全文获取类型
收费全文 | 438篇 |
免费 | 7篇 |
专业分类
化学 | 184篇 |
晶体学 | 4篇 |
力学 | 9篇 |
数学 | 18篇 |
物理学 | 230篇 |
出版年
2020年 | 3篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 22篇 |
2012年 | 10篇 |
2011年 | 21篇 |
2010年 | 11篇 |
2009年 | 9篇 |
2008年 | 12篇 |
2007年 | 16篇 |
2006年 | 17篇 |
2005年 | 11篇 |
2004年 | 17篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1997年 | 7篇 |
1996年 | 17篇 |
1995年 | 6篇 |
1994年 | 21篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 21篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 17篇 |
1985年 | 5篇 |
1984年 | 18篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 14篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1968年 | 2篇 |
1962年 | 2篇 |
1938年 | 2篇 |
1932年 | 2篇 |
1920年 | 2篇 |
1885年 | 2篇 |
排序方式: 共有445条查询结果,搜索用时 15 毫秒
11.
Two-photon induced fluorescence and resonance-enhanced photoionization have been observed in atomic sulfur originating from both the 3P2,1,0 and the 1D2 states. Sulfur atoms are generated by the sequential multiphoton dissociation of CS2 at probing wavelengths. The two-photon absorption process involves the 3 3P2,1,0 → 4 3P2,0,1 or the 3 1D2 → 4 1F3 transitions with resolution of the individual J″ → J′ transitions in most cases. Intensities of the 33PJ″ → 4 3PJ′ transitions have been compared with Hartree-Fock calculated transition probabilities from the analogous transitions in atomic oxygen. Photoionization is observed in a three-photon (two to resonance) ionization originating from the 3P2,1,0 and the 1D2 states. Induced fluorescence is observed at 167 and 180 nm which is dipole-allowed radiation from the intermediate 3S01 and 1D02 states, respectively. 相似文献
12.
Smith BM Lappi SE Brewer SH Dembowy S Belyea J Franzen S 《Langmuir : the ACS journal of surfaces and colloids》2004,20(4):1184-1188
The surface of a germanium internal reflectance element (IRE) was modified to bind 6X-histidine (his)-tagged biomolecules. The step-by-step surface modification was monitored via single-pass attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FT-IR). Initially an adlayer of 7-octenyltrimethoxysilane (7-OTMS) was formed on the Ge crystal through the surface hydroxyl groups, which were produced via ozonolysis of the Ge surface. The vinyl moiety of 7-OTMS was oxidized to a carboxylic acid, which was activated by 1,1'-carbonydiimidazole (CDI) to produce a labile imidazole. The labile imidazole that resulted from the CDI coupling was then displaced by the primary amine of nitrilotriacetic acid (NTA). Nickel sulfate was added to the system, and it coordinated with the three carbonyl groups and the nitrogen on NTA, thus leaving the ability of Ni to coordinate with two adjacent histidine residues. Binding of his-tagged biotin to nickel nitrilotriacetic acid (Ni-NTA) was observed by ATR-FT-IR spectroscopy. The surface modification method presented in this paper had minimal nonspecific binding, the Ni-NTA surface was reusable if stored properly, and complete removal of the organic surface was achievable. 相似文献
13.
The MSR (muonium spin rotation) technique was used to measure the chemical reaction rate for Mu + F2 → MuF + F in N2 moderator at ≈ 1 atm from 295 to 383 K giving the Arrhenius expression: log10k (?/mole s) = (10.83 ± 0.20) - (200 ± 50)/T, with k = (1.46 ± 0.11) × 1010 ?/mole s at 300 K. This is at least 6.8 times the room temperature rate constant for the analogous H atom reaction. The measured activation energy and enhancement over the H reaction rate are indicative of significant tunnelling in the Mu reaction, in agreement with the recent collinear quantum mechanical calculations of Connor et al. 相似文献
14.
Supramolecular bimetallic Ru(II)/Pt(II) complexes [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) and their synthons [(tpy)Ru(L)(BL)](n)()(+) (where L = Cl(-), CH(3)CN, or PEt(2)Ph; tpy = 2,2':6',2'-terpyridine; and BL = 2,2'-bipyrimidine (bpm) or 2,3-bis(2-pyridyl)pyrazine (dpp)) have been synthesized and studied by cyclic voltammetry, electronic absorption spectroscopy, mass spectral analysis, and (31)P NMR. The mixed-metal bimetallic complexes couple phosphine-containing Ru chromophores to a reactive Pt site. These complexes show how substitution of the monodentate ligand on the [(tpy)RuCl(BL)](+) synthons can tune the properties of these light absorbers (LA) and incorporate a (31)P NMR tag by addition of the PEt(2)Ph ligand. The redox potentials for the Ru(III/II) couples occur at values greater than 1.00 V versus the Ag/AgCl reference electrode and can be tuned to more positive potentials on going from Cl(-) to CH(3)CN or PEt(2)Ph (E(1/2) = 1.01, 1.55, and 1.56 V, respectively, for BL = bpm). The BL(0/-) couple at -1.03 (bpm) and -1.05 V (dpp) for [(tpy)Ru(PEt(2)Ph)(BL)](2+) shifts dramatically to more positive potentials upon the addition of the PtCl(2) moiety to -0.34 (bpm) and -0.50 V (dpp) for the [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) bridged complex. The lowest energy electronic absorption for these complexes is assigned as the Ru(d pi) --> BL(pi*) metal-to-ligand charge transfer (MLCT) transition. These MLCT transitions are tuned to higher energy in the monometallic synthons when Cl(-) is replaced by CH(3)CN or PEt(2)Ph (516, 452, and 450 nm, for BL = bpm, respectively) and to lower energy when Pt(II)Cl(2) is coordinated to the bridging ligand (560 and 506 nm for BL = bpm or dpp). This MLCT state displays a broad emission at room temperature for all the dpp systems with the [(tpy)Ru(PEt(2)Ph)(dpp)PtCl(2)](2+) system exhibiting an emission centered at 750 nm with a lifetime of 56 ns. These supramolecular complexes [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) represent the covalent linkage of TAG-LA-BL-RM assembly (TAG = NMR active tag, RM = Pt(II) reactive metal). 相似文献
15.
16.
17.
18.
19.
20.
The mechanism of base catalyzed proton exchange at the 5-position of uracil and its N-methylated derivatives has been studied. These reactions proceed by addition — elimination across the 5,6-double bond when the 1-nitrogen is substituted with a methyl group, or with anchimeric assistance of the N-1 anion if the 1-position is unsubstituted. The base catalyzed hydrolyses of 1,3-dimethyluracil and 3-methyluracil also appear to proceed through hydrated intermediates. A facile method for an acid catalyzed preparation of 5-deuterated uracils is described as well as a simple and accurate method for analysis of deuterium content. 相似文献