全文获取类型
收费全文 | 22123篇 |
免费 | 497篇 |
国内免费 | 95篇 |
专业分类
化学 | 14000篇 |
晶体学 | 149篇 |
力学 | 578篇 |
数学 | 3111篇 |
物理学 | 4877篇 |
出版年
2021年 | 159篇 |
2020年 | 241篇 |
2019年 | 184篇 |
2018年 | 168篇 |
2016年 | 343篇 |
2015年 | 358篇 |
2014年 | 364篇 |
2013年 | 788篇 |
2012年 | 815篇 |
2011年 | 1050篇 |
2010年 | 591篇 |
2009年 | 549篇 |
2008年 | 909篇 |
2007年 | 977篇 |
2006年 | 946篇 |
2005年 | 1002篇 |
2004年 | 850篇 |
2003年 | 681篇 |
2002年 | 614篇 |
2001年 | 522篇 |
2000年 | 479篇 |
1999年 | 333篇 |
1998年 | 306篇 |
1997年 | 320篇 |
1996年 | 378篇 |
1995年 | 352篇 |
1994年 | 323篇 |
1993年 | 377篇 |
1992年 | 342篇 |
1991年 | 325篇 |
1990年 | 257篇 |
1989年 | 288篇 |
1988年 | 325篇 |
1987年 | 290篇 |
1986年 | 257篇 |
1985年 | 330篇 |
1984年 | 292篇 |
1983年 | 247篇 |
1982年 | 285篇 |
1981年 | 253篇 |
1980年 | 260篇 |
1979年 | 250篇 |
1978年 | 246篇 |
1977年 | 206篇 |
1976年 | 218篇 |
1975年 | 164篇 |
1974年 | 214篇 |
1973年 | 183篇 |
1961年 | 166篇 |
1960年 | 216篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Vsevolod Khikhlovskyi Albert J. J. M. van Breemen Jasper J. Michels René A. J. Janssen Gerwin H. Gelinck Martijn Kemerink 《Journal of Polymer Science.Polymer Physics》2015,53(17):1231-1237
In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase‐separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1231–1237 相似文献
4.
5.
6.
Pu Duan Bo Zhi Luke Coburn Christy L. Haynes Klaus Schmidt-Rohr 《Magnetic resonance in chemistry : MRC》2020,58(11):1130-1138
The composition of fluorescent polymer nanoparticles, commonly referred to as carbon dots, synthesized by microwave-assisted reaction of citric acid and ethylenediamine was investigated by 13C, 13C{1H}, 1H─13C, 13C{14N}, and 15N solid-state nuclear magnetic resonance (NMR) experiments. 13C NMR with spectral editing provided no evidence for significant condensed aromatic or diamondoid carbon phases. 15N NMR showed that the nanoparticle matrix has been polymerized by amide and some imide formation. Five small, resolved 13C NMR peaks, including an unusual ═CH signal at 84 ppm (1H chemical shift of 5.8 ppm) and ═CN2 at 155 ppm, and two distinctive 15N NMR resonances near 80 and 160 ppm proved the presence of 5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]pyridine-7-carboxylic acid (IPCA) or its derivatives. This molecular fluorophore with conjugated double bonds, formed by a double cyclization reaction of citric acid and ethylenediamine as first shown by Y. Song, B. Yang, and coworkers in 2015, accounts for the fluorescence of the carbon dots. Cross-peaks in a 1H─13C HETCOR spectrum with brief 1H spin diffusion proved that IPCA is finely dispersed in the polyamide matrix. From quantitative 13C and 15N NMR spectra, a high concentration (18 ± 2 wt%) of IPCA in the carbon dots was determined. A pronounced gradient in 13C chemical-shift perturbations and peak widths, with the broadest lines near the COO group of IPCA, indicated at least partial transformation of the carboxylic acid of IPCA by amide or ester formation. 相似文献
7.
8.
Claudia Poloni Marc C. A. Stuart Pieter van der Meulen Wiktor Szymanski Ben L. Feringa 《Chemical science》2015,6(12):7311-7318
The external photocontrol over peptide folding, by the incorporation of molecular photoswitches into their structure, provides a powerful tool to study biological processes. However, it is limited so far to switches that exhibit only a rather limited geometrical change upon photoisomerization and that show thermal instability of the photoisomer. Here we describe the use of an overcrowded alkene photoswitch to control a model β-hairpin peptide. This photoresponsive unit undergoes a large conformational change and has two thermally stable isomers which has major influence on the secondary structure and the aggregation of the peptide, permitting the phototriggered formation of amyloid-like fibrils. 相似文献
9.
10.
Ieva
Dauickait Amos S. Lawless Jennifer A. Scott Peter Jan van Leeuwen 《Numerical Linear Algebra with Applications》2020,27(5)
We consider the large sparse symmetric linear systems of equations that arise in the solution of weak constraint four‐dimensional variational data assimilation, a method of high interest for numerical weather prediction. These systems can be written as saddle point systems with a 3 × 3 block structure but block eliminations can be performed to reduce them to saddle point systems with a 2 × 2 block structure, or further to symmetric positive definite systems. In this article, we analyse how sensitive the spectra of these matrices are to the number of observations of the underlying dynamical system. We also obtain bounds on the eigenvalues of the matrices. Numerical experiments are used to confirm the theoretical analysis and bounds. 相似文献