全文获取类型
收费全文 | 279篇 |
免费 | 18篇 |
国内免费 | 4篇 |
专业分类
化学 | 171篇 |
力学 | 2篇 |
数学 | 48篇 |
物理学 | 80篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 13篇 |
2020年 | 10篇 |
2019年 | 11篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 8篇 |
2013年 | 13篇 |
2012年 | 19篇 |
2011年 | 22篇 |
2010年 | 12篇 |
2009年 | 7篇 |
2008年 | 24篇 |
2007年 | 16篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 16篇 |
2003年 | 14篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1958年 | 2篇 |
排序方式: 共有301条查询结果,搜索用时 15 毫秒
211.
212.
In the reaction of 4-aryl-1,2,4-triazolium-phenacylides with dimethyl acetylcnedicarboxylate, the initial cyclo-adducts 5 undergo C-N bond fission giving 6–9. 相似文献
213.
Fernandez J Iparraguirre I Aramburu I Illarramendi A Azkargorta J Voda M Balda R 《Optics letters》2003,28(15):1341-1343
We report for the first time to our knowledge an experimental demonstration of wavelength self-tuning in a K5Nd(MoO4)4 broadband-emitting laser crystal (KNM), as well as a theoretical treatment of the system based on its birefringence properties. The self-frequency-tuning of the laser along the full spectral range of the KNM crystal was obtained by rotating a birefringent gain plate in its own plane. The gain plate was placed inside a resonator at Brewster's angle. The tuning characteristics of the spectral filter were obtained by use of the Jones vector formalism. The calculated wavelength-selective tuning precisely matches the experimental observations. 相似文献
214.
Discotic liquid crystals with an inverted structure 总被引:1,自引:0,他引:1
215.
Daning Hu Hsinchun Chen Zan Huang Mihail C. Roco 《Journal of nanoparticle research》2007,9(4):529-542
Academic nanoscale science and engineering (NSE) research provides a foundation for nanotechnology innovation reflected in
patents. About 60% or about 50,000 of the NSE-related patents identified by “full-text” keyword searching between 1976 and
2004 at the United States Patent and Trademark Office (USPTO) have an average of approximately 18 academic citations. The
most cited academic journals, individual researchers, and research articles have been evaluated as sources of technology innovation
in the NSE area over the 28-year period. Each of the most influential articles was cited about 90 times on the average, while
the most influential author was cited more than 700 times by the NSE-related patents. Thirteen mainstream journals accounted
for about 20% of all citations. Science, Nature and Proceedings of the National Academy of Sciences (PNAS) have consistently
been the top three most cited journals, with each article being cited three times on average. There is another kind of influential
journals, represented by Biosystems and Origin of Life, which have very few articles cited but with exceptionally high frequencies. The number of academic citations per year from
ten most cited journals has increased by over 17 times in the interval (1990–1999) as compared to (1976–1989), and again over
3 times in the interval (2000–2004) as compared to (1990–1999). This is an indication of increased used of academic knowledge
creation in the NSE-related patents. 相似文献
216.
Mihail Atanasov Claude A. Daul E. Penka Fowe 《Monatshefte für Chemie / Chemical Monthly》2005,52(8):925-963
Metal–ligand bonding in transition metal halide molecules and complexes with different central ions, oxidations states, and coordination numbers: CrIIIX63–, CrIVX4, CrIIX2 (X = F,Cl,Br,I), MIIICl63–(M = Mo,W), MIII(H2O)63+(M = Cr,Co) and Re2Cl82– has been studied in terms of the Extended Transition State (ETS) energy patitioning scheme within the DFT and electron density analysis (the Laplacian of the electron density and the electronic localization function). Bonding is found to be dominated by ionicity in all cases, especially so for complexes with higher coordination numbers. Covalent contributions to the metal–ligand bond are found to be mainly due to the nd-electrons and to lesser extent due to the metal (n+1)s and (n+1)p-orbitals, contributions from (n+1)s increasing when going to lower coordination numbers. Metal–ligand bonding analysis have been used in order to check some concepts emerging from ligand field theory when applied to the spectroscopy and magnetism of transition metal complexes. It is pointed out that for complexes of high symmetry (MX6, Oh, MX4, Td, and MX2, Dh) electron density analyses gain interpretative power when partitioned into contributions from occupied orbitals of different symmetry. 相似文献
217.
The introduced DFT-supported vibronic coupling model together with the hardness rule indicates, for the title compounds, that the tendency toward lone pair (LP) distortions decreases with increasing coordination number (CN) and upon proceeding from fluoride to iodide as the ligands. Thus, only some hexafluoro complexes and molecules are calculated to actually undergo LP deformations; here, from the possible highest-symmetry deformations, those with C(4v) geometry possess the lowest energy, leading to the complete ablation of one ligand and, hence, explaining the nonexistence of the complexes AsF6(3-), SbF6(3-), and SF6(2-). If a lower-symmetry strain is imposed on the octahedral species, for example, induced by the simultaneous presence of terminal and bridging ligands in oligomers, the vibronic energy potential is activated. It may induce pronounced distortions, which are much larger than those of analogous clusters with central ions lacking the LP. Dimers and tetramers with common edges and faces are investigated, with the predicted and calculated deformations of the constituting octahedra again following the stability sequence C(4v) > C(2v) > C(3v). The model nicely accounts for the observed trends, as well as reproduces the experimental structures and energy balances, at least semiquantitatively; its predictive power exceeds that of the valence-shell electron-pair repulsion concept. 相似文献
218.
219.
The 266 nm photodissociation of bromoform adsorbed on an amorphous solid water (ASW) layer has been investigated for the first time under well-defined ultrahigh vacuum conditions. Time-of-flight (TOF) measurements indicate direct release of gas-phase Br, CHBr2, Br2, and CHBr species, with potential implications for stratospheric chemistry. Furthermore, new, ice-surface-mediated C-C (C2H2Br2) and C-O (CHBrO, CO) species are revealed in postirradiation temperature programmed desorption (TPD) and reflection absorption infrared (RAIR) spectra. A cross section of approximately 5 x 10(-20) cm2 is determined for bromoform photodissociation at 266 nm based on the integrated area of both the TOF spectra of Br and Br2 and the postirradiation TPD curves of CHBr3. The involvement of the free, non-hydrogen-bonded water groups at the ASW surface in the formation of the photoproducts is evident from the RAIRS results. 相似文献
220.
The quantum efficiency and luminescence properties of double activated terbium aluminum garnet samples were investigated in the present study. A mathematical procedure and PL measurement system are developed for express analysis of quantum efficiency of luminescent materials. The energy-level diagram was proposed to explain the luminescence mechanism. Application of TAG:Ce,Eu with improved CIE and CRI in LED device is demonstrated. 相似文献