全文获取类型
收费全文 | 85105篇 |
免费 | 529篇 |
国内免费 | 398篇 |
专业分类
化学 | 29613篇 |
晶体学 | 823篇 |
力学 | 6780篇 |
数学 | 32984篇 |
物理学 | 15832篇 |
出版年
2018年 | 10467篇 |
2017年 | 10293篇 |
2016年 | 6181篇 |
2015年 | 978篇 |
2014年 | 394篇 |
2013年 | 551篇 |
2012年 | 3993篇 |
2011年 | 10763篇 |
2010年 | 5790篇 |
2009年 | 6200篇 |
2008年 | 6842篇 |
2007年 | 9002篇 |
2006年 | 470篇 |
2005年 | 1587篇 |
2004年 | 1791篇 |
2003年 | 2175篇 |
2002年 | 1193篇 |
2001年 | 351篇 |
2000年 | 386篇 |
1999年 | 259篇 |
1998年 | 297篇 |
1997年 | 271篇 |
1996年 | 323篇 |
1995年 | 238篇 |
1994年 | 186篇 |
1993年 | 215篇 |
1992年 | 161篇 |
1991年 | 170篇 |
1990年 | 134篇 |
1989年 | 167篇 |
1988年 | 177篇 |
1987年 | 162篇 |
1986年 | 170篇 |
1985年 | 184篇 |
1984年 | 149篇 |
1983年 | 145篇 |
1982年 | 153篇 |
1981年 | 138篇 |
1980年 | 152篇 |
1979年 | 140篇 |
1978年 | 122篇 |
1977年 | 103篇 |
1976年 | 98篇 |
1974年 | 106篇 |
1973年 | 111篇 |
1971年 | 83篇 |
1961年 | 143篇 |
1960年 | 199篇 |
1959年 | 114篇 |
1958年 | 118篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers. 相似文献
3.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant. 相似文献
4.
5.
Sarah Peluse 《Israel Journal of Mathematics》2018,227(1):379-396
We prove that the group of diffeomorphisms of the interval [0, 1] contains surface groups whose action on (0, 1) has no global fix point and such that only countably many points of the interval (0, 1) have non-trivial stabiliser. 相似文献
6.
7.
8.
9.
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
10.
S. V. Panin I. V. Vlasov V. P. Sergeev B. B. Ovechkin P. O. Marushchak Sunder Ramasubbu P. S. Lyubutin V. V. Titkov 《Physical Mesomechanics》2015,18(3):261-272
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method. 相似文献