全文获取类型
收费全文 | 616篇 |
免费 | 38篇 |
专业分类
化学 | 533篇 |
晶体学 | 5篇 |
力学 | 9篇 |
数学 | 42篇 |
物理学 | 65篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 10篇 |
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 7篇 |
2017年 | 10篇 |
2016年 | 16篇 |
2015年 | 22篇 |
2014年 | 16篇 |
2013年 | 45篇 |
2012年 | 34篇 |
2011年 | 61篇 |
2010年 | 22篇 |
2009年 | 19篇 |
2008年 | 50篇 |
2007年 | 34篇 |
2006年 | 29篇 |
2005年 | 52篇 |
2004年 | 36篇 |
2003年 | 35篇 |
2002年 | 35篇 |
2001年 | 12篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 1篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有654条查询结果,搜索用时 109 毫秒
41.
Jonathan C. Golec Eve M. Carter John W. Ward William G. Whittingham Luis Simn Robert S. Paton Darren J. Dixon 《Angewandte Chemie (International ed. in English)》2020,59(40):17417-17422
A bifunctional iminophosphorane (BIMP)‐catalysed enantioselective synthesis of α,β‐unsaturated cyclohexenones through a facially selective 1,3‐prototropic shift of β,γ‐unsaturated prochiral isomers, under mild reaction conditions and in short reaction times, on a range of structurally diverse substrates, is reported. α,β‐Unsaturated cyclohexenone products primed for downstream derivatisation were obtained in high yields (up to 99 %) and consistently high enantioselectivity (up to 99 % ee). Computational studies into the reaction mechanism and origins of enantioselectivity, including multivariate linear regression of TS energy, were carried out and the obtained data were found to be in good agreement with experimental findings. 相似文献
42.
43.
44.
45.
McNamara N Benham D Sleep D Grant H Stott A 《Rapid communications in mass spectrometry : RCM》2002,16(23):2165-2171
We describe the development of a novel mobile field laboratory, purposely designed for the automated capture and subsequent stable isotopic analyses of multiple gas samples. The multiple capture system is integrated into a mobile laboratory that is fully capable of measuring the concentration of carbon dioxide, methane and nitrous oxide trace gases in a flow-through system connected to a gas chromatograph fitted with both electron capture and flame ionisation detectors. The capture of gases is achieved by routing samples through a series of 135 mL gas flasks that are sealed by micro-solenoid valves triggered by a timing system. Trace gas light stable isotope ratio mass spectrometry can then be carried out on gas samples collected by the system (NERC (15)N Stable Isotope Facility). The excitingly unique potential of the system to the ecological research field is that it will allow the collection of cyclical data for three different trace gases both in real-time and in situ. We present data arising from the validation of this mobile system as well as a preliminary experimental assessment of this technique. This technique was used to measure delta(13)C in CO(2) and CH(4) in soil gases released from waterlogged cores and delta(13)C-CH(4) values were significantly depleted in wet cores compared with dry ones (p < 0.001). 相似文献
46.
Magda D Gerasimchuk N Lecane P Miller RA Biaglow JE Sessler JL 《Chemical communications (Cambridge, England)》2002,(22):2730-2731
Motexafin gadolinium (MGd) oxidizes ascorbate, in neutral buffer and in cell culture, forming reactive oxygen species and a coordination polymer with oxalate. 相似文献
47.
The surface energy of MgO is determined using experimental data collected from equilibrated thermal grooves circumscribing island grains. Local equilibrium assumptions at each groove require that the Herring equations be satisfied at each data site, thereby yielding a large and overdetermined system of equations involving the surface energy . This inverse problem is then solved using a new technique that is statistical in nature and multiscale in implementation. The resulting discrete solution represents a statistically significant representation of the surface energy of MgO as a function of surface orientation. Comparisons to results derived from a more traditional approach, along with suggested further applications, are discussed. 相似文献
48.
Marin-Montesinos I Brouwer DH Antonioli G Lai WC Brinkmann A Levitt MH 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,177(2):307-317
We examine the influence of continuous-wave heteronuclear decoupling on symmetry-based double-quantum homonuclear dipolar recoupling, using experimental measurements, numerical simulations, and average Hamiltonian theory. There are two distinct regimes in which the heteronuclear interference effects are minimized. The first regime utilizes a moderate homonuclear recoupling field and a strong heteronuclear decoupling field; the second regime utilizes a strong homonuclear recoupling field and a weak or absent heteronuclear decoupling field. The second regime is experimentally accessible at moderate or high magic-angle-spinning frequencies and is particularly relevant for many realistic applications of solid-state NMR recoupling experiments to organic or biological materials. 相似文献
49.
50.
We grew SrTiO(3) on SrTiO(3)(001) by pulsed laser deposition, while observing x-ray diffraction at the (00(1/2)) position. The drop DeltaI in the x-ray intensity following a laser pulse contains information about plume-surface interactions. Kinematic theory predicts DeltaI/I = -4sigma(1 - sigma), so that DeltaI /I depends only on the amount of deposited material sigma. In contrast, we observed experimentally that |DeltaI /I| < 4sigma(1 - sigma) and that DeltaI /I depends on the phase of x-ray growth oscillations. The combined results suggest a fast smoothing mechanism that depends on surface step-edge density. 相似文献