全文获取类型
收费全文 | 19294篇 |
免费 | 1261篇 |
国内免费 | 899篇 |
专业分类
化学 | 14046篇 |
晶体学 | 170篇 |
力学 | 481篇 |
综合类 | 66篇 |
数学 | 2998篇 |
物理学 | 3693篇 |
出版年
2024年 | 12篇 |
2023年 | 179篇 |
2022年 | 345篇 |
2021年 | 574篇 |
2020年 | 534篇 |
2019年 | 510篇 |
2018年 | 455篇 |
2017年 | 434篇 |
2016年 | 838篇 |
2015年 | 750篇 |
2014年 | 825篇 |
2013年 | 1300篇 |
2012年 | 1528篇 |
2011年 | 1724篇 |
2010年 | 1162篇 |
2009年 | 1017篇 |
2008年 | 1420篇 |
2007年 | 1337篇 |
2006年 | 1210篇 |
2005年 | 1020篇 |
2004年 | 903篇 |
2003年 | 616篇 |
2002年 | 512篇 |
2001年 | 244篇 |
2000年 | 234篇 |
1999年 | 194篇 |
1998年 | 147篇 |
1997年 | 145篇 |
1996年 | 149篇 |
1995年 | 110篇 |
1994年 | 90篇 |
1993年 | 90篇 |
1992年 | 102篇 |
1991年 | 72篇 |
1990年 | 63篇 |
1989年 | 46篇 |
1988年 | 33篇 |
1987年 | 44篇 |
1986年 | 39篇 |
1985年 | 57篇 |
1984年 | 59篇 |
1983年 | 31篇 |
1982年 | 33篇 |
1981年 | 35篇 |
1980年 | 34篇 |
1979年 | 23篇 |
1978年 | 28篇 |
1977年 | 27篇 |
1974年 | 14篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
The determination of the enantiomeric purity of 2 or 3-substituted cyclanones, particularly cyclohexanones, is conveniently achieved by derivatisation into cyclic aminals with commercially available (R, R)-1,2-diphenylethylenediamine. The derivatisation procedure is directly done into the NMR tube, instantaneously, and 13C NMR allows an accurate measure of the ee. 相似文献
62.
Carlos E. Alciaturi Thais Montero Carlos De La Cruz Marcos E. Escobar 《Analytica chimica acta》1997,340(1-3):233-240
Reduction of the representation of infrared spectra from coal samples by osculating polynomials of degree nine is discussed. The reduced representation contains polynomial coefficients of order zero to four. Mathematical models of the original spectra are obtained by linear combination of the coefficients. These compressed models are statistically correlated to coal properties, namely, volatile matter, fixed carbon, ash content, heating value, hydrogen, carbon, sulphur, nitrogen, and maximum vitrinite reflectance, and the results are compared with those previously obtained from second derivatives of the same spectra. The use of compressed data, while giving slightly better correlations for some of the properties, has the advantage of requiring less computational time. 相似文献
63.
64.
We give several equivalent characterisations of left (and hence, by duality, also of right) supported algebras. These characterisations are in terms of properties of the left and the right parts of the module category, or in terms of the classes L0 and R0 which consist respectively of the predecessors of the projective modules, and of the successors of the injective modules. 相似文献
65.
66.
Márcio D. Lima Mônica J. de Andrade Viera Skákalová Felipe Nobre Carlos P. Bergmann Siegmar Roth 《固体物理学:研究快报》2007,1(4):165-167
A method for the production of transparent carbon nanotube networks (CNTNs) over transparent substrates was developed. In this method, CNTNs were grown directly in the target surface by applying the catalyst in specific zones of the substrate through lithographic techniques. The networks can be also transferred from the original substrate to other surfaces. The newly grown carbon nanotubes have a very high aspect ratio (>50000). Thus far, networks with an optical transmittance of 94% at 550 nm and a surface resistivity of 3.6 kΩ/sq have been produced. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
67.
68.
Robin Harte Carlos Herná ndez 《Proceedings of the American Mathematical Society》2006,134(5):1397-1404
A simple formula for the adjugate of a block triangle offers an alternative route to the determinant theory for Banach algebras.
69.
Beginning with the most general fractal strings/sprays construction recently expounded in the book by Lapidus and Frankenhuysen, it is shown how the complexified extension of El Naschie's cantorian-fractal spacetime model belongs to a very special class of families of fractal strings/sprays whose scaling ratios are given by suitable pinary (pinary, p prime) powers of the Golden Mean. We then proceed to show why the logarithmic periodicity laws in Nature are direct physical consequences of the complex dimensions associated with these fractal strings/sprays. We proceed with a discussion on quasi-crystals with p-adic internal symmetries, von Neumann's Continuous Geometry, the role of wild topology in fractal strings/sprays, the Banach-Tarski paradox, tesselations of the hyperbolic plane, quark confinement and the Mersenne-prime hierarchy of bit-string physics in determining the fundamental physical constants in Nature. 相似文献
70.
Juan E. Nápoles Valdés 《Results in Mathematics》2002,41(3-4):337-345
Qualitative behavior of second order nonlinear differential equations of type y″+p(t)y+q(t)f(y)=0, is studied. It includes properties such as positivity, number of zeros, oscillating nature, boundedness and monotonicity of the solutions. 相似文献