全文获取类型
收费全文 | 661篇 |
免费 | 48篇 |
专业分类
化学 | 455篇 |
晶体学 | 18篇 |
力学 | 3篇 |
数学 | 88篇 |
物理学 | 145篇 |
出版年
2021年 | 12篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2016年 | 21篇 |
2015年 | 24篇 |
2014年 | 28篇 |
2013年 | 35篇 |
2012年 | 31篇 |
2011年 | 36篇 |
2010年 | 13篇 |
2009年 | 16篇 |
2008年 | 22篇 |
2007年 | 17篇 |
2006年 | 13篇 |
2005年 | 17篇 |
2004年 | 11篇 |
2003年 | 19篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 16篇 |
1997年 | 8篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 4篇 |
1975年 | 8篇 |
1973年 | 8篇 |
1969年 | 7篇 |
1965年 | 4篇 |
1934年 | 4篇 |
1912年 | 4篇 |
排序方式: 共有709条查询结果,搜索用时 15 毫秒
131.
132.
133.
134.
135.
Natalya Hessenauer‐Ilicheva Alicja Franke Dr. Dominik Meyer Wolf‐D. Woggon Prof. Dr. Rudi van Eldik Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(12):2941-2959
Two new models for cytochrome P450 in which the thiolate axial ligand is replaced by an RSO3? group, form oxo‐iron(IV) porphyrin π‐cation radicals as sole oxidation products in “peroxo shunt” reactions (see scheme) independent of the nature of the employed solvent (polar or non‐polar) and electronic nature of the porphyrin rings.
136.
Hugo Gonçalves Inês Saavedra Marlene Lúcio Sigrid Bernstorff Etelvina de Matos Gomes Michael Belsley 《Journal of nanoparticle research》2018,20(9):248
Poly(methyl methacrylate) electro-spun fibers with embedded nanocrystals of the paradigmatic donor–acceptor nonlinear chromophore para-nitroaniline have been recently demonstrated to be efficient generators of second harmonic light. To understand the influence of the size and local strain experienced by the embedded para-nitroaniline nanocrystals, a Williamson?Hall analysis was carried out on the X-ray diffraction intensity. Both the mean crystal size and strain can be tuned by simple changes in the deposition parameters of flow rate and applied voltage. The observed second harmonic signal is well correlated with the ratio of the fiber diameter to the mean para-nitroaniline crystal size suggesting that surface effects are the main source of the strong nonlinear optical response. Adjusting the electro-spinning deposition parameters when producing polymeric fibers doped with strong nonlinear organic chromophores with high dipole moments has the potential to provide a versatile and efficient method for developing second-order nonlinear optical materials. 相似文献
137.
Franke A Fertinger C van Eldik R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(22):6935-6949
The present study focuses on the formation and reactivity of hydroperoxo-iron(III) porphyrin complexes formed in the [Fe(III)(tpfpp)X]/H(2)O(2)/HOO(-) system (TPFPP=5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin; X=Cl(-) or CF(3) SO(3)(-)) in acetonitrile under basic conditions at -15 °C. Depending on the selected reaction conditions and the active form of the catalyst, the formation of high-spin [Fe(III)(tpfpp)(OOH)] and low-spin [Fe(III)(tpfpp)(OH)(OOH)] could be observed with the application of a low-temperature rapid-scan UV/Vis spectroscopic technique. Axial ligation and the spin state of the iron(III) center control the mode of O-O bond cleavage in the corresponding hydroperoxo porphyrin species. A mechanistic changeover from homo- to heterolytic O-O bond cleavage is observed for high- [Fe(III)(tpfpp)(OOH)] and low-spin [Fe(III)(tpfpp)(OH)(OOH)] complexes, respectively. In contrast to other iron(III) hydroperoxo complexes with electron-rich porphyrin ligands, electron-deficient [Fe(III)(tpfpp)(OH)(OOH)] was stable under relatively mild conditions and could therefore be investigated directly in the oxygenation reactions of selected organic substrates. The very low reactivity of [Fe(III)(tpfpp)(OH)(OOH)] towards organic substrates implied that the ferric hydroperoxo intermediate must be a very sluggish oxidant compared with the iron(IV)-oxo porphyrin π-cation radical intermediate in the catalytic oxygenation reactions of cytochrome P450. 相似文献
138.
Activity data for small molecules are invaluable in chemoinformatics. Various bioactivity databases exist containing detailed information of target proteins and quantitative binding data for small molecules extracted from journals and patents. In the current work, we have merged several public and commercial bioactivity databases into one bioactivity metabase. The molecular presentation, target information, and activity data of the vendor databases were standardized. The main motivation of the work was to create a single relational database which allows fast and simple data retrieval by in-house scientists. Second, we wanted to know the amount of overlap between databases by commercial and public vendors to see whether the former contain data complementing the latter. Third, we quantified the degree of inconsistency between data sources by comparing data points derived from the same scientific article cited by more than one vendor. We found that each data source contains unique data which is due to different scientific articles cited by the vendors. When comparing data derived from the same article we found that inconsistencies between the vendors are common. In conclusion, using databases of different vendors is still useful since the data overlap is not complete. It should be noted that this can be partially explained by the inconsistencies and errors in the source data. 相似文献
139.
Using scanning tunneling spectroscopy, we study the transport of electrons through C(60)?molecules on different metal surfaces. When electrons tunnel through a molecule, they may excite molecular vibrations. A fingerprint of these processes is a characteristic sub-structure in the differential conductance spectra of the molecular junction reflecting the onset of vibrational excitation. Although the intensity of these processes is generally weak, they become more important as the resonant character of the transport mechanism increases. The detection of single vibrational levels crucially depends on the energy level alignment and lifetimes of excited states. In the limit of large current densities, resonant electron-vibration coupling leads to an energy accumulation in the molecule, which eventually leads to its decomposition. With our experiments on C(60)?we are able to depict a molecular scale picture of how electrons interact with the vibrational degrees of freedom of single molecules in different transport regimes. This understanding helps in the development of stable molecular devices, which may also carry a switchable functionality. 相似文献
140.
Abe Y Aberle C Akiri T dos Anjos JC Ardellier F Barbosa AF Baxter A Bergevin M Bernstein A Bezerra TJ Bezrukhov L Blucher E Bongrand M Bowden NS Buck C Busenitz J Cabrera A Caden E Camilleri L Carr R Cerrada M Chang PJ Chimenti P Classen T Collin AP Conover E Conrad JM Cormon S Crespo-Anadón JI Cribier M Crum K Cucoanes A D'Agostino MV Damon E Dawson JV Dazeley S Dierckxsens M Dietrich D Djurcic Z Dracos M Durand V Efremenko Y Elnimr M Endo Y Etenko A Falk E Fallot M Fechner M von Feilitzsch F 《Physical review letters》2012,108(13):131801
The Double Chooz experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. An observed-to-predicted ratio of events of 0.944±0.016(stat)±0.040(syst) was obtained in 101 days of running at the Chooz nuclear power plant in France, with two 4.25 GW(th) reactors. The results were obtained from a single 10 m(3) fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 flux measurement after correction for differences in core composition. The deficit can be interpreted as an indication of a nonzero value of the still unmeasured neutrino mixing parameter sin(2)2θ(13). Analyzing both the rate of the prompt positrons and their energy spectrum, we find sin(2)2θ(13)=0.086±0.041(stat)±0.030(syst), or, at 90% C.L., 0.017相似文献