全文获取类型
收费全文 | 2501篇 |
免费 | 105篇 |
国内免费 | 23篇 |
专业分类
化学 | 1691篇 |
晶体学 | 15篇 |
力学 | 66篇 |
数学 | 349篇 |
物理学 | 508篇 |
出版年
2023年 | 27篇 |
2022年 | 51篇 |
2021年 | 54篇 |
2020年 | 65篇 |
2019年 | 78篇 |
2018年 | 54篇 |
2017年 | 56篇 |
2016年 | 96篇 |
2015年 | 54篇 |
2014年 | 69篇 |
2013年 | 132篇 |
2012年 | 162篇 |
2011年 | 189篇 |
2010年 | 108篇 |
2009年 | 69篇 |
2008年 | 136篇 |
2007年 | 177篇 |
2006年 | 158篇 |
2005年 | 122篇 |
2004年 | 104篇 |
2003年 | 78篇 |
2002年 | 53篇 |
2001年 | 30篇 |
2000年 | 28篇 |
1999年 | 39篇 |
1998年 | 20篇 |
1997年 | 28篇 |
1996年 | 26篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 17篇 |
1992年 | 20篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 17篇 |
1988年 | 22篇 |
1987年 | 7篇 |
1985年 | 19篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1887年 | 6篇 |
排序方式: 共有2629条查询结果,搜索用时 15 毫秒
991.
Patrícia D. Neuenfeldt Geonir M. Siqueira Solange M.S.V. Wardell Alex F.C. Flores 《Tetrahedron letters》2010,51(23):3106-3108
An efficient solvent-free synthesis of thiazolidinones from reaction of mercaptoacetic acid, aldehydes (benzaldehyde and valeraldehyde) or ketones (cyclopentanone and cyclohexanone), and hydrazines (phenylhydrazine and 2,4-dinitrophenylhydrazine) is reported. The compounds were generally characterized by spectroscopic techniques and specifically for 2-cyclohexanyl-3-(N-phenyl)-1,3-thiazolidin-4-one by X-ray crystallography. 相似文献
992.
Oriented poly(ethylene-2,6-naphthalate) (PEN) has been characterised by polarised FT-IR spectroscopy to determine the structural angles of the transition moments to the molecular chain axis. The bands at 1130 cm−1, 1142 cm−1 and 1602 cm−1, which have been previously assigned as having their transition dipole moments parallel to the chain axis, are confirmed as parallel bands. Bands at 767 cm−1 and 831 cm−1 are confirmed as perpendicular bands. However the band at 1708 cm−1 which has previously been assigned as a perpendicular band, is shown here to have its transition moment at 72° to the molecular axis. 相似文献
993.
Aqueous complexation of Th(IV), U(IV), Np(IV), Pu(III/IV), and Ce(III/IV) with DTPA was studied by potentiometry, absorption spectrophotometry, and cyclic voltammetry at 1 M ionic strength and 25 °C. The stability constants for the 1:1 complex of each trivalent and tetravalent metal were calculated. From the potentiometric data, we report stability constant values for Ce(III)DTPA, Ce(III)HDTPA, and Th(IV)DTPA of log β(101) = 20.01 ± 0.02, log β(111) = 22.0 ± 0.2, and log β(101) = 29.6 ± 1, respectively. From the absorption spectrophotometry data, we report stability constant values for U(IV)DTPA, Np(IV)DTPA, and Pu(IV)DTPA of log β(101) = 31.8 ± 0.1, 32.3 ± 0.1, and 33.67 ± 0.02, respectively. From the cyclic voltammetry data, we report stability constant values for Ce(IV) and Pu(III) of log β(101) = 34.04 ± 0.04 and 20.58 ± 0.04, respectively. The values obtained in this work are compared and discussed with respect to the ionic radius of each cationic metal. 相似文献
994.
We study the ground-state orbital and spin configurations of up to six electrons or holes loaded into self-assembled quantum dots. We use a general phase-diagram approach constructed from single-particle pseudopotential and many-particle configuration interaction methods. The predicted hole charging energies agree with recent charging experiments, but offer a different interpretation: we find that while the charging of electrons follows both Hund's rule and the Aufbau principle, the charging of holes follows a nontrivial charging pattern which violates both the Aufbau principle and Hund's rule. 相似文献
995.
Swift heavy ion (SHI) irradiation is an effective technique to modify the optical properties of the materials. In the present investigation, the effect of 100?MeV?Ag7+ SHI irradiation fluence on the optical properties of ZnO1?x:Nx thin films was studied. The post irradiation spectroscopic characterizations such as UV–VIS reflectance spectroscopy, Raman spectroscopy and photoluminescence (PL) spectroscopy analysis were carried out. The studies imply that when the SHI passes through the solid, the higher electronic stopping power of ions can weaken oxygen bonds in ZnO, resulting in the formation of donor defects such as oxygen vacancies and zinc interstitials. The formation of donor defects has been acknowledged through the increase in bandgap with irradiating ion fluence. The blue shift observed from the Raman spectra for the 3?×?1013 ions/cm2 fluence-irradiated films implies the existence of compressive stress in the films. The PL analysis acknowledges the formation of donor defects upon irradiation. Furthermore, it conveys that the presence of N atoms in ZnO lattice leads to the formation of a less number of defects as compared with undoped ZnO while irradiation. 相似文献
996.
Some properties of two-dimensional boron nitride are treated in a truncated crystal approach, employing the iterative extended Huckel method in a charge self-consistent calculation. The values of the band width, band gap, charges, equilibrium distance, and sublimation energy are in satisfactory agreement with experiment. 相似文献
997.
998.
Molecular dynamics simulations of a series of calcium aluminate glasses have been carried out using empirical potentials with a covalent term. The simulations closely reproduce the total neutron correlation function of glasses with 30 and 38 mol% Al2O3 and physical properties such as elastic constants. For compositions close to the eutectic 37 mol% Al2O3, aluminum is tetrahedrally coordinated by oxygen, but the proportion of five-fold and six-fold coordination and also edge-sharing tetrahedra gradually increases with increasing Al2O3 content. The coordination number for oxygen around calcium atoms is close to 6 and this involves a larger coordination at a shorter, well-defined distance, followed by a smaller coordination with a broader range of distances. When the Al2O3 content decreases, the calcium aluminate structure becomes depolymerised and the average ring size increases. Also reported is an X-ray photoelectron spectroscopy measurement on a glass sample with 38 mol% Al2O3, which shows that 38.6 ± 0.9% of the oxygens are non-bridging, in excellent agreement with the simulations. 相似文献
999.
Wiesenmayer E Luetkens H Pascua G Khasanov R Amato A Potts H Banusch B Klauss HH Johrendt D 《Physical review letters》2011,107(23):237001
It is widely believed that, in contrast to its electron-doped counterparts, the hole-doped compound Ba(1-x)K(x)Fe(2)As(2) exhibits a mesoscopic phase separation of magnetism and superconductivity in the underdoped region of the phase diagram. Here, we report a combined high-resolution x-ray powder diffraction and volume-sensitive muon spin rotation study of Ba(1-x)K(x)Fe(2)As(2) showing that this paradigm does not hold true in the underdoped region of the phase diagram (0≤x≤0.25). Instead we find a microscopic coexistence of the two forms of order. A competition of magnetism and superconductivity is evident from a significant reduction of the magnetic moment and a concomitant decrease of the magnetoelastically coupled orthorhombic lattice distortion below the superconducting phase transition. 相似文献
1000.