全文获取类型
收费全文 | 8294篇 |
免费 | 224篇 |
国内免费 | 25篇 |
专业分类
化学 | 6183篇 |
晶体学 | 41篇 |
力学 | 84篇 |
数学 | 1201篇 |
物理学 | 1034篇 |
出版年
2020年 | 84篇 |
2019年 | 74篇 |
2016年 | 161篇 |
2015年 | 153篇 |
2014年 | 128篇 |
2013年 | 298篇 |
2012年 | 265篇 |
2011年 | 356篇 |
2010年 | 197篇 |
2009年 | 211篇 |
2008年 | 318篇 |
2007年 | 324篇 |
2006年 | 292篇 |
2005年 | 320篇 |
2004年 | 297篇 |
2003年 | 247篇 |
2002年 | 210篇 |
2001年 | 125篇 |
2000年 | 115篇 |
1999年 | 123篇 |
1998年 | 116篇 |
1997年 | 143篇 |
1996年 | 137篇 |
1995年 | 136篇 |
1994年 | 119篇 |
1993年 | 129篇 |
1992年 | 104篇 |
1991年 | 110篇 |
1990年 | 83篇 |
1989年 | 119篇 |
1988年 | 125篇 |
1987年 | 112篇 |
1986年 | 119篇 |
1985年 | 142篇 |
1984年 | 119篇 |
1983年 | 113篇 |
1982年 | 112篇 |
1981年 | 113篇 |
1980年 | 122篇 |
1979年 | 103篇 |
1978年 | 92篇 |
1977年 | 88篇 |
1976年 | 92篇 |
1974年 | 100篇 |
1973年 | 90篇 |
1971年 | 79篇 |
1961年 | 141篇 |
1960年 | 195篇 |
1959年 | 104篇 |
1958年 | 115篇 |
排序方式: 共有8543条查询结果,搜索用时 218 毫秒
1.
2.
The energy per particle BA in nuclear matter is calculated up to high baryon density in the whole isospin asymmetry range from symmetric matter to pure neutron matter.The results,obtained in the framework of the Brueckner-Hartree-Fock approximation with two-and three-body forces,confirm the well-known parabolic dependence on the asymmetry parameterβ=(N?Z)/A(β^2 law)that is valid in a wide density range.To investigate the extent to which this behavior can be traced back to the properties of the underlying interaction,aside from the mean field approximation,the spin-isospin decomposition of BA is performed.Theoretical indications suggest that theβ^2 law could be violated at higher densities as a consequence of the three-body forces.This raises the problem that the symmetry energy,calculated according to theβ^2 law as a difference between BA in pure neutron matter and symmetric nuclear matter,cannot be applied to neutron stars.One should return to the proper definition of the nuclear symmetry energy as a response of the nuclear system to small isospin imbalance from the Z=N nuclei and pure neutron matter. 相似文献
3.
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
4.
5.
Let R be a discrete nonsingular equivalence relation on a standard probability space , and let V be an ergodic strongly asymptotically central automorphism of R. We prove that every V-invariant cocycle with values in a Polish group G takes values in an abelian subgroup of G.
The hypotheses of this result are satisfied, for example, if A is a finite set, a closed, shift-invariant subset, V is the shift, μ a shift-invariant and ergodic probability measure on X, the two-sided tail-equivalence relation on X, a shift-invariant subrelation which is μ-nonsingular, and a shift-invariant cocycle. 相似文献
6.
7.
8.
9.
JPC – Journal of Planar Chromatography – Modern TLC - This paper reports the efficiency of the C30 phase for HPLC and TLC separation of a mixture of tocopherol homologs and... 相似文献
10.
Operators on manifolds with corners that have base configurations with geometric singularities can be analysed in the frame of a conormal symbolic structure which is in spirit similar to the one for conical singularities of Kondrat'ev's work. Solvability of elliptic equations and asymptotics of solutions are determined by meromorphic conormal symbols. We study the case when the base has edge singularities which is a natural assumption in a number of applications. There are new phenomena, caused by a specific kind of higher degeneracy of the underlying symbols. We introduce an algebra of meromorphic edge operators that depend on complex parameters and investigate meromorphic inverses in the parameter-dependent elliptic case. Among the examples are resolvents of elliptic differential operators on manifolds with edges. 相似文献