全文获取类型
收费全文 | 1064篇 |
免费 | 39篇 |
国内免费 | 5篇 |
专业分类
化学 | 875篇 |
晶体学 | 7篇 |
力学 | 17篇 |
数学 | 66篇 |
物理学 | 143篇 |
出版年
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 18篇 |
2019年 | 19篇 |
2018年 | 15篇 |
2017年 | 16篇 |
2016年 | 27篇 |
2015年 | 24篇 |
2014年 | 29篇 |
2013年 | 57篇 |
2012年 | 63篇 |
2011年 | 80篇 |
2010年 | 36篇 |
2009年 | 35篇 |
2008年 | 70篇 |
2007年 | 90篇 |
2006年 | 77篇 |
2005年 | 64篇 |
2004年 | 58篇 |
2003年 | 54篇 |
2002年 | 47篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1966年 | 2篇 |
排序方式: 共有1108条查询结果,搜索用时 15 毫秒
11.
Oguchi T Tozuka Y Hanawa T Mizutani M Sasaki N Limmatvapirat S Yamamoto K 《Chemical & pharmaceutical bulletin》2002,50(7):887-891
The solid-state complexation between cholic acid (CA) and either methyl p-hydroxybenzoate (MPB) or ibuprofen (IBP) was investigated. Powder X-ray diffractometry, IR spectroscopy and thermal analysis suggested the complex formation between CA and MPB as well as between CA and IBP by co-grinding method. The stoichiometry of CA-MPB was 1 : 1 while that of CA-IBP was 2 : 1, reflecting the effect of guest size on complex formation. The guest compounds were assumed to be included in the channel of complexes formed by hydrogen bonds among CA molecules. 相似文献
12.
Attenuated total reflection spectrometry with a slab optical waveguide (SOWG) was explored for the simple, rapid and sensitive measurement of total anionic surfactants by the methylene blue active substance (MBAS) method. A fused-silica sheet used as a guiding layer was modified with trimethylsilane (TMS) to extract and concentrate the MBASs on the SOWG surface. Based on preliminary studies of the adsorption behavior and visible ATR spectrum of MB on the modified silica surface, a detection wavelength of 600 nm was chosen for the sensitive measurement of anionic surfactants. When the concentration of MB was set at 10 microM in the final measurement solution, the calibration curve for a typical anionic surfactant (sodium dodecylbenzenesulfonate) was linear up to 0.6 microM and the detection limit was 0.07 microM. The proposed method was applied to the determination of total anionic surfactants in river water. 相似文献
13.
Geometry optimizations at the UHF/6-31G* and UMP2/6-31G* levels of theory were performed to find the transition state in the interconversion between norbornadiene (N) and quadricyclane (Q) radical cations. Two transition structures, TS+·1 and TS+·2, were obtained which have C1 and C2 symmetry, respectively. Vibrational analysis at the UHF and UMP2 levels of theory and IRC calculation showed that TS+·1 is the true transition state connecting N+· and Q+·, while TS+·2 is a second order saddle point. 相似文献
14.
Hiroshi Mitsui Yuichi Shimizu 《Journal of polymer science. Part A, Polymer chemistry》1980,18(3):1115-1122
The γ radiolysis of polyethylene preirradiated with electron beams to 3 Mrad was carried out at 30–100°C in vacuo with a dose rate of 6.35 × 105 rad/hr. The hydrogen formation in the γ radiolysis was little affected by the preirradiation of electron beams, whereas the formation of trans-vinylene unsaturation and gel was somewhat retarded. The rates of the formation of hydrogen and trans-vinylene unsaturation were described by the zero-order formation kinetics with respect to each concentration combined with the first-order disappearance. The apparent rate constants and activation energies for the formation and disappearance of hydrogen and trans-vinylene unsaturation were almost independent of the preirradiation. The gel fraction was analyzed by using the Charlesby–Pinner equation. The G values of crosslinking and main chain scission were increased by the preirradiation, whereas their activation energies remained unaltered. On the basis of these results the effects of preirradiation on the reactions induced by γ rays in polyethylene were discussed. 相似文献
15.
Optimal control simulation is applied to the cis-trans photoisomerization of retinal in rhodopsin within a two-dimensional, two-electronic-state model with a conical intersection [S. Hahn and G. Stock, J. Phys. Chem. B 104, 1146 (2000)]. For this case study, we investigate coherent control mechanisms, in which laser pulses work cooperatively with a conical intersection that acts as a "wave-packet cannon." Optimally designed pulses largely consist of shaping subpulses that prepare a wave packet, which is localized along a reaction coordinate and has little energy in the coupling mode, through multiple electronic transitions. This shaping process is shown to be essential for achieving a high target yield although the envelopes of the calculated pulses depend on the local topography of the potential-energy surfaces around the conical intersection and the choice of target. The control mechanisms are analyzed by considering the motion of reduced wave packets in a nuclear configuration space as well as by snapshots of probability current-density maps. 相似文献
16.
We have determined the crystal structure of the title compound, which has a triclinic cell with cell parameters of , , , α=76.617°, β=84.188°, γ=74.510° and space group . The crystal structure suggests the chemical formula CoMoO4·3/4H2O. The structure consists of MoO4 tetrahedra and CoO6 octahedra, confirming the earlier X-ray absorption near-edge spectroscopic (XANES) investigation on the hydrate. The comparison of the crystal structures of the hydrate and the α-,β-, and hp-phases shows that the hydrate exhibits metal cation coordinations similar to those of the β-phase, but had arrangements of CoO6 and MoOn polyhedra similar to those of the hp-phase. 相似文献
17.
Chiral urea compounds 10a-g were synthesized as catalysts for conjugate addition of pyrrolidine (2) to gamma-crotonolactone (3). In the presence of a catalytic amount of the chiral ureas, this hetero-Michael reaction was greatly accelerated. Asymmetric induction was observed with the catalysts 10e, 10f, and 10g. 相似文献
18.
19.
20.
Onodera K Nakamura H Oba Y Ohizumi Y Ojika M 《Journal of the American Chemical Society》2005,127(29):10406-10411
Zooxanthellamide Cs (ZAD-Cs), C(128)H(220)N(2)O(53)S(2) (ca. 2.7 kDa), was obtained from a cultured marine dinoflagellate of the genus Symbiodinium as an inseparable isomeric mixture of polyhydroxylated 61- to 66-membered macrolides. The chemical structures of the components were clarified by detailed 2D NMR analysis to be the macrolactonized analogues of zooxanthellamide A (ZAD-A), which had been previously isolated from the same microalgae. Chemical lability of ZAD-Cs suggests that ZAD-A is an artifact derived from ZAD-Cs during the isolation steps. Three of the components possess the largest (63-, 64-, and 66-membered) ring sizes found to date among the natural macrolides. ZAD-Cs exhibited higher vasoconstrictive activity than that of the zooxanthellatoxins, the first vasoconstrictive macrolides from Symbiodinium sp. The structure-activity relationship suggests that the huge macrolactone structure is important for biological activity. The relationship between the structures of the polyol metabolites and the phylogenetic systematics of Symbiodinium sp. is also discussed. 相似文献