7.0. Optimization of the conversion catalyzed by horseradish peroxidase at pH 7.0 by controlled continuous addition of hydrogen peroxide during turnover and monitoring the presence of native enzyme as
well as of intermediates I, II, and III led to the formation of the sulfoxide in high yield (100%) and moderate enantioselectivity
(60%, (S)-sulfoxide).
Received November 18, 1999. Accepted January 21, 2000 相似文献
992.
993.
994.
Hans E. Miltner Christophe Block Guy Van Assche Kurt Van Durme Bogdan Bogdanov 《European Polymer Journal》2010,46(5):984-996
A comprehensive overview of available methods for assessing nanofiller dispersion is presented for a wide range of layered silicate-based poly(ε-caprolactone) (PCL) nanocomposites. Focusing on their respective strengths and weaknesses, rheological, mechanical and thermal characterization approaches are evaluated in direct relation to morphological information. Pronounced changes in the rheological and mechanical properties of the materials are only observed for nanocomposites displaying the highest nanofiller dispersion levels, as confirmed by an innovative and highly reliable thermal analysis approach based on quasi-isothermal crystallization. As such, the data obtained from the different methods also allow a detailed investigation of the crucial factors affecting nanofiller dispersion, evidencing the importance of specific matrix/filler interactions and the need for proper melt processing conditions when targeting significant property enhancements. Finally, the wide potential of the developed methodologies for the characterization of polymeric nanocomposites in general is illustrated by an extension to carbon nanotube-based PCL composites, unambiguously demonstrating their complementarity and broad applicability. 相似文献
995.
Prof. Hans‐Joachim Freund Dr. Niklas Nilius Dr. Thomas Risse Dr. Swetlana Schauermann Dr. Thomas Schmidt 《Chemphyschem》2011,12(1):79-87
We describe four new experimental techniques advanced during the last decade in the authors’ laboratory. The techniques include photon scanning tunneling microscopy; aberration‐corrected low‐energy electron microscopy in combination with photoelectron emission microscopy, microcalorimetry, and electron‐spin resonance spectroscopy. It is demonstrated how those techniques may be applied to solve fundamental problems in surface science with growing demands to tackle complex nanoscopic systems, and, in particular in catalysis science, which, without the availability of those techniques, would be difficult if not impossible to address. 相似文献
996.
Oliver Neudert Dmitry Germanovich Zverev Christian Bauer Peter Blümler Hans Wolfgang Spiess Dariush Hinderberger Kerstin Münnemann 《Applied magnetic resonance》2012,43(1-2):149-165
Power-dependent Overhauser dynamic nuclear polarization (DNP) enhancements and continuous-wave electron paramagnetic resonance (EPR) spectra of nitroxide radicals were measured in the magnetic field of a mobile Halbach-array permanent magnet and compared with results from a commercially available electromagnet. DNP saturation factors for varying microwave power were obtained from both measurement series and used to investigate how the increased magnetic field inhomogeneity present in the Halbach magnet affects the saturation efficiency. An EPR detection system was designed to allow continuous-wave EPR measurements at microwave power up to 20?W. Our results show that despite the lower magnetic field homogeneity, a Halbach-array magnet can be used for EPR and DNP-enhanced nuclear magnetic resonance of high quality providing almost the same performance as a more homogeneous electromagnet. 相似文献
997.
998.
Elisabeth Kallin Hans Lönn Thomas Norberg Mikael Elofsson 《Journal of carbohydrate chemistry》2013,32(4):597-611
Abstract Reducing oligosaccharides were converted in good yields into the corresponding primary glycosylamines by treatment with aqueous ammonium bicarbonate. The glycosylamines were then acryloylated and the obtained oligosaccharide N-acryloyl glycosylamines were copolymerized with acrylamide. High molecular weight, linear copolymers were obtained, which were useful as antigens in immunoassays. 相似文献
999.
1000.
Dirk Pfefferkorn Sven Sonntag Samuel O. Kyeremateng Zofia Funke Hans‐Werner Kammer Jörg Kressler 《Journal of Polymer Science.Polymer Physics》2010,48(17):1893-1900
The pressure–volume–temperature behavior of miscible blends of poly(ethylene oxide) (PEO) and poly(methyl acrylate) (PMA) was studied over extended ranges of temperature and pressure. From pressure–volume–temperature data, the reduction parameters for the Flory‐Orwoll‐Vrij equation‐of‐state were determined. It was found that reduction parameters as well as density, thermal expansion coefficient, and isothermal compressibility vary with composition in a nonlinear manner. The surface tension of the blends in the molten state was measured over the whole composition range using the sessile drop method. The surface tension was found to display negative deviation from additivity pointing toward a remarkable surface excess of PMA. Moreover, surface tension displays a minimum in the range of low PEO content at weight fraction of ~0.19. In addition, the temperature coefficient of surface tension shows negative deviation from linearity. It stays constant when PMA is in excess. Results are discussed in terms of equation‐of‐state thermodynamics. The minimum of surface tension can be well explained by weak self‐association of PEO in the bulk. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1893–1900, 2010 相似文献